[Armyguy15r]

I have read a lot of threads on here about trx250x's not wanting to idle, but I am not finding one that meets what problems I am having. I am not new to the TRX's as I have rebuilt some in the past, but the problem I am having is one that is racking my brain.

I bought the quad used from a guy at work who said it wouldn't idle and further had the engine put together my a dealer local to him as he got in engine in pieces in a crate. Here is what I have done so far:

1) I fixed bored the cylinder .040 over and installed a wiseco 12:1 piston with new top end gasket set from wiseco. I verified the proper gap on the new rings that came with the piston before installation along with making sure the gaps were in the correct places per wiseco instructions.

2) I corrected the dealer not timing the engine correctly as they had it on the F mark and not TDC as per the manual.

3) I further disassembled the stock carb and cleaned every inch of if before re assembling it with a repair kit from Wincycles as the stock carb was missing some parts.

4) I replaced all valve seals with new as they were also provided in the wiseco kit.

5) I replaced the stock coil with a new coil from Wincycles which had the correct ohms readings prior to install.

So on to the fun stuff, the quad will not run off of choke. If I have it in the first choke position or the full choke position it will idle and rev, but as soon as you turn the choke off the engine will act like it is hitting a rev limiter not even a quarter of the way in to the throttle and when returned to an idle position it will die. When this happened I replaced the oring on the carb intake boot to the engine side as I notice the oring did appear to be wet all the way to the outside of the oring from the inner diameter.

When the choke is off it does not matter what the idle speed adjustment or the air/fuel screw is set to, it seems to have no effect on the engine when you turn the choke off.

Now today I received a new carb set to factory specs from Wincycles and installed it on the machine. Long behold I started it with full choke and it idled on both choke settings until warm. When the engine was warm I switched to choke off and the engine idled for about 5 mins and then died again. With the choke off and quad idling with the engine warm it again does not seem to make difference in the engine idle.

Basically the only thing that I haven't replaced are the intake boot and the boot leading from the air cleaner box to the carb of which neither seemed to be cracked at all. I also double checked the intake and valve gaps at the rocker arms, which are at factory specs before verifying the decompression lever adjustment.

I have never installed a 12:1 piston in a quad before and am wandering if this is playing a role in starving the engine of the fuel it needs in the idling circuit for proper operating.

 

[Here 2 help]

My best guess

First it makes no difference what the bore or compression ratio is as to the idling situation.

Carbs are just mixers - they mix fuel with air - get the right amount of fuel with the right amount of air and it works. Since it is quite obvious that reducing or restricting the air flow improves the situation, then you need to get more fuel mixed with the amount of air available or get less air for the available amount fuel.

Check for a vacuum leak between the carb holder and the head. The carb holder is sealed to the head by an o-ring. The o-ring must be in good pliable condition with no cracks - not shrunken and hard. The air filter can play a part. If the air filter is not stock or the air box has been modified, then more fuel may be needed to mix with the potentially less restricted air flow (more air needs more fuel). If the manifold o-ring is in good condition, then you may just need to increase the size of the pilot jet. (hopefully you have fresh 93-94 octane fuel in the system)

Let us know your progress in solving this problem

 

[Ryan20Wright]

First of all. You said the Valve Lash was good? Then you fixed the the Timing from the F to the T. Did you check the valves after you switched it to the T mark? Because that right there can cause your valves to be to tight now that you fixed the TDC issue.

If that's all good. Make sure your Carburetor is jetting up a bit now that your have a Higher Compression piston in it.

Also make sure your plug boot/wire does not have a "Spark Leak" making it misfire and can cause you to think it's carburetor issues. This is a common issue people overlook.

Also check your fuel line. Try replacing the Fuel line the inside of the Fuel line can be cracked up and the out side can look just fine and the inside where the small pieces fall off and clog the line starving the engine for fuel.

To check the Intake Boots Push on the carb see if there is any cracks that open when you apply pressure to the carb and try to move the carb around while its running. If there is a Intake Leak before the Carb it will make a "Sneeze Sound" and die or just sputter for a second. Another thing. Is your Accelerator pump Primed before you start it? What size Pilot jet does it have?? Try being the Low Idle Pilot jet size up.