My NHC 250 revs up very high when I first start it. It also doesn't shut down right away when ignition shuts off. Some white smoke at various rpms. I am hoping this isn't a valve stem oil seal leak or something like that. I have read other comments on fuel system issues but I have found nothing about revving up when first starting. Linkage is at idle position. Also doesn't idle well. Surges some or stalls out. Just throwing this out there for ideas. This weekend I will go through the basics. New fuel filter is installed. Engine sat for a couple years.
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NHC 250 M936 Engine Revs Very High when starting
- Thread starter J4Jenius
- Start date
Sucking air. Check around the motor and pump for wet spots. Especially the end of the throttle shaft. If none are found. Start by replacing the fuel filter and gasket since it has been sitting. Then move on to the filter to pump suction line being the next culprit
BenRoberts
Certified insane
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When my suction hose started to crack it did what you described. Lots of little fine hair cracks
Thank you Gentlemen. The supply line was cracking like you said and the primer pump also had a leaky fitting. It now starts up normally without over revving. It revs up a little but normal. Doesn't have white smoke at idle. BUT, white smoke at 1500 rpms and still doesn't want to idle. I'm think fuel pump has a lot of crud in it... the filter and the line did have crud in them. Should I pull fuel pump out and have it looked at?
There isnt much you can do with the pump internals. Did you delete the primer pump? Simply put a 1/8" pipe plug in that little elbow at the back of the pump. The military filter is 10 micron so not much should get by it.
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If you had an air intrusion issue, it can take a bit to get all the air from inside the pump out. Go drive it then let it sit.
Good idea. I will take it out for spin and let it try and sort itself out. Also I didn't delete the primer pump, I isolated it with an 1/8" needle valve. This way I know it is isolated and still have the ability to use it if needed. Great suggestions everyone, thank you.