1966 20hp johnson twin backfires at low revs

[clanceley]

At the starting position revs, the engine runs fine ,but when I drop it down that, the motor back fires( mis fires ) and cuts out. <br /> All suggestions greatly appreciated .

 

[JB]

Re: 1966 20hp johnson twin backfires at low revs

G'day, Clancely. If this problem just started, after the engine had been working properly, I suspect the low speed circuit in your carburetor is plugged or gummed up. You may be able to clear it by simply dismantling the carb and cleaning it meticulously. Give particular attention to small passages.<br /><br />If that has no effect, try backing the low speed mixture adjustment out (CCW) about 1/2 turn from where it is now.<br /><br />Good luck.<br />Red sky at night. . .<br />JB

 

[corm]

Re: 1966 20hp johnson twin backfires at low revs

Most 20 johnrude that age have a leaking top crankshaft seal also. Which will caus the same problem. Or it could be as simple as a <br />cracked recirclating hose.<br />corm

 

[clanceley]

Re: 1966 20hp johnson twin backfires at low revs

Hi JB an Corm, thanks for your imput, much appreciated, as I am a outboard novice, operating without access to a manual. I'll look in to those two areas this afternoon to see if the problem lies there.Cheers,CL

 

[clanceley]

Re: 1966 20hp johnson twin backfires at low revs

Gday JB, thanks for the tip. It was the problem with the low speed idle jet. I still dont know the correct setting, but on winding it out progressivly today I got it to run at low speed without the back firing.Next will be a test run and then some machine work to repair the worn links in the throttle arm and the ignition advance controls.<br />Many thanks.<br />clanceley