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| Low power Poor performance | Rate Topic |
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| Posted: 04-04-2005 06:18 pm |
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1st Post |
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Rory Clark Member
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Timing perfect, (12^) Gaps point/plugs correct (0.15/0.25). Cams 110ex/110in (0^). Distrib is wired correct (1-3-4-2) Rebuilt both CD-175's. Before the above Had lots of power (with Choke out) lots of carbon build up (soot) on plugs. Engine temp well within normal. The end result is Starts great runs great until it is put under a load. Does not have enough power to get out of its own way. Also now the engine runs hot. (Drove 20-30 miles and now plugs are clean) What do you think ? Rory 73-JH #13218
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| Posted: 04-04-2005 06:39 pm |
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2nd Post |
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Brett Gibson JH5 20497 Member
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Rory, sounds like it's running lean, try with the air cleaner off raising the barrel in the carb about 1/8" quickly to see if the speed picks up, ( it should ) if not you need to play with the mixture needle adjustment, I assume the floats in the bowel were set correctly, plus a couple of other areas would be the temp compensator and that small daiphgram thing (cant recall what they call it) on the sides of the carb, I have both of those blocked off and that gave me better control and responce, becarefull running lean valves dont like that alot richer is better to a point. Hope this helps. Brett.
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| Posted: 04-04-2005 08:48 pm |
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3rd Post |
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Judson Manning Member 
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Even with REALLY bad carbs, you should have some power under load. However, if the jets are clogged w/ varnish, sand, etc., all bets are off. When was the last time you dropped the bowls and cleaned them out? A float could be stuck and/or the needle. Try pushing up the piston as suggested. If the piston doesn't resist check the dampening oil. Again, as suggested, it could be leaning-out if the oil has leaked out. I know you said it's right, but pull off a couple of the plug wires, install old plugs and lay them on the intake manifold. Rotate the engine by hand and watch the firing order. It's the only way to be sure. Additonally, put a timing light on plug #1 and then #4 to check the dynamic advance. Both should produce identical timing measurements when viewed on the front pulley if different, a plug wire is incorrectly installed.
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| Posted: 04-04-2005 11:00 pm |
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4th Post |
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Rory Clark Member
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Sorry should have been more specific. I just finished the rebuild of the carbs. They look GREAT. The needles were a little corroded which a little 600grit took care of. What I mean by won't get out of its own way is: VERY LITTLE acceleration and will not keep speed without down shift going up slight hill. Starting from stop I am the slowest thing going. I will check the wiring Again. I think it is to lean but not sure how to rich up the mixture do not have tool. The carbs are in very close air intake sync. Thanks Rory.
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| Posted: 04-05-2005 02:13 am |
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5th Post |
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Judson Manning Member
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To richen the mixture all you need is a long handled hex tool. The trick is, take the top off the carb and hold the barrel so you don't rip the rubber bellows. What are you using for dampening oil? Also, check the vacuum lines and especially the brake booster line.
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| Posted: 04-05-2005 02:18 am |
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6th Post |
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Rory Clark Member
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Just checked The "Dynamic Timing" with scope on # 4 plug It is interesting it is almost Identical to being on # 1 (8-9^ BTDC) Also checked the "quick lift 1/8th inch" @ idle the motor speed decreased. Engine SN#7306 3238 Chassis 13218 Rory
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| Posted: 04-05-2005 02:30 am |
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7th Post |
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Rory Clark Member
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Damp oil same as motor 20-50, Do you know size of hex tool1/16, 3/32nd, 1/8? Have vac meter will check brake line. One last comment: Before I first started the car (found in barn were it had sat for 10+ years) I replaced the Time belt. I set it at 110In 115 Ex. and while the carbs were realy way to rich the cars power was increadable. When I changed it to 110/110 and before I rebuilt the carbs I lost power Is there a correlation? Thanks everyone Rory the next round is on me
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| Posted: 04-05-2005 04:46 am |
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8th Post |
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Mark Rosenbaum Member 
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The allen wrench used in the adjuster for the mixture needle is 1/8" across flats and about 6" long. The adjuster tool has a hole down the center for its (included) allen wrench, and one or two little pins sticking out to catch the slots in the top of the vacuum valve so it won't rotate and tear the carb diaphragm during adjustment. The tool is $9 or so, only two or three times what one pays for a single long allen wrench, so to me it makes sense to buy the tool. If the carb mixture needles were set to the 'datum' point the mixture should be quite close to correct. However, this assumes needles of the correct contour. Hate to tell you but sanding down the needles is a very bad idea, as a change in diameter of a tenth of 0.001" is significant. New needles are expensive, $25-30 each. But if you were very careful you may have gotten lucky and won't need to replace them just yet. As the correct needles for a JH are often back-ordered for months at a time it's wise to order them long before you expect to need them. The mixture is checked by raising each vacuum valve only 1/32" not 