IDLE SPEED PROBLEMS

[DollarBill]

I want my tractor to be like Dell's "eazy starting 6-volt 8n that idles at 435 rpm"

I'm putting the finishing touches on the engine rebuild and the only thing left is getting the idle right.

The best stable idle I can get is around 600 and the idle mixture screw is bottomed out - If you back out the idle mixture it dies.

I've overhauled the carburetor using the full kit making sure it was clean and tight - Soaked it overnight in carburetor cleaner, blew out and ran a tip cleaner through all the passages, verified jet sizes, float level everything that I can think of. Replaced the venturi. Top/bottom halves of carb mating surfaces are true.

If babied, it will get down to 550 but it sounds like it's gonna die any minute.

Exhaust smells very fat.

To show my determination, I bought a new, (looks like the original) made in the USA carburetor and after fiddling with the adjustments, the best it would do was 750 and it would eventually stumble and die. It actually ran better with the original one.

I've scoured the archives and can't find anything about poor idle quality.

What am I missing?

In case it matters, it's a 1950, 6 volt, pos ground, side mount timed at 4 BTDC.

 

[Dunk]

Going out on a limb, what do you know about the shape of the centrifugal advance springs in the bottom of the distributor?

 

[DollarBill]

It's a new distributor - Should be okay?

What are you thinking? - My clip is empty.

FYI - I was having the same poor idle with the original distributor.

And just to satisfy your natural curiosity :wink: I replaced the distributor because the shaft/bushings and the two little timing advance posts were worn. It was a wash between repair parts and new distributor.

 

[Dunk]

(quoted from post at 23:20:05 12/22/09)
It's a new distributor - Should be okay?

What are you thinking? - My clip is empty.

FYI - I was having the same poor idle with the original distributor.

And just to satisfy your natural curiosity :wink: I replaced the distributor because the shaft/bushings and the two little timing advance posts were worn. It was a wash between repair parts and new distributor.

I'm just trying to cover all of the bases that I can think of.

 

[Dunk]

[color=blue:226b3c0724]I'm putting the finishing touches on the engine rebuild and the only thing left is getting the idle right. [/color:226b3c0724]

This may denote that the rings aren't seated yet, and it needs running.

 

[Den N Ms]

DollarBil,Maybe you need to look again if the venturi is damaged or installed wrong, or the body gasket is bad in that area.

If there is a leak in the venturi or body gasket area, the supply of air to the idle circuit and bowl vent, from the air horn, gets screwed up, and idle is affected.

 

[R Geiger (or)]

if you can screw the idle screw all the way in, I think it is an indication of an air leak in the induction system. bad gasket on carb to manifold, bad manifold gasket or real bad worn intake valve stem and guides. IMHO

 

[Dell (WA)]

$Bill.......you write......"The best stable idle I can get is around 600 and the idle mixture screw is bottomed out - If you back out the idle mixture it dies".......remember the side-pointing idlemix is BASSACKWARDS; out for lean, IN for ENRICH. When you back out the idlemix, guess what??? you are LEANING the idlemix and it will die. Its the LAW.

You do know the idlemix quits working at about 600rpms, don't you? Its all on the mainjet from about 600rpms to WOT. Set yer down-pointing mainjet to 2-turns and LEAVITT!!! Now try adjusting yer side-pointing idlemix.

You write......"If babied, it will get down to 550 but it sounds like it's gonna die any minute"......Check yer 5-nipple distributor firing order, 1,2,4,3 CCW. These N-Engines are soooooo gooood they will start and run on just 2-cylinders and won't have enny power. Usually sparkies 3&4 gitt swapped. .......Dell

 

[souNdguy]

is the carb all squeaky clean with all the pasageways cleaned out with wire or guitar string.. as the others tell you.. idle screw in, is enriching it..

soundguy

 

[DollarBill]

[color=green:05a5db9feb]This may denote that the rings aren't seated yet, and it needs running.[/color:05a5db9feb]

Dunk, I was wondering about the new engine having an affect on the vacuum signal. I've exhausted all the likely tweaks and tricks and was hoping one of the pros would give me more ammo. I'm gonna run it a while and see if it improves with age - It just goes against my grain for it to have the last word.

 

[NOXJohn]

If you did a complete rebuild with new rings, etc. then you may need to put 30-40 hours on it before everything is broken in and it will run correctly. Both the rebuilds I did ran a lot better after working them some.

