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| Dellorto Cough | Rate Topic |
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| Posted: 11-18-2021 04:43 pm |
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1st Post |
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Paulreese1 Guest
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Installed Dellortos in 74, 16857, and getting random (about every 3 -5 seconds) cough/ backflow/missfire out of #4 barrel. Pulled manifold and carbs and reinstalled with gasket sealer this time and same issue. Guessing still have an air leak but would to know if any options other than pulling the carbs again. And if I do, what to maybe do differently. Thanks.
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| Posted: 11-18-2021 06:49 pm |
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2nd Post |
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Esprit2 Member
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Paul, Which DHLA carbs (40, 40E, 45 or 45E ?), what choke size, and how are they jetted? Are the carbs mounted to the manifold with proper soft mounts, O-rings, and either springs (Thackeray washers) or rubber grommets under the Nyloc nuts? Are they correctly tightened 'just enough', or cranked down hard (metal-to-metal)? There should be a 'uniform' 1.0mm/ 0.040" gap between either side of the softmounts' sandwich plate and the carb & manifold mounting flanges (a 0.89–1.27mm/ 0.035-0.050" range works). Have you accurately balanced the carbs? If so, how? 4-tube manometer, Synchrometer, Uni-Syn, by ear? How are the Idle Mixture Screws adjusted... how many turns out from fully seated? Four screws, four answers. How are the Air Bleed Screws adjusted? Ideally, all should be closed and seated. In the event of an imbalance within one carb (like, just #4 is lean), only the one Air Bleed on the stronger throat should be cracked open, and only the minimum amount required to weaken the stronger throat's manifold vacuum to match the weaker throat's. In the videos you emailed to me, the spitting sounds like a lean mis-fire. That could be because the carbs are jetted & adjusted too lean, or there's an air leak somewhere in the #4 inlet tract, or the soft mounts are tightened down too tight (ie, metal-to-metal, and no longer 'soft'). With the engine running, slowly pull the enrichment device ('choke') on. Does the situation improve? If yes, then the choke's richer mixture is compensating for a too lean mixture. That's not a 'fix'. It only confirms that too-lean is the problem, but the question is still 'why'. With the engine running, spray a combustable liquid (aerosol carb cleaner or brake cleaner, etc) around each soft mount's joint perimeter. If the lean-miss goes away, and/or if the idle rpm increases, that indicates an air leak. Similarly, spray around the joint perimeter between the intake manifold and the head. If you find any leaks, fix them before going any further. Answer the above before we start throwing a lot of blind guesses at the wall. Regards, Tim Engel Last edited on 11-18-2021 07:32 pm by Esprit2 |
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| Posted: 11-18-2021 10:42 pm |
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3rd Post |
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Paulreese1 Guest
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Ok! Working on all the carb specs. In the meantime, here are what the idle screws turns were: 1 5 3/4 2 4 1/2 3 4 4 3 1/4 Adjusted 3 and 4, rebalanced carbs (STE synchrometer) and coughing went away. Yay! But plot thickens. Have a carbtune hooked up and could not get #4 to balance with the others. #4 doesn't appear to be firing. Cover intake and no change. Have a good visible spark and checked also with timing gun. Switched plugs. Switched idle and main jets. No change with spraying starter fluid. Grommets on top are 2mm spacing. Thacks at bottom 1mm between coils. Soft mounts all even. Air bleed screws closed. Verified wired for 1,3,4,2 firing order. Disconnected carbtune amd put screw back. Did have some grey exhaust smoke but it went away. Did not smell gas in exhaust. #3 is firing so can't be floats. So also befuddled as to why coughing quit after changing mixture and rebalancing carbs and #4 was not firing...
