Another Stuttering question - Different though!

Information relating to the Matchless G85 500cc Heavyweight, AJS 7R, Matchless G45 and Matchless G50
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Matchymarty
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Another Stuttering question - Different though!

Post by Matchymarty »

Hi all,
Tried searching for my problem, but only found the 'opposite' to what is occuring with my '56 Compy.
After taking delivery only a couple of days ago, I rode to the Transport mob, to get my G80CS 'on the road' with plates.

Funny thing is that when coasting along, or riding along 'easy' with throttle barely open, it stutters like it's missing, almost like a flutter. Then if I open the throttle to accelerate, or go up a hill, it smooths out. Kinda feels like riding a 125 2smoke MX bike!

my '49 G80 stuttered UNDER LOAD, and turned out to be the condensor in the maggie, but this bike stutters with NO LOAD, so is the opposite. It also struggles to keep an even idle for any length of time and will stall if you don't keep a slow blip going. Carburation feels fine and smooth. I haven't checked timing yet, though when I retard all the way, ticks over well.

Any ideas where to look? Points? Timing?
Groily
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Re: Another Stuttering question - Different though!

Post by Groily »

Think I'd start by looking at the pilot jet and/or cutaway on the slide, as it seems the problem is at those sorts of throttle openings and smooths out once you haul the needle up the needle jet a bit. If she starts well, idles well, and pulls well when asked, less likely to be a sparks problem I'd say.
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Rob Harknett
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Re: Another Stuttering question - Different though!

Post by Rob Harknett »

I agree with Grolly, try the easy option first, check/clean carb.
Matchymarty
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Re: Another Stuttering question - Different though!

Post by Matchymarty »

Good Grief.
Pilot screw was way wrong... stupid me. Sorry for bothering yol...

Interestingly though, can someone explain why this bike doesn't like full advance ? Seems to die a bit, but bring it back a bit and it's happy as larry. Timing out??
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Rob Harknett
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Re: Another Stuttering question - Different though!

Post by Rob Harknett »

Rev's should increase as you advance. Some mag's are tight wire some loose, I assume you are actually advancing. One the bikes started and warmed up you should fully advance the lever, as ignition timing is done with the lever in the fully advanced position. Check that out.
Groily
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Re: Another Stuttering question - Different though!

Post by Groily »

If the sparks disappear at full advance, then it is likely if it's an N series that the cam is set a tad over-advanced in the housing. Or, if it's an SR1 on a CS, that the cam is not quite correctly set on the spindle. The points should not open until a few degrees of mag rotation after the flip point of the magnet, at full advance on the lever. If they open too early, there will either be no spark advanced, or if the error is small, maybe sparks at low revs, which disappear with rpm as the magnetic lines 'bend' with speed.

The Lucas instructions on setting the cam on an SR are very specific.
With the N1 (face-cam) or N1C or R (with rotating points), the camplate (N1) or camring is limited in its arc of movement by an eccentric pin under a little button on the cb end housing. Prise off the cap and rotate the pin with a scrooge to retard the position of max advance a fraction. (Need a v fine chisel or sharp thing to get the cap off, but it will come.) Retarding in this context means stopping the plate or ring going quite so far against the direction of rotation of the armature.

Quite often, after replacing parts in this area, or just the points, one finds that the internal timing is slightly affected as the change will have influenced the exact moment at which the points open. Sometimes by a lot.

It may also be that your points gap is simply too big, thus over-advancing things if your set-up is 'on the cusp' of too advanced internally. Set to 12 thou if it's larger, and see - every thou = a degree or so at the mag and 2° at the crank.
Matchymarty
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Re: Another Stuttering question - Different though!

Post by Matchymarty »

Rob Harknett wrote:Rev's should increase as you advance. Some mag's are tight wire some loose, I assume you are actually advancing. One the bikes started and warmed up you should fully advance the lever, as ignition timing is done with the lever in the fully advanced position. Check that out.
Rob, yes, my mag is a 'loose wire' one. So when 'fully loose' ie, advanced, the engine revs die off, and begins to idle and or run uneven and with less power. Clearly timing must be out a bit. Cheers
Matchymarty
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Re: Another Stuttering question - Different though!

Post by Matchymarty »

Groily wrote:If the sparks disappear at full advance, then it is likely if it's an N series that the cam is set a tad over-advanced in the housing. Or, if it's an SR1 on a CS, that the cam is not quite correctly set on the spindle. The points should not open until a few degrees of mag rotation after the flip point of the magnet, at full advance on the lever. If they open too early, there will either be no spark advanced, or if the error is small, maybe sparks at low revs, which disappear with rpm as the magnetic lines 'bend' with speed.

The Lucas instructions on setting the cam on an SR are very specific.
With the N1 (face-cam) or N1C or R (with rotating points), the camplate (N1) or camring is limited in its arc of movement by an eccentric pin under a little button on the cb end housing. Prise off the cap and rotate the pin with a scrooge to retard the position of max advance a fraction. (Need a v fine chisel or sharp thing to get the cap off, but it will come.) Retarding in this context means stopping the plate or ring going quite so far against the direction of rotation of the armature.

Quite often, after replacing parts in this area, or just the points, one finds that the internal timing is slightly affected as the change will have influenced the exact moment at which the points open. Sometimes by a lot.

It may also be that your points gap is simply too big, thus over-advancing things if your set-up is 'on the cusp' of too advanced internally. Set to 12 thou if it's larger, and see - every thou = a degree or so at the mag and 2° at the crank.
Thank You. :) Lots to look for. I'll have a look over the weekend. :)
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