| Any ideas as why I hear a very small puff or pop noise coming out of the carb [message #253660] |
Sun, 29 June 2014 15:34  |
budworks521
Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...
Karma: 4
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Good day folks, I was involved in quite a few topics last fall concerning a new upper half on a 455 engine. Everything went back together fine without issues and have been finally getting it ready for a test drive. With the coach parked and running I hear a very small puff or pop noise through the carb. It is very infrequent but there none the less. I have yet to put the engine under a load to see if the issue is a major concern. I have heard reports about sticky valves causing this issue. Do any of you folks believe a vacuum line or carb adjustment could be at play? The noise is not constant and can only hear it if you put your ear to the carb. Thanks in advance. Also, I must note that I had a mechanic adjust the leanness on the air fuel mixture and only noticed the noise after his adjustment.
1974 Painted Desert
455 upper half rebuild
constant project inexperienced mechanic
Grand Rapids Mi
Always trying to learn
[Updated on: Sun, 29 June 2014 18:11] Report message to a moderator |
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| Re: Any ideas as why I hear a very small puff or pop noise coming out of the carb [message #253722 is a reply to message #253660] |
Sun, 29 June 2014 21:36  |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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If the quadrajet has been rebuilt, immersing it in the carb cleaner will remove the sealant around the caps that are crimped in over the holes where the fuel passages were drilled when it was made. These leaks will drain the float bowl in 3 days or less of non-use and cause a long crank on cold startup because the float bowl has to be filled again. They will still drip when the engine is running and cause those intermittent noises you hear when the drop of liquid fuel hits the floor of the manifold. The caps can be resealed with a super epoxy from GM or also available at A/C repair parts vendors.
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: Any ideas as why I hear a very small puff or pop noise coming out of the carb [message #253723 is a reply to message #253722] |
Sun, 29 June 2014 21:45 |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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It's also possible you have old fuel making varnish on the valve stems making them stick open. If you do, get it outta there or use some Lucas or STA-BIL fuel treatment (or both) to restore the fuel. If the fuel is over a year old and has alcohol in it, it may have drawn water out of the atmosphere and separated with the alky-water down in the bottom of the tank, where the fuel pickup is located. If that is the case, just get it outta there and replace the fuel.
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: Any ideas as why I hear a very small puff or pop noise coming out of the carb [message #253839 is a reply to message #253660] |
Mon, 30 June 2014 12:54 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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budworks521 wrote on Sun, 29 June 2014 14:34Good day folks, I was involved in quite a few topics last fall concerning a new upper half on a 455 engine. Everything went back together fine without issues and have been finally getting it ready for a test drive. With the coach parked and running I hear a very small puff or pop noise through the carb. It is very infrequent but there none the less. I have yet to put the engine under a load to see if the issue is a major concern. I have heard reports about sticky valves causing this issue. Do any of you folks believe a vacuum line or carb adjustment could be at play? The noise is not constant and can only hear it if you put your ear to the carb. Thanks in advance. Also, I must note that I had a mechanic adjust the leanness on the air fuel mixture and only noticed the noise after his adjustment.
I think any momentary miss can cause that noise. It could be a sticky valve, wrong idle mixture, or an ignition related issue.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: Any ideas as why I hear a very small puff or pop noise coming out of the carb [message #253866 is a reply to message #253660] |
Mon, 30 June 2014 17:28 |
budworks521
Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...
Karma: 4
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Senior Member |
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Well I took it for the first test drive under load and ran fine at 35mph and decided to hit the big street and drove about 1 mile at 55 mph without incident. However, I started to get some surging, stalling, and loss of power. I decided to recheck all the vac lines and they are spot on. My vapor lock/canister line to carb was loose. Fixed that and put my fuel mixture back to original mark. I had a mechanic adjust it too lean in my opinion. So far I haven't test drove it again but I also head some dripping noises in the carb about 30 minutes after shutting it down. Went out to the coach and check with the throttle if gas was in the bowl and I did get some squiring into the carb. At a loss, seems like a carb problem. I had 93 octane in the tank all winter long. I need to find out how to check for leaks or drip downs from the bowl?? Thanks for the responses people!
1974 Painted Desert
455 upper half rebuild
constant project inexperienced mechanic
Grand Rapids Mi
Always trying to learn
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| Re: Any ideas as why I hear a very small puff or pop noise coming out of the carb [message #253926 is a reply to message #253866] |
Mon, 30 June 2014 22:48 |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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Run it a minute to be sure the carb is full of fuel. Shut it down and immediately prop the throttle wide open and keep the choke plate wide open also. Grab a flashlight and maybe a brew and assume a comfortable position where you can look down through the carb and watch for fuel to drip onto the manifold floor. When you floor the throttle there will be a squirt of fuel that will need to evaporate for a few minutes before you can start your vigil. Compressed air lightly applied can speed up that process. After it evaporates there should not be any liquid fuel in the manifold. Remove the carb and do this test if it is leaking and it will be obvious where it is coming from. The fix will be what I said earlier.
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: Any ideas as why I hear a very small puff or pop noise coming out of the carb [message #254081 is a reply to message #253660] |
Wed, 02 July 2014 06:07 |
budworks521
Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...
Karma: 4
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Senior Member |
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Thanks for the ideas on the carb. It has been two days and still waiting to find time to analyze for a few hours. I did put the fuel mixture back to the original mark and reconnected the vapor vac line better. I'll see if the popping noise goes away and also see if fuel is getting into the carb from the throttle arm prior to starting. If my float is messed up I know where to start. I want to do a compression check. Anybody know of a decent brand tool that is easy to use and understand??? Thanks again for the ideas.
1974 Painted Desert
455 upper half rebuild
constant project inexperienced mechanic
Grand Rapids Mi
Always trying to learn
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