ATC250SX Resurrection...running @ full throttle

[fastfrontier17]

Trying to get an '85 ATC250SX running at the moment...once I get it to idle properly I'm going to rebuild the rear end (locked up)... I removed and completely cleaned the carb and all of the jets, however when I tried removing the pilot jet it snapped off inside the carb...I don't have the replacement parts and it's going to have to be drilled out... I went ahead and put the carb back on...oiled up the throttle slide...and it started right up with some fresh gas after sitting for a few years... when it started however it would immediately run to full throttle, backfire a few times and then shut off after about 5 seconds... any ideas? pilot jet causing this maybe?

[Jason125m]

Do not run it with a broken pilot jet...
Welcome to the boards.

[RIDE-RED 250r]

Also, make sure the throttle slide is installed in the slide housing properly. It is possible to put the slide in facing the wrong way, and a VERY high idle is the result.....

[Jason125m]

IF you really insist on starting it with a broken jet.. Check for an airleak. Airleak = deathrev..

[RIDE-RED 250r]

The only thing is, I wouldnt think a broken pilot jet would cause and airleak and deathrev. If anything i would think it would be very very rich from off idle to 1/4 throttle. Sounds very much like an incorreclty installed slide to me.


BUT, definatley get the pilot jet situation addressed....

[atc007]

1st,,the Sx carb isn't the typical,,put the slide in 180 out,and hang open. 2nd,,if it IS the pilot broke off,,I don't think there is anyway you're gonna drill it out. Good luck with that. Once all is set right,,I WOULD run it and see how it runs. If it is clear and you can spray carb cleaner up thru the pilot into the venturi. It is open,and MIGHT run ok. Is your throttle cable hooked and adjusted correctly? It should return down to the adjuster for idle. You should be able to see on the side of the carb ,it returning back down to idle. W the 2 screws and plastic cover off. IF it is closing right,,i highly doubt you will have a revving problem left.IF you do,,yes,,it is sucking air. And, Welcome, to the best darn 3wheeler site in the world!

[RIDE-RED 250r]

Did the SX have a carb like the 350x? The one with the linkage controlled slide and butterfly? Im guessing yes as that sounds like what you are describing. I could have sworn they had a conventional roundslide carb, but it sounds like I was wrong... If so, I apologize to the OP for misleading info....

[fastfrontier17]

Do not run it with a broken pilot jet...
Welcome to the boards.

Wanted to make sure that it would start before I spent any money on parts...that way I save on shipping :) ...took some starting fluid to get it going the first time...started on the second kick...putted for a second...then shot up to full throttle while the throttle was closed...after all the starting fluid was dried up (hour later) I kicked it over again and it did the same thing

[fastfrontier17]

anyone have a good picture of all of the lines hooked up to the carb? the 3 wheeler is an hour away from me atm and i'd like to narrow down an air leak because the hoses are split/missing...any other key places where leaks are prone?

went and head and tried removing the rear diff as well...can't seem to get the drive shaft disconnected from the differential...i have the axle partially out and there's a taper keeping me from pulling it out

[fastfrontier17]

something i noticed as well...with the throttle hooked back up after cleaning the carb out...the throttle would not go back down to the idle screw...and i couldn't get the idle screw to come up that high because the knob would hit the bowl of the carb...this is when i removed the throttle cable completely... had the slide as low as it would go...and still got the high revs

[atc007]

As said,,you don't have an air leak. You have a throttle not returning to idle. Figure out what it is. Is it adjusted too far up out on the threads down ON the carb? Is it backed out AT THE HOUSING on your thumber.? One or both is,,or your throttle is dirty,gummed,jammed.. Which I doubt. Someones been in there that shouldn't have. The driveshaft should slide right off the diff,with relative ease. Don't try and adjust the idle screw up!! Get the butterfly to go down to the screw.. When everythings correct. Adjust your idle,,,then with it idling,,adjust your air screw,,underneath the carb ,,so it idles it's highest,,,THEN adjust your idle down with the idle screw.. You're tuned. This will change with weather,,the air screw that is.. Every 20 degrees or so.

[fastfrontier17]

2 stroke carbs are so much easier to mess with!

but, when I thought the slide was sticking I popped the top and the slide was bottomed down, and to be sure I unhooked the throttle cable from the butterfly and pulled it down to the idle screw...didn't want to start...put it back and was a repeat of initial results...going back to mess with it a little tomorrow and rip it apart again