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Re: Backfiring in Amal Concentric Carb #93312
06/26/06 4:02 pm
06/26/06 4:02 pm
Joined: Nov 2005
Posts: 7,406
Back on the mainland!
JubeePrince Offline

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Joined: Nov 2005
Posts: 7,406
Back on the mainland!
Matthew,

Not sure if advancing ignition will get rid of backfire......but the line would be to the left of the pointer for over-advanced.......

Now, shoot that lock off your wallet and get those coils!! smile

HTH,

Steve Prince


'77 T140J
"Vintage Bike". What's in your garage?

"The paying customer is always right."

Fitting round pegs into square holes since 1961...
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Re: Backfiring in Amal Concentric Carb #93313
06/26/06 8:42 pm
06/26/06 8:42 pm
Joined: Apr 2004
Posts: 538
Toronto
Matthew Manton Offline OP
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Matthew Manton  Offline OP
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Hi Guys,

I shot the lock off this afternoon. wink

Cheers
Matthew


Matthew
1970 T100S
Re: Backfiring in Amal Concentric Carb #93314
06/27/06 8:47 am
06/27/06 8:47 am
Joined: Oct 2003
Posts: 3,606
Emsworth, sunny south of Engla...
D
dave jones Offline
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Joined: Oct 2003
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Emsworth, sunny south of Engla...
Advancing the ignition will make it worse as I mentioned before.

Firing back through the carb is caused by the above or a weak mixture at the idle/ cutaway position. This is a simple problem that can be adjusted out without spending a load of cash.

Re: Backfiring in Amal Concentric Carb #93315
06/27/06 10:09 am
06/27/06 10:09 am
Joined: Oct 2004
Posts: 4,429
Melbourne Australia
Tiger Offline
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Tiger  Offline
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Melbourne Australia
I must agree with Dave Jones, it is most unlikely that advancing the timing will do anything but make an existing spitback problem worse.
Wondering if your very old AA mechanism has ever been stripped and lubricated ?
Poxy thing the mech AA but necessary when the bikes were built although the older manual advance/retard lever was better in more sedate times.
If you buy 12V coils now you will possibly regret the decision later, the Boyer runs best with 6V coils and that is where you will end up if you ride the bike a lot.
The problem which you have is probably in the carb, we all get excited and delve into our store of arcane knowledge, been there and done that more times than I would care to remember.
A sticky intake valve is very unlikely unless you have been using lead replacement petrol [spit] an easy and cheap way to pretty much eliminate that possibility is to fit a fresh set of B6ES plugs and run two stroke mix as an experiment.
Given that you have tuned the bike, checked valve clearances and strobed timed ignition etc, my bet is a bowed carb flange.


1969 TR6R
7.62 x 51 is not a maths puzzle.
Re: Backfiring in Amal Concentric Carb #93316
06/27/06 4:31 pm
06/27/06 4:31 pm
Joined: Apr 2004
Posts: 538
Toronto
Matthew Manton Offline OP
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Matthew Manton  Offline OP
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Hi Guys,

Got new 12 volt coils this morning from Walridge Motors, that was quick, I only ordered them on Monday. A little concerned about using them now, I think I will hold off fitting them until I have done a bit more experimentation. laugh

A question about the coil holders, I had them powder coated, is this a problem concerning earthing (grasping at straws here)?

When I rebuilt the bike I took the carb manifold to work glued sandpaper on a granite surface plate and took the high spots off. Also made sure where the manifold mates with the head that it was smooth and level.

I did strip down the AA unit, fitted new springs, cleaned everything up. When I use the strobe and rev the engine you can see the pointer line up and then back off when you close the throttle. I take it this is a sign it is operating OK?

I have adjusted the air mixture screw, and it ticks over well at 1 1/2 turns out. Move it into about 1 turn out and it starts to hesitate. Move it out to 2 1/2 turns and the idle does speed up, but I presume this is to far out? I am not quite sure if my adjustment procedure is bang on. I have the symtoms of a weak mixture and 2 1/2 out seems to much.

I bought a truckload of .015" diameter drills and it goes in the hole no problem.

