C3 Timing question
Thread Starter
Instructor
Joined: Jan 2013
Posts: 122
Likes: 0
From: Phoenix Arizona
C3 Timing question
Hello, it's been a while since I've been on he site. I was wondering if anyone has encountered this before.
Just installed the 290 350 crate motor. Just got it started and timed. Timing mark looked steady @ 10 BTD running smooth. After the engine ran for a few more minutes the timing mark begins to jump. Let it sit overnight and started it again. The timing mark was steady. After it warms up the timing mark begins to jump and seems to miss a little. I'm running my original distributor with the petronixs ignition module. Could the petronixs module be going bad when it heats up or maybe my dist. is bad?
Any feedback is appreciated.
Just installed the 290 350 crate motor. Just got it started and timed. Timing mark looked steady @ 10 BTD running smooth. After the engine ran for a few more minutes the timing mark begins to jump. Let it sit overnight and started it again. The timing mark was steady. After it warms up the timing mark begins to jump and seems to miss a little. I'm running my original distributor with the petronixs ignition module. Could the petronixs module be going bad when it heats up or maybe my dist. is bad?
Any feedback is appreciated.
Racer
Joined: Aug 2008
Posts: 413
Likes: 22
From: Justin TX
Hello, it's been a while since I've been on he site. I was wondering if anyone has encountered this before.
Just installed the 290 350 crate motor. Just got it started and timed. Timing mark looked steady @ 10 BTD running smooth. After the engine ran for a few more minutes the timing mark begins to jump. Let it sit overnight and started it again. The timing mark was steady. After it warms up the timing mark begins to jump and seems to miss a little. I'm running my original distributor with the petronixs ignition module. Could the petronixs module be going bad when it heats up or maybe my dist. is bad?
Any feedback is appreciated.
Just installed the 290 350 crate motor. Just got it started and timed. Timing mark looked steady @ 10 BTD running smooth. After the engine ran for a few more minutes the timing mark begins to jump. Let it sit overnight and started it again. The timing mark was steady. After it warms up the timing mark begins to jump and seems to miss a little. I'm running my original distributor with the petronixs ignition module. Could the petronixs module be going bad when it heats up or maybe my dist. is bad?
Any feedback is appreciated.
http://www.summitracing.com/parts/AN...28?seid=srese2
Thread Starter
Instructor
Joined: Jan 2013
Posts: 122
Likes: 0
From: Phoenix Arizona
My guess is your vacuum is changing and you have a vacuum advance distributor? Are you using a standard or advance timing light? You need to disconnect the vacuum line and plug it to set base timing. I suggest using an advance timing light to make sure everything is working correctly but for base timing either type works.
http://www.summitracing.com/parts/AN...28?seid=srese2
http://www.summitracing.com/parts/AN...28?seid=srese2
Racer
Joined: Aug 2008
Posts: 413
Likes: 22
From: Justin TX
I put on an Edelbrock ProFlow EFI and matching Mallory SSI distributor last year so everything has changed now :-)
Maybe contact Pertronix and see if they have some tips also.
Thread Starter
Instructor
Joined: Jan 2013
Posts: 122
Likes: 0
From: Phoenix Arizona
Maybe check the centrifugal advance springs and make sure it is working correctly. At idle it should not be moving but seems like there was a note I discovered when I installed mine about disabling it while setting timing. I can't find the note but if that moves at all the timing will move. Seems like I put tape around mine to make sure it didn't move, but it has been a few years.
I put on an Edelbrock ProFlow EFI and matching Mallory SSI distributor last year so everything has changed now :-)
Maybe contact Pertronix and see if they have some tips also.
I put on an Edelbrock ProFlow EFI and matching Mallory SSI distributor last year so everything has changed now :-)
Maybe contact Pertronix and see if they have some tips also.
Safety Car
Joined: Apr 2006
Posts: 4,057
Likes: 421
From: BC
Le Mans Master
Joined: Aug 2005
Posts: 6,513
Likes: 1,949
From: Temple Terrace Florida
Heat
A quick way to determine if an electrical component problem is heat related is to use a can of dust off or compressed air directly on the part you think may be bad. The air will cool down the part quickly. I would also check if your dist. hold down bolt is tight. Good luck. Jerry
Thread Starter
Instructor
Joined: Jan 2013
Posts: 122
Likes: 0
From: Phoenix Arizona
A quick way to determine if an electrical component problem is heat related is to use a can of dust off or compressed air directly on the part you think may be bad. The air will cool down the part quickly. I would also check if your dist. hold down bolt is tight. Good luck. Jerry
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Thread Starter
Instructor
Joined: Jan 2013
Posts: 122
Likes: 0
From: Phoenix Arizona
Hello Dochorsepower, The carb was rebuilt not to long ago. Carter Qjet. I do know the float sticks sometimes and makes it hard to start. If I tap on the inlet of the carb the engine will fire right up. Once its running its seems to get plenty of gas and the engine runs good at higher RPMs. I have adjusted the fuel air mixture set screws a little. They are about 2 and 3/4 of the way open. Doesn't seem to effect anything. Is there any kind of carb test I can do, like wiring open the butterfly valves a bit to give it more air?
Thread Starter
Instructor
Joined: Jan 2013
Posts: 122
Likes: 0
From: Phoenix Arizona
[QUOTE=Captainkvan;1589683724]Hello Dochorsepower, The carb was rebuilt not to long ago. Carter Qjet. I do know the float sticks sometimes and makes it hard to start. If I tap on the inlet of the carb the engine will fire right up. Once its running its seems to get plenty of gas and the engine runs good at higher RPMs. I have adjusted the fuel air mixture set screws a little. They are about 2 and 3/4 of the way open. Doesn't seem to effect anything. Is there any kind of carb test I can do, like wiring open the butterfly valves a bit to give it more air?
