both my kt100 motors wierd fuel setup?

B

boostedsil40

Member
I have two kt100 motors built from two seperate guys,When i read I see most guys run,1/16 on the high and 2 1/8 on low side but when i try anything close to this both motors bogs,dies and fowls the plugs,the only way to run it is low 3/4 to 1 full turn and low about 3/4,anymore fuel and it drowns in fuel?They got a wb3a walbro the only thing i can think of is both carbs are missing the rubber membrane gasket that goes on the body in favor of teflon gasket and basically did the pegasis setup,..

https://www.pegasusautoracing.com/document.asp?DocID=TECH00038

can i run it like this?
 
also considering the steve ohare easy idle beginner setup maybe this will make it all good?quote from steve

"robin,

The article you posted has some good information but you do not need to modify the butterfly to make your KT100 start easy, idle and run well on the track through the whole range.
I have been helping a new karter with his KT100 sprinter for a couple months and he has made several trips to the track by himself to practice and this is is routine.... he plugs in the starter and hits the button and the motor starts and sits there idling without touching the throttle pedal while he puts on his helmet and driving apparel. The he pushes the kart over to the grid area and gets in and drives his 10 to 20 laps without touching the carb. The kart is equipped with a 2 disk L&T wet clutch that does not get hot even though he does not lift the rear and let the wheels turn while getting dressed.... the idle is low enough to allow the kart to sit still without a problem.
I set the carb up for him as follows:
Arm height is set with the diaphram end fork approximately .020" above flush with the circuit plate. The pop off pressure is set at 18 pounds (stock spring)
Low speed needle is set and left at 1.25 turns and the High speed needle is set at one half turn. The idle adjustment screw is backed off until the butterfly is fully closed and then brought back until it just touchese the lever on the end of the throttle shaft and then is screwed in 1 full turn.
You should see the people at the track stare at my guy when he walks across the pits pushing his KT100 powered kart while it is idling away like a motorcycle... they never see that but only because the majority of the guys running the Walbro carbs set them up wrong and conclude that they won't or can't idle.
Start with those settings and fine tune... you will probably end up a little leaner on the high speed jet since you are not running long stints.
Good luck
Steve O'Hara "
 
If it is missing that gasket that goes with the diaphragm pump it will throw your arm height off. This will make a motor run rich and foul plugs.
 
There are so many things to check, and you need special tools to check them, I would take the carbs, and the engines, to someone that’s doing this on a regular basis and see what they think.
Have you ever checked the squish height in these engines, or the compression pressure? A good squish would be maybe .029 +/- and a good compression would be 160psi with a minimum of 140ps. Both of these things can have a huge effect on the carb settings.
You didn’t say if you’re running a pipe.
If it was me, after checking the carb, and these other things, I would pull the head and see what’s going on in there.
It’s such a simple thing to check when you have had my experience with the KT.
I like the rubber pumper diaphragm.
There are two main diaphragms; the pumper and the metering. The metering is the one with the metal plate that goes on the needle side.

Do you have a gauge for RPM’s?
We always had the carb set at about H1/8 L2-2 ½. At 2 ½ the low is wide open. Just know that these settings can change a little with the up’s and down’s of the air density.
The compression and the squish and the combustion chamber CC’s can all have an effect on the carb settings. Go slow, check them all out.
The pipe and the header length can also affect things. Tell us what you have for both.

Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.
 
Are you trying to idle the engine at 4000 rpm? The carb will flood the engine at idle if you have the needles set for racing.

Different carbs are different but I've seen none that wanted to be 1 turn on the low unless you're running 3/4 on the high and that's for extended high speed runnings like they do in Jamaica mon. 1-1/2 to 2 is the usual. I would take it apart and make sure the gaskets are in the right places. Like the high speed flapper needs to be against the cover plate.

That Pegasus article is very basic and doesn't have enough info. Your pop off should be about 10psi and arm height should be .050" below the metering gasket.

Sundog
 
ok took it apart and snapped some pics to help out,heres it cracked open fulcrom gasket

Picture302_zps9d69c10b.jpg


so theres only one gasket here is that normal?unless its one stuck to another?

Picture304_zps19f303e1.jpg



NOTE:I can only post 3 pics per post so bare with me thanks.
 
Last edited:
its got a flap and dogbone shape.thats it for gaskets on that side..


Picture306_zps96ff08fb.jpg


now for the walbro side.theres the teflon gasket instead of rubber gasket which i discarded the rubber one in place of this one,maybe a bad idea?

