Idle problems 1992 431A volvo penta, 290DP

[vstol]

Hello all,

I recently have been having some rough idle problems associated with a very rich exhaust. The problem is sometime it does it and sometimes it does not, I tried turning up the idle just a bit (maybe over the years it backed off) that just makes it idle high when not running rough and make it run a little rougher when it is. Other than idle the boat runs great, still hit WOT with not problems, good out of the whole? Initially in think rebuild the carb, but then I think maybe the coil is going or the cap needs changed. Before I start on my list of things to check, I wanted your input? The tune done last year was just plugs, oils, impeller and some corrosion control work. I have not changed any of the ignition parts since I have had, it about 2 years now. Again very rich fuel smell along with a little white smoke when running rough at idle.

I am thinking the following:

First and foremost put some Seafoam in the gas tank, I have not ran as much this year as before, about 1 to 3 times a month I go out and try to run on muffs at least every 2 weeks.
Check the fuel/water filter
Check distributor, cap, and button.
Change coil, can this be checked?
Rebuild carb

Anything else to add?

 

[Don S]

Re: Idle problems 1992 431A volvo penta, 290DP

The tune done last year was just plugs, oils, impeller and some corrosion control work.

Just changing the spark plugs is NOT a tuneup. That is called changing the spark plugs.
A tuneup, includes plugs, cap, and rotor. Timing check both base and advance. Carb mixture adjustment, and idle speed adjustment.
If you are having idle problems, it might be a good idea to do a compression check also. Just to verify it's ok.
Also check the the choke is working correctly. If it's stuck shut it will cause the black smoke. It's electric, so make sure the wire connections are clean and tight.
White smoke could also be some steam, which some is normal to see because you have hot exhaust going into water.
When was the last time you had the risers off and checked the manifolds/risers for corrosion. Here is a picture of what to check, the metal needs to be shiny when clean. A dull black across the areas in red are not metal, and will not seal. Replacement is the only option.

 

[vstol]

Re: Idle problems 1992 431A volvo penta, 290DP

I changed the risers and manifolds about 8 months ago, have not had them apart since.

It sounds like your saying to go ahead and change the cap, rotor, and button, and then to check the timing.

I am not sure what the default setting are for the carb fuel and air mix. I assume u yoalready know what carb I have on it, i think it is a rodchester, i know it is a 4 bbl.

By compression we are talking cyclder compression, pull the plug, insert gauge, turn over motor, right?

 

[vstol]

Re: Idle problems 1992 431A volvo penta, 290DP

I will look throught he shop manauls for the carb setting, I have a few volvo manual and one other, i hope one has the carb info in it.

 

[Don S]

Re: Idle problems 1992 431A volvo penta, 290DP

Those are not "Default" settings, they are nothing more than preliminary settings to get it close enough to run the engine and warm it up for final adjustment . From there they are adjusted to get the proper air fuel mixture for your particular engine. There is no EXACT settings for carbs.
Here is a service bulletin on how to do a Compression test. (Note: It's a Merc bulletin, but almost word for word of the Volvo bulletin. Both came from GM. )

http://www.boatfix.com/merc/Bullet/97/97_25.pdf

 

[vstol]

Re: Idle problems 1992 431A volvo penta, 290DP

UUHHMMMM?

so how do you know when you have properly adjusted the fuel air mixuture, unfortuanly I am not much of a carb guy?

 

[vstol]

Re: Idle problems 1992 431A volvo penta, 290DP

Well I think I may have found one of the problems, besides needing new cap rotor and button. The fuel linkage runs through a bracket with a grove in it that has broken, also a couple of locknuts were loose on the linkage.

Engine seems to run good on the muffs but how could this explaine the rough idle, I did not touch the idle screw?