Installed new valves and springs and they were a good running fit. Checked and adjusted the valve clerances when cold.

Good idea Tiger about new plugs and 2 stroke mixture, I will give that a try. I am using BR7ES plugs, what will the 6ES do? Hou much 2 stroke oil should I put in for a gallon of gas?

I am going to take the carb and manifold off and check that everything is still true.

I will also double check the valve clearances.

Thanks for all your advice guys. bigt

Cheers
Matthew


Matthew
1970 T100S
Re: Backfiring in Amal Concentric Carb #93317
06/27/06 7:28 pm
06/27/06 7:28 pm
Joined: Oct 2003
Posts: 3,606
Emsworth, sunny south of Engla...
D
dave jones Offline
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D
Joined: Oct 2003
Posts: 3,606
Emsworth, sunny south of Engla...
I have just noticed that you said that it spits back when you decelerate on a closed throttle? are you sure it isn't just popping in the exhaust due to an air leak in the exhaust or too rich a pilot mixture? Firing through the carb usually happens when you open the throttle from closed and you can see a puff of smoke/ vapour come out the air cleaner. Without an air cleaner it can start a fire which happened on my B31!

A hot Triumph (hot in tune and hot in temperature will never run perfectly at idle speeds and the occasional stall is unavoidable.

Have you strobed both cylinders. Try retarding the ignition by turning the whole back plate a tiny amount in the same direction that the cam rotates and see if this stops spitting back. Don't go too far or the exhausts will start glowing red instead! The two cylinders will remain balanced.

Re: Backfiring in Amal Concentric Carb #93318
06/27/06 9:02 pm
06/27/06 9:02 pm
Joined: Apr 2004
Posts: 538
Toronto
Matthew Manton Offline OP
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Matthew Manton  Offline OP
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Hi Dave,

It is back firing through the carb.

When I decelerate after burning up to a stop sign I blip the throttle and it then spits back through the carb. At times it cuts out.

I will try rotating the back plate a tad and see what this does.

I have strobed both cylinders, both bang on.

Cheers
Matthew


Matthew
1970 T100S
Re: Backfiring in Amal Concentric Carb #93319
06/28/06 3:45 am
06/28/06 3:45 am
Joined: Feb 2006
Posts: 671
Qld, Aust and Otago,NZ
G
Ginge Offline
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Qld, Aust and Otago,NZ
Matthew,

If the idle speeds up at 2 and 1/2 turns out you need to have your pilot air screw there. It will cause faltering on both sides of the "fastest idle position". You are aiming for the middle. Put it there and drop the idle to a dull roar then go for a ride. Make sure the bike is warm before you play.

If it gets too lean you'll see it as a white plug condition if you leave the bike in the driveway idling for 5mins or so. A short ride running lean on the pilot won't hurt it as long as you don't cane it.

1 and 1/2 is a start point and each bike/carb/fuel/country is different.

Also see Matthew Fredricton simialr thread for my post. I don't think it is your issue but maybe.


Ginge
Re: Backfiring in Amal Concentric Carb #93320
06/28/06 8:03 am
06/28/06 8:03 am
Joined: Oct 2004
Posts: 4,429
Melbourne Australia
Tiger Offline
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Tiger  Offline
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Melbourne Australia
As for two stroke oil run the leanest mix recommended on the container, hardware barns sell it in 100ml bottles for cheap.
Synthetic or mineral will do the job.


1969 TR6R
7.62 x 51 is not a maths puzzle.
Re: Backfiring in Amal Concentric Carb #93321
06/28/06 5:41 pm
06/28/06 5:41 pm
Joined: Mar 2005
Posts: 10,156
Boston, Massachusetts
J
John Healy Online content

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Joined: Mar 2005
Posts: 10,156
Boston, Massachusetts
quout: Ginge
1 and 1/2 is a start point and each bike/carb/fuel/country is different.
--------------------------------------
Unfortunetly the physics behind 1 1/2 turns doesn't vary by country/bike/fuel... That said, because of different tapers on the adjustable needle it can vary from carb to carb.

If the bike settles down outside of the 1 1/2 turns, or the setting recommended by the carb manufacturer, the pilot jet is either too small, partially blocked or too large. On an AMAL you adjust the size of the pilot jet until the pilot air screw settles in the 1 1/2 turn range.

