Loss of power loss of top end 1994 V-max 600

[nosnownogo!]

A recent loss of power and top end forced me to do a compression test and found 90psi in each cylinder. I pulled the jugs and found blow-by on both pistons. The blow-by is on both sides of both pistons.. but not on the intake or exhaust sides, is this normal? Why would it seem to be just on the sides?
pistons and cylinders look great. Does anyone know what the ring end gap should be on this sled? Ive seen posts that state the compression should be about 150 is this right? When I replace the rings should I also do the head gasket mod? and how about rejetting, will I have to re-jet?

1994 V-max 600
GYTpipes
152 mains

Please help!!!!!
This is one Yamaha that has a real need for speed......

 

[daman]

A recent loss of power and top end forced me to do a compression test and found 90psi in each cylinder. I pulled the jugs and found blow-by on both pistons. The blow-by is on both sides of both pistons.. but not on the intake or exhaust sides, is this normal? Why would it seem to be just on the sides?
pistons and cylinders look great. Does anyone know what the ring end gap should be on this sled? Ive seen posts that state the compression should be about 150 is this right? When I replace the rings should I also do the head gasket mod? and how about rejetting, will I have to re-jet?

1994 V-max 600
GYTpipes
152 mains

Please help!!!!!
This is one Yamaha that has a real need for speed......

No..i wouldn't do the head gasket mod that sled with stock HG should have
150-155 stock(thats what our 2 have)Yammie used a thin HG back then.

Ring end gap should be/

top rig/ .45-.60mm(.0187-.024 in)
bottom ring/ same

How many miles on the sled and what kind of oil has it seen?
If you have the $ you may want to do pistons too wile your in there.

not shure on the jetting,,I like stock sleds...there fas enough

 

[nosnownogo!]

Thanks for the info daman, never had synthetic though her. The sled has about 13000kms on it. Everything looks perfect other than the blow-by. Have you ever seen blow-by on the sides of a piston like that? Could the pistons or the cylinders be out of round? I dont know , think i'll just get her honed and install new rings and see what happens.

 

[crewchief47]

Thanks for the info daman, never had synthetic though her. The sled has about 13000kms on it. Everything looks perfect other than the blow-by. Have you ever seen blow-by on the sides of a piston like that? Could the pistons or the cylinders be out of round? I dont know , think i'll just get her honed and install new rings and see what happens.

I'm not sure if this is the case or not, but in automotive engines, they make the piston 'out of round' to begin with. They do this so that it ends up round after it expands from heat.(one axis expands more than the other) If they do this in sled pistons, and it is the pin axis that is smaller cold (can't remember which one, put pin makes sense in my head) then the blow by when its cold would be on the sides.

Of course, my mind is like teflon, nothing sticks to it, and I could be remembering poorly.

 

[nosnownogo!]

Well I dropped $300.00 in the old girl on the weekend and changed the rings, gaskets and a defective thermostat. I honned the cylinders and reassembled her. Like I've noted before that everything looks great pistons cylinders and reeds. I trail tested it,and was soon to find that the problem was still there...... So now I when reaching at straws and removed the pipes and installed the original exhaust and VIOLA!!! she's back,.....sled revs to 8000 again. I looked at and in the pipes and cannot see anything, I've blown the out with air and they don't seem to be plugged. Has anyone ever seen this before? and how can I clean these pipes?

 

[daman]

So now I when reaching at straws and removed the pipes and installed the original exhaust and VIOLA!!! she's back,.....sled revs to 8000 again.

i'd just leave the stock pipe on,, if she's running good why mess with it!!

"Stock Rocks"

 

[Exciter570]

Are you clutched properly for the pipes? You can not run stock clutching with the pipes.

For the GYT twin pipes your engagement RPM should be at 3900 rpm and calls for a pink-pink-pink primary spring with 2 primary spring shims. At WOT your rpms should be at 8300.

As for jetting, if I remember correctly, you should be running 162.5 mains (don't quote me on that) and you MUST update your nozzle jets to Q-8's, get rid of those Q-6's that are in there now otherwise you're asking for a burn down.

You also need to put a 13.9 rivet on the inner hole and leave the outer hole open.

Your air screw should be 2 turns out.

Yamaha updated the tuning specs on these pipes about 1000 times from what I understand. I have a '95 600 with GYT's on it and it shifts up to 8300-8500 rpms just fine. The only top end loss I noticed was due to the '03 RX-1 long travel skid that I put underneath.

Do a search for GYT twin pipes and you will come across a few posts with a scan of the Yamaha tuning specs from the latest update they did.