misfire and backfire

[inohv8]

I have a 50 horse Johnson 1988, all rebuilt, removed the vro, put in a regulare pump. it fires up , timing ok on idle, but misfires out the exhaust with a puff of smoke and intermittently sprays gas out the idle jet. I changed carbs with a similare type but with idle adjust screws.. runs better but still misfires out the exhaust and some gas is seen in the carbs and silencer box. I double checked the timing, opened up the engine again to see if anything is cracked.. but all is ok.. only thing left are the reed valves.. but before I spend the coin, I wanted to get some other thoughts..<br />this is a two cyl. 2 stroke, twin carbs.. the replacement carbs are from a mid 70s engine 55 horse but the choke is different.. oh well, I can work around that.. I just would like to here this purrrr not sputt, cough and choke..<br />thoughts welcomed...

 

[papasage]

Re: misfire and backfire

sounds like a lean condition . could be the jets in the carb are the rong size . think the top and bottom carb has different size jeta and could be ceosse up and the carbs that you replaced them with could be the rong size but a little better . did you rebuild the carbs?

 

[papasage]

Re: misfire and backfire

also post in this site . he might be close to you . http://www.themarinedoctor.com/cgi-bin/YaBB.pl <br /> afte re reading where you from it probabley sits a long winter and will need a good carb carb cleaning

 

[inohv8]

Re: misfire and backfire

I got this engine as a write-off, MY Job...ta-da... re-build.. that was my winter project.. re-bore, new pistons, carbs all re-built.. I could not get the jets out they were in there pretty tight, was afraid to destroy them, the crank was redone.. etc... I know the carbs are spotless.. the ones I replaced them with, did run better but still misfired, I looked at some other comments which mentioned reed valves for the gas spitting at the carbs, and lean mix would make the misfire.. NOte.. the plugs were new and when I pulled them to have a look, they were on the wet side.. I pulled the reed valves out this evening and they look to be within spec. all the comments and books I have say .010 max clearance. and although I could not find my feeler gauge, they looked fine, except for maybe one leaf (questionable) now.. saying that, It looked like the top carb was wetter than the bottom carb. so Now I am a little confused.. is it possible that the upper reed is not closing properly? hope this helps..<br />thanks.