Hitchcocks Forum

Hi everyone,
Yesterday i purchased an bullet 500 with a bit strange brackground.
It has the long original muffler and an amal carb with shown airfilter.
The previous owner has experimented with jetting but didn't seem very technical.
The bike runs okay, but a little hard to start (normally they need 1 kick?) and between (irregular) idling and opening of the throttle there is a moment of 'stall'
Can anyone recommend me jet sizes and needle positions? He told me it had a 160 installed now.

Maybe worth checking your ignition timing too. What you describe could also be a symptom of slightly too-far advanced timing. Especially if it also kicks-back on startup.

A 160 main jet is too small for a smaller Concentric on a 350. That looks like a 928 and I would use anything up to around 250 on the main jet give or take a couple of sizes and possibly a 107 needle jet, although if you have the standard silencer strangling it, that should go, too.

It does not kick back when starting, and have the idea spark timing is maybe a little late,
The previous owner told me there was a 240 main jet and the engine choked on it..
with the 160 now it does respond in 4th gear..
Shoot i gave all the amal stuff away some time ago (also because of my diesel enfield)
Is there a popular baffler less restricting and giving better power?

The main jet won't effect the starting anyway.
Have you tried tuning the pilot?

If it's the old-style Mk1 Concentric rather than the more recent Premier version you can't change the pilot, it's a fixed jet.

A.

I got the bike 2 days ago, didn't open the carb yet..
It will need new tyres and i think adjusting.
For the last years i am riding jawa 2 strokes and my enfield diesel, seem to have 'forgotten'how to find correct jet size for a 4 stroke..
i think a top-down method is the best..
But still, with this 160 jet it runs well? But the again i don't know how much power to expect from a 500 bullet.
I will take out and measure main jet today.

Thats a weird set up - the 500 Bullet usually has a 30 mm right hand carb - this has a 28 mm left hand - jetting on the 30 mm would be 200 main / .106 needle and 3.5 slide. If it has the stock silencer I would expect a smaller main jet ...trial and error really - take it out for a run and see what the plug colour is like.

I’d first do a “plug chop” run or two to check the full throttle mixture and work from there.

I have worked with a couple of 500 Bullets with 106 needle jets and main jets around the 180 - 200 size, both of which were having partial piston seizures, until they were fitted with 107 needle jets and main jets in the mid 200's and their performance was transformed. Just saying.