Forum

[John R]

My '89 350 is a bit of a piggy at the moment. The first annoying habit is difficult starting. It will quite often start OK on a closed throttle, but coughs and dies when the throttle is opened. It will even idle quite nicely until you try to open the throttle to move off. Carb is a Mk 1 concentric; I believe it is running OK on the idle jet but not transitioning well to the main jet and I have heard it suggested that a throttle slide with a different cut out might help. Should I go smaller or larger? And why, when it it was running beautifully not long ago, should it suddenly need changing?

[simon]

Unless its suddenly developed a lot of slide wear or you've started using different fuel it shouldn't have changed the carburation requirements. Sounds like it a tad lean. I don't suppose you've developed an air leak somewhere or perhaps you've got some water in the carb that is obscuring a jet. My advice would be to pull off the carb and give it a thorough clean without changing any settings if you can.

[Mark M]

You know, I think the weather has a lot to do with it. I am trying to iron out a flat (spitting) spot just off idle on my Mk1 Interceptor and it has been much worse in the recent prolonged hot weather. I also had 2 refills of poor fuel at a little local station while I was at a Rally last weekend and that didn't help either.
REgards, Mark

[Presto]

Air temperature can indeed upset carb settings, especially for 2 strokes, but 4 strokes too. Warm air weighs less than cold air while fuel remains at the same weight. In some critical applications carbs may need to be re-jetted – larger jets in cold weather (to balance the greater weight of air being drawn into the engine), smaller jets in hot weather. On a 2 stroke it’s very easy to find that the engine runs noticeably better on a fresh cold morning (or evening!) - grater volumetric efficiency. [But I may be wrong - it's been known to happen before ]

[PeteF]

You are right Presto but the difference you will find on the typical RE will be negligible.

John, if it was running OK before then something has occurred to make it not OK now.
Don't go diving in changing anything till you have checked the obvious.
Air leak at manifold (not so common with the 350 but it can happen)
Air filter bunged up.
Points need adjusting.
Advance mechanism working OK.
Ignition timing slipped.
Dirt/water in carb.
Jets blocked nor partially blocked.
Plug spark breaking down.

[Yorkie]

Hi John R Just gone through this with two Redditch 350cc Bullets after standing 18 months due to my health.
Time had come to service them for the road.As yours, bad starting, would idle ok,would only rev with air control slide nearly closed.
Had to be fuel/carb,on removing carb, removed mixing chamber top,removed throttle slide assembly and there was a build-up of rubbish on the taper needle,thinking that this was the problem as fuel couldn't pass through needle jet. Cleaned needle,put all back on no difference.
Of with carb, strip completly,looking down carb body at flange end you will see two very small holes were the throttle slide sits,I cleaned these out with a jet cleaner(welders kit)put back together,and' bingo'
all working fine.
I have added 100ml of Forte carb cleaner to fuel(available at garages)to clean when running.The amount was suggested by Forte Service help line
Sorry long story.

hope this helps

YORKIE.
ETHANOL????

[ed.lazda]

Don't know about Amals, but my Bullet with a Mikcarb suffered this problem of idling OK but not revving. It turned out to be water in the carburettor float bowl. Take the bowl off and look carefully for two layers of fluid. If you do find water, it's worth switching the fuel tap to reserve and draining off fuel until no more water comes out.

[John R]

Whipping the carb off and servicing seems like the best idea. I drained the float bowl and put a tankful through with Redex in it, which i normally find good for blocked jets etc.

[wilf]

I have the same problem since stripping and cleaning the micarb on my 05 bullet. It starts easily but won't rev without my being very sensitive on the throttle. Turning the pilot air screw in to within a half turn of fully home helps things, but doesn't fully cure the problem, then when the she's warmed up I find I have to reset the idling/pilot air screw again. Once warmed up the bike runs perfectly. If I set the pilot air screw about one and a half turns out, as a starting point, it seems quite loose. I have wondered if air could be getting in through the threads? Any help graciously accepted.

[John M]

A duff condenser can cause non-revving, popping, banging and other strange things.