Stihl MS660 pushing gas out of bottom of carb.

[MADDFELLER]

Stumped, I have done several big bore kits, muffler mods, carb rebuilds. The saw has pretty much everything replaced or checked on it. Complaint was that it would not run with full tank of gas only with about half full. They decided to go ahead and put bigbore kit and muffler mod to it so never paid much mind to running issue due to having the saw pretty much completely apart. Cleaned carb out and new diaphram and gaskets. Got it to fire and idle twice, fuel was just running out of it somewhere. removed air filter cover and base and reinstalled nuts to secure carb, tried again and fuel coming out of hole in bottom of carb. I popped vent out of it and somewhat stops. ???????

 

[pioneerguy600]

Stumped, I have done several big bore kits, muffler mods, carb rebuilds. The saw has pretty much everything replaced or checked on it. Complaint was that it would not run with full tank of gas only with about half full. They decided to go ahead and put bigbore kit and muffler mod to it so never paid much mind to running issue due to having the saw pretty much completely apart. Cleaned carb out and new diaphram and gaskets. Got it to fire and idle twice, fuel was just running out of it somewhere. removed air filter cover and base and reinstalled nuts to secure carb, tried again and fuel coming out of hole in bottom of carb. I popped vent out of it and somewhat stops. ???????

A carb does not leak if properly put together and there are no broken/ cracked parts. Check for proper reassembly and also check the fitting where the fuel line connects to the carb. Hose may be split or cracked, the metal nipple may be loose or cracked also.

 

[fastLeo151]

A carb does not leak if properly put together and there are no broken/ cracked parts. Check for proper reassembly and also check the fitting where the fuel line connects to the carb. Hose may be split or cracked, the metal nipple may be loose or cracked also.

Haha you said nipple........back to the chainsaw stuff

 

[MADDFELLER]

A carb does not leak if properly put together and there are no broken/ cracked parts. Check for proper reassembly and also check the fitting where the fuel line connects to the carb. Hose may be split or cracked, the metal nipple may be loose or cracked also.

Thats all good . Gas running out of hole in bottom of carb just sitting after shaken. Leaning towards tank not venting because it stops pretty much when tank vent removed. Its a new vent though. Never had this create that much trouble. Does seem to want to run with barely any fuel in it. Thought maybe it was timing but does try to run at next to no gas in tank. Plugged all exits in tank and put a little psi in it can not find any leaks or cracks. Just seems like vapor psi not releasing. I am going to try a couple more things and see.

 

[Deets066]

If you bought a new vent make sure the vent is working properly. I bought a nos vent for an 034 but it sat for a while on the shelf and the rubber inside the vent was stuck shut. I had gas coming out of everywhere, air filter and muffer.

 

[ELECT6845]

Junk carb?

 

[blsnelling]

It's not the tank vent. The tank vent on a 660 only prevents a vacuum, but will allow pressure build up.

 

[pioneerguy600]

Thats all good . Gas running out of hole in bottom of carb just sitting after shaken. Leaning towards tank not venting because it stops pretty much when tank vent removed. Its a new vent though. Never had this create that much trouble. Does seem to want to run with barely any fuel in it. Thought maybe it was timing but does try to run at next to no gas in tank. Plugged all exits in tank and put a little psi in it can not find any leaks or cracks. Just seems like vapor psi not releasing. I am going to try a couple more things and see.

Then you have a leak in the metering diaphragm, if it does not have a visible tear or pinhole in it then the rivet holding the round washer like weight onto the diaphragm is leaking around the rivet head. Change that diaphragm and your leak should be fixed.

 

[sld961]

I see that this is a couple months old, but figured I'd give my $0.02 for people searching for the same problem.

I had the same thing happen. I got a WJ rebuild kit, it came with two diaphragms. At first glance, they looked the same, so i just picked one and put it in. The saw would fire, but wouldn't stay running and I noticed fuel running out of a hole in the bottom of the carb.

I pulled the carb apart and compared the diaphragms closer. One (the one I had installed) had one extra hole in it. That hole allowed fuel to flow out of the bottom of the carb. I switched the diaphragm and problem was solved.

Bottom line, make sure you have the correct diaphragm installed.

Edit: The diaphragm I'm talking about is the one on the bottom of the carb, not the top.

 

[snobdds]

I see that this is a couple months old, but figured I'd give my $0.02 for people searching for the same problem.

I had the same thing happen. I got a WJ rebuild kit, it came with two diaphragms. At first glance, they looked the same, so i just picked one and put it in. The saw would fire, but wouldn't stay running and I noticed fuel running out of a hole in the bottom of the carb.

I pulled the carb apart and compared the diaphragms closer. One (the one I had installed) had one extra hole in it. That hole allowed fuel to flow out of the bottom of the carb. I switched the diaphragm and problem was solved.

Bottom line, make sure you have the correct diaphragm installed.

Edit: The diaphragm I'm talking about is the one on the bottom of the carb, not the top.

Great post. I too put in the wrong diaphragm and had fuel coming out of the vent. Had me stumped until I read your post.

 

[ZeroJunk]

Great post. I too put in the wrong diaphragm and had fuel coming out of the vent. Had me stumped until I read your post.

Old thread I know, but I did that on an 056 back when. Had me scratching my head.

 

[snobdds]

Old thread I know, but I did that on an 056 back when. Had me scratching my head.

An old thread, but very much helpful.

 

[2StrokeFondler]

A rebuild kit for my 015 had a plunger on the metering diaphragm that was significantly taller than the old one. Could not explain why it flooded. Until I compared it with the old one which I luckily didn't throw in the bin. Since then, I keep every old part of a project until I'm sure it works. And I thoroughly compare old and new parts.