Tracking Down Air Leak in Fuel System

[Brew2]

1986 Evinrude 140 hp<br /><br />Been having stalling problems for some time now. Mostly during acceleration. I've gone through the carbs using aerosol carb cleaner and compressed air several times, installed new carb kits and replaced all the fuel lines right from the tank through to the carbs. I've done a lync and sync, checked compression (120,120,125,130), ensured fresh gas and used a portable tank for testing purposes. Spark is also good.<br /><br />I'm reasonably convinced that I've got an air leak somewhere, most likely in the carbs. What is the best way to track such a thing down? Mist some premix around all each carb (other than in the barrel) and see if the RPMs increase? Would something other than premix be better? I know you aren't supposed to use starter fluid because it has no lubrication, but would it be more appropriate in this situation (used sparsely) for tracking down a possible air leak?<br /><br />Thanks.

 

[djzyla1980]

Re: Tracking Down Air Leak in Fuel System

Sure it's an air leak? Floats checked and adjusted when replacing???? <br /><br />if it's a fuel prob.... Spray pre-mix from bottle into carbs when prob starts... if you get RPM's then it's a fuel issue... <br /><br />Have you tried pumping the primer bulb when it happens??

 

[Brew2]

Re: Tracking Down Air Leak in Fuel System

Yup...floats have been checked and rechecked. Pumping the primer bulb has no impact on the problem, but bumping the primer (ie. pushing in the key) can usually prevent the stall and get me to a higher RPM. Once the RPMs get high enough to put the boat on plane, everything seems to work great.<br /><br />I assume misting premix into the carb throats would have the same effect as bumper the primer, so I'm pretty sure it is a fuel issue.<br /><br />So...anyone have any thoughts on checking for air leaks? If nothing else, I'd like to eliminate that as the cause of the problem before moving on to other possibilities.<br /><br />Thanks to all for their time.<br /><br />Cheers.

 

[TBarCYa]

Re: Tracking Down Air Leak in Fuel System

My problems started much like yours where it would not accelerate past half throttle unless I hit the choke then it would get on plane and run just fine. <br /><br />I'm no 2-stroke expert, but on car engines, a good way to test for a vacuum leak is to use a propane torch. Turn the gas on but don't light it and move the tip around where you suspect the leak. The engine will suck in the propane and the rpms will change when you get close. Just don't smoke when doing this and try not to breathe in the propane. Try that around the manifold gasket and the carb base gaskets and it *may* help locate the leak. I haven't done it with mine yet because I replaced the gaskets before I had my propane tank available.

 

[Brew2]

Re: Tracking Down Air Leak in Fuel System

Thanks TBarCYa....interesting idea. Same sort of thing as I was thinking with the starter fluid, but a gas like propane might get "sucked in" a little easier than a liquid.<br /><br />I guess the risk might be if it sucked in too much propane and you got too big a "boom" in the combustion chamber...do you think the resulting ignition in the cylinder would cause any damage? I know they run cars on propane, so I guess the combustion characteristics might not be all that different from gas. Anybody got any thoughts on this?<br /><br />Thanks everyone.

 

[jleus]

Re: Tracking Down Air Leak in Fuel System

I like installing a piece of Tygon fuel line between the fuel pump and carbs. Translucent yellow in color and can see what is exiting the pump. I would use Seafoam Deep Creap for spray for testing for air leaks on carbs. It may not suck eneough in on a multi cylinder motor to "bog" rpm down but small amounts of this smokes well and should be evident out the exhaust on the hose.

 

[Brew2]

Re: Tracking Down Air Leak in Fuel System

Hey jleus.<br /><br />Also and interesting technique. What would you be looking for in the clear fuel line? Abnormal quantity of bubbles? I assume the fuel line should be totally full of fuel and essentially no bubbles...correct?<br /><br />Not sure I can get "Deep Creep" here in Canada. Have never seen it in stores. Anything similar in nature you can think of? Maybe some other similar product is available here.<br /><br />Thanks.

 

[djzyla1980]

Re: Tracking Down Air Leak in Fuel System

I guess if it sucks in too much and you hear the kaboom..... you've found your leak... if it's enough you might not have to worry about fixin it <br /><br />aside from that... Thats a good Idea jlues<br />about the tubing.... might have to see where I stand after the reed job and go from there.

 

[TBarCYa]

Re: Tracking Down Air Leak in Fuel System

Unfortunately, I can't say how it will act in the combustion chamber of a 2-stroke. I've never heard of damaging a 4-stroke with this method tho.

 

[jleus]

Re: Tracking Down Air Leak in Fuel System

Air bubbles will be evident. In a tight fuel system there should be no air. Seafoam products may not be available in Canada. I have seen it on-line. Many auto parts houses carry it in my area.

 

[umblecumbuz]

Re: Tracking Down Air Leak in Fuel System

Old trick for finding an air leak in a line is to smear each joint around with grease. The grease plugs any leaks. Then wipe the grease off the joints one by one, and if there's a leak, you'll pinpoint it.<br /><br />Lot safer than playing with propane and hoping the motor doesn't spit back while you're doing it!<br /><br />That said, I think you've got a carb issue rather than an air leak. Might pay to strip the carbs and clean them through again. It takes very little to cause a carb to do what you've described.