Author Topic: Douglas MkV temporary breakdown  (Read 1119 times)

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Offline Pallijen15

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Douglas MkV temporary breakdown
« on: 07 Aug 2018 at 10:37 »
Hi all, took my recently acquired 1951 MkV for a 60 mile trip on Sunday. Sputtered a little on the way to show, broke down on the way back. Each time leading up to this was when I was testing the  speed, 50ish. Waited for about 20 minutes, started first time, straight home. Not very quick and seems to struggle a bit on small inclines. Starts first time from cold after tickling but needs to be tickled a little if I stop engine and start again soon after. I am going to check petrol tank, fuel lines and carbs for any crap and maybe fit a filter on each hose. My question is could this be an ignition problem or am I right in suspecting muck in the fuel system? Should I expect to be attaining 50 to 55mph relatively easily? Thanks for any help. Paul

Offline eddie

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Re: Douglas MkV temporary breakdown
« Reply #1 on: 07 Aug 2018 at 11:35 »
Paul,
       Also check the breather in the petrol cap. As you have just acquired the bike, check the jetting of the carbs - originally it would have been fitted with no.80 main jets, but, these days,  the fuel that masquerades as petrol tends to run weaker, so it pays to increase to 85 or 90 jets, and maybe reduce the slide cutaway a little to get better response from the engine. The richer mixture will also tend to make the engine run cooler.
   If the engine is set up correctly, 60 mph cruising should be easily possible and the engine should give a top speed of 70 - 75 mph. Having said that - don't expect a Douglas to slog like an old single - it is much happier when allowed to rev.

  Regards,
                Eddie.

Offline Pallijen15

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Re: Douglas MkV temporary breakdown
« Reply #2 on: 07 Aug 2018 at 23:37 »
Thanks Eddie. Definitely a lack of power then. Couldn't touch 60mph. Will check what you've said and let you know

Offline Hampshirebiker

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Re: Douglas MkV temporary breakdown
« Reply #3 on: 08 Aug 2018 at 08:15 »
The colour of the plugs will give you a good idea of the mixture situation.

Offline Pallijen15

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Re: Douglas MkV temporary breakdown
« Reply #4 on: 08 Aug 2018 at 08:39 »
Thanks, I'll check the plugs. I'll also be checking the tappet clearances. Sounds a little bit rattly once the engine's warmed up. Previous owner has given me some new pushrods for right hand side which have been specially made 5mm longer. This is because he couldn't get any more adjustment on the ones that are already in, being right at the end of their adjustable limit. Maybe some parts from another model used? Paul J

Offline Pallijen15

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Re: Douglas MkV temporary breakdown
« Reply #5 on: 08 Aug 2018 at 17:07 »
Thanks, I'll check the plugs. I'll also be checking the tappet clearances. Sounds a little bit rattly once the engine's warmed up. Previous owner has given me some new pushrods for right hand side which have been specially made 5mm longer. This is because he couldn't get any more adjustment on the ones that are already in, being right at the end of their adjustable limit. Maybe some parts from another model used? Paul J

Offline Pallijen15

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Re: Douglas MkV temporary breakdown
« Reply #6 on: 08 Aug 2018 at 17:27 »
Ok, checked petrol cap, hole not blocked, spark plugs NGK B6H S, right side nice light brown colour, left side sooty black, both tapped at slack 25thou. Set to 15thou. Fuel hoses are metal braided which can be seen as the outer covering is cracked and peeling off. Black particles in right side float bowl and lots of soft off-white like gritty salt stuff on bottom of left bowl. Throttle slides are both 4/3. Right carburettor is 274/407R, left is 274AK/4A. Haven't taken carburettors off yet as I'm not sure that I need to to clean them out. Book says slides should be 4/5 and right carburettor is not the standard one, runs fine though so don't think there's a problem there. My thoughts are to clean out and inspect the fuel tank, the fuel hoses seem okay, I pushed a thin wire down each one a few times and there doesn't seem to be any loose bits coming off. Thanks for any advice. Paul

Offline eddie

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Re: Douglas MkV temporary breakdown
« Reply #7 on: 08 Aug 2018 at 17:46 »
Paul,
        Tappet clearance should be .005" (as stamped on top LH side of crankcase).  Early carbs were numbered 274AJ/4A and 274AK/4A, later carbs were 274/407 and 274/408 - don't worry that you have one early and one late carb - there was no difference other than the numbering.

  Regards,
                Eddie.

