Help with timing and idle

[ironwill]

Hey guys, bike is '79, with BS38, pods, open pipes, 140 mains, 30.0 pilots. Just installed Pamco, with mikes 17-6822 coil. Read through all posts on idle and timing. Bike tends to idle up as it warms (read thats normal) sometimes I rev it, and it stays high, then drops to low idle. (possibly indicating a lean condition?) I do not have a tach, and am trying to set timing. If I get it to idle around what I think 1200 is, as soon as I adjust the plate to change timing it also changes the idle, which in turn changes the advance.

Is it normal to have the idle change when you adjust the timing?

Does the idle have to be right at 1200, or can it be a bit higher or lower, as I say, I have no tach?

When does the timing actually start to advance, is it immediately after 1200?

If the idle was at 600rpm would the timing be the same as 1200? I'm assuming yes because rpm causes advance mechanism to operate.

Also I read in the carb guide to adjust mix screw to 2 1/4 turns. This may sound stupid, but my mix screw has a plastic cover that only allows it to turn maybe 3/4 of a turn, assuming I'm adjusting the right screw, what am I missing here?

Some places I haven't checked yet, but will:

Advance mechanism, carb butterfly for complete closure, starting fluid for leaks. I've had boots off enough times, and they looked fine, but will try the spray method.

Appreciate any input to get this baby to idle, and get it timed properly.

 

[bloodthirstysystem]

not sure about the pamco timing, but it should advance around 3000rpm.

the covers on the mix screw are from the factory, carefully pull them off. i used a screw driver to gently pry back and forth. throw them away.

i set my idle as low as possible, just enough so it doesn't stall at a light..

 

[pyrocentric]

If the advance mechanism springs are too weak it will advance earlier than 3000rpm. This will cause your hanging idle problem...as will an air leak or carbs not synced right. If it advances too early you can cut off a coil from that little spring and bend the next one into a hook. If it advances past the full advance mark, you can GENTLY bend the tabs in that catch the advance weights.

It would pay to borrow a timing light and one of those mechanic's meters that you can use to check the RPM. Harbor Freight sells them I know.

The timing should stay right in the F mark(near top dead center) until you hit 3000rpm then it shoots to full advance almost instantly. It's a crude system at best.

It's taken me a year to get mine idling right, but it will now purr at 1200(or even 1000rpm) all day long. It doesn't hurt anything to idle it a bit higher(it'll charge the battery better) but it's tougher to shift into neutral.

 

[ironwill]

Thanks for the responses. Next day off, I'm going to dig into the advance mechanism. I have a timing light, but it doesn't have a tach on it.. I have a Suntach that used to be in a Camaro, it has settings for 4,6,8 cylinder engines, but not 2 cyl. I was hoping I could use that, as it has four wires on the back. I figured it must somehow read off the coil, but haven't had success with it.

Also, glad to hear your's purrs like a kitten, thats my goal.

 

[pamcopete]

ironwill,

If you do not have a tach, you can tie the weights so they will not cause any advance and then set the timing as it will not matter what the RPM is at idle, but don't increase the RPM's too much because there will be no advance.

If you have a fluorescent light, you can illuminate the rotor when it is dark and the rotor will appear to freeze at 1200 RPM.

The advance should start just a little faster than idle and get to full advance at 3,000 RPM. It should move rather smoothly. If it suddenly jumps to full advance then the springs are probably too tight.

The tabs on the weights should not be bent to achieve correct timing.

You should get a tach to check your advance more accurately. That SunTach should work in the 4 Cylinder mode except it will show 1/2 of the actual RPM's. Connect it to the green wire of the PAMCO. The four wires are probably battery, ground and both coil terminals, but if I am wrong, you could fry the tach, so see if you can find out what the four wires are for.

 

[Tech7]

4 wires for the tach should be power,ground, neg side of the coil, and the last is probably for a light. Shouldn't have 1 for pos side of coil.

 

[ironwill]

Found this in a suntach search:

RED =12 volts

BLACK=GROUND

BROWN or GREEN = DISTRIBUTOR

BLUE OR YELLOW=Dimmer

I was nervous about trying it, as I didnt want to fry the coil or the Pamco.
I thought I saved the tach and cable in case I needed it, but haven't put my hand on it yet. One disadvantage to having two XS650's with all associated parts, and two VW bugs with all associated parts in the same garage.....

Biggest issue might be getting it to idle steady enough to time it. Guess I was hoping that correct timing would correct my erratic idle. Thanks Pete. If I keep at this, I might be able to ride it before Winter.......

 

[pamcopete]

Tech7 & Ironwill,

Yes. I had forgotten about the light. So, the brown or green wire goes to the green from the PAMCO. It might bounce around a bit if it was designed just for a points ignition because there is no condenser in an electronic ignition.

 

[ironwill]

Bike seems to be running excellent. What I found was the advance mechanism was not snapping back properly. Removed weights, and found rods had a small amount of corrosion. Buffed it off, as well as the rod hole in the weight. Snaps back properly, and idle drops as expected. The slow returning advance was holding the idle high. Took it for about a 15 miles ride yesterday, idle stayed true, bike ran the best ever with the Pamco, and new coil. Thanks for all the help on this one guys.

Cold start-Choke closed, one kick it starts, but won't stay running. Open choke and apply the throttle, and it starts right up.

 

[5twins]

To keep the pivot posts lubed after initial cleaning and greasing, I give them a small shot of foaming chain lube from time to time. I do so after a ride while things are still warm so the lube penetrates better. I also coat the springs so they don't rust.

 

[TeeCat]

ironwill, I saw this thread too late, but I encountered this with my bike too. I ended up replacing my ATU to be safe, as my old one appeared to be worn. Now, my idle actually has to come up a few hundred rpm, as it almost drops too fast for my liking.

Glad you found the problem.

 

[ironwill]

5twins-Thanks, I was wondering about whether lube was a good idea or not. I put a drop of light oil on each post, but wasn't sure if that would make it advance too quickly.

TeeCat-No problem, as you say, glad I got to the bottom of it. I was amazed how much being slighly advanced held the RPM's high. Now its right up and right back down. Just took a 20 mile ride...no problems....

 

[5twins]

Light oil will mostly fling off as the advance spins. The chain lube gels up after it sits a while. As I said, do it when the bike is warm for better penetration but then let it sit so the chain lube can gel. If you ride it immediately even the chain lube will fling off.

 

[TeeCat]

I was amazed how much being slighly advanced held the RPM's high. Now its right up and right back down. Just took a 20 mile ride...no problems....

Indeed... my idle was hanging like yours was, and a new ATU and carb boots seem to have resulted in a fix. But now it returns to idle really fast, like a drag bike almost, and I worry about stalling, so I have to try to bring it up a few hundred rpm without "waking up" the ATU too early. I need to set the idle hot, as well as revisit the timing. I'm not sure I used the light properly when I timed it after installing the PAMCO.

TC