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Old school LEAFER carb Turbo! Looking for help tuning…
This project started out for fun but has quickly turned into a challenge to say the least. I built it for an event a bunch of buddies and I put on where we lake race old school leafers in the UP of MI. Most guys slap in a 670 Rotax, 700 Polaris, 800 doo’s, 800 Liberty’s, 900 cats, etc., and I’m sure there will be at least 1 Mach 1000 motor or Cat 1000 next year and plenty on spray so me trying to do something different has quickly become a slight addiction but I believe it’s close to being a ripper now. Don’t know if it will compete with a 1000 but I’m going to try, might need a little more motor. After some initial bugs (as expected) it runs fairly good. It pulls harder than this setup would be without boost, but not by much currently. Feels like a sluggish modern 600 twin (backup trail sled is an XP600). I hit 83mph gps on ice. OK with me she just needs to get there quicker. On packed snow it only gets up to about 70 with a poor holeshot, nice midrange then flat again. Not ok, it needs more power. Overall, she moves ok but I know just not right on the fueling and perhaps clutching yet. Below explains the build and I attached some pictures I took along the way. Let me know what you think I should try next!
1981 El Tigre 5000, had a scorched jug, so tore it down to the tunnel and steering. Had plenty of 6000 parts just not a good sled so this was born.
Arctic Cat 530 liquid case reed motor, no exh power valves in the 80’s on these twins. Boysen reeds. 130ish psi per cylinder with new oem top end. Rebuilt the bottom end as well and built a custom plate to keep the mag side seal in. PTO side already had a nice plate stock. Oil injection removed, bottom end fully sealed. Should be about an 80hp motor at 8k with the single pipe I have on there. Starts first pull.
Comet 108EXP Clutch - Rebuilt, using a yellow spring with about a 4800rpm engagement point. Weights are currently Type K1, 59.7 gram each. Stock was 48-49 gram range. The ramp shape appears similar? I tried stock first, and these K1’s were the heaviest (heavy tip too) I could find and they helped a ton, before adding weight she would not yank my arms in the midrange. I have confirmed the belt is fully running out on the clutchs yet I’m only turning 7500rpm WOT though? Was hoping to get to 8K so I may need to make some changes. Clutching is not my strong suit.
Gearing: Was 39 lower/24 upper=1.625 and I went as steep as I could at 42/21=2.0.
Stock reverse cam roller secondary with the stiffest spring I could find that could fit. Its orange (HPE maybe), 53deg helix, steepest I could find. Have a 45 and a few less stiff springs if needed.
Stock ¾” track studded, stock suspension rebuilt, added plastic ski skins. All works well, traction is ok. Rolls nicely. All new bearings, etc. I can slap something better under there if I start making some real power but the stock setup rolls nice and with the track flipped backwards it hooks fairly well but I have a weak bottom end so makes sense.
Turbo is a GTX2867R Gen II with internal wastegated .064 A/R turbine. Adjustable wastegate. No boost controller hooked up currently. It builds boost well and holds. 0.5bar spring currently. AEM gauge says 7-8lbs, plumbed from compressor. Basically the same reading in airbox as well. Ceramic ball bearing. I know it seems big but this will flow less than a GT2860 stable, can flow a ton more too. I’m not surging. Turbine might be a little big as well but it builds boost 20ft off a launch so its not that bad? I really should go pro my gauges on a pull to see what the pressure differences are real time. Can’t build boost before a launch even with the recirc valve open just prior to clutch engagement with a warmed up pipe. It’s what I had available but I don’t think is my problem. It’s a nice turbo lol.
Oil system is a 24V Graylor with 1mm orifice. eBay scavenge pump to a vented tank. Works well, gives the ball bearings what they need, shaft seals don’t leak.
eBay Intercooler and 2” piping. Would have been way less painful and a much shorter run to skip the IC but it did start sort of as a joke and I do plan to crank it up eventually. Already cut holes in the hood lol.
Custom airbox, largest that would fit. Ports to feed boost to each carb bowl (through the vents already in the carb) as well as ports to feed to the top of each round slide to help throttle shutting under boost. Vito’s Power jets plumbed from the main jet cover nut.