Offline Hampshirebiker

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Re: Douglas MkV temporary breakdown
« Reply #8 on: 08 Aug 2018 at 19:36 »
I would really take the carbs out and give them a good clean. Best to remove the bottom nuts,  float chambers & main/needle jets before you remove the bodies from the heads. Remove the brass jet blocks, soak them in thinners for a couple of days and then blow all the tiny drillings through with a high pressure C/A nozzle. The jet blocks tap (gently) or press out from the top. Take great care though. It might pay to get a couple of gasket sets before you start.

Offline Vermont-Ian

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Re: Douglas MkV temporary breakdown
« Reply #9 on: 09 Aug 2018 at 21:14 »
Paul,
Another possibility - a magneto whose insulation breaks down when hot, or maybe a failing capacitor.  I had that problem.  Not as easy to fix as some of the other possible culprits already mentioned.  Diagnostic test: do you have a good spark when the magneto is cold?  Is the spark weak or absent when the engine (and magneto) are hot?
Ian
Ian Stokes
Richmond, Vermont, USA
1948 Mk III
1936 Citroen 'Traction' 7C

Offline Pallijen15

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Re: Douglas MkV temporary breakdown
« Reply #10 on: 12 Aug 2018 at 06:18 »
Hi, Thanks for replies. I'm quite sure that it's a fuel problem and not ignition. I've taken both carbs off, the right one seems ok but the  left one had lots of crap in the bottom of the float bowl and particles were present around the needle jet as well. The previous owner had problems with the rings sticking right hand side and I think he must have cleaned the carburettor when sorting that out. I'm now looking for the correct petrol taps as the ones that are on don't have a reserve. Tried the spares scheme and Amal don't seem to have any on their website, any ideas as to where else I could try? Which other marques used this type? Thanks, Always appreciated, Paul J

Offline eddie

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Re: Douglas MkV temporary breakdown
« Reply #11 on: 12 Aug 2018 at 06:59 »
Paul,
        When cleaning out the carbs, make sure the small drillings are clear. There is one in the carb body - from the air screw into the main inlet tract, and another in the brass choke block (on the engine side of the block there is a shallow drilling about 4mm dia - there are 3 holes in it, one at the top, one at the side, and a very small one in the bottom of the drilling).
  Sorry, can't help regarding petrol taps.

    Eddie.

Offline Red

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Re: Douglas MkV temporary breakdown
« Reply #12 on: 12 Aug 2018 at 09:12 »

Offline Pallijen15

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Re: Douglas MkV temporary breakdown
« Reply #13 on: 13 Aug 2018 at 10:01 »
Ok thanks Eddie, do you think it's necessary to remove the jet block? Drained tank, took out fuel taps, nothing on filters looks very clean.
     Roy, thanks for the link. I am thinking of just changing one of the taps, can't see the point of  having a reserve tap on both sides. http://www.classic-bike-shop.com/82-1717-ethyline-resistant-tap-twin-plunger-on-off--reserve-imported-1059-p.asp doing the taps for considerably cheaper. Imported but won't the ones at Feked be too. Thanks, Paul J

Offline eddie

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Re: Douglas MkV temporary breakdown
« Reply #14 on: 13 Aug 2018 at 10:14 »
Hello Paul,
                Yes, do remove the choke blocks - if they are left in place too long, corrosion builds up between them and the carb body, making them very stubborn to move - eventually causing the carb bodies to swell, resulting in fuel seeping between the choke block and body, making tuning very difficult.

  Eddie.

Offline yosemite

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Re: Douglas MkV temporary breakdown
« Reply #15 on: 14 Aug 2018 at 10:11 »
Paul
not sure exactly about your fuel tap set up, but on mine each carb is fed by a single tap,so if you only fit one tap with a reserve the you may be reduced to running on 1 cylinder when you come onto reserve, or if the taps are linked then you may only get to use half the reserve fuel

Offline Pallijen15

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Re: Douglas MkV temporary breakdown
« Reply #16 on: 15 Aug 2018 at 21:21 »
Ok thanks all for info. Have stripped and cleaned carbs, jet blocks removed. Left one is quite black in parts as opposed to the right one. Needle jets 106, main jets 80. Only thing different to the book is the throttle slides are 4/3 and not 4/5. Would this have any effect on power? I struggled to get over 55mph but I am thinking this was through fuel starvation.
The carbs came off with gaskets intact, no sealant has been used. Should I put the same gaskets back on dry. They appear to be in very good condition and I think are graphite. I would have thought by putting only one tap on with reserve would be enough because the reserve would need to be used when the fuel level dropped to below when it should be turned on. The other side hasn't got a reserve so fuel would still be ok. Also drained petrol tank and checked inside with camera. Looks very good. Thanks, Paul J

Offline Pallijen15

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Re: Douglas MkV temporary breakdown
« Reply #17 on: 15 Aug 2018 at 21:33 »
Sorry, just dawned on me why I'd need reserve taps on both sides......

