Douglas MkV 1951 carburettor issue

[Pallijen15]

Hi, on my motorcycle the right hand carburettor is not running as it should. I have dismantled and cleaned it, checked the spark plug, which was black and sooty. When I cover the mouth of the carburettor it has no effect. When I dropped the needle a groove this had no effect. When I dismantled the carburettor the jet block could easily be pushed out by hand and the last 3mm it does not stay by itself but has to be secured by the lower nut of the body. Could this be the issue of sucking in air and are there any sources for replacement/reconditioning jet blocs. Thanks, Paul J
P.S. I still haven't checked the ignition timing, the advance/retard when used, has no effect on the engine, could the timing be out and could this affect one of the carburettor?

[EW-Ron]

The ignition timing will affect BOTH cylinders.
Assuming your magneto is giving a healthy spark on both cylinders (not checked yet.)

And are you sure that twiddling the advance/retard lever is actually doing/moving something ?
A lot of magnetos will lose spark altogether if FULLY retarded.

When I cover the mouth of the carburettor it has no effect.

No effect at all  ??
What if you keep covering it, and try and blip the throttle, to dial up a few more revs

If you tweak the throttle cable on just this carb, can you increase the engine speed
(All the revving will be just on this one cylinder)
(This is to test that your engine is actually capable of running strongly on both cylinders.)

Have you compared the gaskets in both carbs.
It sounds like this one is missing something.

Do the exhaust pipes feel equally hot here - use caution, they are HOT !

[EW-Ron]

P.S. We are assuming this has a pair of the original style Amal sidefloats ?
If you have Mikunis, Bings, Mikcarbs, Jikovs etc you need to say.

Have you done any work on the fuel/float levels in these ?
Black & sooty plug(s) might suggest a flooding carb ?
The taper on the fuel needle can be ground to its seat, using finer valve paste etc.
And proceed from there.

A black & sooty plug could also suggest some oil burning in that cylinder.
Have ye given this engine a compression test.
Best done with the engine warm, and with the twistgrip dialled up to full open.
And the plugs laid out on the engine, with leads attached, don't want to harm the maggie.
(or spark any stray fuel).

[Pallijen15]

Hi Ron, covering the mouth of the carburettor; if I press the palm of my hand on really firmly the engine does slow very slightly. I haven't kept it on for more than two seconds yet though. The left carburettor stops the engine almost immediately when covered.

"If you tweak the throttle cable on just this carb, can you increase the engine speed".
Yes.(I have never tested with one ht lead disconnected as I have been told that running the engine on one cylinder will damage the magdyno but the speed increases when using the throttle. Took it for a short run but the power dies when changing gear)

The slip ring moves normally when operated
Both carbs are Amal 274's

Ah right. So long as I secure one spark plug to the engine to create the spark the magneto will be safe.
If one of the carburettor were flooding would there not be a constant leak when taps open and engine off? Mine don't do this.

I'll cover all the points in your list next time I am available to work on it which will be next Friday or Saturday. Back to work today (Sun to Thurs). Thanks for all your advice, will give me some things to check.

[EW-Ron]

If one of the carburettor were flooding would there not be a constant leak when taps open and engine off? Mine don't do this.

Sounds like the flooding is not an issue then. 
The fuel/float level would be the next thing to check.
Just removing the float chamber tops and comparing things could be instructive.
Don't run it or do any sparking like this !

OR, could be helpful if the floats could be swapped, side-to-side. ?
See if the problem changes sides ...

Comparing gaskets between the carbs still sounds a possibility also.
Have fun ....

[eddie]

Check out the float chamber. In the bottom of the chamber there is a central boss with a guide hole for the bottom of the needle. Carefully clean it out with a sharp drill. Debris can accumulate in the hole and drag on the needle, causing an erratic fuel height (Severe cases can cause total fuel starvation!).

 Regards, Eddie.

[Pallijen15]

Thanks Eddie, I'll add that to the list

[Pallijen15]

Hi all, just to update you on my results. Taken the float chamber off, cleaned out fliat needle hole, no difference. Swapped float chambers around, still the same on the right hand side carburettor, Swapped spark plugs around, no difference. I haven't done a compression test yet as there does seem to be plenty of power. It's only when closing the throttle to change gear and idle it plays up. I mentioned a loose jet block last time but didn't get any feedback on that. There are some carburettor refurbishment specialists, Joe the Carb on Facebook, Alverstoke refurbishment in Gosport, Coln etc. Has anyone any information as to these or other companies specialising in this field? Thanks P.S. I have also removed carburettor and cleaned/flatted joints on a plate glass. No leaks around flanges

[yosemite]

Have you tried swapping carbs from one side to the other, if the fault migrates then the problem is with the carb if not the problem lies elsewhere.

