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| DHLA 45 Idle Mixture Setting Help | Rating: 
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| Posted: 09-24-2013 06:02 am |
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1st Post |
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Bogie07 Member
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The engine is in the car and running, but it doesn't like RPM's below 1200 or so, when it starts rocking and mis-firing. One of the cylinders is backfiring at idle, so I replaced the spark plugs and it's still happening. My question is what should be the starting point for the idle mixture screws with these jets? How do you adjust the idle mixture and know if it's too lean or rich? Here's my carb specs. Choke 36mm Main jet 160 Emulsion tube 7772.8 Air correction jet 230 Idle jet 58 Idle jet holder 7850.9 Pump jet 60 Thanks. Last edited on 09-24-2013 06:04 am by Bogie07 |
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| Posted: 09-24-2013 06:24 am |
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2nd Post |
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subwoofer Member
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First of all, are your carbs accurately balanced? I use a CarbTune II (http://www.carbtune.com/) for this purpose. If memory serves me correct, a half decent starting point is about 4 turns out on the idle screws. Turn all of them all the way in and count the turns as you back them back out. If you have access to a CO meter, adjust for idle around 2.5% CO. It is rich, but needs to be rich to avoid trouble at pickup. I assume you have checked your ignition and cam timing? If not, this is absolutely the time to do so. Also check for vacuum leaks. -- Joachim
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| Posted: 09-24-2013 06:58 am |
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3rd Post |
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Bogie07 Member
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Thanks for your quick reply. The timing is set at 12 degrees and I think the ignition is correct. It has pertronix so there shouldn't be a problem with points or anything. I'll try that setting tomorrow and get back.
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| Posted: 09-24-2013 03:21 pm |
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4th Post |
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Jensen Healey Super Moderator 
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What are the specs on the engine? Do you have high compression pistons and performance cams?
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| Posted: 09-24-2013 03:36 pm |
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5th Post |
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Bogie07 Member
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I know the cams are stock and I think the pistons are also stock. Haven't torn apart the engine though so I don't know for sure.
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| Posted: 09-24-2013 05:34 pm |
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6th Post |
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Jensen Healey Super Moderator
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It looks like you are over jetted for a stock engine. Here's a jetting chart for a stock engine from Greg Flatcher: Choke .............................. 34 mm Main Jet .......................... 145 Main Air Corrector Jet ... 190 Main Emulsion Tube ...... 7772.8 Idle Jet ............................. 55 Float Needle Valve ......... 170 Pump Jet .......................... 45 Starter Jet ......................... 60 Since you are having issues at idle I would start with a 56 idle jet since you have lean idle jet holder.
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| Posted: 09-24-2013 06:37 pm |
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7th Post |
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Bogie07 Member
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Is there any way to tell if anything is modified without taking the heads off?
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| Posted: 09-24-2013 06:44 pm |
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8th Post |
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subwoofer Member
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IMNSHO you should get yourself a wideband O2 sensor before you start messing with jetting. That way you have a way of identifying the problems and fixing them properly instead of just randomly adding fuel in arbitrary places. After all, even though the carbs are 1950's technology, this is 2013 and current tech is cheap. Today's rant: finding literature that accurately describes how the Dellortos work and the interaction between the circuits is close to impossible. -- Joachim
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| Posted: 09-24-2013 08:59 pm |
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9th Post |
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Bogie07 Member
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Any advice as to which/where to get a wide band a/f gauge?
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| Posted: 09-24-2013 09:47 pm |
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10th Post |
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subwoofer Member
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http://Www.diyautotune.com is a reliable source. For a carbed application, the Innovate LM2 should fit the bill, AFAIK it can be connected to the coil for RPM logging as well and possibly also manifold pressure. -- Joachim
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| Posted: 09-25-2013 02:53 am |
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11th Post |
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Jensen Healey Super Moderator
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Since Lotus/ Jensen couldn't even tune these carbs properly at the factory your best bet is to use the jetting that works for others with stock engines. Learning to tune Dellortos is a real commitment of both time and money. If you have the resources and desire, investing in an A/F meter and it's installation will certainly help with tuning. Otherwise go to the club store: http://www.jhps.com/mm5/merchant.mvc?Screen=PROD&Store_Code=jhps&Product_Code=DJK&Category_Code=DEL
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| Posted: 09-25-2013 09:25 am |
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12th Post |
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subwoofer Member
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Jensen Healey wrote:Since Lotus/ Jensen couldn't even tune these carbs properly at the factory your best bet is to use the jetting that works for others with stock engines. Learning to tune Dellortos is a real commitment of both time and money. I saw a post from one of the old geezers a while back; "we'd given an arm to have the instrumentation available for a few hundred bucks now, back in the seventies." (From memory) The information on how to do it properly does exist, but it requires a bit of commitment to find it. John Connelly from aircooled.net has written quite a bit that looks reasonable. I believe the key is to understand the function of the emulsion tube and the effect of float level - I still only have a vague idea. But back to the original matter at hand: did the engine suddenly act up, has it run ok before with the current setup? Did you just mount the carbs, have they been rebuilt? Float levels ok, carb balance ok, brake booster not leaking into #4 runner? Verify and fix all the basic stuff before you start messing with jets.