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| Posted: 11-19-2021 03:03 am |
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4th Post |
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Paulreese1 Guest
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DHLA 40 specs Choke .............................. 34 mm Main Jet .......................... 145 Main Air Corrector Jet ... 190 Main Emulsion Tube ...... 7772.5 Idle Jet ............................. 55 Float Needle Valve ......... 170 Pump Jet .......................... 45 Starter Jet ......................... 60
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| Posted: 11-19-2021 05:07 pm |
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5th Post |
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Esprit2 Member
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You say the Carbtune doesn't read the #4 cylincer. Try swapping the Carbtune's hoses between the two fittings on the rear carb. If the Carbtune now doesn't read #3 (ie, the problem followed the hose), then the vacuum hose is plugged... clean it out. However, if the Carbtune still doesn't read #4, then the throttle shaft is probably twisted such that the #4 butter fly is still closed while #3 is open at idle. Remove the progression hole covers, look in and you'll see the progression holes drilled through the bottom of the passage into the carb throat. Look through the drillings while operating the throttle and you'll see the edges of the butterflies sweeping past the drillings. With the throttle closed, do both #3 & #4 butterflies align with their drilled holes in the same way... ie, are they equally open? If not, then the throttle shaft is twisted. The shaft is weak. If you ever put a wrench on the nut on one end of the shaft in order to hold the shaft from turning while you tighten the nut on the other end of the shaft, then you will twist the shaft. NEVER do that. If the shaft is twisted, then the 'book' fix is to replace it. However, at this point, you have nothing to loose by attempting to twist it back to straight. With the Carbtune hooked up, and with wrenches on the front and rear nuts, twist the shaft a little in the direction that would open #4. Just a little twist, then release it to see if #4's Carbtune reading improves. Nudge it in little steps, checking readings in between. If you're lucky, you might get #4 back into balance with #3. If not, you tried, now replace the shaft with a new one. *~*~*~* Are your carbs just 40, or is there a letter after it, like 40E or 40N ? Plain 40 carbs have Idle Mixture screws with coarse threads and blunt taper needles. They only have a couple of turns available before the needle fully retracts from the orifice and more turns do no additional good. Settings in the 2.0-2.5 range are common. 40E & 45E carbs have Idle Mixture screws with fine threads and long taper needles. They have about 4.5-4.75 turns of total adjustment available before the needle fully retracts from the orifice. Normal running settings in the 3.5-3.75 are typical. For either idle mixture screw, after the needle fully retracts from the orifice, further turning of the screw produces no further meaningful change. If you feel the need to turn the mixture screw out further than normal (3.5-3.75 for 'E' needle) in order to get the mixture rich enough, then the idle circuit is jetted too lean to begin with, and you're trying to compensate in a big way with the screw. No!! The jetting needs to be 'right' in the first place! Then only small tweeks are made with the mixture screws. You report Mixture Screw settings of 5.75, 4.5, 4.0 & 3 25. 1 thru 3 are too many turns for 'correct' jetting. The idle circuit needs to be jetted richer before the mixture screw settings will become 'right'. *~*~*~* Dirt Road Dyno -- When you get #4 figured out, and sorted (new shaft), start the engine and let it warm up to normal operating temp. Adjust the idle speed as slow as possible consistent with smooth running... no missing. Open the throttle slowly enough that the accelerator pump isn't much of a factor. If the engine hesitates off-idle, then the Idle Jet Holder (aka, Idle Air Corrector) is too lean. If it does not hesitate, then you don't know where it is, but it's probably too rich. Go with progressively leaner Idle Jet Holders until the engine just begins to hesitate off-idle. Then go back one step richer until the hesitation just disappears. With the Idle Jet Holder set, go find a quiet bit of road where you can make full throttle runs without attracting attention. From a rolling start, short-shift into a higher gear and accelerate at full throttle. The Idle circuit hands off to t he Main circuit at 3200 rpm. During the full throttle run, if the engine stumbles approaching 3200 rpm, then the Idle Jets are too lean, and the Idle Circuit runs out of capacity before the Main Circuit takes over. Go a couple of steps richer on the idle jets and repeat until the stumble disappears. If there is no stumble during full throttle acceleration, then you don't know where you are... but probably too rich. Go a couple of steps leaner with the Idle Jets and make another run. Repeat until the engine just picks up a new stumble. Then go back richer one jet size at a time until the stumble disappears.. When adjusting the Idle Jet Holders and Idle Jets, each one also affects the other. So after the initial round of the above adjustment routine, go back and start over. Repeat & repeat until no further change results. *~*~*~* The 34mm chokes are not standard J-H, so what car are the carbs originally from? Or are you playing with smaller chokes in hopes of improving low-end driveability? ................................ Paul ....... Jensen-Healey Factory Dellorto DHLA Specs ... Reese .... Emissions ... Non-Emissions Model ......................... __ ......... 40E ............. 40 Choke ........................ 34mm .... 35mm .......... 35mm ... 34mm chokes are not stock JH or Lotus. Main Jet ..................... 145 ........ 130 ............. 130 Main Air Corrector Jet ... 190 ........ 160 ............. 160 Main Emulsion Tube ...... 7772.5 ... 7772-5 ........ 7772.5 Idle Jet........................ 55 .......... 55L, 4-spd ... 50 Idle Jet ........................ __ ......... 52L, 5-spd .... __ Idle Jet Holder .............. __ ......... 7850.5 ......... 7850.1 Float Weight, grams. ...... __ ......... 8.5 gr .......... 8.5 gr Float Height, mm .......... __ .......... 16.5-17.0 .... 16.5-17.0 Float Needle Valve ........ 170 ........ 170 .............. 170 Pump Jet ..................... 45 .......... 45 ............... 45 Starter Jet ................... 60 .......... 70 ............... 70 Starter Emulsion Tube ... ____-_ ... 7482-1 ......... 7482.1 Regards, Tim Engel Last edited on 12-20-2021 11:42 pm by Esprit2 |
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| Posted: 11-19-2021 07:17 pm |
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6th Post |
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Esprit2 Member
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Paulreese1 wrote:(snip)... #3 is firing so can't be floats. A little off track, but... Don't be too quick to dismiss the floats. While they may not be responsible for #4 not firing at all, the fuel level is a foundational setting. The fuel level (float heights) must be RIGHT as a first step, or all subsequent jetting will be wrong. Regards, Tim Engel Last edited on 11-23-2021 10:45 pm by Esprit2 |
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| Posted: 11-25-2021 02:29 pm |
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7th Post |
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Esprit2 Member
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Paul, Any progress with your Dellortos? Tim
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| Posted: 11-26-2021 04:36 pm |
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8th Post |
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Paulreese1 Guest
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Tim, Thanks for checking. By adjusting the idle mixture to max rich was able to drive to a nearby event on Saturday although with a lot of misfiring. Been busy with other things but brother who is more mechanically inclined is in town and will have him take a look at the floats and double check settings.
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| Posted: 11-26-2021 09:07 pm |
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9th Post |
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Paulreese1 Guest
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Tried using glasses and...we have plain DHLA45. Choke is 34. So given a peak power @ 6500 RPM? should have: Chokes 38 mm Main Jet 152 Air Corrector 202 Emulsion 7772.5 Idle Jet 55 And did double check floats. Are we heading in the right direction? Last edited on 11-26-2021 09:09 pm by |
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| Posted: 11-27-2021 06:19 am |
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10th Post |
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Esprit2 Member
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Disappointment is a function of expectations. Some JH owners are running DHLA 40 carbs with chokes as small as 32mm. There seem to be more JH owners who want more low end torque and driveability, while more Lotus owners tend to be biased toward improved top end power and performance. One thing is for certain, you can't have both, you must choose. Smaller throats and chokes favor low end torque and driveability (J-H used DHLA 40 carbs). Larger throats and chokes favor top end power and performance (Lotus used DHLA 45E carbs). Since you already have DHLA45 carbs, that precludes the J-H priority of tuning for optimal low end torque & driveability. You're starting out in the Lotus school of tuning, at least in terms of your small throat size. Perhaps that was someone's attempt to detune the 45 carbs, but 34 chokes are pretty small for 45 throats... ie, not a combination you would normally see. So, what is it you want to get out of your JH 907? Low end torque and driveability, or