Author Topic: Spit back through carb and backfires  (Read 14465 times)

Online lawnmowerman

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Re: Spit back through carb and backfires
« Reply #15 on: 23.01. 2011 15:09 »
Yes Nigel I got it from a guy in Liverpool through eBay just over a year ago - why do you ask?

Well I have just come back in from the workshop after firing up the bike again.

I drained the old fuel out of the tank and removed a load more Petseal which had dislodged, then refilled with some avgas.

Took the carb off and blew out the jets. The needle was on the third notch from the top so I dropped it one notch to the second from the top. Carb looked in pretty good nick - slide was a nice tight fit and operated well, as did the choke slide.

Added some Extralube to the oil in case a valve was sticky.

It would only start on one cylinder until I moved the lever to almost full advance. When it did run I went to full advance, warmed her up and moved the slide stop so it would run without using the twistgrip. She would only run at about 1500 rpm and the speed was not even ? all the time there was a random spitback through the carb. I tried blipping up to about 4000 revs and seemed to be fairly even but did not want to run it too fast for too long.

Shut her off and took her back in the workshop and checked the plugs. There was no soot but I did notice that the pipes were going a golden colour near the head. A mate of mine who rebuilds Manx Nortons called round earlier and I was talking to him about it and he reckons that it is quite normal for the Nortons to blue right round to the footrest!

Sounds to me that the timing may have been progressively slipping over the time I have had the bike. I think my next step is to check the timing and points gap also checking the gap is OK on both sides of the slip ring in case it has been poorly machined.

If that is OK I think I will be looking at a mag recon.


Jim
1959 A10 SR
1938 Wolseley 14/60
1955 Ferguson TEF20 tractor
1965 Ferguson 135 tractor
1952 Matchless G80 rigid
1960 BMW R60
1954 Matchless G80S
1955 Ariel 500 VH
1951 Sunbeam S7DL
1960 Matchless G12 with Watsonian Monza
......and loads of lawnmowers

Too old to Rock and Roll but too young to die  (Jethro Tull 1976)

Offline nigeldtr

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Re: Spit back through carb and backfires
« Reply #16 on: 23.01. 2011 16:51 »
Jim,

You beat me to it! I have been after a Road Rocket for ages - small world. I am sure you will get plenty of good advice here. I would wait to see what the others say first before you do too much more. All sounds a bit suspect to me. I am no expert but if the points and cam ring are in good order and the timing is correct (have you checked this on both LH and RH cylinders) there must be a mechanical problem. I hope its something simple like a naff pickup or something.

Kind regards

Nigel
1951 Golden Flash (engine now rebuilt) 1953 M21 a pain to start and 1961 GF that is turning into a black hole!

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Re: Spit back through carb and backfires
« Reply #17 on: 23.01. 2011 17:04 »
Thanks Nigel. Bet you're glad I did beat you to it after all the trouble I am having  *smile*

Jim
1959 A10 SR
1938 Wolseley 14/60
1955 Ferguson TEF20 tractor
1965 Ferguson 135 tractor
1952 Matchless G80 rigid
1960 BMW R60
1954 Matchless G80S
1955 Ariel 500 VH
1951 Sunbeam S7DL
1960 Matchless G12 with Watsonian Monza
......and loads of lawnmowers

Too old to Rock and Roll but too young to die  (Jethro Tull 1976)

Online bsa-bill

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Re: Spit back through carb and backfires
« Reply #18 on: 23.01. 2011 17:09 »
Jim I had something similar with my project and amongst other things the cam ring had moved back and was off it's peg a bit allowing the cam ring to move from desired position and altering the timing
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

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Re: Spit back through carb and backfires
« Reply #19 on: 23.01. 2011 17:30 »
Hi Bill

I remember reading about that in one of your earlier posts. I did take the cover off and check mine but the ring seems to move backwards and forwards using the lever and also seems flush with the outside of the mag when the cover is off. I did not want to pull the ring right out in case I had a problem getting it back. Does it sound ok or does it need further investigation - it sounds exactly like what could be causing the problem. Either that or a loose gear wheel on the mag drive.

