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Backfire on quick throttle close #360224
02/26/11 5:53 pm
02/26/11 5:53 pm
Joined: Oct 2008
Posts: 1,666
Canada
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LarryLebel Offline OP
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LarryLebel  Offline OP
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Canada
Getting a backfire on quick throttle closing on the B44R. What adjustments do I need to make? Thanks, in advance.

Last edited by LarryLebel; 02/26/11 5:54 pm.
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Re: Backfire on quick throttle close [Re: LarryLebel] #360278
02/26/11 11:53 pm
02/26/11 11:53 pm
Joined: Aug 2001
Posts: 1,719
BC Canada
441/R3cafeSteve Offline
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441/R3cafeSteve  Offline
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Sounds like my exhaust leak around muffler and head gap.
Steve


The 441, most versatile BSA of the 60's
Re: Backfire on quick throttle close [Re: ] #360290
02/27/11 12:36 am
02/27/11 12:36 am
Joined: Aug 2001
Posts: 3,348
Michigan, USA
BONZO R.I.P. Offline
In Remembrance
BONZO R.I.P.  Offline
In Remembrance
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Posts: 3,348
Michigan, USA
I have used a spacer at the muffler joint on my A-65 that tended to shift a bit creating an air leak .A Sudden loud pop or two was the first sign I need to reposition it.As I recall I had some overly rich situation while jetting a carb on another bike and this created a short series of quieter pops,on a twin with big TT pipes I would get a longer series of popping that sounded more like rumbling when I went from full throttle to closed quickly ,I really liked that sound but the pipes were irritating on a trip of any length.I don't recall having an ignition timing issue that caused exhaust popping but I suppose it is quite possible.Cracked valve or worn seat possible,maybe valve adjustment or sticky valve?

FWIW-BONZO

Re: Backfire on quick throttle close [Re: LarryLebel] #360493
02/28/11 5:52 am
02/28/11 5:52 am
Joined: Aug 2001
Posts: 4,266
Santa Barbara, California
KC in S.B. Offline

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Santa Barbara, California
+ 1 more on the exhaust leak............ or rather the exhaust SUCK, on let down. My A65F did it, I sealed the pipe in the head, and it quit. Took the pipe off for somwthing, and didn't reseal......... it's back again. Kind of got used to it.....


Down to 1 BSA, 2 Triumphs, 1 '56 Chevy
Re: Backfire on quick throttle close [Re: KC in S.B.] #360509
02/28/11 8:57 am
02/28/11 8:57 am
Joined: Oct 2007
Posts: 726
bromley uk
N
norton bob Offline
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Posts: 726
bromley uk
There is often a small amount of unburnt fuel passing thro the exhaust on the overun and if fresh oxygen is introduced via a poor fitting exhaust the combustion flame ignites it,a rich mixture makes it worse.I used to deter tailgaters by turning the ignition off for a few revolution, the backfires were like cannon shots.A flimsy modern exhaust wont stand much of this!!.

Re: Backfire on quick throttle close [Re: norton bob] #360546
02/28/11 5:13 pm
02/28/11 5:13 pm
Joined: Oct 2008
Posts: 1,666
Canada
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LarryLebel Offline OP
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LarryLebel  Offline OP
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Canada
Thanks. I will do the silicon seal trick on the exhaust pipe. Currently it is just a push in fit.
Would Permatex Ultra-Black work?

Last edited by LarryLebel; 02/28/11 5:35 pm.
Re: Backfire on quick throttle close [Re: LarryLebel] #360588
02/28/11 8:56 pm
02/28/11 8:56 pm
Joined: Oct 2007
Posts: 1,524
Auckland NZ
Ignoramus Offline
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Ignoramus  Offline
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Auckland NZ
Larry...car parts shops sell all sorts of special exhaust sealants ....you can get realy thick stuff which is kind of like puty which sets rely hard and will take huge temp....takes only a few minutes to set.

