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Mikarb Tuning Question
Posted: Mon Sep 15, 2014 9:32 am
by Tv
G'day All
I have been messing around with a Mikarb VM24 on my Bullet 350. When I'm accelerating, all seems fine, then I start to cruise and the engine splutters and carries on, surges and stutters like Porky Pig. Like, it wont just cruise along. If I gas it, it takes off and behaves OK but it wont ride smoothly in that cruise zone. Any clues. One thing I havent been able to understand is the mixture screw. I can set it by the book and the engine ticks over nicely. Does this mixture affect the whole range of carburation or is it only for the tick over.
Regards
Tv
Mikarb Tuning Question
Posted: Mon Sep 15, 2014 10:39 am
by Brazilla
Someone with more experience may be able to say if I'm wrong on this one but I think the mixture screw only affects the pilot jet which controls idle (although it remains active during other throttle positions) the throttle slide affects 1/8 to 1/4 throttle so could be your issue. I have a similar issue at the moment although when I run with 'choke' all is fine. I have ordered the richer throttle slide for mine to try but I'm not certain that is the issue. Good luck!
Mikarb Tuning Question
Posted: Mon Sep 15, 2014 10:44 am
by Leon Novello
Click on Technical Notes in the menu (Mikcarb carburettors) on the left. Or click on here.
http://www.hitchcocksmotorcycles.com/pi ... s_-_a4.pdf
Mikarb Tuning Question
Posted: Mon Sep 15, 2014 4:49 pm
by Gwilly
May be an idea to do a plug chop after cruising quarter to mid throttle range for a mile or so..
It could be that its running weak or rich in that range and either lifting or dropping the needle by 2 notches may improve things..
Mikarb Tuning Question
Posted: Mon Sep 15, 2014 5:29 pm
by PeteF
Just to confirm - the "choke" plunger on the 350 is down for off unlike the 500 which has a lever and the lever is up for off. It's not a choke at all really, just an enrichment circuit. It might just perform as you describe if you have it wrong.
Mikarb Tuning Question
Posted: Mon Sep 15, 2014 6:28 pm
by wilf
Good point PeteF.
Mikarb Tuning Question
Posted: Mon Sep 15, 2014 7:01 pm
by Brazilla
Yes, thanks Pete. I can confirm I mean enrichment circuit on when the plunger is in the up position. Runs fine like that, problems present when plunger is down, think this may mean I'm too lean? Sorry TV, don't mean to hijack your thread
Mikarb Tuning Question
Posted: Mon Sep 15, 2014 9:34 pm
by Tv
G'day, thanks for the replies. I am familiar with the choke operation. It's not that. I have since moved the needle 1 notch back to where it was before I started my 'carby tuning' education. I did also notice the mixture screw was nearly all the way out as the spring was not holding it in place. I stretched the spring a bit so that looks OK now. I cant ride it for a couple of days but when I do, if it is still playing up, I will try the plug chop. Thanks for your help. Regards Tony
Mikarb Tuning Question
Posted: Tue Sep 16, 2014 2:26 pm
by PeteF
Mmmm - if the mixture screw is screwed that far out it can't be right. Try screwing all the way in, then 2 turns out. That should get you in the ball park.