carb question

[Glenn Keaton]

went from a 24 mm oko, to a21mm keihin, the quad is super fast at mid and even fast at topend, but slower than ever off the line, i had to adjust the free play out of the linkage , when i changed carbs, it came with a 100 main jet, i went up to 115 and it was super sluggish all the way through went back to the 100 main and i had to turnthe idle all the way in just to get it too idle, the air screw is out about 1.5 turns(it seems the best there) the air tempurature here today was about 55 degress, it is a 07 air cooled 90, do they have main jets smaller than 100?, and do you think this would help, thanks

[Nichols Atvs]

Jets go lower you need to look at your plug if its black go down jet size if its white you go up jet size your looking for a tan to brown color on the plug. you may also need to move the position of the needle clip also. up on the clip leans down richens if its new it should be in the middle. What are you running for a air filter stock or aftermarket uni .

[Glenn Keaton]

uni air filter

[tom450r]

i just went through the same thing last week the low end seems to be the idle jet, topend is the main jet, everything in the middle is in your needle, & take my word for it the smallest things can make the biggest difference, move that clip 1 slot & it changes alot. good luck
Originally posted by Glenn Keaton
went from a 24 mm oko, to a21mm keihin, the quad is super fast at mid and even fast at topend, but slower than ever off the line, i had to adjust the free play out of the linkage , when i changed carbs, it came with a 100 main jet, i went up to 115 and it was super sluggish all the way through went back to the 100 main and i had to turnthe idle all the way in just to get it too idle, the air screw is out about 1.5 turns(it seems the best there) the air tempurature here today was about 55 degress, it is a 07 air cooled 90, do they have main jets smaller than 100?, and do you think this would help, thanks

[hotquads1]

Glenn the fact that you had to turn the idle screw all the way in reflects that the pilot curcuit is out of tune this would be corrected with the pilot jet and air screw. If this oko 21 has not been modded then you should not need to be smaller than a 100 on main at 55 degrees, if this is a modded 21 oko the main should be close to a 120 at 55 degrees on a 90cc. the questionable area is the idle or primary curcuit which should be improved by air screw adjustment , out more on the air screw will lean the low end , if 2,5 turns out is snappier than 1.5 turns out, then drop the pilot jet one size and retune the airscrew. the pilot stock was 42 normally and a 40 is used for best performance, but without the mods these carbs can be tough to tune. If you want to call me on monday at the office I will talk you thru the tuning process, 334-705-0084.

marc

[Glenn Keaton]

i put the oko back on and it was awesome, and i could not figure out why, i dropped the main from 122 to 115 , and it got even better, as you know we run alot of harescrambles and with the air filter coming straight off the carb, we could not make 1 lap if it is wet, the filter gets drenched, so somenoe came up with an idea of putting a 90 elbow off the carb and then run a straight out between the fender and the riders left leg and putting the air filter there just above the kicker, and when i was working on it today i was putting the filter straight off the carb, and it was amazing the power i had, ithought the 115 main was the fix, and then i put the elbow back on with the straight , and the filter , started it up and the low end problem was back, it would not take off, so i took the assembly back off went with the filter straight off the carb and BAM the power is back, so now what do i do to fix this problem, i cut a 1 liter bottle plced around the filter with an air gap all the way around made a brkt bolted it to the fender, drilled alot of 1/4 inch holes in the bottle and looks really uncool, but it still runs strong, i use an outerwear on the filter now, i guess it will help some , let me know if you got a better idea, thanks

[bulldogfallon]

Glenn you will need to tune the pilt screw on your Keihin carb..


Here is a link to a great article that makes carb tuning easy


Give me a shout tomorrow and we will get you the jets you need to make the right choice between that OKO and Keihin carb

Adding the snorkel may also require a jet change if you plan on using it.

Sorry I missed your calls this weekend...we were racing and didn't have phone reception

[sldhd700]

Have you got a power jet in that Carb? I m running a 21 mm with power jet and some clutching on Shaydens bike and it has turned this thing into a little rocket of the line and at lowend. Installing the power jet helped to keep the top end also. I have seen the bottle trick done on Quad Junkies sons bike and was going to get something like that set up for Shayden for next year. We run more Quad Cross than anything so I don t know how if that would affect air flow. I would like to have something like that in my tool box just in case we have a real muddy track.

