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I've got a GP 200 with 22mm jettex carb. On the way to the IOW after a few miles it started backfiring and then cut out. Start again and then do the same. I fixed it by changing the carb for a scootopia 22 MM and it run all weekend and the 200 miles back. I've stripped the jettex and its clear of blockages any thoughts apart from jettex are rubbish !!

My thoughts are that a backfire indicates a timing problem....

I changed the carb because I thought it was being starved of fuel, it run perfectly after, if timing problem could it appear intermittently so I may get the problem back?

fuel starvation would cause a mis-fire timing problem would cause a back fire

missing lynx wrote:fuel starvation would cause a mis-fire timing problem would cause a back fire

+1, is it back firing out of the exhaust or spiting back through the carb? An yes, electrical problems are notoriously intermittent

Thanks for this, it was backfiring out of the exhaust. I will check the timing, will have to read up first though

Jim wrote:Thanks for this, it was backfiring out of the exhaust. I will check the timing, will have to read up first though

It's most likely a loose connection or possibly a bad joint on the stator, maybe even the coil winding failing. First check would be to check the green and red wires from the stator are making a solid connection where they are plugged into the CDI. Pull the connectors out and check that they are a firmly crimped to the wires and that there is no corrosion, they should be a firm fit when pushed home. Also check the white wire connection. The next step would be to make sure that the ignition 'kill' circuit isn't malfunctioning. You will notice that there is a 2nd Green wire plugged into the CDI, this goes into the loom and is connected to an earth in the headset via the kill switch or ignition switch. Ignition switches can break down and cause the ignition to short to earth even when switched on but this is really a cheap indian switch problem. The simple test is to pull the 2nd green out of the CDI and ride the scooter to see if the problem persists, you will have to stall the scooter to stop the engine during this test though.

That's the easy stuff, have a go and report back

Thanks again, appreciate the advise

If all of the excellent advice fails to deliver a result then be prepared to replace stator plate that may have a failing LT coil.

CHRIS in MARGATE wrote:If all of the excellent advice fails to deliver a result then be prepared to replace stator plate that may have a failing LT coil.

I was trying to break that to him gently

coaster wrote:

CHRIS in MARGATE wrote:If all of the excellent advice fails to deliver a result then be prepared to replace stator plate that may have a failing LT coil.

I was trying to break that to him gently

One thing at a time, what I don't get is it has run for about 240 miles since I changed the carb with no issues

don't be too hasty in blaming the jetex carb. They are an exact clone of the Dellorto after all.
Once they have been correctly jetted and set up they perform faultlessly.

I suspect that whatever was causing your problem was rectified when you replaced the carb. Exhaust backfiring is not usually due to the carb or fuel mixture but generally due to retarded timing, ignition faults like wiring shorts and air leaks on the exhaust .

I bet that if you refitted the jetex carb it would now work exactly as it did previously.

I take your point, I'll have a play

Just for balance, i had a carb exhuast combo that would always backfire as the tank went onto reserve.
Never a running issue just a backfire as it went on to reserve.
Would do it on demand if i swtched the fuel off.
Easy way to check yours would be to simulate fuel starve in the same way.
Jetex floats are known to be sticky.

Interestingly, as mentioned I changed the carb to one of the scootopia ones and no issues for 240 miles. I went out last weekend and it now goes about 1 mile then starts to cut out. Leave it a bit and it starts ticks over no problem. I've stripped the carb, tank and tap and they are full of bits from the tank. So I'm changing the lot this weekend and then rule this out and then have another go!

Sounds like your stator is on it's way

same thing happened to me on the first long run to the MOT station.
Tank had been empty for years so I washed it out and fitted a new Hi Flo tap but it cut out after about 10 miles .
When I removed the fuel bowl there was a load of fine sediment which I assumed had come from a bad load of petrol.

When I removed the tap it was clear that it was very fine particles of rust that had been washed off the inside of the tank when I filled it up for the first time in years.

I removed my tank cleaned it with a handful of fine stones and petrol and vigerous shaking and fitted a large inline filter and its been fine since.

It wouldn't surprise me that the majority of owners who get crud in their carbs don't remove and flush their tanks out as it is a right pita to do so they ride around with a partially blocked tap filter.
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Thanks for that, that's exactly what my tap looked like, so all I can do is rule fuel out first, easier!! Then start on the electrics.

Ok, just for feedback I have now changed the stator plate and it's running well, looks like electrics it was. Although my fuel tank did need sorting anyway
Thanks for everyone's advice

good to hear it Jim. thanks for the feedback which will be helpful for others that find this thread.