# Engine races high on start up



## Adam F (Feb 29, 2004)

It's my dad's 318. When you start it up, the engine races to a really high RPM, and then falls back down to normal. What's causing this, and what is the fix? Thanks!


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## Archdean (Jul 15, 2004)

There are only two reasons for this to happen !

Too much fuel and two much air!!

Can be because the choke is not working (allows too much air) or the carb is not seated correctly (gap is allowing too much air)!

Fuel float is not working IE allowing full fuel flow!


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## Live Oak (Dec 22, 2003)

Adam, does the engine tend to over rev like that when cutting and you encounter a heavy load such as really thick grass or something that lugges the engine down in rpm? My reason for asking is that I believe your Dad's 318 Onan engine is a governed engine and if the engine govenor is not operating properly, this could be causing the problem. Just be sure to give things a good going over with your owner's manual and look for anything out or place or out of the ordinary. such as a broken or stretched throttle spring or other similar things.


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## chrpmaster (May 5, 2004)

First of all welcome to Tractor Forum!!

I had the same thing happen on my two wheel Gravely when the governor spring came unhooked. I near had a heart attack until I got it shut down :hide: 

Luckily those old tractors are tough enough to take the abuse and continue to keep going strong. 

On yours it sounds more like the throttle or governor is sticking wide open and the governor spring isn't strong enough to pull it back to where it should be. Clean everything up and make sure everything is working well and try it again. Could be the vibration of starting allows the weak governor spring to pull the throttle down but can't do it quick enough to prevent the over reving. 

Does it happen everytime it starts or just when its cold? the cold weather will show you any weak parts on your tractor especially when it is hardest and coldest to fix. 

Good luck and keep us informed on your progress!


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## Adam F (Feb 29, 2004)

Not sure if it rev's high when the engine is loaded, I've yet to cut grass with his new tractor. But I want to say no, but I'll have to ask my dad to be sure.

Happens pretty much every time. Sometimes it revs so high I think the engine will explode! But it only lasts for a second and then it idles normal.

As soon as it dries out and isnt freezing cold outside, I'll take a look at it.

Thanks for all the help guys! This site is going to be a lot of help to me come grass cuttin' time!


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## mark777 (Jul 23, 2004)

IMHO:

Chief & Chrpmaster hit it on the head....had the same trouble with a Tecumseh 10 HP, and went through the tortures of over reving for two days while trying to isolate the problem.

It was the spring...I inadvertnetly stretched it while removing the throttle plate. Just a very small amount, but enough to loose the original tention, and allow the throttle to run wide open for a good 10 seconds if I didn't grab the carb throttle control......every time I started it.


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## HYDROGUARDIAN16 (Feb 14, 2007)

definitely is the governor, this happens to me alot when I rebuild my engines.


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