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Discussion Starter #1
Hey guys, need some help. I have two srvs that ran great but now have the same big problem. After they warm up for about 20 minutes they backfire about mid range, when they are doing this you can pull the starter and they will smooth out and take off to high range but will either backfire again or just plain die. Carb electrical is unhooked, been thru the carbs several times, have good plugs and spark. Both ran great all last season and this season until this. Oh yeah and they have fresh gas also. Please help me thanks in Advance, Eric
 

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sounds like a fuel delivery issue. plugged filter, partially clogged main jet or other passage in the carb, deteriorated fuel lines, etc.

the fact that using the choke helps it out momentarily means that you are increasing fuel at that moment, or reducing air.

both sleds started acting up at the same time? odd.
 

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Discussion Starter #3
I dont know if the other has been or not, we just bought it and seemed to run ok until yesterday but we havent rode it much at all. I have a new fuel pump and all new lines and filter. I thought the problem was the pump because after it did it I noticed it was leaking. Why would it take 20 minutes before the issue occurs? It just happened again today. When the pump started leaking I was riding for about 4 hours.
 

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fuel supply and demand. putting around the fuel delivery keeps up for awhile, full throttle uses the fuel faster. intermittent throttle use, off and on the throttle, alllows the fuel to keep up, until you use it up.

check for a blockage in the tank vent. could be airlocking. i have seen spiders nest up in the vent lines. with the leaking fuel pump, maybe enough air was being introduced to keep the fuel flowing. by eliminating the leak, you cut off the air supply.

compare to your lungs. you can only suck so much through a straw before you have to take another breath.
 

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Discussion Starter #5
Just went through the gas tank, vent is free and clear, double checked everything and no luck. Should I do something with the oil lines? the tank is out and the line going to the oil pump is plugged with a bolt and hose clamp. I am going to get a pressure tester from work and test the cyl.s tomorrow cold and hot. I do not think that is my issue though. Any more input would be greatly apprieciated.
 

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could the tank filter be floating or bouncing? is the tank relatively full or on the lower side?

just for fun, if the tank is say at around 3/4 full or less, ride it with the fuel cap loose. just let it bounce without latching it and see what happens.

for obvious safety reasons try not to splash gas all over you or the sled.
 

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Discussion Starter #7
Alright, I will try that after dinner and report back tonight, I am also going to swap CDI's if I have the same one on the running sled or my exciter. Thank You
 

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Discussion Starter #8
Well it made no difference with the tank open. Still ran like crap after about 20 minutes. I am going to change the CDI and do a compression test after work tomorrow. Any more suggestions on your end?
 

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you could test the stator output. typically one that beginning to fail would cause a loss of spark until the sled cools.

the plugged oil line may be a factor. try running it without the bolt, assuming there is no tank or oil.

did the problem occur before or after the fuel pump swap? was the new pump the same configuration as the old. possibly a misplaced hose? the fact the oil tank and lines were removed by others, perhaps they messed up the hose configuration?
 

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Discussion Starter #10
The problem originally occurred before I changed the pump, the pump was leaking and I thought that was the cause of the problem. The only single outlet pump the dealer could get was square instead of round. Maybe it doesn't have enough flow? The only thing different about the oil injection is the lines running to where the tank was are plugged. If the oil pump is working you want it plugged so it doesn't inject air right? I am dumbfounded, no one has changed anything on this sled in years. How do I test the stator? I will grab a OHMs tester from work also and test tonight.
 

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Does that oil line need to be plugged? I took my oil tank out and didn't plug the line...I'm having backfire issues now on my 570 Exciter and figured it was a carb issue.
 

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Discussion Starter #12
Well I got out of work late tonight, and brought a pressure tester home. My good ol sled that started these issues has 100 psi in both cylinders. The newbie of my dads that just started acting up had 30 on the right and 95 on the left. Removed intake and the genius who built this motor back up doesn't know how to tighten bolts without smashing gaskets. The intake on the right cyl was sucking air and both reeds look like crap. Pulled the heads off and right piston is melted by the exhaust port. We got a whole hour and a half of ride time out of it. The other sled just got a good cdi and coil put on but didn't get to test it because it was 10 pm and the neighbors wouldn't care for it much. Will test tomorrow and update, fingers crossed.
 

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Discussion Starter #13
Does that oil line need to be plugged? I took my oil tank out and didn't plug the line...I'm having backfire issues now on my 570 Exciter and figured it was a carb issue.
I would plug the line if your unsure if the pump is working or not, you don't want to be injecting more air into the mix
 

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sorry for the bad news. at least you know now. i have available 2 fresh cylinders with new rings and pistons if your interested.
 

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i will work on a price. the parts are installed but the engine has never been fired. you would be getting 2 each: pistons with rings, cylinders,and heads. also included would be the wrist pins and wrist bearings.

you would need head and base gaskets, and the circlips for the piston pins. unless you want to reuse the ones that i would be removing. i wouldnt.
 

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Discussion Starter #18
Yay!! My raped ape is alive and better than ever!! :cheeky4: I took the coil off the good running sled and rode her for over an hour tonight and she loves it. It has been rain here in MI all day so my 120 studs grab pretty good and she will stand straight up. Took the coil of mine and put it on the good running sled and she spits and pops after about 20 minutes. Off to the trash you go coil :laugh: Thanks for your help!
 
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