[Glenn Keaton]

mud is not the real problem we deal with, it is the water some harescrambles we cross creeks, sometimes 6-8 inches deep, and it is ok if you can get your rider to yo up and putt through the water, but during the heat of competition it is hard to slow up and let another rider rip past, even if you know that you can catch them and pass them back , in our series there is several drrs and we all deal with the same issues, sometimes we have to pit and change air filters and sometimes even the plug, i guess most of this would go away with a watercooled setup.

[humboldt hills]

Glenn,
We had the same issue with the kiehn carb.
I spent a week on jetting it. Changed pilots, mains, needles, you name it. Even though we got it running great, it still didn't compare to how the oko works on the drr. I know lots of people on here hate the oko's, but we have them figured out. They need a little more tlc, but thats par for all these minis.

I am going to have to try the uni without the 90 elbow on it now that you say it works better.

[bulldogfallon]

The OKOs don't run the same each time out and will eventually lose their performance....

Keihin is a good choice for the majority for parents that don't want to tune a carb everytime they race

[jetmedic]

I use an OKO 28mm with power jet. I removed from box, installed, and have never touched it since. Maybe I am just lucky?

[humboldt hills]

Originally posted by bulldogfallon
The OKOs don't run the same each time out and will eventually lose their performance....

Keihin is a good choice for the majority for parents that don't want to tune a carb everytime they race

Yeah, I can see your point.

[QuadJunkies]

So tell me a little bit about what the power jets are?
We run the Keihen,but should we see more performance out of a power jet?
If this is an OKO ,Ill pass.:p

[Hetrick Racing]

This carb is called a power jet because it has another jet on the intake side of the venturi with a small hose that goes into the float bowl.
Yes it is OKO, lectron uses it as well(lectron with this are also hard to tune)
When ever you change any power delivery to your clutch you have to change the clutch to match.
In other words the carb you had on the machine had a specific power curve,when you put the Keihin on it has another so after you get it tuned adust the clutch for the problem your having.
Also here is a general rule of carb tuning
Idle
air screw at 1.5 if you have to have your idle screw(not idle air) all the way in you need to lean out the pilot jet until you have adjustment.
general mid- if in fact you did lean the pilot now you probably have a slight sag in the 1/4 throttle range so adjust the needle clip until that goes away(moving the clip down raise the needle adding more fuel)
Top end- start going up( never down) until you have a noticable loss of power or a surge then lean it untill it runs the best and then always check your plug.

The big thing is do all of this then tune your clutch for the best performance .

Now to the air box or change of air delivery
When you are running a pod filter the engine has a small amout of what you would call high speed air( the air inside the filter) when you move the filter away from the carb now you have increased the amount of high speed air to your carb.
What you have to figure out is
1 how much did you increase the high speed
2 the volume of the delivery at WOT
3 how to adjust it from there
An easy way to do it is like this
if you have a 2 inch filter 4 inches long
you want to try to keep it in the same standard,its all math
so add 4 more inches of the exact dimension tube and you have basicly doubled your high speed delivery, if you add 4 more inches you have tripled it .
This is where it gets goofy
now in a general rule if you try to add any more tan 2.5 to 3 times the amont of air ,you have to help it speed up so you need to create a choke point or a venturi similar to your carb to do this it is easiest on the little motors to increase the size of the velocity tube, in other words put a bigger filter with a cone or wedge approx 1/3 the length of the tubes overall into the 2 inch tube your running.
This is all general and it is not at all as easy on four strokes
but i hope you get the point im trying to make

[QuadJunkies]

Great info.
Thanks for taking the time to explain it . Troy probably knows about this carb, but I didnt, now I do . :)

What does the Carb run in price? And is it preferred over the Keihen? We have been fine with Keihen,the OKO that we had prior(we done the carb mod as well) def. did not perform as well.
We can make some changes if its reccomended.
As soon as Brandons frame returns from Pappy, we need to put it together and get some seat time in before Jan. sneaks up on us. :p