Picture308_zpsfc63ff38.jpg


Picture309_zpsbbfc92f0.jpg
 
theres two gaskets on walbro side,the pumper and the gasket that seals as shown here.
Picture310_zps18fac8f6.jpg


i measured the fulcrum hieght as suggested but I used digital calipers instead of feeler guages,mine have 3 ways to measure and one method seemed to work great as when you open the calipers a rod pretrudes from the bottom which in turn you can use the rod to measure the fulcrum height,unfortunate the pics came out crap but please let me know if this was the correct proccedure,I measured not from the deep hole to the top of the fulcrum arm but the flat spot on all sides of the arm to the tip,It measured 1.40mm or 0.055" inch so the 1.40mm/0.055"inch again was from the tip of fulcrum arm to base on all sides NOT IN THE HOLE OR WHERE THE SEALING GASKET RESTS BUT THE BASE I GUESS IS WHAT ITS CALLED I hope that makes sense hard to explain.

Picture313_zpsbe6ea6bc.jpg


notice the insides were taken out to get measurment is that right?

Picture323_zps2468d31d.jpg
 
Picture315_zps3e067869.jpg


let me know how i should have set this up.Thanks guys.I dont have a way to check the popoff for the time being i will get one soon.thanks guys let me know some knowledge.
 
Usually you measure from the metering gasket down to the fulcrum arm. The diaphragm with the aluminum disk peals off the gasket and the gasket should be about .032" thick. Put just the gasket on and measure from the top of that down to the fulcrum arm should be about .050". All the other gaskets look like they're in the right places.

Still didn't answer my question in post #5. The carb looks ok maybe it's the way you're trying to operate it.

Sundog
 
You've went from the top of the arm down to the top of the plate, I'm not sure how that will relate to the more common way of checking the arm height, which is the distance from the bare body where the diaphram gasket sets, down to the top of the arm. I like .045, which is what Walbro recommends, that's if using a stock or modified WB3A demand diaphragm, if using an uncapt. diaphragm out of a WB20 then .055, because it's stub is longer by .010. Apparently there is some disagreement as to how to check it, the guys that check it with a gasket on are running some very high arm heights, more than what Walbro recommends but obviously it still works. Jon
 
boost...

I see you found my post from some time ago. If you set the carb up that way it will be very user friendly and still run fast lap times. Just a couple remarks to clarify things.
I make reference to the circuit plate when talking about the arm height. The "circuit plate" is the little steel plate you removed by taking out the two screws. Either replace the membrane with the flapper or massage it to get the flap to lay flat against the underside of the steel plate and then re-install it. With the plate installed, adjust the arm height as described in my previous post. You can use your caliper in the way you show in the photos or just eyeball the arm height to a level so the free end is just a little above the circuit plate. Don't worry about the spring rate at this stage, use the spring you have and just measure the length of the spring. If it measures less than .4" stretch it just a little to get it to that length or a bit more and then re-install. You can use either of the pump diaphragms, I like the nylon version best but both work the same. Clean the small filter screen and then reinstall the pump side with the pump diaphragm against the body of the carb then the gasket and then the cover.
On the metering diaphragm side make sure the little mushroom on the center rivet of the diaphragm is hooked into the fork of the arm when installing. In your pictures the metering diaphragm and the gasket are stuck together so it may appear that they are one piece to you. If you install new stuff make sure the gasket goes on first, then the diaphragm. Don't worry about the barbell shape vs non barbell gasket under the circuit plate, it makes no difference.
When the carb is all cleaned up and re-assembled the last step is to pressure test the carb to make sure you have it together right. To pressure test you need a pop-off gauge that you connect to the fuel inlet. Pump up to 5 psi and not more... it should hold steady. If it leaks down you have a problem and the carb will not work as it should. The most common reason for a lack of seal is the fulcrum arm is set too high but if you follow my instructions that is covered. The next most common cause of a leak is the fork and mushroom did not get hooked together and the arm is being pushed down by the diaphragm. If those two items are done right then the leak may be due to warped plates, a crack or other defect in the carb body. If the carb leaks and you can't see where hold it under water while pumping the air in to see where it comes out.
Remember to set the idle control screw and jets as described above. Also remember to make sure you safety wire the fuel line and both ends of the pulse line when you reinstall the carb.
Good luck!
Steve O'Hara
 
I have learned that when checking pop off the needle/seat need to be wet . I use wd40 ( less flameable) other wise pressure will not hold correctly. In other words,you get some pretty messed up readings.
 
Steve O'Hara said:
boost...

