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CrucifiedYZ

Carburetor question on my YZ426

25 posts in this topic

Quick question, I have a 2000 YZ426F, I was wondering if a 2004 YZ450F carburetor will fit and work with my bike? I was told it will but I want to double check before I fork out the cash. Thanks for your help in advance.

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Throttle cables are a direct fit, as is the TPS connector, and most everything else. (DO NOT REMOVE the TPS from the carb. You should plan to check the adjustment of it per the manual, however). The thing that's different is the hot start. It's cable operated by a handlebar mounted lever from '03 up. Ask for as much of the original setup as you can get; plunger, seal, nut, cable, etc. The lever mounts to the clutch perch clamp, somewhat like the OEM decomp lever on the 426, and if you are still using manual decompression, it will conflict with that, and you'll need an aftermarket hot start lever for the throttle side.

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Thank you so much, I feel like an idiot with all these terms such as TPS connector but thats why I am on here to learn. I am going to look that up, Also do I really need the hot start? I have never used one before, Just trying to plan, Thanks again

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If you want a little of the hesitation out you can cross the 2 wires on the TPS plug coming from the bike ( look at the plug there is one wire on top and 2 side by side you want to cross those together) NOT ON THE CARB. This is a trick that is used on the yfz.

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If you cross the two leads from the CDI to the TPS, it will cause the timing to be mapped as if the throttle were always closed, serious engine damage could result. If it is left disconnected, the timing will be mapped as if the throttle were at WOT full time, which is far safer for the engine.

Crossing the leads should never be done.

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If you cross the two leads from the CDI to the TPS, it will cause the timing to be mapped as if the throttle were always closed, serious engine damage could result. It it is left disconnected, the timing will be mapped as if the throttle were at WOT full time, which is far safer for the engine.

Crossing the leads should never be done.

Is this different from the yfz??? they selll a plug that does this for you on the yfz. I do this to every yfz with no problems.

Im not trying to ruffle feathers just wondering.

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The YFZ quad has a completely different electrical system, top to bottom.

The TPS in any case is a potentiometer. The CDI sends a base voltage, often around 5, to the TPS, which sends a variable voltage back to the CDI based on its position, which the CDI uses along with the tach signal to calculate engine load. It's less accurate than a MAP sensor, but it works. This information is used to vary the ignition timing according to load, and that almost always means more advance for cruising speeds than is tolerable under a full load.

Because of this, TPS's are virtually always set up so that a low return voltage means heavy throttle, and a hig return voltage means a closed or light throttle. Since almost any failure the TPS sub-system can have will result in a low voltage to the CDI, the timing in a failed mode will be set as if the engine were at full throttle full time, which neatly avoids over-advancing the engine under any situation. When it's left unplugged, the return voltage is 0, ant the timing is mapped for full throttle; safe. If it's shorted, the voltage is high, the timing is more advanced, and there could be problems.

This would be real trouble in a YZ, but it might not be for the quad, depending on how it is timed, and what the map looks like.

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I'm glad I read this thread since I'll be there when CrucifiedYZ puts his new carb on his 426 :thumbsup:

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Thanks for all your help guy's I really appriciate it, I ended up purchasing a 2004 YZ450F Carb off of ebay for 207$ with shipping not bad at all considering the ones I was finding. Thanks again for everything and if I run into any issues I will definatly create another post, Thanks again

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Throttle cables are a direct fit, as is the TPS connector, and most everything else. (DO NOT REMOVE the TPS from the carb. You should plan to check the adjustment of it per the manual, however). The thing that's different is the hot start. It's cable operated by a handlebar mounted lever from '03 up. Ask for as much of the original setup as you can get; plunger, seal, nut, cable, etc. The lever mounts to the clutch perch clamp, somewhat like the OEM decomp lever on the 426, and if you are still using manual decompression, it will conflict with that, and you'll need an aftermarket hot start lever for the throttle side.

I bought a 450 carb from grayracer awhile back and could not be more happy. My 426 runs so much better and the jetting is dead on. Oh and by the way, Grayracer you were right. Split the cases, lugs were worn down, and the teeth on third gear were very worn. Also, put a new piston in and adjusted the valves.

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Cool, Thanks bro as soon as I get installed I will let you guys know, Thanks again for all your help

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Grayracer, what kind of TPS plug does the yz450 have? Because the one on my yz426 is square and the one on this carb I got is a triangle.

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Going back at least to the '99 YZ400, the TPS connectors were triangular, and hold 3 wires, blue, yellow, and black. If it comes down to a complete mystery/mismatch, you can simply leave it disconnected.

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OK Gray, one more question and hopefully I will get this whole carb situation figured out, On the hot start issue, The carb unfortunatly did not come with the hot start assembly, When I get this assembly what exactly do I need? Does the cable come with a bolt that screws into the carb or is everything seperate? I called a shop here in cali and he did not know crap, So I am once again back here. Thanks ahead of time for all your help.

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