Il try and keep this as short as possible. Im no expert btw.
My son was having ' smooth running' problems with his ltz250. backfiring etc. The carb had been messed with by the previous owner, idle adjuster missing, couple of the lines from the carb blocked off etc split in carb boot going to the head.
So a new carb and boot fitted and it started up first turn, i adjusted the idle screw a little and it was running beautifully on tick over. Reving up nicely etc
I watched him take it for the first drive and thought it sounded like it had a miss. Only travelled 100 yards, then died out completely, wont start but turning over no problem. Battery good, fuel from the tank to the carb running ok. Plenty of fresh fuel.
i checked the plug which was dampish but the spark was yellow. I will be replacing the plug tomorrow.
i doubt it could be as simple as this, but as i say im no expert.
Anything else i can try ?

 

If the new plug doesn't fix it, put the old carb back on and see if it then runs. If it does you have a problem with the new carb. Either it is way too rich, and acting as if on choke, i.e. starts when cold but chokes itself as it warms up. Or some dirt has got into a jet. Disconnecting the fuel line or tank, to fit a new carb can disturb dirt, which then gets into the carb and blocks a jet. Or possibly some dirt has been in the new carb and again moved to block a jet.

 

Thanks. Ok so fitted a new spark plug and the new carb wouldnt start or would start but needed half throttle to keep it idling, also didn't sound right at all. So removed the new carb and put back on the old carb. Fired up and idling without any choke BUT fuel is coming out of the middle of the carb somewhere, hard to see exactly but looks like where the carb joins in the middle / gasket .
any ideas?

just went back out to try and start it , its turning over but not starting with or without throttle, maybe flooded?

 

Take a look inside the new carb, remove and blow the jets and the holes they came from out with compressed air. No altering adjusters, put it back together, fit that carb and old plug and try to start bike. If it again fails after a short run, check for a spark. Have the other plug with you so you can just take lead off the plug in the bike and put it on spare plug to test for a spark. If it is sparking, remove the plug from engine and see if it is black and sooty, this would indicate a rich mixture. If it is, check choke is working properly and, if that is OK, swap out jets from old carb into new one.

 

Thanks. So i blasted the new carb jets etc with air ( i should mention its non suzuki ) put it back on and tried to fire it up but with the same symptoms, actually smoking a little from the airbox area and needs 1/2 to full revs to even start, as soon as i let go of throttle it dies.
i put back on the original carb and it fired up straight away and was running nice, well idling nice, i didn't drive it, but the carb bowl started over flowing, not v bad, but enough. After a google search i thought the float needle might be sticking so i swapped over the float needle from the new carb to the original suzuki carb. This made the fuel leak alot more from the float bowl. The needle was shorter on the new carb than on the original one.
so thats basically where im at, any further thoughts?

 

Trouble with Suzukis is most don't have a drain pipe, so if the float needle does stick, they dribble where they can, usually into inlet port and/or airbox. Float needles usually fail because of dirt in between needle and seat, or the little spring loaded plunger, which the float contacts, sticking. If it is dirt, a clean will fix it, if the plunger, get a new genuine needle. If it is leaking between float chamber and body, it may just need a new gasket. As for the new carb, see if you can find the reason it is way too rich, (assuming this is the problem) as I wrote before, a sticking choke, or wrong jets seem to be the most likely.

 

Ok so i sealed the old original carb with some sealer stuff, carb bowl to the top part, which has so far stopped the leak. Started up after a little fiddling and now idling nicely and starting first turn.
However when i took it a quick spin and tried to give it half to full throttle it wouldnt go smoothly, like bogging. Also spitting small flames out the exhaust and a little back firing.
Any more thoughts what the next step should be are appreciated. Cheers

 

It may still be the mixture. As I wrote above, plug nose colour indicates mixture, black and sooty = rich, very white = lean. Only white at the tip = fairly near right. If it does seem OK, I think it is time to start checking valve clearances and timing, also compression.

 

The plug has definitely went black very quickly.
I did notice earlier than after it idles for a couple of minutes i can rev it slowly up to full revs without it boging down but it still backfires alot with a small flame from the exhaust. Seems to be using alot of fuel even when just idling and me trying to rev it etc.
as i say im no expert but do think its still a carb issue
im thinking of buying a better branded non chinese carb to see if that cures it.

 

Are you sure the choke is working properly and air filter clean? I don't know the LTZ250 but Eigers etc, had a choke lever that rotates round the handlebars and this could get rust underneath and stick. Also had one where the outer cable had rusted, lengthening it, thus putting the choke slightly on all the time. On some carbs the mixture can be adjusted by moving the main jet needle up or down in the slider, having different notches for the circlip, or spacer washers under the circlip.