1992 Force 70-loss in compression but not speed?

BTAAA · Jul 8, 2010

I have a 1992 Bluefin Spectrum with a 70hp Force that just recently has begun stalling at low speed, mostly at the dock, both launching and loading, and is more of a nuisance than anything else. Took it in thinking it was probably something simple and was told that my compression was 125/25/125 (single carb unit), and that it would be about $2,500 to fix.

My question is, if this were a loss of compression problem (basically 33% of it), wouldn't I have also lost some speed, or the ability to troll at low speed? As well, it starts up just fine. I have basically dealt with it by shifting into gear a little faster.

The shop owner asked me if I had noticed a loss in power and seemed only slightly surprised when I hadn't. As well, I had compression checked last summer and all was fine, so whatever the cause it is recent.

I consider myself a good mechanic but I always let a shop take care of my boat. Just want to make sure that this is feasible. Thanks.

maxum_man · Jul 8, 2010

Re: 1992 Force 70-loss in compression but not speed?

I would get it back and try a decarb. It may just be a stuck ring or something simple.(Hopefully). From past experience, I wouldn't take the mechanic's word for it...No offense to anyone who may see this who is a mechanic, but I have had some shady ones!

further · Jul 8, 2010

Re: 1992 Force 70-loss in compression but not speed?

Doesn't sound right at all. I would check the compression myself. Funny how they just throw a # out there $2500 to fix without knowing what the problem is exactly.

BTAAA · Jul 8, 2010

Re: 1992 Force 70-loss in compression but not speed?

Yea, I have reason to be a little suspicious. Same mechanic tried to charge me 2 hours labor for a bad primer bulb. The owner, while ringing me up, didn't think it was right either so he only charged 1 hour.

How difficult is a decarb or compression check?

jerryjerry05 · Jul 8, 2010

Re: 1992 Force 70-loss in compression but not speed?

Check out the head gasket first.Remove the head and check for damage.It just might be a $35 gasket.J

wan2live · Jul 8, 2010

Re: 1992 Force 70-loss in compression but not speed?

jerryjerry05 said:
Check out the head gasket first.Remove the head and check for damage.It just might be a $35 gasket.J

I'm with Jerry on this.

My force 125 had a blown head gasket and #1 #2 were 120 PSI and #4 was at about 90 but #3 was at 60 PSI, I got lots of great advise as a first time owner of a Force and it turned out to be a $18.00 part and my own labor.

So worse case scenario is that you pull the head cover and see that you do not have a blown gasket but if you do then you have extra gas money when you fix it yourself.

roscoe · Jul 8, 2010

Re: 1992 Force 70-loss in compression but not speed?

If the compression is as bad as he said, you would have difficulty getting on plane, and would likely only run at 2500 - 3000 rpm, max.

I wouldn't do anything till I had the compression checked again.

Then a decarb.
Then recheck compression.

Then I might check the head gasket IF the compression is still low.

BTAAA · Jul 10, 2010

Re: 1992 Force 70-loss in compression but not speed?

Thanks. I certainly have no loss in power. My fishing spot is a 12 mile run from the launch, which I've done many times over the last three years, so if there was anything out of whack I would certainly feel it. Thanks for the advice. I'll report back.

BTAAA · Jul 18, 2010

Re: 1992 Force 70-loss in compression but not speed?

Ran the boat this weekend after decarbing and adding can of Seafoam to fuel. Still stalling at low idle and was kind of difficult to start at times, but when running it was still topping out at 35-37 mph, like always, at about 5100 RPM (Believe RPM's reading correctly because they had to recalibrate it a couple years ago, although I was told that they adjusted the max RPM to 4400).

Does this still sound like a compression issue? Again, the compression tester I borrowed from Autozone wasn't giving me the same readings the mechanic said he was getting (see above). Little confused, but hoping I can hold out to winter if its a major problem. As of now, I'm happy with my power and speed, but just want to get rid of the stalling issue. Thanks for any advice.

