Exhaust valve seat for unleaded

Information relating to the Matchless G5 or AJS Model 8 350cc Lightweight
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Re: Exhaust valve seat for unleaded

Postby clanger9 » Sat May 23, 2020 1:23 pm

Should be zero ohms with the points closed. Don't forget to compare the reading with the measuring leads shorted together - you won't necessarily see "0" on the meter due to the resistance of your measuring leads...

Check your wiring to the points - it sounds like the points lead may be shorted to earth...
1966 AJS Model 14 250 CSR cafe racer
1989 Moto Morini Dart 350
1993 Ducati 750SS

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Re: Exhaust valve seat for unleaded

Postby vigo » Sat May 23, 2020 1:36 pm

Significant thing I forgot to mention, the ameter never shows battery discharge at any points position open or closed.

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Re: Exhaust valve seat for unleaded

Postby clanger9 » Sat May 23, 2020 2:00 pm

Have you got 6V at the points (when open)?

[edit] Sorry, it seems you do have 6V at the points.

Does the voltage at the points fall to zero when the points are closed?
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1993 Ducati 750SS

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Re: Exhaust valve seat for unleaded

Postby Mick D » Sat May 23, 2020 3:27 pm

Hi

With the points closed do you see 6V at the coil? If yes, does breaking the LT circuit at the coil give you a spark? If yes the coil plug lead etc. are good.

You say you have 6V at the input to the CB so remove the wire from the CB and put a bulb in the circuit - you only have to hold the wire against the bulb and touch the other contact on the engine - the bulb should light and you should see a -ve deflection on the ammeter.

If the bulb doesn't light or only glows dimly you have a poor supply to the CB - check the wiring and connections back to the battery.
If the bulb lights brightly but no ammeter deflection you have a knackered ammeter or the wiring to it is supect.

As said earlier with the points closed the resistance across them should be very close to zero - before reconnecting the supply lead clean the points to achieve this.

With the points open the resistance across them should be infinite, (open circuit), if it is not check you have the insulators correctly fitted to isolate the points from each other. The image below is taken from a heavyweight manual but I think the points are the same for lightweights.

CB Fault.png


If you still cannot get the points to indicate correctly take the capacitor out of the circuit and try again - if this fixes things replace it.

With the capacitor out of the system you should still see a spark if you activate the points - though if you run the engine in this condition you will burn the points quickly and the engine will run roughly.

If all of the above are good you should be able to induce a spark by opening the points with your finger nail.

Regards Mick
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Re: Exhaust valve seat for unleaded

Postby vigo » Sat May 23, 2020 5:11 pm

Thanks fellas, I'll make some notes and look again tomorrow

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Re: Exhaust valve seat for unleaded

Postby Jam23a30 » Sun May 24, 2020 9:58 am

I read this post begins with the bike running and sense the frustration you are feeling so suggest you take a step back and check some basics. Sorry if I'm raking up old ground or stuff you have already checked

1) check the battery well charged and that it is connected properly. My G5 as many older british bikes need the Positive terminal connecting to earth. Some things like lights are not sensitive to how the battery is connected but others like your ignition and charging system are.

2) once you are sure you have the battery connected properly you should see a discharge on your ammeter if you switch the lights on and should also see a discharge with the lights switched off, ignition switched on and as you turn the engine over slowly the ammeter will move left and then back to the centre as the engine turns.

3) think of the points as nothing more than a switch which the engine flicks on and off by itself as it turns. Simplistically when the points open current can't flow to earth and the coil sends a high voltage shock to the plug which causes a spark to jump the gap

4) to confirm if you have a fault with the way the points are working you could disconnect the "feed" wire coming down to the points from the loom and measure the voltage from the free end of the wire to somewhere on the engine case. This should show 6V with the ignition switch turned to the right (which may be marked "I" on your switch)

5) If you have 6V between the free end of feed wire and earth, then you can connect up the spark plug into the cap and rest it on the cylinder head so it is in good contact. Turn the ignition on and try to replicate the action of your points by touching the end of the feed wire onto the engine casings. You should see a spark at the plug as you make and break the circuit by tapping the feed wire on the engine casing briefly. You will also see or sense a spark as the feed wire makes contact so don't repeat too often or anywhere too shiny!

6) if you see spark at the plug then you have something wrong in the way the points are assembled. Again think of the points as a switch, you do need to make sure they are as per the diagram above with the insulating washers and connectors all in the correct order so current from the end of the feed wire can only flow to earth as and when the points close

7) if you don't see a spark then there may be a fault in the way the coil and or HT lead are connected up or perhaps a faulty component


These are simple systems which generally work well but they really do need good connections all correctly assembled to be reliable. Hope this helps

Andy

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Re: Exhaust valve seat for unleaded

Postby vigo » Mon May 25, 2020 1:10 pm

Well I have a running motor. It went like this; took points and condenser out of circuit and switched supply lead to earth (good tip that one chaps). There was a half hearted plug spark. Corrected plug gaps (2 plugs one a new idium). I had them set to 25thou, wrong! Then good spark. The points by this time was continuous open circuit. Took them off and dressed faces, reinstalled. Success, all as it should be, started and choke came off quickly, too quickly.
Went off up the road and after 3 or 4 mins started running rough but responded well to full throttle. Result fouled plug (pic nearby) black sooty in the main dry. Now this carb is probably the original but has had work on it by PO.
I'm considering dropping the needle a notch it's currently in the middle of 5. What do you think?
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Re: Exhaust valve seat for unleaded

Postby clanger9 » Mon May 25, 2020 5:04 pm

Glad you finally got it running!

To set up an Amal, first you need to confirm the float level is correct and put the right jets in for your bike: 220 main, 25 pilot, 0.106 needle.
If it's still not right, follow the 5-step guide: https://amalcarb.co.uk/downloadfiles/am ... _guide.pdf

Otherwise you'll be going round in circles...
1966 AJS Model 14 250 CSR cafe racer
1989 Moto Morini Dart 350
1993 Ducati 750SS

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Re: Exhaust valve seat for unleaded

Postby vigo » Tue May 26, 2020 2:35 pm

I think I have some success but this G5 is not to be trusted. Started easily after small outing yesterday, smoke I mean lots of it not blue but grey smoke for several minutes. Maybe unburnt fuel in exhaust from running rich. Anyway it eventually cleared. Removed carb and checked as you recommended Paul. 0.106 needle jet but 30 pilot and could not get to the main jet. With the base nut in vice could not open it, I was afraid I'd break something and have no spare. Needle D also correct.
Anyway I dropped the needle one groove and is a world different pulling full throttle up hill great. The plug is as clean as when fitted in the engine does seem rather hot though, maybe normal. Still to work on the idle.
Let's see what tomorrow brings.

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Re: Exhaust valve seat for unleaded

Postby vigo » Wed May 27, 2020 2:29 pm

Started today easily, lots of smoke again, tickover did not want to set. Hearing Pauls advice I removed the 389 carb again, removed main jet, bottom union very tight anyway there is a 470 jet fitted not a spec 220. So oversize pilot 30 instead of 25 and the main very oversize. Order to Amal I think.
Q. The very oversize main could not be because the piston is +40? What reason could such a large deviation from standard justify?

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