Author Topic: It just stops.  (Read 1453 times)

Online Gavin

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It just stops.
« on: 02.12. 2022 10:40 »
Hi, hoping to get some help for a local mate who has a Super Rocket which runs sweet for 30 mins then stops. Half hour later it's all good, starts n runs again for another 30mins.
As tempting as the obvious answer is.... please read on before that savage temptation with the obvious overwhelms you....

He has had the maggy rebuit, and condenser replaced. He has also tried a spare maggy of mine.
He has checked that the tank can breathe freely.
The motor has been recently rebuilt from the ground up.
The guy's a retired aircraft engineer, so he must have a few clues, and yes he is very tidy and thorough. But the mighty rocket has him dripping tears on the tarmac.

Any helpful insights from those who have previously been this journey (after the maggy has been eliminated) would be of considerable value.

Thanks.

Offline Greybeard

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Re: It just stops.
« Reply #1 on: 02.12. 2022 11:32 »
A quicky: Has he tried opening both fuel taps?
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Online Gavin

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Re: It just stops.
« Reply #2 on: 02.12. 2022 11:39 »
Not sure GB. He did say that when it stops it has fuel and spark. But I seriously doubt he  could run for 30mins if it takes another 30mins to replenish fuel from just one tap.

Offline Klaus

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Re: It just stops.
« Reply #3 on: 02.12. 2022 13:17 »
Hello Gavin,

If he has a spark and Fuel after the engine stall, and no other mechanical disaese, I will give a shot to the carb itself. The carb is cold the engine runs fine, after half an hour the carb is runing  hot and opend a haircrack inside. The carburation getting to much  rich to fire up.
I had a similar problem with my A10 Scrambler it wont start. The only chance was to get off the airscrew, so the pilot jet get the full dose of air.
He should trie another carb.

cheers Klaus


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Offline rocker21

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Re: It just stops.
« Reply #4 on: 02.12. 2022 13:34 »
i agree its a possible carb fault, maybe its icing up, had that once and i needed an additive to fix it,  this modern fuel is bad for that, tried different carb and that was no good, why it iced up is still a mystery , it was impossible to use in cold weather . eventually i found a replacement for the heat block between carb and head that had a heater element in it and that fixed it. came off a car but i cant remember which one.
 turned that on via a switch and a relay before starting and kept it on till the motor was good an hot then it was ok.
1960 A7SS, 1954 Ariel fieldmaster 500 twin, motoguzzi Monza 500, motoguzzi V7III special, Yamaha sr400 (2014)

Online KiwiGF

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Re: It just stops.
« Reply #5 on: 02.12. 2022 18:30 »
Hi, hoping to get some help for a local mate who has a Super Rocket which runs sweet for 30 mins then stops. Half hour later it's all good, starts n runs again for another 30mins.
As tempting as the obvious answer is.... please read on before that savage temptation with the obvious overwhelms you....

He has had the maggy rebuit, and condenser replaced. He has also tried a spare maggy of mine.
He has checked that the tank can breathe freely.
The motor has been recently rebuilt from the ground up.
The guy's a retired aircraft engineer, so he must have a few clues, and yes he is very tidy and thorough. But the mighty rocket has him dripping tears on the tarmac.

Any helpful insights from those who have previously been this journey (after the maggy has been eliminated) would be of considerable value.

Thanks.

What carb has it got? Monobloc or concentric?

If monobloc then check float chamber vent (tickler) is clear and float operation is good (that the spacer is fitted to keep the float away from the cover). It can be useful to fit a transparent float chamber cover to see whats going on with monoblocs.
New Zealand

1956 A10 Golden Flash  (1st finished project)
1949 B31 rigid “400cc”  (2nd finished project)
1968 B44 Victor Special (3rd finished project)
2001 GL1800 Goldwing, well, the wife likes it
2009 KTM 990 Adventure, cos it’s 100% nuts

Online Ted_Flash

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Re: It just stops.
« Reply #6 on: 02.12. 2022 19:23 »
Too tight valve clearances can see the valves unable to fully close when hot.
Ted Wilkinson, Ramsbottom, Lancashire
1950 Golden Flash