Offline eddie

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Re: Douglas MkV temporary breakdown
« Reply #18 on: 16 Aug 2018 at 06:11 »
Paul,
        The smaller 4/3 cutaways will only affect the pickup from tickover to about 1/4 throttle. The main jets control the mixture at full throttle. As I have already said, modern fuel is far removed from that available when the bikes were new, so re-jetting to 85's or 90's should give an improvement in power and top speed. Also, be aware that, unlike most other British bikes, the Douglas advance/retard is set up  to be 'tight wire advance'. You may need to play with the advance/retard to find the 'sweet spot' where the engine performs best - it is usually at almost full advance.
  With regard to carb gaskets - the original flange gaskets were 1/8" thick Tufnol - repro gasket sets normally have softer thick Hallite gaskets - these should be thrown away as they will eventually cause the carb bodies to distort and crack. The original Tufnol was intended to be more of a heat barrier than a gasket, and can be re-used with just a smear of red Hermetite to ensure an air tight joint.

  Regards,
                Eddie.

Offline Pallijen15

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Re: Douglas MkV temporary breakdown
« Reply #19 on: 16 Aug 2018 at 09:17 »
Damn. Was going to put carbs back on today as well. Ok, thanks Eddie, looks like I can get the insulators from Hitchcocks for that size carburettor. I'll leave changing the main jets until I've tried the bike again with fuel system cleaned out, might be all it needs. Going to try also with just the one reserve tap fitted, I'm sure it must work. The bike was going best with the ignition advanced most way but the idling was a little fast so I'll reduce the tickler. Thanks Eddie, much appreciated, Paul J

Offline tck

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Re: Douglas MkV temporary breakdown
« Reply #20 on: 16 Aug 2018 at 12:24 »
That adjuster at the limit and longer push rods keep bugging me
Are you sure that the valves are not recessed excessively

Offline Pallijen15

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Re: Douglas MkV temporary breakdown
« Reply #21 on: 16 Aug 2018 at 12:44 »
That adjuster at the limit and longer push rods keep bugging me
Are you sure that the valves are not recessed excessively
I haven't taken the head off yet so I don't know. The standard pushrods are still being used, just that the previous owner had a new set made 5mm longer because there was no more adjustment available on the one's fitted at present. Does sound slightly rattly after it's warmed up, not sure if this is normal for these motorcycles. Thanks, Paul

Offline Jonathan Hewitt

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Re: Douglas MkV temporary breakdown
« Reply #22 on: 16 Aug 2018 at 16:15 »
Surely if the valves were recessed Shorter push rods would be needed !
Jonathan

Offline Pallijen15

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Re: Douglas MkV temporary breakdown
« Reply #23 on: 16 Aug 2018 at 17:03 »
Tufnol heat spacers from Hitchcocks are 5 each but they only have 22mm dia hole. The 274 carburettors are 19mm dia. Would this be a problem? Hitchcocks advised that I should try to source the correct diameter one. Might have to get from Amal although they're over twice as much. Does the Douglas spares scheme stock them? Sent an email off but haven't had a reply. Any ideas who else might stock them? Thanks, Paul J

Offline Hampshirebiker

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Re: Douglas MkV temporary breakdown
« Reply #24 on: 17 Aug 2018 at 07:38 »
Be careful, I could be wrong, but something tells me that the Douglas flanges are smaller than the standard 274 carb.

Offline Pallijen15

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Re: Douglas MkV temporary breakdown
« Reply #25 on: 17 Aug 2018 at 09:56 »
Be careful, I could be wrong, but something tells me that the Douglas flanges are smaller than the standard 274 carb.
Hi, just checked with Amal and yes, your right, the studs for this size spacer are 2 inches apart, on the Douglas carb the holes are about one and a half inches apart. Are these easy to make?

Offline Pallijen15

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Re: Douglas MkV temporary breakdown
« Reply #26 on: 17 Aug 2018 at 10:32 »
Hi, just so as to know what heat resistant grade of Tufnol to buy could anybody please tell me what sort of temperature the material needs to withstand in this particular area. Thanks, Paul J

 

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