Loud popping sound upon start up

htown16 said:

Popping generally indicates a lean condition. Does it go away as the engine warms up? Is the new exhaust more open than the old. Does it do it at idle, then turn the air screw in a bit. Does it do it at mid throttle, try raising the needles a notch, ie put the clip in a lower notch. Do you still have the chokes on. If you lower them that will create a richer mixture and if it runs better having the chokes on
then you have confirmed it is too lean.

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Tornado said:

Confirm pilot jets, two tiny holes in carb throat floor, are clear and a good spray is seen up out of them when spraying in through the air mixture screw hole (block off the fuel and air inlet holes oncarb body when doing this). I like to also reverse spary these jet holes from above using long spray can straw....should het good spray up one when blowing down into other.

Have you confirmed needle/needle jets are correct size? These can wallow out at higher mileage and will give poor idle characteristics, even popping.

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quawk said:

Have not had the carbs back off since starting recently after installing the new exhaust because wasn't having this problem prior to that, or at least not nearly as noticeable as it has become now.

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Tornado said:

Changing exhausts will alter the mixture required as you've altered the back pressure of the system. The bike may have had carbs adjusted/jetted for those non stock silencers. Best to confirm what number jets (needle, main jets) are in there and compare with recommended for stock setup ( also assumes the stock air cleaner is present and not plugged up).

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johnm said:

You changed the exhaust system and now you have popping.

I bet you have an exhaust leak somewhere.

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quawk said:

Have a new air filter/screen (ham cam) and carb to filter boots since acquiring the bike earlier this year.

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quawk said:

Well, I installed a totally new exhaust system, with new crush gaskets/seals at the header pipes to cylinder head, new header pipes, new mufflers and new muffler to header pipe clamps. As recommended by others here on the forum, I used nickel anti-seize on the threads on the finned header exhaust rings, and used the correct "c" spanner tool to tighten them. Although I guess it's possible, I don't suspect an exhaust leak is the problem, but will check that also. The mufflers I used are the Emgo replacements and aside from the inner tube having some louvers along its' length they are pretty much a straight through design. Don't know if that would be enough to change things.

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johnm said:

I try a dummy assembly to check the exhaust rings screw in far enough to fully crush the gasket seal. And then check where the rings face up onto the headers. Sometimes they don't take up all the gap even when fully screwed in. Then I use two crush gaskets. I use high temp RTV on the ring threads and in the crush space. Tighten the rings two or three cycle times after running. When both hot and cold. Then check again after a week or two.

I also use the RTV at the muffler joint making sure the clamp does compress the sealing surface.

In the first instance I'd run it a bit and then carefully check to see any sign of exhaust leakage.

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quawk said:

I'll consider all your suggestions and look/check closely all my exhaust connections. I had given some thought to possibly using two crush gaskets when I was installing the new system if I thought the rings weren't threading in far enough, but they seemed to seat properly. I know you do what you need to do to correct a problem but I'd like to avoid using RTV if I can. Does the RTV eventually cease giving off an odd odor after being heat cycled a number of times? I know it's a different product but I used JB Weld to seal leaks on an old Gold Wing exhaust system and that stuff gave off an odd smell every time you started and ran the engine for a long time after I originally used it.

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quawk said:

Progress report: Removed the carbs and because when I started this revival project earlier this year they were removed and ran through my ultrasonic cleaner so they were, what I felt like at this point already pretty clean. I disassembled, and this time, again, just shot carb cleaner and high pressure compressed air through them. I did raise the needle one notch, (thanks htown16 for the suggestion). Reassembled and started it (fingers crossed). Well, the popping was gone. After running the engine for several minutes (3-4?) I was able to snug down the header exhaust rings a little bit more (thanks to members suggesting it may be exhaust leak related}. Unfortunately, upon removing and reassembing the carbs, I've found that the new (6-7 months old) carb to filter boots are both split. Disappointing. Will be getting another new pair from a different vendor. I've only started and ran it once before I posted this, so, of course will do so more times, but at this point another small victory in the revival and thanks to all the guys here that have responded with help and suggestion.

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Tornado said:

Did you confirm good spray up out the two tiny throat holes? Ultrasonics will not clear hard precipitated fuel residue from tiny passages.a strong solvent soak and or mechanical force is needed. Look up Bushmans Guide to Amal Carb Tuning guide for excellent breakdown of qhere these carbs have problems and how to resolve.

Split boots, hmmm Ive never had one split after many r&r's, surprised how well they've stood up to my rough treatment. Might be a quality issue with supplier. My 2 pairs are presumably originals, so 50 yrs old and inexplicably still great.

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