Got the jetting dead on... still pops when hot

[mattmanz71]

ok.. i posted a couple weeks ago about pilot jets and what not the bike has been sitting for a minute since we figured out the jetting... the bike runs amazing now through all rpm ranges with no hesitation or popping.. until about 10 minutes of run time!(when it reaches operating temp. i do have a much larger cam.. do i need more valve lash?? or how can i remedey or tell if i have a sticking valve guide because nearly everyone i have spoken to suggested it was in my my valve train.?? any help is always great!!!

 

[boxhead]

It's more than likely still your mixture. I've been through bad valves and such but the only time I've had popping was when the mixture was a little off. When exactly does it pop on the rpm range? The problem may not be the jets but rather the float bowl running dry or similar. Is the popping coming out the exhaust or air filter? And also is the popping happening upon engine braking or when you let go of the throttle? We need the specifics with throttle position, rpm range, and location of the popping before we can help you. If the valves are bad it's gonna be a bitch to start (since the compression is gonna be low from it) or you're gonna be burning oil from the seal getting wasted in the process. I think it's more than likely still your mixture though. If you smell burning oil from the case vent or out the exhaust than don't run it anymore, just get it apart and do a upper end overhaul asap. You'll know if it's oil coming out the exhuast (and not just gas) since it smells like burning dog **** to say the least.

 

[mattmanz71]

well as soon as you give it any throttle after ten minutes of riding it will pop especially going straight into WOT, IT IS POPPING OUT OF THE EXHAUST how can engine temp effect fuel mixture?? and is the popping and flame shooting a result of rich or lean?? and with a larger cam do i need to allow more valve lash?? the jetting right now is a #45 pilot and a 157.5 mikuni main jet and the plug is pretty damn close to being normal with the amount of carbon on it

 

[mattmanz71]

and it idles down fine no popping... and basically as soon as you give it gas it will start to pop and shoot flames there is also no burning oil the top end is fresh!

 

[yamarider]

The engine temp does effect the fuel mix, I don't know how to explain why this is, it's just the nature of the beast I guess. It's partially because it heats he incoming air, and warmer air is less dense, meaning less oxygen to burn. Flames out the exhaust could be either too rich or too lean, 157.5 is richer than most warriors need though. I'd back it down to a 155 or less and see what happens.

Did you check the fuel level in the bowl? If the float height is set wrong it'll throw off the jetting, especially when it starts pulling a lot of fuel like it will at WOT. I don't know that would actually cause your problem but its easy to check.

A simple way to check the float height is with a small piece of clear tubing. Connect this to the overflow/vent line at the bottom of the bowl and hold the end of the tube straight up alongside the carb. Crack the drain screw open and the plastic tubing will work as a sight glass to see the fuel level. I'm not sure on the exact height on this carb, but it should be close to the seam between the bowl and carb body.

 

[boxhead]

Your main jet and needle needs work if it's shooting flames. Your running really rich if it's shooting flames. The best way to tell is hold a sheet of white paper below the exhaust, if it's still rich there will be some black smoke coming out, or the flames that can be seen at night if it's rich enough. If you're lean it'll pop a bunch through the filter and you can sometimes see a white haze in the exhaust. It'll also be hard to start when too lean. You can't really give numbers for correct jetting since it'll depend on each machine in particular, they are all different.

 

[mattmanz71]

what is the proper float height and how can i adjust to this?? im pretty sure i got it but i did not know when you open the drain screw fuel comes out of the over flow i thought it came out the screw hole?!?!

 

[yamarider]

No, that screw on the side of the bowl is a needle valve that will drain fuel from the bottom of the bowl directly into the overflow line (directly beside the screw).

The float height is adjusted by carefully bending the small metal tab at the float valve.

 

[jasonp]

I'm going to guess and say it is something other then jetting. Maybe like ignition or valve timing. Something just doesn't sound right. Never had jetting do this on a four wheeler from what I've found. And I've been pretty far off left base with jetting. Just my opinion.
What type of cam you running and what are your valve lash settings? Maybe the exhaust valve is not seating and as it gets hotter it gets worst.

 

[mattmanz71]

yeah the hotter the worse basically the cam mfg. recommends 6 thou on intake and exhaust... its set at that today it ran like **** let it idle for 5 mins ran it, it ran amazing then fell on its face again! so i dont even know i cleaned my carb set everything back to stack with a 152.5 because of my hmf pipe and i will start over tomorrow... maybe the jettionmg isnt on im getting very frustrated at this point i also have athe mega cycle cam 450 lift 276 duration... 12:1 je piston open airbox mild port and polish.. jason p what is yours jetted at and whats your elevation??? our set ups are very similar i also have the kw valve springs and retainers with new oem valves (i did lap them) im seriously ready to give up and it is a stock carb i have a whole mess of jets though if anyone reads this far along a step by step guide on how to jet an atv carb would be great haha again thanks to all!!!!