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2007 Gg 250 Txt Pro - Hot Start Issues


miner
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That's the size needle jet I think actually?..... I didn't realise that the jet/float bowl bolt was the main jet on the GG/Dellorto carbs, not the case on the Keihin carbs on the KTM. Hadn't seen the numbers on that one, must have missed them.

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  • 7 years later...

Still facing issues with this… thinking its too rich… its definitely hot here…. Kicks over ok from a cold start, sometimes when its hot and other times completely not. Could kick it till the cows come home and it wont start. Technique and timing issue sorted. 😅

Ignition (CDI/Coil & Rectifier) changed out for on of the Hell Team’s aftermarket Ducati replacement (discontinued) units. When it starts it runs well. Curve feels a little different but solid, nice to have it back. Stator looks OK, noting obvious. Plug is gapped ok, looks ok, not fouled. 

Had a play about with the mixture and idle settings the other day, it seemed better… then wouldn’t start eventually. Still getting a fair few kick backs when repeatedly kicking it… no obvious air leaks so could indicate overly rich in the first place? 

Jetting is stock 35/60/118 combo… might give a leaner jetting setting a go… still got a few months before when it’ll need the stock settings. 

Thoughts? Part of the fun of owning these things? 

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1 hour ago, miner said:

 Still getting a fair few kick backs when repeatedly kicking it…

Thoughts?

 

Although jetting has an effect on rate of combustion, that's not what causes kickbacks. 

When a kickback occurs, the force from combustion pressure exceeded the force from flywheel inertia.   Basically, the combustion pressure was high enough (too much burning too early) before TDC (rather than after TDC) to cause the piston to turn the crank backwards. 

Ignition timing for starting is retarded from normal running for this reason.  It's possible the stator plate is too far advanced.  Or it's possible the ignition system is intermittently behaving badly.

Do you have a timing light, a helper, and a dark place to work?  If so, you can see it the ignition timing is different from normal when a kickback occurs.

 

 

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I was wondering about that… it’s more of an issue when it’s hot but it can do it when cold starting. 
 

Not sure if there is any adjustment on the plate for the pickup coil… it’s just two bolts. No offset on it from what I saw. 
 

It’s sometimes blubbering and dying when it sounds like it’s firing, tried cracking it open to rev it and it doesn’t catch either. Sometimes it’s popping and cracking instead of starting. 
 

Generally from cold it’ll go in a kick or two. It’ll also run fine when it’s really hot, fan on. It just won’t kick over sometimes when starting it hot. 
 

It is rich for the temps here, it was over 40°C last time I took it for a quick play in the evening and was messing about with the carb. 

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@miner The timing is fixed on the pro the woodruff key gives the position on the crank  and the pick up fixing plate gives no adjustment nor the stator plate. As you had this problem when you had the old ignition system fitted and now the brand new system is giving you similar results it may be better to look at things you did not replace,  maybe try a different carburettor and also decoke the head combustion chamber and crown of the piston then polish it to a mirror finish. Make sure your coolant hose from the cylinder head to the top of the radiator is not touching the bottom of the fuel tank and set your cooling fan to run permanently when the ambient temperature is 40 C etc by putting a thick copper wire from the earthing bolt at the top of the frame on the exhaust side then put a bullet connector of the correct size on that wire and plug it to the female ended wire that comes off the little black box that is held onto the fan shroud by a small pozi drive screw. That is of course if you are running a standard 2007 model position  thermostat fitted to the top right hand head of the rad and situated at the front side of the rad facing toward the front forks , also check your carbs float arms are set parallel to the edge of the carb body so that you have plenty of fuel in the bowl. There is still something that needs changing on your set up if you still have problems. starting and also kicking back , coked up piston and combustion chamber? . After all this buying a new ignition set up you have to keep going ,  it cannot be much of a big problem to solve the issue now. Regards Alan. 

Edited by Tr1AL
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@miner Another thing you could look at is to check your air gap between the flywheel and the pick up it should be approx 0.6mm . Standard  carb needle clip position is 3rd down from top. if you have a different setting I would try it standard. Fuel screw is 3 to 3.5 turns out usually.

Edited by Tr1AL
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11 hours ago, lineaway said:

This has been going on a long time. Try it without the gas cap. And if you can a pic of the routing of the vent tubes on the carb.

Tried without the vent cap and proved it’s flowing. Not running any vent lines on the carb, it’s never had any on it. 🤪 Carb was fully cleaned and put back together just a few hours ago after rebuilding the bike from its crate. 
 

It’s been going on a while but it’s never been fully resolved… just less noticeable until stripped and left in a box. Definitely worse when it’s really hot outside. 

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10 hours ago, Tr1AL said:

@miner Another thing you could look at is to check your air gap between the flywheel and the pick up it should be approx 0.6mm . Standard  carb needle clip position is 3rd down from top. if you have a different setting I would try it standard. Fuel screw is 3 to 3.5 turns out usually.

Thanks, I’ll check that out… I couldn’t find anything on the fuel screw setting. Clip is at 3rd grove down. 

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"Stator looks OK, noting obvious."  Are you testing the stator coils with test equipment or by eye 🤔 looking at coils tells you nothing unless they are burnt to a crisp, you can meter test coils for resistance or you can oscilloscope test the AC output and confirm it is fully functional.

Sparkplug cap and wire has been changed?  They don't last forever.

"Plug is gapped ok, looks ok, not fouled. "  Sometimes the insulation is cracked and the defective plugs will spark way up inside the plug body and not at the electrode gap.  Try another new plug.

If you can't narrow it down to being either a carburetor or ignition issue there is not much anyone here can help you with.  Do you have access to another GasGas TXT you can swap parts with, that is what a dealer would do to eliminate the carburetor as being your problem.  Parts swap is also the only way you can reasonably test the ignition module.

Edited by lemur
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