Hey friends,
So I recently had my mechanic rebuild my carbs and jetted them to fit a 4into1 exhaust (MotoGP Werks). The bike ran great for a few days, started right up...until yesterday. Tried to start it and it tried start...but wouldn't fire. Finally got it started...but took a ton of effort. Once I got it running, it would not idle. I had to keep on the throttle to keep it running...if I let off...it would die. I adjusted the idle screw but nothing would work. Any thoughts about why this is happening?
One thought I had, was when I had the bike running well, I adjusted the idle screw to idle normally on a warmed up engine. Could this adjustment cause it not to idle at all?
Thanks!
Chris
I'd suspect the answer to this one is related to the "rejetting" your mechanic did? There is NO rejetting required for ANY pipe change on these bikes save one: the old Dunstal 4-2 header set, which is longer than the bike. That's what it takes to make the pipes effect a change in jetting, and no 4-1 on this planet will require "rejetting" be done with these bikes. That's not to say it isn't done: I maintain still that it isn't required and only leads to unintended consequences, usually in the form of gas-fouled sparkplugs from over-rich jetting.
Pull out a couple of sparkplugs and see if they are black. That would be a fouled plug and would act much like what you are describing here.
The F2/3 bikes had lean-burn PD42 series carbs with accelerator pumps, which were added because of the lean-burn situation, to improve take-off from a stop. The mainjets were normally #105 size, with the idle jets being #38 on the PD42a and #35 on the PD42b carbs. The mainjets were Keihin new: if Keyster jets are used then the #112 should be used, as they run about 7% leaner by their numbers than the Keihin versions. Many "rebuild kits" supply #110 or #115 Keyster jets, which supply the same fuel mix as the #102.5 or #107 Kehin jets, respectively. Hence the confusion over jetting sizes and the endless posts about "rejetting for [this or that]".
