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Engine very snatchy on over run.
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carpetralph
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September 21, 2019 - 9:49 am
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Hi all (again), 

Although my D14 is now running great whilst under load, it is very snatchy on the over run to the point where I am pulling the clutch in to prevent it happening. I am wondering if this could be caused by wear in the primary chain or whether the carb settings could be the cause. I found that when setting the tickover according to the book it was best with the primary air screw fully in, but realising that this really couldn`t be right I settled for having it about a quarter turn out.

Any thoughts?

Also, had lots to do with earlier bantams, but new to D14s, to access the clutch will I have to remove the points cam from the end of the crank thus needing to re-time it all, or will the clutch cover come off over the cam.

Ta.

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mikef
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September 21, 2019 - 1:58 pm
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Hi Ralph.
         I think your problem of snatchy over run could be due to a worn air slide or carb body. If you are sure that there is no air leak at the manifold then I think the best action in the long run is a new carb. The metal that the Amals are made from is very soft and wears over time.
On my D14 I first replaced the slide only to find that the new slide was a sloppy fit in the carb body, so ended up buying a complete carb. Problem solved.
I also find that the best idle is with the mixture screw about a quarter turn out, even with the new carb. I put it down to modern fuel, I have no other explanation.
From memory the clutch cover can be removed without removing the points cam.
Mike.

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AdrianS
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September 21, 2019 - 4:37 pm
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You can remove the clutch cover leaving the points cam in place. Just be careful on reassembly that you don't damage the oil seal in the clutch cover that fits over the crank.

When you say "snatching" , do you mean the jerkiness of the engine on over run?  If so, I suffer this to some degree, but my old D7 was much better.

I have got a brand new carb on the bike too. I also agree that the mixture setting is better screwed in a bit from the 1 1/2 turns sometimes recommended. In fact mine is probably 1/2 to 3/4 turn out.

I did change the primary chain which helped a bit, and also make sure the drive chain is not too loose. I also think this jerkiness is a bit of a D14 trait but others may say differently! 

One other thing to mention re clutch cover. Obviously the gearbox oil needs draining first but after doing that see if you can lay the bike over a little. I put some wood under the centre stand to jack the bike over and rest the bike on my garage wall. This stops further drips of oil from the chaincase and helps a lot when refitting the gasket and cover.

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carpetralph
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September 21, 2019 - 5:48 pm
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Thanks for the advice guys. I have been out on it today making the most of this fine weather, and done 110 miles bumbling about aimlessly. It`s not bad when cold, gets worse as it warms up, and when trying to keep at, say, 30mph in a built up area its almost feels like a misfire, but as soon as it gets even the slightest load on it settles down to a nice crisp 2 stroking. Think I will order a new primary chain and gaskets anyway ready for an investigation, but in the meantime just enjoying re-living my youth so I won`t dismantle it just yet unless the weather takes a turn for the worse. I will have a look at the carb slide too.

Do the primary sprockets suffer a lot from wear, is it worth changing them at the same time?

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SpacedMarine
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September 21, 2019 - 7:18 pm
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carpetralph said
Thanks for the advice guys. I have been out on it today making the most of this fine weather, and done 110 miles bumbling about aimlessly. It`s not bad when cold, gets worse as it warms up, and when trying to keep at, say, 30mph in a built up area its almost feels like a misfire, but as soon as it gets even the slightest load on it settles down to a nice crisp 2 stroking. Think I will order a new primary chain and gaskets anyway ready for an investigation, but in the meantime just enjoying re-living my youth so I won`t dismantle it just yet unless the weather takes a turn for the worse. I will have a look at the carb slide too.

Do the primary sprockets suffer a lot from wear, is it worth changing them at the same time?  

I'd leave the primary chain for now.Are you sure you have the timing set spot on?I had a similar problem recently.I had a spare throttle slide I ground a bit off seemed to improve it quite a bit however.I set the timing using a dial indicator on the piston to get the exact point where the ignition should have been set.It was like a different bike where before it would struggle to pass 55 it now does an indicated 70.I also had electrical issues which probably didn't help hence the 12v conversion. I'd double check your timing 1st though.Does make you wonder why these bikes end up stuck at the back of a shed for 30 years sometimes.

What's 7/16 in mm again?

