Compression on 1994 J150 motor

[jwellcraft]

I bought a new compression guage (OTC) and checked the compression on this motor and it read 105-120 staggered figures which I know is normal. But I then realised that my guage needle wasn't returning to 0 and was stopping at 20. I opened the back of the guage and set the adjustment bar so that it started at 0 and not 20psi. I then rechecked my compression and they varied from 75-80 psi, do these numbers sound right and are these considered bad. I was told by a freind that this motor has never been pulled down (he said this just by looking at it) so if so is this ok or is it time for a rebuild. I will confirm #'s with another guage as well.

 

[psteurer]

Re: Compression on 1994 J150 motor

The key to compression testing is that all the cylinders are within 10% of each other which you have. Numbers vary because of the different brands and qualities of the compression testers. Your numbers are low but I would not think there is a problem. The reason is because it would be very rare for all cylinders to have a problem that reduces compression equally. If you have access to another tester, give it a try and see what numbers you get.

 

[tashasdaddy]

Re: Compression on 1994 J150 motor

i would do a decarb on it. probably way overdue.

 

[jwellcraft]

Re: Compression on 1994 J150 motor

Thanks, yes I will try another tester to verify and this was immediately after a decarb with 1 can of engine tuner which I treated one evening, left it overnight to sit then ran it on the hose for 15 mins @ 1,500 rpms then put it in the water and did about 10 wide open throttle runs and it has been 4 days now and no draining from the foot end exhaust port. I hope the 1 can of engine tuner worked or do you think I should do another one?

 

[jonesg]

Re: Compression on 1994 J150 motor

I have a 1994 J150 too, same compression numbers as yours, they started out around 70 psi, after decarbing they settled around 83psi.
Its normal. I hear the big loopers can be 90psi even when new.
Definately do the seafoam routine, I bet you get 10 psi more.

Then give it a good going over, do the maintainance and it will be a good runner. Get the factory manual for it below.
www.outboardbooks.com

 

[jwellcraft]

Re: Compression on 1994 J150 motor

Ok thanks for the info..Yes I have the factory manual for it. Which spark plugs are you using in yours?

 

[jonesg]

Re: Compression on 1994 J150 motor

QL77 I think, whatever the manual suggests. Electrode type plug.

 

[jwellcraft]

Re: Compression on 1994 J150 motor

Ok so you are using the suggested ones by the manufacturer then which are QL77JC4 but everyone on this forum suggest that I use QL78YC. Did you ever here of using those? A few machanics has also told me that the 78YC are for these 94 150's and on this forum when I said I was using the 77JC4's someone said they were the wrong plugs.

 

[ezeke]

Re: Compression on 1994 J150 motor

The QL77JC4 is not the plug recommended by the manufacturer for the 1994 60? J150, the QL78YC is.

 

[jwellcraft]

Re: Compression on 1994 J150 motor

Ok well I only went by what the parts site recommends for my year and model. I have got the QL78YC's now but haven't installed yet.

 

[trooperguy90]

Re: Compression on 1994 J150 motor

I've got a 76' 135hp and compression is 145-150psi across the board... is that normal?

 

[emdsapmgr]

Re: Compression on 1994 J150 motor

You did not state the model number of your engine. The compression on these engines may vary somewhat, depending on what heads the factory put on. The 150GL models are the powerheads with high compression heads. The compression on these can run around 120 on the top four cylinders. I believe that starting around 94, the factory machined the two bottom cyl heads (sections) differently on purpose-and the compression is about 10 lbs less on the two bottom cyls. Non "GL" models run lower compression heads. I'd definitely try another compression gauge.

 

[jwellcraft]

Re: Compression on 1994 J150 motor

I have a 1994 J150 too, same compression numbers as yours, they started out around 70 psi, after decarbing they settled around 83psi.
Its normal. I hear the big loopers can be 90psi even when new.
Definately do the seafoam routine, I bet you get 10 psi more.

Then give it a good going over, do the maintainance and it will be a good runner. Get the factory manual for it below.
www.outboardbooks.com

Hey again, are you not seeing a steam cleaned #1 piston / spark plug in this motor? It's kind of hard to tell it without pulling the plug and looking at the piston / plug because it still runs strong depending on how much water/ moisture is getting in but check your #1 for me and let me know.

Thanks

 

[jwellcraft]

Re: Compression on 1994 J150 motor

Hey guys got another block (1992/1993) and got the pistons / crank all new. I have put 6.5 hrs on the motor so far and I am running 25:1 mix but motor has started running kind of rough now. Anyway I did a compression check with another guage on this powerhead and I got 100 psi on #1 and #3 but all the others are at 80 psi. Is this ok? Do you think things will changed once fully broke in at 10 hrs?

 

[boobie]

Re: Compression on 1994 J150 motor

When performing a compression check on V-6 models some have staggered compression.
1992 and newer 175 models
1994 and newer 150 GL and SL models
1993 and newer 200 & 225 models
Cylinders 1-4 have close to equal compression and 5&6 have lower compression.
This was done to improve idle quality.

 

[jwellcraft]

Re: Compression on 1994 J150 motor

Ok thanks boobie so do you think mine is fine then?

 

[boobie]

Re: Compression on 1994 J150 motor

They seem a little low but what I would do is give it a good DE-CARB and if the numbers come up, give it another one. Follow the directions on the can. Personally I've always found BRP engine tuner to work the best. Again follow directions. You may also want to borrow another compression gauge and recheck cause yours was off from the start. You may be able to rent one from a parts house.

 

[jonesg]

Re: Compression on 1994 J150 motor

Hey again, are you not seeing a steam cleaned #1 piston / spark plug in this motor? It's kind of hard to tell it without pulling the plug and looking at the piston / plug because it still runs strong depending on how much water/ moisture is getting in but check your #1 for me and let me know.

Thanks

No steam in any cylinders on mine.
..yet.

 

[boobie]

Re: Compression on 1994 J150 motor

I just read a post of yours I missed. If this mtr has just been rebuilt forget the de-carb. After the mtr has been broken-in (10 hrs) re-check your compression again. Sorry for the mistake.

 

[jwellcraft]

Re: Compression on 1994 J150 motor

Thanks boobie I figured you just missed that part and I knew everything was fresh and carbon free when rebuilt so no worries and I will recheck once fully broken-in and use another guage..Thanks again.