BOV, one of those adjustable ones that can also blow off to atmosphere or split it. Cut the spring so its open before the clutch engages and closed under boost. Plumbed to a T into each carb just before the boots. Works well, I don’t really feel any difference except when its turned off (put in a ball valve), it will run on (Scary AF!) so I know it’s working.
Fuel system is MSD 2225 with Mallory 2309 1:1 regulator with the source off the center of the pipe. It works well. Running 3psi base (might be my issue?) and my gauge shows this rise further with the blip of the throttle and even though it gets blurry I see it rising with boost, definitely over 10psi so I know its working correctly. Again, I really should try to get some more accurate numbers with a go pro or multiple pulls looking at one thing. EFI and datalogging would be nice but where’s the fun in that.
Carbs are Mikuni VM-38’s with Power Jets about 1/3rd the way into the inlet. Pic below. Ignore the backwards carb boot, you are looking into the carb.
6DH8 Needles - with the clip all the way down now (leanest). Started in the middle and it got peppier each time I lowered. I don’t know if a different needle will help. I have some 6DH4’s
30 Pilot Jets – Carbs had 25’s but it idled high on those and I could not get my AFR to even register. Blip the choke and you see it work but the AEM had ---. Switched to 30’s got it to idle nice and sit around stoich to 15.5ish at idle depending on temp. This might be part of my fueling problem.
280 Main Jets – Stock was 370 and it would not even move in my garage on a warm day. AFR’s over 10. Switched to 310s and AFR’s were better (low 11’s) and it cleaned up but was still fat down low. Down to 280’s could get it to run in the 12’s just about everywhere. Goal is to run 14.5 part throttle, 13.5 half, and 12.5 WOT. I can only achieve the 12.5 WOT but it feels a little flat. AFR does bounce around a bit at times when WOT (lean spikes?). EGT's about 1050F which seems low. Perhaps my expectations are too high on 7-8lbs with a 530 or I have to get the rest right. I could turn the boost up but would prefer to get it running better first. I have a 0.8bar spring ready. This is why I intercooled it btw. Plan to run more boost eventually.
Clutches are aligned, I have a fancy tool a buddy made.
Cooling system is an XS 800 etec 120” heat exchanger flipped backwards to clear the fuel tank. I had one lying around. Keeps her steady in the 130’s up to about 140F with a 50C thermostat (122F). Stock it would run a little cooler close to 120F but I doubt 20F hotter is my issue. Stock had a radiator as well as two smaller tunnel coolers. I could add the rad back fairly easy if needed.
Pressure tested entire system air filter to downpipe 15psi, no leaks except out my throttle cable at the carbs. There is fuel on top of the carbs after running in boost. Rest of the bay is clean and dry. I doubt this was my issue as during the leak test it could hold pressure fine, it holds boost solid at WOT as well. Was thinking Teflon tape to help.
Fuel: Running a mix of 40:1 Redline with 3 gal E90 and 2 gal 110 leaded race gas = 98 Octane.
Runs best with Power jets turned out 1 to 1.5 turns. In further it gets too lean (according to AFR) and runs/feels worse as well. Out too much and it won’t clean up at WOT. It also runs very fat at part throttle, let’s say it makes a few pounds at 25% throttle but AFR in the high 11’s. Was in the low 11’s when I had 310’s in and mid clip position. Half throttle to maybe 2/3rds it runs fairly good and pulls hard. Its maybe in the mid 12’s AFR. EGT’s close to 1100F. ¾ throttle to WOT it does not pull much harder but AFR can be controlled anywhere I want with the power jets. I would say it runs best about 1 turn to 1.5 turns out (temp dependent) to get AFR around 12.5. The odd thing is that EGT’s are similar to part throttle maybe a little lower at 1050F vs. 1100F. I pretty sure this motor would run 1250F at WOT before being boosted so I’m a little confused. Same thermocouple locations.
