Honda ATV Forum banner
1 - 18 of 18 Posts

·
Registered
Joined
·
4 Posts
Discussion Starter · #1 ·
Hello everybody.

I recently purchased a 1987 Honda 250X FourTrax. It had been sitting for a year or two before I bought it and thus would not idle properly, so I cleaned and rebuilt the carburetor. Now, it stays running at idle but has these problems:
1. the RPMs vary up and down more than I feel that they should
2. it backfires out the exhaust quite a bit (it did that before the rebuilt as well)
3. the throttle response is a bit hesitant if it is accelerated hard from idle
4. the exhause head pipe glows orange/red sometimes

I have done a bunch of maintenance, all to no avail:
1. adjusted valve clearance
2. cleaned/oiled air filter
3. adjusted carb pilot jet screw (does not seem to make much of a difference in the run quality) and idle screw
4. adjusted throttle cable
5. new gasoline
6. new fuel filters/fuel line

It seems that it must be running lean (at least at times) because of the head pipe getting hot enough to glow.

So, is it possible that the carb is wore out and not responding to the adjustments or quick throttle inputs and I need a new one?

If so, what are the differences between the carbs for the different year 250Xs and the 300EXs? The repair manual I have states different pilot jet screw settings for the different year carburetors, which leads me to believe that there are some differences between some of the carburetors.

Or does anybody have any other suggestions or things to try?

Thank you for any help.
 

·
Super Moderator
Joined
·
18,228 Posts
Welcome to the forums.

if my memory serves me the 250x carb is jetted at 35 slow and 122 main the 300ex is 38 slow ans 128 main but they are the same carbs. if you have aftermarket exhaust and filtration you will need to step up the jets I suggest 130 main and 40 slow. then turn the pilot screw in until it seats and back it out 3 turns and reset the idle. that should solve the lean issue. the backfiring is due to the slow jet being too small or you have a leaking O-ring on the intake boot. the glowing pipe is in fact a lean condition. but if you are above 5000 ft elevation you need to drop down to a 118 jet on the 250 carb and turn the pilot in 1/2 turn. If the airbox lid is off put it back on and try it. Also make sure your choke is all the way OFF (in the down position)

NOTE: In the winter the air is more dense so uping the jets is a must. it's better to be a little rich than to run lean. That will melt a piston.
 

·
Registered
Joined
·
2,735 Posts
If the head pipe glows it is lean.Go up on your main and pilot jetts.Stock are 38 pilot and 122 main.
 

·
Registered
Joined
·
4 Posts
Discussion Starter · #4 ·
Thanks for the replies/advice.

TRX2fiveO:

The bike is completely stock (as far as I know/can tell) and when I rebuilt the carburetor I replaced the jets with the stock size, which was what also was already in there.

I will try to reset the pilot jet screw at three turns out from fully seated and see if that helps.

If not, I will take it apart and take a look at the intake boot and the o-ring between it and the engine.

I am not located in high altitudes, do not run it with the airbox lid removed, and have been operating the choke properly.


Billy250X:

Being that the bike is stock, I should not have to increase the jet sizes, right?
 

·
Premium Member
Joined
·
23,581 Posts
If the ATV is stock, then stock size jets should be fine. Just make sure the jets in your carb ARE the stock size. Someone could have changed them before you got the ATV. You may still have some debris in your carb. Sometimes it's easy to miss something. The fact that it had been sitting for a year or two makes me think the carb is the problem, but I could be wrong.
 

·
Registered
Joined
·
4 Posts
Discussion Starter · #6 ·
Yeah, I may end up having to tear back into the carb to re-clean it and to double check the jet sizes. I did put in the stock size listed in the service manual, but maybe I screwed up somehow.
 

·
Super Moderator
Joined
·
18,228 Posts
the 87 had a 122 main and 35 slow it wasn't until the 90s they upped the jet sizes to what the 300exs are . 122 and 38 stock setting on the pilot for a non modifyied engine is 2 1/2 turns out from seat. I woould set it there and then turn it in 1/4 and reset the Idle
 

·
Registered
Joined
·
4 Posts
Discussion Starter · #8 ·
I took it out riding last night. I tried the pilot screw at 2 1/2, 3, and 3 1/2 turns out from the fully seated position. It did not matter, the head pipe would still glow at all settings. Also, the idle raised up as I was riding it and I kept having to try to adjust that back down.
 

·
Registered
Joined
·
748 Posts
i have to do the same to mine now guys mine is runnign very lean exhaust got very hot the other day, so im sure ill be getting yall to give me the specs on jets and everything soon when i get rdy to do it.
 

·
Super Moderator
Joined
·
18,228 Posts
I took it out riding last night. I tried the pilot screw at 2 1/2, 3, and 3 1/2 turns out from the fully seated position. It did not matter, the head pipe would still glow at all settings. Also, the idle raised up as I was riding it and I kept having to try to adjust that back down.

Pull the carb and remove the bowl. Pull the jets out and let us know what jet sizes are in it. we can make a better diagnosis as to what you need to be running from your reply. also while you have it out go ahead and give it a good cleaning again. there are very tiny orfices in these carbs and even the most minute piece of trash will screw with you head enormously. But if I had to guess I would be running a 40 slow jet and a 130 main.
 

·
Registered
Joined
·
2,735 Posts
If the idle kept going up maybe you have an air leak in the intake.
 

·
Registered
Joined
·
4 Posts
I'm having the same problem with mine I let my bunny ride it n he put the chain through the stator cover and it hit a bolt so I swaped the motor with one that's not bored over now it will idol but when u give it some gas it bogs out do I have to change the jet or can I just adjust it? Any info would be helpfull
 

·
Registered
Joined
·
4 Posts
im having simular prrblems i have to hold my throttle in a litle bit so it wont die and also at about 1/4 trottle it will die out there no noise coming from the motor or anything any info would be great
 

·
Premium Member
Joined
·
23,581 Posts
How do I tell what size it is?
The jets? The size will be stamped on the jet. You will probably need a magnifying glass to see it.
 

·
Premium Member
Joined
·
23,581 Posts
im having simular prrblems i have to hold my throttle in a litle bit so it wont die and also at about 1/4 trottle it will die out there no noise coming from the motor or anything any info would be great
If the jetting isn't the problem, it sounds like you may need to clean the carb. The pilot jet might be stopped up.
 

·
Registered
Joined
·
1 Posts
would i have to jet the carb if i have a stock exhaust and a k&n air filter or can the jet stay stock cause i cant keep my atv runing with out pushing the throatel and it also backfires alot when i let off the gas and it seems like i dont have the power i should be getting
 
1 - 18 of 18 Posts
Top