Ajs 1937 Model 8 Oil In Carb

Information relating to Matchless and AJS Models built prior to 1939
Member
Posts: 16
Joined: Mon Jan 25, 2016 8:50 pm
Location: KENT UK

Ajs 1937 Model 8 Oil In Carb

Postby Diana3899 » Sun Jul 23, 2017 7:00 pm

I seem to be getting oil in my carb. Can anyone suggest reasons why this is happening.

Committee
User avatar
Posts: 9130
Joined: Mon Jan 01, 1990 12:00 am
Location: ESSEX UK

Re: Ajs 1937 Model 8 Oil In Carb

Postby Rob Harknett » Sun Jul 23, 2017 7:35 pm

Could this be residue from evaporated petrol ? I cannot think where oil could come from, as the is no oil supply to the top end of the engine. Except to the rocker box. If it was getting in the carb via a blown head gasket, you should see this as oil may be all over the carb.

Member
Posts: 16
Joined: Mon Jan 25, 2016 8:50 pm
Location: KENT UK

Re: Ajs 1937 Model 8 Oil In Carb

Postby Diana3899 » Sun Jul 23, 2017 8:17 pm

Thanks Rob, there is an oil feed to the inlet valve and I wonder if this may have something to do with it. The bike cut out when on a ride and would not start again and so needed a recovery. Once home I could get it started with difficulty and take it around the block but it cut out on more than one occasion so had to push it back. Opinions from friends was that the Mag was playing up so I took it off and brought it to a chap named Samond in Essex. He tested it there and then and said that there was nothing wrong with it. So I decided to take off carb and check it out and found it to be black throughout with sooty/ oily deposit. Have cleaned it up and am about to put it back on. I am reluctant to take the head off at this stage as I thought I would re set the ignition and replace the carb and then run the bike before rechecking the carb for black deposit. I have drained the tank and will put fresh petrol in it before taking it for a run assuming I can get it started. By the way the spark plug was very sooty indicating the carb was running rich or possibly burning oil but not sure which. The carb may have been running rich because it was sooted / oiled up. I have cleared all the jets so hopefully the bike will start and run well. By the way I have not had the bike long so don't know the state of the engine and the problem with the engine dying happened soon after buying it. One other thing, when I put a rod down the plug hole to find TDC the end of the rod came out with sooty/oily deposit obviously picked up from the piston crown. Would appreciate any ideas, comments and advice so that I can check out possible causes.

Committee
User avatar
Posts: 9130
Joined: Mon Jan 01, 1990 12:00 am
Location: ESSEX UK

Re: Ajs 1937 Model 8 Oil In Carb

Postby Rob Harknett » Sun Jul 23, 2017 8:50 pm

Yes there is a little U pipe from the rocker box, also an adjuster for the inlet valve stem. The manual states the correct setting is, the adjuster screw should be fully tightened home then, opened one half revolution. I would not had thought oil from the valve stem lubrication would get in the carb. As the carb sucks not blows, except on kick back?? Rings could be worn to make the carbon oily. Or the PO may have poured oil in the plug hole upon layup. I would have thought, there is more chance of a post war machine getting oil in the carb, if it was possible. By oil pooling in the fully enclosed rocker box. But I do not ever recall a complaint of oil in a carb.

Member
Posts: 16
Joined: Mon Jan 25, 2016 8:50 pm
Location: KENT UK

Re: Ajs 1937 Model 8 Oil In Carb

Postby Diana3899 » Sun Jul 23, 2017 10:06 pm

I am aware of the adjuster and the recommended half turn from home and just in case I have reduced the adjustment to quarter of a turn from home. I am equally confused and did wonder if the previous owner over oiled the throttle cable. I wonder if the inlet valve is not fully closing on the combustion stroke but I was not seeing any blow back through the carb when the bike was running. I think the thing to do is to reset the ignition, replace the carb and try to run the bike. |If I am still getting problems I will have to take off the head and see if I can see any obvious problems.

Return to Prewar

Who is online

Users browsing this forum: No registered users and 1 guest