Topic: Air mix screw adjustment tips / strategies? Pop vs stumble...

[Reganator]

Ok, my bike is running fairly well.  I think I just about have it dialed in, but I'm still having one slight issue.  Since I've posted about it a few times, I'm going to leave the specifics of the bike off, but I'm going to put them in my signature in a minute.

Here's the deal:  It seems like I have to choose between two less than ideal situations with my idle.  Version 1:  With my screws out about 1.25 I have less exhaust pop and rumble on decel and at idle, but when first coming off idle at low rpms the bike sort of bogs down / stumbles / hesitates.  It's pretty jerky and jarring.  Version 2:  With my air adjustment screws about 1.5 or a little more turns out the stumbling and hesitation seem to go away but in their place I get a pretty regular popping from the exhaust.  Letting it idle for a moment at the gas station it was setting up a nice steady 4:4 tempo.  Could have almost set a clock to it.  It also pops and rumbles a bit on decel.

So what's your strategy on these adjustments?  And for grins and giggles, should I be checking somewhere else?  Worth mentioning that I do occasionally hear a ping / pop sort of sound from the front of the bike when it's doing the hesitation dance.  Not sure what to make of that, if anything.

[phil71]

if your bike is stock, your carbs are dirty. If your bike has pods and a pipe, you've got a long road ahead that doesn't involve mixture screws.

[scottly]

Since I've posted about it a few times, I'm going to leave the specifics of the bike off

Starting new threads about your problem will not help to solve it...

[Reganator]

Since I've posted about it a few times, I'm going to leave the specifics of the bike off

Starting new threads about your problem will not help to solve it...

Posted a few times about this specific bike, not the specific issue.  New issue, new observations, new thread. 

Just looking for hints / resources on the air screw adjustment, or if some hawkeyed forum member knows of something else I should check.  Frankly, I can live with the bike as is, it runs very nicely now, but I'm a bit of a perfectionist and to whatever degree that I can smooth everything out I'm going to attempt to do so.  I view it as a learning exercise. 

So anyway, back to the matter at hand, my other issues are resolved.  I think I'm going to adjust back towards the popping end since the hesitation and stumbling just off idle seems like the less desireable problem.

It's just been one of those fix one problem and here comes another deals in bringing this thing back to life.  I'm pretty satisfied that its mostly ironed out now though.

[scottly]

Posted a few times about this specific bike, not the specific issue.  New issue, new observations, new thread. 

Seems to be the same issue to me; just new observations on your part.

[Reganator]

Nah, turned into a totally different bike after I changed that breather hose.

Anyway, it would be nice to get rid of the popping, but I might live with it as its good to go otherwise now.  Just carrying a screwdriver with me and tinkering here and there.

[phil71]

Assuming squeaky clean carbs: try bringing the needle up one click to get past the stumble the kerker is causing.
 Make sure your sync is dead on or anything else is a waste of time. Then adjust mixture screws for highest idle.

[Reganator]

I assure you, they are.

I'll try moving the needle then.  I'm going to scrub up the plugs first though based on a recommendation from my old thread when the bike was smoking and fouling one of the plugs constantly.

While I'm in there I might go ahead and clean that slow jet circuit again.  I don't really think it's at issue, but I might as well be thorough if I'm going to be in there.

[dave500]

have you gone right over your ignition?

[Reganator]

have you gone right over your ignition?

Electronics are all good.  Fought those battles early on.  They weren't pleasant, but they are done.  I haven't looked at the spark advance very closely so I suppose I am guilty there.  Anyway, just based on the results I'm getting from the air screw adjustment it seems like it's got to be something with the carbs as far as how I have them set up.

As a few people pointed it out to me I am going to clean my plugs tomorrow and tripple check float height.  Not expecting any surprises there really.  If that all checks out I'm going to go ahead and adjust that needle to see if that does the trick. 

[dave500]

check your advancer is working with a strobe,make sure its not sticky.

[gregripko]

check your advancer is working with a strobe,make sure its not sticky.

it's funny that you can have a perfectly tuned and clean bike....and then have a sticky advancer and the bike can run like poo..... +1 on checking this and also check plug colors before making any serious carb changes

[greenjeans]

+1 on the advance.  Very easy for it to get sticky, especially if it hasn't been cleaned in a decade or so...
How are you cleaning your plugs ?   Just because they look clean does not mean they will fire correctly - learned that the hard way.
New ones are cheap.

The carbs on these things just can't be clean enough.   Clean, sparkling carbs = happy bike.

Also - how many miles are on it since you got her running ?

