Help - can't get low idle on Volvo 3.0 GSP-A

[fcawth]

I have been getting this "new to me" boat ready for the last few weeks thanks to everyone here. I couldn't get it to idle below 1000 rpm even with the throttle plates fully closed, and I noticed some fuel leaking from the throttle shaft, so I bought a rebuilt carb from "Flying Fish". Now with the new carb, I get slightly better results but it still idles high with the throttle plates fully closed.

Now that I've seen this with two carbs, is there anything else that could be going on? If I put some forward tension on the thottle cable, I can get it to idle at around 800 on the muffs, and maybe it will idle lower in the water, so I might be OK.

I replaced the PCV valve. If I plug the PCV valve with my finger, I can get the idle to drop to maybe 600 or lower. When I got the boat, the idle speed screw was all the way out so this problem must have existed for the previous owner or perhaps even from the factory.

I replaced both the carb gasket and the "spacer" gasket with OEM volvo ones.

I drained all of the gas and replaced with new.

I checked the timing in "base timing mode". It was right on.

I put a vacuum gauge on the PCV port (with the PCV valve disconnected), and I get 18-19 inches of vacuum at idle, vibrating quickly less than 1psi (not pulsing for a single cyl.).

My compression is 150 -155 in each, but my #1 cyl. has to pull 3 times to build up to 150 (starts at 60, next 100, next 155), #2 goes to about 120 on the first stroke, then to 155. The other 2 cyls. get to 150 right away. Put oil in #1 and then it goes to 100 on first stroke then to 155.

All spark plugs look the same.

Verified RPM with an optical tachometer.

Boat is 2001 freshwater only. It was supposedly garaged and winterized every year.

I'm not quite sure what else to do????


Thanks,
Fred

 

[Don S]

Re: Help - can't get low idle on Volvo 3.0 GSP-A

Disconnect the throttle cable and see what your idle is.

 

[fcawth]

Re: Help - can't get low idle on Volvo 3.0 GSP-A

It actually goes up to 950-1000. The tension (I guess it's not really tension, but compression of the throttle cable) pushing on the throttle is actually dropping it 150RPM or so.

I have been working on this all day and I did spend some time connecting, adjusting, and disconnecting the throttle cable. ):
Thanks,

Fred

 

[fcawth]

Re: Help - can't get low idle on Volvo 3.0 GSP-A

Should I pull and inspect the manifold? Could the manifold gasket be leaking air?

Is there anywhere else that would leak air (valve oil seals?). Is there any way to check for air leaks without pulling things apart?

What's the deal with PCV valves on boat engines anyway, doesn't the hose to the flame arrestor keep any vacuum from being pulled on the crankcase?

Another thing to mention is that I pulled lots of impeller bits out of a water hose (more than was missing from the impeller in there), so it might have run hot for the previous owner. (Now it stays right at 160 when warmed up)

Based on my compression and vacuum tests, does it seem that the engine is generally in good shape?


Sorry for all of the questions.
As always, any ideas or help would be really appreciated...

Thanks again,
Fred