It has to do with the flow (speed) of the air in the pilot circuit and resultant vacuum on the pilot jet.
2c
john
john


Re: Backfiring in Amal Concentric Carb #93322
06/28/06 11:19 pm
06/28/06 11:19 pm
Joined: Feb 2006
Posts: 671
Qld, Aust and Otago,NZ
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Ginge Offline
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Qld, Aust and Otago,NZ
Noted, thanks John.

So the point is if Matthew gets a faster idle at somewhere well beyond the 1 and 1/2 turns out (or as per his manual) his pilot jet is rich, (too big) or the air circuit is partially blocked somewhere (carb cleaner?).

A little bit off is probably acceptable and he looks elsewhere.


Ginge
Re: Backfiring in Amal Concentric Carb #93323
07/01/06 8:27 pm
07/01/06 8:27 pm
Joined: Apr 2004
Posts: 538
Toronto
Matthew Manton Offline OP
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Hi Guys,

Re-set the tappets, put new plugs in and retarded the timing.

When it is strobed and revved the line on the rotor is about 1/4" to the right of the pointer. Just went for quick 30 minute ride and the backfire did not show up. Will the retard situation have any adverse effects?

The pipes did not seem to change color on this ride, and I did not notice any ill effects when accelerating.

Cheers
Matthew


Matthew
1970 T100S
Re: Backfiring in Amal Concentric Carb #93324
07/01/06 11:15 pm
07/01/06 11:15 pm
Joined: Oct 2004
Posts: 4,429
Melbourne Australia
Tiger Offline
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Tiger  Offline
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Melbourne Australia
I will measure a rotor and roughly convert your 1/4" to degrees but that seems a lot.
Maybe mark your points plate at where you are and and try advancing a little to see if and at what point the spitback problem re-occurs.
Will get bact to you on the rotor dimension, I wonder does your rotor TDC mark line up at actual TDC ?
Fresh premium grade fuel etc ?


1969 TR6R
7.62 x 51 is not a maths puzzle.
Re: Backfiring in Amal Concentric Carb #93325
07/02/06 12:05 am
07/02/06 12:05 am
Joined: Apr 2004
Posts: 538
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Matthew Manton Offline OP
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Matthew Manton  Offline OP
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Hi Tiger,

I will experiment with backing it off and see what happens. I will set it to an 1/8" and give it a go there.

TDC does line up with the mark, checked it using the hole on the fly wheel.

Using the best grade fuel at the pumps.

Cheers Mate bigt

Matthew


Matthew
1970 T100S
Re: Backfiring in Amal Concentric Carb #93326
07/02/06 2:49 am
07/02/06 2:49 am
Joined: Mar 2005
Posts: 10,156
Boston, Massachusetts
J
John Healy Online content

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Posts: 10,156
Boston, Massachusetts
Mathew posted:
TDC does line up with the mark, checked it using the hole on the fly wheel.
----------------------------

TDC lines up with what mark?

Don't you want the timing mark to line up with the pointer when the 38 degrees before top dead center slot in the flywheels is engaged?

What ever happened to timing the motor so the pointer lines up with the line at Full Advance?

You know, I haven't seen Richard make one post to this question... does he know something I don't?
john


Re: Backfiring in Amal Concentric Carb #93327
07/02/06 3:28 am
07/02/06 3:28 am
Joined: Apr 2002
Posts: 716
Out There!
N
Nick Offline
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Joined: Apr 2002
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Out There!
You do, of course, have the phenolic heat spacer between the carb and the manifold, don't you?


When people who should have known better cautioned me about the dangers of motorcycle racing, I always told them that a fear of death is nothing more than a fear of life in disguise.
Re: Backfiring in Amal Concentric Carb #93328
07/02/06 1:19 pm
07/02/06 1:19 pm
Joined: Apr 2004
Posts: 538
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Matthew Manton Offline OP
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Matthew Manton  Offline OP
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Hi Guys,

John,
Lines up with the mark on the rotor.

Nick,
I have the heat spacer installed.

