Quick idle mixture question...99 5.0L GL Volvo 2bbl Holley

[craze1cars]

Hello,

After a fairly comprehensive tune-up completed over the winter (plugs/coil/wires/cap/rotor/set timing/compression test/rewire and/or clean all connections), my boat is now running like an absolute top. One last nagging little annoyance I'd like to dial out...some minor sooty residue that I find on my transom after pulling it out of the water.

It does seem a tad rich at idle...so I'm gonna systematically start tweaking the carb's Choke and/or idle mixture screws. I went to the garage today to document my starting points.

1999 Volvo 5.0GL PWTR, 2 bbl Holley carb, all stock. Factory says base setting for idle mixture screws is 3/4 to 1 turn out. I popped the caps and checked mine. Starbord side was 1 turn out. Port side was 1 and 3/4 turns out. Hmmmmm. Likely be my reason for rich idle? (used boat...I know nothing about the history). So for the time being I just turned that Port side in 3/4 turn so that now they are the same, both are set at exactly 1 turn out. I will see how she runs next time I'm on the water, and I will do some on-water tuning at that time...

My question is this: Is there ANY compelling reason that someone would have set one side differently from the other on this carb? Manual says they should both be set the same...but I know the realities of tuning sometime cause us to need to deviate at times.

Thoughts? Or am I simply doing the right thing by now just setting them the same and then tuning the idle from there?

Thanks!

 

[Black as]

Re: Quick idle mixture question...99 5.0L GL Volvo 2bbl Holley

Irrespective on how you found the mixture screws you need to adjust them while the engine is running and up to full temperature with the spark arrester fitted.

Do you know how to do this ?

Have a read of this link http://forums.iboats.com/showthread.php?t=342393

 

[Don S]

Re: Quick idle mixture question...99 5.0L GL Volvo 2bbl Holley

Adjust it and see what happens. Who knows what all a previous owners can do to his boat. Especially if he doesn't know what he's doing..
Read this forum for a while and you will see what I mean.

 

[craze1cars]

Re: Quick idle mixture question...99 5.0L GL Volvo 2bbl Holley

Guess this isn't really a quick question. Maybe I got too wordy when I asked it. And the link didn't answer it either. So I'll ask again:


Is there any reason when properly tuning a 2bbl carb, that opposing idle mixture screws might end up being set differently from one another? Or should opposing screws ALWAYS be set in the same position when adjustment is completed?

Thank you.

 

[Black as]

Re: Quick idle mixture question...99 5.0L GL Volvo 2bbl Holley

To answer that question NO they can end up being in different positions

 

[craze1cars]

Re: Quick idle mixture question...99 5.0L GL Volvo 2bbl Holley

To answer that question NO they can end up being in different positions

Thank you Black. That's what I was looking for. But now I guess I need to expand this question and ask how and why they might actually end up in different positions?

My Volvo service manual says:


"initially set idle mixture by turning screws inward until seated, then outward the specified turns." (this is why I set mine evenly at one turn out in my garage)

"final adjustments are to be made with engine running and at normal operating temp" (which I will do on the lake soon)

"Turn idle mixture screws inward until RPM begins to drop due to lean mixture. Back screws out EVENLY AND ALTERNATELY...If RPM begins to drop due to overly rich mixture...turn screws inward until maximum engine RPM and smoothness is achieved."


Note Volvo makes a clear point to say they should be first set evenly (to book spec), and then after warm-up screws (plural) should be turned in/out "EVENLY AND ALTERNATELY" to reach max RPM/smoothness. So to me this book says the screws should ALWAYS end up at the same position as each other when I am completed doing this mixture adjustment.

Yet your answer contradicts my manual and says they may end up in different positions. And this is the precise reason I have asked this question...I am just trying to understand why this might be. Could it be because after obtaining some plug readings later one finds the port side cylinders are running richer or leaner than than starbord side? That's all I can think of as a possibility. Just curious...

Any further explanation or discussion from you or anyone is appreciated. Thanks again.

 

[Silvertip]

Re: Quick idle mixture question...99 5.0L GL Volvo 2bbl Holley

The reason they tell you to START at an even setting is just that -- its a starting point. Evenly and alternately means the same thing but the end result is that you turn inward until the engine gags, outward until it gags, and happiness is somewhere in between which may NOT be exactly the same on each side. Intake passages to all cylinders are not the same length, exactly the same shape and exactly the same air flow characteristics. Therefore the idle mixture screws may not end up the same.

You also said you will "tweak the choke". There is one choke setting -- the correct setting. It is adjusted on a stone cold engine. With the throttle slightly open, adjust the choke open then gradually bring the adjustment so the choke plate just closes (not slammed tightly closes). Done.

 

[bruceb58]

Re: Quick idle mixture question...99 5.0L GL Volvo 2bbl Holley

The idle mixture is not that big a deal in the scheme of things. Although it will be nice to get it dialed in , as long as you idle well, you are fine. Once you have your engine at higher RPM, the idle mixture is basically irrelevant as its the main jets that determine your air/fuel mixture. A little bit of soot wouldn't bother me. That is usually caused by the choke opening slower than it needs to...which you have little control of. Just make sure it opens fully.

 

[craze1cars]

Re: Quick idle mixture question...99 5.0L GL Volvo 2bbl Holley

Thanks for the input guys...helps me understand a little better.

Silvertip, as for tweaking the choke...yes I fully understand how to set the baseline choke and be done with it. That's where it is now. And yes it opens all the way after it warms up.

BUT...if the engine will still start easily when cold with LESS choke, is there any reason I shouldn't go ahead and turn it a notch or two leaner so it's cracked open a touch, and therefore doesn't burn any richer than absolutely necessary to get the motor to fire and warm up? And then if it still starts quickly when cold, turn it yet another notch or two leaner if it will still start well the next time? Especially if they tend to open slowly as Bruce says it might.

Obviously if I end up going too far with it, it simply won't start very quickly when cold. And at that point I'll have reached the limit and will need to go back richer a little bit.

I guess that's what I meant by tweaking the choke.

I suppose the ultimate goal in my small mind is to have the idle mixture AND the choke both set as lean as possible while still having good cold starts and good idle quality...with my objective being to reduce the bit of soot on the transom and reducing fuel usage and pollution at idle. It's just my constant and anal persuit of perfection. I don't see much harm in the experimentation...correct me if you do.

You've both helped me with my original question. Just bouncing ideas and questions around and nothing more. Much appreciated...