Author Topic: Spit back through carb and backfires  (Read 14472 times)

Online lawnmowerman

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Re: Spit back through carb and backfires
« Reply #30 on: 02.02. 2011 01:44 »
Hi Nigel

I have ordered a bike lift so I can work in a bit more comfort - should arrive in the next few days and then the plan is to check the timing. If it is way out then that may be the problem, otherwise it's off with the mag and get it reconned. I think it may well be a mag problem and this winter has finally killed it - I was going to remove it and put it in the oven on a low heat overnight to see if it improves things but I will probably bite the bullet and go for a recon - at least it will eliminate one area.

I will let you know what I find when I check the timing.

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 wilko

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Re: Spit back through carb and backfires
« Reply #31 on: 02.02. 2011 19:06 »
For all it's worth, it simply sounds too retarded. Just advance your timing some more as an experiment before you lash out with more dosh!

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Re: Spit back through carb and backfires
« Reply #32 on: 02.02. 2011 22:18 »
Hi Wilko

It was ok before the winter layup - just the ongoing misfire on one side problem but no carb spitback or backfires so I doubt if it is ignition timing but anything is possible. When I get it on the lift later this week my plan is to check the static timing as a last resort as the gear wheel may have slipped.

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 #33 on: 03.02. 2011 16:09 »
Now I'm confused.
The bike lift still has not arrived but I could not resist going into the workshop for half an hour to do a rough check on the timing. I bent a piece of flat tin and bent it over the plug hole and secured it with zip ties to give me a datum and put a piece of thick wire through a hole and down the plug hole. I then used top gear and turned the engine with the plugs out and marked TDC with a file mark on the wire. I then marked 5/16" BTDC and made another mark. When I turned the engine over I thought I would see the points start to open later than 5/16" but it looked like they were strating to open at about 1/2" BTDC  *dunno*
If the timing had slipped I would have expected it to make the timing more retarded rather than advanced as the mag would be lagging the engine - can't see how slipping would advance it.
I can move the manual A/R and get the correct timing within the range of the lever so it should have run ok when I fiddled with it.
It would explain the spit back if it were too advanced but when I manually retarded it when running I got backfires.

Any ideas?

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 #34 on: 03.02. 2011 17:20 »
Another update.
Thought I would take the carb off and have another look. I know this should probably go in the carb section but may be part of the problem on this thread.
Plenty of muck in the banjo filter due to the ongoing process with the petseal dissolving so I cleaned that.
Pilot jet was partially blocked so cleaned that. Main jet looked clear.
Carb settings (389 stamped M5 on the flange):
Pilot jet 30
Main jet 106
Needle D set second notch from the top (was third before I started tinkering but plugs were sooty - now ok but bluing pipes)
Slide 389-3 1/2
Pilot screw one turn out.
Do these sound OK?
Another thing I noticed was that hole in the drip tray measured 1.135" but the carb bore measured 1.175" so is 40 thou undersize so will need some work with a file.
There is also no air filter just a gauze - covered bellmouth.

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 muskrat

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Re: Spit back through carb and backfires
« Reply #35 on: 03.02. 2011 19:29 »
The plot thickens !
 Might be time to clean out all the petseal from the tank. Try acetone or tetra-ethel-keatone (just woke up).
 Timing will slip in the advanced direction. The pinion goes anti-clockwise, tightening the nut goes clockwise.
 Use a vernier or dial indicator to get a more accurate measurement,
 I have made a tool to find the timing position. Once you get the piston at the right height. Knock out the porcalin part of an old spark plug, run a 3/8 tap down the hole. Take the washer off the plug and screw into the spark plug hole. Now screw in a long bolt till it just touches the piston. I use red loctite so it sets there. Now every time you want to check the timing just screw in the tool and bring the piston up to touch it (gently).
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
Australia
Muskys Plunger A7

Offline nigeldtr

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Re: Spit back through carb and backfires
« Reply #36 on: 04.02. 2011 07:00 »
Jim,

Just a thought, if you are going to do the timing, perhaps change it by 180 degrees on the mag drive and then swap the leads over, see if the misfire changes side?

Don't really want to mention it but might be worth a quick check of the valve timing.

Good luck

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 #37 on: 04.02. 2011 10:04 »
G'Day Muskrat

Great idea with the "spark plug timing tool". It is starting to make some sense if a slack bolt on the mag gear wheel causes the timing to slip to advance direction. I think all the chunks of Petseal are now out of the tank and I have filled up with ethanol free avgas. I think I will have to sort out the tank soon as you say. In the UK with our nanny state and crazy health and safety laws, it is difficult to buy any chemicals like acetone or TEK which could injure you if you accidentally make a cup of tea out of them so I may have to get a cleaning kit with the POR15 lining kit which I believe is ethanol proof.
Nigel, I think that moving the timing by 180 degrees could well be the next step if I have to take the timing cover off but rather than change too much in one go I will probably start by resetting the timing as it is and get the points gap down to 12 thou where it should be.
Before I put the bike on the lift (when it finally arrives) I think I may put the needle back to where it was (three from the top), put the carb back on and see what she runs like after having cleaned out the pilot jet. It may be that she was running weak and advanced which may have contributed to the blued exhaust - bear in mind I had to wind up the throttle stop to keep it running so may have been running on the main jet alone.


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 #38 on: 04.02. 2011 12:44 »
An update on my current woes.

I inspected the carb this morning and it looks like it is jetted wrong (see related post http://www.a7a10.net/forum/index.php/topic,3754.msg25867/topicseen.html#msg25867 It has a 240 main jet instead of a 420. The needle may be wrong - it has a D stamped on it and the alcohol version is D2. The slide is a 389/3 1/2 and my service sheet 216 says it should be a 389/3. It's amazing it ran at all?
I think I will fix this and try starting before I go any further.

