Yz 426f Carb Problem

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#1
I HAVE A 01 426F AND HAVE RIDDEN IT 5 TIMES AND GONE THROUGH 3 PLUGS TRAIL TRACK AND DUNES. I LIVE IN MICHIGAN AND HAVE NO IDEA WHAT IT COULD BE. I HAVE A TWIN AIR FILTER AND THOUGHT MAYBE THAT WOULD HELP NO DIFFERENCE. I ALSO TURNED PILOT FUEL SCREW NO CHANGE. THIS THING IS BRAND NEW AND NO ONE CAN FIGURE IT OUT. ANY HELP WOULD BE APPRECIATED

THANKS
 
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#2
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Put up a post and give all your jetting, main and PJ, needel clip positions. Explain and conditions it has running and describe the color of the fouled plugs too. Mention if you have an aftrmarket bike and any starting problems. I have noticed these carbs are VERY touchy, but rock solid once dialed in correctly. Dont worry, youll get it straight :)
 
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#3
Why do you think it is the carb? Have you tested any of the plugs for spark? Or did you just replace them, then it starts and runs fine, and therefore you assume it was fouled? Just curious.
 

firecracker22

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#5
Some good friends of mine who are mechanics (Hi, Pete, Duane, Chris! Where are you guys? :confused: ) tell me that two mistakes a lot of people make with 4-strokes are:

Octane. High octane gas, like over 100, will make it run crappy, like the choke's on all the time.

Oil. Since the oil is meant to be checked hot, and a lot of people don't know this, checking the oil when it's cold will make it look like it's low, so when you put more in, it's overfilled and the extra will blow by the rings and foul plugs.

That's the extent of my four-stroke knowledge. Other than--how much oil did you put on the air filter? I over-oiled my first one and went through a couple plugs.

PS--take off the caps lock key. It's hard to read that way. Thanks, and welcome.
 
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#6
Originally posted by firecracker22
Some good friends of mine who are mechanics (Hi, Pete, Duane, Chris! Where are you guys? :confused: ) tell me that two mistakes a lot of people make with 4-strokes are:

Octane. High octane gas, like over 100, will make it run crappy, like the choke's on all the time.
.
I have nothing but respect for the those guys FC , but that statement isn't accurate when used in that general a fashion. While you can find SOME high octane fuels that will make the 426 run richer, it's NOT a fundamental characteristic of high octane fuels, or this engine. I've yet to find a conventional race fuel that will foul a plug in the YZF, and given the lean settings that come standard on these bikes, a fuel that runs a bit richer tends to be an advantage in many cases.

It's not uncommon for people who are new to riding a bike with an accelerator pump carb (like the YZF) to foul a few plugs in the begining because of excessive throttle movement when starting.
 

firecracker22

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#7
Really? I was told that the higher octane makes the engine run cooler, which I already knew, and that running too much cooler makes it stumble and act as if the choke is on. It made sense to me . . . but I'm no expert. Duane rattled that off as one thing he gets calls on all the time. Unless I garbled it somewhere . . . I hope not, b/c I checked back with him after I wrote it down. I understand that the high idle and off-idle stumble were the main problems associated with high octane fuel but it could foul plugs too.

Sorry, didn't mean to be the first offender after your flame! :eek:
 
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#8
Originally posted by firecracker22
Really? I was told that the higher octane makes the engine run cooler, which I already knew, and that running too much cooler makes it stumble and act as if the choke is on.
Sorry, didn't mean to be the first offender after your flame! :eek:
FC no reason to apologize :) The idea is to share info and decide what is workable as we go along.

It's a MYTH that higher octane fuels make engines run COOLER. If you hold the air/fuel ratio constant and you aren't supressing knock with the higher octane, it will have no measurable effect on combustion temperature'. If an engine is experiencing pre-ignition or the engine is suffering from spark knock the cylinder head and combustion temperatures will be abnormally high. Squelching either of those conditions with high octane fuel will lower temps, but that is the ONLY way there will be a major temperature difference with conventional race fuels. I think this is probably the most common misconception about high octane fuels.

I'm actually kind of glad you brought this up, I was working on a little article about combustion fundamentals and this will make a great lead in for it. I'll post it in the Advanced Tech forum this weekend.

FWIW, the BEST throttle response in my YZF4 comes from running 118 octane Pro Stock fuel cut with MTBE (RON octane +115). If the loads aren't too heavy my engine won't knock on pump gas, but it performs significantly better (throttle response, and top end pull) on higher octane fuel. Just for fun we ran some of the 118 octane fuel (without the MTBE) in Okie's bone stock 250F on Sunday. The verdict? I don't think he'll be going back to the Shell station to fill up :)
 
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#9
Well since we've shifted to octane levels...

Is there no risk in running race fuel. I had seen several magazine comments warning against the use of race fuel due to accelerated deterioration of the carb's rubber seals (MXA article on the 250F). Is this just another magazine myth?
 
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#10
Originally posted by slowmo
I had seen several magazine comments warning against the use of race fuel due to accelerated deterioration of the carb's rubber seals (MXA article on the 250F). Is this just another magazine myth?
YEP, put it in the box with the other IDIOTIC things that Jody and little Timmy have written.
 
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#11
YZF Race Gas

I have heard that using high octane racing fuel in the YZF can prematurely damage some of the internal seals on the Keihin. I can't recall where I read that, and they weren't specific as to what additives in the race fuel did the damage (i.e. which fuels reacted with the polymers used for the seals). As far as throttle response, is the R&D Performance P-38 accelerator pump worth using on the YZF?
 
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#12
Race Gas

I guess I took too long to post my reply! You guys answered the first part of my question, what about the P-38? (BTW, Jody is definitely not too bright).