Author Topic: D14 Runaway  (Read 656 times)

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D14 Runaway
« on: 27 June, 2021, 14:04:28 »
Hello all.  I need help to understand something new to me.  I have no experience with 2 stokes at all but I am a B31 member of the club and thought I would ask yourselves.  I am doing a favour for a friend by getting his 1971 D14 running, it had stood unused in his garage for 5 years.  I have taken off the tank, seat and air filter.  Removed and ultra-sonically cleaned the Concentric. Charged the battery.  Checked the timing.  Got a good spark.  Fitted a temporary petrol supply and after a LOT of kicking eventually got it running.   Then after roughly 5 minutes it took off at full revs.  Closing the throttle had no response, removing the plug lead the same, disconnecting the battery which made no difference, bike still at full revs.  Only stopped when I blanked the carb air intake with my hand.  Can anyone explain in a way I can understand?
Also, how big a job is it to re-place the seals, and how expensive would it be as my friend doesn't want to spend a lot on it. I ask because someone told me that they would need replacing after such a long time standing.
The bike is in really good condition, only had 2 owners and has a genuine 1800 miles on the clock.
All replies gratefully received.  Thanks.

idie

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Re: D14 Runaway
« Reply #1 on: 27 June, 2021, 15:43:04 »
May be one of the crankshaft seals has let go and air is being sucked in to the crankcase. Like opening the throttle.

Dean Southall

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Re: D14 Runaway
« Reply #2 on: 27 June, 2021, 16:49:25 »
I woud definately replace the crank seals and with Viton ones https://www.ebay.co.uk/itm/153240876297?hash=item23adde3509:g:xpsAAOSwrg1fhCYn

On the down side its a complete engine strip to replace them, on the up side its a Bantam so there isn't much to strip!
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Stubaker58

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Re: D14 Runaway
« Reply #3 on: 27 June, 2021, 17:44:06 »
Frightening isnít it!

Sometimes a carbon build up on the piston gives enough glow to keep the engine running with no spark.  The seals may also be letting in air and sucking in the gearbox oil to keep things going.

Stripping the engine down is no great job and if the bearings and rings are ok then replacing the seals gaskets, gear return spring and tab washers will cost somewhat less than £50.  Take note of the shins on the crank and ensure the endfloat is correct. Make sure too that the seals go in the correct way around, itís surprisingly easy to get it wrong.

Rex Caunt is probably your best bet for a one stop shop.

Hope it goes well.

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Re: D14 Runaway
« Reply #4 on: 27 June, 2021, 19:03:14 »
Many thanks everyone who replied.  All your remarks makes sense to this 2 stroke illiterate.  I shall contact my mate and see if he wants me to go ahead.  I will let you know the results if he agrees to the work.  Thanks again.

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Re: D14 Runaway
« Reply #5 on: 14 July, 2021, 20:28:15 »
Hello all.  I need help to understand something new to me.  I have no experience with 2 stokes at all but I am a B31 member of the club and thought I would ask yourselves.  I am doing a favour for a friend by getting his 1971 D14 running, it had stood unused in his garage for 5 years.  I have taken off the tank, seat and air filter.  Removed and ultra-sonically cleaned the Concentric. Charged the battery.  Checked the timing.  Got a good spark.  Fitted a temporary petrol supply and after a LOT of kicking eventually got it running.   Then after roughly 5 minutes it took off at full revs.  Closing the throttle had no response, removing the plug lead the same, disconnecting the battery which made no difference, bike still at full revs.  Only stopped when I blanked the carb air intake with my hand.  Can anyone explain in a way I can understand?
Also, how big a job is it to re-place the seals, and how expensive would it be as my friend doesn't want to spend a lot on it. I ask because someone told me that they would need replacing after such a long time standing.
The bike is in really good condition, only had 2 owners and has a genuine 1800 miles on the clock.
All replies gratefully received.  Thanks.

Hello-again.  Re the above Bantam.  I have changed the seals and all the bearings are fine so I left them alone. Used all new gaskets.  Ignition spot on at 16.5degrees BTC. The carb ultrasonically cleaned, the sticking kick start lever sorted and with the tank, seat, air filter removed and a temporary fuel supply rigged up I got it running-after a lot of kicking.  It was running fine,  the choke fully open and responding well to the throttle. But after a few minutes it took off again at full revs and not responding to the throttle at all.  After a while I found by trial and error that it could only be controlled by the throttle with the choke closed.  Open the choke fully and it was back to square one with no throttle control.  Tomorrow I will put the air filter back on to see if that makes a difference. 
The are no carbon deposits on the piston or head so its not that.  Any ideas anyone? 
 

LightningAndStarfire

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Re: D14 Runaway
« Reply #6 on: 14 July, 2021, 21:01:28 »
Hi, must be an air leak, through the seals or the carb, a worn slide or between carb and inlet to the engine. I would try a brand new carb, if the slide or the carb body is worn it could be worse when the engine heats up and some heat is transfered to the carb. Fuel evaporating has a cooling effect of course. A carb issue is more likely than the seals since air leaks through the seals would not give any additional petrol.

Stubaker58

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Re: D14 Runaway
« Reply #7 on: 15 July, 2021, 07:24:36 »
Hi,
I would agree with LighteningAndStarfire.
Check that the carb mating surface is flat, only use the O-ring, no paper gasket (unless you have a tufnol spacer then itís paper gasket, spacer, O-ring, carb).  The carb flange can be ground flat, Iíve used wet&dry lubed with WD40 and taped to an old fridge shelf to keep it flat, figure of eight movements and keep checking.
If that doesnít work then a new carb is the way to go.

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Re: D14 Runaway
« Reply #8 on: 15 July, 2021, 17:29:02 »
Thanks for the possible causes.  I tried it again today after fitting the air filter and it was still the same.  Will take it off again tomorrow, remove and check the carbs possible fault areas-again-and give it another go.  Will keep my fingers crossed >:(

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Re: D14 Runaway
« Reply #9 on: 17 July, 2021, 16:55:07 »
Well, After removing the carb again and removing the studs in the barrel I checked  the face fits of the carb and the barrel (again).  They seemed OK to me but I spot faced both surfaces anyway and refitted the carb using a new gasket and "o" ring.  When I next started the bike the fault was still there so perhaps you are both right and it needs a new carb.  Will advise the owner as such.  Thanks for all your help, much appreciated.

bluebell

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Re: D14 Runaway
« Reply #10 on: 09 August, 2021, 19:19:20 »
the concentric is more finicky  than the  monobloc,,and i have seen a porus casting,on one of these, check the cable top is relatively air tight,,i had a small runaway with an unkown monobloc,,turned out to be a missing venturi  block  seal washer,,,