I have no idea of brands in USA but one i used was "holts firegum"....even the name inspired confidence


"There's the way it ought to be and there's the way it is" (Sgt Barnes)
Re: Backfire on quick throttle close [Re: LarryLebel] #360590
02/28/11 9:07 pm
02/28/11 9:07 pm
Joined: Sep 2002
Posts: 7,813
Seattle
Alex Offline

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Alex  Offline

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Seattle
+1 on the exhaust leak causing backfire.

And, as Iggy sez, there is a sealant that works better than silicone. "Muffler Mender" is one brand sold here in the US at major auto supply stores.

Also, make sure the pipes are a tight slip fit in the head. Any wiggle and it won't matter what you use to seal it.


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
Re: Backfire on quick throttle close [Re: LarryLebel] #360592
02/28/11 9:10 pm
02/28/11 9:10 pm
Joined: Aug 2001
Posts: 1,852
The Northwoods... Michigan
Steve Erickson Offline
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The Northwoods... Michigan
Permatex Ultra Hi-Temp I think it is called, copper color... used it in a lot of Victors (they often seem to have this problem), holds for about a year.

Re: Backfire on quick throttle close [Re: ] #360656
03/01/11 5:07 am
03/01/11 5:07 am
Joined: Oct 2008
Posts: 4,934
Gnashville
DavidP Offline

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Gnashville
Originally Posted By: 1968BSA

can be caused by over rich mixture,
or leanness causes my gaining air around the header pipe.

Any wonder that carb tuning will drive one batty!?!?

I vote for an exhaust leak. The BSA tactic of just shoving the pipe into the head ranks as one of the engineering world's dumbest designs.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
72 T120V cafe project "Mr. Jim"
Re: Backfire on quick throttle close [Re: LarryLebel] #360848
03/02/11 5:39 am
03/02/11 5:39 am
Joined: Aug 2001
Posts: 1,719
BC Canada
441/R3cafeSteve Offline
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BC Canada
Next head I am welding a steel flange on header and tig welding an alloy one to head! wait! I can do that on the bike! My header is quite stock and snug and silicone pops out after 200-300 miles 30-60 days my guess. larry I would get some brass shim stock at a hobby shop and shim it with that and then hose or collar clamp it so it cannot blow out. Should be snug, I have had best results that way and it expands as it heats.
:o)
Steve

Last edited by 441cafeSteve; 03/02/11 5:49 am.

The 441, most versatile BSA of the 60's
Re: Backfire on quick throttle close [Re: LarryLebel] #360868
03/02/11 1:50 pm
03/02/11 1:50 pm
Joined: Sep 2002
Posts: 7,813
Seattle
Alex Offline

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Alex  Offline

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Seattle
I have never had a problem with the slip-in pipes. When they are a good, snug fit and sealed with exhaust sealer, they don't leak and they stay put.


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
Re: Backfire on quick throttle close [Re: LarryLebel] #360936
03/02/11 9:31 pm
03/02/11 9:31 pm
Joined: Oct 2007
Posts: 1,524
Auckland NZ
Ignoramus Offline
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Ignoramus  Offline
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Auckland NZ
Like CafeSteve recons shimming out excessive clearance is a good one....I used some compressed asbestos fiber gasket paper (cause it was what i had) and liberaly plastered with the type of (non silicon) sealant Alex is talking about, it worked well (admitedly that was on the mighty M20, but the pipe was soooooooo loose it was ridiculous)

I have always thought too LEAN will cause backfire more than too rich assuming evething esle is ok? because it casues the motor to run much hotter.


"There's the way it ought to be and there's the way it is" (Sgt Barnes)
Re: Backfire on quick throttle close [Re: Ignoramus] #361009
03/03/11 3:51 am
03/03/11 3:51 am
Joined: Oct 2008
Posts: 1,666
Canada
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LarryLebel Offline OP
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Canada
I sealed it with the Permatex Copper RTV today. It seemed like the pipe did not fit snug against the lip on the exhaust port when I tightened the bracket which has been welded. I'll see how it works out and maybe use the exhaust pipe sealant next time. I have the needle at the top groove (instead of the middle groove) so can't get the mixture any leaner with the current carb setup which I think is stock for a B44R. In normal riding its not a problem only when panic stops are required if such a thing is possible with a BSA. I recall one panic stop in particular where I was about a car length shy of what was required (I bailed out to the right) with a big back-fire and the motor stalled. Pretty funny actually but scary also. We all know the safest motorcycle is the one parked in the garage.