199675hpforce · Jul 18, 2010

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Make sure engine has been warmed up, then pull all plugs,turn landyard off. You should be ok putting comp on each cyl maybe have someone help kick the starter. Some mention you can damage cdi packs if not ground but I think if landyard is off electrics are off. Give us a report before you try decarb. I wonder if your reeds maybe broken, im wondering if mine are. I get stalling at lake, runs great all out then when I return either hot or cold to dock run the motor tie the boat up it usually stalls out. I just put autolite 2852s in and switched pennzoil xlf semi syn, checked my plugs and now very clean? My comps were posted long time ago guess I will do search. My rule dont trust mechanics unless you either know them or are the mechanic! Have you been mixing 50to1 oil in tank? What do your plugs look like. No way you could hit 35mph with 25 in one cyl

BTAAA · Jul 19, 2010

Re: 1992 Force 70-loss in compression but not speed?

Yes, I always pre-mix my 50:1 real carefully and never do the guessing game at the gas pumps. When I last pulled my plugs they seemed a little oily but that is it. A game them a quick brush and through them back in. I can take a pic and post it tomorrow.

jerryjerry05 · Jul 19, 2010

Re: 1992 Force 70-loss in compression but not speed?

Bent /broken reeds should make no difference in comp.
Different comp testers will give different readings.A good screw in one is a MUST!!! I paid about $100 for mine.I know it's giving the right reading.
Cold or warm won't make that much difference.Remove all the plugs and then open the throttle all the way(my opinion that's not really necessary),then do the test.Record the results.The low cylinder spray oil in it and see if that raises the pressure.An increase might mean the rings are stuck.No real difference the head gasket may be leaking.
The danger of running it like it is.You can cause LOTS more damage.It might be a stuck ring which will turn into scored cylinder and a ruined piston.J

BTAAA · Jul 19, 2010

Re: 1992 Force 70-loss in compression but not speed?

Thanks, will try and measure comp again.

BTAAA · Jul 21, 2010

Re: 1992 Force 70-loss in compression but not speed?

Just noticed last night that a couple of my plug wires are damaged/cracked at the boot. Could this have anything to do with my issue?

199675hpforce · Jul 23, 2010

Re: 1992 Force 70-loss in compression but not speed?

Yes lol I had an Audi with broken spark plug wires. Get some electrical tape cover those suckers see if it improves. If your 70 is like my 75 run different plugs. I found champions run to cold. Autolite 2852 and using higher grade semi syn oil like pennzoil xtr makes a huge improvment. Now my plugs come out clean go figure?

BTAAA · Jul 24, 2010

Re: 1992 Force 70-loss in compression but not speed?

199675hpforce said:
Yes lol I had an Audi with broken spark plug wires. Get some electrical tape cover those suckers see if it improves. If your 70 is like my 75 run different plugs. I found champions run to cold. Autolite 2852 and using higher grade semi syn oil like pennzoil xtr makes a huge improvment. Now my plugs come out clean go figure?

Thanks. I'll try it and get back. Probably won't be able to get on the water this weekend though.

BTAAA · Aug 21, 2010

Re: 1992 Force 70-loss in compression but not speed?

Well, found out why I have no compression on #2. Took it to another shop where they pulled off the head and saw that the #2 piston was damaged. Said it looks like something passed through between the piston and cylinder. They, as well as others, still don't understand why I never noticed any loss in speed. I'm just wondering now if I bought it like this 3 yrs ago? They said it's going to be around $1,500 to fix.

Anyway, now I'm debating on whether to have it fixed or invest in a new one. I love the boat and plan to keep it many years. Quick question for the experienced gear heads. I'm a pretty good mechanic but I've never messed with my boat motors. If I were to buy the the repair/rebuild manual and take my time this winter working on this, would I reasonbly be able to work my way through it?

I feel like I have nothing to lose now by trying to do it myself. Don't care to dump $1,500 into a 18 yr old motor, and if I screw if I screw something up it wouldn't be much of a loss at this point. I would just buy a new one. Thanks for any advice.

1983rinker · Aug 21, 2010

Re: 1992 Force 70-loss in compression but not speed?

you should do it for 400.00.

1983rinker · Aug 21, 2010

Re: 1992 Force 70-loss in compression but not speed?

Its not that hard to do, just take your time and read.

roscoe · Aug 22, 2010

Re: 1992 Force 70-loss in compression but not speed?

Yes, try it.
You can replace the one piston only if you like.
Even if it needs honing or boring.
Might want to consider replacing the rings on all 3 pistons as long as you are in there.

You can replace the piston without completely tearing down the motor, just remove the carb/intake/reed blocks, and gain access through the front.

One member just did a one piston job on his in a day, but he only required a bit of honing.

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