1987 120 VRO no power under throttle

[455 HO]

Hi all. This motor has very low hours on it since new. I am having problems with it idles fine, but has now high rpms or power under throttle.

Awhile back, it got water in the gas that jelled up in the 4 carbs. I have since cleaned the carbs twice, replaced fuel lines, bulb and portable tank. I had a boat guy replace the diaphragm in the fuel pump, which had a hole or rip in it. I have also tried the squeeze bulb test under throttle and it does not change anything.

It used to just try to rev and die when you hit the gas and then hard to start. Now it just runs slowly at wot.

I will check the compression. Re testing ignition components, do you need to remove the flywheel and how difficult is this?

Any input is appreciated. Could it still be the fuel pump?

 

[boobie]

Do a cylinder drop test on it to see which cylinders (if any) aren't firing.

 

[Bosunsmate]

I will check the compression. Re testing ignition components, do you need to remove the flywheel and how difficult is this?

You dont need to remove the flywheel to do the testing. Do a drop test as mentioned above, ie pulling out each sparkplug wire in turn with insulated pliers and checking that the engine drops by a similar amount on each cylinder being pulled.

Also check that the timing base is moving to its full advance against the stop, if the linkage comes undone (the balljoints can come out now and again) the engine wont advance its timing and will thus run slow.

You should first pull out the sparkplugs and look for any difference in colour between them or normal colour on all of them

 

[455 HO]

We checked some things out and it in not a compression or timing issue. Definitely a fuel related problem.

It seems that there is some debris in the carbs again, Maybe the high speed jets were not cleared or cleaned well.

When we took the boat out, it actually performed well at wot but gradually weakened to where is was not going very fast at wot, at rather low revs.

Something odd happened when I removed the carbs cover today. There was a lot of fuel pooled up at the base of the cover. I thought I had been losing fuel from the portable tank. When I pumped the bulb and started the motor, there was no fuel leakage.

What could be causing this? Could there be a syphon effect while the boat is sitting in the sun, causing fuel to flow through the carbs and pool and drain out of the cover eventually?

I will rebuild the carbs tomorrow, but if there is something else afoot, it would be good to know before doing so.

Any input is appreciated.

 

[455 HO]

Also, the motor is never tilted and the fuel was very fresh, not residue.

 

[robertd338]

do not overlook the fuel vent & anti-syphon valve at your fuel tank, check if it's working ok.

 

[455 HO]

There was junk in the high speed jets areas. Gave the carbs a good cleaning and it now runs well.
I'm still not sure what caused the pool of fuel sitting in the bottom of the air box.

 

[Bosunsmate]

There was junk in the high speed jets areas. Gave the carbs a good cleaning and it now runs well.
I'm still not sure what caused the pool of fuel sitting in the bottom of the air box.

On some motors theres a hose at the bottom of the airbox that sucks fuel/oil in from the bottom bearings to be burnt.
Check that your primer bulb holds firm with engine off, if it doesnt a carb could be leaking/overflowing from a worn valve seat etc