Help with overheating

I was riding to school for the first time and traffic was slow as can be, lots of idle and low speeds... When I was close I tried to give it some gas and it choked hard, so I rode it to the parkade and it just died without me turnin it off... Very hot, so I let it sit 10 minutes and it fired right back up.

Maybe is is too lean at idle? Which jet do I change for this and how do I get at it?

Thinking it might be that as I cannot start it with just a kick, I need to give it a few throttle pumps and it will start one kick...

You need to get some electric fans on it, you can use a termo switch to control them. The bike was made for moving :banghead:

Check out the stickied posts for how to jet properly for your elevation, temps etc. These bikes can overheat when moving slowly, although with proper jetting it can be reduced to a degree. I would suggest making sure your jets are proper (especially the pilot jet for idle or near idle situations) and if you are not moving, shut the bike off. Without fans, the only way to cool the bike is to be moving, or shut off.

Just for fun, try starting the bike with the choke on instead of the throttle pumps. If this makes the bike start easier, you definitely need a larger pilot or to richen the fuel screw if the pilot is proper.

I'd also look through the "Jetting Database" thread to see how others who live and ride in the same elevations and conditions, with the similar amount of mods, have set up their bikes.

Edited by Pooley

My friends wr never overheats in the same rides, I need the throttle pumps with the choke OPEN to get it to start that's why I figure it's too lean ?

Choke + hot bike is definitely too lean. Choke + cold/ambient is normal. Any idea what sizes your jets are? If you know that, and your elevation, it should be pretty easy to sort out. I think the typical pilots for 450s are a 48 or 50. If you have an adjustable fuel screw, count how many turns out it is. Anything over 2.5-3.0 definitely requires a larger pilot. In the meantime, if you do have a adjustable fuel screw, turn it out some to richen up the low end until you can re-jet. Be careful how many turns though, don't want that thing falling out :banghead:.

Ok first off what is the stock jet? Does turning the fuel screw out make it richer or leaner? The bike is stock for jets and I have only done the main jet, not sure how to change the pilot (if anyone can tell me that would be great)

Do I also need a richer starter jet since I need to crank the gas to start it?

I am at Calgary elevation

On a 4 stroke, turning out the fuel screw opens it up, allowing more fuel to make it richer.

Turning the throttle before starting just primes things, and doesn't mean it needs a different size jet. I consider my 426 to be almost perfectly jetted, and when cold, I use the choke and twist the throttle 1-2 times max before starting. The pilot jet is what controls fuel flow at idle, and near idle throttle openings. Once off idle the needle takes over from about 1/4 throttle until the main jet at about 1/2 to full throttle.

What other performance things have you done? Airbox mods, exhaust, etc? All those things add up dramatically when considering jetting.

Check out the following. and you should have enough resources to help you with virtually every question you might have.

Under the "Jetting Database" thread you will find this format, which would be super helpful towards getting you where you won't overheat, increase the durability of the bike, and your enjoyment too. :banghead:


Model (400 - 426 - 450):

Cam Timing (WR/YZ):

Main jet:

Pilot Jet:


Leak Jet:

Starter Jet:

Fuel screw (turns out):

Needle Model/Clip position:

Grey Wire Mod (Y/N):

TPS Connected (Y/N):

Airbox Snorkel/Lid (on or off):

AIS Removed (Y/N):

Airfilter Brand:

Exhaust Brand:

Average Altitude:

Average Temperature:

Average Humidity:

Degree of Satisfaction (0-10):

Additional Mods/Comments:

All I did was exhaust and grey wire mod. One mechanic is saying the gytr ais removal will make things richer and should fix the overheating ?

You can't really just pick and choose mods to do, hoping for a desired effect like making things richer or leaner. Regardless of any mods done, you still need to go through the process to see if you are jetted properly for your level of mods done and elevation. If you have done an exhaust only, but didn't change anything but the larger main jet, you are likely lean everywhere else. An aftermarket or modded exhaust will allow more air through the engine, but without more fuel too, it becomes leaner across all RPMs. That is why you need to go through the process, basically each and every time you mod the bike because the ratio of fuel to air will also be changing.

That being said, the biggest culprit here, at low speeds especially is the pilot and fuel screw. Set those properly now to protect things, and then also after doing anything else. Once the pilot is tuned, you can move on to the needle position, leak jet, AP pump etc. But remember each time you mod something, you should check the jetting as outlined on TT to make sure its proper.

The immediate, quick and dirty fix is the pilot and fuel screw just to keep it cooler when at slow speeds.

Big thanks for the info, the exhaust is stock but with the baffle removed. How can I adjust that fuel screw without the tool? Do you know how to change the jet? I've only done the main

We're do u live? I live in Columbia sc, not sure of elevation but there is a marker right down the street, needa go look at it to get elevation. But what is the grey wire mod and what does it do. And I have a white brothers e-series exhaust and pretty sure stock jets.

Calgary at 3800 feet

What's the grey wire mod?

And if mine just shuts of right when I take choke off. I'm guessing go up on the low speed jet Or turn mixture screw out. Btw how many turns out is yours. Just so I have a rough estimate of we're to start

Gives a yz timing curve and I'm trying to fix mine so not the best one to ask :banghead:

We're is the grey wire? And lol past owner screwed mine up for me. Carb was missing half the stuff. Striped screws broke jets. I've just been doing a little here and there

The fuel screw can be adjusted via screwdriver with the carb off, or you can make a special tool from a screwdriver, and turn the screw without removing the carb. I can't say for certain, but I thought in some years Keihin somehow made adjusting the screw a huge PITA. What year is your WR? How to make a tool, is in one of the stickied posts. With a properly tuned pilot jet, the bike should run best with the fuel screw between about 1.5-2.5 turns out, adjusting for temperatures. More or fewer turns normally indicate the pilot jet is the wrong size. Make sure you read the stickied posts on how to tune this.

The pilot jet is the one that is about an inch long, with the upper end a bit tapered with several holes in it.

The info for the grey wire, as well as how to do any other mods is in the stickied posts I linked above. Look through those for the "how-to's" for pretty much everything, including the shop manuals.

Pretty much first and foremost, before any tuning, make sure all jets are clean and not plugged with gunk. The air jets get plugged easily if you over-oil, or don't let your airfilters dry properly before riding. Fuel jets get plugged and varnished by old gas. Clean both air and fuel jets in carb cleaner then blow out with compressed air.

I can see you want to correct this ASAP and I really don't want you to run too lean and risk the bike, but I would highly suggest doing some reading of the FAQ, Jetting Database, Mod Database, Jetting Tutorial, Motoman 393s tech articles for the fuel screw, etc. This will provide you with the answers to most of your questions, and answer them much better than most of us can. After reading this information, please post any questions you may have.

Only question now is I don't know where the jet is located and how to get at it and replace it?

I turned the fuel mixture screw out 2.5 turns (considering open air box and after market exhaust) and that solved my overheating problem but not idle. I got my stepdad to do the. Carb( he's done for more than I have). For me when I got the bike. And still won't idle. What could it be?

Only question now is I don't know where the jet is located and how to get at it and replace it?

Look at the above links to find the service manual for your specific bike. The manual will show you everything you need to know.

I talked to my mechanic and he said its not meant for riding on the street... I told him buddies Wr450 doesn't overheat like mine and he didn't understand... Would also one of those upgraded eBay rads make this better? I saw people talking about them a month ago

Also when my bike turned itself off because it was so hot could that caus any damage? I let it sit for 10 mins and fired it back up fine

Edited by Stealth13

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