2016 turbo overheating when in boost. Headshim?

[zx4ever]

So I purchased a 2016 viper turbo this summer off a guy. I have not had any good luck with it so far. First ride out it Vapor locked on me and took some time to start. Had to pressure the tank up to get it to go. So I added heat shield and venting to the side panel and fuel line covers to keep the heat down and seemed to work, but could have been the outside temp was cold the 2nd time out. But now the sled is running super hot and going into limp mode on climbs. In a foot of fresh at about 12 lbs of boost. The old owners said the sled had the boost it kit with Carrillo rods and low compression pistons. While I was inspecting I noticed and measured it has a .66 head shim. So that makes me wonder if it also has low compression pistons? All my reading on here points to head shim leak. So I did a leak down test on the cylinders and it was 2% on 2 of them and 3% on the other. I also did a compression test and they were all 170 lb which I’m not sure is in range with the head shim and pistons or just headshim. Anyone have any numbers of what they have with just head shim? While I was doing a leak down test there was no air bubbles in coolant and colour of coolant is good. Could a major air lock cause these problems under boost? As on the trail in low snow conditions the temps are good and the fan kicks on and cools it off. Any other ideas on what I should test before I tear into this motor?

 

[zx4ever]

Here are the pics and specs if anyone recognizes it

 

[Lunch_Box]

Why not give Chad a call at CR Racing and see if he can give you a run down on the sled.

 

[climbmax]

I dont think you have an engine issue. Its likely more of a coolant issue. They could be bugger to "burp" in the past. Try flipping this thing on each side many times. Listen for it burping cause Im pretty sure it will. Or get a system refiller for your coolant to really work it well.
I know most of the sleds Chad has built but don't recall this one. Sounds like it may be more of a Boost It Build if it has built motor. They did several of these. If your on a climb I doubt it would be overheating with Fresh snow on the cooler. If it goes into limp then good chance its low on oil as they have a very sensitive Oil pressure switch. You need to run a little bit extra oil to help this. Also check to see if there is a "pigtail" on the oil pressure switch on the bottom of motor. Just drop the inspection plate. Boost it was known for tricking the oil pressure switch with this pigtail and resistors to avoid the limp mode at super vertical chute climbing attempts. If its hanging there just make sure you always run a tether and pull it if the sled is on its side or upside down. Otherwise big damage could occur.
Chase your cooling thing first and the rest will come into play. If its a built motor then Chuck at Lakeside would have built it. Could possibly have Low comps. He is a master of these engines.
Good luck in your efforts.
RS

 

[zx4ever]

Why not give Chad a call at CR Racing and see if he can give you a run down on the sled.

Tried this already. Thanks for the suggestion.

 

[zx4ever]

I dont think you have an engine issue. Its likely more of a coolant issue. They could be bugger to "burp" in the past. Try flipping this thing on each side many times. Listen for it burping cause Im pretty sure it will. Or get a system refiller for your coolant to really work it well.
I know most of the sleds Chad has built but don't recall this one. Sounds like it may be more of a Boost It Build if it has built motor. They did several of these. If your on a climb I doubt it would be overheating with Fresh snow on the cooler. If it goes into limp then good chance its low on oil as they have a very sensitive Oil pressure switch. You need to run a little bit extra oil to help this. Also check to see if there is a "pigtail" on the oil pressure switch on the bottom of motor. Just drop the inspection plate. Boost it was known for tricking the oil pressure switch with this pigtail and resistors to avoid the limp mode at super vertical chute climbing attempts. If its hanging there just make sure you always run a tether and pull it if the sled is on its side or upside down. Otherwise big damage could occur.
Chase your cooling thing first and the rest will come into play. If its a built motor then Chuck at Lakeside would have built it. Could possibly have Low comps. He is a master of these engines.
Good luck in your efforts.
RS

Thanks Randy. I am wondering if it does have air in system. I am going to get one of the vacuum coolant tools and try it. As for the oil pressure switch I don’t think that was it cause my overheat light kicked on and fan was going but I will definitely keep that in mind. Does anyone know what compression just a head shimmed motor would be? Wouldn’t having a shim and low comp pistons be really low compression?

 

[zal]

If I remember right, and Randy might be able to attest to this, later Vipers had different connecting rods that did not handle boost well. Unlike the early Yamaha motors. Hence why they installed Carrillo rods and pistons.
As for the headship, they installed a headshim so you can use pump fuel (premium) instead of mixing with av gas/C12 etc. you could safely run 290HP on an Apex motor with a headshim on pump fuel.