1/8". If the engine then speeds up the mixture is too rich, and if it slows down the mixture is too lean.. This is quite subtle and it takes a lot of practice to do it right (I'm still learning how). Alternately you can stick a $150 carbon monoxide tester up the car's exhaust and get the two carbs set just about perfect. In any case, to adjust mixture, turn the allen wrench part of the adjuster tool CLOCKwise to make more rich, or COUNTERclockwise to make more lean. Adjust 1/6 turn at a time -- no more, no less. Recheck carb balance after the mixture seems correct. Generally the whole process needs to be done 3 or 4 times before it's right. See section C11 of the shop manual for the factory's way of describing all this. An engine that's running hot where previously it ran normally most likely has too lean a mixture, or ignition timing that is too retarded, or a combination of these. Check for vacuum leaks. Make sure that the distributor's centrifugal advance works. Make sure that what the timing mark claims is TDC, really is. The throttle bypass valves don't really affect mixture, they just act as a partly open throttle when activated during deceleration. The effect of the temp comp valves on mixture really only shows up during an emissions check. If in doubt, though, these valves can be disabled temporarily for troubleshooting, but I don't think they're part of your problem. You do have a problem if the timing light flashes triggered by the #1 and #4 spark plugs don't occur at exactly the same relative time (i.e. within one crankshaft degree or less). There is definitely something screwy there -- radically different compression in the two cylinders, really loose distributor bushings, bad distributor cam, weak coil, bad or different type plug wires, etc. This needs to be looked at. Wrong or no damper oil will result in less acceleration but does not have any effect on peak power. Start with 10W40 or 20W50, which usually works quite well. Thicker oil means a richer mixture during acceleration. If you get black smoke out the exhaust but only while accelerating, go to a lighter oil. Don't use anything that will absorb water, though, or your carbs will eventually freeze up due to rust. If the power dropped off a lot when you changed the cam timing from 110 IN / 115 EX to 110 IN / 110 EX, something is screwy. Perhaps you have a non-stock exhaust cam, or the exhaust cam gear is mis-marked, or the cam or gear has the key slot in the wrong place, or something like that. You can try restoring the cam timing to what you started with (110/115) and see if the power comes back. If it were my car, I'd want to compare the two gears -- they should be absolutely identical in terms of key cut and timing marks. I've attached an annotated photo of the most common type of cam gears. Remember that you may have several problems that act together to confuse the issue. You'll surely get things solved eventually. CORRECTION (7 Apr 2005): Tom Thomson caught a mistake I made in the above, and advised me of it. Per section C11 paragraph 6 of the shop manual, the mixture is too rich if engine speed increases noticeably when the vacuum valve is lifted, and too lean if it stumbles. The text above has been altered to be correct. Sorry for the inconvenience. -- Mark Attachment: engine cam gears annotated.jpg (Downloaded 30 times) Last edited on 04-08-2005 03:44 am by Mark Rosenbaum |
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| Posted: 04-05-2005 12:15 pm |
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9th Post |
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Brett Gibson JH5 20497 Member
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Rory you recieved a lot of very good tips here to follow up on, the one statement you made about sanding your mixture needles though scares me, I to did that when I first rebuilt my carb's and spent the summer tweeking the timing and mixture trying to get more out of my car, the follow summer though I broke down and purchased the new needles and was astounded on just how much more responcesive my adjustments to the carbs became, even though they are not cheap it is money well spent in replacing them and if memory serves me correctly it's recommended that they be replaced around 40K miles, (help me out with that one Mark). While I did replace the needles I should also mention I went with a flame thrower coil and new plug wires from Delta at the same time, this year I'll be trying out a set of Dellorto carbs, it never ends. And buy that carb tool it save taking the tops off plus it's something you'll end up using a lot, tuning carbs is a thankless job made a little easier with it. Good Luck Brett.
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| Posted: 04-05-2005 01:24 pm |
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10th Post |
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Brian Kelly Member
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Is your fuel filter plugged? Fuel lines clogged? What's the condition of your tank? Take fuel line off carbs and stick end in gas can. Turn on fuel pump and look to see if you're getting a good stream of fuel. Sometimes it's the simple things. Brian
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| Posted: 04-05-2005 04:01 pm |
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11th Post |
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Mark Rosenbaum Member
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Brett, You're right. The shop manual says to replace the mixture needles at 48K miles, and also replace the main jets every 96K miles. This seems to be bit pessimistic for recently manufactured needles but was quite optimistic back in the 1970s and '80s. When you compare this to the 6K miles the shop manual calls out for virtually all maintenance and inspection services, it seems apparent that the factory actually thought that Strombergs were remarkably reliable.
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| Posted: 04-06-2005 03:39 pm |
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12th Post |
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Dan (Florida) Member
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Just to add my 2 cents, I would check to see if the slides are going up and down as the throttle is blipped. The slides in my stroms can be installed in any direction and I don't believe they will work too well if installed wrong. I just went around with an eroded needle in the rear carb and while it would run it would idle very rich and partially foul at a stop sign. I actually fixed it by filling in the eroded part with jb-weld epoxy and filing it back down. I can't comment on the condition of the jet that it serves, but it does run better.
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