[Bankerdanny]

If all aof the above cleaning an d adjusting tips leave you with the same issue, I would take some burbeling and popping on decel over a stumble pulling away from a stop. The former is 'character,' the latter dangerous.

[Reganator]

If all aof the above cleaning an d adjusting tips leave you with the same issue, I would take some burbeling and popping on decel over a stumble pulling away from a stop. The former is 'character,' the latter dangerous.

My thoughts precisely.  I'd really like my acceleration to be smooth and predictable.

Anyway, I've tried a few different screw settings but the stumble is present at all speeds.  I'm also wondering if the sound I'm hearing at low speed isn't the advance fumbling around and binding.  It does seem like it could be coming from that portion of the case.  So I'm planning on checking it out tomorrow.  Any more tips there?

As for the plugs, I cleaned them with a toothbrush and some electrical contact cleaner, then with a propane torch.  They almost looked new again. 

One final note on diagnosis here... I can't seem to find anything on this.  The stumble only occurs under load.  Revving in neutral at idle does not produce the same stumble.  Let me know if this sounds consistent with a misbehaving spark advance.

[phil71]

that's fuel baby. bring them needles up.

[Reganator]

Oh right, almost forgot that.  Well, I kinda did.  I'll adjust the needle and see what happens tomorrow.  Might as well nix it for good if I'm going to spend any time on it. 

Again, I really do think the sound I'm hearing is related.  I'm not sure if I can get it on a video while I'm riding, but I might try.  I just can't quite imagine what it might be though...

EDIT:  Thanks again for all the help everyone.  Just really frustrating that for that one brief moment everything popped into perfect harmony and for at least a block and some revving at idle I got to hear what these bikes are really supposed to sound like.  Gave me goosebumps, looking forward to getting it back there again.  Amazing that a 40 year old machine can just hum smooth as silk up and down through it's range without a hiccup.  Really want to nix this last issue and get that back, 3 minutes of it was not enough.

[scottly]

I'm also wondering if the sound I'm hearing at low speed isn't the advance fumbling around and binding.  It does seem like it could be coming from that portion of the case.  So I'm planning on checking it out tomorrow.  Any more tips there?

Quick and dirty test of the advance: grab the point cam and twist it to the right.(clockwise) It should move freely, and return to it's original position when released. The more precise test involves a strobe and a tachometer.

[dave500]

fork out for new plugs,often cleaned ones look good but still dont perform as well.

[Reganator]

fork out for new plugs,often cleaned ones look good but still dont perform as well.

This hold for week old plugs?  My plugs are new, but were a bit carbon fouled so I thought I'd do that first.  I'm pretty sure it isn't that now, so I'm moving on to that needle adjustment and spark advance.  If that doesn't get me anywhere ill consider ponying up for some new plugs.  Think I'm going to do the advance first.  It's just that weird sound I'm hearing from the case when the bike stutters at low rpm... It makes me wonder if it is the advance I'm hearing binding and breaking free.  I suppose there is only one way to find out.

First time dealing with a spark advance here.  Plenty of literature online, but all the cleaning and testing tips I can get will surely be appreciated.

[Reganator]

Spark advance confirmed as the issue.  I repeat, spark advance is buggered.

I took it out, it binds, sticks in any position it's put in, and is generally rusty and crusty.  Sounds like I've got to rock and roll with what I've got though.  How can there be no new advances for this bike?  I should pull out my force meter and try to extrapolate the original spring force and find a suitable replacement.  Anyway, I'll be cleaning this thing up and getting this thing tuned and running nice.

Here's a couple pictures.  In the second you can see I opened it and its just sitting there, perfectly happy to be open.

[Reganator]

And here it is cleaned up and lubricated.  Not sure how much free play should be on those springs, but it seems to be responding pretty well now.

Spark Advance weak?

[iron_worker]

From what I understand, there shouldn't be any free play in the springs. The should return the arms firmly to the resting position on the cylinder. I had read (and have tried) cutting off one of the hooks and reforming it with the next loop. It definitely tightened them up ... I'll have to check with my strobe if it has tightened them too much... they may need a touch of stretching to get them just right again.

The pinging you heard could be detonation since your advancer was probably stuck open and remained too far advanced for lower RPM.

IW

[bjbuchanan]

I just wrote up a thread about setting your points that has stuff about the advancer in it. It is probably on the second page now, gotta search for this stuff

[70CB750]

From what I understand, there shouldn't be any free play in the springs. The should return the arms firmly to the resting position on the cylinder. I had read (and have tried) cutting off one of the hooks and reforming it with the next loop. It definitely tightened them up ... IW

That's Hondaman about the springs.  I done that and I like the result.  before it would sometimes just hang in higher turns in idle, after the snip it jumps right back.