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An old UJ (1974) engine badly maintained. Cold compression figures low at approx. 50,60,55,90. Completed routine maintenance but engine will only ignite enough to blow a spurt of exhaust, but not start despite excellent spark. Floods quickly. Any suggestions!
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Hello Bob.
You may have already done all this, but just in case, I've copied below an old post by msmith10 on checking compression that I find helpful.
"I usually test the engine while its warm, as you'll get different readings hot and cold, but you may not want to run it that long on the cart. Your readings will be higher on a hot engine, but if it passes cold it will pass hot.
1. Make sure water intake is shut off so you don't fill exhaust system with water which will then enter the cylinders. You're not actually going to run the engine during the test so it won't need cooling.
2. Remove spark plugs. Cover holes with a rag.
3. Remove coil wire, disable fuel pump if electric (remove fuse or disconnect wire)
4. Open throttle to wide open and leave it there.
5. Screw tester into spark plug hole 1 and crank engine with starter for a few seconds. You'll see the pressure on the gauge go up in steps and max out. When it tops out, that's the reading. Repeat on other cylinders.
6. If the readings are low or vary more than about 10% from one cylinder to the next, add a tablespoon of motor oil through the spark plug hole of the low cylinder(s). If this increases the pressure significantly, it indicates worn rings or valve guides (the oil acts to seal the gap somewhat). If it doesn't change it's more likely a valve that's sticking or not closing all the way.
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Mark Smith
1977 c&c30 Mk1 hailing from Port Clinton, Ohio" -
Welcome to the forum, likely the most helpful forums on the web.
You have enough compression to run, so that's a good start and I would make sure the choke is fully operational.
I would do a quick check of the disti and make sure the plug wires are correct (you can see the 360 motor on the moyermarine.com site). Then check to make sure the centrifugal advance it not stuck. Then I would do a quick static timing check make sure it's set to 0 deg BTDC on #1 (closest to the flywheel)
If that does not show improvement, I would venture into the carb. I've had plenty of carb issues over 3 motors... but would still check the spark side first before going into the fuel side.
I'm sure others will have more ideas and good luck.
Thanks,
Ron
Portland, ORComment
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If the engine ran normally before the maintenance please detail the maintenance procedure(s) accomplished.
Also have you been keeping the raw cooling water valve closed while no start cranking, including the compression test? See item #1 post #2.
Not sure what you mean by "floods quickly". Is is almost impossible to flood* an updraft carburetor. If for some reason the mixture is to rich try starting with little or no choke.
*Flood - to much gas in the air\gas mixture.
Another welcome to the forum.
ex TRUE GRITComment
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Flooding
I used the term 'flooding' to describe a collection of gas, about three tablespoons worth, at the neck where the choke butterfly and the flame arrester join. And the motor simply does not fire up despite lots of spark.Comment
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You need to rebuild the carburetor. The flooding is occurring because the needle valve that controls the amount of gas that enters the carburetor is not sealing or metering correctly. The amount of opening of this valve is determined by the position of the float.
This is a dangerous situation. Gas can escape from the carburetor and go BOOM.
ex TRUE GRITComment
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