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18hp Evinrude backfires when cold

S

scrubs

New member
"Hello all,
My 18hp(whic

"Hello all,
My 18hp(which i think is a 1958)back fires thru the exhaust when it is cold, to the point of almost killing it. It has electric start, and it takes a bit of cranking to get it to start. Once its warm it runs great,and starts great. I have had this motor running great(cold), started right up,no backfiring until i ran it out of fuel one time, and it has backfired ever since. Thinking i sucked something out of the tank, i pulled carb a part(several times now) and thoroughly cleaned it, as well put a rebuild kit in it the last time. Still back fires??????
I took it to a local boat shop, they couldn`t get it to, and said it was fairly normal for these type of motors to do that????? I`m not thinking so, especially since i have had it running better myself.
I have no idea what to try now???? Any help would be greatly appreciated."
 
"if the carb is spotless,..i w

"if the carb is spotless,..i would pull the flywheel and clean,and regap,the points to exctly .020 now,try and move,the stator plate,i would expect quite a bit of play..that,throws ur ign timing off,by not keeping an exact brkr point setting...there r a few...less desirable temp fixes...i choose,sierra, magnatune ign modules,that do away w/brkr points,and wk fine."
 
"Is it a "Cough" or a

"Is it a "Cough" or a backfire??? Coughing is a sign of a cylinder running lean. Check your fuel lines, bulb & connections."
 
"It could be a cough, not sure

"It could be a cough, not sure of the difference??? The motor jerks violently when it does it.Is there a definitive way to tell the difference?

My motor/tank is a pressurized system, does not use a bulb.I will double check the fuel though.

With a single carb, dual cylinder motor, how does one cylinder become lean?

Dan P, thanks for your advice."
 
"Your double line fuel system

"Your double line fuel system can still have a leak or bad fitting between the motor and tank (cracked hose, lose fitting, etc....) A coughing motor indicates a lean condition."
 
"David,opening the low speed j

"David,opening the low speed jet has no affect on it, niether does the choke????

Dan, ok, it only has one fitting, i will replace it and see what happens.

Thanks for the advice guys,i really appreciate it, this thing is getting frustrating."
 
When you had your carb apart d

When you had your carb apart did you remove needle valves and blow compressed air through passages?
 
"Sounds to me like your primer

"Sounds to me like your primer system on your tank isn't putting enough pressure to the tank to supply sufficient fuel to the motor until the motor starts building pressure in the tank. Hence, the cold cough."
 
"I apologies for the delayed r

"I apologies for the delayed response, been very busy moving.

David, yes i did blow air thru all the ports and passages, several times.

Dan, thanks for link to the great article, very informative.

I went thru all the hoses and hose connections, all looked good. i had the tank in the front of the boat, so i decided to move it to the back and shorten the hoses, still the same thing.

I will pull the top cover off of the tank and see if there is some noticibly wrong in there. When using the priming button, it get hard to press after a few pumps, so i assume it is functioning properly.

Again thank you all for the help."
 
"Bob,

I have replaced them,

"Bob,

I have replaced them, checked all hoses, pulled top off the tank, everything looks good, resealed. all to no avail, still coughing hard when cold?????"
 
"I believe there is a sintered

"I believe there is a sintered metallic fuel filter located inside a glass fuel bowl located under the carburetor or on the side of the motor. These filters often clog and become a problem. Remove it and try blowing through it. If it is clogged and you cant find a new one, backflush it with starting ether. I believe the normal flow direction is from the outside to the inside of the filter."
 
"Yes there is a fuel bowl with

"Yes there is a fuel bowl with a filter, i will backflush it and see if that helps.

thanks"
 
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