top end power? In Lotus own first 907 powered car, the 1974 Elite 4-seater, Lotus went with 38mm chokes. That heavily favored top end power. Lotus marketing hadn't really accounted for the berzerker boy-racers who where rat-racing around in Elans and Europas would not be the same people who would buy the 4-seater executive express. Early buyers complained heavily about the car's lack of low end performance, and the need to rev the engine. Duh! For the second model year, Lotus over reacted and went wtih Spec 3, 45E carbs, and 35 chokes. The customers were then pleased with the low end performance, but complained about the loss of top end power. Yeah, double duh! For the third model year, Lotus finally got it about right with Spec 5, 45E carbs with 36mm chokes. They stuck with Spec 5 through the rest of the 907's Euro/ROW production run. Only when the 2.2 litre 912 came out did they go with Spec 9 and 37mm chokes. All of those Lotus set-ups 45 or 45E carbs, and were a hotter state of tune that the J-H 40 or 40E carbs with 35mm chokes. So, again, what do you want your engine's personality to be like? If you wish to stick with your DHLA 45 carbs, and are willing to accept a more sporty state of tune, then I recommend Lotus Spec 5 The 36mm chokes are about right for a near stock 2.0 liter 907 with DHLA45E's, and a 'sporty' personality. Tag Number . . Front . . . 5295A . . . . . . . . . . . Rear. . . . 5294P Carb Type. . . . . . . . . . . DHLA 45E Choke . . . . . . . . . . . . . 36 mm Main Jet. . . . . . . . . . . . 160 Main Air Corrector Jet . . 230 Main Emulsion Tube. . . . 7772-8 Idle Jet . . . . . . . . . . . . 50 (Too lean! Try 55-58 range) Idle Jet Holder . . . . . . . 7850-7 (Lean to Rich . . –5, –10, –9, –4, –1, –3, –6, –7, –2, –8). Float Weight (grams). . .10 gr Float Height . (mm) . . . 16.5 - 17.0 mm Float Needle Valve . . . . 170 . Pump Jet. . . . . . . . . . . 38V 42H Starter Jet. . . . . . . . . . 70 Starter Emulsion Tube. . 7482-1 . Power Jet. . . . . . . . . . . None Slow Running Speed . . . 900 - 1000 rpm Idle CO Level (hot) . . . . 2.0 - 3.0% Paulreese1 wrote: (Snip)... So given a peak power @ 6500 RPM? should have: "IF" you went with 38mm chokes (I'll bet you wouldn't like them), then I would recommend the following: Main Jet. . . . . . 142 Air Corrector . . 110 Emulsion . . . . . 7772.5 Idle Jet . . . . . . 55L In other words, Lotus Spec 1 (that Elite customers complained about). Regards, Tim Engel Last edited on 12-20-2021 11:43 pm by Esprit2 |
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| Posted: 11-27-2021 06:22 am |
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11th Post |
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Esprit2 Member
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Each carb should have an aluminum tag under one of the screws that secures the large top cover. What are the numbers that are stamped on them (separate numbers for the front & rear carbs)? Given those numbers, I can determine how your carbs were jetted & set-up when they left the factory. In reality, there's no guarantee that the carbs are still jetted the same after 47 years... who knows what others might have done to them over time? But it might help you get a handle on what you have. Back in the day, Dellorto offered three different float weights, and each weight required a different, specific float height to go with it. If different floats have been installed due to (lack of?) availability issues, then the float height must be what's correct for the floats that are installed, and not the original applicaton spec height. Regards, Tim Engel Last edited on 11-28-2021 04:47 am by Esprit2 |
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| Posted: 11-28-2021 02:40 am |
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12th Post |
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Paulreese1 Guest
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No aluminum tags. Dells are from JHPS and tuned for lower speed drivability which is my goal. He has sold multiple similar setups with no problem. So trying to figure out why I am special. Compression: 1 110 2 110 3 112 4 115, Fresh gas, gas filter clear, static at 12 degrees BTDC and advances. Changed out points carb for electronic distributor. Little stronger but still missing on the road. 10 grams floats set at 16.5mm with gasket at vertical just touching the needle valve. Gas pressure at 6psi. Verified jets, emulsion. idle screw same as spec'd. Replaced prior "dark" sparkplugs. New ones are very light indicating lean mix. Have to go to idle mixture screws 4 turns out from seat to get smooth idle. Revs up smooth but when driving starts missing bad at around 2K rpm even at cruise so appears not to be accelerator jets. With choke on, still runs rough at 2K rpm.
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| Posted: 11-28-2021 03:21 am |
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13th Post |
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Jh092 Member
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Fuel pressure seems high.
