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#88382
I wasn’t thinking of fuel flow into the carburettor was the problem. Again such a sudden cut out wouldn’t be accounted for in that way.

But I am thinking that it is fuel flow faltering not into the float bowl but directly into the main jet. I could see that a combination of steep angle of the engine and the effect of gravity on the sudden drop may momentarily inhibit fuel into the main jet. As soon as the bike stabilised the problem would disappear.
#88383
The Concentric Mk 1 carburettor was designed to operate up to 30 degree off the vertical, (though some suggest 40° and others 20°. I guess that the Mikcarb would be similar. Maybe your angle of precipitation exceeded that.
#88384
Wheaters wrote:
Mon Mar 16, 2020 1:29 pm
Which trial was it? Well done on having a go.

My attempt at the MCC Edinburgh Trial was a disaster. The bike attracted a lot of interest among other competitors and one rider asked me what my bike weighed. He told me his new Beta weighed only about 60% of what mine does! The big advantage there is that a lighter bike is far better on hills; less likely to suffer wheel spin.

Not forgetting he was probably a far better off-road rider anyway! :mrgreen:
It was the Durham Dales Long Distance Trial with the Middle-England Classic Vehicle Club. Yes, most of the competitors were on much more trials-specific machinery, although there was a C90 and an SS90 with a pitbike engine. One brave soul took a standard RXS100 on road tyres but his clutch bombed on one of the later sections. Quite a bit of classic brit iron too, a matchless and a couple of ex WD BSAs.

I'd be interested on hearing from someone who's done this and one of the MCC trials to get an idea of how the sections compare. Some of the ones on this were more akin to what I've seen on "proper" trials.

I did refuse two sections which started with a long, very steep straight-drop down into a quarry. I decided it went well beyond pushing my limits and into the realms of pushing my luck. It would not have been a controlled descent, it would have been a slightly slowed-down crash while hoping the bike got to the bottom before I did. Happily, other competitors agreed this was a good decision.

Yes, wheelspin was my main issue, a combination of too much weight and not enough tyre.

Gearing too. it really does need lower gearing. One section was a straight climb and I ran out of puff less than half way up but I don't want to go the gearbox route becauase I'd like to use the bike for road trips too. I've got a spare sprocket/drum so I've just ordered some blank sprockets. I'll get my local light engineering guy to turn the teeth off it and make me some bolt-on gear rings.
Presto wrote:The Concentric Mk 1 carburettor was designed to operate up to 30 degree off the vertical, (though some suggest 40° and others 20°. I guess that the Mikcarb would be similar. Maybe your angle of precipitation exceeded that.
I just rotated a picture of a bullet 30 degrees and yes, almost certainly was a fair bit more than 30 degrees momentarily, especially since I have over-standard shocks to start with. The bash-plate certainly came into play on one of them.

I'll check out the electrics and I'll check the float height but the solution may simply be lower gearing/more revs to carry me through any momentary dead-spot.

I'm toying with the idea of making up an alloy manifold with a slight angle on it so the carb slopes down slightly. Similar idea to the one our hosts make for attaching a big amal to the 500 headss but with a slope on the carb side.
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#88385
I bought one of our host's modified rear drums (see page 174 of the Bullet catalogue); they sell a variety of sprocket sizes to fit.

My 350 has a 46 tooth sprocket, rather than the standard 38T. When I did the trial it had a 16T gearbox sprocket. TBH, it seemed low enough; as I said wheel-spin was the main problem and the bike tended to drift sideways on muddy uphill sections. 50 mph was the top speed before revs got too silly.

Since I fitted the 5 speed gearbox I left the standard 18T on; the bike will now do about 65; it's just slightly "shorter" geared than standard. I might now fit a 42T rear which will put it more or less to "standard 350" road gearing because I'm doing more on the road and I've tuned the bike up a bit since I first bought it.

If you were really serious about the off-road stuff you could fit a 50T rear and as low as a 13T on the front. It's not a cheap experience because you might also need to buy a new chain.
#88386
I've already got the drum and sprocket blanks are about £25. My local guy loves lathe work and I think is quite tickled by some of the projects I bring him. He sees it as "proper" engineering and a change from fixing totally worn out farm machinery so he rarely charges me much.

I'm on 14/38/4-speed gearing for now so I was going to change up to have the option of that (which I think is as low as is realistic for road use) or a 42t sprocket. In fairness, I was factoring in having a seperate chain for the trials use anyway. I'll just get a normal non o-ring chain and a couple of split links it can sit in my tub of used engine oil when not in use. I've been using swift chains recently and they are good value for money. Even have one on my VFR and it's lasting well.

The question will be what to do if first gear lets go again. Do I stay standard or drop some trial gears in...
#88389
I avoided the trials gears because it seems more of a permanent change and I do far more road riding than off road. I was lucky to be offered a 5 speed box which has a lower 1st and gets rid of the annoyingly big gap between 3rd and 4th, which is in my view the most irritating thing about a standard Bullet. Fitting a trials gear set to a 4 speed box will make that gap even wider.

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