1991 90HP V4 Cylinder Compression Range

racerone

Supreme Mariner
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Dec 28, 2013
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36,032
Well ----What are your compression numbers ?----These motors suffer from broken rings.-----Should be around 120 PSI.-----If you get 120 on 3 and 95 / 100 on 1 then there are issues.
 

Culpy14

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Mar 27, 2022
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They range from 105-109psi. It's tough to start it, and it's surging. I replaced the crankcase seals, all the gaskets for exhaust, intake, heads, etc... Carbs have been cleaned multiple times with no resolve. It surges at every RPM too.

It's also a whole new ignition system, since I ended up throwing parts at the motor. Loves to blow coils every run, even after replacing all the upstream ignition parts.
 

racerone

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Remove bypass covers .---There are 4 of them.---6 small bolts each.----Might cost you $16 on gaskets.-----Inspect pistons and rings.------And are you pushing key in and holding it in while cranking it over?----Running with VRO in service or 50:1 mix?----Battery load tested ?-----Starter motor inspected ??-----Does spark jump a gap of 3/8" on all leads on a test device ?----Perhaps test run with another tank and hose.----High speed jets in bottom of float bowls confirmed clean.-----Sorry to sound like a slave driver , but I cannot see or touch your motor.
 

Culpy14

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I'll remove the bypass covers tonight. I just did two of them on the starboard side and the pistons have the normal grooves and the rings look good. I have some gaskets in the pack I bought, so I will stick those in. Is there suppose to be oil sitting at the bottom of each bypass?

Yes I use the primer when I start it over.

I use a 50:1 mix.

I replaced the battery last month and the starter was actually just crap, so that got swapped out too.

The spark jumps that gap, yes. Although when the coils are blown it obviously won't. Leading up to that, it will.

I am at the brink of just offloading the boat and not overly interested in buying a new tank. The hose and bulb was replaced last year.

The jets on those carbs have been cleaned way too many times in the last 3 months. Enough that I am ruling out the carbs being dirty. I sprayed carb cleaner around the gasket to the intake manifold and carb, which didn't make any difference.
 

Culpy14

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Mar 27, 2022
Messages
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Remove bypass covers .---There are 4 of them.---6 small bolts each.----Might cost you $16 on gaskets.-----Inspect pistons and rings.------And are you pushing key in and holding it in while cranking it over?----Running with VRO in service or 50:1 mix?----Battery load tested ?-----Starter motor inspected ??-----Does spark jump a gap of 3/8" on all leads on a test device ?----Perhaps test run with another tank and hose.----High speed jets in bottom of float bowls confirmed clean.-----Sorry to sound like a slave driver , but I cannot see or touch your motor.
I changed out the gaskets and it didn't do a whole lot. The pistons and rings looked good. The rings weren't stuck or anything.

When starting it from a cold start, I have to keep giving it shots of gas on the choke to keep it running until it gets hot. Then I noticed that the fuel in the filter was pretty low, while the engine was bucking and surging and misfiring. I grabbed the primer bulb and it was pretty soft (was hard when started) and so I pumped it back up. It still had some surges but it smoothed out the motor a lot more. I put the can above the engine to see if that would help and it didn't. So I just kept my hand on the bulb and kept it pressurized. Definitely ran better, but not problem free.

Should the bulb and fuel filter get low like that? Doesn't seem normal. Maybe you were right about another tank and hose, but the hose is pretty much brand new. It was low on my list of items to inspect. I did also throw a cheap amazon fuel pump in there rather than the VRO pump.
 

racerone

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Dec 28, 2013
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The bulb does NOT need to be hard when motor has started.-----What part # pump did you get ?-----And is the pump mounted directly over the pulse port on the intake manifold ?----That would just beside the starter motor.
 

Culpy14

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Mar 27, 2022
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The bulb does NOT need to be hard when motor has started.-----What part # pump did you get ?-----And is the pump mounted directly over the pulse port on the intake manifold ?----That would just beside the starter motor.

438556​


Yes, the VRO port is plugged with epoxy and the new pump is over the pulse port.
 
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