4.3 volvo won't plain

[Raffo]

Hello,
This is my first post, ever, I hope I don't mess it up. I have a 1990 Carver Santiago that won't plain most of the time. I have twin 4.3 Volvo Pentas. They have no problems starting but when I try to go on plain, the boat tops out at 3000 rpms. I can hear the engines pitch get higher as if there's a serge of power. At that point I can plain out but after a few minutes, the engines seems to drop in power and I fall back down to 3000 rmps and can't plain again. Seems the engines get a rush of power for a few minutes then looses power then gets another rush of power then drops. Usually the interval is about 10 minutes between rushes. I'm thinking it's my carbs but was wondering if anyone has had this kind of problem.

Any suggestions would be greatly appreciated.

Thanks,
Raffo

 

[Bondo]

Re: 4.3 volvo won't plain

Ayuh,.... Welcome Aboard,...

The 1st thing I'd do is change the Fuel Filtes,+ inspect the contents when you do....

Here's how Volvo says to Test the boats fuel system,...
Courtesy of Don,...

 

[chiefalen]

Re: 4.3 volvo won't plain

The boat sit in the water i would first see if it has a dirty bottom.

Maybe alot of water in the bilge?

 

[Raffo]

Re: 4.3 volvo won't plain

Thanks for the replies!

I will try the fuel vacuum test this weekend. Seems that my port engine is the problem with low RPMs. I was able to get the starboard engine up to 3500 but I think the drag on the port side is bringing the RPMs down on the starboard side. I hauled the boat out Sunday so I won't be able to bay test it until next Spring. Surprisingly, the boat bottom and props were clean.

Thanks again.
Raffo

 

[mthieme]

Re: 4.3 volvo won't plain

What length is your Santiago?
I've seen these from 27' to 38'.

 

[Don S]

Re: 4.3 volvo won't plain

I will try the fuel vacuum test this weekend. I hauled the boat out Sunday so I won't be able to bay test it until next Spring. Surprisingly, the boat bottom and props were clean.

You really can't do the vacuum tests properly out of the water. Here is that same testing process with a little more info added.

http://forums.iboats.com/showthread.php?t=283269

 

[Bondo]

Re: 4.3 volvo won't plain

Here is that same testing process with a little more info added.

Ayuh,.... I just updated my saved favorites list.....

 

[jerryjerry05]

Re: 4.3 volvo won't plain

Has it always done this? Or did it start slowly.
After you change the filters.Do a compression test. Jerry

 

[Raffo]

Re: 4.3 volvo won't plain

Thanks again for all the replies.

I have a 1990 27' Santiago with the original engines. I did the heads in 2006 on the starboard engine. At that time the Port engine's compression was OK. By Ok I mean that the cylinder compression varied from each other by no more than 5% - 8%. I read the link on how to do the vacuum test not realizing that it had to be done in the water. I'll have to wait until Spring. I pickled the engines this weekend and noticed some black oil mixed in with the exhaust water (BUMMER!). Not a lot but enough to say ugh! I think I'm going to have a lot of work getting the boat ready in the Spring.

Thanks again for all the suggestions.

Raffo

 

[Raffo]

Re: 4.3 volvo won't plain

Forgot to mention that this started in 2006. I did a compression test and found a burnt valve on the starboard engine. Worked fine after I did the starboard heads then late in the 2006 season had some problems intermittently plaining. 2007 was on and off but toward the end of 2007 I could not plain. 2008 started ok then trailed off bad very quickly. I would say for most of 2008 I could not plain.

Thanks,
Raffo

 

[chiefalen]

Re: 4.3 volvo won't plain

Who adjusted the valves after the head work?

Was the motors tuned correctly?

In the spring tune the motors correctly.

Full tune up.

Do the fuel test.

Make sure there is nothing heavy like water hiding in the boat.

Clean bottom.

If the fuel checks out good, and the problem is still there, vacuum test.

Heres the link.

Post the results, see you in the spring.

http://www.secondchancegarage.com/public/186.cfm

 

[Raffo]

Re: 4.3 volvo won't plain

One more observation. As I pickled the engines I noticed the clear plastic hose that leads from the fuel pump to the flame arrester kept pushing out gas. My starboard engine's hose does not do this. Could this be an indication of a ruptured diaphragm on the fuel pump? I don't know if this is normal or not. I was reading in the Volvo manual that a bad fuel pump could cause problems at high speeds.

The values were adjusted by my boat mechanic and then given a full tune-up.
That was done on the starboard engine. I got that engine turning at 3500 so I believe it's the port engine.

Thanks all,
Raffo

 

[Don S]

Re: 4.3 volvo won't plain

As I pickled the engines I noticed the clear plastic hose that leads from the fuel pump to the flame arrester kept pushing out gas.

That is a tell tale hose to tell you the fuel pump is bad.
It also makes the engine run real rich, raw fuel pumped into the carb.
Replace the fuel pump, then see how it runs.

 

[Raffo]

Re: 4.3 volvo won't plain

Thanks Don,
I'm leaning to that being the problem. The port engine began running rich about the time I started having the problem. I thought it was the carb.
I'll replace the pump and let you know how it turns out in the Spring.

Thank you all for all the helpful comments! Have a great winter!

Raffo