Generator hunting problem

[Beckytek]

Ever since I bought my boat 13 months ago the Onan generator 6.5k gas has had difficulty maintaining constant speed. If I adjust the idle and main carburetor jets it gets better then I put a load on it and it'll run all day long in spec. Just when I think I got it the next time I go to the boat it starts all over again. I have tried all the suggestions in the manual to no avail. Changed governor spring, adjusted arm length, sensitivety, idle srews but nothing seems to work permanently. Any suggestions would be greatly appreciated.
Ron

 

[spartonboat1]

Re: Generator hunting problem/ old guess

This goes back a way...but in the old days, carburators incorporated pot metal in their construction, although I would have thought that a marine genset would be all brass or similar material. At any rate, modern gas, since about the early 1970's can include some degree/percentage of ethanol.

I used to fight a battle keeping a double carburator Mercedes I that I once owned, in tune. Then I observed, plus researched, that ethonal and some carburator parts do not like each other and a grey gum can form on the very small idle passages.

When I learned where to spray with a can of carb clearner, i.e. on and through the fine idle passages, which are just where the throttle plate sits next to the wall of the venturi, then I no longer needed to do any more adjusting. A couple shots in the correct places was the cure, since that cleared the fine passages.

A telltale at the gas pump is a sticker that the gas complies with all state standards and does not exceed 10% ethanol.

That's one possible answer...

 

[67hat34c]

I can help with the MCCK problem with hunting. I have the shop manuel etc.

There are many reasons for hunting but the main reason is the governor. there is a sensitivity setting that can be adjusted. also the spring gets old and looses some properties and should be replaced. Lastly carburator deposits etc can cause this.

To adjust the sensitivity, look at the gov arm. there is a clip on the arm, slide towards the shaft for higher sensitivity and away for less. also there is a ball joint that needs to be lubricated, Onan recommends using graphite.

My books are all at the boat in stuart, i can bring them back this month and fax you what ever you need.

Recommend obtaining carb kit and rebuilding the carb, special attn to needle valve setting/float valve. this can also cause hunting.

Steve Hierholzer
E Mail. Shierh@aol.com

 

[Beckytek]

Thanks Steve,
I have the manual also, so no need to fax. I did all those adjustments they suggest in the manual to no avail. I will try the carb cleaner Sparton boat recommended first and if that doesn't help I'll rebuild the carb as you suggest.
What's crazy is when I get it adjusted and put a load on it, it runs great for the rest of the day, right within spec and no hunting. When I put a load on it, it settles down and works great. When I return to the boat a few days later it starts hunting all over again. Crazy.
Ron

 

[Kathy L]

Ron, We are changing out our 6.5 MCE gas to diesel. Check out "Parts for Sale" It replaced our mcck.

 

[67hat34c]

That sounds more like gunk in the carb. you can try pulling the 2 jet adjustment screws out and blowing cleaner through it. Rebuild is easy, not that much in there. I will say that I used a fuel addative last year that seems to have cleaned the system up. I had to re adjust the high speed jet on the onan, leaned way down after using the stuff. AJX is a fuel system attative that I am putting in a vote as a good product. Took care of the bacteria problem that we had, Onan running better was a bonus.
By the way, what fuel pump are you using? I bought a new electric pump from an auto parts store and installed it 2 yrs ago. it cured all the problems the prior owner could not fix. 35-40 pump, way cheeper than buying one from onan.

These MCCK's are old, very heavy and bulky. However, mine runs strong, very quiet and is fun to tinker with. I plan on pulling it next year, sandblast and paint with Imron. Might as well look as good as it runs.