Help with new ski compression issues

[mdemco]

Ok... I just bought a 98 rn.

It has -

A factory type 4 dry pipe
msd water injection
bored carbs
maybe an enhabcer
maybe a milled head
has a race port and polish job
supposedly was built to the nuts but who knows???

Now today I went and rode it for the first time, it hauls ass, has decent bottom end and the top end is insane. Reminds me of a banshee with a light switch power band. Keep it in the band and it is insane. I felt the bottom end was crap though, I want the ski for flatwater freestlye so assume I need all bottom end.

I got home and for curiosity sake I checked the compression and it was 115. I wet tested and it jumped to 150. So I think it needs a top end.


What would I do to get more bottom end. Should I tear it down, look at the porting and just put it back together with a fresh bore. Or maybe sell all the pipe and water injection, buy a b-pipe etc?

Also would anyone know if I should dump the water injection? Can I make this setup better or just plan on dumping that stuff? I also have a protec head and R&D intake sitting in a box, these worth anything on the ski?

Thanks for any opinions, the goal here is bottom end BRAP!!!

 

[Speedfreak]

Sell that pipe and the water injection and look for a B pipe or a Speedwerx Freestyle pipe while you are doing a top end on the ski. Make sure it has a MSD enhanser and not a modified cdi.

When it goes back together bump the compression to about 185 and your bottom end will be there. Along with boring the nozzle and sending the prop off to Impros to have it pitched down to a 12-15.

If that was a race ski I would check the prop first thing... well that and you need a top end... Or I would install the Protec head first to see what you get. You might be able to ride it this way this year and do the rebuild over the winter

 

[Mouthfulloflake]

dont tear it down.

if its running well, why would you possibly tear it down?

 

[mdemco]

On the box for the prop that came with it it says it is a kawi prop, I could not remember if the pumps were the same in the SJ, or if this is just the wrong box. But it is a skat swirl 750/900 with a 14/19 pitch. Maybe this is a top end prop?

On tearing it down, I would think if I I put on the protec head the compression would bump. But in doing so it would blow the rings completely. But maybe I am wrong. I cant believe it runs like it does and has such low compression.

If I do tear it down should I switch the intake to the R&D one? Or sell it and my dual bored carbs setup for a single carb for bottom end?

Any help is greatly appreciated, if I do tear it down I want to do it now, the season is still early and the lake cold, now is the time.

 

[Mouthfulloflake]

if its running that good, it has more than 115 psi of comrpession, I wouldnt trust your guage.

that is a kawi impeller ( the 750/900 part leads me to think this)

kawi impellers dont fit yamaha pumps, so youve got something wierd there, probably the wrong box.

 

[mdemco]

Is the pitch marked on the prop? If the prop is a top end prop I would try and swap it.

On the gauge it show 145 on my buddies 650, today I will go buy a new gauge and recheck it, but I feel it may be accurate.

 

[Speedfreak]

Hook your gage to your air compressor and chech that gage try to borrow a gage from a shop or something before you buy a new one yours might be right. I would put the protec head on to see what the compression is.

Id the intake grate a top loader, does it have a fin in the middle of it. If so then you want that one. What is on there now?

The rings will be fine, the dual carbs will be fine and pull the prop it will either have markings on it or it is stock which needs replaces anyhow.

 

[mdemco]

The intake grate is a protec. I know because it is bright purple, I am not sure which style. I will pull the prop and put the protec head on and double check compression. I think I should dump the pipe and water inejction, prolly on ebay.

 

[tor*p*do]

get a new compression gauge! :biggthumpup: