Forum

[Mark B]

I've just bought a 1999 500 Bullet, having ridden Enfields in India and Nepal and got rather addicted. It starts easily and ticks over with a bit of popping, but as soon as I touch the throttle from fully closed it dies. it's got a Mikcarb with S&B conical filter, 27.5 pilot jet and 130 main jet, and Boyer Bransden Micro 4 ignition. The exhaust system is standard. I've taken the carb off and the pilot jet is rather clogged up, but apart from that it all looks clean inside. The air adjuster screw is fully in and the throttle screw is 4 1/2 turns out. The engine (and presumably the carb too) has apparently only done about 2,000 kms. I'm going to put in a new pilot jet, gaskets and o-rings, and hopefully it'll tick over like a waiting bomb. Is there anything else I should investigate? Thanks for any suggestions. Mark.

[papasmurf]

Most likely cause is something blocking any more fuel than tick over uses getting through.
Blocked filter, dirt in a jet.

[jefrs]

Air screw fully in and throttle screw out sounds wrong. Why? Check float valve? Rebuilding the lot should fix it.

[PeteF]

Air screw all the way in can't be right. Try backing that off a couple of turns.

[Mark B]

Thanks for the suggestions. I put in a new pilot jet, replaced the seals and O-rings, took the air screw out two turns and the throttle screw three turns, and after the petrol got through she fired up happily, sounding like a contented cat. A bit of fine tuning to do but I think we're going to be OK. It's so satisfying solving problems! Cheers, Mark.

[PeteF]

I think you are a bit confused with the function of the throttle screw. All it does is lift the throttle slide off the completely closed position to give the correct amount of air for the tickover. There is no correct setting as such, so quoting 3 turns doesn't mean much as far as carb tuning is concerned. You just screw it in or out to achieve a decent speed tickover.

[Presto]

Mark why don't you take a few moments to read the technical note on tuning the Mikcarb, it tells you (almost) all you need to know to get this carb set correctly. Far better than guess work - 'a few turns on this screw; a few turns on that screw; a new jet here; a new jet there'!

[Mark B]

This is all a process of discovery for me; I found the Mikcarb tuning notes yesterday, so proper tuning is the job for this weekend. I didn't mean to suggest I'd found the right settings, just that I was delighted I'd got it to run!

[jefrs]

It's a long time since I've done Mikunis so memory's maybe a bit off but the Yam 350s had a pair of them to fettle... Mark B, you say the pilot looks clogged, problem with any stored bike will be sediment and crud has settled - strip and clean the carb, especially jets, filters and float bowl. I seem to remember little tea strainer filters; the float valve can jam and/or the float can sink. Stored petrol 'blows' and becomes no good.

The bike runs on the main jet and slide, that has to be right for running, otoh there's little to go wrong. If it is shutting down coming up off idle then it's not getting fuel, look there. My number one would be check main jet is getting petrol. A full clean should fix it - carb spray and petrol.

Lift the throttle slide on the screw so it runs fast and reduce the idle screw as low (idle setting) as it will go. Gradually lower throttle slide until it 'hunts' then increase idle screw, repeat process to get a nice steady idle. [which is why I observed air screw should not be screwed home]. With filter off you can get a finger in there and feel the slide, get a visual and check it drops smoothly home.



On the Yams we had a pair of them to do simultaneously and get balanced. The term 'tuning' came from doing it 'by ear' like tuning a piano. Have fun!