Idle not steady honda 250SX

[sweetip2000]

Well its a totally clean carb. It runs strong and does what its supposed to do except idle smooth.
I never removed the exhaust on the bike. If there is no copper gasket at the exhaust port on motor
will that cause a leak ? I am also thinking maybe a pin hole in head pipe ? I put my hand near the head pipe near motor and I do not feel any exhaust leaking. All my cables are routed as they should be. I am stumped.
All the boots to the air have no rips and are on secure.

[tri again]

Same as 250 es an sx.
Been through quite a few of those.
Who know's who's been in there in the last 30 years. unless you got it new.

umm...I'll have to get back to you with actual jet numbers just to be sure.
unless someone else has them handy.
How about that delicate jet in the front bottom of the carb with the brass ears that break easily?

so describe it like a 'surge' at idle?
is it sipping water from the sediment bowl?
gas cap vent funky but works better off idle?
different with the cap off?

flyingw is the ultimate carb guru, including throttle plate 'timing' which I never even thought about.
maybe search key for 'sx carb' ?
fuel stabilizer, heet, maybe mystery oil and just run it?
They sure sound pretty when they idle right, especially
when there are 2 running together. Nice like 5 parts Eagle harmony,
so yes, I feel your frustration.
Mouse nest in exhaust?

[Flyingw]

The reality is these carbs on our machines are 30+ years old. Carbs do wear out in that things like the Teflon coating on the slide does wear off. Passageways within the carb do become obstructed. I have a couple of carbs here that are beautiful inside but will not work right. I did have one carb that blubbered real bad when the throttle was fully open. I found the vent that feeds air to the main jet was plugged. I had to drill out the brass plug ball and ream out the blockage but it fixed it. I've also had carbs that were so corroded inside and out that I thought no way will this thing work but turned out to run beautifully. Surging at idle indicates the carb is getting additional fuel from somewhere. When the carb is at idle, fuel is normally supplied by a small hole right behind the butterfly. In this configuration, the butterfly is barely open and the slide is barely up. The choke circuit is not a choke in the conventional sense. Its actually a fuel enrichment circuit. When the choke is engaged, the brass valve that's in the hole is lifted. On the end of the brass choke valve is a small stinger. When that stinger is lifted out of its hole, it unblocks a tiny passageway to provide additional fuel for cold start. If fuel is leaking past that stinger when the choke is off (choke and stinger all the way down), it will cause the motor to surge at idle. The fuel has to come from somewhere.

Now, with all that said I am in no way encouraging the support of the Chinese economy but in lieu of a Japanese made replacement, there is one carb I would recommend. A couple of guys bought these and said they ran great so I bought one and put it on my SX test stand and it did run very well. Before I ran it, I disassembled it and found the slide tab that touches the split linkage was bent up. I bent it back down per the synchronization adjustment that's in the end of the fuel section of the manual. I thought the linkage compared to the OEM carb was a little cheezey but it works. They also used countersink screws to retain the butterfly whereas the OEM carb had pan head screws but that's not a show stopper either. Overall, the Chinese did a great job at copying the OEM carb. A standard rebuild kit fits. The carb is in the 86/87 configuration in that the jet stack is in that configuration with the updated startup jet. It also has the 86/87 vent tubes installed which I'm not a fan of because it makes installation on the SX difficult so I stripped their vent tubes off and put two simple vent hoses on. I only ran it on my test stand and like I said, it ran very well. I just shipped that carb to Capt Wheezey (Shane) so he can install it on his Big Red for further evaluation. For you guys looking for a replacement for your Big Red or SX, DO NOT buy the carbs with the domed top. Those are TRX300 replicas and are not a suitable substitute. Here is the link to Wincycles direct replacement. At 110.00 for a new carb that works is a good deal however, we all know the consistency with Chinese products sometimes has a little to be desired but so far, I haven't heard of anybody that bought this carb of getting a bum one. This carb will work on any year ES or SX. If you do buy one, please post up a critique of the carb and how it ran. This carb has the potential of putting me out of the carb rebuild business but I'm good with that.

http://www.ebay.com/itm/Honda-ATC250...dVIUtD&vxp=mtr

[Flyingw]

Oh ya, the carb came with the choke valve and boot assy. Those alone are 25 bucks on Ebay.

[atc007]

The rubber boot rots off in a year or two....

