75 evinrude back fire?

[hawk-eye]

Ive got a 1975 20hp rude model/ser # 205b62bc96523

I had to repalce the rings due to low compression and now I can not get it going again. When I try to start it up the first time she fired up and ran for a few seconds then backfired and stopped. Trying to restart it it will do the same. I cant get it to run for more than a few seconds than it backfires.

What could be causing this to happen. I have had the ignition system tested by a dealer who assured me that the electrical was fine. My thoughts is that it must be in the intake somewhere. Possible worn reeds?

Thanks

 

[Monte1961]

Re: 75 evinrude back fire?

sure it isn,t idling to lean?

 

[hawk-eye]

Re: 75 evinrude back fire?

Thqanks for the reply.

Ive been reading quite a bit and it sure sounds like its a sneez and not a backfire. The carb has been cleaned with a new kit along with the core caps. I have the low speed needle out 1 1/2 turns. Should I be backing it out more than that?

 

[hawk-eye]

Re: 75 evinrude back fire?

I tried moving the s/s needle in and out a few times and it did not make a difference. Im thinking it may not be a sneeze, it is popping out of the exhaust. Ive got good spark and good fuel, what else can I look at?

 

[Monte1961]

Re: 75 evinrude back fire?

Have you tried to do a link and sync? However if you don't hear a difference when adjusting, (witch you should) I would still be looking at the carb/s Good luck

 

[hawk-eye]

Re: 75 evinrude back fire?

Thanks, link and sync is done per manual, there is no difference when moving the s/s needle cause it wont run. It pops when I yank the rope.

 

[Monte1961]

Re: 75 evinrude back fire?

Are you sure the shearkey is ok?

 

[hawk-eye]

Re: 75 evinrude back fire?

Yeah, i just pulled the fly wheel off again, key is fine.

 

[Monte1961]

Re: 75 evinrude back fire?

What about plug-wires? Are they on the proper plugs? Just a thought. post results

 

[Monte1961]

Re: 75 evinrude back fire?

And for sh*ts and giggles, what is you compression readings now?

 

[hawk-eye]

Re: 75 evinrude back fire?

Haven't swapped the plug wires, worth a try i guess. Compression 120 on both.

 

[hawk-eye]

Re: 75 evinrude back fire?

Well thats it for today. Thanks for your help. Ill be back at her in a couple days.

 

[hawk-eye]

Re: 75 evinrude back fire?

Just an update.

I pulled the carb and the intake manifold off her yesterday. There was quite a bit of aluminum oxide on the reed plate which was holding a couple of the valves open about 20 thou. Cleanned it, reinstalled, and she ran for the first time in almost 20 years. I ran outta time today to tinker arround with it to smoothen it out but at least it is doing something now.