[Pallijen15]

No, have only swapped the floats. I will give it a try. Thanks 

[eddie]

On the offending side, remove the float chamber and bottom cap nut. Carefully, push the jet block out of the bottom of the carb. Look at the side of the block that faces the cylinderhead, just below the main bore, there is a very shallow drilling about 4mm dia. In that drilling, there are 3 more drillings - one is the fuel supply (coming up from where the float chamber attaches) - the second is a small drilling that goes up into the main bore of the carb - the third is an even smaller hole in the centre of that shallow drilling. This hole
 sometimes gets blocked and is not easy to detect as it looks like the normal flat that you get in the centre of a drilled hole. This problem seems to have become more common since the introduction of unleaded fuel (as it tends to block small jets if left to dry).

Hope this helps,
                        Eddie.

[Pallijen15]

Okay thanks, will give that a go as well tomorrow when off work 

[Pallijen15]

Hi Eddie, I took the jet block out and found the hole you  described. The smallest of the three. I took a very fine copper wire and pushed it in the hole. This didn't go all the way to the centre but as far as another corridor in the block. Is this correct or does the small hole extend through the corridor to the centre? Thanks. By the way, the jet block is so slack it just falls out  of the carburettor now. Maybe it's not getting pushed up to align with the carburettor intake holes. What thickness fibre washer should it be under the jet block?

[eddie]

Providing that small drilling connects to another drilling, it should be OK. Regarding the fibre washer under the let block - the original was of a soft material that often disintegrated as the base nut was unscrewed. It can be replaced with a red fibre washer, but it needs to have a large bore so that it doesn't obstruct any drillings in the base of the jet block. While you have the jet block out, check that the small drilling in the bottom of the main bore of the carb body is also clear. The drilling is at an angle up from the slow running screw into the main bore.

  Regards,
               Eddie.

  P.S. The jet block fits direct against the bottom of the carb body - there is no washer needed between the two.

[Pallijen15]

Have you tried swapping carbs from one side to the other, if the fault migrates then the problem is with the carb if not the problem lies elsewhere.

Hi Yosemite, yes, just swapped carbs around today and the problem migrated. I have cleaned thoroughly jet block holes and the holes in the carburettor body, all clear. The only thing I can do now is send the carburettor away for refurbishment and get a sleeve put in for the loose jet block. Any other ideas? Thanks 

[Pallijen15]

Providing that small drilling connects to another drilling, it should be OK. Regarding the fibre washer under the let block - the original was of a soft material that often disintegrated as the base nut was unscrewed. It can be replaced with a red fibre washer, but it needs to have a large bore so that it doesn't obstruct any drillings in the base of the jet block. While you have the jet block out, check that the small drilling in the bottom of the main bore of the carb body is also clear. The drilling is at an angle up from the slow running screw into the main bore.

  Regards,
              Eddie.

  P.S. The jet block fits direct against the bottom of the carb body - there is no washer needed between the two.

Thanks Eddie. After swapping carburettors the problem switched to the other side. First I checked carburettor body holes and all were clear. Anything else you can think of? I can get the carburettor refurbished to fix the loose jet block etc. which is all I can think of

[yosemite]

If the jet block is slack, there would seem to be three likely culprits, the first is that the carb body is worn or distorted, or the second that the jet block is worn and finally a combination of both, do you have a spare jet block to try, or compare the one in use to. If not I think I may have a spare block you could borrow unfortunately not sure where it may be, will have a search tomorrow to or Monday and let you know. 

[Pallijen15]

Hi, no I don't have a spare jet block . However, if you do have a spare it would be advantageous in finding out the problem so I can send my carb away to be refurbished. Alternatively, if you're quite sure I can send it away anyway. Thanks for your kind offer

[dalgrae]

Hi,Brit Bits in Christchurch did have some new jet blocks ,if that helps


Colin

[Pallijen15]

Hi,Brit Bits in Christchurch did have some new jet blocks ,if that helps


Colin

Thanks Colin I'll give them a call tomorrow 

[dalgrae]

Hi not open Mondays 

Colin

[Jonathan Hewitt]

Has the LDMCC post war spares got any of the carb bodies they had cast left ?
Jonathan 

[Jonathan Hewitt]

Not sure if it will help but do have a look at my carb picture post for 26 August 24. I have tried to copy to here but with no success .
Jonathan 

[Doug]

Link to post mentioned by Jonathan Hewitt:

https://www.douglasmotorcycles.net/index.php?msg=39702


-Doug

[Pallijen15]

Thanks Jonathan and Doug for the link. I'll take a look again but I don't think there is a hole there on my carburettor 

[Pallijen15]

Okay, just checked the carburettor again and seen the hole. I took out the air screw and saw the light. (I wish that was true). Still, thanks for the idea, keep 'em coming. Paul J 

[DJS]

Has the LDMCC post war spares got any of the carb bodies they had cast left ?
Jonathan

I'm afraid not Jonathan. We have tried to track down the supplier who made the previous batch without success. Another member is looking into this for us but no joy as of yet.

