help,rx1 w alpine turbo, started backfiring - sputtering

[925rotax]

well found the carb filters plugged solid [all 4],cleaned the filters, re assembled carbs. wot sled is pulling it eventually starts acting up agai and dies,while acting up, turn choke on fulland makes no difference. immediatly starts up only w choke on and runs good until wot, seems to be starving of fuel at 3/4 to wot, air fuel way lean when it problem cuts in!

 

[925rotax]

fuel regulater! checked fuel pressure at fuel pump outlet 20 psi @ idle/checked at fuel reg outlet at idle o psi, can these be rebuilt, disassembled its red/aluminum colour?

 

[925rotax]

replaced the fuel reg, now have 5 pds at idle, but sled is running with a sputter and backfirring ,right after startup at idle

 

[hlmrx1]

Could the filters be plugged up again from some debris in the tank or something?

 

[925rotax]

compression test today #1-130psi #2 -131 psi #3- 111 psi #4 130 psi. leakdown test on cylinder #3 = losing air straight out exhaust, assuming burnt valve.

 

[rxrider]

That is a small loss, have you measured valve clearances? If you're out of spec changing valve shims may fix the problem for you.

 

[925rotax]

thinking of why @ #3 cylinder @111pds the air during leak down rushed out exhaust. i thought maybe i was on wrong stroke, did the compression test again today cold #3 111 pds/ leak down about 3% minimal this time, no audible air loss out exhaust intake or dipstick tube. compression test again with some motor oil dropped into cylinder, about5 drops, reading came up to 135 pds compression,rings?hear no loss at oil tank?will do a comp test again with warm motor. still cant figure out why its backfiring and sputtering still, all the time now, even at initial start up?checked carb filters again and jets and all clean.will remove head and check valves, thanks everyone

 

[925rotax]

started sled and warmed up, have to use throttle a little to keep running. motor is popping and backfirring, sounding like 3 cylinders firing only.started to pull off plug caps one at a time #1 pull cap and continues to run poorly and same when #2 was pulled.notice very little difference in engine run. pulled #3 and motor dies and same with #4 the motor dies. noticed that all 4 caps are arcing.compression test at warm #1 130 #2 130 #3 120 #4 140. rxrider i will pull the head off next to check valves. hlmrx1, i did check the carb filters again and did install new filters- all clean, tank steamed, new lines throughout, tank filter,flushed new pump in gas container, new regulater and everthing in fuel clean? thanks

 

[rxrider]

I would like you to measure valve clearance before removing the cams and pulling the head, then you have the opportunity to change valve shims on any valve out of spec.

Take a look at this post by lakercr

http://www.ty4stroke.com/viewtopic.php?t=32636

 

[WesG]

Stator/rotor/timing pickup

You could try pulling the stator cover and checking the stator/rotor and timnig pickup for damage. Maybe theres a piece of sh!t on the timing pickup. Just other crap to try. FWIW I did a comp test on my motor after sitting for 2-3 weeks and it came abit low also. Soon as I ran it and got some oil around and some heat it came right back up. Had me freaked for abit though.

 

[givemeaboost]

I see that you are running JE pistons. Are they 10-1 or 9-1 ratio ? If they are the 10-1 ones that compression seems low. Mine used to check out at 160-165 at 3200 ft elevation with 10-1 Wisecos. Also what size mains are you using with that updated header. I built mine like need for speed builds and had to go from 135 to 147 mains just to get the a/f numbers even close and that is riding at 8000 ft. The first two times out I was hitting high 13's wot and I think I took the rings out as it lost a bunch of compression.