I see you found my post from some time ago. If you set the carb up that way it will be very user friendly and still run fast lap times. Just a couple remarks to clarify things.
I make reference to the circuit plate when talking about the arm height. The "circuit plate" is the little steel plate you removed by taking out the two screws. Either replace the membrane with the flapper or massage it to get the flap to lay flat against the underside of the steel plate and then re-install it. With the plate installed, adjust the arm height as described in my previous post. You can use your caliper in the way you show in the photos or just eyeball the arm height to a level so the free end is just a little above the circuit plate. Don't worry about the spring rate at this stage, use the spring you have and just measure the length of the spring. If it measures less than .4" stretch it just a little to get it to that length or a bit more and then re-install. You can use either of the pump diaphragms, I like the nylon version best but both work the same. Clean the small filter screen and then reinstall the pump side with the pump diaphragm against the body of the carb then the gasket and then the cover.
On the metering diaphragm side make sure the little mushroom on the center rivet of the diaphragm is hooked into the fork of the arm when installing. In your pictures the metering diaphragm and the gasket are stuck together so it may appear that they are one piece to you. If you install new stuff make sure the gasket goes on first, then the diaphragm. Don't worry about the barbell shape vs non barbell gasket under the circuit plate, it makes no difference.
When the carb is all cleaned up and re-assembled the last step is to pressure test the carb to make sure you have it together right. To pressure test you need a pop-off gauge that you connect to the fuel inlet. Pump up to 5 psi and not more... it should hold steady. If it leaks down you have a problem and the carb will not work as it should. The most common reason for a lack of seal is the fulcrum arm is set too high but if you follow my instructions that is covered. The next most common cause of a leak is the fork and mushroom did not get hooked together and the arm is being pushed down by the diaphragm. If those two items are done right then the leak may be due to warped plates, a crack or other defect in the carb body. If the carb leaks and you can't see where hold it under water while pumping the air in to see where it comes out.
Remember to set the idle control screw and jets as described above. Also remember to make sure you safety wire the fuel line and both ends of the pulse line when you reinstall the carb.
Good luck!
Steve O'Hara
Click to expand...
Great thanks i'm very glad your still on this site,Do you have an email I can get ahold of you as I would like to pay you if you would be willing to setup both my carbs for the user friendly idling kt100 setup it would be well worth the piece of mind knowing it was built by you steve.

I'm very new to karting and only driven both karts an hour or so as I'm worried I will damage the motors with its current setup or my lack of knowledge with kt100,At least with it setup right that would be a great start in karting. please let me know if your interested you can email me we can discuss a price i would much rather have this done by you since its your setup,Id be most grateful and pay you what you think its worth to do.I will PM you my email thank you.
 
sundog said:
Usually you measure from the metering gasket down to the fulcrum arm. The diaphragm with the aluminum disk peals off the gasket and the gasket should be about .032" thick. Put just the gasket on and measure from the top of that down to the fulcrum arm should be about .050".

Sundog
Click to expand...
thank you very much,ok so since i measured without the gasket and my measurment was 0.55"of a inch with no gasket,The gasket is 0.32" you say that would mean my measurment would be 0.23" if it was from gasket to fulcrum arm fork.
 
boostedsil40 said:
I set the carb up for him as follows:
Arm height is set with the diaphram end fork approximately .020" above flush with the circuit plate. The pop off pressure is set at 18 pounds (stock spring)
Low speed needle is set and left at 1.25 turns and the High speed needle is set at one half turn. The idle adjustment screw is backed off until the butterfly is fully closed and then brought back until it just touches the lever on the end of the throttle shaft and then is screwed in 1 full turn.
You should see the people at the track stare at my guy when he walks across the pits pushing his KT100 powered kart while it is idling away like a motorcycle... they never see that but only because the majority of the guys running the Walbro carbs set them up wrong and conclude that they won't or can't idle.
Start with those settings and fine tune... you will probably end up a little leaner on the high speed jet since you are not running long stints.
Good luck
Steve O'Hara "
Click to expand...

How does having the high needle open 1/2 turn not flood the engine at top end? This must only work for tracks with short straights and motors set up for grunt work.
 
Because the low side is only at 1 1/4, if you ran more low the high would have to be leaner. On a Walbro the low + the high is what you get on top end, unlike a Tilly which is more just the high circuit at top end. Jon
 
In addition to what John explained the higher popoff setting and lower arm height both force a larger pressure delta to move fuel so the HS jet must be opened more to provide a larger exposure to the signal. I have done tests with the popoff as high as 30 psi and the HS open as much as one full turn with reasonable results
One caveat I should provide to this conversation... all of my testing with the KT100 engines has been done using real expansion chambers for the exhaust system. When the proper exhaust system is replaced with the crappy little can mufflers it can make big changes to the way the carb behaves. From some recent limited experience with can type exhaust systems I've found that the carb behavior is unpredictable but it can still be made to function with a consistent and steady idle and easy starting while maintaining jet settings that work well on the track without having to change the setting during the session.
Steve O'Hara
 
You must log in or register to reply here.
Back
Top