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carpetralph
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September 22, 2019 - 8:38 am
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SpacedMarine said

I'd leave the primary chain for now.Are you sure you have the timing set spot on?I had a similar problem recently.I had a spare throttle slide I ground a bit off seemed to improve it quite a bit however.I set the timing using a dial indicator on the piston to get the exact point where the ignition should have been set.It was like a different bike where before it would struggle to pass 55 it now does an indicated 70.I also had electrical issues which probably didn't help hence the 12v conversion. I'd double check your timing 1st though.Does make you wonder why these bikes end up stuck at the back of a shed for 30 years sometimes.  

I have a dial indicator, but the info I have on timing a D14 (Haynes manual) necessitates use of a degree disc. How many mm ( or fractions of an inch) should the piston be before TDC when using a dial gauge.

I must confess I did retard the ignition a few weeks ago to get rid of the pre-ignition, but it runs well and romps up to 60 and will do more.

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AdrianS
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September 22, 2019 - 9:05 am
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Long post - bear with it!

I discussed the problem you are having with Rex Caunt a year or so ago.

He suggested making sure the correct head gasket was used as BSA advised a thicker gasket on later D14 models. I use his "thick" head gasket - I think it is 1.5mm thick but would need to check on this. Also he suggested with modern fuels that the timing could be retarded to 13.5 degrees from 16.5 degrees.

Finding TDC is not as easy as you think. You can move the crank quite a few degrees with the piston not moving at TDC. You need to put something down the plug hole which stops the piston getting to TDC. Slowly rotate the crank till the piston makes contact. Make a mark on the alternator rotor and a pencil mark opposite it onto the crankcase. Turn the engine backwards until the piston again hits the stop down the plug hole. Make another pencil mark onto the crankcase level with the mark on the rotor. Half way between these marks will be TDC. You can make permanent marks for TDC as a reference. You can then use a dial guage to make timing marks on the crankcase for future reference.

It is easy to work out how much before TDC any degrees will be. A bit of simple maths. I'm not very good at explaining but bear with me!

Draw a circle on a piece of paper, the diameter the same as the engine stroke. Make a vertical line through the middle of the circle.

Make a mark 16.5 degrees ( or what ever figure you want for the timing) on the circle to the left of the vertical line.

Draw a line at right angle from the vertical line to the mark on the circle. The distance from the top of the circle to the line at right angle to the vertical is the distance you need for timing through the plug hole. This is how you work it out for any timing degree and for any engine as long as you know the stroke.

I hope you can follow this!

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SpacedMarine
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September 22, 2019 - 10:26 am
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Pretty sure its 60 thou before top dead centre.I'll double check and get back to you.As for the piston not moving at tdc if you creep up to it and zero the dial you'll be ok.Just wind it back a little and check a couple of times to make sure you have it bang on.As adrian says best to make a mark on something.I just used a sharpie on the alternator rotor and you have a reference mark for the future.Then just set the points as you normally would.Good luck.

What's 7/16 in mm again?

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nickjaxe
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September 23, 2019 - 12:07 am
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I use the same method as AdrianS for timing and finding TDC...bar I use a timing disc for finding the angle.

As well as snatching it sounds like your 4 stroking at light throttle openings.

I have a brand new carb...I get some snatching...I have a theory its not helped by me having a slight richer idle just...I fit this to keep the lube supply going when the bike is going downhill throttle closed...

To aid with the snatching I partly release the clutch...just a bit is all thats req...just to protect the internals...it can't do things any good.

By chance, I bought a supposedly British made condenser...as the cheap £5 one dont seem to last long...this British one cost over £20...soon as I fitted it the snatching improved quite a bit...not completely but a noticeable amount...I still need to de-clutch a bit but not till I am going quite slow with low RPMs.

The 4 stroking I got rid of by fitting a weaker carb slide...I had put a number 3 in...it started to 4 stroke so I put the 3.5 back in...that sorted it.

Nick.

My Bantam video              https://www.you.....jpOFmzRZRI

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SpacedMarine
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September 23, 2019 - 9:06 am
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Little changes eh Nick 😆 I have a degree disc but I find it a pain to be honest.The fact i have a permanent mark on the flywheel means i can use a strobe light to check it which i find more convenient but horses for courses 👍🏼

What's 7/16 in mm again?

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nickjaxe
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September 23, 2019 - 10:14 am
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They are a pain and a fiddle...but spot on if used right.

I did make a mark for a strobe on mine.

