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main jet effect on idling


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Main jet starts to affect the engine at about 7/8's throttle and mainly controls WOT. If the main jet was missing, the bike would still idle fine and run fine up to about 7/8's throttle. If it were completely clogged, it could affect idle as there is some bleed through at the needle (which the main jet feeds). If the bike were tuned taking this bleed through into account, and the jet was then clogged, the bike would not idle.

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so here is my question, on my 2003 drz e, i open up the airbox and installed a full muzzy and the bike was idling super lean, but after i put in a larger main jet (from 142 to 165) and changed the needle (blue needle jd jet kit) it is idling much richer (too rich in fact). According to the graph neither of those two changes should have effected it. (I also put in an aftermarket fuel screw) anyone knows the reason?

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so here is my question, on my 2003 drz e, i open up the airbox and installed a full muzzy and the bike was idling super lean, but after i put in a larger main jet (from 142 to 165) and changed the needle (blue needle jd jet kit) it is idling much richer (too rich in fact). According to the graph neither of those two changes should have effected it. (I also put in an aftermarket fuel screw) anyone knows the reason?

im assuming a full muzzy is a new air filter hence idling lean / at that point you should only have adjusted your fuel screw ......

which brings me back to another thread we were both involved in with the same problem , cant rem the thread heading but the problem was i think a hanging idle ? or something to do with the fuel screw .

back to the fuel screw

bear in mind im trying to dial in a second hand fcr mx 39mm to a 441 big bore with ported head with original exhaust system on an 1991 dr350s so kinda having to learn this stuff as well .....

I had one of those anodised aluminium type bought of the flea bay for a few £ that could be adjusted ( sounds good in theory) truth is it was an absolute useless terrible piece of aluminium

having gone through 3 new pilot jet changes 3 new orings a new spring and much frustration I couldnt get a decent idle or a consistant result .. Eddie aka burned advised me to change back to the original fuel screw which helped but i couldnt adjust it therfore I

Fitted an R&D Flexjet this morning and dialed in my carb within 10 mins 👍 WELL WORTH the cost , if you choose this route rem the flexjet is not a fix and forget it needs to be lubed reg to prevent binding I lubed mine well with wd40 b4 fittment..

as for your Main #142 - #165 is a massive jump , so yes there will be some leakage into the venturi, but you have changed the wrong items ......

return your needle to its previous spec and also return your main to previous spec and concentraite on your idle firstly🤣 , let us know how u get on 🙂

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I have got the zip-ty fuel screw which i think is aluminum (http://www.ziptyracing.com/products/product_detail.aspx?id=MTEwMg==), it seems to have the identical shape as the original fuel screw except for an extended arm so i dont see how it would change anything, that being said I'll try to change it back and see if that was the problem.

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my screw was very similar to the one you are using Ambog , with the naked eye they appear exact same as the original brass one at the fuel end, i now know for a fact that the aluminium one didnt seat properly as the bike would still idle even when the screw was screwed full in regardless of which size pilot jet i fitted, so first thing i tried with the flexjet was to screw it full in and sure enough the bike cut out almost instantly

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So I just replaced the fuel screw with the original and sure enough it idles great and i can actually adjust the screw to control the idle. from a visual inspection the zip-ty screw seemed to be 2 millimeters shorter (from the tip to where the threads start) I guess thats why the difference. thanks for your help guys!👍

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