426 over heating BAD and popping

OK so got a 01 426 that is being a thorn in my side. It sat for about a year and when I got it I went through the carb and changed the plug and it fired up. went down the street and back and it was dumping coolant like mad and was popping and blowing flames out the pipe when I was giving it throttle. went back through the carb just incase and cleaned it again and everything was clean, pulled the plug and it was black so it was definitely running rich so I pulled the needle and dropped it 2 spots. I decided to check the valves while I was at it and valves all had 6 thousands + clearance so they all checked out so I buttoned it back up. fired it back up and popping and over heating right off the bat this time it was heating up bad enough to melt the plastic above the back of the pipe and the side of the mud flap. think I had it running 2 min for all this to happen so I hit the forms and found some posts with the same problems but no fixes that I seen.

would the TPS have anything to do with the popping? is the popping the reason for the over heating?

can anyone help me with this one? its driving me bonkers, any help is better than no help

thanks in advance.

Shooting flames is rich.

But overheating quickly and popping is usually lean.

How is it starting and at what throttle opening is the popping etc. ?

is the jetting stock?

Sounds lean except for the plug being black.  You need to get the service manual.  Re jet to stock jetting and go from there.  Is the coolant coming out the over flow or leaking from somewhere else?  Stock pipe or aftermarket?  Baffle in place or gutted?  What did the coolant look like, light green water/coolant mix or brown muck?  Radiators and hoses OK?  Has somebody added an inline fuel filter?  I've seen these flow poorly if they are made for cars and pressurized systems and cause lean running.  

sorry for not getting back to you guys sooner I left town for the weekend. jets look to be stock 72, 42 low, 162 main and everything is clear and nothing plugged. coolant is coming out the overflow and before I changed the coolant it was a clean green 50/50 mix, I drained it and put in motuls high temp coolant and it still did it within like 1 1/2 - 2 min. there is a clear fuel filter in line that is made for atvs and it is getting fuel the whole time. everything on the bike is stock pipe etc, all hoses are in good condition and water pump appears to be moving the water.

I ordered a carb kit for it this morning to put a new needle and nozzle in and replace the jets just because (if they are the stock jets).  

I think a bad radiator cap would allow coolant to go through the overflow easier than it should, maybe you should try replacing your cap? If your spark plug shows rich you should trust your plug. But just to make absolutely sure I would put a new plug in there and if you think you can safely make a couple good passes and then read the new plug to confirm you get the same results. I've put plugs that where in a rich running bike and then put them into a lean running bike and even after several rides in the lean bike the plug still looked like a rich plug would, so that might be your problem, that if before sitting it was running rich and now it is running lean you might not be able to see it on an already dirty plug.

don't think its the cap since the bike is getting hot enough to melt the plastic at the back of the bike within a few min (mud flap and part of the fender) I have put brand new plugs in and run it for a few min and pulled the plug and it is black and sooty, I have a carb kit on its way but its taking its sweet time getting here.

I would check out all the timing marks, also intake for an air leak.

Check the hot start plunger also.  It needs to be seating all the way down and not leaking around the cap.  

ok installed the new kit and rechecked valves and timing. timing was right on the money valves are still good and all new parts in the carb. still popping and heating up way fast. hot start seemed to be working fine and sprayed pj1 contact cleaner all over hell and gone and no leaks that change the way it runs. anything else you guys can think of to change look at? tps sensor?  

You need to:


- pull the hot start plunger out and inspect the cavity. They corrode inside, preventing the hot start from closing. Then polish everything and use a small amount of anti-sieze in there

- pull the pilot jet and clear the passage above the pilot with fishing line and spray cleaner

- replace the fuel screw oring with a fresh one

- pull the choke plunger and make sure it is sealing properly at the bottom. Polish cavity and pluger and use some anti seize in there

- replace the slide plate seal


After bringing the carb back to spec, now you should be able to adjust the fuel screw (starting with a very low idle) and eliminate the lean condition

so inspected everything and everything looks good and is all back to oem spec.


could it be running to lean and popping and blowing flames out the ex? would rasing the needle help or rejetting to richen it up work you guys think?

timing is off or your slide plate is in upside down

^^ what he said


but you need to also confirm your symptoms

backfiring/flames = rich

popping when decelerating  = lean

Edited by Thommo_400f

If it's an FCR carb, your slide plate might be upside down. Square end down. I fought this myself! Thanks Kah!!! Haha

Edited by rah7777777

Deleted...re-read previous posts and found answer.

Edited by Pooley

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