 

[DollarBill]

[color=red:bf14ebe9de]if you can screw the idle screw all the way in, I think it is an indication of an air leak in the induction system. bad gasket on carb to manifold, bad manifold gasket or real bad worn intake valve stem and guides. IMHO[/color:bf14ebe9de]

More info; same idle problems with with two different manifolds/gaskets, two different carbs (one was brand new and ran worse than the old one), overhauled engine=new valve train.

 

[DollarBill]

[color=darkblue:f6a356053e]If you did a complete rebuild with new rings, etc. then you may need to put 30-40 hours on it before everything is broken in and it will run correctly. Both the rebuilds I did ran a lot better after working them some.[/color:f6a356053e]

I'm liking the way that sounds - I'm am kinda new to these old tractors and wanted to hear someone elses experience. Just what I needed - Thanks.

 

[DollarBill]

Hi Chris, yes I scoured the archives for the most likely culprits and did all the things everyone recommends.

[color=green:8f62f22789]"I've overhauled the carburetor using the full kit making sure it was clean and tight - Soaked it overnight in carburetor cleaner, blew out and ran a tip cleaner through all the passages, verified jet sizes, float level everything that I can think of. Replaced the venturi. Top/bottom halves of carb mating surfaces are true."[/color:8f62f22789]

 

[DollarBill]

Thanks Dell, ......you write......[color=green:5d2b9b25b8]"The best stable idle I can get is around 600 and the idle mixture screw is bottomed out - If you back out the idle mixture it dies".......remember the side-pointing idlemix is BASSACKWARDS; out for lean, IN for ENRICH. When you back out the idlemix, guess what??? you are LEANING the idlemix and it will die. Its the LAW."[/color:5d2b9b25b8]

Ok - It leans out and dies when backing out the idle mix screw - Possible causes?

[color=green:5d2b9b25b8]"You do know the idlemix quits working at about 600rpms, don't you? Its all on the mainjet from about 600rpms to WOT. Set yer down-pointing mainjet to 2-turns and LEAVITT!!! Now try adjusting yer side-pointing idlemix."[/color:5d2b9b25b8]

I can get it to run at 550 for a short time but it still runs raggedy. It's real happy above 600 rpm.

[color=green:5d2b9b25b8]"If babied, it will get down to 550 but it sounds like it's gonna die any minute"......Check yer 5-nipple distributor firing order, 1,2,4,3 CCW. These N-Engines are soooooo gooood they will start and run on just 2-cylinders and won't have enny power. Usually sparkies 3&4 gitt swapped."[/color:5d2b9b25b8]

I actually fell into this trap last year when replacing the distributor - After reading it as a possible solution to many other's problems, I didn't think it could happen to me - Took me forever to get all that egg off my face.

Engine performance is good everywhere but idle and it's really buggin me.

 

[DollarBill]

[color=darkblue:f545367b46]Den N Ms - "DollarBil, Maybe you need to look again if the venturi is damaged or installed wrong, or the body gasket is bad in that area.

If there is a leak in the venturi or body gasket area, the supply of air to the idle circuit and bowl vent, from the air horn, gets screwed up, and idle is affected."[/color:f545367b46]

[color=green:f545367b46]What I've done: Replaced the venturi for S&G. Verified proper orientation. Gasket shows full contact on both halves of carb. Same poor idle qualities between two different carbs? I know it is possible to get a new/faulty carb but what is the probability of it displaying the same tendencies as what your are replacing?

Thanks and keep em coming. [/color:f545367b46]

 

[Grits]

Ok, it wouldn't idle on 2 different carbs and wants the air mix screw all in to run. Sounds like it may not be the carb. May be an intake manifold leak so lots of air is getting in and not through the carb. Can you get a manifold vacuum gage onto that? You can read some here:
http://www.gregsengine.com/vacuum.htm
My manifold has a 1/8" plug just above the carb where I can put a gage. It can tell you a lot.

 

[DollarBill]

[color=brown:f93f697cae]Ok, it wouldn't idle on 2 different carbs and wants the air mix screw all in to run. Sounds like it may not be the carb. May be an intake manifold leak so lots of air is getting in and not through the carb.
[/color:f93f697cae]

I agree with you about the vacuum leak.

Same problem transferred through two manifolds - Unlit propane torch test results were good.

Since engine has less than 2 hours on it, think I'm gonna hold off on further troubleshooting until the rings have a chance to seat.

Will post back then.

[color=red:f93f697cae]To all who responded - Thanks for your help!![/color:f93f697cae]