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Okay, fixed fuel leak..why is it running rough?

1058 Views 5 Replies 4 Participants Last post by  altair
Started another thread in the hope of catching an experts

Have fixed the fuel leak in the pulsa jet with Wurth sealer, now I have posted a video of it running. Sounds tinny in the video, just a poor quality camera I think, sounds better in real life.

Anyway have replaced:

Plug (have also tried another)
electronic ignition fitted, have tried adjusting gap between flywheel, no difference
clean fuel, air filter
fresh oil
mixture right
carb and tank cleaned several times with carb cleaner and compressed air

Motor does not smoke at all and has heaps of compression pulling it over.

Any ideas why it has a constant miss? Its hard to hear in the video unfortunately, you have to concentrate hard to hear it...almost sounds like an electrical problem.

Apologies for all the questions, but I would love to keep this old motor if possible, grew up with them as a kid!

Thank you very, very much for any ideas, much appreciated!
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Maybe a vacuum leak? Not familiar with these old engines but if there's a manifold tube between the carb and engine, it could be cracked or have a leaking base gasket. Check all gasket surfaces for flatness and correct as necessary.
Governor adjusted, did you try it under load, valves ?
Yeah I wondered about valves, might pull the head off and have a look.
Would have to take it to a shop I think to get the valves done properly, I don't know how to adjust clearance once the valve grind is done.

Governor looks okay, moves freely...haven't tried it mowing a lawn but it revs freely and the miss is constant through the rev range.

As for air leaks, that's a possibility, has an o-ring where it connects to engine, could replace that, bit looks like a Briggs part only as it is square.
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Sounds like an ignition miss to me. When you say "electronic ignition fitted", do you mean a module or a Magnetron coil?
Hi, it has a magnetron I think it is? Guy i bought it off (a scrap metal dealer) fitted it to see if it would run before I bought spark through original points.
Its just a bolt on part next to the flywheel off a newer Briggs and Stratton motor.
I have been pulling off breather tubes etc and resealing gaskets etc, and the
GOOD NEWS is......I pulled the flywheel off, and the key was half sheared through, but still in one piece, so the flywheel was locked slightly away from where it should be. Have fitted a new alloy key and it now runs much, much better!...still has a slight miss but I'm really happy with how much better the old girl runs now.
Started smoking when revved for a few minutes after I changed the key (who can explain that?) but I've just mowed the lawn for 10 minutes with it and no no smoke again..weird. So I've changed the oil again, hoping to flush out all the old stuff.
So what grade oil would you guys advise? Small mower mechanic here has always run 20W40 car oil (so have I for the last 20 years to be honest) but some swear by the 30 weight oil. Bearing in mind this is an old 1960's motor I want to put in the best weight oil for protection. Never really gets cold here, never freezing, that's for sure.
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