[Legns]

Now, with all that said I am in no way encouraging the support of the Chinese economy but in lieu of a Japanese made replacement, there is one carb I would recommend. A couple of guys bought these and said they ran great so I bought one and put it on my SX test stand and it did run very well. Before I ran it, I disassembled it and found the slide tab that touches the split linkage was bent up. I bent it back down per the synchronization adjustment that's in the end of the fuel section of the manual. I thought the linkage compared to the OEM carb was a little cheezey but it works. They also used countersink screws to retain the butterfly whereas the OEM carb had pan head screws but that's not a show stopper either. Overall, the Chinese did a great job at copying the OEM carb. A standard rebuild kit fits. The carb is in the 86/87 configuration in that the jet stack is in that configuration with the updated startup jet. It also has the 86/87 vent tubes installed which I'm not a fan of because it makes installation on the SX difficult so I stripped their vent tubes off and put two simple vent hoses on. I only ran it on my test stand and like I said, it ran very well. I just shipped that carb to Capt Wheezey (Shane) so he can install it on his Big Red for further evaluation. For you guys looking for a replacement for your Big Red or SX, DO NOT buy the carbs with the domed top. Those are TRX300 replicas and are not a suitable substitute. Here is the link to Wincycles direct replacement. At 110.00 for a new carb that works is a good deal however, we all know the consistency with Chinese products sometimes has a little to be desired but so far, I haven't heard of anybody that bought this carb of getting a bum one. This carb will work on any year ES or SX. If you do buy one, please post up a critique of the carb and how it ran. This carb has the potential of putting me out of the carb rebuild business but I'm good with that.

http://www.ebay.com/itm/Honda-ATC250...dVIUtD&vxp=mtr

Now you tell me lol I have been running the dome one for a year now it has been doing the job. When I rebuild my ES i will be getting a new one so I will get the proper one then.

[tri again]

I have some oddball on an sx.
Has a flapper choke and an accelerator pump.

hit the throttle a couple times and vrooooom.
also scary fast on acceleration because of the accel pump squirting gas.

I'll have to go look and see if I can get a name and numbers off it.

sx carbs are not my favorite to get off and back on. seems to take me a couple days.
unlike the older 185 / 200 models.
off, apart, cleaned and back on in under 15 minutes.

[tri again]

The reality is these carbs on our machines are 30+ years old. Carbs do wear out in that things like the Teflon coating on the slide does wear off. Passageways within the carb do become obstructed. I have a couple of carbs here that are beautiful inside but will not work right. I did have one carb that blubbered real bad when the throttle was fully open. I found the vent that feeds air to the main jet was plugged. I had to drill out the brass plug ball and ream out the blockage but it fixed it. I've also had carbs that were so corroded inside and out that I thought no way will this thing work but turned out to run beautifully. Surging at idle indicates the carb is getting additional fuel from somewhere. When the carb is at idle, fuel is normally supplied by a small hole right behind the butterfly. In this configuration, the butterfly is barely open and the slide is barely up. The choke circuit is not a choke in the conventional sense. Its actually a fuel enrichment circuit. When the choke is engaged, the brass valve that's in the hole is lifted. On the end of the brass choke valve is a small stinger. When that stinger is lifted out of its hole, it unblocks a tiny passageway to provide additional fuel for cold start. If fuel is leaking past that stinger when the choke is off (choke and stinger all the way down), it will cause the motor to surge at idle. The fuel has to come from somewhere.

Now, with all that said I am in no way encouraging the support of the Chinese economy but in lieu of a Japanese made replacement, there is one carb I would recommend. A couple of guys bought these and said they ran great so I bought one and put it on my SX test stand and it did run very well. Before I ran it, I disassembled it and found the slide tab that touches the split linkage was bent up. I bent it back down per the synchronization adjustment that's in the end of the fuel section of the manual. I thought the linkage compared to the OEM carb was a little cheezey but it works. They also used countersink screws to retain the butterfly whereas the OEM carb had pan head screws but that's not a show stopper either. Overall, the Chinese did a great job at copying the OEM carb. A standard rebuild kit fits. The carb is in the 86/87 configuration in that the jet stack is in that configuration with the updated startup jet. It also has the 86/87 vent tubes installed which I'm not a fan of because it makes installation on the SX difficult so I stripped their vent tubes off and put two simple vent hoses on. I only ran it on my test stand and like I said, it ran very well. I just shipped that carb to Capt Wheezey (Shane) so he can install it on his Big Red for further evaluation. For you guys looking for a replacement for your Big Red or SX, DO NOT buy the carbs with the domed top. Those are TRX300 replicas and are not a suitable substitute. Here is the link to Wincycles direct replacement. At 110.00 for a new carb that works is a good deal however, we all know the consistency with Chinese products sometimes has a little to be desired but so far, I haven't heard of anybody that bought this carb of getting a bum one. This carb will work on any year ES or SX. If you do buy one, please post up a critique of the carb and how it ran. This carb has the potential of putting me out of the carb rebuild business but I'm good with that.

http://www.ebay.com/itm/Honda-ATC250...dVIUtD&vxp=mtr

yo! whoa!

do these really exist?
why do they even make them and why did it take so long?
even trying to get parts for the enrichment piston etc etc was nothing but heartache.

It's worth 100 bucks to save an r&r alone on an sx carb in my opinion.
thanks again fw.
oh, I might be ready for some sx racks soon.
Safer than carrying a chainsaw on my lap.

Be safe everyone

[Dirtcrasher]

Have you played with the aircrew at all??

Could you have an air leak??

Get that pilot/starter jet spotless.