[dalgrae]

Hi ,when I bought mine from the club when Dick was the spares officer he told me they came from Australia if this helps

Colin

[DJS]

Hi ,when I bought mine from the club when Dick was the spares officer he told me they came from Australia if this helps

Colin

Thanks Colin. A couple of members have confirmed the Australian connection but sadly we have no record of the actual supplier. If any of our Australian members recall this project or are aware of a suitable company I would be pleased to hear from them. 

[yosemite]

Paul
Finally got into shed, found a spare jet block, if you send me your address will get it in post for you

[Pallijen15]

Paul
Finally got into shed, found a spare jet block, if you send me your address will get it in post for you

Thanks Yosemite, just ordered one from Britbits this morning. He has only charged me a tenner plus postage, said he thinks it could be new, just shop soiled N.O.S. Even if it's not correct then it's only £16.50 wasted. I'll let the group know of the results when it arrives. But thanks for your offer. Now you've got it out, can you tell me the numbers stamped on each end please?

[yosemite]

Numbers on bottom are 30t, numbers on top are 21 

Paul
Finally got into shed, found a spare jet block, if you send me your address will get it in post for you

Thanks Yosemite, just ordered one from Britbits this morning. He has only charged me a tenner plus postage, said he thinks it could be new, just shop soiled N.O.S. Even if it's not correct then it's only £16.50 wasted. I'll let the group know of the results when it arrives. But thanks for your offer. Now you've got it out, can you tell me the numbers stamped on each end please?

Hope this helps

[EW-Ron]

Hi ,when I bought mine from the club when Dick was the spares officer he told me they came from Australia if this helps

Colin

Do we know if these were recently made, or supplied from NOS spares ?

Reason for asking is that a mob here just post WW2 made tons and tons 
of Amal spares - from melted down WW2 scrap brass shell casings collected from PNG. !
These were indistinguishable from genuine Amal - but the raw brass bodies give the game away.
Amal reportedly sued - but had no idea of the scale of this, so a slap on the wrist.

[Hutch]

Hi All,

more on this here;

https://www.douglasmotorcycles.net/index.php?topic=9512.msg37937#msg37937

I have a friend who has commented many times on similar endeavours here in Australia post WW2. I suspect the brass castings were from quite a while ago, say post war into the fifties or sixties (but it could have been later?) , but not sure about the cast aluminium ones tho'. I have a AMAL 74 copy in sand cast brass, obviously not an AMAL, but I'm sure it would work ok. fairly sure it is an Allparts casting, with the rest of the carby made up of used and NOS AMAL parts.

Not sure if the stock that the LDMCC procured was Allparts "NOS" or other?

Cheers

Hutch

[DJS]

Thanks Ron/Hutch for your comments. 
When I took over post-war spares for the club c5 years ago I inherited a small stock of these carb bodies. They were definitely new, rather than NOS, and were cast aluminium rather than brass.

Sadly, none of the records for the supply of these have been retained so we are unable to track down the original supplier. I have had it confirmed that they did come from Australia though.

Any leads would be very welcomed!

[Pallijen15]

Hi,Brit Bits in Christchurch did have some new jet blocks ,if that helps


Colin

Thanks Colin, I ordered the jet block yesterday morning, arrived this morning. What a great service! Brand new as well. £10. 

[Pallijen15]

Hi, I fitted the new jet block this morning but not much difference. My old one was well worn. It nips up slightly when the bottom nut is tightened up fully onto the bottom of the carburettor body. The slide is new also. When running, the engine slows when putting my hand over silencer or bell mouth, but stops immediately on the other side still. The engine runs nice, just when I take it on the road can't cope with changing gear, starts to run on one side and risks stalling, like fuel starvation 

[Jonathan Hewitt]

You said that you had seen the light ! Did you physically poke the holes out ?
   Just a thought if this resin is clear in small amounts.
Jonathan 

[Pallijen15]

You said that you had seen the light ! Did you physically poke the holes out ?
  Just a thought if this resin is clear in small amounts.
Jonathan

No. Can't really access the hole where it goes into the air screw but I saw the light through it straight away 

[EW-Ron]

starts to run on one side and risks stalling, like fuel starvation

When this happens, can you tug on the throttle cable on just that side that isn't,
and get the engine to rev up a bit - or at all.
Might be tricky out on the road, take care doing this.

