d17 series III will not run below medium acceleration

trpaul1

Member
I was spraying at medium rpm. As I started it, it would not run below medium rpm but would run normal at accelerated rpm. I cleaned the carburater and air cleaner. I inspected the linkage and discovered no fault. I checked the points and timing which are ok. Is there a vacuum that controls the feed to the governor? Help! thank you
 
Can you expand on the symptoms... It won't run at lower speeds as in it will not idle down? It dies? Misses
or lacks power?
 
thx steve; it dies. if I leave the starter on it will run.
as soon as I let off the starter button it dies until I increase the acceleration. It seems that it does not get sufficient gas at lower rpm. It doesn't sputter, it just dies.
 
Couple things come to mind, hard to tell though without hearing it run...

If it is a fuel problem, could be major vacuum leak, or something clogged in the idle circuit. Does choking help? If no vacuum leak found, revisit the carb, be sure the passage to the tiny holes beside the throttle plate are open to the main circuit.

My other concern is compression. If you can run a compression test, look for differences between cylinders, dead cylinder, low compression, below 70 would be a concern.
 
choking doesn't help. How could I identify a major vacuum leak? I'm going to remove the carburator and clean & check again. thx.
 
"How could I identify a major vacuum leak?"

A vacuum leak so bad it won't idle should be obvious, should be able to hear it sucking air. Look around the manifold to head gasket, the carb flange gasket, any missing plugs in the intake.

To find small vacuum leaks, with the engine running, (if you can keep it running!), spray flammable carb cleaner around the suspected areas it could leak. The rpm will change, smooth out when the spray gets drawn in through the leak.

Another rare occurrence is for the exhaust manifold to burn through to the intake internally. That only happens when the intake and exhaust are joined together as one casting or bolted together for preheat transfer. Need to remove the manifold, fill the exhaust with water, watch for it to pass through into the intake if this is suspected. But just keep that in mind for now, happens very rarely.

"choking doesn't help" That is a good indication it's not lean fuel related. Are there any other symptoms?

Black smoke?

Gas running out the carb?

Popping or backfiring out the intake or exhaust?

How do the plugs look? All the same color? Wet, dry, oily, black, white?
 
I have no vacuum leaks, smoke, gas and plugs/points look ok. I had a suggestion that it is probably the governor. The suggester said it was common practice on ac's to repair the governor during any overhaul. He said it's not a bad job. Have you had any experience with repair and/or any tips. thx
 
The governor wouldn't have an effect on starting. It only controls RPM. The hand lever on the dash controls a spring attached to the gov arm. The spring tries to pull the throttle open. The governor senses engine speed, counteracts the spring and pulls the throttle back far enough to keep the RPM at the desired speed.

You should be able to manually override the gov by operating the throttle plate by hand. Try to adjust the carb so it will idle. Set the throttle stop, adjust the idle mixture...

If you can get it to idle, then observe the gov action. Watch the throttle linkage, with the engine speed set to idle, quickly push the hand lever to fast. You should see the throttle plate go wide open, then return to part throttle as the RPM comes up. If it will do that, the gov is doing it's job.

If the RPM surges, or the engine tries to die when quickly accelerated, it's too lean.

But, if there are other problems, if it won't idle, it will be difficult to diagnose the governor.
 
thx steve, I disconnected the throtle and manually operated the butterfly to idle. Then as you suggested, I got run by adjusting fuel feed and slow rpm. I then reconnected the throtle and it runs both idle and fast. Sometimes a novice like me makes things more difficult than necessary. I really appreciate your help.
 

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