Engine Skip

-
6

62 Signet

62 Signet
Joined
Nov 5, 2010
Messages
64
Reaction score
1
Location
Statesboro, GA
I just rebuilt a '62 aluminum 225. The engine cranks good and idles smooth. When it builds up a little RPM's, the engine starts to skip, but when accelerating, the skip disappears and the engine pulls strong. When you level out at cruise, it starts to skip again.

I installed a mild cam (210/212 duration), Holly 390, headers, MSD Blaster2 coil, & Mopar EI. I have set the valve gap at .018 on both (per the cam manufacturer), checked for vacuum leaks, flushed the fuel tank & lines, set the timing, & checked the plugs & wires. I am baffled at this point. Do I need to use different plugs since it was converted to EI? Also, I was told by a mechanic that I might need to change the vacuum advance springs in the distributor? Does anyone have any suggestions?
 
sounds like its getting lean. what jets you running? what is your timing set at and curve?
 
Doesn't really sound like it's lean because you don't have the problem accelerating, sounds more like cruising RPMs. I'd check the manifold vacuum on it & see what you have. That can tell you a whole lot. I'd also check the float levels & make sure they aren't too high or being pushed off their seats from too much fuel pressure. Make sure the correct power valve is in it & that it's not blown out.
As for the ignition, any plug that can fire from points should be able to fire in an electronic ignition system. The only real difference in EI vs point is how the coil is triggered. Timing of course needs to be correct.
Is this a solid lifter cam or hydraulic? Valve clearances need to be correct on a solid & lifter preload on a hydraulic.
 
Lonewolf3165 said:
Doesn't really sound like it's lean because you don't have the problem accelerating, sounds more like cruising RPMs. I'd check the manifold vacuum on it & see what you have. That can tell you a whole lot. I'd also check the float levels & make sure they aren't too high or being pushed off their seats from too much fuel pressure. Make sure the correct power valve is in it & that it's not blown out.
As for the ignition, any plug that can fire from points should be able to fire in an electronic ignition system. The only real difference in EI vs point is how the coil is triggered. Timing of course needs to be correct.
Is this a solid lifter cam or hydraulic? Valve clearances need to be correct on a solid & lifter preload on a hydraulic.
Click to expand...

accel pump and PV on accel, light throttle and cruise would be on the jets
 
Thanks for the suggestions. I drove the car again today to observe a little closer. Even though it cranks good, it is skipping when idling and at most RPM's. I didn't notice it earlier. However, it stops skipping completely and runs smooth when accelerating. I'll have to check with the mechanic who tried to tune it to see what the timing was set at and what the vacuum is. I'll also try to see what jets I have. They are what came in the carb from Holly.
 
Doesn't sound like an ignition problem, since one typically starts missing sparks at wide throttle where cylinder pressures are higher. I also agree a lean condition, which I can both feel and see in my 383 w/ Holley Pro-jection and O2 indicator. I play with the knobs to fix it, which is much easier than tweaking a carb. The downside is that system needs constant fiddling.
 
bring out the idle mix screw 1/4 turn and up the jet 2 and see what it does...
 
Thanks. I intend to check the vacuum this weekend. I'll also try some of the suggestions to see if it will help.
 
You need to isolate the skip. Pull plug wires one at a time until you get to the cylinder that makes no difference. Look at the plug real good. I've seen more than once where the center electrode was broken. At idle and low RPM, it would fall against the ground electrode and ground the plug. At higher RPM, the compression would blow the broken center electrode up and it would fire. Also too, could be a weak or broken valve spring.
 
This may sound a bit ridiculous, but check the engine to firewall ground. If the connection is poor there, when you accelerate grounding improves via the drive train. Hard on bearings and often difficult to diagnose.
 
Our car, on manifold vac to distributor will be fine under heavy load but when cruise or light throttle pull - timing goes too high and the engine becomes less smooth and a bit of ping is heard. (Stock smog era 440)

Your total timing at cruise may be too high. If you can eliminate the symptom by dialing back the timing a little, that's your problem.
 
I changed my mind, like what rice nuker said. If the skip is more like a lope, it is what happens with to much advance at light load. The lope is more of a horse term, but if you know cars and horses it fits.
 
Rice Nuker said:
Our car, on manifold vac to distributor will be fine under heavy load but when cruise or light throttle pull - timing goes too high and the engine becomes less smooth and a bit of ping is heard. (Stock smog era 440)

Your total timing at cruise may be too high. If you can eliminate the symptom by dialing back the timing a little, that's your problem.
Click to expand...

thats because vac adv dosnt belong on manifold vacuum... of course you'll have to much timing at light load with no metering ofthe throttle blade... if you put the vacuum advance on the correct ported vacuum you'll see you can run alot more timing...
 
also you running a drool tube head? you should be running a NGK 3459 @ .037 gap. your timing curve depending on compression will be about 12-16 initial, 30 total by 2500, 55 with vacuum adv (depending on gas and temps your vacuum timing can go as low as 40*)

EDIT: also the pod VC208 works really well.
http://www.summitracing.com/parts/smp-vc208
 
Vacuum @ 550 rpm is 18.5. Shouldn't it be some higher? Also, the engine originally had a drool tube but it has been converted to a PCV valve since the new Holly 390 had a port for it. Will this work or should I convert it back to a drool tube and plug the carb PCV vacuum port?
 
62 Signet said:
Vacuum @ 550 rpm is 18.5. Shouldn't it be some higher? Also, the engine originally had a drool tube but it has been converted to a PCV valve since the new Holly 390 had a port for it. Will this work or should I convert it back to a drool tube and plug the carb PCV vacuum port?
Click to expand...

the PCV is a better system. and 18.5 at 550rpm is great!
 
Oldmanmopar said:
Adjust are (<OR??) remove the vacuum advance. see this alot
Click to expand...

OP, remove the line from the vacuum pot on the distributor and suck on it, see if it holds a vacuum. if not replace it. if it does, plug port and leave line off, then set base timing and 12*.slowly rev up until you finish the mechanical advance curve (probably end up about 28* at 2750rpm or so). then plug in the vacuum advance and rev it back up to that rpm and see how much the vacuum advance added.

so then you will know your initial timing (12* Adv) total timing (x*) and the rpm you get full mechanical Adv. lastly you'll know your how much vacuum advance you have.

what you want is something about like this, 10-14* initial, 30 total by 2500, 50 with vacuum advance.
 
You must log in or register to reply here.
-

Back
Top