NEED HELP tuning my KEIHIN carb!!!

[Scspeed]

i have a 240 blaster with an lrd race exhaust and aftermarket reeds + reed spacer.. I am trying to tune my keihin carb, i have the right jets, i belive its a 140 main and a 90 piolet jet.

I know the jets are perfect because i have done a couple plug chops and the plug looks perfect.. and it is a light cocoa brown. SO THE JETS ARENT THE ISSUE>

I need to know how to tune the air/fuel screw on the side, and the idle knob as well, i have tuned stock carbs, they are really easy for me but this one seems soo hard to tune between the air/fuel screw and the idle knob. What am i doing wrong!? Is there like so many turns out that i should start at? Where should i keep the idle at while tuning?

I can get it to idle ok, but then when i hit full throttle when there is a larger load on the engine it breaks up and pops, its driving me nuts! it even does it at half throttle sometimes if i hit it real fast under heavier load.

Someone teach me!! haha

 

[brandoz28]

a 90 pilot jet?? that seems massive...most guys land between 45-55.

have you checked the float level, and what kind af Keihin carb is it? 34mm pj?

 

[Scspeed]

the guy i got it from said it was a 40mm? and suposadly he used to ice race it.. so maby thats why he had such a large pilot jet??

It could of been a 60 maby.. but still even if it was too big, the pilot jet has nothing to do with half and full throttle correct?

 

[brandoz28]

correct, the air screw has little to do with that as well, that's needle territory.


if its a 40 mm, you're way over carbed

 

[Scspeed]

way over carbed?? this is the carb that was on this quad while the guy raced it...it worked fine... like a said he used to go ice racing with it so maby is it the jetting? i just dont understand why the plug looks so damn perfect..

The motor he said was a stroked 240 motor..

 

[OldSkoolBlaster]

Are You sure it is not a Keihin 34mm PJ or a 35mm PWK?From my experience your main jet size is lean and the pilot is rich.I just put a 35mm PWK on my Blaster and I started with a 162 main and a 55 pilot and worked down from there.I am currently running a 158 main and a 50 pilot with my mods.Just my .02.

 

[Scspeed]

i guess ill do what you said ^^ and yes it very well could be a 35mm wasnt 100 persent on that. but i just dont understand why my plug looks so good.. perfect light cocoa brown. how could that be??

 

[super noober]

i guess ill do what you said ^^ and yes it very well could be a 35mm wasnt 100 persent on that. but i just dont understand why my plug looks so good.. perfect light cocoa brown. how could that be??

mabey you have a big ole airleak thats messng with ya, so fat jetting is covering it up

 

[Scspeed]

where would it have to be?? before and after the carb right? or the reed gaskets?

Iv checked everything and all the gaskets look tight and the clamps and on good as well as the gromits... maby ill take the reeds out again and double check.

Like i said. i realllyyy wanna rejet it but i just CANT see rejetting it when the plug looks so damn good. Im just so confused.

 

[super noober]

could be anywheres.. base gasket, intake boot or gaskets. im not saying you do have a leak just tossing it out there as a possibility, you can build your own leakdown tester for liek 20 bucks, there is a diy here someplace or holeshotman sell em for $30 i belive. definately a good deal I:I

 

[royalt67]

A 90 pilot huh? Wow. It sounds like you are fat down low and then you lean out (yeah kinda repeating everyone else) but where is your needle in all this? My point is, with all that fuel down low, did the guy drop the needle in deep to compensate off-idle? If the needle clip is on the 2nd or 1st slot from the top, change it to the third if you are going to rejet.

Reality is that all those circuits are pulling fuel mid to high. The big pilot is helping out the small main for the first half, then when serious airflow kicks in, it just isn't enough. Think of it this way, where you are riding, low to mid, is very happy and giving you a nice plug color. Obviously it's crapping out up higher so you let off. Once again you are in the happy range, you ride and check your plug and you still have good color. It's LYING to you.

