Author Topic: B31 Loss of power after 25 Miles or so  (Read 256 times)

Offline DartmoorStar

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B31 Loss of power after 25 Miles or so
« on: 10.07. 2019 18:04 »
Hi
Since getting the B31 (1955) up and running again, hoping to put in some more longer runs and feel confident to get out on some VMCC Club runs and the like, but I have hit an issue losing power after a short while on some local test runs which arn't overly taxing. I thought at first the Clutch was overheating as there was a slight burning smell, the clutch rod was adjusted, this seems to have cured that particular issue , I have since discovered that the choke was sticking, this is now rectified, New Spark Plug (L82C)  is on order (N3C currently fitted, which I am told is not correct). I have ensured the fuel cap vent is clear, along with fuel reaching the carb, as i did originally have a few rust particles from the tank standing for 20 plus years. Other suggestions include Magdyno coil failing and the bore being too tight? Is there anything else I should check?
There is what i describe as a pinking noise in the minute or two before I lose Power. It will then kick over again after a 10/15 minute cool down.
I know 'RogerSB' has witnessed a restart of my first issue and didn't believe the engine was over hot, so suggested posing here for your thoughts.
Today I ran for about 45 minutes covering 26 miles.

Spark Plug looks good I believe (attachment)

A short Video is posted of one test run without incident - Vimeo- did find post this that the Choke was stuck.
https://vimeo.com/346589412

another here in a facebook thread if a member of the group, with both power failure videos
https://www.facebook.com/groups/britishmotorcyclemechanics/2419028874826402/?comment_id=2424240434305246&reply_comment_id=2420474111348545&notif_id=1562704242912486&notif_t=group_comment

same link here for Vimeo ( see 06:00 and 11:50 minutes, or enjoy the full video)
https://vimeo.com/347347004

I HAVE ORDERED AN INLINE FUEL FILTER FROM TANK TO CARB

Appreciate the groups helpful advice as this is the third time in a week.

Offline muskrat

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Re: B31 Loss of power after 25 Miles or so
« Reply #1 on: 10.07. 2019 21:07 »
G'day
My first thoughts are tight bore, tappets set too tight, condenser failing.
Ony saw the first video. Rejoining fb BMM to see the second and third link not there.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
Australia
Muskys Plunger A7

Offline DartmoorStar

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Re: B31 Loss of power after 25 Miles or so
« Reply #2 on: 10.07. 2019 21:29 »
G'Day Muskrat, third link is now there, it was still processing I believe, but just checked it and it is working. Tappets may be too tight, so will double check this.

Offline Shark

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Re: B31 Loss of power after 25 Miles or so
« Reply #3 on: 10.07. 2019 23:11 »
https://www.a7a10.net/forum/index.php?topic=10874.0

Dartmoor, those links went off into space for me, the above is my experience of "unexplained power loss", I was lucky that I didn't trash the thing. Cheers.


Online ironhead

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Re: B31 Loss of power after 25 Miles or so
« Reply #4 on: 10.07. 2019 23:38 »
Hi
Since getting the B31 (1955) up and running again, hoping to put in some more longer runs and feel confident to get out on some VMCC Club runs and the like, but I have hit an issue losing power after a short while on some local test runs which arn't overly taxing. I thought at first the Clutch was overheating as there was a slight burning smell, the clutch rod was adjusted, this seems to have cured that particular issue , I have since discovered that the choke was sticking, this is now rectified, New Spark Plug of two grades higher is on order (N3C fitted). I have ensured the fuel cap vent is clear, along with fuel reaching the carb, as i did originally have a few rust particles from the tank standing for 20 plus years. Other suggestions include Magdyno coil failing and the bore being too tight? Is there anything else I should check?
There is what i describe as a pinking noise in the minute or two before I lose Power. It will then kick over again after a 10/15 minute cool down.
I know 'RogerSB' has witnessed a restart of my first issue and didn't believe the engine was over hot, so suggested posing here for your thoughts.
Today I ran for about 45 minutes covering 26 miles.

Spark Plug looks good I believe (attachment)

A short Video is posted of one test run without incident - Vimeo- did find post this that the Choke was stuck.
https://vimeo.com/346589412

another here in a facebook thread if a member of the group, with both power failure videos
https://www.facebook.com/groups/britishmotorcyclemechanics/2419028874826402/?comment_id=2424240434305246&reply_comment_id=2420474111348545&notif_id=1562704242912486&notif_t=group_comment

same link here for Vimeo ( see 06:00 and 11:50 minutes, or enjoy the full video)
https://vimeo.com/347347004

I HAVE ORDERED AN INLINE FUEL FILTER FROM TANK TO CARB

Appreciate the groups helpful advice as this is the third time in a week.