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| Posted: 11-28-2021 05:02 am |
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14th Post |
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Esprit2 Member
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The fuel pressure IS high. Install an inline fuel pressure regulator as close to the carb inlets as practical, and set it to 2.5 psi. However, that's a side-issue and doesn't explain why cylinder #4 isn't running correctly. Compression pressures are in spec. Jensen-Healey specifies checking the compression on a cold engine, and calls for a minimum of 7.58-8.96 bar (110-130 psi) COLD. Lotus specifies checking the compression on a hot engine, once it's up to full operating temperture. In that case, with the same 8.4:1 compression ratio, they spec 10.2-11.6 bar (150-170 psi). For both the J-H and Lotus compression tests, the throttle is to be held fully open, and the engine cranking at least 200 rpm (ie, battery fully charged, or use jumper cables). Regards, Tim Engel Last edited on 11-28-2021 05:04 am by Esprit2 |
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| Posted: 11-28-2021 05:36 am |
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15th Post |
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Esprit2 Member
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Paulreese1 wrote:By adjusting the idle mixture to max rich was able to drive to a nearby event on Saturday although with a lot of misfiring. (Snip)... Don't tune for max "rich". Adjust each idle mixture screw as necessary to produce peak manifold vacuum in that inlet tract. Start with all the Air Bleed screws seated closed. After the first round of peak manifold vacuum adjustments, "IF" the vacuum levels between throats in one carb are not equal, then open the Air Bleed screw in the stronger throat in order to weaken it's vacuum to match the vacuum in the other (weaker) throat. When you're done, only ONE Air Bleed screw should be open per carb. When both throats on each carb are equal, if the two carbs are not equal, then adjust the balance screw in the linkage coupler between the carbs to bring the two carbs, ie, all four throats) into balance (ie, the same "Peak" manifold vacuum level. Then screw each Idle Mixture screw in until seated, carefully counting turns as you go so you can put it back where you found it. Record the number of turns, then put the screw back where you found it, carefully adjusting for peak manifold vacuum. There can be a slight difference in the number of turns out for each screw, but they should be close... in the same ball park. If there is a big spread in the number of turns out, then something is wrong... like twisted throttle shafts. If the idle mixture screw settings are pretty uniform, then they should be about 3.5-3.75 turns out for a DHLA45E (fine pitch threads and long taper needle), or about 2.0-2.5 turns out for DHAL45 (no letter suffix). If the Idle Mixture screws are turned out more than that, then the idle circuit is jetted too lean and you're trying to compensate by over-adjusting the mixture screws. Don't. Re-jet richer, then re-adjust the mixture screws for peak manifold vacuum. Repeat until the Idle Mixture Screws are in the ranges given above. Also, use the 'Deserted Road Dyno' to confirm the Idle Jet size (no stumble approaching 3200 rpm). Regards, Tim Engel Last edited on 03-23-2023 04:58 am by Esprit2 |
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| Posted: 12-15-2021 07:55 pm |
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16th Post |
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Paulreese1 Guest
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Installed: Main Jet 160 Air Corrector 230 Idle Jet 58 And it ran with no misfiring. But it's still running lean. Plugs are white, and could not get idle mixture screws out far enough to where the rpm or vacuum would decrease. Also had some 36mm chokes so tried those and it would not start. Then I noticed oil in the radiator so planning on a new head gasket. I plan to measure the displacement while that's going on.
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| Posted: 12-17-2021 05:41 am |
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17th Post |
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discogodfather Member 
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Can't speak for Dell's but with the Webers my long long long story of tuning kind of came full circle when I realized messing with jets and chokes produced bad results. Engine is very built and nothing is stock, so it made things even worse- plus chasing an old demon in the way the cam was timed. But once I got everything sorted with the cam, the primary problem was the transition, and I had the same coughing and sneezing. After installing an AFR meter I could see some aspects of the problem as being lean but it was still kind of inconclusive. I would richen things up but it would solve part of the transition, not the other conditions including WOT or idle or top end. It was also hard to tune off manifold vacuum because of the extremely high overlap Dave Bean DB9 cam I was running (even more overlap than a 104). Everything changed when I started messing with the emulsion tube. Like magic, transition was achieved and the other issues then became about jetting and messing with the idle air jets, especially setting for max vacuum like Tim always suggests. No expert here, but the observation is that the emulsion is kind of the "camshaft" of the carb. It seems to determines when primary and secondary happen. I've used this method now to tune a few non-standard built Porsche's, etc, even a old 289 Ford engine running 4x IDF's, and it seems to work as long as you get the choke and auxiliaries generally right. But maybe this is more for high rpm and higher performance engines, not much experience tuning stock. I remembering reading an interesting story years ago that a British manufacturer, maybe it was Bentley or Aston (pretty sure it was Aston) had secretly contracted with the Weber company to get one of every single emulsion tube they ever produced, and they keep a library of them still at their facility. Many emulsion tubes have been lost to history, and of course the racers were modifying their own. A black art indeed, but when I married my Dave Bean 2.0 built engine with the F3 (weber), it was a match made in heaven.
