Fourtrax 250 motor in 250sx, having engine troubles.

[ChrisB]

I put a 1987 250 fourtrax motor in my 1985 250sx frame recently, with the fourtrax wiring harness, the motor was running perfect, would go first kick and idle fine after warming up for a minute, drove it a fair bit over the past week and never had a hitch. Yesterday i took it out of the shed and it took a few kicks to get going then when it did it cut out, then finally i got it going and started driving it and i was holding the throttle still but she would catch and speed up for a second, then lose power and almost die then rev high and take off again, it did this for about 100ft then cut out, after that i could get her going and she would idle for a bit until i put it in gear or shook the bike (making me think electrical rather than fuel). Does anyone have any idea what this could be?.. before i end up taking it to a shop and dishing out a pile of money.. Thanks a million.

[toddy]

im thinking about putting a 300cc trx engine in my big red 250.did it all go together easily enough

[Dirtcrasher]

To rule out fuel, next time it does it immediately shut the fuel off while it's cutting out.

Now, open the fuel bowl drain screw and you should have half a shot glass or more of fuel.

That will help you narrow it down.

I have done the same thing, thinking electrical or fuel but this tells you. If fuel is not flowing, junk the stock fuel filters above the petcock and run a clear sintered bronze inline fuel filter in it's place.....

[ChrisB]

Im not the most mechanically inclined person and i managed to do it no sweat in under an hour.. shouldnt be a problem, just bolted right in place for me

[ChrisB]

And as for checking if its a fuel problem, i cant even get her going now to check the fuel but i did take off the carb and clean it out (have done this dozens of times so i dont think i messed anything up there), and it still wont go so i dont think its fuel, plus is cut out kinda quick not like bogging as if it was running out of fuel

[jeswinehart]

The shake it part and it will run a wee bit makes me think fuel issue too.
Vent open on the tanks ?, good flow coming out of the fuel line to the carb,,,, ?

[6speedthumper]

Could have garbage in the fuel tank plugging up the petcock sock. When you shake it, you move the garbage around, and fuel can flow freely.

[ChrisB]

the bike would cut out when i would shake it, not keep running, making me think its electrical with a bad connection somewhere, also recently replaced the fuel valve so its a clean filter.. the pulsing when i was driving down the road also makes me think it was electrical, it would catch and take off and die down again for the same time intervals, like she would fire for a second or two then stop for a second or two?

[jeswinehart]

Heck I don't know,,,, loose ground wires perhaps ? Why you not using the electric start Chris ?
Is the battery in place ?

[ChrisB]

havent even checked to see if the electric start works with this motor and wiring harness.. it didnt with my last one so i didnt bother getting a battery, havent got around to getting one or testing it

[ChrisB]

Just thinking about it, it would make sense if it was my ground wire, ive got it connected right under my seat by the airbox, and the bike would cut out when i would sit down on it.. also makes sense why it wouldnt start when i cleaned the carb and put it back together because it was connected right by my airbox and i probably broke it putting that back it.. i'll take a look when i get home and let you know

[ChrisB]

Wasnt the ground but i found the pulse generator... unplugged... couldnt check it for sure because i put jb weld on a leak on the tank today but i'm really thinkin that was the problem

[fallguy666]

Hope that was it man.electrical gremlins really get to me!!!

[ChrisB]

Turns out the root of the problem was loose connection to the cdi box, the plug was halfway out when i looked at it.. this only really happened because the 87 fourtrax got a bit more wiring than the original sx, but i still sorta stuff it all in behind the headlight, i guess after taking the headlight on and off a few times it loosened it up.