Jitsie mixture screw

[stu109]

I have managed to source a Jitsie mixture screw for my Evo 3004T.  Does anyone have experience of fitting these?

The parts diagram shows a spring and an o-ring on the screw.  Are these likely to come out with the  screw?

My plan is to fully tighten the existing screw to note the current setting and then put in the Jitsie item.  Ideally I would like to do this without removing the carb.

Any suggestions would be welcome.

 

[carlos]

I got an aftermarket one from a Suzuki DRZ 400 (same Mikuni carb). It fell out a few day's later. Back firing, flames (unburnt gas) coming out of the pipe, as long as i kept the revs high i was able to make it back to the truck. The crappy part was having to buy a complete rebuild kit to get the replacement spring and washer. Put the original mixture screw back in and never bothered adjusting it again. It's not like you need to adjust it that often.

[thall1]

The spring and o ring should come out with the old screw..there should also be a small washer between the spring and o ring.. You won't get in to screw in and back out with the carb fitted so the carb will have to come off.. You may find the position of the new screw is not the same as the original as the tip profile may be slightly different but shouldn't be too far away. On our 3 beta 4ts we have extended the original screw with a thumb wheel to enable tuning. The rev3 we've got came with a jitsie screw but it was close to falling out to get it to run correctly so we bought an original screw and modified it

[stu109]

Thanks for the info.

Might I be able to rotate the carb sufficiently to allow the old screw out and the new one in?

 

[thall1]

i would advise not to try that....too many pipe and cables, wires etc. in the way....its a bit of a fiddle getting it out but that's the way I would go..

remove:

mudguard

airbox with the two rear subframe brackets.  You don't need to remove the subframe brackets but it gives you a lot more room and saves poking yourself in the eye whist you work! There are two pipes that fit on spigots and pushed into the bottom of the airbox on rubber grommets. If the back wheel is removed you can allow the airbox to hang with these two pipes still connected.

throttle cable from the throttle and then from the carb 

fuel line

airbox to carb rubber boot

carb to engine rubber boot - you can ease the carb backwards to get this out

on 2014 bikes with the hydroform frame remove the top shock mount bolt and allow the shock to drop down and backwards. On the square box frame bikes up to 2013 you don't need to do this but it would give a bit more room.

with a bit of manoeuvring the carb will come out of the left hand side.

take note of the breather pipe locations and how they run. You may find the ends clamped behind the rectifier mounting bracket. You can loosen the bracket by undoing the two bolts with an 8mm socket. There should be a drain hose on the bottom of the carb, I've removed this from my bikes as I've never yet had to drain the carb to remove water and if I do I'll just let it drain over the top of the engine casing and it means one less pipe to fiddle with - your choice...

With the carb off you can also give it a good clean on both the carb and rear of engine.

on refit:

check the carb to engine boot goes on the correct way round - it is handed!...look for the distance between the end of the rubber and the locating ring on the inside. Some bikes have silicon aftermarket hose fitted in place of the beta rubber hose. Personally I don't like these as with silicon you can overtighten and distort rubber causing an air leak..

also the airbox to carb rubber has slightly different diameters so orientation also needs to be checked.

The airbox to carb jubilee clamps are best located so the airbox side screw is accessed from behind the kick start and the carb side is accessed from the gap in the top of the frame on the left hand side.

just check and double check that the two rubber boots don't slip off when tightened, and the carb is sitting straight without fouling the frame.

I can get ours out and back on within an hour including a bit of a clean..will take a bit longer the first time 

hope this helps..good luck

 

[stu109]

I'd already figured out about taking the tyres off!

Thanks for the comprehensive instructions I will get the carb out when I next have an hour or so to spare.  Will probably do the work next time I re-grease the linkage bearings as the rear wheel and shock are out at the time.

[nigel dabster]

I and others have had problems with jitsie mixture screws (kehien) so be careful if you go down this route (not just jitsie either)

Edited February 25, 2018 by nigel dabster

[maxwell smart]

I purchased jitsie bicycle trials parts last year when building a bicycle and the stuff was so cheap and so far out of tolerance I threw them away , I believe they are selling a lot of cheap  china made parts . I personally will never buy anything jitsie again.

[stu109]

Have managed to fit the Jitsie mixture screw without taking of the carb.

I took off the rear silencer and pulled the various breathers out of the way to get access.

I unscrewed the OEM screw with a small screwdriver bit.  It was very difficult to tell if the bit was engaged with the screw so, rather than screwing it in first to record the setting, I just had a go at unscrewing it. After a bit of fiddling the screw came out with the spring and O ring attached.

Jitsie screw was relatively easy to get in. I set it at 3 turns open and it started fine.

Will play about with the setting next time out to get the best result .

[thall1]

well done!