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| Posted: 12-20-2021 11:27 pm |
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18th Post |
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Esprit2 Member
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Paul, Since the beginning of this thread, you have never mentioned which Idle Air Corrector (aka, Idle Jet Holder) is installed. You have listed a few jets from time to time, including the Idle Jet, but never any mention of the Idle Air Corrector. So, direct question: which Idle Air Correctors are currently installed. For all your tuning, have you ever changed them? If you have, then from what, to what, and what were the results? The Idle Air Corrector's basic part number is 7850-x, with the 'x' being a number from 1 to 10, indicating the size. The sizes aren't in numerical order from lean to rich... instead, they seem quite random: Leanest -- 5 – 10 – 9 – 4 – 1 – 3 – 6 – 7 – 2 – 8 -- Richest (I posted that back in msg #10). Stock JH Dellorto DHLA "40" throat carbs, both emissions and non-emissions, used 7850-5... the leanest available. In general (very broad strokes), a 9XX on DHLA "45" throat carbs likes 7850-7. That's probably a little rich, and -6 should suffice, but the engine just seems to like -7... emissions requirements not withstanding. Regards, Tim Engel Last edited on 12-20-2021 11:54 pm by Esprit2 |
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| Posted: 01-23-2022 10:45 pm |
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19th Post |
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Paulreese1 Guest
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Tim, With the below it bogs down bad at around 1,200 rpm DHLA 45 Choke 36mm Idle Jet 55 Idle Jet Holder 7850-6 Main Jet 160 Air Corrector 230 Emulsion Tube 7772-8 Changed idle jets to 62s and it bogged down around 2,200 Changed main jets to 145s and pretty much the same. Pulled the main jets and just ran on the idles. Ran better, could get almost to 3,000 rpm. Found a "how a dellorto works" post you did in 2017 and thinking I may have the floats too low and the "gas froth" is not high enough and starving the engine?
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| Posted: 01-25-2022 09:01 pm |
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20th Post |
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Esprit2 Member
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Paul, Back in message #12, you wrote that the fuel pressure was 6 psi. Is that still true, or have you installed an inline fuel pressure regultor and dialed the pressure down? The pressure at the carb inlets should be 1.5-3.0 psi. I use an inline regulator set to 2.5 psi. Do not exceed 3.0 psi at the carb inlets. 6.0 psi will over-power the float-controlled inlet valve, and force too much fuel into the float bowls. If the fuel pressure is still 6.0 psi, then install an inline fuel pressure regulator, and get the pressure 'at the carb inlets' dialed down to ~2.5 psi. *~*~* In that same msg #12, you stated the float weight was 10 grams, and the float height was 16.5mm. Is that still the case? *~*~* With the Main Jet assemblies (the brass sticks) removed, look down into the jet wells (the open holes), and you can see the surface of the fuel pool. The question is, how far is it from the top/ rim of the jet well to the surface of the fuel pool. It should be 25mm regardless of the floats used. Heavy floats set deeper, or lighter floats set higher... each float weight/height combination should result in the same fuel LEVEL... 25mm. What is the fuel level in your carbs? Run the electric fuel pump until you hear it slow a bit, indicating the float bowl is as full as it's going to get. Then switch off the pump, and measure the fuel level in the main jet well. If the fuel pressure is really 6.0 psi, then I suspect that the fuel level is too high. If 25mm is corrrect, then a smaller number (like, 24) is higher. Higher is richer, and may be why your engine bogs down... it's flooding out. Regards, Tim Engel
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