Advice wanted-will not run with choke off

74 commando, with electronic ignition and single 32mm Mikuni carb. Has run faultlessly for the last 6-7 years but during last run started missing and then cut out. Can start on full choke, then engine races uncontrolable over 5000, with choke then eased off, can run engine over the 4000 - 5000 (while standing) but throttle under 4000, engine dies? Removed carby and cleaned all through, actually fitted brand new Mikuni and same problem. In bad boy corner at moment, any suggestions before starting to strip things down? Any advice taken on board and investigated

Air leak at the intake manifold?

Yup, airleak somewhere. Take the carb off and check the two bolts inside the manifold that bolt to the head. Happened to me. One of the bolts came completely out, went down the intake and luckly hung up on top of the intake valve, no damage. Had to fish it out with a magnet but all was good once I put it back in (with blue locktite this time). Those two bolts holes are not blind and will let a bunch of air in.

Ben

What ignition system? You changed carb.. Single Mik to single Mik? You checked manifold bolts for tight, visual on gaskets?

Hi Fellows, and thank you to all, nailed it in one. It was that inner fixing bolt sure enough, was bouncing about on top of the inlet valve, all unseen when trying to find out where the air leak was getting in. Will have to run the die over the thread and make sure it is lock tighted in this time.
Cheers to all

classic said:

Hi Fellows, and thank you to all, nailed it in one. It was that inner fixing bolt sure enough, was bouncing about on top of the inlet valve, all unseen when trying to find out where the air leak was getting in. Will have to run the die over the thread and make sure it is lock tighted in this time.
Cheers to all

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Locktite

Glad you have it sorted, thanks for checking back and closing the loop. :mrgreen:

BEFORE there was LOCTITE . Parts Recovery Team . " Im Sure it Fell Off Arounf Here , Somewhere . "

swooshdave said:

classic said:

Hi Fellows, and thank you to all, nailed it in one. It was that inner fixing bolt sure enough, was bouncing about on top of the inlet valve, all unseen when trying to find out where the air leak was getting in. Will have to run the die over the thread and make sure it is lock tighted in this time.
Cheers to all

Click to expand...

Locktite

Click to expand...

Thanks mate, but you know what I mean, but actually I use Permatex "Threadlocker", made in the USA. Used to use the Locktite many years ago.