Offline muskrat

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Re: It just stops.
« Reply #7 on: 04.12. 2022 10:25 »
G'day Gavin.
I agree with Ted. My Cafe did the same thing after a rebuild. Another two thou on the tappet clearance did the trick.
Cheers
'51 A7 plunger, '57 A7SS racer now a A10CR, '78 XT500, '83 CB1100F, 88 HD FXST, 2000 CBR929RR ex Honda Australia Superbike .
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Offline BSA_54A10

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Re: It just stops.
« Reply #8 on: 06.12. 2022 12:29 »
Just stops ?
Surley an engineer can tell the difference beween lean running , rich running, lost sparks & nipping up
And FWIW my first road bike was a horrid mix of long & short stroke bits & peices with massive 11:1 's
It would run for anything from 5 minutes to 15 minutes the die
I would fiddle about with it, have a ciggy and sure enough it would first up on the first kick.
Eventually I became one with the bike & could tell when this was going to happen so would pull in for a milk shake / beer / burger etc
One day when riding to the beack, and not wanting to wait the 20 minutes for it to self correct I pulled the pick ups out & attempted to give them a clean
As there was bugger all of the carbon left I assumed that might be the cause
As luck would have it I was about 2 minutes from an auto electrician so I took my pick up down the road for some new brushes.
The counter staff asked what they were for then handd me what I knew was the "wrong" brushes because they looked nothing like to ones that were in there.
When I protested he looked at me in one of those "knowing father " types of looks and said " Usuaally if you run Bocsh brushes ina Lucas magneto it will only run for an hour or so then the springs go soft and the bike starts to misfire .
The new brushes cured the random stopping & my riding mates thought I was a genuius for fixing the bike .
Bike Beesa
Trevor

Offline BSA500

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Re: It just stops.
« Reply #9 on: 06.12. 2022 12:58 »
In some sort of defence my A7 was doing that before I took it off the road to try and solve an oil burning issue(leaking between the cylinders). I would be riding along and stop for a junction and it just stopped, no spit back, no roughness IT.JUST.STOPS. There is fuel, sparks, compression. After sometime it would start, extensive checks so far have found no issues with mag-everything does what it should/fuel-fresh petrol and new taps with good flow/carb-twice cleaned with ultrasonic bath and all blown through with compressed air. Timing checked and double checked. It's completely stripped down and the only thing the leak down tester found was the leaking head gasket and one inlet valve in need of a session of lapping in. It may well be that but I would expect spit back, I shall lap in all the valves and she will have new pistons as some numpty-me-broke the skirt of one of the pistons. Maybe that will be the solution, ask me in spring *smile*

1960 A7 (57 motor to SS spec)

Online Gavin

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Re: It just stops.
« Reply #10 on: 10.02. 2023 13:59 »
An Update:

Deeply appreciative of all help offered here, his tears have finally stopped. He found the problem in the carby by swapping out the slider with one in a spare carby I had. He's ridden for over an hour and not had to push it home, or wait it out on the side of the road, so there it is at last, simple, but as we all know, heaps of patience required while waiting for the last option we try to turn up.

So thanks everyone. This is exactly what the site is meant to do. Another happy A10 rider heading down the highway and safely back home.

Offline Jules

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Re: It just stops.
« Reply #11 on: 11.02. 2023 11:57 »
Hmm, I'm intrigued Gavin, how does a slider change fix an engine stopping issue??
While I'd be happy that it appears to be the solution, I think I'd need to know why, before relaxing and going on a trip somewhere, any ideas??

Online Rex

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Re: It just stops.
« Reply #12 on: 11.02. 2023 12:12 »
I can't see that it would or could.
I would suggest that in swapping the slide over he unknowingly fixed the original problem, probably while the carb was being disassembled/reassembled. Possibly a floater or water globule which was then dislodged when the carb was removed.

Offline RDfella

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Re: It just stops.
« Reply #13 on: 11.02. 2023 14:40 »
Maybe the slide has less cutaway?
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Online Gavin

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Re: It just stops.
« Reply #14 on: 11.02. 2023 14:51 »
Yep, I think you are correct RD, but I have no idea how that would be a cure, so I kept my ignorance to myself, and never pressured him to offer an explanation. He'd been at it for over 12 months, so I just let him enjoy the win. i'll check him out soon and see if I can get a theory from him, and let you know.