@vtrn_raptor post some pics mate

@vtrn_raptor You have just answered your own question there dude. Just like fire, combustion engine's require three elements to produce combustion or energy; Air + Fuel + Spark = Energy. If the mix is wrong then the combustion will be imbalanced. As long as your spark plug is fine you should be producing a good spark to ignite the fuel and air mixture. Did you fit a new spark plug after the rebuild? If not then I would recommend that you get a new one ASAP.

Too much fuel will cause the engine to run rich, with un-burnt fuel getting pumped out of the combustion chamber by the piston. Basically the mixture will be too wet. Too much air will cause the mixture to run lean aka dry. In effect too much air will dry out the mixture. Have you looked at the spark plug since the rebuild? Refer to a Haynes manual to check the colour of your spark plug? This will tell you if the mixture is correct or not? Adjust accordingly if required? If the mixture is fine then I would look at the timing next, perhaps the engine is miss-timed, which would give you a rough idle and poor running at RPM.

If your bike runs good with the choke ON, that's because you are adding fuel to the mixture, aka over-fueling, which tells us that your mixture is wrong. Perhaps it was poorly set-up by the previous owner, or there was an air leak due to the top-end or a gasket being worn. Now that you have an air tight barrel, your engine requires a different set-up, one which is as it should be.

If you don't have a Haynes manual for your bike then I would suggest that you get one ASAP. They are a wealth of info for home maintenance and have a great section's on diagnosing problems too. There well worth their weight in gold, plus there's always some for sale on ebay. 😉

@Raydt Yeah that's how you would test.

In fact WD40 everything whilst it's idling high will tell you if its an air leak.

Some times it can be something simple like throttle cable sticking too high.

Again I was just under the impression the float shut off the fuel to the bowl.

But obviously it's it's too high it'll shut off the fuel too early, and too low will cause it to overflow.

You can also try a Delorto VHSA32 which is a 32mm carb used on the TZR 4DL which shares the same engine as the DT125R.

Only putting it out there, if it were me, I'd go for a tm28ss which is standard on DT125R from 1991 as Darty says.

The jetting changed in around 1996 as well but that will depend on the conditions of where you ride so you'll have to experiment with that.

Yup, get it sorted with a new floatvlave and seat.

DOH! didn't look at the back of the haynes manual (pg140) where they added later bike models. From 2004 onwards the main jet was 210 and pilot was 17.5 - so my bike was set up correctly! Problem now is my jet needle is a little bent and shows excessive wear on the bent side which means I need to replace my needle and needle jet ( 5j40 and q2m(939) ) but I can't find those anywhere on the web.

Yeah which is why it was a side note rather than a big point. Still not something I would do personally.

@mezzaaa rough inlet helps with fuel atomisation. This helps to burn the combustible mix properly.

However this only occurs once the fuel and air are together. Polishing the bell mouth helps draw air in. You want to be doing that as fast as possible.

@Calum Thanks 😃

@MIGHTYMAN couldn't comment other than its a round slide carb which is a no no for performance.

try adjusting air/fuel mixture this should help mate i had a similar problem with mine so got it cheap he thought it had bad problem. i will probably get around to buying after market crab as mine has a small crack on the carburettor body i have my tick over screw screwed in
all the way

@MIGHTYMAN said in Is upsetting necessary?:

4FU from Germany.

Not talking about the cylinder pal. Was talking about the Chassis/Engine code. Not that it makes too much difference but the 4DL's are ever so slightly different internally compared to the 3BN.

Finding out it's a 4GW model will tell you what spec the engine was, I.E 4DL ran VHSA carbs over the 3BNs Mikuni TMX28. Stuff like that just tells you a bit more about the problem.

Yea tried the needle position when all was standard but the leaner I put it the worse it ran the richer the better but still didn't cure the hesitation.

Thanks for the help.

Ah - thanks, now it starts to make sense. Been fiddling with it this afternoon and it seems to run great with a 260 main jet and 30 pilot jet - the only thing I wanted to achieve is reliabilty, making sure it not runs to lean, not to maximize performance..

Respect!

thanks callum the carbs all working fine now but cant seem to get the powervalve set right now...