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Retest the questionable cylinder to be sure. The compression tester should have a schrader valve (check valve) in it... so it will pump up... but should never go down (release pressure) until you press the button on the tester. So your report of pressure going up then down... sounds like a bad...

Compression tests are done without starting/running the engine... only cranking with the starter. That said... you did get compression numbers your way... and they all seem in the same ballpark... at least none were zero or very low... which would indicate a problem cylinder. A better method...

Yes. 10psi is too low... I can't imagine it will start. Should be ~35psi. So could be a failing VST pump. But check for sufficient fuel in the VST... perhaps the VST pump is starving for fuel.

Welcome. I have same boat/engine. The recommendation to disconnect the auto-oiler (oil pump) and premix is actually a highly recommended modification... due to the fact that the plastic gears on the crank that drive the oil pump get old and brittle with age and will fail causing the oil pump...

On mine, the fuel pressure regulator had a clogged screen and the fuel pressure was 70psi. I took the FPR off, disassembled and cleaned the screen. Put it back on and fuel pressure is normal now. So it is removable and cleanable. I've read of others who have rewired the VST high-pressure...

Hi. Agreed, not normal (I have same engine). Things I would check Is the throttle binding? Is it hanging open when warm? Is it returning to idle position? I would check this at the throttle linkage on the engine (lower port side - below VST) The port cylinder head temp sensor. It ties...

That is where the bleed system of hoses connects to the VST. The hose coming off the upper right you see in the diagram... that's the one that connects to the VST where you're pointing. Cheers!

It's a 5-1/2" long socket... not your normal deep socket. From previous post:

I have an engine (240efi) I'm rebuilding that was majorly damaged starting at the top. The actual sequence of events is unclear, but it is clear the flywheel magnet liner/protector came un-done and wadded up under the flywheel damaging the stator. This appears to have lead to a cracked upper...

Since the issue is repeatable, should be able to troubleshoot. First thought... ensure you are not overheating the engine. The external tell-tale (pisser) out the back flowing normally when running? When the engine dies... put an in-line spark tester on some plugs and see if you still have...

The 'Throttle Guardian' is an add-on (not everyone has it) electrical box that cuts/interrupts ignition if rev'ed too high in neutral... (not 100% sure about this... I don't have one). All recommendations I've read say remove it. Pics I've seen show it behind the helm next to the helm fuse box.

This is the diagram from the Service Manual... 240 EFI

Do you have the Throttle Guardian on your boat?

Dang. That is major. I'm sorry to say, but you have a large whole in your block. You can see a rod cap on the crankshaft! That engine is done. Was there a "bang"? I can't see how a stiff throttle cable could cause that kind of damage.

There is a single fuel line from the fuel tank going into the pre-filter attached to the electric primer pump (the clicky-clack pump). Follow this line toward the fuel tank. Mine has a brass check-valve installed in this line. If fuel starvation issue... also check/clean-replace that pre-filter.

I would remove the FPR (it unbolts) and inspect it. There is a small screen that can get clogged in it... but when that happened to me, the pressure went too high. Fuel pressure will read ~35psi when the pump primes, when running, and after shutting off engine... for a few minutes until the...

My boat is a Challenger 2k... so more engine bay room than on a Speedster. So pulling the intake is very do-able. I also make life easier by remove the engine hatch cover allowing me to sit on the rear deck and straddle the engine. Not sure the layout on a Speedster... you might be reaching...

You might also check the bilge pump. Those are wired to run even when the battery switch is turned off.

You have the 240efi (gen1 - round flywheel cover)? The injectors can be removed. You have to unbolt the ECU first, then unbolt the entire intake manifold (injectors inside). Then on the bench you can remove the injectors from the intake. I had injector issues (240efi gen1). Some leaked...

Welcome. Which engine do you have in your boat? The engine wiring diagrams are separate from the boat wiring diagrams. Cheers!