Choke is wide open.
Choke is wide open.
Race Director
Joined: Oct 2008
Posts: 19,147
Likes: 1,667
From: Long Island
[QUOTE=Captainkvan;1589683732]
Sounds like you have a vacuum leak and the idle is lean.
Make sure the accelerator pumps are squirting into the carb when you hit the throttle.
Hello Dochorsepower, The carb was rebuilt not to long ago. Carter Qjet. I do know the float sticks sometimes and makes it hard to start. If I tap on the inlet of the carb the engine will fire right up. Once its running its seems to get plenty of gas and the engine runs good at higher RPMs. I have adjusted the fuel air mixture set screws a little. They are about 2 and 3/4 of the way open. Doesn't seem to effect anything. Is there any kind of carb test I can do, like wiring open the butterfly valves a bit to give it more air?
Choke is wide open.
Choke is wide open.
Make sure the accelerator pumps are squirting into the carb when you hit the throttle.
Racer
Joined: Oct 2008
Posts: 278
Likes: 5
From: illinois
I also had a similar problem in my 71 with petronix and distributor. P/O had pryed the module up to get the recommended gap in order to get the correct timing at idle, but when going to a higher RPM it started to jump x dergee to x degree. what he failed to do was check the distributor. the distributor shaft gear was traveling up and down depending on the engine RPM, I order a shim kit, flatten the petronix module. Problem gone. My 2cents.
Mike
Mike
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,114
From: Crossville TN
I don't believe you mentioned checking or re-lubing the mechanical advance system in the dizzy. If that gets dry/sticky, it will give you exactly the same symptoms as you described.
If it does not "jump" with the vacuum advance can vacuum line removed and plugged off, but you get "jumping" when it is connected to vacuum..the vacuum can could be defective.
If it does not "jump" with the vacuum advance can vacuum line removed and plugged off, but you get "jumping" when it is connected to vacuum..the vacuum can could be defective.
Last edited by 7T1vette; May 23, 2015 at 09:42 PM.
5th Gear
Joined: Jun 2015
Posts: 5
Likes: 0
Same issue??
Hey, I'm pretty interested in this thread, as I am encountering the same issue...
75 L48 68,000 mi stock
Stock dist recurved, all in around 3k.
Shimmed to ~0.015" end play.
New vacuum advance can @ manifold (vacuum plugged off to check tho).
at idle, get about a 4 degree sporadic jump (ahead) in timing... my portable tach picks it up too. tried both ends of the NR 1 wire, different springs, same thing...?
Just rebuilt the Q-jet, but based on the timing jumping and tach being funny, REALLY looks like an ignition problem.
Thanks, any ideas would be great.
Mike
75 L48 68,000 mi stock
Stock dist recurved, all in around 3k.
Shimmed to ~0.015" end play.
New vacuum advance can @ manifold (vacuum plugged off to check tho).
at idle, get about a 4 degree sporadic jump (ahead) in timing... my portable tach picks it up too. tried both ends of the NR 1 wire, different springs, same thing...?
Just rebuilt the Q-jet, but based on the timing jumping and tach being funny, REALLY looks like an ignition problem.
Thanks, any ideas would be great.
Mike
Last edited by mdearman; Aug 18, 2015 at 11:30 PM. Reason: Added year/model
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
Check end play in dizzy first. .020" for ALUM, .010" FOR IRON
Check cent. weights for slop on pivots.
Check for weak advance springs.
Disconnect the vacuum advance while checking timing.
Check for slack in timing chain.
If you have 20* mechanical advance, try 16* advance at idle.
If using points, check for slop in the base plate.
If using points, check dwell and spring tension.
Check cent. weights for slop on pivots.
Check for weak advance springs.
Disconnect the vacuum advance while checking timing.
Check for slack in timing chain.
If you have 20* mechanical advance, try 16* advance at idle.
If using points, check for slop in the base plate.
If using points, check dwell and spring tension.
5th Gear
Joined: Jun 2015
Posts: 5
Likes: 0
Check end play in dizzy first. .020" for ALUM, .010" FOR IRON
-End play is 015"
Check cent. weights for slop on pivots.
- Using teflon bushings that came in recurve kit
Check for weak advance springs.
- There is tension on the springs static, seems to be all in by 3k
Disconnect the vacuum advance while checking timing.
- Yup!
Check for slack in timing chain.
- Need to do...
If you have 20* mechanical advance, try 16* advance at idle.
- Base timing ~12*, with advance plugged off.
If using points, check for slop in the base plate.
If using points, check dwell and spring tension.
-End play is 015"
Check cent. weights for slop on pivots.
- Using teflon bushings that came in recurve kit
Check for weak advance springs.
- There is tension on the springs static, seems to be all in by 3k
Disconnect the vacuum advance while checking timing.
- Yup!
Check for slack in timing chain.
- Need to do...
If you have 20* mechanical advance, try 16* advance at idle.
- Base timing ~12*, with advance plugged off.
If using points, check for slop in the base plate.
If using points, check dwell and spring tension.
Thanks, I'll check the timing chain for slop. Just funny, sporadic until revved - could very well be the timing chain
R
Mike
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
Use stock weights and two gold springs from a Mr Gasket curve kit. Re-curve kits can be real crap.
Sporadic at idle? How is the gear? Cam end play?
All in by 3000 rpm is good.
What is the total mech advance at 3000RPM?