2001 yzf426 problems

started having problems awhile back where the bike wouldnt rev out like it was holding back and back firing . i have checked all the electrics and they are ok . choke and hot start ok also .... i notice that when i took the radiator cap off the water had alot of air bubbles in it and started to spill out like it the water was getting really hot and boiling .... anyway i have just taken the head and barrel off and replace the bottom gasket head gasket and replace the rings also....i have put it all back together and it starts up ok but it seems to be poping and i have notice that the exhaust downpipe is glowing redhot on tick over and when i rev the bike it wants to rev right up but it dont its like something his holding it back as anyone got any ideas on what it could be .


The exhaust glowing red is normal, unless it does it so that it's visibly bright red in the daylight in less than 30-45 seconds.

Something that you might want to look at is the blue wire that runs to the neutral switch, and the switch itself. The switch performs 2 functions. When in neutral, it grounds the blue wire, which tells the CDI to set the rev limit down from 11,500 to more like 6500, and retard the ignition timing.

If the wire is shorted to ground, fix it. If the switch shows continuity to ground in any gear besides neutral, it is defective.

Otherwise, try a new plug, and be sure all your wiring harness connections are clean and secure. The kill switch could also be closing intermittently.

is there any way to bypass the netural switch . is it a case of just unplugging it . there are more than just a blue wire going to it !!

There should only be a single blue wire leading to the switch, which is located below the countershaft sprocket, near the shift shaft.

Disconnecting that should eliminate any problem that it may have.

i can see a light blue wire but there are more than just one blue wire going to the switch . if i cut the blue wire and if there was a probblem with shorting would that sort it out on the switch

According to the manual, there are 4 wires built into the switch, but only the light blue in the harness goes into it. I would not cut anything. There should be a connector up under the tank near the front of the head that you should be able to unplug without disconnecting anything else. It would have one light blue on the harness side, and that and 3 other wires running down to the engine.

Look at the schematic on 6-1, and the switch test procedure on 6-6 of your manual. If you don't have one, go Here or Here to fix that.

thanks grayracer513 i will have alook at it tomorrow morning

thanks again

A lot of people disconect this light blue wire anyway. The idea is the bike should be easier to start without it. Whether it does or not is frequently debated. I tried it and didn't notice a difference. In any case though, if you disconnect the light blue wire like grey suggested and it fixes your problem, you can just leave it disconnected and be done. There are a lot of 426's out there running with it disconnected. Do a search on "blue wire mod" and you will find a ton of info on it.

i have disconected the light blue wire and tryed it and its still the same you can start the bike up leave it on tickover and in about 10 to 15 seconds the header starts to glow red . if you rev the bike up alittle then it glows even more... i know that it is normal for the header to glow alittle but not like this .when you start to rev the bike up its very flat like the timing is out . i have checked the timming to what it says in the book at it looks ok .apart from in the book the lobes are facing down.. would having the timming out one tooth make it run like this ...i noticed aswell that on the fly wheel for tdc asnt got a line. its only got a dot. so im not sure weather the flywheel as been changed because its got the charger on it ..also the left cam as something on it . its not like the one in the manual what i will do is take off the cover and take a photo of the cams when the engine is at tdc

If your cam looks like the one in This instruction sheet, it has been upgraded to the auto decompression cam, and in that case, you need to know whether the person doing the upgrade used and OEM YZ450 cam, or an aftermarket part from Hot Cams, or something similar.

If it looks like an original 450 cam, follow the timing procedure laid out in the sheet. The stock 450 timing marks don't line up right in a 426 head, and if you don't follow the alternative procedure, the cam timing will be way too far retarded. As for the lobes facing up or down, just turn the engine one more time around. The cam turns at half speed.

Another thing worth checking is to see if the TDC mark on your flywheel coincides with the actual TDC at the piston. Use a long thin screwdriver to reach through the plug hole and see where the mark is at TDC. Hint: If you remove the flywheel nut, you can see the keyway in the flywheel. With the piston at TDC, it should be pointing straight up in line with the center of the cylinder.

thanks mate yes the cams look what you said... i think i have found the problem . i think the keyway as sheered off .. wont know untill i get the flywheel off. but i can push a small screw driver in the slot all the way and cant see the key...i will know more tomorrow when i get the fly wheel off

hello mate the punch mark on the fly wheel is tdc. i have looked at the upgrade and i sort of set it to what it looked like in the photo . the bike ran better but i think the timming is still out by one tooth .. it would be nice to know what the Measurement between the bottom of the hole to the head face is..people have been saying make sure they look the same on both cams and yes you can do that but you can still have it wrong . i cant dial the cam in because i dont have one .

on the inlet cam i ahave a red punch dot at the top and it as red paint on it . is that tdc???? for the right cam . the other one doent have it on because its not the standard cam . so if i set the inlet cam so its a 12 oclock with the red dot and then look on the other side of the engine and see where the cam lobe is and set the other the same on in exhaust cam. do you think that should be somewhere near


revs up now but still popping but its better

The coolant will allways boil up when the cap is removed. how did the problem occur? suddenly?, over time? Sounds like your really lean, try cleaning your carb out and see if there is any improvement.:mad:

it did it suddenly. got the bike out one day started it up was fine on the stand . then took it out and there was just no go ..so cleaned the carb out thought there might of been some dirt in there . all was clean put it back on . got the same .anyway i noticed lots of water was comming out of the over flow so might of been head gasket so i have took it off replace all gaskets and also have put new rings in it put it all back together and now i find i have the upgrade cam which i dont know if its a oem or a hot cam. so really its just a case of messing with the timming .i know the header gets hot and glows red but this is comming down the pipe around 8 or 9 inch in about 10 to 15 seconds . that cant be right can it plus its still spluttering abit but kickes over first or second kick so that cant be to bad

If the bike has been sitting for a length of time. you probably have some blocked

air passages in the carb. this would explain the pipe glowing red. always run the gas out before shutting it down for prolonged periods,

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