Jim
1959 A10 SR
1938 Wolseley 14/60
1955 Ferguson TEF20 tractor
1965 Ferguson 135 tractor
1952 Matchless G80 rigid
1960 BMW R60
1954 Matchless G80S
1955 Ariel 500 VH
1951 Sunbeam S7DL
1960 Matchless G12 with Watsonian Monza
......and loads of lawnmowers

Too old to Rock and Roll but too young to die  (Jethro Tull 1976)

Online bsa-bill

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Re: Spit back through carb and backfires
« Reply #20 on: 23.01. 2011 17:39 »
Ah sorry Jim I forgot yours is cable
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Online chaterlea25

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Re: Spit back through carb and backfires
« Reply #21 on: 23.01. 2011 23:00 »
HI lawnmowerman,
"Normally" the camring is a litle below the outer face when fitted,
They can and will move outwards if and when the engine is run *sad2*
It depends somewhat on the exact type of end cover, there were/are some pattern plastic/bakelite ones around that allowed the cam to move outwards!!
This affects the timing as the ring is no longer tied to the actuating thingy!
If you have a clip on strobe light (not one that is in series with the plug lead) you can see if the miss is ignition or not
by shining the light on the primary or timing case, its easy to spot the break in the light pulses

Last year I had an A10 in that would not run evenly at all, it turned out to be a soft valvespring, that along with the fact that it was totally knackered *eek*

HTH
John O R
1961 Super Rocket
1963 RGS (ongoing)

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Re: Spit back through carb and backfires
« Reply #22 on: 24.01. 2011 09:47 »
Thanks John

The cam ring moves when I operate the A/R lever so on that basis could it have moved or be out of engagement? Is it ok to pull out the cam ring and inspect it with the points still in place. You mention that the cam ring should be slightly below the body - is there anything which holds it back or is it reliant on the cover, in which case it could creep forward until level with the body and the cover will stop it moving forward any more.
Hopefully the engine is still mechanically ok as it was professionally rebuilt recently but not sure about the mag as I cannot see any receipts for that from the PO. It ran OK last autumn apart from a misfire on the drive side which seemed to get worse when manually retarded when it would run one one side only. This was there ever since I bought the bike a year ago.
It is looking more and more like a mag problem. The first winter I had the bike I kept it in the conservatory over the winter, however this winter under pressure and threats from SWMBO I kept it in my new workshop whch is dry and well insulated but unheated so perhaps the mag was on its way out and the damp over the winter has finally killed it. The intermittent carb spit back when running has only started now after the winter layup. Perhaps I could try disconnecting the drive side plug and starting on one and see if the spit back goes - if it does it could point to arcing on the mag split ring and sending random sparks to the drive side causing the spit back.

I do have a clip on strobe which I bought for the car so I will give that a go. I will also check that the the
timing has not slipped using a rod down the plughole and the point at which the points split.

Jim
1959 A10 SR
1938 Wolseley 14/60
1955 Ferguson TEF20 tractor
1965 Ferguson 135 tractor
1952 Matchless G80 rigid
1960 BMW R60
1954 Matchless G80S
1955 Ariel 500 VH
1951 Sunbeam S7DL
1960 Matchless G12 with Watsonian Monza
......and loads of lawnmowers

Too old to Rock and Roll but too young to die  (Jethro Tull 1976)

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Re: Spit back through carb and backfires
« Reply #23 on: 24.01. 2011 12:27 »
G'day Jim,
              while you have the strobe light on, check the timing is the same on both cylinders. A worn cam ring will do that and if bad enough will make one side out of time enough to misfire or spit back.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
Australia
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Offline nigeldtr

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Re: Spit back through carb and backfires
« Reply #24 on: 24.01. 2011 18:28 »
Hello Jim,

Have you checked the timing on both cylinders, is it the same? If you want to take the cam ring out, just turn the engine over slowly (plug leads off) and make sure the points are closed, off the cam. At this point you can simply slide the ring in and out - just need to locate the A/R plunger in the grove when you put it back in.

Regards

Nigel
1951 Golden Flash (engine now rebuilt) 1953 M21 a pain to start and 1961 GF that is turning into a black hole!

Online chaterlea25

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Re: Spit back through carb and backfires
« Reply #25 on: 24.01. 2011 23:12 »
HI Jim,
The cam can move out but still be engaged with the plunger (couldnt think of the name of it last nite *conf*)
As it moves towards the cover it may slip past the wee peg that limits the advance/retard range, and so the timing may be out in this position *eek*
Push the camring fully home in mid position, this will ensure it goes in correctly!!
The end cover is all that holds it in place
Sometimes the limiting peg can be damaged or bent!! if this happens symptoms like you are having can occur
ie, losing sparks on one side when the lever is towards the retarded position

(Its coming back to me now ???? ????)

