This Forum is now CLOSED use the link to get more details viewtopic.php?f=3&t=13924#p102587
User avatar
By ssepiol
#98336
What's a good replacement for the stock carb and also carb to engine manifold. The Mik carb I have is very finicky and always seem to have to adjust the idle screw.
#98340
A VM28 mikuni carb on a mikuni manifold. The actual carb the existing mikcarb is a copy of. MK1 Amal concentric are an alternative but I find their slow running circuit is prehistoric, glitchy and difficult to adjust compared to the mikcarb.

Or you can replace the internal componants of your existing mikcarb with Japanese ones. Our hosts do a kit but they are out of stock just now. https://accessories.hitchcocksmotorcycl ... -Kit/19941

If it's going out of adjustment on slow running, it suggests something is moving or worn? So maybe worth a shot replaceing just the slow running jet and mixture screw assembly? That can be done for sweetie money. An inlet manifold air leak could also result in erratic idle so probably worth getting a new sleeve rubber at the same time.

In the absence of our hosts stocking them, Allens performance list a repair kit for the VM28 for an enfield 500 part number RK-0058. https://www.allensperformance.co.uk
By ChrisD
#98354
Ssepiol. The Mikcarb on my 1996 500 wore out - threads gone in the carb barrel. So I replaced with a Mk2 Concentric (32mm so I bored out the inlet port and did other things). But it goes well now. BUT you may find problems with fitting it under the tank - I had to lift the tank ~2cm at the back and offset the manifold by ~10degrees too. Cheers, ChrisD
User avatar
By Adrian
#98356
That seems to be the problem with two-piece mountings, i.e. the alloy flange and then the hose, it can put the carb far enough back for the throttle cable to foul the underside of the tank. It's better if you can find a single rubber mounting flange that doesn't need the alloy piece and therefore keeps the carb closer to the head. A 90° ferrule for the throttle cable can also help.

A.
User avatar
By ssepiol
#98364
Isn't the Mikcarb and the Mikuni the same? I put a one piece intake on it. Had to drill out the mounting holes and trim it a little bit to make it fit. Didn't make much difference still hard to start and some backfiring thru the carb when the throttle is applied. Also is it normal to have to adjust the idle screw all the time?
#98368
No, it's not normal to keep adjusting the idle screw all the time. I've never touched the one on my 350 except when I've made alterations to the engine. So something is wrong with either the slow running circuit itself (is it unscrewing itself? Maybe mark the screw position?) or the overall setup. As I say, an air leak at the inlet manifold will cause erratic idling.

An old test for an air leak is to get the bike idling then spray some starter fluid over the inlet manifold area, if the revs increase when you do this, there's an air leak (be aware doing this is a fire risk!).

Backfiring through the carb isn't likely to be carb setup, that'll be more likely to be ignition timing. If it's too far advanced, it'll be a pain to start and do a lot of backfiring or kicking back when you start it. Maybe worth a check, and make sure the auto-advance mechanism is in good order and not sticking or malfunctioning. Or maybe even just retard it a touch and see if there's an improvement. I had issues with the auto-advance on my 350 once because there was so much lateral play on the distributor shaft, the bob-weights were sometimes catching on the points plate.

A leak at the inlet valve could also cause backfiring issues, either the valve itself, or an over-tight pushrod. Is the rod straight? Backfiring can bend the rod itself or the adjuster as I found recently. Spinning the rod in position would usually make any bends obvious.

Shop for accessories at Hitchcocks Motorcycles