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 wilko

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Re: Spit back through carb and backfires
« Reply #39 on: 04.02. 2011 15:31 »
The "D" is right for a 389 and if you want to save some dough just file tha bottom of your slide down a tad (1/32nth) and try that then maybe a little more. The mainjet won't affect anything until it's wide open.

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Re: Spit back through carb and backfires
« Reply #40 on: 05.02. 2011 11:06 »
The bike lift has finally arrived so I am going out to the workshop to have a tidy up to make some space, unpack it and get the bike up onto it.
My can of carb cleaner, gasket set and a new pilot jet has just arrived so I am going to strip the carb down and clean out any congealed fuel residue and petseal.
My neighbour who is a Manx Norton specialist reckons that the mag is duff (probably the capacitor or a dodgy slip ring tracking to earth) having heard the bike running with the backfires and spit backs from three gardens away last Saturday. He was bang on when I had problems with a duff rotor arm on my Wolseley last year. He recons mags so I will take it off and get it to him.
I will keep this thread running as it will be good for other members to know the final outcome and to identify what the problem was.
Up to now I have identified three problems:
Partially blocked pilot jet
Undersize main jet
Timing too far advanced 1/2" ish BTDC on full advance.


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 wilko

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Re: Spit back through carb and backfires
« Reply #41 on: 05.02. 2011 21:56 »
As an experiment, you could wire a car condensor into the cutout wire on the end of your mag. An old get you home trick! I'm still skeptical.

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Re: Spit back through carb and backfires
« Reply #42 on: 05.02. 2011 22:34 »
Hi Wilko

That would work if there was an intermittent open circuit on the capacitor but my mate the specialist reckons they usually go intermittent short circuit producing weak and random sparks which would explain the spit backs and backfires - almost like a second set of points opening randomly I would imagine. It has always misfired and run on one occasionally ever since I bought it and is difficult to start when hot - all of which points towards a mag problem. I may ask him if he can put it on his test rig before he strips it just out of interest - he normally runs them at 3000 RPM for three hours with some test gear hooked up to measure the spark strength.
I have resigned myself to a mag rebuild and with the superior insulation materials now available it should outlast me and also rule out ignition problems if the fault remains.
The other thing is that I want to get the bugger running before the sun comes out and we get our usual couple of decent weeks which we call summer.

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 starfield

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Re: Spit back through carb and backfires
« Reply #43 on: 07.02. 2011 21:13 »
Hi,

Not sure if you have resolved your problems, if so ignore the following though its an interesting tale.

Just like you, I have been wrestling with similar problems on my 52 Star Twin - running on one and spitting back. In the end the spitting back proved to be primarily caused by tappets that had been allowed to close up. Resetting them initially seemed to cure the problem. Then the LH inlet valve stuck open and bent a pushrod, almost certainly caused by the carbon build up on the permanently open inlet valve. Naively I though the problems would go away after I stripped the head and did all the valves. Indeed the spitting back was cured but the ticking over on one cylinder and the hiccupping at lows revs remained causing a few hairy moments.

Interestingly, the bike would tick over perfectly as a 250 single on either cylinder so proving which was at fault was difficult. As the carb had already been well sorted by the previous owner, I took the plunge and had the mag serviced. What a good decision that turned out to be. There were numerous issues which were sorted out for a very reasonable cost:
1. The slip ring was badly worn and was probably the major culprit, under test it sparked like a catherine wheel.
2. The pickup brushes were wrong and may have contributed to 1.
3. The oil seal had hardened and was beginning to let oil into the armature
4 The cam ring housing was badly worn and had to be shimmed.

The last point was interesting. My mag had been converted to auto advance and the cam ring had of course been locked by grub screws. The wear had allowed the grub screws to push the cam ring off centre so the points gap differed on each side. I knew there was a problem as I could never get the timing set properly and had to equalize with 8.5mm on one side and 11mm on the other  but had assumed a worn cam ring and did not notice the points gap changing. I am not sure how such wear would affect a manual a/r situation but it cannot help and shimming is probably not an option.

Fitted the new mag, timing now identical on both sides and first kick start. No more ticking over on one, no hiccuping and no spitting back. Totally different bike. Previous owner took it for a ride today and now wishes he had not sold it. Minor moment of panic when it went on reserve on the way home and stalled at a roundabout just to shake my over confidence.

If you still have problems, maybe some of the above helps. I used the guy down at Langton Matravers who advertises in the VMCC mag. He came well recommended and I can see why. Thorough checkover, only replaced that which needed replacing and back in a week looking like new. I hasten to add that I  have no association with the business, just a satisfied customer.

Reminds me of the old story that 90% of carb problems are electrical. For the relatively small outlay compared to the value of the bike I would think a mag checkup by a specialist a good insurance.

regards

Peter

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Re: Spit back through carb and backfires
« Reply #44 on: 08.02. 2011 13:05 »
Hi Peter

A very interesting story. My engine has only done about 500 miles since rebuild so probably does not have the same problems with carbon build up but could possibly have tight valve guides I suppose.
I think my problem is mag related so I removed it today and will get it rebuilt by a friend of mine who rebuilds Manx Nortons.
The timing was just over 1/2" BTDC and the points gap was 15 thou though even on each side so needed retiming. The pinion was tight on the taper so does not look like it had slipped.
At least when the mag is back I can rule out ignition problems and stop chasing red herrings caused by intermittent random sparks and with the modern materials now used the mag will probably last longer than I will.

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)