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Joined: Apr 2020
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Hi!

First time posting but have been lurking in the shadows for a while. Not a native english speaker so please excuse any misspelling.

I recently took over my dads AJS 350. It has been in his possession since 94 and before that the only previous owner received it as a graduation gift when it was brand new and drove it for four years and then kept it in a garage. It is in a fabulous original condition with very little parts exchanged. My father drove it alot and it has always been starting and running like the 16 horsepower dream it is. The last 3-5 years it has been standing unused in my fathers garage since he has been losing interest and getting older.
When I got the bike a couple of weeks ago it would not start easily and it ran pretty bad. I have since taken apart the carb and given it a thorough cleaning and exchanged all the gaskets and replaced the missing air valve (choke). This sorted out the starting issues and it is now very easy to start and when giving it throttle when standing still it runs very good without sputtering from carb or exhaust. One problem still remains..

When running it runs okay on first and second gear but feels very sluggish on third and fourth gear it is like the engine cant go more than idle. It does not matter what position the twist grip throttle is at it just feels heavy and sluggish. I feel like it just will not rev up as much when driving as it will when throttling standing still.
I have checked the jets and needle position and it is as it should be.
I am by no means a mechanic and have reached the end of my skillset sadly. I would greatly appreciate any advice on what might be the issue.

Kindly,
Erik

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Just a shot in the dark but try riding with the gas cap loosened off as there is a possibility
that the small vent hole in the cap is blocked.,as the bike sat for such a long time .Also you need to make sure that you are advancing the ignition ,if manual advance ,or you may need to open the timing cover to check the auto advance is working
and not gummed up from sitting.

Last edited by johnnie690; 04/08/20 7:31 pm.
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I see the problem, there is no carburettor !!
Lovely bike.

I think Johnnie is on the right track, are you sure you are running with the choke slide pulled right up,
and the ignition advance pulled fully advanced. ??

Running with either the choke on or the ignition fully retarded could well give the symptoms you describe.
The engine won't like it for long either...

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P.S. It could be that you may need to check the ignition timing.

This is traditionally done with a pencil down the sparkplug hole, and a cigarette paper in the ignition points.
What you are checking is the amount of advance before tdc that the spark is occurring, fully advanced.
If you need further instructions, just say.

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Thank you very much for your response and suggestions.
I have made some progress.
I tried the trick with the gas cap and cleaned the vent hole. No real difference in running sadly.

I checked and cleaned the contact breaker which were quite black and dirty but when cleaned had the correct gap(checked with LTK-5 spanner).The tappet and small wick were quite dry so oiled those up lightly.

I also took a look at the ignition timing following this guide (http://qmentis.com/vintage-motorcycles/ajs/setting-ignition-timing/) and the manual. From what I could tell the timing was not off. I only checked it and did not see a reason to adjust it. Regarding that, is it mm precision when setting it or a few mm?

I also changed out the spark plug. It now runs a bit better but the engine still will not really rev when on third or fourth gear.

Maybe this is just the way it runs? According to my father it is geared high and should run 80-100 km/h. Right now I barely reach 50.

I am truly loving the process and learning alot while trying to figure out whats wrong although some more progress would probably make the process more enjoyable :-)

Last edited by Erik Pettersson; 04/09/20 3:38 pm.
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I am running with the ignition fully forward (no tension) according to my father he never touched that lever at all. And the choke is used only when started and then fully lifted.

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So long as you know the choke is pulled up after a cold start, by the handlebar lever pulling the cable.

There is such a thing as a tight wire advance magneto. Does the bike go faster or slower when you make the spark lever pull the cable?

There is normal servicing to do, such as points gap and valve clearances.

Fuel supply can be restricted by blocked gauze in the tap or the carburettor banjo.


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1/2 an inch sounds like a lot of advance, I'll dig out my AJS handbook and check that is correct.
That would be 12.7mm before TDC, is that the figure you checked ?
A trace more or less is not going to make much difference

I think you have to try pulling that ignition lever fully tight while riding it.
The normal setup is that it is you relax the lever for starting, and then pull it tight to give full advance for riding.
If you never touch it, I think it would give the fully retarded timing all the time.

Apart from running hot, I think it would explain why it is easy to start, and also why it cannot rev more then 50 kph.
It may also explain why your muffler is looking a bit blue.

Hey, you are in the spotlight at the moment....

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The official figure for 350cc ignition timing for the earlier Model 16 is 7/16 of an inch.

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Yeah the measure I used was 7/16 out of the manual. Which is 11.1 mm so not that different from 12.7 or is it? Would that difference cause the symptoms? I found it pretty hard to make a super accurate measurement and just settled with a "close enough"..

I will try pulling the ignition fully when riding it. The wire is quite hard to retract and i tried it a few times when the contact breaker cover was removed and saw I could actually retract it a lot more than i originaly thought when just pulling the lever it on the handlebar.

So just to be clear, when starting the ignition lever should be forward which is the same as no pull on the wire and when riding it should be pulled towards me "shortening" the wire?

Really appreciating all the time you guys are spedning on my problem!

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Okay just got back in! The ignition was the problem. The wire had som how got stuck half way so what I thought was the ignition fully retracted was actually more like 25% pulled back. When putting a bit more force into it the bike just sprang to life and now runs like an absolute beast :-)

I am very very thankful for your help and advice.
Now for the first of many sunset rides!

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Sounds like you’re sorted, but advancing the ignition is turning the cam ring or cam plate in the opposite direction to that of the rotating points.

We can’t know the arrangement of your handlebar lever, or whether your magneto is slack wire advance or tight wire advance.


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Good that you have solved it !

It sounds like you need to make sure the cable is oiled and has a nice smooth run.
The advance lever itself also can use a spot of lubrication.
And the plate in the magneto can have a trace of lube too, so it can advance and retard nice and smooth.

I wouldn't think 11.1 mm makes much difference to 12mm, there seems to be some variation in the recommended number.
You can experiment of course, but if it doesn't make much difference....

Have fun !

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Great to read about a successful outcome.
I took over my 16M when my Dad found it became too heavy for him.
Just been to start it and it's very reluctant, a damp winter does them no favours so some tinkering needs to be scheduled.

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Looking to remain upright and socially distanced throughout 2021

All the best,
David

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Originally Posted by DaveNKAS
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Just been to start it and it's very reluctant, a damp winter does them no favours so some tinkering needs to be scheduled.
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All the best,
David

My mongrel AMC 500 hibernates in an unheated garage. Not particularly damp but temperature changes probably create moisture in the tank and the magneto. Following hibernation, I lightly clean the mag points with wet n dry and then spray the mag internals with electrical cleaning spray, leave the mag cap off, let it sit for a bit and then try and start it. Do not try and replace mag cap with the engine running! Fresh petrol might help


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