Last edited by LarryLebel; 03/03/11 3:51 am.
Re: Backfire on quick throttle close [Re: LarryLebel] #361109
03/03/11 7:53 pm
03/03/11 7:53 pm
Joined: Oct 2007
Posts: 1,524
Auckland NZ
Ignoramus Offline
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Ignoramus  Offline
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Auckland NZ
Larry :"I have the needle at the top groove (instead of the middle groove) so can't get the mixture any leaner with the current carb setup "

that might be part of the problem....its running too lean maybee....ASAIK lean will cause backfires...try raising the needle one notch (ie nove the clip down one) and see if it makes a diffrence ...no harm trying.

could also be excessively worn slide effectively leaning out the mix by passing too much air


"There's the way it ought to be and there's the way it is" (Sgt Barnes)
Re: Backfire on quick throttle close [Re: LarryLebel] #361136
03/03/11 11:01 pm
03/03/11 11:01 pm
Joined: Sep 2007
Posts: 1,815
Charleston SC
Ob1quixote Offline
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Ob1quixote  Offline
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Charleston SC
I kinda like a little crackle and pop on decel. When the pipe is good and hot, a quick stab of throttle will throw a nice flame out the muffler about 1/2 second later.

Still, the 441 is quite tame compared to my XR416 dirt machine. 103db, folks know when they need to move over!


When singing "Kung Fu Fighting" is outlawed, only outlaws will sing "Kung Fu Fighting"
Re: Backfire on quick throttle close [Re: LarryLebel] #365067
03/27/11 2:20 am
03/27/11 2:20 am
Joined: Oct 2008
Posts: 1,666
Canada
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LarryLebel Offline OP
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Canada
Two rides in 11 now and no backfiring.

Re: Backfire on quick throttle close [Re: LarryLebel] #365094
03/27/11 9:07 am
03/27/11 9:07 am
Joined: Aug 2001
Posts: 1,719
BC Canada
441/R3cafeSteve Offline
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BC Canada
Is your air screw responding and effecting the idle when running? or are you compensating for an old carb? 3-1/2 slide 25pj 230-240mj needle in middle 106 nj. That is stock anything off that without hop-up tuning may indicate a leak or stuffed passage imo. With even my manifold I just raise needle one to bottom groove and put in a 250 and #4 slide (not req') so even the slightest change can throw things off. Is there a wear hole in pipe? leaky carb to head? Hard to say why it would quit but if your oil is getting to 160+ after 30 minutes it may be running too lean. That and ticking of alloy after only 20-30 minutes is also a sign. At worse go out at night like I did once and see if the header is glowing cherry! they can do that and survive even!
I just rewelded my header because the nut on lower engine bolt ate a hole through it! I also put a 5/16" on the back of the Campbells again. Also replaced centre clutch hub re tapped the detent spring nightmare and got the gearbox back in without breaking it.
You will solve it, header to muffler leak?
S
Having no running bike 20 days before bike show is not an option here. Maybe I will even wash it.


The 441, most versatile BSA of the 60's
Re: Backfire on quick throttle close [Re: 441/R3cafeSteve] #365158
03/27/11 4:31 pm
03/27/11 4:31 pm
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Posts: 1,666
Canada
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LarryLebel Offline OP
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Canada
I just RTVed the exhaust pipe and did not raise the needle. At the middle groove the plug was very sooty so its now on the top groove. The back firing might have started when I replaced the exhaust pipe and muffler with a new old ones. Steve, the carb could well be worn out but I would be hard pressed to figure this out. I have riden by your place on a few occsions but you have never been out and about. I might try again today after I vacuum the house.


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