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Discussion Starter #1
I own a 2005 TRX250TM2 and a few weeks ago it stopped running. Thinking that it was the carb that had been giving me issues for years, I decided to replace it. I bought a cheap one off of eBay and installed it. The engine started, idled smoothly but stumbled upon hitting the throttle and die. Figuring the pilot valve needed adjustment, I attempted to adjust and it wouldn’t move. I took the carb off and removed the stiff pilot valve, ran a tap and die over it and got it to operate smoothly. I reinstalled it and tried adjusting the pilot valve but it didn’t seem to make a difference. Thinking the carb was bad, I contacted the seller and he sent me another.

In the meantime I took the original carb apart think it needed cleaning again, cleaned and reinstalled but it acted the exact way it did before. It would not start. Didn’t matter if I choked it, held the throttle wide open, somewhere in between, but to no avail. Thinking it maybe a fuel delivery issue, I removed the tank, shutoff valve and found no issues. I replaced the hose going to the carb. Reassembled everything with the same results.

Once I received the replacement carb I installed it. Again it started up, idled but this time it would not only die upon hitting the throttle, it died within ten seconds of starting and would not restart.

I pulled the spark plug, grounded it and I had spark. I sandblasted the plug and reinstalled but still no change.

At this point I’m stumped. The only thing I want to add is the valves have been tapping occasionally for the last month or so. I was going to adjust them when this happened.

I thank you in advance for any advice you can give me.
 

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Loose valves may make noise, but will not affect running except at extremely high RPM - tight valves on the other hand (and in overhead cam engines the valves will tighten over time) will make the engine hard to start when cold - the reason to adjust valves is to maintain a minimum clearance for easier starting.

Yes, you have a carb or ignition problem and I suspect the carb. Typically when the engine bogs and dies it's an indication of not getting enough fuel mixed with the air. The cheap Chinese "fits" carbs are notorious for not being jetted correctly for the application. They might bolt up and all the parts connect, but it is up to the installer to calibrate it to function satisfactorily. Now the BIG downside to most Chinese carbs is while they look the same from the outside, the internal dimensions are far from identical to the OEM carb. The jets typically have no size markings and the air passages vary in diameter. I have a collection of micro drills and when replacement has to be other than OEM, I first try to find a quality Mikuni or Keihin that can be installed, but when forced to use a Chinese carb, I drill the jets to get the correct mixture for satisfactory performance. This is necessary because the sellers of the Chinese carbs do not offer replacement parts and the OEM parts don't fit (in most cases). Sometimes you get lucky and the Chinese counterfeiter manufactured their product using over-the-counter Mikuni jets and other critical parts and you can buy the needed replacement parts.

Now the screw you tried adjusting - it adjust the fuel/air mixture at idle only - it is set close enough that the engine will start and idle, but the final adjustment should be made after having operated the engine (not idling it, but using it) for about 15 to 20 minutes.

New carb from Honda (16100-HM8-B01) is $356 so I understand your reluctance to fix it the easy way and went the cheap way, but when you have exhausted all other possibilities and have determined that the problem is caused by THE CARB, consider buying the one that will fix the problem without major calibration.
 

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Discussion Starter #3
I will buy a genuine Honda carb if that is determined to be the problem. They sell them on eBay for less than $150.

How can I eliminate it as an electrical issue?
 

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Yeah, crossroadsatvdiscountparts has them; with free shipping, you pay shipping, with air filter and other packages including engine oil - they might also offer other 'kits', but I didn't check their online store.

Almost forgot - eliminating it as electrical is a bit trickier - easiest is to first install a new spark plug and connect a timing light - ride it and as it dies, trigger the timing light to see if it is flashing as the engine dies - if it is flashing it indicates spark and directs you to a fuel issue.
 

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Discussion Starter #5
I can’t get it to ride and at this point I can’t get it past idle. I will install a new spark plug and see how it goes.
 

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I bit the bullet and ordered a kit from Crossroads ATV Discounts Parts, that includes the carb, plug and air filter, that is specifically for the 2005 Recon. I’ll let you know the results.
 

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Discussion Starter #9 (Edited)
I put the carb on and replaced the plug and it had no effect. It acts like the original honda carb. I performed a compression test and got 185 ft. lbs. so I believe that rules out mechanical.

Now I’m thinking that even though I have spark, it may not be strong enough.
What about the ignition control module or the coil?

My TRX is actually a 2002 not a 2005. Not sure it makes a difference but I figured I should mention it.
 

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If you suspect spark, you can usually check it with an inductive timing light - if the light flashes then current passed through the wire meaning a spark occurred at the plug - if no flash, no spark - if it sparks outside the cylinder, but not in, then it's a weak spark - check the spark plug cap first - it has a resistor in it that can fail. If you get any spark, the CDI unit is working - that leaves coil, plug cap and plug.
 

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Discussion Starter #11
I checked it with a inductive timing light and the light flashed. I just ordered a genuine Honda coil and plug cap. I’ll let you know when I receive and install the parts.
 
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