Struggles At Low RPM

[paddy1998]

I'm not very good with carburetors so I don't really know where to start. I have a Simmons Super Power.

Before I pulled the engine to do some other things everything ran fine. Since I put it back together the engine struggles and dies at low (idle) rpm. It needs a LOT more throttle to run

Removal consisted of disconnecting the fuel line and removing it with the intake manifold. I opened the drain on the bowl to drain the fuel, re tightened it and put the whole thing on the workbench where it stayed until I reinstalled it.

I never touched the needle adjustment, or anything else for that matter. I put it back on there exactly how it came off.

I'm flummoxed and don't know where to start troubleshooting this kind of thing.

Any advice would be appreciated.

[Mark Gregush]

Does it have the flapper in it ? Try adjusting the spray needle. These are not plug and play carbs they need to be adjusted to meet the demand of the engine, you might be running too lean.

[HPetrino]

I'd be looking for a vacuum leak.

[TonyB]

Seems to me that you are telling us that the carb has not been touched from before the rebuild. It would seem reasonable, assuming you are correct, then the problem is nothing to do with the carb.
Vacuum leak seems reasonable.
Did you put new copper rings and steel rings on the manifold?
Is the camshaft timing correct?
Have you got compression on all four cylinders.
What are the values?
Is the ignition timing correct?
On a 3 1/2” pulley The 5 degrees ATDC is little over 1/8” and the 30 degrees BTDC is about 3/4”.
Seriously the vacuum lesk is your best bet but without knowing what you did, everything is a guess

[paddy1998]

Seems to me that you are telling us that the carb has not been touched from before the rebuild. It would seem reasonable, assuming you are correct, then the problem is nothing to do with the carb.
Vacuum leak seems reasonable.
Did you put new copper rings and steel rings on the manifold?

I'd be looking for a vacuum leak.

Vacuum leak!

Yes I did put new copper rings a steel rings on the manifold.

Time to get out the stethoscope . . .

Thanks! I'll get on it.

[Kerry]

The carbie will need to re-set the mixture, after a re-build the engine has a new vacuum value, tune it to match.

[Norman Kling]

What did you do to the engine while it was apart? Perhaps the problem is a tight engine. It will take a bit more gas to idle the engine until it breaks in. In fact sometimes the engine cannot even be started with the crank or starter and has to be pulled for the first start. Drive short distances at slow speeds letting the engine cool off between drives. As you begin to break in, gradually increase speed for short spurts then slow down again. After 100 miles or so, the idle might be lowered a bit and as the engine wears in it will have more power and idle more smoothly.

This is additional information, the cause of the problem could be any of the above posts.
Norm

[RustyFords]

My tried and true vacuum leak detection method is to spray something flammable around the possible vacuum leak areas. If you have a leak, it'll suck in the spray and make the engine rev up.

Spraying flammable things on a hot engine is probably not the safest thing in the world so use caution and don't get carried away with too much spray.

Also...if you use brake cleaner like I have a few times, there's a chlorinated and non-chlorinated version. Don't use the chlorinated version. You could give yourself something similar to a WW1 phosgene gas experience.

[Susanne]

Also...if you use brake cleaner like I have a few times, there's a chlorinated and non-chlorinated version. Don't use the chlorinated version. You could give yourself something similar to a WW1 phosgene gas experience.

Friend of mine wanted to clean something prior to welding it, used brake cleaner, and put himself in the hospital with severe lung damage from this. Please be careful and read the labels!!! Phosgene is nothing to play with...

[paddy1998]

What did you do to the engine while it was apart?

The carbie will need to re-set the mixture, after a re-build the engine has a new vacuum value, tune it to match.

Norm and Kerry,

This adventure began because as I set about to do a simple valve job (which may or may not have been absolutely necessary ) the rearmost head bolt seized in the head which required the engine be moved forward to get a drill on it. Because that is pretty much the same amount of work as pulling the engine altogether I just pulled it out and and put the engine on a stand to do the work there.

All I did was clean up the carbon, seat and adjust new valves, and since it was on the stand I cleaned up the clutch pack, tested the clutch spring, and installed new bands.

I'm going to check for a vacuum leak and then fool with the carb adjustment.

Thanks!

[Jerry VanOoteghem]

Did you do a compression test after your valve job? Are you certain that all of your new valves are seated well? If not, it may explain your "struggles at low RPM".

[Norman Kling]

If the engine is hard to turn over in neutral, I would suspect a problem with the clutch. If you put the parking lever in the neutral position, and push the car it should roll with some effort but the engine not turn. Likewise when you turn the crank, the engine should turn but the car would not roll.

The other possible and more likely cause would be the valve adjustment is off. Were you sure that you adjusted the valves when the lifter was on the heel of the cam. That is the cam lobe should be pointing down at the position where you adjust the clearance. A compression check should rule that out. Compression should be around 50 psi and all should be approximately the same. On a worn engine or at higher altitude the compression would be lower but still the same on every cylinder, and if you have a non stock high compression head, the compression would be higher but still same on each cylinder.

Another possibility. The head should be torqued again after it is warmed up. Torque to 50 ft lbs and warm up the engine. If an iron head re-torque when hot. If an aluminum head re-torque after it cools off.

And there could also be possible vacuum leak as noted above.
Norm