1984 force 125 low compression question?

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slimmer57

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cylinder 1 2 and 4 are getting 105 compression cylinder 3 only gets around 30-40

thats also the one that controls the fuel pump is there another issue that could be causing the low compression i checked the diaphragm and its good for the fuel pump. am i missing something or is it time for a rebuild
 
topgun3690

topgun3690

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Is the fuel pump gasket good? Might be time to pull the head and take a looksy.....could be a bad head gasket.....or scored #3 cylinder/piston.....post some pics if you find anything damaged or don't look right.
 
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slimmer57

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topgun3690 said:
Is the fuel pump gasket good? Might be time to pull the head and take a looksy.....could be a bad head gasket.....or scored #3 cylinder/piston.....post some pics if you find anything damaged or don't look right.
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Will do don’t take much to pull the heads anyways but I did replace the gasket for the fuel pump the diaphragm and the transfer port gasket also had to put rtv on the transfer port gasket to get a good seal because I noticed it was leaking some there when I put soapy water on the outside it would bubble
 
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bjly92

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If you want to know if it's the fuel pump you can pull the hose leading to that cylinder and start priming. If fuel comes out then the fuel pump needs to be rebuilt. Other than that I second pulling the head.
 
topgun3690

topgun3690

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slimmer57 said:
Will do don’t take much to pull the heads anyways but I did replace the gasket for the fuel pump the diaphragm and the transfer port gasket also had to put rtv on the transfer port gasket to get a good seal because I noticed it was leaking some there when I put soapy water on the outside it would bubble
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The transfer port gaskets can be a source of trouble.....can cause a cylinder to suck air and run lean. You can test them by spraying starting fluid all around the intake side while running...the engine will stall if they are leaking. I too used a sealer on those gaskets.....against the advice of some folks. One good backfire can blow them out. The sealer helps to prevent that. Just let it cure good before running.
 
jerryjerry05

jerryjerry05

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Start treating the bolts NOW!! PB Blaster and a small propane torch and a small hammer. Heat/spray and tap the bolt head, turn GENTLY.
It was put together with 20#'s torque and shouldn't be real hard but if it is go easy.
ONE BIG TIP: a motor with lots of hours, don't remove the exhaust chest cover. It will never seal right again unless you resurface all the mating surfaces. The screws will leak and never reseal right.
 
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slimmer57

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jerryjerry05 said:
Start treating the bolts NOW!! PB Blaster and a small propane torch and a small hammer. Heat/spray and tap the bolt head, turn GENTLY.
It was put together with 20#'s torque and shouldn't be real hard but if it is go easy.
ONE BIG TIP: a motor with lots of hours, don't remove the exhaust chest cover. It will never seal right again unless you resurface all the mating surfaces. The screws will leak and never reseal right.
Click to expand...
can i do something to seal the bolt holes? it seems like the only cylinder loosing compression was after i took off the port on the side for the fuel pump
 
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brodmann

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Don't tear the motor down, replace the fuel pump!!!! The fuel pump is more than just the diaphram, it's got check valves too. The check valves prevent fuel from going into the cylinder and compressed air going into the fuel line. Fuel pump is probably less expensive that buying head gaskets.
 
topgun3690

topgun3690

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brodmann said:
Don't tear the motor down, replace the fuel pump!!!! The fuel pump is more than just the diaphram, it's got check valves too. The check valves prevent fuel from going into the cylinder and compressed air going into the fuel line. Fuel pump is probably less expensive that buying head gaskets.
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See post #6....jerry says that a bad fuel pump or gasket should have nothing to do with low compression in that cylinder......OP said he resealed the port cover and new gasket for fuel pump. Time to take a look at #3 cylinder I think.....
He should have been able to see the side of the piston and some of that cylinder when he had the port cover off.....
 
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slimmer57

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topgun3690 said:
See post #6....jerry says that a bad fuel pump or gasket should have nothing to do with low compression in that cylinder......OP said he resealed the port cover and new gasket for fuel pump. Time to take a look at #3 cylinder I think.....
He should have been able to see the side of the piston and some of that cylinder when he had the port cover off.....
Click to expand...
im going to attempt to take the port off again and look at it one more time and see if the rings are bad or not
 
topgun3690

topgun3690

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slimmer57 said:
im going to attempt to take the port off again and look at it one more time and see if the rings are bad or not
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The torque spec for the port cover bolts is not much at all.....don't have my manual handy but Mastertech Marine shows 70 inch lbs for 1/4-20 size bolts....or about 6 FT Lbs. If over torqued can cause it to leak.....FYI
 
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slimmer57

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topgun3690 said:
The torque spec for the port cover bolts is not much at all.....don't have my manual handy but Mastertech Marine shows 70 inch lbs for 1/4-20 size bolts....or about 6 FT Lbs. If over torqued can cause it to leak.....FYI
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Will leak out the bolt holes?
 
topgun3690

topgun3690

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Back firing could be a timing issue.....maybe a sheared flywheel key. I would not run it again until you figure out what is going on with the low compression on cyl#3....that is a known problem that needs to be addressed first.
 
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slimmer57

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topgun3690 said:
Back firing could be a timing issue.....maybe a sheared flywheel key. I would not run it again until you figure out what is going on with the low compression on cyl#3....that is a known problem that needs to be addressed first.
Click to expand...
Turns out I had the cdi boxes hooked up backwards fired up in 2 seconds now
 
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