Cheers
Matthew


Matthew
1970 T100S
Re: Backfiring in Amal Concentric Carb #93329
07/02/06 11:02 pm
07/02/06 11:02 pm
Joined: Apr 2004
Posts: 538
Toronto
Matthew Manton Offline OP
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Hi Guys, it's me again,

I was re-setting the points (6CA) and re-strobing today and have a question.

My cam has two scribed lines on it - 180 degrees apart! When I set the gap using the scribed line to .015" and then rotate around and check the same gap against the other scribed line I find it is way out, about .025".

The cam has a slot in it, do you use the scribed line just forward (clockwise) of the slot to set the gap? Or is my cam buggered up?

Cheers
Matthew


Matthew
1970 T100S
Re: Backfiring in Amal Concentric Carb #93330
07/03/06 3:29 am
07/03/06 3:29 am
Joined: Apr 2002
Posts: 716
Out There!
N
Nick Offline
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Joined: Apr 2002
Posts: 716
Out There!
My first Triumph would only run on one cylinder. I was going crazy trying to figure out why. Turns out the points cam was bent and was only opening up one set of points!
When I set point gap, I just measure the gap at its widest setting, not relying on any lines. If yours gives a different reading on each set of points, it may be bent. If so, this might be Lord Lucas' way of telling you to just get a Boyer and eliminate all ignition problems forever, more or less....


When people who should have known better cautioned me about the dangers of motorcycle racing, I always told them that a fear of death is nothing more than a fear of life in disguise.
Re: Backfiring in Amal Concentric Carb #93331
07/03/06 6:32 am
07/03/06 6:32 am
Joined: Oct 2004
Posts: 4,429
Melbourne Australia
Tiger Offline
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Melbourne Australia
The AA could be "cocked" in the internal taper in the bore of the exhaust cam.
Is the centre of the AA fixing bolt rotating eccentrically ?
Also there is a pin in the exhaust cam which engages a slot in the tapered [male] section of the AA, maybe pull the AA and check all of the above ?


1969 TR6R
7.62 x 51 is not a maths puzzle.
Re: Backfiring in Amal Concentric Carb #93332
07/03/06 10:21 pm
07/03/06 10:21 pm
Joined: Feb 2006
Posts: 671
Qld, Aust and Otago,NZ
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Ginge Offline
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Qld, Aust and Otago,NZ
Matthew,

My bike (71 T100C) has two scribed lines on the points cam as well, but when I really got into it, only one actually opened the points. RF set me straight.

There's only one high point on the cam. You might have to slacken off the contact set adjusting screws and back off the contacts until you get one set roughly opening and closing on one point of the cam, then do the other side, then do the gap.

Sort of, rough it all in, then do the fine stuff (then mark the line you are using with a dot of white paint)


Ginge
Re: Backfiring in Amal Concentric Carb #93333
07/03/06 10:54 pm
07/03/06 10:54 pm
Joined: Sep 2005
Posts: 461
sunshine coast, queensland, au...
bonnie john Offline
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sunshine coast, queensland, au...
call me stupid...
but i just can't see how a bent cam could upset 1 set of points without having EXACTLY the same effect on the other set


SPEED KILLS
do not exceed 250mg ...
Re: Backfiring in Amal Concentric Carb #93334
07/04/06 2:42 am
07/04/06 2:42 am
Joined: Apr 2006
Posts: 1,708
Virginia, USA
SBoyd Offline
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Virginia, USA
Bonnie John: "but i just can't see how a bent cam could upset 1 set of points without having EXACTLY the same effect on the other set"

Admittedly, i've had a couple brewski's tonight as it is the eve of our big USA holiday and pretty sad about what we're doing trying to control the world........

Anyway, I agree with you. Just went out and looked at the breaker cam on my T140. There is only ONE scribe line. Since that cam rotates at 1/2 crankshaft speed, the same part of the cam that opens one set of points opens the other set. Assuming you set each point on the scribe line, both cylinders will get the same dwell regardless of bent cam. Thus it would seem that running on one cylinder can't be blamed on a bent cam as long as the SAME scribe line is used to set each point.
Steve


Stop the insanity.
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