Advance weights hanging

[Pat D]

So I'm about 150 miles into a fresh top end rebuild, just re-torqued the head bolts, getting ready to do 1st oil change and valve adjustment. Bike is running great, but is a bit lean based on the plugs and a wee bit of hunting at steady throttle. Idle is pretty stable, but once in a while will hang at 1600 or so, I've got the stops set at around 1200-1300. It is possible I have an air leak somewhere, but I've also got a much less restricted muffler set than stock, so jets are also suspect.

The advance weights seem free, and want to snap back, but it is the actual advance rod that seems to have some resistance keeping the weights from snapping back. I put a little fresh grease on the bushings when the head went back together, and the rod seems to turn freely, but not "frictionless" to the level that the advance springs would pull it back to full retard. Now, these springs are 40 years old, so they may be tired.

What are the pitfalls if I tighten up the springs and can't get full advance out of 'em? Is this likely, or do the weights have enough mass to overcome a slightly stronger spring? Seems to me I should be able to rotate the advance rod by hand to the limit, and the springs should pull it right back to the stop. Now, should I expect this same snap back when the engine is at 50 deg. F and the oil/grease are cold as I would when it is fully warmed up? Or is it reasonable for cold grease to influence the movement of the advance rod?

As stated above, bike is running great, pulls strong, no flat spots, just the "tickle" at steady speed and the occassionally hanging idle. Stock airboxes with filters, but the mufflers don't have much in 'em. Thanks!

 

[gggGary]

The free snap back depends on where the points fingers are sitting on the points cam ramp, they will slow down the snap back if they are going down the ramp. check the advance action with a timing light.

Try clipping one coil of of one spring to start with then one coil of the other spring if it wasn't enough. I polish my rod (yeah yeah) and use a very light silicone grease. See if that gets r done. Bike will go full advance just a bit later.

 

[CDNTX650]

Honestly, get rid of the points....pamco, boretech, boyer etc. Many good ones to pick from to get rid of that mechanical system. The difference from my mechanical adv pamco to eadvance was honestly amazing.

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[retiredgentleman]

The springs on the advancer are a crude device. If the advancer rod is rotating freely and if the springs have the right amount of tension, they do provide the advance needed. The problem is, that the old springs don't have the same tension as they did when they left the factory.

I tried the cutting one coil trick, but then I found the springs were too strong, and this delayed the advance. My engine would not want to accelerate, then all at once the weights would jump out and the rpm would take off too quickly.

When I heard that Pamcopete was bringing out the E-advancer, I was quick to buy one.
I agree with CDNTX650.................the E-advancer is a huge improvement over the fly-weights and springs.

 

[Tomterrific]

The friction of the points heel on the cam will assist the advance springs pulling the ignition into retard. IOW, the springs don't need to 'snap' the advance mechanism back. The rod does need to turn freely without a hint of bind.

Tom

 

[Pat D]

Aye, the rod turns freely, as noted the only resistance is from the grease in the bushings. Checked the timing with the light and everything appears to be in order, advancing as designed and retarding as well. I raised the needle a notch to see how that effects the plug color, if they are still white after another tank of fuel or so, I'll look into the jet situation. The hanging idle happens at maybe 1 in 10 stoplights, I would have thought based on my automotive experience that a vacuum leak would manifest itself a bit more aggressively, but maybe not. I used new oiled gaskets on the manifolds, they were clean and in great shape, and I used a bit of petroleum jelly on the carb spigot to help seal it to the manifold.

 

[5twins]

If you have the stock '74 carbs then the stock needle setting is the #4 slot, one step richer than the normal or more common middle #3 slot. When your jetting is very close, often the only way to see if a jet change will improve things is to try it. If the needle change doesn't help, I would go up one on the mains. Your gutted exhaust may need that.

 

[retiredgentleman]

I recommend you replace the needle jet O-ring on your BS38 carbs. If they are old, they may be allowing extra air/fuel mixture to sneak by the outside of the needle jet. That extra mixture can cause the hanging high idle that you have occasionally.

 

[Pat D]

If you have the stock '74 carbs then the stock needle setting is the #4 slot, one step richer than the normal or more common middle #3 slot. When your jetting is very close, often the only way to see if a jet change will improve things is to try it. If the needle change doesn't help, I would go up one on the mains. Your gutted exhaust may need that.

Yep, thet's where they were, in the #4 slot. But I'm wondering- my style of riding almost never goes over 5k rpm, I need to do some clutch work so I'm not getting anywhere near wide open throttle, if I hammer it hard it'll slip(new springs and maybe plates are on the list, but I'm not drag racing so I can live with it for the moment). I've read that the slides don't even start to lift until 5-6K, if this is accurate then it seems all the action hangs on the pilot jet in my case. I'll pull 'em and see what sizes are in there, and adjust accordingly. It's a little bit of adjustment for me since I'm used to working on pushrod auto engine carbs, where the idle circuit is out of the picture after 1200-1500 rpm. Then again, redline is 5k rather than 9 ... I'll look into that O-ring as well, hopefully I've got some around here that are in the same size neighborhood. These appear to be the mufflers on the bike ...http://www.motorcycle-superstore.com/39114/i/emgo-dunstall-replica-universal-muffler