Next Steps:
This project started out for fun but has quickly turned into a challenge to say the least. I built it for an event a bunch of buddies and I put on where we lake race old school leafers in the UP of MI. Most guys slap in a 670 Rotax, 700 Polaris, 800 doo’s, 800 Liberty’s, 900 cats, etc., and I’m sure there will be at least 1 Mach 1000 motor or Cat 1000 next year and plenty on spray so me trying to do something different has quickly become a slight addiction but I believe it’s close to being a ripper now. Don’t know if it will compete with a 1000 but I’m going to try, might need a little more motor. After some initial bugs (as expected) it runs fairly good. It pulls harder than this setup would be without boost, but not by much currently. Feels like a sluggish modern 600 twin (backup trail sled is an XP600). I hit 83mph gps on ice. OK with me she just needs to get there quicker. On packed snow it only gets up to about 70 with a poor holeshot, nice midrange then flat again. Not ok, it needs more power. Overall, she moves ok but I know just not right on the fueling and perhaps clutching yet. Below explains the build and I attached some pictures I took along the way. Let me know what you think I should try next!
1981 El Tigre 5000, had a scorched jug, so tore it down to the tunnel and steering. Had plenty of 6000 parts just not a good sled so this was born.
Arctic Cat 530 liquid case reed motor, no exh power valves in the 80’s on these twins. Boysen reeds. 130ish psi per cylinder with new oem top end. Rebuilt the bottom end as well and built a custom plate to keep the mag side seal in. PTO side already had a nice plate stock. Oil injection removed, bottom end fully sealed. Should be about an 80hp motor at 8k with the single pipe I have on there. Starts first pull.
Comet 108EXP Clutch - Rebuilt, using a yellow spring with about a 4800rpm engagement point. Weights are currently Type K1, 59.7 gram each. Stock was 48-49 gram range. The ramp shape appears similar? I tried stock first, and these K1’s were the heaviest (heavy tip too) I could find and they helped a ton, before adding weight she would not yank my arms in the midrange. I have confirmed the belt is fully running out on the clutchs yet I’m only turning 7500rpm WOT though? Was hoping to get to 8K so I may need to make some changes. Clutching is not my strong suit.
Gearing: Was 39 lower/24 upper=1.625 and I went as steep as I could at 42/21=2.0.
Stock reverse cam roller secondary with the stiffest spring I could find that could fit. Its orange (HPE maybe), 53deg helix, steepest I could find. Have a 45 and a few less stiff springs if needed.
Stock ¾” track studded, stock suspension rebuilt, added plastic ski skins. All works well, traction is ok. Rolls nicely. All new bearings, etc. I can slap something better under there if I start making some real power but the stock setup rolls nice and with the track flipped backwards it hooks fairly well but I have a weak bottom end so makes sense.
Turbo is a GTX2867R Gen II with internal wastegated .064 A/R turbine. Adjustable wastegate. No boost controller hooked up currently. It builds boost well and holds. 0.5bar spring currently. AEM gauge says 7-8lbs, plumbed from compressor. Basically the same reading in airbox as well. Ceramic ball bearing. I know it seems big but this will flow less than a GT2860 stable, can flow a ton more too. I’m not surging. Turbine might be a little big as well but it builds boost 20ft off a launch so its not that bad? I really should go pro my gauges on a pull to see what the pressure differences are real time. Can’t build boost before a launch even with the recirc valve open just prior to clutch engagement with a warmed up pipe. It’s what I had available but I don’t think is my problem. It’s a nice turbo lol.
Oil system is a 24V Graylor with 1mm orifice. eBay scavenge pump to a vented tank. Works well, gives the ball bearings what they need, shaft seals don’t leak.
eBay Intercooler and 2” piping. Would have been way less painful and a much shorter run to skip the IC but it did start sort of as a joke and I do plan to crank it up eventually. Already cut holes in the hood lol.
Custom airbox, largest that would fit. Ports to feed boost to each carb bowl (through the vents already in the carb) as well as ports to feed to the top of each round slide to help throttle shutting under boost. Vito’s Power jets plumbed from the main jet cover nut.
BOV, one of those adjustable ones that can also blow off to atmosphere or split it. Cut the spring so its open before the clutch engages and closed under boost. Plumbed to a T into each carb just before the boots. Works well, I don’t really feel any difference except when its turned off (put in a ball valve), it will run on (Scary AF!) so I know it’s working.
