1968 johnson manifold backfire

[invader_1230]

hey, i just bought a 1968 40hp johnson electromatic outboard, which thankfully shifts and runs. BUT when it is idling it backfires, but when it does a flame shoots out of a threaded hole in the intake manifold and when it is running full speed exhaust is shooting out and there is oily gas that sprays out of this hole also. i thought that there should be bolts in this hole, but i checked another engine and it too does not have anything in these holes. i feel i am probably not getting full performance since it must be sucking in way to much air through the holes. any information would be great, thanks

 

[Paul Moir]

Re: 1968 johnson manifold backfire

You should definitely not be getting flames shooting out of any holes on your engine.<br /><br />I'm trying to place the 'threaded hole' you're talking about, but I'm really drawing a blank. Can you describe where it is exactly? There are screw holes all around the intake, and there's one in the middle directly beneath where the carb bolts on, and just to the left of that is a nipple for the vaccum cutout switch.<br /><br />(PS, the sneezing at idle is caused by running lean. A hole in the manifold will cause a lean condition).

 

[invader_1230]

Re: 1968 johnson manifold backfire

hey, yeah, the bolt hole is on the lower left hand side of the manifold. it follows exactly where a manifold bolt should go around the edge of the manifold. basically if you follow the bolts that hold the manifold on, it looks like the bottom 2 are gone, but it looks that way on an other engine i have laying around. i was going to just put a bolt in it, because im probably getting a fraction of the fuel im supost to, but i didnt want to plug anything and cause an explosion or backfire through the carb.<br /><br />(also the engine has been sitting for many years, but it doesnt look like anythings been fooled around with)

 

[Paul Moir]

Re: 1968 johnson manifold backfire

Oh yeah, I know what's going on now.<br /><br />For the larger (Prestolite) electric starters, there's a heavy guage steel bracket that bolts to the bottom of the starter, the bottom bolt/stud of the cast aluminium starter bracket, and those two manifold screws. If the starter got pulled and the bracket lost, the screws would be missing from those two holes.<br />This bracket isn't used for the older, shorter Autolite starters.<br /><br />Now, here's something: the lefter screw (#10, 24tpi) doesn't go anywhere. But the righter one goes right into the bottom crankcase chamber, beyond the reeds. So with it missing the bottom cylinder isn't getting charged properly. <br />That particular screw I like to put some gasoline proof sealant on (Permetex #2 or #3 aviation stuff).<br /><br />If you want, I can post a photo of the bracket.

 

[invader_1230]

Re: 1968 johnson manifold backfire

OH YEAH. THANKS alot, thats EXACTLY whats going on,i didnt even think about that. the starter it came with did not work, so we pulled one off an other outboard that didnt have that bracket, it was just temporary because we have another with that bracket but the starter without it wasnt mounted on anything, so we thought we would use it. i have no idea how i didnt see that, i took the bolts out of those holes, ahah oh well. who knows how long it would have been before i figured that out, ill be switching starters soon. i dont even know how we got it to start.<br />thanks