SRV540 problems lean backfire when giving throttle

[hansenmac]

i have a 86 srv540 fan that i got for free. had been sitting for ten years or so. got it started but wouldnt idle or rev very well. it was better when headlights were unhooked. added a ground wire from the coil to the frame and then it would idle nice. put a new fuel filter in the tank and cleaned the carb. idled great but try to drive and lean bog and backfire. theres no choke just an enrichment jet flip that on and it would rev up and drive ok at best. air leak or not enough fuel. cleaned the carb a few more times nothing. figured crank seals were shot so rebuilt the motor all new seals new pistons and rings. started up idled great but same problem. rebuilt fuel pump same problem pulled the carb again cant find an issue with it. seems like fuel since when you flip the enrichment jet it will rev. any one have any insight? what am i missing?

 

[boondocker97]

Is the pickup in the tank weighted so it sits down in the fuel? I've heard of them floating if not, or if the hose in the tank is hard and it somehow gets rotated to where it holds the intake end up.

 

[hansenmac]

Is the pickup in the tank weighted so it sits down in the fuel? I've heard of them floating if not, or if the hose in the tank is hard and it somehow gets rotated to where it holds the intake end up.

i will check, thanks for the reply.

 

[volcano buster]

I assume the carb boot(s) were checked?

 

[Old & slow]

Check your exhaust and air box I have seen rodents pack them full of food etc. When you clean the carb do you verify the passage is clear with a wire or air? The pilot circuit is pretty small. The other thing to do is use a small amount of either and spray around the crank seals and intake boots see if the idle changes if so you have a leak. Wouldn't be the first time a new seal leaked. When you say it backfires where is it backfiring from the intake or exhaust? Intake usually indicates timing , exhaust excessive fuel. Did you get all the old fuel out and replace it with fresh fuel? Good luck and keep us posted as to what you find. Thought of some more things did you confirm reed valve condition? Make sure the vent lines on the carb are clear also. Some of those sleds had a safety switch on the carb that can give problems did you try unplugging it. If i remember right Yamaha ran a open ignition so unplugging it should be bypassed.

 

[hansenmac]

single carb and the boot looked in decent shape. air box was thoroughly cleaned. the exhaust seems clear sounds normal and didnt notice anything when i had it off, could take a better look inside but ive driven the thing maybe a mile total and ran it a decent amount so you would think it would have blown out or cought fire already but never know. It sure seems like all the passages are clear this is probably the 4th time cleaning the carb but could be a stubborn spot. Its a pop out the exhaust and it instantly runs better with the enrichment jet. The fuel tank was dry and i filled it with fresh fuel and put a new filter in. Reed valves looked in good shape. The safety switch looks to be unhooked and then plugged back into itself was like that when i got it. I'll check more of the things you guys said and report back. thanks a lot for the ideas.

 

[Teth-Air]

I had one and it sounded lean and had a hard time accellerating but would rev once I got it past a certain rpm. Turned out to be a broken reed.

 

[davesilb]

Check both your carb jets. Both main and low speed and compare to what is called for for your elevation. I use to own one of these and you would have to re-jet for every 1500' feet in elevation to keep them running great. Some one may have jetted for 6000" and you are trying to run at sea level and the symptoms you indicate would occur. Good luck

 

[hansenmac]

i appreciate all the help. i checked the jets and they were good on size. Its the wifes uncles old sled and he lives at the same elevation. for the last few days ive sprayed the carb ports with cleaner every time i walked by it (3 or more times a day) and today took the air hose to it. put a new O ring on the enrichment jet and slapped the carb back on. ran awesome took it for a 1/4 mile grass and gravel ride and pulled really well for a 540 fan single carb. must have been a blocked port in the carb, i had cleaned it with carb clean at least 3 times but 10 years of sitting gunked it up good im guessing. sure is a good feeling when something finally runs right after all the work. i swapped on a skinny dragon rmk seat, now for the lower gearing and 1.25 track.

 

[Old & slow]

Good to hear you got her running good!