Running rich, where should I start / continue

[Natesms]

I have been fighting a long running issue with both my motors running rich. I have 7.4 gls. I rebuilt the carbs last year and it ran great for a while then slowly the white smake started back up a few months later and now its to the point I will see a small fuel sheen on the waters surface.

The boat starts and runs great. No other issues other than running rich. I have adjusted everything I can on the carbs from floats to new mixture screws etc.

My question is should I invest in new carbs or should I look at something else prior to dropping the cash? I would buy 1 carb for one side and see what happens first but still don't want to spend $500 if there are other ideas our there.

 

[Bondo]

Ayuh,..... What carbs did Volvo use,..?? Holleys,..??

 

[Scott Danforth]

I would start with a pair of rebuild kits and new power valves

 

[bruceb58]

Your engine has multiple carbs?

 

[Scott Danforth]

each engine should have a single Holley 4160. if its running rich, especially at idle, would first suspect a failed power valve. could also be a dead cylinder

 

[jerryjerry05]

Did you rebuild or have them done?
Do a compression test.​

 

[Pesimist]

White smoke is usually a sign that your burning oil, a rich gas mixture puts out black smoke.

 

[Natesms]

Sorry for the delay. They are Holley 4160's. I personally did the rebuild last spring and followed the directions direct from the Volvo manual. It had no issues for a few months then both motors started running rich again. I have since re-done the power valves and adjusted floats with no change. When I attempt to adjust the idle mixture screws I can bottom them out and the it doesn't kill the motor, which it should, so fuel is getting around somehow.

I originally used a sierra rebuild kit, which was a mistake. The genuine holley gaskets are of much higher quality. I put in holley gaskets on the metering plates but that didn't have any effect.

I purchased a vacuum gauge to do a test but haven't gotten to it yet. I haven't done a compression test in 3 years but will try to do that prior to winterizing.

I have been contemplating the dead cylinder thing. How does one test for something like that? Just start pulling plug wires one at a time?

When I first did the rebuilds it ran fantastic, no white smoke. It still runs great. The motors idle smooth, there is no hesitation when you get into the throttle, its just smoky is all.

 

[bruceb58]

Just so you know your idle jets do nothing past idle.


Have you ever done a long hard run, turned off the motor and done a plug read? The best way to do it is to shut down the motor with minimum idle time and pull the plugs.

 

[Natesms]

Just so you know your idle jets do nothing past idle.


Have you ever done a long hard run, turned off the motor and done a plug read? The best way to do it is to shut down the motor with minimum idle time and pull the plugs.

I should probably have said the smoke only happens at idle. Once under throttle I don't see any issues.

I haven't tried doing plug reads. I've actually been reading on it this morning some.

 

[bruceb58]

That should make life way easier.

Still do the plug reads. That will at least insure tha your main jets are working properly.

How is the float level?

 

[Natesms]

Floats are good, when I did the rebuild I put all new floats in. I have adjusted them a couple of times to try and lean it out. I really wish these carbs had the site on them. I started with them perfectly level as the instructions stated and have since started bending them down to run more lean. No change.

 

[kelleyja]

Something to try before tearing into those carbs........

I had this same issue on a 4160, boat started, ran and idled great but ran super rich at idle with a cloud of white smoke from the drive. This happened right after a fresh rebuild. My issue turned out to be the air bleeds on top of the primaries. The high speed bleed was blocked (probably idle air bleed too) which caused fuel to siphon out of the venturi and drip down the primaries at idle. You can check this by opening the choke plate and looking down the throat at idle and drip from the venturi should be apparent. A quick shot of carb cleaner will fix it right up.

 

[Natesms]

Something to try before tearing into those carbs........

I had this same issue on a 4160, boat started, ran and idled great but ran super rich at idle with a cloud of white smoke from the drive. This happened right after a fresh rebuild. My issue turned out to be the air bleeds on top of the primaries. The high speed bleed was blocked (probably idle air bleed too) which caused fuel to siphon out of the venturi and drip down the primaries at idle. You can check this by opening the choke plate and looking down the throat at idle and drip from the venturi should be apparent. A quick shot of carb cleaner will fix it right up.

Thanks for the suggestion. I will give that a try before a winterize it in a week or two. Should I pull the carb off before hitting with the carb cleaner? Not sure where those go, don't want to shoot something deeper into the carb.

 

[HalfFish5087]

So the engines run great, but due to the white smoke and sheen you believe they're running rich?

 

[Natesms]

So the engines run great, but due to the white smoke and sheen you believe they're running rich?

Yes, the sheen, the strong smelling exhaust, and the fact that I got it to quit doing it for a while right after I did the carb rebuilds.

 

[Silvertip]

Hi idle speed and vacuum leaks will cause idle mixture problems. The fact both carbs have the same problem says you did something wrong.

 

[Natesms]

Hi idle speed and vacuum leaks will cause idle mixture problems. The fact both carbs have the same problem says you did something wrong.

I don't disagree. What's weird is they did so well for a couple of months right after the rebuilds. That's what I can't figure out. I've often wondered if I got the right metering plate gaskets in the kits. Those Sierra kits are junk, I'll never use another one of those again. I've been debating rebuilding again with a holley kit. I'm winterizing this weekend so I'll shoot some carb cleaner in the idle bleeds and see what happens then deal with it in the spring.

I have a feeling the most economical route is to hunt around for a good, local, carb rebuilder.

 

[Natesms]

Well I cleaned out the primary air bleeds. No change. I think I'm throwing in the towel and going to find someone that knows what they are doing to rebuild the carbs / tune the motors up. I'd rather pay a local mechanic $500 than Summit racing for a new carb.