1990 e120tles compression

Csummjr

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Sep 29, 2017
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Hi , I have a v4 Looper 120 and got a compression reading of on starboard side 92, 95 port 90, 90.
Is this ok? I also have an issue with it not going over 2000 rpms. It starts and idles great. It doesn't die, just won't get going.
 

Bosunsmate

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Apr 7, 2012
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Not sure about compression, someone else may chime in on that. You can often remove the bypass covers to check integrity of the rings. Being all even is a sign all may not be lost.
You should check you are getting spark on each cylinder and its jumping a 7/16 gap
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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compression a little low, however motor will run

as far as going over 2000 RPM, start at the fuel tank anti-siphon valve and work towards the motor following the Low WOT guides in the stickies
 

Csummjr

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I'm sorry I didn't mention that the test was on cold motor with cheap harbor freight gauge. I don't know if that would make a big difference.
 

Bosunsmate

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Cold, not really but if you squirt a bit of oil in the cylinder and then test it if the compression goes up then it indicates rings but as said above it should still run if those numbers a true.
Has it ever worked for you?
Check that with flywheel at 0degs with the marker on it that the top cylinder is at top dead centre
 

Csummjr

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Sep 29, 2017
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Ok thanks for replys. I got about 5 months ago. The first time I took it out, it started up and idle past no wake. I put the throttle down and it jumped on plane and I continued at wot for about maybe 5 minutes then it bogged down to around 2000rpm. It wouldn't open up for the rest of day. I thought it might be over heating and going into slow mode. The previous owner only used a couple times a year if that so everything was still stock on the motor. I changed thermostats and thermos seats, water pump. I took carbs off and cleaned. There were clean as can be. Seocond time out it ran great most of day till the end of fishing I wanted to fly around to see if it was fixed 10 min of hard running it bogged back down and will not exceed 2000. I tried unhooking heat sensors. No different.
 

racerone

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Dec 28, 2013
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Tried running with a seperate portable fuel tank and hose ?-----Checked venting of your fuel tank?
 

Csummjr

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Sep 29, 2017
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Yes, and I just removed gas tank to clean and not bad with dirt and vent seemed clear
 

Csummjr

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Sep 29, 2017
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Ok, so I went back to do another compression check. Instead of using the hose that goes to cylinder I used the hand held rubber nose to hold on and I got 120 120 115 115. I feel a lot better now about that. I looked in to see Pistons and a Little carbon up so should I use some deep creep to see if it cleans it up at all?
 

racerone

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Dec 28, 2013
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The fact that the engine bogs down and is limited to 2000 rpm suggests that there are issues.----Carbon on the pistons is not the problem !-----Run with a timing light hooked up and see if you are loosing spark on one or more cylinders.---Run and use a strong flashlight shining into carburetor bores and see if fuel flow changes when motor falters.
 
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