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#1
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Help Lean cylinders
I have a 72 dodge challenger with a 340 4bbl. I put a rpm air intake on it and now everother cylinder is lean what can i do about this.
Thanks |
#2
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If you have a hollley install different jets on all 4 corners or mod the intake. Better still trash the thing and get a better intake with better fuel distrib.
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#3
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the carb is a speed demon and if i put bigger jets in the lean cylinders get better but the others get bad ritch.
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#4
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UNless it's a bad intake, I would look into something else.
RPM's have pretty good dist. What ignition? Wich cylinders are lean? |
#5
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Quote:
If there's nothing wrong with the ingnitions system and you can't play with the jets to get the fuel dist. decent then you'll need to mod the intake tracts or get another manifold that has better fuel dist. than the one you have now. Might look at an Air Gap. |
#6
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Try switching carbs and see what happens. It could be that the Speed Demon has a severely worn throttle shaft bore and is leaning out the carb on the linkage side.
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#7
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Would like a list of the lean cylinders, how different they are.
We can all take stabs, and say change carb, change intake, ect, ect, but without the nitty gritty on the plug color, I actually have no suggestions. As far as I know, the RPM, and RPM air gap, are almost identical, other than a space between the runners and the valley, not sure how that would fix anything. A story on the engine too, piston type, compression, was it cc'd? Were the rods reconned. A 1/4 point of compression difference is not hard to get in a few cylinders when you start nit-picking plug color, and makes a world of difference, on how the mixture needs. Bad valves also change plug color, bad intake valves, make the plug appear to be rich. Pictures of the plugs, would be nice too! |
#8
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Quote:
It is a air gap. The speed demon is brand new. The lean ones are 1 and 5 on driver side and 4,8 on other side. I have a msd 6al with msd distributor and msd wires. if i put in bigger jets i go from white / tan plugs to tan / black plugs. |
#9
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it is a 340 with about 425hp 10:1 compretion heads have had work done to them 2.02 intake 3 way angle job ported and polished. I have about 400 miles the motor. The motor runs around 160-170 degrees and has 36 degrees over all timing.
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#10
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Quote:
Sorry about that. I saw rpm and I thought you had one of the cheaper manifolds. Your engine runs too cool too. Need to up it to around 195-200 to get the most out of it. May be one of the reasons it's not brunign the fuel correctly. You need enough heat in the engine to vapor the fuel and to make it effiecent. |
#11
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160-170 is fine. And sure wont make it run lean.
Your plug problem kinda makes sense, but kinda doesn't. How tight are the valves? Are you running a spacer under the carb? |
#12
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No, it's not fine, it's too cold. And it wont make it run lean, but it will help it from running too fat if he jets up to get rid of the lean condition. If you'll do a search on here you will also find comments on how cooler engine temps create more wear cause the parts do not heat up to temp and expand like they should.
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#13
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Cooler, like, under 160, or running a 160 thermostat below zero. it also depends on the weight of oil you run, what type, how much compression, what the heads are made of, and what kind of duty the motor is intended for. It has also been proven, that there is a big HP difference, between a 200* temp, and a 160* temp (in the 160* favor). Good chance if he ran a 190* stat, he would also have to drop the timing a couple of degree's, or run a cooler plug, and that is counter productive.
Instead of starting out with a one fix for everything plan dw, go ahead, and look at a RPM manifold, since I am sure you have dozens of them in your speed shop, ready to put on your 400+HP 2bbl 365's (don't forget to add the 5 to 360 when you bore it), and try to imagine what is going on, in the motor, in the manifold, and see if you can figure out a reason, OTHER than changing the COOLANT TEMP 20*, why it may be running lean, on #1, and #5, and #4 and #8. Usually, lean/rich conditions I have chased down, had to do with spreadbore carbs, leaking gaskets, poor manifold design, (action plus, SP2P, and a stock port o sonic really erk me). Before I would dive further, I would check the plug gap, and do a leak down, to make sure some valves aren't too tight, or not seated. Next question is, one I should have asked first, is your lean problem at cruise, or at WOT? Do a plug test for both, and see if it is the same at WOT, if it is, I would almost certainly look at the combustion chamber, and related pieces. |
#14
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I was told i should run my motor at a min of 160 so i did. I have a carb spacer 1 inch. When i did a plug check i ran the car all out befor pulling the plugs. I do not know if the valves are to tight i did not put the heads together but i can have the guy that did them come over and take a look. The plug cap looked fine when i first put the plugs in. The plugs are the stock plugs for the 340 motor if that maters.
How can i do a leack check on my car that you talked about? Is there anyway to check if the valves are to tight on my own and if so how i have never messed with them. Thanks for all the help guys please keep it coming. |
#15
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What plugs you running, 12's or 14's, I hope they are champions.
I would put a colder plug in the holes that are lean. |
#16
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You can perform a cylinder leakage test with one of these;
Much more in depth test than just a regular compression test. Sam |
#17
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I think I'd get about 2000 miles on it before really getting to concerned about this, could very well be rings not seated and cylinders not firing equally. When you put bigger jets in, how big did you go? Were the heads milled down? If so, how much? Did you check to make sure intake is sealing at the heads? Intake bolts tight? And lastly, I would run a 180* stat until at least 2000 miles to help seat rings. My .02
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