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Looking for some ideas on where to look for the problem Im having on this sled.
1999 Poo xcr 800. Its piped, pored, and has a 180hp kit on it. Has Boysen Reeds and Megatron carbs on it.
Running C-12. / premix
My friend got the sled set up this way. Its ran low 10s (a high 9 at sea level) Its never sounded to me like its had a nice idle sound (sounds like one cyl was off). One you get up in the rpms a bit it cleans up and sounds nice and crisp.
The compression was (135 I think) even across the 3 holes. I wanted to test the theory that while idling it sounded like one cyl was weak. When I pull the primary cyl spark plug wire while its idling it seems to make very little difference in how the sled is running. When you pull the center or mag plug wire the sled nearly dies.
We ran the sled a few weekends and performance was sub par...high 10s. With crap 60ft times. We thru new plugs in the sled and it perked right up and ran low 10s and 60s dropped a fair bit. We though prob solved. I tried pulling the plug wires again and the prim cly was making a bigger difference but still not as much as the other 2. The sled ran good for that weekend and the next and then the following weekend it fell off again.
My initial thoughts were that the sled idle circuit must be fat and is fouling a plug (as a drag only sled though the sled rarely idles) I looked into how to tune the Megatron (Lectron) carbs and found they were quite diff with no pilot jet. Interestingly the sleds idle once you rev it up doesnt drop as quickly as most engines. Ive got my mach z to compare it to for example. It will drop to say 2500 and eventually fall to idle (1600 eg) According to Lectron carb tuning docs this can indicate that it is lean on the idle end.
We pulled the slides and needles and measured the needle length and they looked to be equal (as near as my manual caliper could measure). We first leaned the mix across the 3 needles by 1/4 turn and ran it. The rpms took forever to come down to idle, which seemed to indicate that it was even more in the too lean direction. We decided to go fatter than the original setting by 1/4 turn. The idle dropped much quicker but still not quite as quick as Im used to.
We even pulled the center carb body and the prim carb body and switched them (slides and needles stayed where there were) The carbs also have clear bowls and the float levels look good. Switching bodies made no difference.
We swapped coils from primary to center cyl and that also made no difference. There seems to be an equal amount of spark in all 3 holes.
I asked Lectron which needles would be good to start with as a baseline and they said Metering rods should be 8-1XL. Adjustable power jets at 1 turn out to start. The sled has a 7 needle in it which should be leaner than the 8.
Oh one last thing. The idle set screws dont effect anything at all. The slides are high enough (from cable tention) that the set screws do touch the slides apparently. This should indicate that the slides are open more than normal at idle. If we do have a weak cyl they might have to be open this much to stop it from stalling.
Any thoughts on where we should look next?
1999 Poo xcr 800. Its piped, pored, and has a 180hp kit on it. Has Boysen Reeds and Megatron carbs on it.
Running C-12. / premix
My friend got the sled set up this way. Its ran low 10s (a high 9 at sea level) Its never sounded to me like its had a nice idle sound (sounds like one cyl was off). One you get up in the rpms a bit it cleans up and sounds nice and crisp.
The compression was (135 I think) even across the 3 holes. I wanted to test the theory that while idling it sounded like one cyl was weak. When I pull the primary cyl spark plug wire while its idling it seems to make very little difference in how the sled is running. When you pull the center or mag plug wire the sled nearly dies.
We ran the sled a few weekends and performance was sub par...high 10s. With crap 60ft times. We thru new plugs in the sled and it perked right up and ran low 10s and 60s dropped a fair bit. We though prob solved. I tried pulling the plug wires again and the prim cly was making a bigger difference but still not as much as the other 2. The sled ran good for that weekend and the next and then the following weekend it fell off again.
My initial thoughts were that the sled idle circuit must be fat and is fouling a plug (as a drag only sled though the sled rarely idles) I looked into how to tune the Megatron (Lectron) carbs and found they were quite diff with no pilot jet. Interestingly the sleds idle once you rev it up doesnt drop as quickly as most engines. Ive got my mach z to compare it to for example. It will drop to say 2500 and eventually fall to idle (1600 eg) According to Lectron carb tuning docs this can indicate that it is lean on the idle end.
We pulled the slides and needles and measured the needle length and they looked to be equal (as near as my manual caliper could measure). We first leaned the mix across the 3 needles by 1/4 turn and ran it. The rpms took forever to come down to idle, which seemed to indicate that it was even more in the too lean direction. We decided to go fatter than the original setting by 1/4 turn. The idle dropped much quicker but still not quite as quick as Im used to.
We even pulled the center carb body and the prim carb body and switched them (slides and needles stayed where there were) The carbs also have clear bowls and the float levels look good. Switching bodies made no difference.
We swapped coils from primary to center cyl and that also made no difference. There seems to be an equal amount of spark in all 3 holes.
I asked Lectron which needles would be good to start with as a baseline and they said Metering rods should be 8-1XL. Adjustable power jets at 1 turn out to start. The sled has a 7 needle in it which should be leaner than the 8.
Oh one last thing. The idle set screws dont effect anything at all. The slides are high enough (from cable tention) that the set screws do touch the slides apparently. This should indicate that the slides are open more than normal at idle. If we do have a weak cyl they might have to be open this much to stop it from stalling.
Any thoughts on where we should look next?
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