Onan Surge on 416-8

[mikeeyre74 289]

I’ve  taken this apart and cleaned it a couple of times, but I’m missing something and can’t figure out what it is. Can you take a look at this video and let me know where I need to go next? 

 

https://flic.kr/p/2eMwbdu

 

 

[Reel Mower Freak 125]

I would remove the exhaust cover plates and do a spray test around the intake manifold to see if the seam or gaskets have failed allowing air in. 

[mikeeyre74 289]

I’ll give that a shot, thank you. 

[cleat 5,771]

Sounds like you need a good carb cleaning.

 

Pull the carb top off and clean it well.

 

Cleat

[mikeeyre74 289]

That I’ve done a couple times already. I think there’s more to it. Definitely missing something. 

[wallfish 16,963]

Can you smooth it out with some choke adjusting? If it will smooth out by adjusting the choke closed, then there's too much air getting in compared to fuel when the choke is in the wide open position. Did you try the advice in post #2 yet?  Spray some carb cleaner around the gaskets and manifold while it's idling. If the rpm changes then it is sucking in air wherever you're spraying at the time it does change.

Float adjustment is a possibility?

 

[cleat 5,771]

First try checking for air leaks as Wallfish said.

 

How far did you take the carb apart for cleaning ?

 

You might have missed something or some passage.

 

Does it do it more when warm or cold ?

 

I had one that would run fine for 15 minutes or so then begin to surge.

 

Don't know why the time delay but another (likely around the 4th) carb cleaning and it finally ran properly.

 

A weak fuel pump might cause this as well and could likely cause hard starting after sitting for a few days.

 

Cleat

[mikeeyre74 289]

I haven’t been home to try checking for air leaks yet. Working the choke a bit does not have any effect on the running condition. Choke on once warmed up and she’ll just die. It doesn’t help matters by putting it on partially either. It doesn’t matter to the engine wether it’s warmed up or cold. It seems to run the same either way. I probably won’t be able to look at it closely again until the end of this week. I’ll get back with some results. 

[lynnmor 7,300]

Sounds like a missing welch plug to me.  That plug is just above the idle mixture screw.  If the plug is in place, next time you clean the carb, remove it to clean inside properly.  You will need a new 3/8" aluminum plug to replace the old one.