H100 help?

[Madandy]

My sons H100 just been rebored. It ran ok for a short while, we changed the gearbox oil and then nothing. I cleaned the plug, and rechecked for a spark, which was a little weak. Charged the battery which gave a much better spark, but still not running. Next we cleaned the carb out, decoked exhaust and checked for air leaks. Now it fires occasionally but only for small bursts 5 or so firings then nothing. He needs the bike for work, so any suggestions would help.

[Okeydokey]

Welcome to the forum, I am sure someone who knows what they are talking about will be along soon... do you have any compression in the cylinder, more a matter of interest than anything else, I read on another forum that it was paramount, someone suggested putting a wooden plug, into where the spark plug goes, add a little oil and seeing if blew out?
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Knowledge is knowing a tomato is a fruit. Wisdom is not putting it in a fruitsalad!
YB100 v. Ford Sierra (1982 I came 2nd place) Honda H100S (Currently 0 - 0) CX500 Cafe project (me 1 - wife 0.... maybe!)

[stinkwheel]

First thing with a poorly running 2-stroke is change the plug. Not clean, not wire brush. A new plug out of the box.

The gearbox oil change should have absolutely no effect on the running of the engine.

From your description of running for a short while then dying again, it does rather sound like it's short on fuel.

Presumably you've been kicking it over until you're sweating cobs and about to collapse. If you've been doing this there SHOULD be a strong smell of fuel and the plug should be soaking wet.

If it isn't, look again at your fuel system (so is fuel coming out of the tap, is it coming through to the float bowl, is it getting through the jets) and keep in mind that it could be leaky crank seals.

Leaky crank seals tend to lead to the bike drawing air in through the crank seals instead of the carb. So you have good compression (it'll blow your thumb off the sparkplug hole when kicked over) but poor vacuum (won't suck your hand against the end of the carb with the airbox rubber removed).

Has it run normally since the rebore?
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[truslack]

Is it a points (SD) model, or a CDI (A, SG, SJ2) model?
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Current: Suzuki RG 125 Gamma, Honda H100, Triumph Tiger 800XC, Suzuki SV650 (minitwin)

[cb1rocket]

Having 5 H100s, its mostly down to the plug. I had my H100 rebored and they didn't replace the poxy plug and the bike died on me!
And check the fuel is fresh? Had it been laid up?

Battery will have no effect on spark, its a self ignition system all run off the genny

[trisers]

My contribution from experience with my H100, firstly the plug...the whole electrical system is pants, and although mine runs perfectly it's never had what you'd call a big fat blue spark...so the plug really needs to be in top condition.

Secondly the carb still needs cleaning, specifically the delivery tube for the idle jet. I made the mistake of taking the idle jet out, cleaning it and reinserting it to find it wouldn't start unless i put a teaspoon of petrol in the plug hole and kept the throttle wide open. When you remove the idle jet it reveals an internal delivery tube that runs to the mouth of the carb, there's probably some crap in there.

[Madandy]

Thanks everyone for your advice. The bike was ticking over nicely just after the rebore, but sounded a little rough in the gearbox, hence the oil change. The fuel is only a fortnight old, although the plug isnt getting soaked, so Ill have the carb apart and a good blast through with an airline. A new plug is on the shopping list for saturday.