'98 Exciter 270HP Top End Rebuild Kit/Questions

[ltjackson]

Morning everyone!

I've been following various forums for this jetboat/PWC engine for some time and I've also posted on there. But I wanted to bring this over to the iboats crowd because I seem to get a faster response. Anyway I have a 1998 Yamaha Exciter 270HP twin engine jet boat that I recently did a compression check on. The compression of the starboard engine on all three cylinders was around 100-105psi. The compression of the port engine on all three cylinders was around 95-100psi.

Needless to say it's low and I need to rebuild them. I don't want to buy another boat and I figure it will be cheaper all around if I just do a top end rebuild but I've never attempted anything like this on marine engines. I have quiet a bit of knowledge on engines in general but I figured I might as well ask my questions to the experts. So far the only thing I've found is this,

http://www.watercraftsuperstore.net/yamaha-top-end-kit-1200-npv-gp-xl-suv-exciter-pwc.html

It matches the engines I have now (1200 non-PV). Is this the only kit I'll need to rebuild one of the engines? I know I'll have to purchase 2 whole kits for the boat but I just wanted to make sure I was ordering the right equipment. Also on a difficulty scale how difficult of a job am I looking at? I also see that is has a size selection of "standard, 0.5, 1.0, 1.5" which I'm assuming is the bore size if I need to do any cylinder work.

Any and all help is greatly appreciated guys!

 

[jester31]

I don't know what specs are needed for compression on your jet boat, but I had a 96' Waverunner 1100 cc 3 str. that had 110 compression all around, and after reading the posts on a jetski forum, I found out that this was normal on an older ski. I never worried about it because the ski always ran good, with no loss of power. I could do 54mph with my 200lb butt on it, no problem.

Just a suggestion, have you tried using SeaFoam engine spray first, to see if you can get rid of some of the carbon buildup, & gain some compression.

 

[ltjackson]

I have not, what exactly are you talking about? I've never heard of SeaFoam.

 

[sixfigures]

The most important thing is the compression for the cylinders is close and not all over the place, your numbers are ok, I would not rebuild those engines, Until you have a cylinder that is at or below 80 p s I. Also remember each gauge is different, also while doing a compression test you need the throttle wide open.

 

[ltjackson]

How much of a difference would the throttles make? I didn't have them up at all.

 

[sixfigures]

Allows more air in you can't compress air if it can't enter the cylinder.

 

[jester31]

This will help break down, and get rid of excess carbon in your engine. Depending on how much carbon is there, it can help increase compression. It will also clean up any fuel system gunk as well. You might need to replace your plugs after a good cleaning, but it is well worth it!

http://seafoamsales.com/

 

[jester31]

Here's a similar product that works the same way: http://forums.iboats.com/forum/engi...-tohatsu-nissan-outboards/8533785-power-tuner

CRC has been around for years as well, I've used some of their products, not so much this one, but have been very pleased with them.

Whatever floats your boat!

 

[ltjackson]

So how do I use this seafoam stuff? I got 2 bottles of the engine cleaner that says marine on the bottle. From what I can find all I need to do is warm the engine up to operating temp, then pour a little down each of the spark plug holes. Reinstall the plugs and let it sit for a few days then crank it? Or is that wrong?

 

[jester31]

Sea Foam is made to be sprayed into the carbs liberally with the engine running, probably CRC is used the same way. Once soaked well, let the engine sit, & soak overnight, then start it up, & run it like usual. I'm sure there's directions on the label!

 

[ltjackson]

Sea Foam is made to be sprayed into the carbs liberally with the engine running, probably CRC is used the same way. Once soaked well, let the engine sit, & soak overnight, then start it up, & run it like usual. I'm sure there's directions on the label!

Thats the thing, there is no instructions or directions It's not the spray can of SeaFoam its the bottle....

 

[jester31]

Are these SeaFoam bottles? If so, how big are the bottles.

 

[ltjackson]

They are 16oz bottles that look like this,

 

[jester31]

No directions? Jeez! I've used the spray cans myself, no problem? IMO, I would add 4oz. to the fuel tank, and run it on the garden hose for awhile, then let it sit overnight, and run it again the next day to burn the rest out. Then as you use the ski, it will continue to do it's job along the way. You want it to get in there, and clean, & lube every part, instead of just pouring it into the cylinders and let it sit.