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Discussion Starter · #1 ·
I have 72 cb350, with vm30's on it. I have been chasing carb settings for 2 years and have worked through pilots, needles, clip settings, needle jets, and slides to go from rich to lean at every throttle setting up to 1/2. Through it all, whether rich or lean, there's always been a little irregular stutter when cruising. (Throttle around 1/8-1/4, maybe around 5K rpm) I always assumed it was a lean condition, and would monkey with it until the plugs came back black. But even when set super rich, the stutter was still there.

In my searches, came across a thread yesterday that said half of the carb problems out there were probably timing/advancer problems. Considering I've tried almost everything with the carbs, I'm willing to give the electrical side a shot.

With the timing strobe, both sides are dead on at idle. Left side points are at 0.014. When I rev, (to about 3500/4000) the left side goes to the second advance mark, but the right side goes about 1/4 inch further than the second mark. (does that count as advanced or retarded?)

Is this possibly the cause of my stutter? Can I fix it from the points plate, or do I need to adjust the springs on the advancer?

Thanks,
John
 

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Discussion Starter · #2 ·

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Neither place, the #13 washer goes under the head of the bolt to hold the advancer assy. on the shaft. #11 is the whole advancer assembly, putting a washer behind it will keep it from being located in the right spot by the pin in the shaft. Take a hold of the points cam and try to push/pull it in and out, that movement you find there is what needs to be shimmed out . The shim washer to adjust that goes behind that points cam.
 

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Discussion Starter · #5 ·
Neither place, the #13 washer goes under the head of the bolt to hold the advancer assy. on the shaft. #11 is the whole advancer assembly, putting a washer behind it will keep it from being located in the right spot by the pin in the shaft. Take a hold of the points cam and try to push/pull it in and out, that movement you find there is what needs to be shimmed out . The shim washer to adjust that goes behind that points cam.
I think the terminology is confusing me. When you say points cam, do you mean the removable tube-like portion of part 11? I'm sitting here with a spare advancer (part 11) in my hands right now. There's the part that people make the mistake of putting in 180 degrees wrong, and I'm thinking of that as the "cam". But it's got the cutouts so that it'll grab the weights, so there's no way a washer can go under it. And like you mentioned, it can't go under #11, because the notch is there to position it right.

In the post, Hondaman says, "thin washers at the base of the rotating cam on the advancer are often gone". I don't see any place on the advancer for a washer.

Mike, I remember seeing a video from Common Motor about fixing points and shimming the cam follower on the points. Is that what you mean?

Thanks,
John
 

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Discussion Starter · #6 ·
Not to stir things up, but a PAMCO Ignition will solve this.
Haha. I can't deny not considering it at least a few times. Especially with points getting scarce and advancers going for $100.
 

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There IS a shim/thrust washer below the flyweights, at/beneath the bottom of the slots in the breaker cam...

It MAY appear to be just a wear mark, and it's often "glued" to the advance base plate with dried oil....

It SHOULD have been serviced when the advance unit was disassembled , cleaned and lubricated...... ID ~ 15.5 mm, OD ~18.5 mm and VERY THIN (think foil).....

Many also don't realize the felt rubbing block must have a couple drops of 90 wt oil to lube the breaker cam followers of the points....
 

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If you needed an endorsement for the PAMCO, there's one right here. I fruitlessly - and blindly - chased what turned out to be an advancer problem on my '450 for nearly nine years (admittedly on and off).

My issue manifested itself at idle. The bike would idle but every ten or fifteen seconds or so it would cough. Off-idle, it ran fine, but there was always this cough from one side that I couldn't cure. During that time, I changed and/or renewed all sorts of components - carbs, coils, other electrics . . . without spotting that the issue was being caused by one of the tiny springs on the advancer having stretched too far. The lack of tension meant the weight on the spring would occasionally flick outwards, advancing the timing enough to cause occasional out-of-time firing. It took reading HondaMan's book on the '750 to realise the advancer might be the issue and by that point I'd very nearly lost my rag with it.

Figuring that no new advancers have been made for a very long time (and therefore it wouldn't be beyond the realms of possibility that I might be throwing good money after bad buying other units that might also be worn) I cut my losses and went with a solution that allows me to ditch the advancer entirely. And since then I've had no trouble with it whatsoever. Yes, it would be nice to keep it stock - the rest of the bike is pretty much standard - but I got to the point where I was constantly questioning my sanity. I seriously considered selling the bike on more than one occasion just to get rid of the headache that seemingly wouldn't go away.

If you want to stay stock, I notice David Silvers have more than 20 NOS units in stock. And if you want to read more on the subject of advancers, HondaMan adds some detail on the 750 advancers in his book, describing how to increase the advance range by tweaking the ears (weight limiters).
 

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I have done the SHIM-FIX and – Yes, it will correct a problem where the advance system can TILT under load and cause uneven advance.

To do this correctly you will need a dial indicator and some method of mounting it to determine the PLAY in the advance system on the shaft.
I ended up making a NEW-Replacement shim from brass as mine was totally worn down to almost missing.

To make the shim I determined the thickness i would need then sandwiched a piece of flat brass stock between (2) pieces of wood and drilled the main hole.
The thin stock will twist and bend and will have nasty burrs if not sandwiched and kept flat while drilling.
Then I cut the outer diameter to close to correct size with aviation snips, finally filing and sanding it to the correct size.

