98 GS Low Compression ?

[djmjr77]

Hello to all !! New member and just bought a 98 GS 717. I ran a compression test before I bought it and knew it was low, right around 88-90 on both cylinders. Previous owner started it up for me and it ran OK, could tell it at least needed the carb rebuilt, that's not to hard so I bought it because I enjoy a project. I'm pretty experienced with mechanics, nothing professional though, and this engine is new to me so I need the communities experience. I was rebuilding the carb I noticed the oil pump cable wasn't hooked up right, might as well not been there, I need to get that straight, so haven't tried it on the water yet. I replaced all of the Tempo fuel lines except vents. Cleaned screw on fuel filter, added additional inline fuel filter. New spark plugs and some general cleaning. I checked the compression with two different testers, one is old and the other just bought new from HF. Unfortunately I don't have proof that either are good other than they read the same.. End Background ..

It runs great after the carb rebuild (out of the water on the hose). How bad is 90 pounds in both cylinders on these engines ?

Usually if all cylinders are low, it is either just an old engine or there is something common to both cylinders causing it. What are some of the common reasons anyone has seen with these readings? I can name a bunch of generic reasons, but you all are experienced with these particular engines.

Thanks in advance for anyones help and suggestions.

 

[mwat65]

It won’t run in the water at 90. 150 is great 120 and below and it needs a topend rebuild. Verify that you have a good compression tester. Some of them won’t go past 90 lbs. Try it on another ski if you have one.

 

[Dr Honda]

If it's running at all, and your gauge says 90 psi... you have a bad gauge.

 

[djmjr77]

Thanks for the replies!! I'm really hoping it's just the guage. My cousin has an auto repair shop, I'll see if I can borrow his tester tomorrow and I'll post back my results.

 

[djmjr77]

So, got anxious and borrowed a Matco guage from my cousin, and guess what ..
MAG Cylinder 155, PTO Cylinder 160..
Those Harbor freight guages are crap, usually I read reviews but just figured how could someone go so wrong with something that basic.. Those crap guages two bought a year apart almost cost me a bunch of money if I didn't double check it.
Thanks for the reassurance and help !!!

 

[mwat65]

The inline fuel filter can restrict your fuel flow. You don’t need it.

 

[djmjr77]

Honestly I put it on there to help protect my carb rebuild a little. The engine runs great, but I still need to dump the old fuel and clean out the tank. It's a fairly free flowing screen though, not super fine mesh. If it becomes a problem once I'm sure the fuel system is clean, it will be "outta hee".
Also can't wait to check my boats compression, I have thought it was low from the day I bought it a year ago. Kinda feel bad now, because I got a better price on the boat because the HF guage showed the compression was so low 70, on all three cylinders. Hopefully dishonest people don't figure that one out.. go around getting deals because things have "low" compression.. some Harbor freight tools are great, this is not one of them ..
Thanks again guys !!

 

[mikidymac]

You risk seizing the engine with that additional filter, as said previously remove it.

 

[Dr Honda]

Those Harbor freight guages are crap, usually I read reviews but just figured how could someone go so wrong with something that basic..

Yep... it's a shame. They use to be great. Cheap and accurate. The issue is... they took the Schrader valve out of the tip of the adaptor. (where it screws into the head) With the valve in the tip... it takes a few rotations to pressurize the gauge... but you get an actual pressure reading. When they took that out... it basically adds the volume of the hose to the volume of the combustion chamber. In turn, lowering the ratio, and the pressure. IF you have a steady hand... you may be able to tap the new adaptors to put a tire steam valve into them, and then you will get a real reading.

So... for anyone else reading this... before you buy a gauge... just look in the tip of the part that goes in the head, and make sure there is a valve in it.

 

[Dr Honda]

The inline fuel filter can restrict your fuel flow. You don’t need it.

You risk seizing the engine with that additional filter, as said previously remove it.

I hate going against you guys... but that's false. Sure... if it's plugged up, or a crappy little filter, meant for a lawnmower... it can restrict flow. But a big automotive filter will flow plenty of fuel. Mater of fact... I made a thread long ago telling people to put an in-line filter into their toys. It will reduce carb maintenance.


OK... just found it. Can't believe it was 8 years ago.

How To: Adding an in-line filter

 

[mikidymac]

I hate going against you guys... but that's false. Sure... if it's plugged up, or a crappy little filter, meant for a lawnmower... it can restrict flow. But a big automotive filter will flow plenty of fuel. Mater of fact... I made a thread long ago telling people to put an in-line filter into their toys. It will reduce carb maintenance.


OK... just found it. Can't believe it was 8 years ago.

How To: Adding an in-line filter

No problem Dr. Honda we all get our own opinions and I respect yours too.
I have seen the inline ones plug with water and also send fibers into the small carb filters so I don't like them. Again this is from people that install them and never touch them again. It all comes down to lack of routine maintenance which is very common. But that is just me. The stock separators work great if you keep the fuel tank clean so that is what I go with.