My Bantam video              https://www.you.....jpOFmzRZRI

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cocorico
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September 23, 2019 - 10:57 am
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carpetralph said
...Although my D14 is now running great whilst under load, it is very snatchy on the over run ...

Have you checked the drive chain's tension? If that's too slack it can feel similar.

1956 D3 running, lights to sort. 7 other bikes in the Barn, 6 runners (when I get time!) and a still in progress Morini 250

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SpacedMarine
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September 23, 2019 - 11:59 am
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cocorico said

carpetralph said
...Although my D14 is now running great whilst under load, it is very snatchy on the over run ...

Have you checked the drive chain's tension? If that's too slack it can feel similar.  

Simple things 1st 😆👍🏼

What's 7/16 in mm again?

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cocorico
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September 23, 2019 - 12:16 pm
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AdrianS said
...Finding TDC is not as easy as you think. ...

I take the head off, straight edge across the cylinder, then rotate the flywheel forward until you get to TDC (which may not be at the top of the cylinder). Measure the gap between the piston and straight edge, then add the distance BTDC for your timing - eg from Spaced Marine's post 60thou (1.5mm) - to that figure, use a suitable spacer and mark-up your flywheel - or just set your points. Takes a bit of time to do first time (measurements, etc), but then it's part of your service kit.

Don't forget to take all your measurements with the piston moving in the running sense.

1956 D3 running, lights to sort. 7 other bikes in the Barn, 6 runners (when I get time!) and a still in progress Morini 250

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carpetralph
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September 24, 2019 - 7:14 pm
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I have taken this week off due to the international cycle race in Harrogate, where I normally work, so have been spending some time in the garage. Today I re built the carb on the D14 with all new jets, gaskets etc, and put in a new 3.5 slide. 

Seems to start and run nicely with a good idle, but it has been raining all day so not taken it for a run yet.

I have not done the timing yet, as I like to change one thing at a time otherwise you don`t know what ( if anything) improves it.

Hopefully may get chance to run it tomorrow and will report back.

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carpetralph
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September 25, 2019 - 10:54 pm
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Sun shone for a minute or two today so I hopped on the D14 and took it down the road.

The carb overhaul has done wonders for the performance, I thought it was good before, but it rockets away now and revs right up past where I was changing gear before. Very impressed, however the snatchiness is now worse than before, and after the short run the tick over had gone astray, so got some fine tuning to do. There must have been wear in the needle jet because with the new one in it is running weaker and needs the choke on longer till it warms up, but there is no hesitation once it is warm.

Going to try to find time to double check the timing next.

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nickjaxe
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September 25, 2019 - 11:04 pm
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Very well done...is it std jetting now in the carb?

The only other thing I was going to try to get rid of the snatching was put a smaller idle jet in...but I can live with it...just got used to de-clutching very slightly...second nature now....but do let us know how you go on with it in future.

My Bantam video              https://www.you.....jpOFmzRZRI

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cocorico
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September 26, 2019 - 8:03 am
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nickjaxe said
...just got used to de-clutching very slightly...second nature now....but do let us know how you go on with it in future.  

So what does de-clutching do? It takes the load off the engine for a moment, which to me means that either you are in too high a gear for the engine to drive, or that at that load the engine is not getting enough fuel. Does the 'snatching' occur at the same sort of load in a lower gear? If so, I think I'd look at the carb settings again. If not, I think you need to use the gearbox a bit more. dunno

1956 D3 running, lights to sort. 7 other bikes in the Barn, 6 runners (when I get time!) and a still in progress Morini 250

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nickjaxe
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September 26, 2019 - 8:31 am
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EH!

My Bantam video              https://www.you.....jpOFmzRZRI

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SpacedMarine
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September 26, 2019 - 9:07 am
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Getting there.Mine pops and farts a bit on a closed throttle but you get used to it.Its an air cooled two stroke single from before the war basically so it makes all sorts of funny noises that would probably indicate disaster on a modern vehicle.

I've got mine so it's nice and crisp at a steady throttle and likes being under load but it's a two stroke they like load.

Also after a couple of miles at 60+ my idle goes a bit wobbly.I put it down to heat but I could be wrong.

I went for ten miles yesterday and the only thing that broke was the speedo!thought it was broken but was just the cable that had come loose at the headlight end.

I always end up going for another gear aswell as 4th seems a bit low 🤣

What's 7/16 in mm again?

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