Trials Australia Forums

Hi folks, looking for some guidance...

Bike: Beta Rev-50
Carburettor: Dellorto PHB619 BS

Symptoms: From idle, when I give it a handful (full throttle), it just dies. Wind it on slowly and no problems.

I've cleaned the jets, fuel flow from the tank is fine. Mixture screw is 1.5 turns out from fully in. I've tried variations of that, and it seems to get slightly better when I wind that out, but then it idles like a dog.

What next? Is this solvable? Or is it purely a limitation of small bikes?
It's a real pain for the young'un to get half way through a section, faced with a hill, wind on the gas and it dies...

Keith,
I would be having a look at the pilot jet and maybe increasing the size of the jet.
I have had a similar situation with my Montesa 247 and after referring to David Lahey I went up from a 25 to 35 pilot and I have sorted out that problem, now to tackle the rest of the carby, unfortuanatly David is going away tomorrow.
Cedric

Thanks Cedric..

So which is the pilot jet? There's three jets in there... the biggest is the one the needle slides into, there's a tiny one next to that, and another largish one next to that.
And where does one buy new jets from?

Question for you Keith....

Does it go up that hill WFO with the choke on?

Hi Keith,
We had a Rev-50 and had it ran as well as any 50cc bike could. It started very easy and the jetting was spot on right through the rev range.
Having said that, it had very little grunt down low from very low revs. It did however perform surprisingly well if ridden with a good dose of revs. It could not be ridden like a traditional plonking trials bike. The rider must ignore the mx-like noise.

Anyway a question: has your bike always been this way, or is this a new condition?

If it's a new condition, then changing jets will not fix it. Something has changed.
We had 2 occassions of "dying".
1st occassion, he had forgot to turn the choke off - surprisingly the bike would actually start okay at each the section, but then would die during the section.
2nd occassion was a faulty kill switch.
Assuming you've addressed these causes, tried a new spark plug, air filter is clean, and slide needle is in the default position, rear disc brake has not siezed on a bit, etc, then you may need to look for either
a) a vacuum leak (intake manifold or crankshaft seal under magneto), or
b) stuck piston ring, carbon buildup on piston/head, glazed bore. etc.

Just some suggestions.
Jim