KEIHIN carb settings

[StP]

Hi there, can anyone tell me what these numbers mean? I know they’re probably jet sizes but how do you interpret them? Thanks 

 

125 Min 50 - Max 115

250-270 Min 48 - Max 110

[peterb]

For a 125cc, pilot jet size 50, main jet size 115

For a 250/270cc, pilot jet size 48, main jet size 110

Seems a bit odd though, would have thought the larger motor to have the larger jet sizes. I don't know Beta specific Keihin set ups, but for a 250/300 GG, pilots around 40, main jet around 125-130 needle GJH. The standard JJH needle for GG tends to run lean for me. Bye, Peter B.

[StP]

Thanks for your answer. Beta say to adjust needle height to notch 5 and a max 1 turn out on air screw. This would usually make it run too rich? So that’s why the jetting is leaner? Thanks 

[pindie]

Smaller motors need bigger jets as the “pull” for fuel from the cylinder isn’t as much as it is on a bigger motor. Basically a 125 piston going down does not create as much suction as a 300 piston going down the cylinder. 

[nigel dabster]

On 3/6/2020 at 12:59 AM, peterb said:

For a 125cc, pilot jet size 50, main jet size 115

For a 250/270cc, pilot jet size 48, main jet size 110

Seems a bit odd though, would have thought the larger motor to have the larger jet sizes. I don't know Beta specific Keihin set ups, but for a 250/300 GG, pilots around 40, main jet around 125-130 needle GJH. The standard JJH needle for GG tends to run lean for me. Bye, Peter B.

Slide?

[nigel dabster]

On 3/6/2020 at 7:20 AM, StP said:

Thanks for your answer. Beta say to adjust needle height to notch 5 and a max 1 turn out on air screw. This would usually make it run too rich? So that’s why the jetting is leaner? Thanks 

tickover and needle positions need to be se to suit where you are fuel youre using etc. Competent person needs to do this.

[robertthomas]

Hello, I have a beta rev3 125 cc Keihin 28 pwk carburetor. I have an idle problem. I set the idle to a normal speed and very quickly the speed drops and the bike stalls. Sometimes it's the opposite, the engine accelerates for no reason which forces me to lower the idle. . Do you have any idea?

[RonH]

I had a similar problem and the answer for me was the throttle cable and not the carburetor. The rubber boot on the cable that fits over the end of the throttle was pulled away slightly causing stretch sometimes and slack sometimes. It was hard to see because I was concentrating on the carb. If this is the problem put a zip tie over the throttle end of the rubber boot and sinch it down tightly against the throttle.
 

I hope this helps. Good luck!

[lineaway]

Sounds like the Death Barble. The jet tower leaks. You need to try a new jet tower o ring. You need security torx to get to it.

Google below its on adv rider.

Keihin Death Barble

Edited August 13 by lineaway

[robertthomas]

hello friends, i think i solved my problem. i looked at the death barble joint and cleaned it. i unblocked the small holes. i also changed the idle jet. i went from 50 to 55. the bike holds the idle and i was able to lower it without the engine stalling.tomorrow I will continue the tests. Thank you already for the precious help you have given me. I will finally be able to have fun without fear of stalling

[robertthomas]

Hello everyone, I replaced the diffuser gasket as recommended by adrider. Unfortunately this did not improve the situation. I often need to adjust the idle speed either increase it because the bike stalls or reduce it because the engine runs too fast. Does anyone have any ideas?

[lineaway]

 Well you thought it did! Too, bad as with a bike that old it could be time to replace the main bearings and seals. A quick check would be to remove the mag cover and tug on the flywheel to see if you have any up and down play in it.

[konrad]

I agree with lineway.  

Have you examined where the idle screw contacts the slide?  Wear on the slide will cause difficulty setting the idle speed.  But brass slides are less susceptible to that trouble than aluminum slides.

[robertthomas]

19 hours ago, lineaway said:

 Well you thought it did! Too, bad as with a bike that old it could be time to replace the main bearings and seals. A quick check would be to remove the mag cover and tug on the flywheel to see if you have any up and down play in it.

   .Hello Lineway, thank you for your valuable advice. I removed the flywheel cover and looked at the play, there is no play and I prefer it because changing the bearings and gaskets of the engine is not very simple. I removed the carburetor again and cleaned the throttle cable. I put the 55 jet back and set the needle to the second notch. I will see if it works.

[lemur]

Carburetor can't work great if the bottom end seals are not great.  I'd be inspecting the bottom end seals for signs of leakage on any 2-stroke engine that has constantly changing carburetor type issues.

... when it runs does it fire with a nice clear compression pop-pop-pop or does it have a ring-ying-ying engine sound ?

Edited September 2 by lemur