Poor Running

Information relating to the Matchless G3 or AJS Model 16 350cc Heavyweight
steadyrider
Member
Posts: 23
Joined: Wed Aug 25, 2021 1:41 pm
Location: Northumberland

Poor Running

Post by steadyrider »

I have a 1958 16MS - Nice bike that I've owned with very few problems for 4 years or so but haven't done a lot of mileage on. It is coil ignition (6V) and only has 400 miles on since extensive rebuild by a previous owner.

I lost compression last year and had to seek help from my local motorbike mechanic - they did all the obvious checks but couldn't find anything - the head went off to be diagnosed and it was found the exhaust valve seat had moved - this was rectified and (3 months and £ 650 later !!) I went to collect the bike - it started fine but had been standing at this point so there was the usual petrol leakage because the corks were dry - I only got about 2 miles up the road but it started back firing and got red hot. It went back to the mechanics and they did further work on it - I finally collected it in June (which was now 9 months after the original problem).

It starts fine and revs fine, it has a new plug, new battery, it's had a new coil and condenser, clean fuel, the carb has been cleaned, points checked and the spark looks ok, the oil is returning fine but I only have to get 100 yards up the road and it starts back firing and cutting out - I've tried adjusting the choke, the air screw and the timing - I'd welcome any suggestions I'm a whipper snapper at 52 and not experienced enough to start dismantling the head again - It's not going back to the mechanics either !!
Mick D
Posts: 2886
Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: Poor Running

Post by Mick D »

Hi

Sounds like the valve clearances are too tight - or the choke is closing due to vibration.

Getting red hot will probably have been due to the timing being too far retarded.

Regards Mick
SPRIDDLER
Member
Posts: 8541
Joined: Wed Sep 01, 2004 1:00 am
Location: WEST SUSSEX UK

Re: Poor Running

Post by SPRIDDLER »

Welcome, Sean.
Just so that I have the picture.......
The bike has done 400 miles in 4 years. It was unused for 9 months until June this year whilst the zorst seat was being sorted and the subsequent work on it to sort the backfiring (which hasn't been sorted).
I only have to get 100 yards up the road and it starts back firing and cutting out - I've tried adjusting the choke
If you need to use the choke to start it the choke should be opened (tight wire) once the engine is warm and ridden like that.
.....the air screw and the timing [adjusted]
By 'air screw' I assume you refer to the Pilot jet. This should be about one and a half turns open from fully screwed in.
Did you adjust the timing? Did you do that with the points set at full advance?

Since it has stood for a while I'd check the carb again for sludge - initially the main jet and Pilot jet with the carb in situ.

It's a long shot but easy to check if the petrol tank vent is blocked by a test ride with the tank cap removed.

As Mick has said, check the pushrod/rocker clearance.

Do you have the Owners and the Workshop manuals? If not, they can be found here under 'Books'.
http://archives.jampot.dk/
- It's not going back to the mechanics either !!
I may be out of touch as I do my own maintenance but £650 to remove the head, replace the zorst seat and refit the head sounds very dear to me.
'There is a tide in the affairs of men
Which taken at the flood............'
steadyrider
Member
Posts: 23
Joined: Wed Aug 25, 2021 1:41 pm
Location: Northumberland

Re: Poor Running

Post by steadyrider »

Thanks Mick and Spriddler

I'll check the tank vent - that makes sense - yes the repairs were steep, I had a full breakdown including how much it had cost them to send the head off to have the valve seat corrected (£ 250.00) - I'd put 90% of the cost down to labour charges for 'trial and error'... most annoying when I got it back and it still isn't right.

There are marks on the crank case and points plate which I've always aligned and they've been spot on in the past - the gap on the points is 12 thou when fully opened.

I'll check the carb again and reset the pilot jet to one 1/2 screws out, the petrol feed is good.

I've just checked the plug again and its sooty round the edge but not on the electrode ?

It might be my imagination but it's also developed a rattle on either the valves or small end.

