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XR400 Carb Rebuild

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I recently bought a 2001 XR400 and I'm cleaning/rebuilding the carb. The main jet is a 140 and the slow jet is a 52. The needle jet is stuck inside. The throttle drum screw is frozen, so I don't know the needle position; But I can see a few rings atop the needle. 

I run the bike at about 1,000 feet with a UNI filter and stock snorkle. 

I bought a Moose carb rebuild kit and replaced the gaskets. I also replace the main and slow jets but I already don't remember the numbers. I'll post them later. But I do remember that they were different than 140 and 52.

I also replaced the float valve and set the minimum and maximum float height at 14.5mm and 19.5mm per Trailrider42's video. Previously, the float was hanging down way too low. 

Overall, for a neglected bike the inside of the carb looks pretty good.

Is there anything else that I should be looking for while I got it apart? Are there any further adjustments that I should make?

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Someone might have used Loctite on the drum screw or, like you said, it's just a little frozen. A technique commonly used for such screws/bolts is to subject them to an impact. Use a brass punch or something similar (softer than the butter head stock screw) and hammer. Set the punch on the screw head and give it a few good whacks.

On frozen screws like that, once the driver tip starts to slip, you should stop. Put an abrasive like Comet or Ajax into the screw head and coat the driver tip as well. That provides more friction between the driver tip and screw head.

If that doesn't break it free, you'll need to try some heat. In a case where using a torch in an area to heat a screw like that might heat up more of the surrounding area than you want, it's best to use a wand lighter. A soldering iron works well for introducing heat to only the desired part.

Seeing a few rings at the top of the needle means it's most likely still in the stock 3rd (middle) from top position. That's ok.

As for jetting, yeah, you should write down what you put in it. Knowing your jetting will help us determine if its right for your bike configuration and elevation. While you have the carb apart, I highly recommend the extended pilot jet mod shown in my video. Don't know what kind of riding you'll be doing, but it helps prevent stuttering on hill climbs.

Is the exhaust still stock? If it was the PO that put the UNI on it, look to see if he also did the Gordon mod to the exhaust. Between the silver trim ring and outlet hole of the exhaust, check for extra holes that may have been drilled around it.

And replace the butter head Philips bowl screws with Allen head screws.

Make sure you use only ethanol rated fuel line between the petcock and carb.

Edited by Trailryder42

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Main jet: 140

Slow jet: 52

I know the 52 is stock, but the 140 seems low according to the correction factor. I'm using the stock exhaust, snorkel but have a UNI air filter. 1000' above sea level. Sound right? 

 

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142/52 is stock jetting. Even tho you have a UNI filter, it's not effecting jetting much because the snorkle is installed and the exhaust is stock, so that is a bit of a bottleneck compared to what the UNI can do. So if the 140 is lean, its not by much.

What jetting factor are you using and how are you figuring it to get a number that suggests the 140 seems low?

Does the engine seem to be anemic in the upper throttle range to make you think it's lean?

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The #140 is what I took out and #140 is what came with the Moose carb rebuild kit. My correction factor is .98 which puts everything much higher:

162 x 0.98 = 158.76

60 x 0.98 = 58.8

So, how was my bike running fine at 1200' with a #140 #52? 

The higher the number, the leaner---right? So my bike is running rich? The plug was black and fouled out shortly after I got the bike. A new plug and the bike ran great on a 20-mile trip. But in the long run, am I going to foul out on the trail eventually?

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No, the higher the jet number the richer it is.

And the 162/60 jetting you're using for reference in figuring with your correction factor is wrong. That jetting is for a completely modified intake and exhaust with its increased flow at sea level. Your bike is not set up like that. All it has different than stock is a UNI filter, that's not enough to require such rich jetting.

The 140 main is going to be very close to what your bike should be running. It's the pilot that might be a little rich.

 

Edited by Trailryder42

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