Rough Idle Part 2

[meadowbrook]

Hello, all.

 

 

A while ago I asked the forum about a possible reason for my '50 Meadowbrook to idle rough when I utilized its fluid drive capability by stopping and not pressing the clutch. I received some advice to raise the idle speed in neutral above the 450 rpm in the spec sheet, which I did.

 

I have never been able to get it to idle as smooth it does in Neutral. (it idles smoothly in neutral or in gear with the clutch pressed, aside from a few misfires here and there.

 

The idle drops from around 650 to 450-500 RPM when I release the clutch pedal while stopped and in gear, then the engine does not sound too happy, running rougher.

 

I believe I have the original Fluid Drive Fluid, the idle mixture is perfectly set to highest vacuum, timing is set to 8 degrees BTDC at idle (I know spec is 0, but it also behaves the same way at that setting and it sure is perkier at 8 deg, with no knocking  ).

 

Last bit of info, my plugs are a couple of years old, porcelains look tan, wires are recent, coil is original, but also tried a new one with no difference. Dwell is within spec, no vacuum leaks.

 

The only thing I can imagine is the fact it is an original engine (never rebuilt as far as I know) and the compression is below spec, with cylinders 2-5 at 100 psi and #1 at 85 PSI. It does not smoke, ever, though.

 

Oh, and valve clearances are to spec, I set them with the engine running.

 

Any thoughts?

[P15-D24]

Plug your vacuum advance line at the carb base and see if the miss stops. I would also check the intake for vacuum leaks.  

[55 Fargo]

Hello, all.

 

 

A while ago I asked the forum about a possible reason for my '50 Meadowbrook to idle rough when I utilized its fluid drive capability by stopping and not pressing the clutch. I received some advice to raise the idle speed in neutral above the 450 rpm in the spec sheet, which I did.

 

I have never been able to get it to idle as smooth it does in Neutral. (it idles smoothly in neutral or in gear with the clutch pressed, aside from a few misfires here and there.

 

The idle drops from around 650 to 450-500 RPM when I release the clutch pedal while stopped and in gear, then the engine does not sound too happy, running rougher.

 

I believe I have the original Fluid Drive Fluid, the idle mixture is perfectly set to highest vacuum, timing is set to 8 degrees BTDC at idle (I know spec is 0, but it also behaves the same way at that setting and it sure is perkier at 8 deg, with no knocking  ).

 

Last bit of info, my plugs are a couple of years old, porcelains look tan, wires are recent, coil is original, but also tried a new one with no difference. Dwell is within spec, no vacuum leaks.

 

The only thing I can imagine is the fact it is an original engine (never rebuilt as far as I know) and the compression is below spec, with cylinders 2-5 at 100 psi and #1 at 85 PSI. It does not smoke, ever, though.

 

Oh, and valve clearances are to spec, I set them with the engine running.

 

Any thoughts?

I think you may have answered your own question.

Your engine is worn, most likely some valve seating issues, and general uneven and less than optimal over all compression.

i cold be wrong, but you may be just dealing with a well worn engine, and it may take a ring and valve job or complete overhaul to get the desired results

[1941Rick]

Sounds like a loss of vacumn. Your compression is not the problem. Hook up a vacumn gauge and let us know what it reads when running smooth and when it runs rough.

[Jeff Balazs]

In order to work properly my fluid drive needed a good steady vacuum reading. When I first put my truck back together I could not keep it from stalling at idle in gear. I had hooked up the VPW PCV valve install kit and it was causing the vacuum reading to fluctuate too much. Once I removed and capped off the PCV line the problem with the idle in gear went away. I have a good vacuum gauge installed and get a steady reading of 20.5".

 

I am finally in the process of refitting a PCV valve.......hopefully I can find one that actually works as it is supposed to. I would like to have the benefit of better crankcase ventilation to go along with the nice smooth fluid drive.

 

I don't know if you have a PCV on your car.....but if you do it could well be what is causing the problem you are having with the idle. Either way you need a steady vacuum reading.

 

Hope this helps.

Jeff

 

Jeff

[meadowbrook]

Thanks for the responses. My vacuum is steady at idle, but I will check what happens if I place it gear.

[Jeff Balazs]

What sort of reading are you getting? Is it well above 18".

You may need to turn the idle up some. 550 rpm.....maybe a bit more. Also is the dashpot working on your carb?

 

Jeff

[meadowbrook]

I think it is over 18, like 20 or so. Need to check again. No dashpot in my carb, for some reason it has a Carter BB. But I don't see how the dashpot would matter just during steady idle. It is currently set to 650 or so and as I said, pretty steady vacuum readings if in neutral. Will remeasure in gear.

[Jeff Balazs]

It almost sounds like maybe it could be idling a bit too high and dragging a bit. Maybe there is a sweet spot as far as idle speed goes? I do know mine has a bit of drag and like a conventional automatic.seem to want to pull some at idle and in gear. I just figured that as long as it doesn't have a tendency to stall all is well. I only really use this feature if I am only going to be sitting still for a pretty short time....or on a hill where it really shines.

 

Jeff