Author Topic: Popping in silencer  (Read 336 times)

Online RoyC

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Popping in silencer
« on: 19.08. 2018 09:52 »
Started my bike up for the first time in two months, went second kick.
I have a popping sound in the left silencer, had it for quite a while.
Could this be due to tight rocker clearances ?

New carb and plugs, none resistor type leads.
My bike is a 1958 A7SS
Stafford UK

Online morris

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Re: Popping in silencer
« Reply #1 on: 19.08. 2018 10:27 »
Exhaust popping or banging usually caused by unburned fuel detonating in the exhaust. Maybe your left pot runs a bit richer?
Does it pop when opening or closing the throttle?
'58 BSA A 10 SA
'52 BSA A 10 Plunger
'55 MORRIS ISIS
The world looks better from a motorbike
Belgium

Online RoyC

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Re: Popping in silencer
« Reply #2 on: 19.08. 2018 10:52 »

Does it pop when opening or closing the throttle?

No, most noticeable on fast tick over,
My bike is a 1958 A7SS
Stafford UK

Online morris

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Re: Popping in silencer
« Reply #3 on: 19.08. 2018 14:12 »
Leaking exhaust valve?
'58 BSA A 10 SA
'52 BSA A 10 Plunger
'55 MORRIS ISIS
The world looks better from a motorbike
Belgium

Offline Triton Thrasher

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Re: Popping in silencer
« Reply #4 on: 19.08. 2018 14:55 »
Can be weak mixture.  Maladjusted pilot screw, blocked pilot jet or slide wear.

Air leaks into the exhaust pipe, at the cylinder head, usually cause banging on the over-run.

All this assumes that your engine gets serviced according to the schedule.  I don’t have much sympathy for people who ride around until the valve and points gaps close up and then moan on the Internet.


Online RoyC

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Re: Popping in silencer
« Reply #5 on: 19.08. 2018 16:16 »
Leaking exhaust valve?

This could be too tight a setting on exhaust valve. I will have to look at it.
I don't ride the bike, just start it up occasionally.
Brand new carb, so no wear on slide. All set up for me as per BSA factory specs. 

  https://surreycycles.com/carburettors/amal-monobloc-376-389/
My bike is a 1958 A7SS
Stafford UK

Offline Triton Thrasher

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Re: Popping in silencer
« Reply #6 on: 19.08. 2018 18:32 »
If the problem arose after fitting a new carburettor, suspect a too-big slide cutaway.

Also check for inlet manifold air leaks by spraying WD40 or something on the carb to manifold joint while the engine is idling.  If rpm changes, there’s a leak.

Online RoyC

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Re: Popping in silencer
« Reply #7 on: 19.08. 2018 19:40 »
If the problem arose after fitting a new carburettor, suspect a too-big slide cutaway.

Also check for inlet manifold air leaks by spraying WD40 or something on the carb to manifold joint while the engine is idling.  If rpm changes, there’s a leak.

It was there before the new carb (one reason that I replaced the carb).
Already checked the for leaks.

I am still going with valve not closing properly.
My bike is a 1958 A7SS
Stafford UK

Offline chaterlea25

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Re: Popping in silencer
« Reply #8 on: 19.08. 2018 19:41 »
Hi Roy,
Quote
All set up for me as per BSA factory specs.

Those settings were for the fuel available at the time, this is only a very distant relation to the crap sold now  *sad2*
Any new carb that I have had to look at after being fitted to old bikes has run lean on the factory settings  *conf*

Starting up a bike without riding it and getting everything up to working temp's will cause all sorts of issues


John
1961 Super Rocket
1963 RGS (ongoing)

Offline Triton Thrasher

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Re: Popping in silencer
« Reply #9 on: 19.08. 2018 19:45 »
A valve not sealing will show up on a compression test.