Just looking at the plug photo, is that a long reach plug? I thought all iron head motors have short reach.
EG: champion L 82 / 86 etc.
SA

Offline DartmoorStar

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Re: B31 Loss of power after 25 Miles or so
« Reply #5 on: 10.07. 2019 23:46 »
Hi
Since getting the B31 (1955) up and running again, hoping to put in some more longer runs and feel confident to get out on some VMCC Club runs and the like, but I have hit an issue losing power after a short while on some local test runs which arn't overly taxing. I thought at first the Clutch was overheating as there was a slight burning smell, the clutch rod was adjusted, this seems to have cured that particular issue , I have since discovered that the choke was sticking, this is now rectified, New Spark Plug of two grades higher is on order (N3C fitted). I have ensured the fuel cap vent is clear, along with fuel reaching the carb, as i did originally have a few rust particles from the tank standing for 20 plus years. Other suggestions include Magdyno coil failing and the bore being too tight? Is there anything else I should check?
There is what i describe as a pinking noise in the minute or two before I lose Power. It will then kick over again after a 10/15 minute cool down.
I know 'RogerSB' has witnessed a restart of my first issue and didn't believe the engine was over hot, so suggested posing here for your thoughts.
Today I ran for about 45 minutes covering 26 miles.

Spark Plug looks good I believe (attachment)

A short Video is posted of one test run without incident - Vimeo- did find post this that the Choke was stuck.
https://vimeo.com/346589412

another here in a facebook thread if a member of the group, with both power failure videos
https://www.facebook.com/groups/britishmotorcyclemechanics/2419028874826402/?comment_id=2424240434305246&reply_comment_id=2420474111348545&notif_id=1562704242912486&notif_t=group_comment

same link here for Vimeo ( see 06:00 and 11:50 minutes, or enjoy the full video)
https://vimeo.com/347347004

I HAVE ORDERED AN INLINE FUEL FILTER FROM TANK TO CARB

Appreciate the groups helpful advice as this is the third time in a week.

Just looking at the plug photo, is that a long reach plug? I thought all iron head motors have short reach.
EG: champion L 82 / 86 etc.

L82C is ordered

Online orabanda

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Re: B31 Loss of power after 25 Miles or so
« Reply #6 on: 11.07. 2019 03:17 »
When I had the same experience with a B31, the main jet was too small.

Offline Swarfcut

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Re: B31 Loss of power after 25 Miles or so
« Reply #7 on: 11.07. 2019 08:56 »
Managed to view the longer video, on my big screen it was just like being there. Now although the sound track can't be accurately reproduced, the bike didn't sound like a big single, and seemed to lack the bite in the exhaust note, making me think it's set a bit retarded, and what is happening is that under heavy load a tendency to overheat and nip up. In the early section, before the background music, the exhaust pops irregularly, like a spasmodic misfire.

 But on a flat road, ridden gently, it looks a nice ride. I could just see the ammeter flicking and the miles clocking up, and hear the gearbox reassuringly grumbling away in the lower gears.

  For the the location, what a lucky fella you are....'til the rains come. Then it gets a bit wild!

 Swarfy.

 Additional. Don't forget to cut off the smaller sections of the stubs on the new in line fuel filter, and if you have bought cheap plastic ones like me, keep a spare on the bike, as insurance against a stress crack and a roadside failure from cheap disposable plastic.

Offline DartmoorStar

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Re: B31 Loss of power after 25 Miles or so
« Reply #8 on: 11.07. 2019 19:11 »
Bought a Glass and Steel Inline fuel filter

Offline muskrat

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Re: B31 Loss of power after 25 Miles or so
« Reply #9 on: 11.07. 2019 21:54 »
G'day DS.
I like those filters. Easy to clean and reuse, mine last for many years.
Re-reading it all again I'm going with ignition timing either too retarded or not advancing as Swarfy has mentioned.
I had similar with my A10SSR (Shooting Star turned Super Rocket) when first recommissioned. Lucky it was just the tappets closing up and holding the valves open a tad.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
Australia
Muskys Plunger A7

Online duTch

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Re: B31 Loss of power after 25 Miles or so
« Reply #10 on: 12.07. 2019 10:14 »

 
Quote
........... (Shooting Star turned Super Rocket) when first recommissioned. ............

 So is it now a Shooting Rocket or a Super-Star.... *conf2*
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Offline coater87

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Re: B31 Loss of power after 25 Miles or so
« Reply #11 on: 12.07. 2019 18:19 »
 off the wall a little,

 but make sure you are not dragging anything, like a front or rear brake a little.

 That type of load is going to build up, engine is going to hot.

 This happen to a friend after a complete restore of a Hardley panhead, and was not figured out until after motor was removed and tore down again for no reason.

 Lee
Central Wisconsin in the U.S.