Bogging down - why

[HoggyF]

I've just replaced the engine on my sons pitbike with a brand new unit re-using the old carb and exhaust, engine is the same type but not same make.

When you blip the throttle wide open from tickover it bogs down and trys to stall but if you open the throttle a bit more gentle like it'll rev quite nicely. Plug is a bit sooty though thats just from tickover and reving in neutral (can't do a plug chop in the street really)

To me it feels like its getting too much air at first but thats just a feeling. Mixture screw doesn't make any difference either way.

What do I try next?

[Supermotard37...]

It could be pulling in air mabye one of the carb rubbers are split or rottern or maybe one of the jets is blocked or it may well be the vaccum pipe is blocked thus starving the carb of fule wich would cause the bogging down i hope this helps

[HoggyF]

HI

Carb rubbers are brand new with the engine, jets are clean, what do you mean by vacuum pipe? if you mean the breather on the tank, tried it without tank cap on with no difference.

[Supermotard37...]

hi
yeah by thats what i meant by vacume pipe my bad...

so it will idle but as soon as you give it some revs it dies...hmm
have you tried spraying wd40 over the rubbers and seals on the carb to see if the revs pick up? and apprently if the revs do pick up theres most probably an air leak thus pulling to much air and killing the engine..

you did say you put new carb rubbers on there tho
and that the jets are clean so it should run and what you described does sound like air leak..

is the carb setup correctly? ile keep hunting for answers for you ? ile ask my mate he is good with carbs ;

[HoggyF]

Hi

I'll try the wd40 thing and see what happens

the carb is probably not set up for it as the engine is different and could have different cam, valves etc. Don;t know what the original engine was so hard to say.

I still think its too much air as is you open the throttle up ajust a little more gently it will rev cleanly its just when you go full throttle from nothing that it bogs which says to me that on full throttle its opening the slide up too far too quickly.

I can clean carbs out etc but when it gets into the "tuning" side of it i.e. changing jets, adjusting needles etc I just don't know what I'm doing.

[Fairies attack]

Have you tried the mixture screw?

It could need a bit of a tweak. Look up the standard setting then work from there.

[Slacker24seve...]

I had a very similar problem with my hornet - the rubbers on the airbox were not seating porperly. Check those
____________________
Triumph Daytona 675 track bike + girlfriend's Honda Hornet 600
Selling a hack/winter bike for less than a grand? PM me.
Banger rallies are ace

[dangerousdave]

bogging down when you snap the throttle open is likely to be the pilot jet. Its likely that the replacement engine requires different jetting.

This jet affects the engines behaviour off idle.

Try installing a pilot jet one or two sizes larger, and see what the result is then. If the bike accelerates better then you have solved your problem. If it makes it worse, then try a pilot jet one or two sizes smaller.

It's a little trial and error. Pilot jets are a couple of quid each, so not expensive.
____________________
1988 Kawasaki KMX 200

Previous: Yamaha YZF1000, ZZR600, KMX200, DT50, KX80, CG125, PF50

[HoggyF]

Cheers Dave
that was the type of advice I was looking for, now all i've got to do is find out where to get jets for a pit bike from.

Snow rider - mixture screw doesn't make any difference - tried that 1st

[dangerousdave]

What type of carb is it ?
____________________
1988 Kawasaki KMX 200

Previous: Yamaha YZF1000, ZZR600, KMX200, DT50, KX80, CG125, PF50

[HoggyF]

tried adjusting the needle today dropping it was worse and lifting the needle to the highest setting improved it but still bogs slightly when you snap open the throttle from tickover. Mixture screw still doesn't solve it

Carb is the world famous TAOTAO brand as used by various MotoGP, world superbike etc teams.

No size imprinted on the pilot jet so not sure what size is next.