Carb Spitting Gas 1990 70hp

"I have a 1990 Force 70hp Outboard with a single carb. At 4000 rpm and above it has foamy gas coming out of a hole on the side. At higher speeds it starts to spit and then surges. The hole connects to the top of the fuel bowl and also to the throttle body. Obviously, it is part of the bowl vent. But why would it be vented to the outside of the carb? Most marine carbs vent back into the carb.

Is it possible that the hole should be plugged? The carb has lots of little plugs all over it that cover the ends of cross-drilled passages. The only thing is that this hole is chamfered whereas the others are not.

The carb is a Tillotson TC-111A-019. A picture of it is posted on Photobucket - http://i38.photobucket.com/albums/e117/gizmoe107/IMG_4818.jpg""

"Different carbs have differen

"Different carbs have different types of jets.

There are air jets that let air into the carb and back-draft jets that let excess pressure out of the carb to go along with the fuel jets.

Excess pressure in the carb which causes fuel to expell or spit from the air or back draft jets or worse yet, spit right out of the carb throat can often be tracked back to a busted or chipped reed which is allowing crankcase pressure to escape back through the carb blowing mixed gas out with it.

The Tillotson carbs were always a kinda "leaky" thing to start with, even if there is nothing wrong with them, but in this case I would pull the carb and get a look at the reeds - if for no other reason than to rule them out as an issue at this point..."

"Thanks for the insight into t

"Thanks for the insight into the Tillotson carb, Graham. I'll check out the reeds next weekend. I'm not used to working on 2 strokes so I tend to forget about the reed valves.

I suspect I might have a partially sheared flywheel key since I can only adjust the timing to 20 deg instead of the required 28 deg. Could the timing being off cause the same sort of symptom?"

"Timing could cause a backfire

"Timing could cause a backfire, but that still shouldn't result in gas spitting.

Any amount of back pressure in the crankcase should force the reeds to close tightly, preventing a spit back.

So you could have two unrelated issues here..."

Re: Carb Spitting Gas

Update - the reed valves were in good shape. But I did find the gasket around 2 of the 3 reeds was leaking. I made a new gasket and installed.

I took the boat out for a spin but it still spits gas out of the vent hole over 4000 rpm's. Additionally, the acceleration seemed rougher. Now I'm running out of ideas. Anybody else have a suggestion?

BTW - I checked the flywheel key and its fine but I still can't set the timing more than 20 deg. Next I'll check the linkage. But like Graham said previously, I probably have 2 separate problems.