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| Posted: 09-25-2013 08:49 pm |
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13th Post |
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Bogie07 Member
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We drove it around the block three years ago but that's it. The rest of the car was rebuilt but the motor was left untouched other than some cleaning. After more troubleshooting and compression testing, I found that the cause was a weak spark to that cylinder. The combination of some wearing between the rotor and plug contact on the cap and old wires was causing misfiring and excess fuel buildup in that cylinder. Thanks for your help, the engine seems to like about 4 1/2 turns out on the idle mixture screw. One last thing: The compression test gave the results of 1:120 2:105 3:141 4:115. I realize with those numbers it will never run great, but is #2 OK for just driving around town and such? Or does the engine need new rings, etc.?
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| Posted: 09-25-2013 09:22 pm |
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14th Post |
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subwoofer Member
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Squirt a bit of oil into the offending cylinder and retest. If that helps, the problem is with the rings, otherwise the valves are leaking. Have you checked valve clearances? -- Joachim
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| Posted: 09-27-2013 02:43 am |
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15th Post |
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Bogie07 Member
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I have not checked the valve clearances. Well, it may be a 2.2 stroker after all. My dad said the ad from 3 years ago said it was, but I didn't remember that. Would those jet sizes be correct if it is? Last edited on 09-27-2013 02:43 am by Bogie07 |
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| Posted: 09-27-2013 04:20 pm |
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16th Post |
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Jensen Healey Super Moderator
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If you have a 2.2 with HC pistons and 104 cams then you may indeed have success with: Spec 9 Carb Type ...................... DHLA 45E Choke .............................. 37 mm Main Jet .......................... 160 Main Air Corrector Jet ... 230 Main Emulsion Tube ...... 7772-8 Idle Jet ............................. 55 (maybe a little lean, try up to 58) Idle Jet Holder ................. 7850-9 Float Weight .................... 8.5 gr Float Setting Height ........ 14.5 - 15.0 mm Float Needle Valve ......... 170 Pump Jet .......................... 50H Starter Jet ......................... 95 Starter Emulsion Tube ..... 7482-3 Power Jet .......................... --- Slow Running Speed ....... 900 - 1000 rpm Idle CO Level (hot) ........... 0.7 - 1.5%
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| Posted: 09-27-2013 09:47 pm |
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17th Post |
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Jim Ketcham Member
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For a 2.2 liter your previously mentioned jetting should work fine. For a 2.0 liter JHPS recommended jetting mentioned by Jensen Healey should work very well on a good engine. Alot of work has been done to optimize jetting for the 907 so you should be able to get a very good idea on what you need without "reinventing the wheel". Remember, the engine has to be healthy before you start straying from the recommended jetting. I have found the most common issue with poor idle to be air leaks at the carb to intake O rings and bad spark.
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| Posted: 11-12-2013 02:26 am |
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18th Post |
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timeforwalkies Member
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FYI. Mine is the 2.2 high compression, 104 cams, Pertronix, adjustable cam pullys....all the good stuff. And it seems we have had this conversation before. The below information is from Matt Cooper at the factory. R5326 carbs. had the following jetting originally: 36mm choke 158 mains 58 idles 60 pumps 7772.8 emulsions 230 airs 7850.9 idle emulsions They were O.E. on Lotus Talbot 2.2 engines. The E signifies that it has 6 progression holes, exclusive to Lotus. I am getting a build up of black soot at the tailpipe and while the engine sounds great it seems to be down on power. So with what I have done to my engine, what kind of power should I be seeing at the wheels. Note the Talbot: Additional FYI. The Talbot had these engine specs. And it makes me wonder how JH managed to get 140 HP out of the 2.0 liter Stromborg set up? Brand : Talbot Model : Sunbeam Version : Lotus Engine Power : 110 kW (150 PS - 147 hp) Cylinders : 4 cylinders (Inline configuration) Volume : 2172 cm3 Fuel supply system : 16 valves Torque : 203 Nm (4800 RPM)  And a question from me. Does anybody know what these filters are? Thanks, Clif Last edited on 11-12-2013 03:33 am by timeforwalkies |
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