what would be your diagnosis?????

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duster360

duster360

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Very rough idle. To the point I can"t hardly catch the carb to adjust idle screws. Not from cam profile. Cam is not that big. Engine has roughly 80 miles on it and has ran like this from the start.

1. Good leakdown test.
2. Good compression test.
3. Both above test show me that valve adjustment is good.
4. Cam is in good condition.
5. Cam was degreed when installed.
6. Initial and total timing are verified with timing light. Vacuum advance not connected at the moment and all vacuum ports plugged at carb.
7. Firing order is correct from distributor to plugs.
8. All plugs are firing.
9. Did ohm test on plug wires, all are good.
10. Tried 2 different distributor caps with same results.
11. Tried 2 different carbs with same results. Both in excellent condition. Idle adjustments turned out 1 1/2 turns.
12. Sprayed carb cleaner on top of intake runners, no change in idle.
13. I have done a check on intake gaskets and all seem to seal well. Checked any way you can think of.
14. I removed the hose from the PCV valve and the engine idled up but still idled very rough. Plugged it with my finger and it idled back down with the still rough idle.

I have oil on the backside of the valves in the intake ports. No oil in the intake manifiold. Engine does not really smoke which tells me it is not enough oil to foul the plugs and cause the rough idle. Plugs are not corroded or wet with oil. Little darker than normal though. I have a thread with this that is ongoing but this is a quick and simple breakdown of what has been checked and done. Could it be an issue with my coil or MSD 6AL box? I have a new 6al box on the shelf I could slave in.

Here is a link to the lengthy thread if anyone needs to see it. http://www.forabodiesonly.com/mopar/showthread.php?t=339841

WHERE WOULD YOU GO FROM HERE?
 
If everything is the way you say it is then it pretty much has to be cam timing.

But it could also be any number of dumb little things causing it also.

A loose electrical connection that intermittently disconnects when the engine idle vibrates the car or even as simple as not getting enough air in the mixture at idle.
Might be a real good idea to verify that cam installation.
It could be the spark getting blown out when under compression because it's to weak.
Heck it even could be that you have never heard what a lumpy cam sounds or acts like, I don't know. LOL

Sounds like a fun one.
 
Did you have your intake machined correctly? What were the compression test results? What cam again? Is this the same problem you have been fighting in your other thread? J.Rob
 
Might be a weak spark. Put a vacuum gauge on it?
 
RAMM said:
Did you have your intake machined correctly? What were the compression test results? What cam again? Is this the same problem you have been fighting in your other thread? J.Rob
Click to expand...

1.Intake was machined and I have checked it any way you can think of.
2. Compression was 165 psi all around plus or minus a little. Not enough difference to matter.
3. Cam is XE275HL.
4. Same problem.
 
TrailBeast said:
If everything is the way you say it is then it pretty much has to be cam timing.

But it could also be any number of dumb little things causing it also.

A loose electrical connection that intermittently disconnects when the engine idle vibrates the car or even as simple as not getting enough air in the mixture at idle.
Might be a real good idea to verify that cam installation.
It could be the spark getting blown out when under compression because it's to weak.
Heck it even could be that you have never heard what a lumpy cam sounds or acts like, I don't know. LOL

Sounds like a fun one.
Click to expand...

1. I degreed the cam, but I am also not an expert at it.
2. I have run cams this size before.
3. MSD throwS out a heck of a blue spark.
 
Here is a link to a video with vacuum gauge and engine running.

[ame="https://www.youtube.com/watch?v=KpVEyHSvmmY"]IMG 0865 - YouTube[/ame]
 
Initial verified???

What is the initial timing?

It better have about 18-20...
 
What about valve adjustment? Are you using nonadjustable rockers? Even if the camshaft was degreed correctly you could still have too much preload. I just ran into this myself.
 
1967 'cuda said:
What about valve adjustment? Are you using nonadjustable rockers? Even if the camshaft was degreed correctly you could still have too much preload. I just ran into this myself.
Click to expand...

I am using hughes engines adjustable roller rockers. Wouldn't the leakdown test show if the valve adjustment was incorrect?
 
I just noticed you have aluminum heads, are they Edelbrocks? If so did you have them checked or just install OOTB? There should be no oil on valves at all. I am going to guess that either your valves are adjusted too tight, which you think eliminated by comp and leak down but not really if your lifters pump up when its running or a few tight valves that are sticking and probably a few sloppy ones that are leaking oil, or tuning issue-carb adjustment, ignition timing or cam timing.

I would look at Edelbrock first...have had same exact experience with 2 sets hen never installed them OOTB again.
 
magnummopar said:
I just noticed you have aluminum heads, are they Edelbrocks? If so did you have them checked or just install OOTB? There should be no oil on valves at all. I am going to guess that either your valves are adjusted too tight, which you think eliminated by comp and leak down but not really if your lifters pump up when its running or a few tight valves that are sticking and probably a few sloppy ones that are leaking oil, or tuning issue-carb adjustment, ignition timing or cam timing.

I would look at Edelbrock first...have had same exact experience with 2 sets hen never installed them OOTB again.
Click to expand...

My machinist went through them and removed the valve springs and seals. Put in spring cups, installed new valve seals and matching springs for my cam.
 
duster360 said:
I am using hughes engines adjustable roller rockers. Wouldn't the leakdown test show if the valve adjustment was incorrect?
Click to expand...

Our motor didn't reveal any issues with leakdown test but the valves were set just tight enough to throw timing off. - Barely wanted to run. Intakes were opening too soon then and had a tendency to pop back through carb.
 
Was the cam broken in with the stiffer springs? Vac gauge looks a little erratic, maybe a lobe or two wiped out?
 
spl440 said:
Was the cam broken in with the stiffer springs? Vac gauge looks a little erratic, maybe a lobe or two wiped out?
Click to expand...

I removed the inner springs during breakin. The intake manifold is off at the moment and I have verified that all lobes look great.
 
1967 'cuda said:
Our motor didn't reveal any issues with leakdown test but the valves were set just tight enough to throw timing off. - Barely wanted to run. Intakes were opening too soon then and had a tendency to pop back through carb.
Click to expand...

That is a thought. When I decide to put the intake back on I may back the valves off a 1/4 turn. I adjusted them with a 1/2 turn as suggested in the instructions. No popping back through the carb issues though.
 
I've read several threads about adjusting valves on various websites. I've come to believe that rotating the pushrod as a means of determining zero lash can be deceptive. Some of the best builders say not to use that as your guide. Instead they recommend feeling for 'up & down' play.
 
1967 'cuda said:
I've read several threads about adjusting valves on various websites. I've come to believe that rotating the pushrod as a means of determining zero lash can be deceptive. Some of the best builders say not to use that as your guide. Instead they recommend feeling for 'up & down' play.
Click to expand...

Up and down play is how I check mine also.
 
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