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Slp 727 motor running poorly

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Jul 25, 2013
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So I just picked up a 08 iqr that was one of Ross martins old sleds, it has a 726 that has had the cylinders reworked and a 727 head put on. When I got it I could t get it to idle right, and no power on the bitten end, found out it had bad crank seals, so I tore it down, replaced crank seals, put it back together and it still won't idle, has 45 pilot jets and 350-360 mains, ( I ride at 6-8k feet) and running it in the shop it is boggy on the bottom but snappy mid to top, and if it idles for more than a few seconds it loads up and is super boggy. Also I noticed that running the engine for about 30 seconds the crank stub where the clutch goes is hot, like can't hold your hand on it for more than a few seconds hot, this doesn't seem right. Sound like a crank problem? I'm trying to decide what to do with this sled. I tried the only lower pilots I had from 45's which were 17.5's I know crazy difference but it didn't seem to make a difference in it loading up. I have also noticed this motor does seem to be a noisier, almost sounds a little like a knock, but when I had the cases apart changing seals I looked at each hearing and didn't notice any heat marks or anything
 
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sled_guy

Well-known member
Premium Member
Jul 5, 2001
3,566
843
113
Riverton, Utah
Ok, the hot crank end is NOT a good thing. I was going to guess a bad bearing or poorly lubed bearing causing that. Not easy to heat that much mass up that quickly, something is definitely not right. Do you know what year the motor? The early race motors were greased on the PTO bearing, not oiled is why I'm asking.

IF that PTO bearing is dragging it for sure can cause a poor idle. I've had sleds with bearings that were "sticky" (right before they seized :) ) that wouldn't idle. Everything else was fine.

Did you look the reeds over closely? One of the first signs of bad reeds, either not sealing good or ends flaking off, is that the sled won't idle and is a dog off idle when you crack the throttle.

sled_guy
 
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Jul 25, 2013
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Wellll

Turns out I got the wrong tq specs for the case halves and over torqued it a little and squeezed out any and all three bond so it was sucking air at the case halves, spilt and re sealed and letting sit and dry for two days this time, been real cold here. Hope this solves it, guessing hot crank could have been from being over torqued and running lean, inspected all bearing and crank and everything looks good, keeping fingers crossed:face-icon-small-con
 

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Jul 25, 2013
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Still not fixed

Okay still not right. Alright, so I bought a sled with a 600 ves motor that's built into a slp 727, when I got it it wouldn't idle worth a damn and had no bottem end power, found out it had bad crank seals. I tore it down, replaced crank seals, cleaned and re seAled the cases and rejected the carbs since someone tried to bandaid the lean condition with huge pilot jets. I then got it running and same thing, runs terrible, wide open it screams but won't idle at all and loads up and dies, if you pull the choke out halfway it will idle and run better but still boggy on the bottom to mid. I then found the case halves were sucking air so I re split the cases, re sealed, let the three bond cure for 3 days, then put together and same exact problem, I then swapped fuel pumps and noticed that the fuel pump seems to lose prime while running, when revving up a bunch of bubbles appear in the inlet side fuel like at the pump and then the fuel falls back to the tank for a few seconds then catches back up again. I'm at a loss, I'm ready to sell that 727 and buy a dragon 700 and convert it to carbs if I can't get this figured out, anyone experience this before?
 
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Jul 25, 2013
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Also it runs great from mid rpms, say 4000+ but with the choke off the minute you get under 4K it's drops off fasttt and then dies, pulled all jets out and blew air through all ports and they were all clean, ran all new fuel line, new floats, changed needle positions, adjusted air screw and fuel screw and nothing seems to make a difference in the way this sled runs, also pulled reeds and cleaned and checked for sealing and they looked great
 
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Jul 25, 2013
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Got it narrowed down to the carbs at least, changed out the carbs with some old separate keihn carbs off a 99 700 rmk I had Latin around and it runs great, now I'd like to fix my carbs since they are bored so time to try and figure out what could be causing this
 

sled_guy

Well-known member
Premium Member
Jul 5, 2001
3,566
843
113
Riverton, Utah
Ok, carbs are bored, let's start there.

For grins, make sure the needle jets were pressed back in correctly. The hood should be open towards the motor. I have actually seen them pressed in backwards. Do you know how big over the carbs were bored? Pull them off and take them in a dark room with a flashlight, shine the light in one side and make sure you don't see light around the sides of the sliders. If they were bored too big or done poorly then they won't be sealing around the edges and can cause leaking which will affect low RPM performance.

When you poked the Keihins on did your air bubble in the gas line issue stop? I ask because I have had several sleds in the past 2 years that the feed line in the tank was cracked/broken from having sit in Ethanol fuel... had to replace them. They would cause funky problems like bad running when the tank wasn't clear full or fuel starve problems.

sled_guy
 
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Jul 25, 2013
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Thanks! Yes the air bubble went away and it runs pretty good with the keihn's, just a little rich. I was just tearing into the minkunis and notices there is a gap on the sides of the slides large enough to put a toothpick through, thought that didn't seem right. I didn't have the carbs bored the sled came with them on it, which I find weird because a buddy owned it before me which he never could get it jetted right, but it didn't run that bad. And the guy before him owned if for years, I'm pretty sure running that setup, I guess he could have swapped carbs before he sold it
 

sled_guy

Well-known member
Premium Member
Jul 5, 2001
3,566
843
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Riverton, Utah
Sure seems like something in carbs, doesn't it? The air bubbles in the fuel line going away with the Keihens makes we wonder if there is a vacuum leak in the carbs or something.

I wonder if the TPS being out of wack could cause it?

sled_guy
 
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Jul 25, 2013
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Ok fixed the old carbs and they are back in and it's running, so the previous owner had tightened the fuel screws down too tight at one point and snapped the tips off both in the carbs, just happened to pull out the screws and had some spares laying around and notices these were a lot shorter than the others, drilled it out, put new fuel screws in and it's dialed now! Thanks for the Input guys!
 

sled_guy

Well-known member
Premium Member
Jul 5, 2001
3,566
843
113
Riverton, Utah
Woot, Woot!!!

I have had people do that to the fuel screws before, it is pretty easy actually, those tips are easy to break off.

sled_guy
 
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Jul 25, 2013
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So I finally talked with slp, ordered a new top end, pistons, rings, wrist pin bearings gaskets etc, decided to put it back to how I got the motor with two base gaskets stacked, because with a single gaskets the squish was tight, .025 -.029", checked ring end gap, came in at .018" which the specs I found online for 600's and 800's I believe we're .016-.022" so it was in spec, although Pistons seems a little loose, put it all together, fired it up, did 4 heat cycles, then checked compression cold and it was only 108-110 psi at 400' elevation....wtf... Thats what it was before the top end rebuild... Although I only had one base gasket in it roughly .019" conpressed and got like 108-110 psi, so with .040" base gaskets I'm still only getting 108-110 psi. This engine has had the cases decked and the cylinders decks and the specs that came with the motor said to run two base gaskets. I think the proper base gasket should be roughly .030" but do you think .010" would make my compression so low? Could it be rings arnt seated yet and will get better the more I break it in? Cylinders looked in good shape, no gouges out bad spots.
 
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Jul 25, 2013
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I mean it seems to run fine, havnt ridden it yet but I'm half tempted to pull a base gasket and just run a single base gasket. 110 psi seems crazy low, I mean old school non ves motors were 120 at least
 
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w browning

Member
Mar 21, 2009
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Might want to try another gauge, I have seen some of the lower quality gauges that read 15 to 20 lbs low. Pat
 
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