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1985 Suzuki LT 250 EF - Fuel issue


BFloyd

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Hello all, my first post, be gentle.  My son just purchased a 1985 LT 250 EF and we can’t seem to get fuel to carburetor?  The fuel lines are good, we vacuumed some fuel from the main and reserve lines, but still can’t get it to the bowl when starting.  Our compression isn’t the greatest (120), and we will be doing a leak down test when the test kit gets here.  In the meantime, I’m thinking fuel pump issues?  Is there a way to test the fuel pump? Or any other suggestions?  Thanks

And no we don’t have the service manual for the LT 250 EF yet, it came with the “1985-1990 Suzuki LT230 & LT250 Service * Repair * Maintenance Manual” which is close but not correct.

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  • Admin changed the title to 1985 Suzuki LT 250 EF - Fuel issue

!20 lbs should be enough to get it going. I'd check the valve clearances though because a tight inlet(or exhaust), will bugger up the vacuum which the pump needs.

If your fuel tap has off, on and res then fuel should flow out freely on either of the two running positions. If the tap has on, prime and res, then it needs a vacuum applied to the back of it to make fuel flow on either of the two running positions, but fuel should flow freely in the prime position. If fuel doesn't flow freely in either type then you need to take the tap out and check it's sieve which is inside the tank.

The fuel pump operates off vacuum.
The way to test the fuel pump is, with the tap on, pull the fuel hose off the carby, and lay it on it's side into a bottle. Then find the vacuum hose that goes to the pump. On most models it's a fatter middle hose on the left side of the carby. The fuel hose is left rear. Trace both hoses though to be sure. The other hose on the left side supplies vacuum to the tap. So, with the fuel hose on it's side in a bottle, suck two or three times hard on the pump vacuum hose till there is a good strong vacuum built up, then release it suddenly. The fuel should come out of the fuel hose as a full diameter slug of petrol about ten or so mills long. If the fuel comes out full diameter then the pump works, but we need to test it is getting enough vacuum with the motor running. The pump needs a nice strongly fluctuating vacuum to work, so if the vacuum hose is old and soft, or been replaced with thin walled hose, the hose can partially collapse with the fluctuations causing not enough fluctuation at the pump. Check the vacuum hose is thick walled and sound.

You could prime the carby by putting the fuel hose back on the carby and sucking repeatedly on the pumps vacuum hose, or, gravity feed fuel to the carby to fill it for the next test.


To test it running, we leave the fuel hose in the bottle, on it's side(on it's side is important), but we reconnect the vacuum hose to the carby. Start the motor and with it idling the fuel should come pulsing out of the fuel hose, still pretty near full diameter but a shorter squirt.

There's one more test for the pump once you get the bike running, which is to check the vacuum the bike produces is adequate when the motor is under load. To test that we do all the same test, tap on prime, fuel hose in bottle, vacuum hose on, but we hop on the bike, put the brakes on , start it, put it into gear, and open the throttle till the motor starts laboring. With a load on the motor the vacuum drops away, but if the motor is tuned, the valves adjusted, no air leaks anywhere loosing vacuum, there should still be enough vacuum to keep a near full diameter slightly pulsing flow of fuel out of the fuel hose laying on it's side. If you have the hose dangling down, the fuel dribbles out continuously and it's real hard to tell if it's a decent full diameter flow.

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