This might eliminate that its just a weakness at idle, or more generally on that side.

[Pallijen15]

starts to run on one side and risks stalling, like fuel starvation

When this happens, can you tug on the throttle cable on just that side that isn't,
and get the engine to rev up a bit - or at all.
Might be tricky out on the road, take care doing this.

This might eliminate that its just a weakness at idle, or more generally on that side.

Yes, wh3n pulling cable engine does rev up

[EW-Ron]

What happens then when you screw in the idle mixture screw on this weak side, 
to richen up the idle mixture.
Remember, the idle mix screw controls the AIR SUPPLY at IDLE.

If'n you richen up the mixture enough, you should be able to dial out this foible ?
As always, you may also need to adjust the height of the slide to get a strong consistent idle.

If the idle mix screw has no effect, then  ...

[Pallijen15]

What happens then when you screw in the idle mixture screw on this weak side,
to richen up the idle mixture.
Remember, the idle mix screw controls the AIR SUPPLY at IDLE.

If'n you richen up the mixture enough, you should be able to dial out this foible ?
As always, you may also need to adjust the height of the slide to get a strong consistent idle.

If the idle mix screw has no effect, then  ...

I can screw it in or take it right out but it seems to have very little effect.  I can't adjust the slide any more by the carburettor top adjuster

[EW-Ron]

Have you poked through the petrol idle passages, to make 
sure the petrol can actually be delivered to make it idle ?

Sounds like at present that isn't happening.
But if air is getting past this jet block, then that needs to be sorted.
Hence your quest here ...

[Pallijen15]

Have you poked through the petrol idle passages, to make
sure the petrol can actually be delivered to make it idle ?

Sounds like at present that isn't happening.
But if air is getting past this jet block, then that needs to be sorted.
Hence your quest here ...

Hi Ron, could it make a difference if a new needle jet/air screw was fitted? The new jet block is not tight all the way in, just about the last 4mm

[EW-Ron]

I don't know, I don't think I have met your problem.
It sounded to me that you were on the right track with the new jet block.
But if that has not made any difference, maybe it is the body  ?

If that were mine, I'd try a lashup of inserting the jetblock with some soap paste as sealant
Yes, soap paste - common soap worked up with some water into a paste.
Works a treat as a sealant for petrol (and air) leaks. And quite long lasting too.
But easily removed, to enable a more permanent fix - once the solution has been determined
You'd need to be careful to not block any of those vital holes and passages.
Good luck !

[Pallijen15]

I don't know, I don't think I have met your problem.
It sounded to me that you were on the right track with the new jet block.
But if that has not made any difference, maybe it is the body  ?

If that were mine, I'd try a lashup of inserting the jetblock with some soap paste as sealant
Yes, soap paste - common soap worked up with some water into a paste.
Works a treat as a sealant for petrol (and air) leaks. And quite long lasting too.
But easily removed, to enable a more permanent fix - once the solution has been determined
You'd need to be careful to not block any of those vital holes and passages.
Good luck !

okay thanks Ron, I think the new jet block has made a little difference, I took the bike on a short ride after it was fitted and it ran a little better although a couple of times it did still falter when changing gear. I read of someone using low strength loctite which solved the problem. I'll try the soap paste method although a bit worrying of blocking holes 

[EW-Ron]

I hesitated to suggest loctite, in case it was too hard to remove.
But if it worked, it would be easier to apply accurately
You could lightly wick it in to where it is needed ...

[Pallijen15]

Hi Ron, a bit busy at the minute, where would I be applying the loctite or soap paste on the jet block? I'm a bit apprehensive of using the low strength loctite in case of damaging the old carburettor body when it needs to be dismantled 

[EW-Ron]

I'm thinking just a smear right around the flange, to try first.

So just at the base of this pic (selected at random).
You don't want to block up any of the drillings or passages.
https://www.oldtimervergaser.de/images/product_images/original_images/AL-MKE-div1.jpg

You said it was loose in the body, so it might be that this isn't enough to prevent too much air
being able to be drawn in at idle - and bypassing the idle circuit.
In which case you might be right in hunting for another body.

But it can't hurt to try this ...

You are sure that all the gaskets are the same in both carbs ?
And the fuel levels are identical in both carbs.

Can you get the jet block out of the other carb ? 
To try swapping bodies over ...