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Popping through muffler

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Popping through muffler


Post by ArizonaMike » Tue Aug 09, 2005 11:46 am

My '62 has a butterfly Kehin with the Mallory Unilite ignition. Assuming the timing's correct, what should I look at to stop the popping through the muffler when upshifting and coasting in gear with the throttle closed? A leaner low- or mid-range jet was installed, increasing the miles per gallon by about 14 (gets about 50 now), but the plugs look correct. Thanks in advance for any help.


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Re: Popping through muffler


Post by Skip » Tue Aug 09, 2005 7:20 pm

I sealed my exhaust with silicon and mine stopped..........

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Re: Popping through muffler


Post by 57pan » Wed Aug 10, 2005 1:08 pm


That's quite an improvement in gas mileage. Do you know what jet size you have in it now and what the jet size was before? Just curious because I am running a Keihin butterfly carb too. I ran a #85 jet for about 5500 miles and then something changed and I had to go up to a #90 to keep it from coughing and sneezing thru the carb.
I picked up a CV carb off eBay and I'm going to go thru it and get it set up for the panhead and will convert over to the CV later.
But, I think Skip is on the right track - sounds like it is sucking air into the exhaust pipes.

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Re: Popping through muffler


Post by 108 » Wed Aug 10, 2005 3:45 pm

Mike, In general, too lean a idle mixture causes decell popping and a air leak into the pipe would make things worse. Is that Unilite distrbutor single-fire? If not ,the"waste spark" may be helping cause the pop also .

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Re: Popping through muffler


Post by fourthgear » Thu Aug 11, 2005 7:21 pm

108 & all
If you got the newest flier from JP cycles , They have an interesting article in it about fuel inj. programming with a lap top for newer HDs and it says basically that too lean a mixture or too rich can cause popping in the exhaust . Unburnt fuel entering the hotter exhaust pipe on deceleration , like you said 108. I will copy the paragraph word for word tomorrow and you all can make of it what ya will. Interesting stuff , ya learn something new every day.

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Re: Popping through muffler


Post by kickerdel » Thu Aug 11, 2005 7:51 pm

Hi Mike,I would check your pipes first.I used to run my 45 with a leak to get the popping,great for frightening little old ladies.

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Re: Popping through muffler


Post by fourthgear » Fri Aug 12, 2005 2:49 pm

Here is an excerpt from the article written by Dave Brickford aka Ultraboy in Jp cycle flier,
Decel popping: one thing that seems to be common on F>I> Harley's with after market pipes is a popping on deceleration. Annoying to some , embarrassing to others , its mostly caused by a mixture that is too lean to ignite in the combustion chamber , but rich enough to ignite and pop-pop-pop in the hot pipes when the throttle is closed. deceleration is one of the engines " dirtiest times of operations , where the engine is in transition from higher RPM and throttle positions to a closed throttle , and decreasing RPM. To solve the popping issue we may need to starve it, or flood it,and or add timing Now if its a muffled popping, its too rich; if you have a loud crack popping , its too lean. The rest goes on to tell you how to do it with a lap top PC and soft ware, I know this article is about fuel injection on newer Harley's , but there is some useful info in it that may help you trouble shoot you Panhead motor if you have the decel popping. I know we can not adj. timing on Pans @ certain RPM ranges with a lap top computer, but may be you can experiment on where and how it is set with the timing mark in what part of the window it is in and carb adj. , jet sizes what ever to eliminate the popping. Mine does not pop on deceleration , but I have had some that do , may be it has something to do with after market pipes , who knows , just some added info to confuse us all.

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Re: Popping through muffler


Post by hplhd » Fri Aug 12, 2005 7:46 pm

i know it's off topic but i just wanted to say dave,aka ultraboy, is one of the most generous and helpful guys i have been associated with in a long time. a bunch of us chipped in and bought a shovel basket case for a shop teacher to rebuild with his students with dave donating the lions share and handling all logistics. i just had to take this opportunity to let you all know since 4thgear brought his name up. thanks guys and sorry for going off topic.

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Re: Popping through muffler


Post by ArizonaMike » Sat Aug 13, 2005 2:06 pm

Hi 57Pan,

To answer your question about which jet produced the 14 mpg improvement, the person who installed it couldn't remember which one it was, but did say that he replaced the mid-range-idle jet and that you should start with a #66 there. Hope this is helpful.

Mike Colaizzi, PghPA

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