Fuel system is MSD 2225 with Mallory 2309 1:1 regulator with the source off the center of the pipe. It works well. Running 3psi base (might be my issue?) and my gauge shows this rise further with the blip of the throttle and even though it gets blurry I see it rising with boost, definitely over 10psi so I know its working correctly. Again, I really should try to get some more accurate numbers with a go pro or multiple pulls looking at one thing. EFI and datalogging would be nice but where’s the fun in that.
Carbs are Mikuni VM-38’s with Power Jets about 1/3rd the way into the inlet. Pic below. Ignore the backwards carb boot, you are looking into the carb.
6DH8 Needles - with the clip all the way down now (leanest). Started in the middle and it got peppier each time I lowered. I don’t know if a different needle will help. I have some 6DH4’s
30 Pilot Jets – Carbs had 25’s but it idled high on those and I could not get my AFR to even register. Blip the choke and you see it work but the AEM had ---. Switched to 30’s got it to idle nice and sit around stoich to 15.5ish at idle depending on temp. This might be part of my fueling problem.
280 Main Jets – Stock was 370 and it would not even move in my garage on a warm day. AFR’s over 10. Switched to 310s and AFR’s were better (low 11’s) and it cleaned up but was still fat down low. Down to 280’s could get it to run in the 12’s just about everywhere. Goal is to run 14.5 part throttle, 13.5 half, and 12.5 WOT. I can only achieve the 12.5 WOT but it feels a little flat. AFR does bounce around a bit at times when WOT (lean spikes?). EGT's about 1050F which seems low. Perhaps my expectations are too high on 7-8lbs with a 530 or I have to get the rest right. I could turn the boost up but would prefer to get it running better first. I have a 0.8bar spring ready. This is why I intercooled it btw. Plan to run more boost eventually.
Clutches are aligned, I have a fancy tool a buddy made.
Cooling system is an XS 800 etec 120” heat exchanger flipped backwards to clear the fuel tank. I had one lying around. Keeps her steady in the 130’s up to about 140F with a 50C thermostat (122F). Stock it would run a little cooler close to 120F but I doubt 20F hotter is my issue. Stock had a radiator as well as two smaller tunnel coolers. I could add the rad back fairly easy if needed.
Pressure tested entire system air filter to downpipe 15psi, no leaks except out my throttle cable at the carbs. There is fuel on top of the carbs after running in boost. Rest of the bay is clean and dry. I doubt this was my issue as during the leak test it could hold pressure fine, it holds boost solid at WOT as well. Was thinking Teflon tape to help.
Fuel: Running a mix of 40:1 Redline with 3 gal E90 and 2 gal 110 leaded race gas = 98 Octane.
Runs best with Power jets turned out 1 to 1.5 turns. In further it gets too lean (according to AFR) and runs/feels worse as well. Out too much and it won’t clean up at WOT. It also runs very fat at part throttle, let’s say it makes a few pounds at 25% throttle but AFR in the high 11’s. Was in the low 11’s when I had 310’s in and mid clip position. Half throttle to maybe 2/3rds it runs fairly good and pulls hard. Its maybe in the mid 12’s AFR. EGT’s close to 1100F. ¾ throttle to WOT it does not pull much harder but AFR can be controlled anywhere I want with the power jets. I would say it runs best about 1 turn to 1.5 turns out (temp dependent) to get AFR around 12.5. The odd thing is that EGT’s are similar to part throttle maybe a little lower at 1050F vs. 1100F. I pretty sure this motor would run 1250F at WOT before being boosted so I’m a little confused. Same thermocouple locations.
Next Steps:
- Wait for snow again! Early MI spring!
- Jetting is off. Back to 25 pilots? I need to mess with the idle screw again perhaps. Other thoughts?
- Base fuel pressure may be too low?
- Clutching off still. I have a bunch of other less stiff springs and lower weights if needed. Take out weight, less stiff primary spring, Wind up the secondary some more?
- Geared out?
- Adjust timing?
- Something hooked up wrong or causing a problem?
