jetting assistantce needed asap

[Pappy]

ok, needle is in the lowest clip position, runs strong unless you stab the throttle from an idle then she will just bog and cut off unless you release the throttle.

im assuming lean?

so i need a larger pilot?

this is for a TRX90, and im also suspecting maybe a vacuum issue but not positive, because when you gas it moderatly it will run fine and makes no indication of popping etc.

[Pappy]

and also, when i lift the choke to the 1st position it runs much better:huh

im almost positive im having a problem with the needle....help:scary:

[400exrules]

if it runs better with the choke on your pretty lean, if your jetting is right, it should run the same or worse with the choke in

[Pappy]

ok, a few hours jerking around with this sucker:mad:

needle its at the bottom clip (richest setting)

air screw is 1 1/2 turns out (tried more but it got worse so im thinking fat on the pilot, so i went down from a 38 to a 35. somewhat better.)

still looking for ideas..lol

i geuss its a good thing the dyno will be here in 6 hours:eek2:

[Pappy]

ok, dyno time is over.


ended up with the 38 pilot and the 95 main. needle in 3rd clip and 4 turns out on the airscrew. runs good, but still has the lag if throttle is stabbed from idle (i assume this maybe able to be tuned out if i can get a slimmer needle)


engine made 1.4 more hp with the 20mm carb and 3 ft lbs torque over the stock carb. the power curve was very broad and the carb showed a curve above the stock carb from idle to redline.

luckily i had 2 20mm carbs here, after dialing in the first carb, and a few laps around the track, fuel filled the carb and airbox:ermm: everything looked ok when i diassembled it, i still havent an idea why it did this. installed the other carb and so far so good.

[Pappy]

the dyno showed an increase of 4 mph on top end with the new carb. i may even have to go back to a stock rear gear to keep the power where we need it.

[Spike99]

.

Based on your progress and multiple tests, do you think the orginal carb is a POS? re: Not matter what one does to it, it isn't going to work properly with your specific configuration????

.

[Pappy]

if you mean the first 20mm, i have to figure out what exactly went wrong with it etc. the first 20mm carb(actually both are new khein units) was the one we dyno'd with and ran until it crapped out. the original problem that prompted this thread may very well be related to the carb developing the later issue with regards to the float sticking(not sure if thats the cause or not)


if you mean the stock carb, id say the performance we gained from switching to the 20mm is worth the effort on a modded engine

[MikEXtreme]

Pappy,

What jetting would you suggest for an '06 TRX 90 with a Big gun and K&N with no lid?

[Pappy]

stock carb id say a 90. i have a full system(big gun) 11-1 piston and open lid and we run a 85 main with the stock carb.

[MikEXtreme]

Do you think I need to change the pilot or needle clip?

[Pappy]

you may, depending on how the bike runs with the exhaust and filter.

id install the exhaust and filter and take it for a ride. from the ride, you should get an idea if you need to make adjustments or not. ive installed several systems on the honda's and with the stock carb havent had to do much if any tweaking.

[MikEXtreme]

Thanks. Are you running wheel spacers up front on the 90 as well as the back? If so, what size?

[Pappy]

yes, we run 1 1/2 spacers front and rear. im working on coming out with a new a arm set up and hopefully a new axle this winter for the honda:D

[MikEXtreme]

Sweet!! I will be sure to buy a set!!!:D

[wilkin250r]

Do they have different needle tapers available for the TRX90?

[Pappy]

Originally posted by wilkin250r
Do they have different needle tapers available for the TRX90?

i am not certain about the stock 90 needle,

but seeing this carb is for a dirtbike they should offer it.

i have since discussed this issue with the engine builder and my thoughts were verified. at idle there is little to no vacuum and that initself is the root cause for the bog if the throttle is stabbed.

the cure....

possibly run the pilot jet very very rich, bump the idle to help create vacuum and the different taper needle.

[wilkin250r]

Originally posted by Pappy
i have since discussed this issue with the engine builder and my thoughts were verified. at idle there is little to no vacuum and that initself is the root cause for the bog if the throttle is stabbed.

the cure....

possibly run the pilot jet very very rich, bump the idle to help create vacuum and the different taper needle.

This is probably the conclusion I would have come to. You are going from the stock 15mm carb to a 20mm carb. That is a HUGE change. 30% In comparison, that's like going from a 38mm on a 400EX up to a 50mm, without an accelerator pump!

Unfortunately, this is the drawback of large carburetors, especially since they are often couples with aftermarket filters and no airbox lid. Without that vacuum, and without an accelerator pump, throttle response really goes to chit.

Look around for a small carb with an accelerator pump. Even if it's larger, a 25mm pumper will have better throttle response than a 20mm without.

[212racing]

pappy that is what we are most likely going with in the 06nats,
is a 30mm street bike carb that has an acc. pump. one of our teammates tested one this year. wow, instant response, we are also running the fuel pump with it as well.

[Pappy]

please keep me in the loop on the 30mm. id have to build a new airbox but that can done!