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FatJackDurham

Carb issues Onan 16

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On my 416-8 with an Onan, I had the carb cleaned and the engine tuned earlier this year. Even after tuning, the engine would surge a lot immediately after starting, but less after warm up.

 

Lately, even after warm up, if I throttle DOWN, the engine settles to an idle, but when I start to throttle up, the engine almost stalls before it then revs up.

 

This reminds me of when I used to try to tune my car in high school. Sometimes, I would get it so that when I started to step on the accelerator, if I opened it too quickly, the car would stall. 

 

What kind of carb ajustment does this call for? Is it running too lean? Too rich? It seems like when the throttle place opens, allowing more air, is when this happens. I suppose this indicates a temporary drop in vacuum, or low pressure through the carbs venturi, drawing less gas, but I don't know how to remedy it. 

 

Thoughts?

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Generally - if there is a flat spot when opening the throttle it's caused by a plugged jet , incorrect idle/main mixture settings or a vacuum leak in either the carb gasket or throttle shaft seals on most engines . It can also be caused by incorrect point gap or timing - if the timing is off by a few degrees it will make it harder for the engine to increase in rpm's with any decent response . When everything is right - they should snap right up...most times a simple carb rebuild will cure that issue .

 

Sarge

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3 hours ago, Sarge said:

Generally - if there is a flat spot when opening the throttle it's caused by a plugged jet , incorrect idle/main mixture settings or a vacuum leak in either the carb gasket or throttle shaft seals on most engines . It can also be caused by incorrect point gap or timing - if the timing is off by a few degrees it will make it harder for the engine to increase in rpm's with any decent response . When everything is right - they should snap right up...most times a simple carb rebuild will cure that issue .

 

Sarge

 

Thanks. So by flat spot, you are including that the engine firing completely stops? Its not like I open the throttle and the engine keeps firing, just doesn't speed up. It's as though the gas stops completely.

 

 

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5 hours ago, FatJackDurham said:

Even after tuning, the engine would surge a lot immediately after starting, but less after warm up.

From this statement I presume the same problem existed prior to the work that was performed. Could be a vacuum leak or intake gasket leaking. Lean adjustment of the carburetor could do this and valve lash too great could do it too.

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jack

i,m not familiar with all of the wheel horse/ onan combinations

can you please list the model of the engine and the carb model?

 

a pic would also be nice.

 

thank you. boomer ( the used onan engine parts guy, also NOS and new ) 

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My 416H does the same thing lately (surging after start).  However, here in MA, it has been colder than normal so I just leave the choke on a bit and within 5 minutes all is good.  Winter gas which evaporates faster than summer gas has not yet hit the stations yet (at least in premium which is all I run), so I am thinking that once winter gas is here, the problem will go away.  I do not have the "almost stall" problem you mention.

 

As 953 Nut said, I could have a vacuum leak which goes away once things warm up.  If you have a real bad vacuum leak, you will know it.  It will run like crap all the time.  My neighbor has a JD 318 from the 80's and he finally fixed the leaky manifold.

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