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hey guys, i just got the project bike back together and i must say it runs STRONG
however, i have a jetting related question

the bike came with a FMF pipe, boyesen power reeds and open airbox
the only "Change" i made was having the cylinder rebored from stock to 2 MM over
(its actually closer to a 220 then a 200 now)

now, the bike runs strong even though i havent jetted it yet
(once the weather clears up i will)
but untill then i figured we could do some bench racing

would a good jetted carb that works well on the 200 also work well on the overbored cylinder?
or does the change in displacement warrant a change in jetting aswell, and which way would i want to go, up or down
(and no, i dont know what jets are in there right now)

so, thoughts?
suggestions?
random remarks pertaining to the KDX?

Common sense would say that if you bore bigger, you should have to reduce the jet size, but not all motors play by the rules. You'll have to ride it and see.

shows what i know, i would have guessed a bigger bore needs a bigger jet to get more fuel to fill the bore
i cant wait to ride her, i got her fired up last weekend and rode her around the yard..twice
then i went out of town for a long weekend and when i came back that was all this nasty white stuff on the ground :(

got any rough guesses as for what size jets to go with...ballpark?

zomby woof wrote:Common sense would say that if you bore bigger, you should have to reduce the jet size, but not all motors play by the rules. You'll have to ride it and see.

why not? what s the theory behind that?

I would say very little change if any. Over boring the cylinder will reduce the port size, mainly the boost port. If they weren't re worked, they will even be lower= more low end. Jetting should be relatively the same.

i dont think they reshaped the ports...its not on the bill and im sure something like that would be mentioned

um. its actually more like a 210cc...jus sayin`

Redrum wrote:um. its actually more like a 210cc...jus sayin`

the way i figured it the 200 is a 66 bore, while the 220 is 69...68 is closer to 69 then to 66 right ?

diymirage wrote:

Redrum wrote:um. its actually more like a 210cc...jus sayin`

the way i figured it the 200 is a 66 bore, while the 220 is 69...68 is closer to 69 then to 66 right ?

It would be a 210. A 200 is 198cc and a 220 is 216cc the difference of the two is 18cc with there being a 3cm difference in the bore that works out to 1cm = 6cc. So with the gain of 2 you would add 12cc (6 x 2) to the 198cc and end up with 210cc.

thanks for the explenation Bates, i was working under the (insert different word for assumption) that the 200 was actually a 200 and the 220 was actually a 220

i guess both my statement and Danny's statement are true, he was right when he calculated it to be a 210 CC and i was right in saying it was actually closer in bore size to a 220 then a 200 (which still stands)

now, back on topic, jtting advise?

opened her up and i found a 48 pilot with a 160 main, seems a bit rich no?

That is stock jetting. I had mine out last weekend with that jetting in about 15 degree weather and it was too rich.

that might explain why i had those exact same jets in the toolbox, i must have removed them from my othe KDX
i went and replaced the 160 with a 150 and ill go out and buy a 42 and a 45 pilot after work
maybe it will start up on its own then

(strangest thing, it runs really strong but it wont start without a little spray)

It should still start with the stock jetting. Sounds like the carb needs to be cleaned good. Might want to get a size or two bigger on the main also.

Had a similar issue awhile back and found some crud in the idle circuit...good carb bath and problem solved.

bufftester wrote:Had a similar issue awhile back and found some crud in the idle circuit...good carb bath and problem solved.

the wife had to work last night so i had the oppertunity to clean the carb out in the sink
thats when i replace the 160 main with the 150
didnt seem to help
i just bought a 45 pilot jet for it but i havent had a chance to install it yet

rbates9 wrote:It should still start with the stock jetting. Sounds like the carb needs to be cleaned good. Might want to get a size or two bigger on the main also.

bigger you say?
i was under the impression that the 50/160 combination was pretty rich to begin with
(just for review, heres a list of mods)

full FMF exhaust
no filter lid
boyesen reeds
210 CC

this should flow enough to warrant the stock, or even richer jetting then?


on a very important side note
i decided to swap spark plugs today
took out the brand new plug that was in there and put in an old spare that i keep in the fender bag off the DD
kicked it once, without the choke, nothing
put the choke on and kicked it again....fired right up
bogged a bit with the choke on but as soon as that came off she was crisp

Did you check your float height and fuel valve? Sounds like you're just not getting fuel first kick or two...all the usual culprits should be double checked too...clean filter, all boots/clamps tight, etc.

did not check the float, but i did notice if i pull the fuel line off the carb and open the valve it pours out
(regardless, that valve will be replaced soon ;) )

as for the float, i would imagine that would cause intermittent problems (starvation) under full bore?
i havent run it enough yet to verify if this is going on but it looks like it is just a start up issue

ill let it sit in the cold garage for a while and try again later, see if i cant get her to start on the first kick with the choke on :)

I meant the fuel valve that is operated by the float in the carb. It has a rubber tip and a little spring loaded plunger. If your float is too high it could be closing off the fuel flow until you get it started and pull enough fuel to lower the float in the bowl? That and I'd make sure the pilot jet is clean, that you can see daylight through it. (but don't go poking any wires in there) Just pulling at straws now lol

ahhh, that one
i gave it a good once over last night, looked good
im gonna get some food with the boy later and try to kick it on, see what she does

i guess a good way to check this is to pull the acces plug to the jets right?
if its full its good?