94 GTX Low Speed Acceleration Issue

[wabash]

I have a strange issue I'm trying to figure out. I have a 94 GTX (657). 100% stock. Motor was rebuilt last year with a reman crank SBT pistons and rings and bored stock jugs to match the new pistons. I did all the work myself except the machine work and the crank. I have a fair amount of experience with this, I have one other 94 GTX I rebuilt and have done several Rotax motors in Ski Doo s as well as many other motor rebuilds over the years. Rebuild the carbs with Oem parts from OSD. So on and so on. I guess what I'm saying is that this wasn't just a quick cheap rebuild, more of a well educated restoration.

I have read thru Bills86 post on carb adjustments many times. Good stuff. And I've had the carbs back apart twice to double check everything. So I'm missing something here.

Here's my phenomenon. Acceleration from a standing start in a straight line is good. Seems to be matched to my other GTX. No funny business nice and clean. Acceleration from a slow cruise is also just fine. Top end is great as well. Pulls nice. Good top speed.

BUT when I take it into a tight right hand spin and try to pull the nose up out of the water it feels like it has no power. Slam on the throttle and it struggles to build revs like it's got one heck of a load on it. Motor pulls clean its just like it has a huge load on the prop. The other GTX will pull this maneuver just fine.

anyone got any suggestions?

 

[Mickirig1]

Did you read OSD's section on carbs on the web site? I think the problem was addressed in it. Between this forum and OSD's I have read about it somewhere.

 

[wabash]

Yes I have read thru the info on SeadooSource Several times. I understand carb tuning pretty well. Not sure this is a carb issue as it seems to accelerate fine under light load. It's when under heavy load it has issues. If it is a carb issue it appears it may either be in the main jet or transition circuit and it would be I suppose a slightly lean condition. I'm just sure the carbs are perfect tho. I've been thru them a couple of times.

Just looking for ideas to find something I didn't think of. I've searched the forum several times and I didn't find what I was looking for or at least didn't know it when I saw it.

 

[hotrodssnova]

Is your pulse line clamped tight?

 

[wabash]

Hey that's a good thought. I used a zip tie as the bottom clamp on the pulse line cause it's a bugger to get to and I didn't have any more spring clamps. Put a worm clamp on top. The other GTX I used two spring clamps. I will definitely change that. I think m gonna pull the carbs one more time. Anyone else got any suggestions. Oh and thanks nova, how's your GTX coming along?

 

[Mickirig1]

Did I mention to check your entire fuel system for air leaks? I chased issue like this and it was the gasket on the water separator.

 

[wabash]

Funny you bring that up. Just got in from the shop where I did a pressure test on the fuel system and guess what? Major air leak at the fuel cap. Couldn't even build any pressure. I took the cap off and put it back on and built some pressure maybe a pound or two and pressure started coming out the inlet vent. Yes I had the pressure relief vent line pinched. So 1 I have an intermittent bad cap and 2 not sure about air leaking from the inlet vent. Should it do this? Shop manual says to build to 5 psi and hold. I didn't get to 5. The system would hold maybe 2 psi any higher and it would leak thru the vacuum relief in the inlet vent.

 

[Mickirig1]

It's easier to suck air then fuel. I chased an air leak for a month. Found a bad gasket on water separator. Once it was bypassed the ski ran great!

 

[wabash]

I'm assuming the check valve in the vent line is bad? It shouldn't be relieving pressure at 2 psi right? The relief valve did pop off correctly then I pinched that line off. The check valve is in the vent that goes up high by the steering post right?

 

[wabash]

Question. I've read where the 1 psi or so allowed build up of pressure in the fuel tank helps feed the carbs. The air leaks I've found so far, gas cap and check valve, would not leak air into the fuel system per se but would prevent the build of pressure in the tank. Is this really an issue or do I need to look further?

 

[Mickirig1]

It's easier to suck air then fuel. It's all inter connected to create pressure with fuel fumes. So you are not replacing the gas used with air from off the water. I think this is the design intention

 

[wabash]

Ok I have the fuel system good and tight. Never did find any leaks in any of the fuel lines just the cap and the vent system. The only issue I can see is it would not have built up any pressure in the tank. I put some spring clamps on the pulse line however I think the zip tie was doing just fine. Checked the cooling hoses, removed the two calibrated 90 deg elbows where cooling water is injected and drawn off the pipe. That all looked good. The spark plug boots looked to be original so I ordered some replacements. When I took the old ones off one was split at the mold mark. Both didn't look to have the best contact with the wire so I cut some off the wires to get to clean wire. I'll get that all back together and see what it does.

 

[beergut]

just a shot here... I had a similar issue with my 2000 gtx- every time I turned right, the ski would really slow down and struggle, but if I kept the bars straight, it was a rocket- turned out I had a cracked nozzle and it was impeding the water flow- couldn't visually tell out of the water- then one day I was pulling on the nozzle for no good reason and it pulled apart. fixed the nozzle and it sailed like new again

 

[wabash]

I think I may have found the issue. I had checked compression on this motor a few times to make sure the rebuild was setting in good and it has been a consistent 140psi. I didn't think much of it 140 isn't a bad number. But out of curiosity I checked my other GTX and it showed 160. I knew there wasn't a failure issue with the one showing 140 because both holes were the same and it didn't change much. So I thought what could cause this and remembered that on this machine I exchanged the original cylinders for refinished ones so what if the shop exchanged me the wrong cylinders? Sure enough the casting numbers are different from the originals on my other machine. After much investigation on the web I come to find out they are 657x cylinders and are 1mm taller. The 657x head has the squish bands set 1mm lower to make up the difference apparently the combo results in the piston not coming as close to the top of the bore and helping with ring wear... But anyway the combo of 657x cylinders and a non x head results in lower compression. So it looks like I can correct the whole mess with a 657 X head.