The clunk continues (and other issues)

[sms986]

So, I'll start off with saying this is an 89 Mercruiser 305 with a 350 short block. I've got 3 issues to tackle. I chose to put them all in the same post so that I didn't clutter up the form with a bunch of posts all at once. First, I believe I have a vapor lock issue. The boat starts fine cold, but when warm it doesn't want to start. It'll take at most 10 seconds to fire, then another 5 of fiddling with the throttle to get it to idle. It isn't over heating, water temp is 120 degrees. When warm it also surges at idle. Goes up to about 1000 rpms then almost dies, then repeats. Possible fixes? I think I'm going to go with an aluminum spacer and insulation on the fuel line.
​​​​​​Second, the boat stalls when shifting from reverse only. I've scoured the forums for an answer since I thought it was fairly common. Found nothing. It shifts to and from forward fine, and into reverse fine. When shifting from reverse it completely dies, no matter how fast I shift. Lower cable was just replaced.
last and most important, I still have this mystery clunk coming from the rear of the boat when under load. I drive it at 3/4-full throttle for 20 minutes no problem. On the way back, I was at no wake speed through the channel and acclelerated to full as soon as I got out. Got to about 3/4 and heard a loud clunk that shook the boat. Dropped it down to half and went back to the dock. Anything above 1/2 and the clunk comes back. Ujoints are good, I am positive. Gimbal bearing was replaced. Trim was all the way down. This one has me puzzled. I can't find anything in any forums that solves this, nor can I find a video of a similar sound on the tube. Any help appreciated. Thanks!

 

[Rick Stephens]

Take the easiest first. Have someone watch the shift interrupt switch while you shift out of reverse. My bet is it is still activating the switch, even with a new cable. Something is dragging - tight bend, ding on the end, gear box shifter problem.

I would bet you don't vapor lock. Marine engine at 120ƒ shouldn't be able to cause a vapor lock. Something else going on there. I'd probably start with a carb rebuild, and to go along with, I'd pull the anti-syphon valve and check all the fuel supply system. Make sure the pump is supplying 5-7 lbs always - means you have to hook in a gauge.

On the clunk, only thing I can think of is pull the top cap and inspect the upper gears. Make sure they are perfect.

 

[achris]

1989, still the Rochester Quadrajet carb? Pull it and either have it cleaned and set up professionally, or if you're confident, clean and set it up yourself.

Does it stall coming out of reverse on the flushers? If so, you have a binding problem. If it only does it on the water, then it's a set up problem.

Chris........

 

[sms986]

As for the vapor lock, my reasoning for this is that there is an abnormal amount of haze in the carb after running it, and the accelerator pump squirts out haze as well, not liquid fuel. Fuel lines, filter, check valve, and fuel pump have all been replaced. I did the qjet (not my first) under supervision of a seasoned engine builder. Cleaned it all out and "rebuilt".

The boat only stalls on the water. Did fine on the muffs. The cable moves very, very freely.

The clunk remains a mystery. I suppose I better rebuild the outdrive anyway.