1997 Challenger 1800 running away

[Jrf0007]

I am having a problem with one of the twin 787 engines. I have been testing it on the trailer. When I start the port engine it will idle at about 3000 rpm in neutral but bogs if I try to give it more while in neutral. When I put it in forward and give it a little gas it will over rev to over 7000 rpm, will not back off and I need to pull the key to shut it down. It reacts like it is stuck at WOT. The carbs were recently rebuilt and pop-off pressures were within range. I am at a loss to figure it out. Any idea what the cause is or how to fix it? I have been chasing carb issues with this sport boat for several years and there always seems to be something amiss.

 

[mikidymac]

There is a neutral safety switch so it is normal to not be able to rev them up in neutral.

If you are getting a runaway it is typically an air leak and if you have done the carbs it is usually the carb base gaskets.

 

[Jrf0007]

Is there a way to test the base gasket seals without removing the carbs? Also is there an in-boat diagnostic procedure for leak testing? I suspect it is sucking air somewhere causing it to run extra-lean. My brother suggested spraying some starter fluid judiciously in key areas while it is running and monitoring for increased revs. Wondering if that works and if it is safe?

 

[Theguyinmi]

That would also be my recommendation but always keep a fire extinguisher handy.

 

[WhiteZombie]

Is there a way to test the base gasket seals without removing the carbs? Also is there an in-boat diagnostic procedure for leak testing? I suspect it is sucking air somewhere causing it to run extra-lean. My brother suggested spraying some starter fluid judiciously in key areas while it is running and monitoring for increased revs. Wondering if that works and if it is safe?

Did you figure out where your leak is? On the spraying starter fluid, one thing that is safer is to spray WD-40 around the manifold gaskets. Lawn mower guys do this to find leaks, but maybe won't show up as good the way a 2 stroke smokes, but I would think you could see a difference. Leaks happen at the crank bearings too