1979 85HP V4 with low compression (80psi) in all cylinders

greggilo

Cadet
Joined
Sep 20, 2014
Messages
22
I have been using the boat for two seasons but it was hard to start last season. Once running it ran fine (about 30mph WOT on a 17' trihull) I had work done about 3 years prior and they said it has good compression at 110psi. I have replaced all electronics on motor (CDIs, rectifier, coils) rebuilt the carbs, new fuel lines, new fuel pump, new prime bulb, and new spark plugs and wires. This season it ran fine for three outings on the water then, this last time it ran fine until I turned it off. I thought it was electronics because it seemed like it was not running on all cylinders. I tried squeezing the prime bulb and choke when it lost power but this made no difference. I took the carbs apart again and inspected but found nothing wrong. I replaced a new coil and spark plug because one cylinder looked oily compared to the rest. I then tried it on the water again and it ran fine until I shut it down for a while and then started up. I had no power but it would fluctuate from no power to normal power very intermittently. I then pulled the gas line and let the carbs run dry and the motor died. Once I primed and started again the motor was fine. When I got home I wanted to inspect the reeds; which looked OK. Checked the spark, which was fine. The spark plugs all looked the same with a dry brown color. I then checked the compression and notices that all cylinders were at 80psi. I am thinking this is why the motor was hard to start. It always idled fine but need to find out why the power loss.
Any ideas? One other question- are the remanufactured power heads the way to go if I need a ring/cylinder job?
 
Last edited:

RBoyd1971

Petty Officer 2nd Class
Joined
Oct 20, 2020
Messages
165
I would have to try again with a different gage and see if I got the same results if it were me. 80 seems hard to believe. Is it spinning over fast when you check it?
 

greggilo

Cadet
Joined
Sep 20, 2014
Messages
22
I would have to try again with a different gage and see if I got the same results if it were me. 80 seems hard to believe. Is it spinning over fast when you check it?
Thanks for responding! I thought the same thing but I connected it to my air compressor and the gauge checked OK. It is turning over and will start right up after choking.
 

greggilo

Cadet
Joined
Sep 20, 2014
Messages
22
I have been using the boat for two seasons but it was hard to start last season. Once running it ran fine (about 30mph WOT on a 17' trihull) I had work done about 3 years prior and they said it has good compression at 110psi. I have replaced all electronics on motor (CDIs, rectifier, coils) rebuilt the carbs, new fuel lines, new fuel pump, new prime bulb, and new spark plugs and wires. This season it ran fine for three outings on the water then, this last time it ran fine until I turned it off. I thought it was electronics because it seemed like it was not running on all cylinders. I tried squeezing the prime bulb and choke when it lost power but this made no difference. I took the carbs apart again and inspected but found nothing wrong. I replaced a new coil and spark plug because one cylinder looked oily compared to the rest. I then tried it on the water again and it ran fine until I shut it down for a while and then started up. I had no power but it would fluctuate from no power to normal power very intermittently. I then pulled the gas line and let the carbs run dry and the motor died. Once I primed and started again the motor was fine. When I got home I wanted to inspect the reeds; which looked OK. Checked the spark, which was fine. The spark plugs all looked the same with a dry brown color. I then checked the compression and notices that all cylinders were at 80psi. I am thinking this is why the motor was hard to start. It always idled fine but need to find out why the power loss.
Any ideas? One other question- are the remanufactured power heads the way to go if I need a ring/cylinder job?
Just a follow up on this issue. It turns out the stator was causing the power loss issue. Seems it would heat up after running awhile and then start acting up. Replaced everything else and finally the stator which cured the problem.
Currently rebuilding the engine because of low compression.
 

BrettNC

Petty Officer 1st Class
Joined
Feb 6, 2005
Messages
298
Running well with 80 psi on those motors is not unheard of. Probably better for the motor's longevity imho to run on lower compression. Especially with fuel not being of the same quality as it was in 1979.
 

flyingscott

Fleet Admiral
Joined
Apr 8, 2014
Messages
8,088
Running well with 80 psi on those motors is not unheard of. Probably better for the motor's longevity imho to run on lower compression. Especially with fuel not being of the same quality as it was in 1979.
where are these motors? Any Video of these low compression crossflows Running?
 
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