250sx dies after being held wide open

[beastybaconman]

I have a 250sx and usually it backfires a lot when I let off the gas to slow down, because its got a cobra exhaust, but sometimes when I go down the road and have the throttle wide open for a little bit, when I let off it just bogs. When it starts bogging I try to give it more gas to keep it going but it'll just keep bogging and sometimes the rpms will come back up, but the same thing happens when I let off the gas again. Then once I stop and it dies I have to kick it over a lot before it starts back up. It only happens going down the road, around my house it runs tit and starts first kick every time. Does anyone know what could be causing this?

[Flyingw]

the cobra exhaust has leaned it out. This cab be bad for your motor.

[beastybaconman]

the cobra exhaust has leaned it out. This cab be bad for your motor.

That's kind of what I was thinking, do you think re-jetting the carb would fix it?

[Flyingw]

Yes but you have to rejet the slow speed and main jets or go back to the stock exhaust.

[beastybaconman]

Yes but you have to rejet the slow speed and main jets or go back to the stock exhaust.

Ok, I don't have the stock exhaust, any idea what the jets should be for the cobra?

[Keepah Rolln]

Check your compression.

[beastybaconman]

Check your compression.

I'll check, but it seems to have plenty of power when I'm just driving around my house

[shortline10]

My guess would be a fuel flow issue or an obstruction at the float valve . Make sure the gas cap is venting correctly .

[beastybaconman]

I don't have a compression checker, but I just went out and kicked it over with my finger on the spark plug hole and it seems like it has all sorts of compression. The spark plug does look like it has been running a little lean, so I think I'll richen the mixture with the air screw a little and go easy on it, until I can get the right jets. And I'm pretty sure there isn't anything blocking the fuel flow, I just had the carb apart the other day and cleaned it out pretty good. Which way do I turn the air screw to richen the mixture?

[Flyingw]

Ok, I don't have the stock exhaust, any idea what the jets should be for the cobra?

There is no magic number for any given exhaust. Every motor breathes differently. Fatten it up 2 or 3 sizes and do a plug chop. The plug will tell you how its burning. Since its popping on deceleration, then fatten up the slow speed jet until the popping stops.

[beastybaconman]

There is no magic number for any given exhaust. Every motor breathes differently. Fatten it up 2 or 3 sizes and do a plug chop. The plug will tell you how its burning. Since its popping on deceleration, then fatten up the slow speed jet until the popping stops.

Ok thanks I'll try changing them. When I took the plug out to check compression it definatly looked like it was burning a little hot.

[Trike_crazy]

I don't have a compression checker, but I just went out and kicked it over with my finger on the spark plug hole and it seems like it has all sorts of compression.

You can get a really cheap one from harbor freight. Or you can spend a bit more and get one from the parts store. If you are going to do any type of work on an engine it is a convenient tool to have. Checking with your finger isn't an accurate way to check. Not that your engine needs a compression check but I was just letting you.

[beastybaconman]

There is no magic number for any given exhaust. Every motor breathes differently. Fatten it up 2 or 3 sizes and do a plug chop. The plug will tell you how its burning. Since its popping on deceleration, then fatten up the slow speed jet until the popping stops.

I just took a look and the main is a 130 and the slow jet is a 38. How many sizes do you think I should go up? It's probably pretty lean right now because there isn't much for baffles inside the muffler.

[Flyingw]

Try starting at 134 and 42 and see what that gives you. Its a bit of trial and error.

[beastybaconman]

Try starting at 134 and 42 and see what that gives you. Its a bit of trial and error.

Alright thanks