- Joined
- Dec 20, 2022
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- 630
This reminds me that I should make an update, gasket was the same.
Holley 4160 - Mixture screws not doing anything
- Thread starter MurkyAsparagus
- Start date
- Joined
- Dec 20, 2022
- Messages
- 630
Update - Got it fixed!
I went through just about everything with no luck. I was able to get in contact with a person that's very well known in the MasterCraft community with these Holley 4160 carburetors. He told me to go 1.5 out on the mixture screws and 1.4 turns in from contact for the speed screw. These were nearly what I had, but it fired right up and worked as it supposed to. So, either some very finnicky settings or, like how things seem to go, it magically works after I exhaust every options and don't know why.
This boat has never idled the way it does now. If I could upload a video, I definitely would. Don't feel like going through the hassle of uploading to YouTube.
I went through just about everything with no luck. I was able to get in contact with a person that's very well known in the MasterCraft community with these Holley 4160 carburetors. He told me to go 1.5 out on the mixture screws and 1.4 turns in from contact for the speed screw. These were nearly what I had, but it fired right up and worked as it supposed to. So, either some very finnicky settings or, like how things seem to go, it magically works after I exhaust every options and don't know why.
This boat has never idled the way it does now. If I could upload a video, I definitely would. Don't feel like going through the hassle of uploading to YouTube.
Congrats @MurkyAsparagus. Curious.. What was the idle speed when you started? Is it possible the idle speed adjustment was just a little too high?
Just spitballin' here.
Regardless, isn't it great when you get it and they work right?
Just spitballin' here.
Regardless, isn't it great when you get it and they work right?
- Joined
- Dec 20, 2022
- Messages
- 630
I was right around 750 RPM idle speed on my tach. Honestly, I thought I was in the right RPM range and everything for what it was supposed to be. RPM didn't exactly change with the speed screw adjustment when I got it working. It may be at 700 now. It's hard to tell on a mechanical tach. I have one of those photo tachs I can use, just forgot it.
I'm just happy it works! I don't know what changed, who knows?
That is odd, you'd think with a totally clean carb and throttle plate in the right position you'd see some response from the idle mix screws, as in screwing them in all the way really should stall the motor.
I tried one of those on my old 4.3 V6 (original was a Quadrajet, but the 4160 was used by both OMC and Volvo after Rochester quit building carbs) and had no end of trouble with it. The carb did respond to the idle mix screws but no matter what I did it ran too rich at idle. Carb was brand new BTW. I went back to the old Quadrajet and it actually ran better!
Out of curiosity I took it all apart a few months later. What I found was that the clutch bolts that hold that secondary metering plate on, were loose. A guy on the Holley site bulletin board felt that more fuel was flowing from the secondary side than was supposed to be hence the excessive rich mixture that didn't respond to any of the normal Holley fixes. Put it back together but since it ran so well with the old Quadrajet, I left the Quadrajet on it.
BTW just for information, on a Holley, some fuel is always fed from the secondary bowl to the idle/main system to keep the fuel in that bowl from going bad. Also there is an adjustment for the secondary throttle plates that has to be right on the money.
I am curious if what I learned/fixed cured my Holley problem but will wait till my Q-Jet acts up again to find out.
Last point, when you were watching for idle speed change when adjusting the screws, were you using a separate tach or the dash tach? Dash tachs are really not accurate/sensitive enough for that job, I always use a digital tach, you can see small differences in RPM much easier.
I tried one of those on my old 4.3 V6 (original was a Quadrajet, but the 4160 was used by both OMC and Volvo after Rochester quit building carbs) and had no end of trouble with it. The carb did respond to the idle mix screws but no matter what I did it ran too rich at idle. Carb was brand new BTW. I went back to the old Quadrajet and it actually ran better!
Out of curiosity I took it all apart a few months later. What I found was that the clutch bolts that hold that secondary metering plate on, were loose. A guy on the Holley site bulletin board felt that more fuel was flowing from the secondary side than was supposed to be hence the excessive rich mixture that didn't respond to any of the normal Holley fixes. Put it back together but since it ran so well with the old Quadrajet, I left the Quadrajet on it.
BTW just for information, on a Holley, some fuel is always fed from the secondary bowl to the idle/main system to keep the fuel in that bowl from going bad. Also there is an adjustment for the secondary throttle plates that has to be right on the money.
I am curious if what I learned/fixed cured my Holley problem but will wait till my Q-Jet acts up again to find out.
Last point, when you were watching for idle speed change when adjusting the screws, were you using a separate tach or the dash tach? Dash tachs are really not accurate/sensitive enough for that job, I always use a digital tach, you can see small differences in RPM much easier.
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