1987 TRX250 Fast Idle After Carb Rebuild - Honda ATV Forum
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post #1 of 15 (permalink) Old Yesterday, 06:06 PM Thread Starter
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1987 TRX250 Fast Idle After Carb Rebuild

Hello. I am trying to help a family member with their quad.
Bit of a novice at this so I’ll try to explain the best I can.

The initial issue was it wouldn’t start because it appeared that no fuel was getting to the motor/spark plug. After googling and reading threads here I did the following:
thoroughly cleaned the carburetor.
installed a carburetor rebuild kit.
installed new fuel line with an in-line fuel filter.
installed a new spark plug, as the old one was jet black and a little worn looking.
Filled it up with fresh gas.
Inspected inside the fuel tank and petcock-both were surprisingly clean.
Everything else seems clean/proper (air filter, no oil leaks etc.)

After doing all that, it starts up right away now, but it immediately goes to a very high idle. Too high to safely put it into gear. But, if I slide the choke halfway on, the RPMs drop dramatically, to just a little above stalling out. It’s drives good now, but the choke has to be halfway on to put it into gear. I can slide the choke off and drive it but probably not a good idea.

So back to the shop.. I have taken apart the carb several times now.. giving it another heavy cleaning, double checking and triple checking everything so that I’m not missing anything. I’ve checked the throttle cable, it’s fine, not binding, a slight bit of slack. The choke/plunger cable is clean, o’rings in decent shape. Adjusting the pilot screw does absolutely nothing. I’ve checked for vacuum leaks. I’ve even started swapping the old jets, needle back into the carb. Nothing seems to make a difference.
I haven’t done a compression test yet... and I have not adjusted the valves, because given my lack of experience, I don’t think that’s something I should be touching.

Basically as it is now, it has a super high idle, the new spark plug has already turned black (after 1 hour of use) and there’s a tiny bit of smoke coming out the exhaust (can’t tell what color). I assume it’s running rich now? But I have no idea how to fix this, since I’ve pretty much covered everything I can find.

This is my last hope before it goes to a proper mechanic shop.
Any suggestions are greatly appreciated.
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post #2 of 15 (permalink) Old Yesterday, 06:11 PM
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ummmmmmm..maybe use the black knob on the right bottom side of carb to turn the idle down ??..lol.
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post #3 of 15 (permalink) Old Yesterday, 06:16 PM
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.. could it be as simple as lowering the idle with the idle adjustment knob on the bottom of the carb ------maybe the reason the idle went up after a carb rebuild might be cause someone idled it up before because the low speed jet was clogged and it wouldn't idle and die , now that it ain't clogged no more , it is idled high
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post #4 of 15 (permalink) Old Yesterday, 06:18 PM
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Quote:
Originally Posted by fishfiles View Post
.. could it be as simple as lowering the idle with the idle adjustment knob on the bottom of the carb ------maybe the reason the idle went up after a carb rebuild might be cause someone idled it up before because the low speed jet was clogged and it wouldn't idle and die , now that it ain't clogged no more , it is idled high
lol..that was my response ^^^^^ !!..lol. scary thought huh ?..lol.

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post #5 of 15 (permalink) Old Yesterday, 06:55 PM Thread Starter
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I wish it was that easy. I’ve already covered that several times over... Rear tires screech when putting into gear without choke half on.
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post #6 of 15 (permalink) Old Yesterday, 07:05 PM
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Quote:
Originally Posted by shadetree View Post
Quote:
Originally Posted by fishfiles View Post
.. could it be as simple as lowering the idle with the idle adjustment knob on the bottom of the carb ------maybe the reason the idle went up after a carb rebuild might be cause someone idled it up before because the low speed jet was clogged and it wouldn't idle and die , now that it ain't clogged no more , it is idled high
lol..that was my response ^^^^^ !!..lol. scary thought huh ?..lol.
I seen you bet me too it , I started typing and went to get a drink
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post #7 of 15 (permalink) Old Yesterday, 07:06 PM
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I wish it was that easy. Iíve already covered that several times over... Rear tires screech when putting into gear without choke half on.
The only thing i can think of:

Are you sure the carb linkage is synchronized with the throttle cable? Sounds like itís too tight to start.
When you install the carb, the idle screw should not be in contact with the throttle linkage. Take the slack out of the cable firstóit has to be snug without opening the throttle pistonóthen begin running in the idle screw. Does this sound like it might address your condition?

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post #8 of 15 (permalink) Old Yesterday, 07:57 PM Thread Starter
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I’ll go over all of what you said again. Hopefully this evening. It’s totally possible for sure. Thanks.
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post #9 of 15 (permalink) Old Yesterday, 08:30 PM Thread Starter
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Just went over everything mentioned above (again). Same result. I even unscrewed the idle screw all the way and took off the throttle cable from the linkage, throttle piston as low as it can go. Zero affect. Grr.
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post #10 of 15 (permalink) Old Today, 03:58 AM
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What about the piston which slides in from the top of the carb, I have been in the 250 carb many times but it has been a while , some pistons(slide valves) have a cut out on one side , can't remember if the 250 is like that or not , if it does have a cut out then it can only go one way and be right , if you turn it around it will run fast

you wouldn't happen to be in Louisiana ??? I bet I could dig up 10 or more 86-87 250 carbs

I think I would take the idle adjustment screw all the way out the carb and use my finger or even pliers to be sure that the arm is going all the way and not sticking at a point
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