Engine Problem-Need Your Ideas Please

Posted By: Rodder

Engine Problem-Need Your Ideas Please - 08/23/13 01:53 AM

I have a 360 that I race just for fun. It has a rough idle cam. I have been trying different carburetors just to see if there is any improvement. But I have developed a problem that is driving me crazy. The engine will start right up and will run great as long as you keep it about about 1500 rpm and up. I had a holley double pumper on it and I thought that was the problem. I changed to another double pumper same problem. Now I put a nearly new edelbrock thunder on just to eliminate the holley could be problems. I have the same trouble with the edelbrock. I figure its not the carb. So today I started on the electrical system. It has a stock electronic mopar dist. with light springs and chrome box. I took the distributor out and checked everything it seems good, bushings tight, springs in place, changed the cap and rotor. I have the timing set at 32 degrees advance at 2000. It wont idle at all so I don't know what idle is. It also seems like a vacuum leak possibility but I have checked the intake bolts and replaced the carb/ manifold gaskets, don't see any place for a leak. Watching the tach there is some rpm variance at slower speeds like 1500-2000. Anything under about 1500 and it dies just like I shut the switch off. Has anyone had anything similar I am at the end of my check list. Thanks

Posted By: dennismopar73

Re: Engine Problem-Need Your Ideas Please - 08/23/13 02:06 AM

Vacume leak on the intake, possible miss adjusted valves, or both!
The intake needs o be checked put it on dry checkit with feeler gage top bottom side to side, do not use cork end gaskets if it is aluminum just use gasket sealer . nice 1/4 bead will work great.
If intake checks out, use small amount o sealer around the intake ports top bottom of gasket .
Most small blocks love to leak on the valley side

Posted By: VernMotor

Re: Engine Problem-Need Your Ideas Please - 08/23/13 02:09 AM

How much timing does it have at idle ?

Posted By: Crizila

Re: Engine Problem-Need Your Ideas Please - 08/23/13 02:37 AM

Quote:

Vacume leak on the intake, possible miss adjusted valves, or both!
The intake needs o be checked put it on dry checkit with feeler gage top bottom side to side, do not use cork end gaskets if it is aluminum just use gasket sealer . nice 1/4 bead will work great.
If intake checks out, use small amount o sealer around the intake ports top bottom of gasket .
Most small blocks love to leak on the valley side

A sure test to see if you have a manifold to head port vacuum leak on the crankcase side is to block off all the openings on the valve covers ( breather, PCV, Oil fill cap, Etc. ) and see if the idle improves with everything blocked off. If it does, you have a vacuum leak to the crankcass.

Posted By: Rodder

Re: Engine Problem-Need Your Ideas Please - 08/23/13 04:24 AM

Thanks guys, I am on it. Intake coming off tomorrow.

Posted By: cheapstreetdustr

Re: Engine Problem-Need Your Ideas Please - 08/23/13 04:28 AM

just start it up and let it idle..
then spray some carb cleaner around the areas you suspect may have a leak...like intake gasket area.
carb base ect...
if the idle changes drastically you have found the source of the vacuum leak

Posted By: dodgeboy11

Re: Engine Problem-Need Your Ideas Please - 08/23/13 05:19 AM

I've forgotten to plug the brake booster line up before and it ran that way. Makes me wonder if the pcv valve is stuck open or there's a hole in the brake booster diaphragm. Before pulling the manifold I would disconnect all vacuum lines and cap them to see if the problem goes away.

Posted By: blown71duster

Re: Engine Problem-Need Your Ideas Please - 08/23/13 12:10 PM

Quote:

Quote:

Vacume leak on the intake, possible miss adjusted valves, or both!
The intake needs o be checked put it on dry checkit with feeler gage top bottom side to side, do not use cork end gaskets if it is aluminum just use gasket sealer . nice 1/4 bead will work great.
If intake checks out, use small amount o sealer around the intake ports top bottom of gasket .
Most small blocks love to leak on the valley side

A sure test to see if you have a manifold to head port vacuum leak on the crankcase side is to block off all the openings on the valve covers ( breather, PCV, Oil fill cap, Etc. ) and see if the idle improves with everything blocked off. If it does, you have a vacuum leak to the crankcass.

With everything blocked install a vacuum gauge on the dipstick tube and see if you have vacuum with it running from the valley side of the intake.
Also use a water bottle and spray on the header tubes after it runs for a little bit and make sure each tube is getting hot, great way to find a cylinder down.

Posted By: Crizila

Re: Engine Problem-Need Your Ideas Please - 08/23/13 02:44 PM

Quote:

Quote:

Quote:

Vacume leak on the intake, possible miss adjusted valves, or both!
The intake needs o be checked put it on dry checkit with feeler gage top bottom side to side, do not use cork end gaskets if it is aluminum just use gasket sealer . nice 1/4 bead will work great.
If intake checks out, use small amount o sealer around the intake ports top bottom of gasket .
Most small blocks love to leak on the valley side

A sure test to see if you have a manifold to head port vacuum leak on the crankcase side is to block off all the openings on the valve covers ( breather, PCV, Oil fill cap, Etc. ) and see if the idle improves with everything blocked off. If it does, you have a vacuum leak to the crankcass.

With everything blocked install a vacuum gauge on the dipstick tube and see if you have vacuum with it running from the valley side of the intake.
Also use a water bottle and spray on the header tubes after it runs for a little bit and make sure each tube is getting hot, great way to find a cylinder down.

2 good ones

Posted By: gregsdart

Re: Engine Problem-Need Your Ideas Please - 08/23/13 03:28 PM

Quote:

How much timing does it have at idle ?

You said you had light springs in it, if they advance too quickly, and you try and set your idle it will either run fast or the timing will fluctuate, reducing idle speed, which lets the timing back off, motor stumbles and dies. If this is the case (check with timing light) Find a bit stiffer spring that won't let advance start till 1200 rpm or so, and the bigger the cam you have in it, the more initial advance you will need and the less coming in through the advance plate. A moderate street strip cam may need 12 to 16 initial degrees timing, to a race cam demanding a locked distributor for best results.
This may be a problem along with a large vacuum leak. Check both.