Lean Sneeze...Common Causes ?

I have a 1979 35 hp Evinrude, model 35953A that has a terrible sneeze. On muffs, low to a little higher throttle, it runs for a moment then gives a cough, revs back up and coughs again and again. Are there common things to look for ? I have new coils, stator, power pack and rebuilt the carb. The only thing I haven't replaced is the fuel pump ( there goes another $50). Any help at all would be greatly appreciated.

Re: Lean Sneeze...Common Causes ?

Hi Ray. It sounds like the ignition is ok, so I wold check the carb. Even though it was recently rebuilt, they can get gummed up pretty quickly. I would clean/inspect/rebuild the carb just to be sure. If you think it's the fuel pump there are a few tests you can do to check and see if it is working properly. Start by squeezing the primer bulb it should get and stay firm. If not, the the pump may be bad. If the motor picks up rpms when you manually squeeze the bulb, then the pump may also be bad. Another test is to brielfy disconnec the fuel line that leads from the the pump to the carb. If you see fuel pulsating out, the the pump is ok. Better still install one of the litle inline fuel filters in the pic below inline between the fuel pump and the carb and it will not only filter the fuel, but give you visual confirmation of fuel delivery. Here are some good carb links too. If it is the pump. No worries there's a link below where you can get them for about $20 and they install in about 5 min.



http://forums.iboats.com/showthread.php?t=167352

http://www.duckworksmagazine.com/04/s/columns/max/25/index.cfm

http://www.aircraftspruce.com/catalog/eppages/mikunifuelpump1.php

Re: Lean Sneeze...Common Causes ?

Sounds like a lean sneeze. Ill assume you tried to richen the mixture screw 1/4turn or so?

Re: Lean Sneeze...Common Causes ?

Kfa.....Thank you so much for the help....the 1st link/thread helps a lot, the 3rd link, well...not real close to the pump I need but it all helps immensely

Re: Lean Sneeze...Common Causes ?

HighTrim.....yes, I started at 1 & 1/4 out from tight and adjusted 1/4 turns from there......not much of a difference when i did it. Would air getting in ( i'm thinking thru the fuel pump ) cause the hiccup ?

Re: Lean Sneeze...Common Causes ?

Yes. Remove the two screws that hold the fuel pump onto the engine, and pull the fuel pump away from the block. Pump up the primer bulb and see if gasoline leaks out of the little hole on the back of the pump. You won't need a new gasket: you can reuse those gaskets many times.

Other possibilities....bad lower crank seal (hopefully not lets leave that as a last resort), faulty reeds

Pull the spark plugs after running, what is their condition? Is there a difference between them? Any water present on them? What is the compression of the motor? Possible water in fuel or leaking through head gasket or exhaust gasket.

Is it sparking a good 7/16" on an inline tester?

Is it "spitting" out of the carb throat when it sneezes?

Have you tried running at half choke, does that solve it?

Try spraying some extra oil into the carb and see if it goes away.

Other things to try are running it on one cylinder at a time to see if the problem dissapears. This is done by removing and grounding one of the plug leads at a time.

Let us know how you do.

Re: Lean Sneeze...Common Causes ?

Open that slow speed needle some more. Some of them require quite a bit (mine included). Cold weather will do it too. Were you doing it as a cold front went through our sunny state??

Another big cause is improper carburetor/spark synchronization. If the carburetor butterfly is opening too soon, or not closing completely, it will sneeze like crazy.

EDIT: Oh, so you rebuilt the carburetor. Did you replace the little plastic bearing in the slow speed needle hole? Is it even in there? They call it a bearing, but actually it is a seal that keeps from sucking air around the needle. Air sucks easier than gas, so too much air/too little gas equals lean condition, equals sneeze.

Re: Lean Sneeze...Common Causes ?

You might disconnect the fuel line from the carb and squeeze the bulb. Check and see if the fuel flows good and free. Also, poke the fuel line into a jar and fire the motor up and see if the fuel pump is pumping good. You may possibly have a weak fuel pump.

Re: Lean Sneeze...Common Causes ?

Wow...lots o' help, thank you guys. Didn't get back to the motor yet but if theres no rain later today I will after work. I did notice when I get the hiccup it spits a small amount of gas out of the line that goes to the carb. I will get a filter today and look closer at that line and tighten up the clamp. Keep you posted......thanks again, Ray

Re: Lean Sneeze...Common Causes ?

Thanks again to everyone. Got the motor running ok.....takes about 5 minutes to get a hiccup, and even then its not bad. I think the problem stemmed from an air into fuel leak as one of the hoses would spit fuel when it coughed. Cut the hose end, retightened it back on and looks like that was the problem. Hoping for no rain tomorrow so I can take her out and run WOT for the last adjustments. If the lone cough continues, off comes the carbs for a better cleaning. I dont get much of a differance when I adjust the needle, which is why I am thinking another carb clean. Thanks to everyone, let you know how it goes after I get it on the water..........Ray

Re: Lean Sneeze...Common Causes ?

Good luck Ray. keep us posted.

Re: Lean Sneeze...Common Causes ?

If the hose was cracked and leaking you may have to remove and clean the carb as broken pieces of fuel line may have entered the carb , and replace that fuel line if it was cracked