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Discussion Starter · #1 ·
I have a 1994 150 Johnson which is running about 1500 rpms lower than usaul and is very sluggish. I decided to check the compression first and all cylinders regestered between 78 to 80 Pounds of pressure. The manual did not give any numbers for compression only that their should not be any more than 15 psi between cyl. My question is does anyone know the range that the compression should run or what is considered poor compression? Thanks for any help.
 

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Some of those of Johnsons ran low compression rates and even varied considerably from bank to bank. If you don't have a problem with it starting or idling and your within 5 all the way around I'd say you don't have a compression problem.

How's your fuel flow and supply? Are you using extra fuel? Have you checked for spark at all the cylinders?
 

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Discussion Starter · #5 ·
Thanks for the advise guys and I think I found the problem. I found that a carb bowl was leaking air and it seems to run much better on land. I'm going try and throw it in for a quick test run after work one day this week to see how it performs under a load.
 

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It will probably run ok but likely to be tempermental starting and idling, especially when the weather turns colder.
 

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Running on the hose doesn't tell a thing other than it will run. Good move putting in the water with load on the motor. That will certainly tell you whether or not you nailed it.
Jim
 

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I don't think a leaky carb bowl should affect compression unless the intake valves are leaking back thru the induction passages. Typically once the compression drops below 120psi you will notice low power.
 

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Those V6's tended to normally have pretty low compresion (i.e ~ 85 to 90 psi). I wouldn't worry too much about the compression. Difference between cylinders is more important than the absolute number and BTW you won't find any compression figures in any shop manuals (that I've seen anyway).

If you haven't decarbed the motor, that may help if the rings are stuck. Use Deep Creep (available at NAPA, etc.) or any similar product ... spray into carb throats at fast idle (empty the can). Let sit for an hour or so. The start and run at a fast idle (should see a lot of smoke). Done!
 

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Discussion Starter · #10 ·
[Q]WildeOne originally wrote:
Those V6's tended to normally have pretty low compresion (i.e ~ 85 to 90 psi). I wouldn't worry too much about the compression. Difference between cylinders is more important than the absolute number and BTW you won't find any compression figures in any shop manuals (that I've seen anyway).

If you haven't decarbed the motor, that may help if the rings are stuck. Use Deep Creep (available at NAPA, etc.) or any similar product ... spray into carb throats at fast idle (empty the can). Let sit for an hour or so. The start and run at a fast idle (should see a lot of smoke). Done!
[/Q]I did the decarb and ran for about 20 mins. and checked the compression again and all where around 80 to 82. I spoke with a Johnson Mech. and he said the numbers where very good for a 1994. After I fixed the carb bowl that was sucking air it realy sounded much better. I will see after work when we take it for a test ride. I realy can't complain this is the first problem I have ever had with this motor after ten years of use. Knock on wood.
 

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Now, back to your original question, since you've ruled out compression (which is a good thng, since bad compression usually means big $'s). What are WOT RPM now and earlier? What have you done to check this out? May be a fuel starvation issue (i.e. air leak on suction side of fuel pump, bad fuel pump, restricted tank pickup, tank not vented properly, etc. One way to confirm fuel problem is to pump on primer bulb at WOT and see if there any RPM gain or activate choke/primer, same deal. Let us know what you find.
 

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Discussion Starter · #12 ·
[Q]WildeOne originally wrote:
Now, back to your original question, since you've ruled out compression (which is a good thng, since bad compression usually means big $'s). What are WOT RPM now and earlier? What have you done to check this out? May be a fuel starvation issue (i.e. air leak on suction side of fuel pump, bad fuel pump, restricted tank pickup, tank not vented properly, etc. One way to confirm fuel problem is to pump on primer bulb at WOT and see if there any RPM gain or activate choke/primer, same deal. Let us know what you find.
[/Q]When I was pumping up the gas pressure I notice that somthing with one of the bowls on the bottom carb. After I took a closer look I noticed the bowl had a slight leak and when I started the engine it was realy sucking are so I think its fixed. I'm taking it for a test run tonight.
 
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