compression 93 15hp?

[dkonrai]

what should the compression be for a 93, 25hp? i have read the manual,but there is nothing saying what the compression should be.
talked to a marine mechanic, and was told 90 pounds is on the low side, and is the cause of the motor not running. correct me if i am wrong, but when it comes to 2 strokes, does compression really matter? i mean if the compression is low, shouldnt the motor still run? i know it may run rough, but should it still run? i cant seem to get this stupid motor running.
should have bought a old evi................

 

[JB]

Re: compression 93 15hp?

If you are getting 90psi and within 15% compression is not your problem.

Try "Outboard won't start" in the Engine FAQs Forum.

Let us know what you find.

 

[7920hpMercury]

Re: compression 93 15hp?

what should the compression be for a 93, 25hp? i have read the manual,but there is nothing saying what the compression should be.
talked to a marine mechanic, and was told 90 pounds is on the low side, and is the cause of the motor not running. correct me if i am wrong, but when it comes to 2 strokes, does compression really matter? i mean if the compression is low, shouldnt the motor still run? i know it may run rough, but should it still run? i cant seem to get this stupid motor running.
should have bought a old evi................

I have a 93 15hp Mercury and compression is/was like this too from new. It has compression relief ports for easier pull starting. (Assume this is a 15hp and not 25hp) For a motor without the compression relief ports, I agree & think this is a little low. My 93 15hp with the compression relief ports, by the way, has always ran great with great power for a 15hp. If it is running rough, I would say that you have other problems. I think the 93 15 is a great motor with 15hp and about the weight of the old 9.8hp and close to the power of the old 20.

 

[dkonrai]

Re: compression 93 15hp?

yes it is a 15hp, sorry about the typo.
a little history. the motor was seized. its in new condition. the previous owner ran it in salt water, then didnt flush it, stored it for 6-7 years.
put some marvel oil in the chambers and the next day she was free.
rebuilt the carb installed a new needle valve, bought a spare parts motor, used the coil, stator, switch box off the parts motor.
dropped the lower unit, replaced the impeller (the old one was in perfect condition, as well as the oil.)
new plugs
new fuel, fuel lines, cleaned the filter, new fittings on tank.
shot some starter fluid in the carb, and she wont fire. it seems like it wants to fire, but wont really start.
tested the ignition system with my ohmeter and everything checks out.
it appears that i have spark, compression and gas.
i have succesfully rebuilt a 62 evi 5 1/2, 59 3hp evi, 54 3 hp evi. now i have this darn merc that has me biffed.

 

[7920hpMercury]

Re: compression 93 15hp?

Bummer indeed, a thought for you, if it was seized, and assuming carb and ignition is all good as you have reworked it all, you might want to check the reed box. With the carb off, you should be able to feel a compression and suction when holding your hand over the carb opening while turning the crank over. The reed box on this motor is right behind the carb and can be removed without taking the powerhead apart if you decide to inspect it. Good luck.

 

[dkonrai]

Re: compression 93 15hp?

7920hpMercury,
thanks for the tip. i pulled the reeds, and checked the gap, and it was ok. i didnt think about trying to see if the reeds are pulling air.
assuming there is no pull (vacuum) would it be the reeds? they looked brand new, but that doesnt mean they dont stick.
i will give that a try. i have to pull the carb apart, remove the stupid plastic air horn to see if i have vacuum .

 

[dkonrai]

Re: compression 93 15hp?

got the motor started. i had to soak the motor in gas, cleaned out the clynders. now it runs really rough.
i have compression
rebuilt the carb
have spark
new plugs
now what??