Thanks for your help - process of elimination I suppose.
SPRIDDLER
Member
Posts: 8541
Joined: Wed Sep 01, 2004 1:00 am
Location: WEST SUSSEX UK

Re: Poor Running

Post by SPRIDDLER »

steadyrider wrote: Wed Aug 25, 2021 6:39 pm
There are marks on the crank case and points plate which I've always aligned and they've been spot on in the past - the gap on the points is 12 thou when fully opened.
Sorry to nag the issue but even though the points gap is correct at 12 thou did you fix the A/R bobweights in the fully advanced position when timing the ignition? (Details are in the Owners Manual for which I gave you a link).
(I've never had a mag with auto advance retard so not clear as to what mark on the c/case you are using).
I've just checked the plug again and its sooty round the edge but not on the electrode ?
That sounds O.K. if the centre electrode insulator is a beige/straw colour. (Not easy to describe definitively).
'There is a tide in the affairs of men
Which taken at the flood............'
User avatar
clive
Member
Posts: 5657
Joined: Mon Jan 01, 1990 12:00 am
Location: LONDON UK

Re: Poor Running

Post by clive »

(I've never had a mag with auto advance retard so not clear as to what mark on the c/case you are using).

" It is coil ignition (6V) and only has 400 miles on since extensive rebuild by a previous owner."

Do keep up Spriddler :rofl:

Ps because its coil ignition I haven't a clue either!
clive
if it ain't broke don't fix
User avatar
Duncan
Member
Posts: 2118
Joined: Thu Jul 10, 2003 1:00 am
Location: HAMPSHIRE UK

Re: Poor Running

Post by Duncan »

The ignition can be set either way (Advanced/Retarted) on a 1959 coil ignition single:
1959 Extract - Coil Ignition.PNG
You do not have the required permissions to view the files attached to this post.
SPRIDDLER
Member
Posts: 8541
Joined: Wed Sep 01, 2004 1:00 am
Location: WEST SUSSEX UK

Re: Poor Running

Post by SPRIDDLER »

clive wrote: Fri Aug 27, 2021 10:51 pm Do keep up Spriddler :rofl:

Ps because its coil ignition I haven't a clue either!
:oops: Coil ignition and auto A/R technology is rather too modern for me too, although I have recently put techy manuals onto a tablet as I found that although it's very heavy to move around it's more practical and durable for use in the shed than the papyrus originals.
Last edited by SPRIDDLER on Sat Aug 28, 2021 10:54 am, edited 1 time in total.
'There is a tide in the affairs of men
Which taken at the flood............'
Groily
Member
Posts: 2151
Joined: Thu Jul 04, 2002 1:00 am
Location: NORMANDIE FRANCE

Re: Poor Running

Post by Groily »

Duncan wrote: Fri Aug 27, 2021 11:42 pm The ignition can be set either way (Advanced/Retarted) on a 1959 coil ignition single
Indeed it can. But unless you know that the auto-advance unit is providing the prescribed degrees of movement for the model, I'd set things at full advance personally if possible, as that's where the engine is running most of the time. (With the possible exception of some side valve engines where you can't get down the plug 'ole to measure, but can find tdc by other means.)
Nine times of ten it won't matter, but the tenth time, it might. A few degrees more or less than 'book' at full retard and low rpm won't usually cause any grief, but at full advance it can be a bit different.
I've never been quite sure why manuals adopted the either/or approach for battery/coil systems, when they are all pretty insistent on 'full advance' with auto-advance on magnetos - unless there is something that makes it painfully difficult to wedge open the bits?
User avatar
1608
Member
Posts: 2493
Joined: Mon Oct 05, 2009 1:00 am
Location: ESSEX UK

Re: Poor Running

Post by 1608 »

With problems arising after only about 100 yds I'd suspect a tight push rod clearance as already mentioned. Hows does the compression seem when it gets hot and problematic?
Locked