After full rebuilding misfire problem

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Thomasdunstall

Thomasdunstall

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Jan 18, 2012
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Hi guys

after a full rebuilding ( I've already post few pics look the link below ) I've spent a couple of weeks working on correct timing and carbs setting
The engine start very easily and rev up very good
but I have a problem of misfire at one cylinder
I mean pulling the throttle and revving the bike I've backfire from one of the exausts!
any advice?

A bit frustrating but setting properly a commando I believe is the most difficoult part of the rebuilding...
Thanks for your help :D

http://www.accessnorton.com/black-roadster-first-starting-after-restoration-t19356.html
After full rebuilding misfire problem
 
Need type of ignition to help more but obvious you have some element in spark path on one side failing, plug, HT lead, coil connection or tigger leads bad or something interfering behind trigger plate mechanism, d/t bad fit or such. Its possible an air leak adding its annoyance too. I have had loose tail lens ground strap shorting out do this but cut whole ignition intermittently until completely dead before finding reason. After dark look sometime helps. Blocked pilot passage, sticking float or loose carb needle must be kept in mind too.
 
I've a new mkIV Boyer Bransden electronic ignition, brand new leads, spark plug Champion n7y
Lucas 6v coils (10 or 15 years old i guess...)
+ standard wiring, capacitor, rectifer and zener diode (found on the bike)
12 ah yuasa battery
 
Thomasdunstall said:
I have a problem of misfire at one cylinder

I've backfire from one of the exausts!
Click to expand...

Left or right?

You could try swapping over the following parts in turn (plugs, plug caps, HT leads, coils) and see if it moves the misfire to the other cylinder?
 
Hobot
Carbs are the original amal 932, but I've replaced all internal parts

Les
Backfire is on left cylinder, I'll start swappin' spark plug, caps, ht leads and then coils
 
I don't now how is correct in english,
the engine sputtered? burst?
he means that revving the engine it makes noise and flames from the left exhaust pipe
 
Thomasdunstall said:
I don't now how is correct in english but
he means that revving the engine it makes noise and flames from the left exhaust pipe
Click to expand...

Thanks, that is a better description.
 
Les it's a burst! an explosion like a thunder and not a pop/sputter ok?

If you remember, the bike had a bad kickback problem on the bike and we tried to solve it by retarding the timing, moving the trigger anticlock
do you think it could be a timing problem?

I'm explaning that because the "thunder" seems more a detonation

I didn't check yet the timing with a strobo
 
IMO if it backfires/thunders and cracks "after" the rev up and happens when winding/reving down its a timing or mixture problem.... Just retard it a bit and rev again will answer a few problemo's..
 
olChris said:
IMO if it backfires/thunders and cracks "after" the rev up and happens when winding/reving down its a timing or mixture problem.... Just retard it a bit and rev again will answer a few problemo's..
Click to expand...

I will check once again all the spark pack in the w-end
It could be also a carb problem but I'm inclined to exclude this 'cause I've spent many hours working on
but I believe the best things to do is a proper timing setting with a strobo
 
Thomasdunstall said:
Les it's a burst! an explosion like a thunder and not a pop/sputter ok?
Click to expand...

Yes, the noise is what we would call a 'backfire', although it can often be accompanied by flames so a 'backfire with flames'.


Thomasdunstall said:
If you remember, the bike had a bad kickback problem on the bike and we tried to solve it by retarding the timing, moving the trigger anticlock do you think it could be a timing problem?
Click to expand...

If the backfire only occurs on one cylinder then it seems unlikely to be caused by incorrect ignition timing.

Thomasdunstall said:
I didn't check yet the timing with a strobo
Click to expand...
:roll: :wink:
 
L.A.B. said:
If the backfire only occurs on one cylinder then it seems unlikely to be caused by incorrect ignition timing.
Click to expand...

Piero told me the same...timing problems would occour to both cylinder, he supposed was an electric problem

Thomasdunstall said:
I didn't check yet the timing with a strobo
Click to expand...
L.A.B. said:
:roll: :wink:
Click to expand...
I will work on it anyway
 
To troubleshoot, I recommend to install known good OEM points ignition. Then see how it runs. If still there, swap parts as recommended by L.A.B. :) Then ... go install electronic ignition if you want. That's what I did ... and I'm still with the points. :)

Just my 2 cents ...
 
Yes to substitution approach to Norton issues, Substitute a known good part to back-step and then trace in the enjoyable process of eliminations and subsequent rewards. 8)
 
I've checked all cables and fix them all properly
Then I've start the bike

Now it has no more backfire but a problem still on the left cylinder
Leaving it warming up, the left cylinder still cold!
I mean, the bike start and rev up and down well, but from the left exaust a cold air came out!
Any suggestion?

To me seems an electric problem :cry:
 
I just went through a similar situation, cold on the right side, started easy, but the right side was cold, would not rev well

start it and pull the right plug wire, se how it runs on only one plug and see if it revs up Then try running on the other cylinder.

Mine was a carb problem, some bitts in the low speed jet passage and the needle had stuck in the springs also make sure the carb slides are moving together

does it respond to changing the idle needle stop and does it lean or richen with the idle needle mixture

Dennis
 
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