Seizing engine

[muskrat]

But cruising at 60mph your not on the main jet till you hit a hill. Mark your throttle body and twist grip in the closed position, then the twist grip in the wide open position. Now divide into 4 segments. You'd be surprised how little throttle is used when just cruising at 60mph on flat ground.
In saying all that a too small main jet will affect the needle taper.
Cheers

[JulianS]

The main jet size marking was unreadable but I compared it with the correct 270 jet & it looked smaller. I've since fitted the 270 since the last seize. Running fine but not tested on highway yet. I wonder if that could have been the problem.

If the cause of a seizure was too weak a mixture then I would expect to see serious signs of a weak mixture on the plugs - colour towards white .

The A7SS would also have been fitted with a 1 inch bore carb, so the 15/16 one fitted would tend to give a richer mixture  due to smaller bore.

I still think you need to look inside or that threat of seizure will always be there.

[orabanda]

Musky offers good advice for when tuning.
A mark on the side of the twist grip, and a piece of masking tape (temporary) stuck to the throttle body on the left. Mark the tape in quarters (or eights) and setting up the carby becomes easier / more accurate.

Richard

[chotus52]

Thanks for all the tips gents. I'll advise the outcome. Regards

[chotus52]

KCC pistons

[chotus52]

I mean JCC pistons

[Topdad]

What are the bores like ??

[bikerboy]

Sorry to come in late but IMO it was always going to be pistons. Have you measure the bores yet? I must admit I dont like the sound of "tight" valve guides either I would check that while I had the head off for sure

[chotus52]

Thanks for all the pointers. We pulled the top end, cleaned up the pistons & honed to 6 thou. It seems like problem solved. Cheers