The Ford Barn

Brother A · 09-14-2011, 05:41 AM

I recently reset my timing and adjusted the carb to get the idle right. I've been noticing a "pop" or two when I push in the clutch. It's not a backfire just a "pop". I think it may be coming from the carb but I've been driving with the top down so I can be sure. My engine is a low mililage rebuild and has a Simmons HC head and Zenith carb. I had to adjust the carb quite a bit to get the idle speed down. I've since turned the mixture up a bit but no change. I thought I'd ask here before going further. Any suggestions would be appreciated. Thanks

Steve

Patrick L. · 09-14-2011, 03:45 PM

Well, I'll bite and take a stab at this.. I'm going to assume that you're talking about a 'bloop' between no throttle shifts.. I have no idea what is meant by turning the mixture up.. How much have you played with GAV, idle mixture, idle speed, or timing setting ?? You could well have a slight vacuum or exhaust leak.. Since you call this a 'pop' when pushing the pedal I'm also wondering if this has nothing to do with engine operation and may be something mechanical such as dry or binding clutch linkage,etc.

BRENT in 10-uh-C · 09-14-2011, 03:54 PM

Yep, I think Patrick is correct in that it appears your fuel mixture is too lean. Could be GAV setting, ...or a vacuum leak. One thing to note is generally if there is an exhaust leak at the manifold or muffler clamp, it will cause the fuel mixture to be a tad rich if anything because the carburetor is trying to inhale the exhaust fumes which the carbon monoxide tends to kill the oxygen in the fuel mixture thus richening up the mixture.

PC/SR · 09-14-2011, 05:56 PM

Are you sure it is an engine pop? Maybe the clutch pedal hitting a battery cable?

Brother A · 09-14-2011, 06:43 PM

I'm sure it's a pop. I think that you are on to something with the GAV. I've always kept it about a quarter open and I never changed that habit after I made the timing and carb adjustments. I feel like an idiot for not thinking of that.

What I meant by turning the mixture up was richening the fuel to air ratio.

Dave in MN · 09-15-2011, 01:58 PM

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The pop is most likely from a gas air mixture that is lean. It happens when you push in the clutch because you also just took your foot off the gas pedal. It is the closing of the carb that forces the fuel mixture to an even leaner condition. My guess anyway!
Good Day!

09-14-2011, 05:41 AM	#1
Brother A Senior Member Join Date: Jul 2011 Location: Southern CT & Southwest FL Posts: 115	Engine pops when I push in the clutch I recently reset my timing and adjusted the carb to get the idle right. I've been noticing a "pop" or two when I push in the clutch. It's not a backfire just a "pop". I think it may be coming from the carb but I've been driving with the top down so I can be sure. My engine is a low mililage rebuild and has a Simmons HC head and Zenith carb. I had to adjust the carb quite a bit to get the idle speed down. I've since turned the mixture up a bit but no change. I thought I'd ask here before going further. Any suggestions would be appreciated. Thanks Steve Last edited by Brother A; 09-14-2011 at 11:23 AM.

09-14-2011, 03:45 PM	#2
Patrick L. Senior Member Join Date: May 2010 Location: Largo Florida Posts: 7,225	Re: Engine pops when I push in the clutch Well, I'll bite and take a stab at this.. I'm going to assume that you're talking about a 'bloop' between no throttle shifts.. I have no idea what is meant by turning the mixture up.. How much have you played with GAV, idle mixture, idle speed, or timing setting ?? You could well have a slight vacuum or exhaust leak.. Since you call this a 'pop' when pushing the pedal I'm also wondering if this has nothing to do with engine operation and may be something mechanical such as dry or binding clutch linkage,etc.

09-14-2011, 03:54 PM	#3
BRENT in 10-uh-C Senior Member Join Date: May 2010 Location: Eastern Tennessee Posts: 11,971	Re: Engine pops when I push in the clutch Yep, I think Patrick is correct in that it appears your fuel mixture is too lean. Could be GAV setting, ...or a vacuum leak. One thing to note is generally if there is an exhaust leak at the manifold or muffler clamp, it will cause the fuel mixture to be a tad rich if anything because the carburetor is trying to inhale the exhaust fumes which the carbon monoxide tends to kill the oxygen in the fuel mixture thus richening up the mixture. __________________ . BRENT in 10-uh-C . www.model-a-ford.com ...(...Finally Updated!! ) .

09-14-2011, 05:56 PM	#4
PC/SR Senior Member Join Date: May 2010 Location: Santa Rosa, CA Posts: 1,285	Re: Engine pops when I push in the clutch Are you sure it is an engine pop? Maybe the clutch pedal hitting a battery cable?

09-14-2011, 06:43 PM	#5
Brother A Senior Member Join Date: Jul 2011 Location: Southern CT & Southwest FL Posts: 115	Re: Engine pops when I push in the clutch I'm sure it's a pop. I think that you are on to something with the GAV. I've always kept it about a quarter open and I never changed that habit after I made the timing and carb adjustments. I feel like an idiot for not thinking of that. What I meant by turning the mixture up was richening the fuel to air ratio.

09-15-2011, 01:58 PM	#6
Dave in MN Senior Member Join Date: May 2010 Location: Jordan, MN Posts: 1,416	Re: Engine pops when I push in the clutch Sponsored Links (Register now to hide all advertisements) The pop is most likely from a gas air mixture that is lean. It happens when you push in the clutch because you also just took your foot off the gas pedal. It is the closing of the carb that forces the fuel mixture to an even leaner condition. My guess anyway! Good Day!