adjusting the idle fuel mixture

[TitanTn]

Any tips on how to adjust the idle mixture? The engine doesn't seem to run any different no matter where I put the screws (unless I run them all the way in). The instructions I've read say to back out until the rpms run higher. I can't get the rpms to change at all. Suggestions?

[haugy]

Check a few things first:

-Is the choke opening all the way? My electric choke stuck and I was fiddling with the mixture screws for nothing.
-Idle set screw on the side all the way out?

Make sure those two are good to go. Then turn the screws one and half turn open. Once the engine is warm and the choke is open all the way, slowly work them in like you've been doing. With the idle screw all the way out and the mix screws closed, it should make a difference.

Check your choke and idle screw, report back.

[michael hunter]

When was the last time you had the carb overhauled? Sounds like you have internal leakage?

[DAFF]

When was the last time you had the carb overhauled? Sounds like you have internal leakage?

A carb which needs some love will act like yours...... I'm thinking its time to let her soak and add some new gaskets.....

[kvand347]

My first thoughts were with Haugy...choke is not pulling off or you are not waiting for the engine to warm up to operating temp before trying to adjust carb. I'd check that first as he recommended.

My second thought could be the primary float set too high if you just rebuilt the carb. That will negate the idle adjustment.

My third thought could be timing related. Might want to check and see if you are timed properly.

Assuming you have a Holley 4160 on there with electric choke?

[TitanTn]

My first thoughts were with Haugy...choke is not pulling off or you are not waiting for the engine to warm up to operating temp before trying to adjust carb. I'd check that first as he recommended.

My second thought could be the primary float set too high if you just rebuilt the carb. That will negate the idle adjustment.

My third thought could be timing related. Might want to check and see if you are timed properly.

Assuming you have a Holley 4160 on there with electric choke?

I am letting the engine warm to operating temp, and the choke is off. Yes, I have the 4160 with electric choke.

I did just rebuild the carb, and that process went smoothly. I didn't adjust the floats. How do you adjust them?

I do need to check the timing.

Haugy - I followed you on what you were saying except for the idle screw being all the way out. If I backed that screw out, the engine wouldn't stay running.

[kvand347]

I am letting the engine warm to operating temp, and the choke is off. Yes, I have the 4160 with electric choke.

I did just rebuild the carb, and that process went smoothly. I didn't adjust the floats. How do you adjust them?

I do need to check the timing.

Unfortunately our carbs are internally adjusted floats. To adjust, you need to take the primary fuel bowl off. Once off, you turn the bowl upside down and check to see if the top of the float is horizontal with the top of the bowl (keep in mind the top of the float and bowl are now at the bottom since they are upside down). Confuse you? That is just kind of baseline. The way to adjust is to bend the metal tab connected to the float.

Wish I had a picture for you...I will be doing this this weekend because my primary bowl is cracked and leaking fuel.

What kind of rpm's are you getting?

[kvand347]

One more thought could be a vacuum leak somewhere. Make sure that the carb is securely attached to the spacer and the spacer to the intake manifold. An unlit propane torch or carb cleaner around those areas while running will tell you if there is a leak.

[Moose]

I am letting the engine warm to operating temp, and the choke is off. Yes, I have the 4160 with electric choke.

I did just rebuild the carb, and that process went smoothly. I didn't adjust the floats. How do you adjust them?

I do need to check the timing.

Haugy - I followed you on what you were saying except for the idle screw being all the way out. If I backed that screw out, the engine wouldn't stay running.

Sorry for jumping in here but your engine should start and stay running on just the idle mixture screws. usually about 1 1/2 to 2 turns out will get ya close. It might run rough but as long as it stays running. Then you can adjust your idle with the adjustment screw on the throttle. But it does need to stay backed out for the first idle mix adjustment. After you have both where it will idle smooth I like to tweek the mix screws a 1/4 turn or so either way to get the best performance. Anyway thats my way may not be exactly right but it works.

[haugy]

Did you try the mixture screws at 1.5 turns out? As Moose said, it should stay running fine with the idle set screw out.

If it won't stay running at all like that, try 1 3/4 turns out on the mixture. if it won't after that. Your floats need to be adjusted.

[TitanTn]

Thanks guys. I think I was missing an important part of the adjustment process (backing out the idle screw before beginning). I have high hopes that I'll see a different result with this process. Hopefully I will be able to attempt it tonight. I'll let you know.

[TitanTn]

Outside working on it right now. Backed out the idle screw and it still runs. Motor is warm. When adjusting the screws, it almost shuts off when I crank them in (makes sense) and it runs okay when I turn them 1.5 turns out. But I don't feel like there any difference between 1.25 turn and 2 turns. Doesn't seem like I can fine tune. For now I've adjusted the idle screw and everything seems to runs fine.

[TitanTn]

Here's a video of it running.


http://youtu.be/al9tFMREUUs?hd=1

[kvand347]

Motor sounds nice!

I was always told that you are supposed to adjust idle mixture in gear. Obviously something you wouldn't do off the hose...

If you truly wanted it dialed in, you would attach a vacuum gauge to find your highest vacuum reading when turning the screws in 1/4 at a time.

[TitanTn]

Thanks Kevin. I've never heard that "in gear" part, but I've done all I can do on the trailer for now. I need to get it on the water and see how it behaves. I do feel that it starts really easy, idles great, and doesn't smoke like it did.

[kvand347]

I'm not sure if it pertains to boats, but I do know it is something you would do for a vehicle with an automatic trans. I had a '75 corvette and that is how I tuned the carb after it was rebuilt. I just figured it would be the same on the boat...could be wrong here...