Try my fav jetting site. Good info here. Most importantly, do it in order.
http://www.angelfire.com/pa5/cannondale/carb.html

 

[Scspeed]

Well i farther checked into things, i removed the gaskets and the reeds and i found that one of the reeds were split down the middle and the gaskets looked pretty spanked.. I thought YESSS found the problem. Cleaned everything replaced the reeds, replaced the gaskets, put everything back together, runs a tinnyyy bit better but still breaks up pretty bad in full throttle under a heavyer load. Mainly 3rd and 4th gear.

This is driving me crazzyy!! again i put another plug in, checked it, looks f*cking mintt. Couldnt be better. agh :/

I think tomorrow i am going to adjust the needle in the carb. Think im going to try and raise it one notch to richen it up a bit more during full throttle.. What do you guys think?? Like i said i really don't think its the jets seeing that they are clean and the plug looks mint.

Also the top end was just rebuilt not too long ago, the head and jug gaskets look good and the bolts/nuts holding them on are tight. Just seems like i cant find that "sweet spot" with this PWK carb!!

 

[Scspeed]

hey royalt67, good point. I did think of this but thought maby i was over thinking it lol. I thought about how when i ride it i just ride it in the sweet spot low/mid range where it runs the best. It craps out at full throttle so the plugs not really seeing it... i see exactly what you mean.

So where should i start? Moving the needle? checking the needle? or changing my main and or pilot jet?

Im thinking raise the needle to start. if that doesnt work, bring it back and up in the main jet? seems like its not getting enough fuel in full throttle if its popping and breaking up. Besides, if it was doing all that popping and breaking up all because of too much fuel id really think that id see that on the plug. at least a little.

 

[royalt67]

Exactly, too much fuel up top would have made itself known and it would bog, add more throttle and it just doesn't go any faster. I'm sure a bigger main and smaller pilot is in your future. Raising the needle without other changes might actually make it run worse, because it will fatten up the low-mid more than anything. Frankly I would determine exactly which carb it is and then start out with standard jetting, for example, a PWK35 (non-airstriker) has 68, 160, needle on 3rd slot (most likely). (not sure why the pilot is so huge, thats bigger than the PWK39). Take ten minutes (or more) and read that link I added earlier, it spells it out better than I can. The best thing you can do is write down exactly where you start and what you do, that way you can always go back.


Here is a link to CPW. It has links to standard jetting for these carbs.
Keihin Offroad Carburetors

 

[Scspeed]

hey man, yah i did read your link last night.. i saw taht the pilot jet is more like a 40mm. idk if it was the stock one or maby it was the 35mm and then he went bigger..

I whipped it around a bit this morn and held it wide open even tho it was bogging real bad and popping, i did it like 3 good long times then shut it down. i checked the plug agian and the plug was no longer really brown after i checked it, it was more greyish. Im now deffinetly thinking it is leaning out at WOT.

What im gunna try is ordering a jet kit for the pwk.. ill throw a larger main in it and see how that goes and go from there. I really think its just too small of a main jet which is causing it to lean out at WOT.

Where can i get some jets from? should i just bring the main jet out of the carb and to the yamaha dealer near me? they told me that they could prolly match it up to somthing they have or even order it. i told them it was a keihin carb.

 

[brandoz28]

jetsrus.com has good prices

 

[royalt67]

and so does rockymountainatvmc.com as long as you want to order several. I bought all of mine at 5 bucks a pop at the local Yamaha dealer. It's the way to go if you only want to buy 1 or 2 at a time.

No surprise on the main jet, but it sounds like you have proven it. Personally I would try a smaller pilot too, but the question is, "What is your throttle response like?" If it is boggy at all on initial throttle (under load) then the pilot is too big.

 

[Scspeed]

Nope not boggy at all, the throttle snaps as fast as you push your thumb.. def thinking im in need of just a larger main. When i get it in i will let you guys know what it did.

Thanks again for all your help.

 

[royalt67]

Cool, then. It will be interesting to know if that changes with a larger main.