Compression problem or no compression problem

[WaterDR]

I have a 2002 Yamaha 1200 SUV with 100 hrs. No salt water and in excellent condition. I have owned it for four years and got with 80 hrs.

Before buying it, I had compression tested by a dealer and it was around 130 from what I can remember.

Anyway, while getting it ready for the summer yesterday and replacing plugs, I borrowed a tester and checked it myself. Only 90 on all cylinders. 90 would be extremely low, but it starts right away and gets to 51 mph. The fact that I got the same reading on each cylinder I would view as positive because I can't imagine all three would be bad for the exact same reason thus netting the same result. Makes no sense.

Anyway, I suspect a bad guage. OR, when using the guage, I was only able to get the first few thread of the guage in. I am not sure if the threads are the same or the right size. Wondering if air is just escaping around the threads.

 

[DoGood]

Re: Compression problem or no compression problem

well if the threads are not the same size you won't be getting a good air tight seal. I suspect since they are all even there probably isn't a problem. I would think you have a bad seal between the head and the tester, the tester is not precise, or the engine wasn't warm when you tested it this time. For a good compression test the engine needs to be warmed up.

 

[jerryjerry05]

Re: Compression problem or no compression problem

Compression???
The results are what's important.
All 3 cylinders at 90.That tells me the guage you have isin't any good or the test was done wrong.
The threads on the guage should be the same on all plug holes.Unless they are the adapter for tractors.
The important thing is all 3 cylinders are the same.
Any more than 15-20% difference on any one cylinder would be a problem.
Cold or hot,shouldn't matter.
Remove all the plugs.Install the tester,advance the throttle.
Jump the solenoid.
Then record the results.

 

[WaterDR]

Re: Compression problem or no compression problem

Yeah, I am happy they were all the same. The units starts on the first crank.....never would with compression that low, right? And, it made 50+ mph. Which is good too and that is in chop.

 

[bently]

Re: Compression problem or no compression problem

Your jet ski will be faster in rough water than in glass like surface. Water adds resistance and an improve intake grate will give you some more umph in chop.

 

[WaterDR]

Re: Compression problem or no compression problem

Your jet ski will be faster in rough water than in glass like surface. Water adds resistance and an improve intake grate will give you some more umph in chop.

I actually see the opposite. Faster on smooth water. Anyway, tell me more about the grate, where I can find one, and how much they cost. What kind of speed increase should I see?

I am not overly concerned with it, but if the investment is minimal, perhapos it would be good to try. Ont he other hand, the grate does a nice job of keep crap out of it.

 

[bently]

Re: Compression problem or no compression problem

The intake grates have added angled veins the scoop or catch more water and helps distribute it all the way to the upper section of the impeller. That allows you to get the full thrust from your pump, stock grates only load half to mayb 3/4 of the impeller.You could gain 5 to 10 mph. You can slightly reduce the size of the outgoing nozzel by add a 4 to 6 in piece of pipe (similar to PVC) that reduction will increase thrust but it will also create a snappier turning ability, something you may not want. Almost any PWC catalog has aftermarkey intake and ride grates. An extended ride grade will give you a more control or steady feeling when installed.