Newly Assembled Engine Falters on Hills

Information relating to the Matchless G3 or AJS Model 16 350cc Heavyweight
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Re: Newly Assembled Engine Falters on Hills

Postby Rob Harknett » Thu Apr 20, 2017 9:43 am

On my 55 G3LS, from when new, I always used a little red hermatite. First making first making sure all 4 surfaces ( carb, spacer and head ) are clean and flat. Also the spacer slides up to the head freely on the studs. Apply a thin coating of Hermetite on each side of the spacer, then the two paper gaskets, so they are flat. Then a coating on the other side of the gaskets. This assembly should then easily slide on the studs. If you think the carb bore has gone oval. First check the carb flange where the O ring fits. On the inner side the wall is very thin, it may be cracked. If a bit breaks off that's not really a problem. But don't leave a loose bit on it, to break off and go in the engine. Now get a steel ball bearing the same dia. as the carb bore. Tap the ball through the carb from the bell mouth side, there's a little radius that will help centralise the ball. The ball may get a bit tight as it exits, as it's this end that usually goes oval.
The only time I have really lost revs up a very steep hill was at Jampot Rally at Oakhampton. There was a steep climb out of the town to the rally site. My little 1936 250 AJS had been playing up, like 8 stroking until you opened up. It was really struggling up the hill 2 up. Back at the rally site I discovered the carb nuts were almost off, the carb rattling on the studs. I thought I would clean the jets while I was at it. Undid the bottom of the mixing chamber and the main jet fell out. No wonder it 8 stroked. It should not had run at all with no main jet. It went like rocket on the Sunday run round Dartmoor. The Burger van girl offered me free breakfast if I took her for a ride on the old bike. Got another free breakfast next morning for taking her kids round the rally field on it.

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Re: Newly Assembled Engine Falters on Hills

Postby Mick D » Thu Apr 20, 2017 3:06 pm


Although your symptoms could be indicative of an air leak in the induction I wouldn't rule out timing or ignition breakdown.

Quick check to rule out an air leak at the carb flange - wrap some duct or masking tape around it and go for a ride uphill

My money would be on the timing and the first thing I'd try would be to check / adjust it - if the timing is OK I'd replace the spark plug.

Regards Mick

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Re: Newly Assembled Engine Falters on Hills

Postby Johnobirches » Thu Apr 20, 2017 4:44 pm

Just a quick update on this folks - and thanks for the further ideas.

I checked the main jet and apart from being a bit scaley it was actually loose in the bottom of the cover - the needle jet above it was secure.

I cleaned everything up and screwed the jets in tight.

Started the bike and gave it a very short run {because the oil leak from the rocker inspection cover is really quite impressive} ... it pulled like a train!!

Hopefully that's one off the snagging list.

Best Regards


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