A tedious excursive but it worked out well
 
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Back to your original post, a part throttle stutter at 5,000 rpm, the ignition is fully advanced at that point. Set the right hand points so both cylinders hit the mark at full advance to see if the part-throttle stutter changes. Once you sort out the stutter thing(either spark knock from too much advance or bad carburetion) , then move on to the spark advance issues.
 

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Follow Mike's advice and adjust the right point.....
I'm assuming that when using a strobe the advance (paired) lines appear to have moved too far rotationally CW beyond the index...
Your error might simply be too large a gap on the right point causing it to open too soon.....
Even though you only deliberately set the left points to a specific gap setting, the right points must fall within the .012 to .016 gap spec as well when checked....
Sometimes it is necessary to open (or close) the left points gap slightly (but still within spec) and start the timing process over to get BOTH points sets within spec.......
While it would be nice to have identical gaps on both sets, it's not necessary...They simply must both be within spec when the adjusting is done.......
 

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Discussion Starter · #12 · (Edited)
Got it. Thanks Mike and Steve.

Will opening the left, generally close up the right? I remember a thread where someone was mentioning you gave them advice to open the lefts to 0.016 and apparently it solved all of his problems.

Today or tomorrow after work, I'll check both gaps, then set the left to 0.016. Then retime it all and check advance.

Edit: wait, am I supposed to set the left points to 0.016, and time everything dead on at idle? Or am I supposed to time the right side slightly retarded at idle in hopes that it advances to the right place?

Will report back. Thanks a million for the suggestions.
 

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Static Time both to exact/correct alignments......Only thing actually changing is the GAPS.....

Then check dynamically with strobe at 3K plus........
 

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Discussion Starter · #14 ·
As it was, the points plate was rotated more towards the clockwise side. Left points were at about 0.013 gap. Right side seemed similar.

Took it all off to look at the advancer. Springs look good, and I can see the thin washer under the cam.

Started from scratch and reset timing. Left points to a light drag on the 0.016. Points plate ended up rotated a little counter-clockwise, compared to the setting notch. Right points end up with around a 0.016 gap when timed to F.

When running at 3500, right side still shows about 1/4 inch further than the second advance mark. Left side still falling nicely in between the two advance marks.
 

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Discussion Starter · #15 ·
To round out the possibilities, went back in today and set the left points gap to 0.012. After setting timing, right gap is about 0.13.

When revved, right side is still about 1/4 past the second advance mark.

Read in a thread about people timing to the advance marks at 3500K, since the bike exists 95% of the time in the advanced stage. Besides a less than pristine idle, is there harm in this approach? I think it's what I'm going to try next.

I postponed my last motorcycle test to May 19, and it's not possible to postpone it any more. I need this to be running somewhat reliably by then.
 

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Bad Migraine, so might not be thinking clearly, but ... leave left point and plate as-is..... Dynamically (while running 3K+) set/adjust right point to within the advance lines....
Shut off bike, measure right points at their widest gap.... IS it within specs?...... 540-525-5199....
 

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Discussion Starter · #17 ·
Started on it even before I got your message.

Left gap is still at 0.012 from the last experiment and timed on the LF and falling in between the advance lines.

Right timing is now set so that at full advance, it's hitting the second advance line. (Ends up firing on the "T" at idle.) Gap is giving a little drag on 0.012 feeler. I'm sure I could get it comfortably in spec if I opened up the left side again to 0.014 or even 0.016. The two sides seem to follow each other pretty closely.

Took it out for a spin and it still has the stutter once it's fully warmed up. Right plug with a black ring on threads, but left plug is dull grey. Carbs are synced, but it would appear they're not quite set right. Out for the night, but back to it tomorrow.
 

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Discussion Starter · #18 ·
Tried to start it this morning, and it seems very unhappy with its new timing.

Trying to start with the starter and no choke, it's having problems catching, and when it does catch, it does a slow chug until it dies. With choke, it fires up and revs up quickly, but as soon as the chokes are off, it dies.

New symptom showing up is a *snap*, that sounds like loud electrical shock, and the engine dies immediately. It can happen while on the starter button, or during the slow chug before it dies.

Moving forward, my next plan is to gap the left to 0.014, set its timing dead on, then set the right timing slightly retarded (halfway between F and T) I'm hoping this will get things closer to spec, and back to the starting/idling reliability I had before.

I'm thinking about the advancer shim, and wondering if foil tape might work? (thinking about what Steve said about foil) It looks like the thickness is about 0.004.
 

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Discussion Starter · #20 ·
I took everything off again. Putting the advancer on the table, and placing the bolt and washer into the cam, I could feel the bit of up/down in the cam, and even a little bit of side to side. Took out my spare advancer; same thing.

Took them both apart, with the thoughts of doubling up the super thin washer under the cam. (Both of them were intact). While cleaning the oil and gunk off of them, noticed one is significantly thicker than the other. (flexible vs inflexible) Like Steve said, the worn down one is literally like foil.

To cut to the chase, by mixing and matching parts between the two advancers, and doubling the washers, I seem to have built one advancer which will hopefully work. Much less slop up and down, as well as side to side.

I figure I'll attach the picture of the disassembled advancer here, and on the other thread too. Noticed a bit of slop in the cam followers on the points too, so will do those too while it's apart. Hopefully tightening everything up will be the answer.

advancer apart.jpg
 
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