How much compression on 40 hp force ?

[NC waterboy]

Me again,<br /> I bought a compression test kit today and I will be testing my motor this weekend, wondering how many pounds I should be getting. It is a 1996 force, 40 hp.It has been sitting up for 2 years. I plan to do a complete tune up and would like to do before and after test just for experience.I have not decarbed or anything yet so I'm not expecting it to be the greatest , I'm just hoping theres not a big difference in the 2 cylinders.<br /><br />I will gladly take any extra advice and helpful tricks of the trade.<br /><br />P.S. I also ordered a clymer manual but I'm not expecting it to arrive for several more days.<br /><br />Thank you in advance.

 

[roscoe]

Re: How much compression on 40 hp force ?

The factory never published a compression number for your motor, but hopefully it is between 120-150psi.<br />No more than 10-15 psi difference on the 2 cylinders.<br /><br />If possible, warm up the engine.<br />Trip the kill switch to the "stop" position.<br />Remove both sparkplugs.<br />Set throttle control to FULL throttle.<br />Connect compression gauge.<br />Crank the engine 4-5 revolutions.<br />Observe reading.<br />Repeat on other cylinder.

 

[NC waterboy]

Re: How much compression on 40 hp force ?

Thank you for such a quick reply again.I just would like to be clear, am I supposed to take both plugs out at the same time so that I have the test hose hooked up in one hole and the other remains open ? I trust your call but it seems that you would loose some, just asking so I get it right.Also will the decarb or lack there of have a great effect on the "hopefully" 120 to 150 psi, should I still reach that much pressure either way.<br /><br />The reason behind the full throttle is just to hold the carb plates open, correct ?<br /><br />I bet you're glad that I'm not your neighbor !! <br />Thanks for your time.

 

[roscoe]

Re: How much compression on 40 hp force ?

Yes remove all plugs, both of them in your case.<br /><br />If your motor is in good shape, your compression will be high.<br />If the rings are gunked up and stuck, compression will read low.<br />A good thorough decarb can free up the stuck rings and increase compression numbers. Some motor will show lower compression due to wear, decarb will not change that.<br /><br />Yes, full throttle is to hold the throttle plates open and allow freeflow of air.<br /><br /><br />"I bet you're glad that I'm not your neighbor !! "<br /><br />Why not? We could decarb together and fog the entire neighborhood for mosquitoes.

 

[Bry21317]

Re: How much compression on 40 hp force ?

Roscoe,<br />Nice quote there. I have done this a few times, it is pretty funny. I try to do it once it gets dark, so the Neighbors can't see it as bad. That stuff is a thick cloud of smoke and doesn't go away easy, lol.<br /><br />I will be doing mine again, I like to try to do it quite often on the Force Engine that I have, as they seem to always have alot of carbon, from what I have noticed.<br /><br />Thanks for all the help you guys give on here. I have been on here since about 2002, when I found the board, and now I always come back when I need to find answers. Been away for a while, due to getting married and having a baby, so now I am back and ready to get the boat back in the water. I am hoping to have a good season, if I can get mine running right.<br /><br />Bryan

 

[roscoe]

Re: How much compression on 40 hp force ?

<br />Congrats on the baby.

 

[NC waterboy]

Re: How much compression on 40 hp force ?

Yes, congratulations Bryan. Sounds like we are in about the same boat. My son just turned 1 year old on 3-21-06 and we are expecting another little boy on 5-15-06. In case you're doing the math that's 2 crumb snatchers about 14 months apart, talk about busy. Good luck and may God bless you and your family.<br /><br />Roscoe, let's do it! If possible I'll be decarbing the Force Thursday after work. I did the compression test this evening and the top cylinder had about 127 on about 6 revolutions ,the bottom cyl. had 121 on the same amount best I can estimate. It was difficult to really tell how many revs I was turning so I tried a couple different times. The highest reading was the 127 and the lowest was 118 that was about 3 maybe 4 revs. The bottom spark plug was gummed up more than the top so maybe the decarb will give me a little more psi.<br /><br />I installed the pee'r that I mentioned before and it worked well. I let the motor run for 10 minutes at about 1700 rpm and the water coming out was only as warm as a room temp. cup of water. I could place my hand any where on the engine for as long as I'd like. The pee'r was stronger at higher rpms than lower. This is very logical but it makes me think, would the water pressure gauge be accurate when at idle or even slow trolling. Seems that it fluctuate with the rpms.<br /><br />The worst thing that I learned today was gas is leaking out of the carb. bowl nut. When I first started the motor it was tilted forward and gas came out of the front of the carb. also. I will inspect further tomorrow. If you would like I'll do a different post on that.<br /><br />

 

[roscoe]

Re: How much compression on 40 hp force ?

Sometimes they leak if they are tilted.<br /><br />Sorry, I decarbed in the fall, and test ran the motor last Sunday.<br />So the next time I fire it up will be on the river Friday nite, for 3 or 4 days of walleye fishing.<br /><br />Yes the water pressure gauge will give different readings at different rpm. Typically around 3-4 at idle, 8-9 at 3000rpm, and 13-14 at full throttle.<br /><br />It is still a valuable tool.<br />If you are cruising along and suddenly the pressure drops to 0-2-or 4 psi, you know you have a problem, impeller, sand,debris, weeds, etc. It can also tell you if the impeller is getting weak. If you are only getting 10psi at full throttle, you know its time to change it, before it fails.

 

[NC waterboy]

Re: How much compression on 40 hp force ?

Roscoe,now that I know what to expect with the variating rpms you have me convinced on the water pressure guage, that will be the first upgrade after I make sure the motor is going to be ok.<br /><br />I know the compression looks a little low but do you think the engine has a chance or should I be getting prepared for a large investment in the near future? Maybe even a new one.<br />In my opinion it appears to run pretty good considering the 2 year sit up, but I don't claim to be an engine person. I'm just a person who enjoys learning and tinkering. <br /><br />Thanks

 

[roscoe]

Re: How much compression on 40 hp force ?

There is nothing wrong with those compression numbers.<br />Start to worry when the get down below 105, or there is 15+ psi difference between them.<br /><br />Have fun with the decarb.

 

[NC waterboy]

Re: How much compression on 40 hp force ?

Thanks for the good news. I decarbed last night so now I'm on hold for some p.m. parts. Got my clymer manual so the bolts are really fixing to fly (yea right) . It will take more than a manual for me to do much more on an outboard or any other type engine for that matter.<br /><br />Thanks for all the help, I planned to test run it this weekend but there is a boat race at the lake. Maybe next weekend ?