Some time ago I had problems with a K2F similar to yours,
The peg which is factory set and a rivit fitted at the end so as you cant fiddle with it
in the retarded position the points were opening when the brass segment of the slipring had passed the pickup brush
I carefully drilled off the rivit head and was then able to turn the screw with the peg which is eccentric to the screw
to advance the camring.
I set it the same as another K2F I have and glued it in place with some araldite
This mag had a steel points plate, and when compared to a brass plate setup I found that the points opened sooner
in relation to armature position.
To "fix" this I filed away the leading edge of the fibre block to delay the points opening so as to make it the same as the brass points plate
Then the mag has to be retimed to the bike!!

HTH
John O R



1961 Super Rocket
1963 RGS (ongoing)

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Re: Spit back through carb and backfires
« Reply #26 on: 25.01. 2011 10:32 »
Thanks Guys - some really useful information.
I do remember soon after I got the bike that the A/R lever tightened up but I thought it may have been a corroded cable so I gave it a bit more force and it seemed to free up - perhaps I have pulled the cam ring off the stop or bent the stop.
I will have a quick look and do a rough check on the timing but I do not have a timing disc yet so will use the "straw down the plug hole" method posted by alanp a while back.
If things look ok I will pull out the cam ring and reseat it then check the points are the same gap on each side.
If I then need to take the timing cover off and rermove the mag for a rebuild I will wait until I have bought a bike lift so that I can do the job in a bit more comfort. I will also invest in a timing disc so I can strobe it when I replace the mag rather than using the static method.
I also like the idea of slotting the mag mounting holes to give some adjustment once the mag gear wheel is back on and the timing case fitted.
Thanks again

Jim
1959 A10 SR
1938 Wolseley 14/60
1955 Ferguson TEF20 tractor
1965 Ferguson 135 tractor
1952 Matchless G80 rigid
1960 BMW R60
1954 Matchless G80S
1955 Ariel 500 VH
1951 Sunbeam S7DL
1960 Matchless G12 with Watsonian Monza
......and loads of lawnmowers

Too old to Rock and Roll but too young to die  (Jethro Tull 1976)

Offline MG

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Re: Spit back through carb and backfires
« Reply #27 on: 25.01. 2011 10:37 »
Hi Jim!

That sounds very much like a problemm I had with my A7. The advance lever was stuck, but then freed with some gentle persuasion. A few miles afterwards the bike would start to backfire and finally stall.
Turned out to be the (pattern) magneto end cover, that wouldn't hold the camring in place properly, so that it would move off its' stop and turn 'round in the housing. I then fitted an original Lucas cover taken off another mag and had no more trouble ever since.

Cheers, Markus

*edit*
I just read chaterlea's post above, so has obviously been mentioned before. One more good reason to check ;-)
1955 A7 Shooting Star
1956 A10 Golden Flash
1961 Matchless G12 CSR

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Re: Spit back through carb and backfires
« Reply #28 on: 25.01. 2011 11:53 »
Just spent half an hour in the workshop before I have to get on with non-A10 work.
I removed the mag end cap, moved the points off the cam and pulled out the cam ring. Everything looked ok - the A/R lever moved the actuator back and forth and the slots in the cam ring did not look unduly worn so I put it back. The cam ring sits just below the face of the mag and is a snug fit - checked the lever movement and the cam ring went from stop to stop.
Checked the points gap and it was the same on both lobes, albeit a little wide at 15 thou - I think it should be around 12. I could also feel a slight step on the face of the contacts so may need a little work with a points file before I reset them.
That's as far as I have got at the moment - next step is to check the static timing. I am not too bothered if it is spot on but it should show if it is way out and the drive gear wheel has slipped on its taper shaft.

Jim
1959 A10 SR
1938 Wolseley 14/60
1955 Ferguson TEF20 tractor
1965 Ferguson 135 tractor
1952 Matchless G80 rigid
1960 BMW R60
1954 Matchless G80S
1955 Ariel 500 VH
1951 Sunbeam S7DL
1960 Matchless G12 with Watsonian Monza
......and loads of lawnmowers

Too old to Rock and Roll but too young to die  (Jethro Tull 1976)

Offline nigeldtr

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Re: Spit back through carb and backfires
« Reply #29 on: 01.02. 2011 22:13 »
Hello Jim,

How are you getting on - have you managed tracked down the problem yet?

Regards

Nigel
1951 Golden Flash (engine now rebuilt) 1953 M21 a pain to start and 1961 GF that is turning into a black hole!