Carb Synch giving me fits

[natemoen]

It isn't like you are going to see a HUGE jump in vacuum. So as you are adjusting your mix screws you might only see a rise of 1 to 3 inches of mercury, and I agree that it is a little hard to notice that change on a carbtune (cheap vac gauges especially!).

At idle my bike is pulling around 18-20 inches of mercury on my carbtune.

[jetmechmarty]

Go back to the post by mlew. Are the valves adjusted within spec?

Also, this will be a major PITA if a proper bench sync was not performed before you broke out the sticks. I hope you did that first.

Davinci is correct about the mixture screws. With the Morgan Carbtune, the change is going to be very subtle when you find the sweet spot.

[BillyRok]

Valves are in spec and bench sync was done. Reattached the hose from the vacuum advance sender to #2 carb body (I assumed this was my vacuum leak) and tried again. The rods inside the tubes on the carbtune want to bounce up and down pretty good most of the time making it harder to tell what the true reading is...is this normal? I got a pm from another member suggesting that the rods and tubes may need to be cleaned, he had better results after cleaning his. If I drop the idle to 7-800 the rods are pretty steady but then the slightest adjustment often causes the motor to stall...then I need to open the throttle slightly while cranking it to get it to fire up again. Still not clear on the proper adjustment for the throttle at the grip. If I thread the mechanism in towards the grip the rpm's drop, threading out increases rpm's. You guys think I still have a vacuum leak someplace that is causing the erratic idle speed? What should I expect to see/hear as I adjust the mixture screws and is there any harm in screwing them all the way in and/or out to see what happens?
Thanks for the help so far guys!

[motoman]

Valves are in spec and bench sync was done. Reattached the hose from the vacuum advance sender to #2 carb body (I assumed this was my vacuum leak) and tried again. The rods inside the tubes on the carbtune want to bounce up and down pretty good most of the time making it harder to tell what the true reading is...is this normal? I got a pm from another member suggesting that the rods and tubes may need to be cleaned, he had better results after cleaning his. If I drop the idle to 7-800 the rods are pretty steady but then the slightest adjustment often causes the motor to stall...then I need to open the throttle slightly while cranking it to get it to fire up again. Still not clear on the proper adjustment for the throttle at the grip. If I thread the mechanism in towards the grip the rpm's drop, threading out increases rpm's. You guys think I still have a vacuum leak someplace that is causing the erratic idle speed? What should I expect to see/hear as I adjust the mixture screws and is there any harm in screwing them all the way in and/or out to see what happens?
Thanks for the help so far guys!

Your idle adjustment is done at bottom of carb bank, not at the throttle cable. Back it off so it has no interference and set idle at the carb bank. If all is working correctly, adjusting one idle mix screw all the way seated SHOULD and will kill the motor. do the idle mix setting, then sync with idle in the 800rpm range. If all done correctly, it should idle down to 500rpm before starting to lope at 450rpm. Normal idle is set at 1100rpm.

[CaptonZap]

One other point that is not mentioned enough is that the idle speed should be lowered as far as possible and still have the engine continue running. The reason is that if the butterfly's are open past the idle bypass holes in the carb throat, the idle circuit is being bypassed just a little. Which makes the mixture screws less effective in changing the total amount of gas being inducted into the cylinder. (Some is sneaking by in the low speed circuit).
After you get the idle down as low as you can, using the knurled knob under the throttle cable, adjust the idle mixture screw to give the highest vacuum reading on #1 cylinder.
You should notice that the RPM's increase as the vacuum increases. Set the idle down again using the knurled knob..
Go to the next cylinder. Repeat the idle mixture screw adjustment. Once again, the RPM's should increase. Set the idle down again.
Continue that process, reducing the idle speed after each mixture screw adjustment.
Now do it once more for each carb.
Now go through, and adjust cylinder 1 to 2, and 3 to 4, getting the vacuum even for each pair. Don't worry if the 1-2 pair doesn't match the 3-4 pair.
Lower the idle speed down, as it should have increased as you balanced the carbs.
Now balance 1 &2 to 3&4. Reduce the idle speed again with the knurled knob.
I do mine at about 800 RPM. Yours may vary due to mechanical differences in your engine.
Now go back and start all over with the mixture screws. If the RPM's do not change, and you do not see a rise in vacuum, you're good to go. If you do get a rise, get them all as high as possible, re balance one to two, three to four, then one and two to three and four.
NOW, you can set your idle speed up to 1100, or what ever you think is right.
The main point is to set all of the adjustments at the slowest RPM's that the engine will run smoothly, and then after adjusting, raise the RPM's to your normal idle speed.
CZ

[IanDMacDonald]

I'll try this tomorrow.

[BillyRok]

It's been a few days since I've had any time to mess with the bike but I hope to get back to it this week. The last time I had it running I pointed my laser temp sensor at the head pipes and saw #4 was much cooler that the others. I pulled the plugs and all were black/sooty and #4 was also wet. Did some more searching about starting points for mixture screws and kept seeing 2 - 2.5 turns out for early carbs and 3 turns out for later carbs. My question is if I start at 3 turns out would I expect to see the vacuum increase as I lean out or richen the mixture...assuming 3 turns is starting out beyond the sweet spot and wondering which way to dial it in. Thanks.

[skids]

What can happen is if you start tweeking the mixtures, you will need to adjust your idle. It will undoubtedly speed-up when you get No. 4 firing. If you think you can work your way to the sweet spot by adjusting the mixture screws in only one direction, you will need luck on your side. I say just get it as close to optimum as possible, check vacuum balance, color some plugs, check head pipe temperatures, and repeat the iteration if needed. As I have said before, when you get it pretty close, you will not be afffecting differential vacuums by tweeking the mixture screws as long as idle speed is held constant.

[motoman]

What can happen is if you start tweeking the mixtures, you will need to adjust your idle. It will undoubtedly speed-up when you get No. 4 firing. If you think you can work your way to the sweet spot by adjusting the mixture screws in only one direction, you will need luck on your side. I say just get it as close to optimum as possible, check vacuum balance, color some plugs, check head pipe temperatures, and repeat the iteration if needed. As I have said before, when you get it pretty close, you will not be afffecting differential vacuums by tweeking the mixture screws as long as idle speed is held constant.

Actually does affect vacuum Skids. As for Ian having issues with vacuum jumping around, I would also suspect the bike actually has voltage issues at low idle rpms not properly firing the coils.......specially if bike is still running the 3+ decade old coils. That doesn't mean to say that bike STILL doesn't has a low voltage cond. at idle........my bets are it does. So, with that, Ian, give us the voltage when idleing at the red wire coil plug-ins.

[skids]

Actually does affect vacuum Skids. .

Brant, this has not been my experience.

[BillyRok]

give us the voltage when idleing at the red wire coil plug-ins.

Happy to do it if you'll tell me exactly how to obtain the readings. I'm pretty clueless electrically so I appreciate the patience and guidance sorting this out.

[motoman]

Happy to do it if you'll tell me exactly how to obtain the readings. I'm pretty clueless electrically so I appreciate the patience and guidance sorting this out.

Key on, voltage at battery on pos/neg. term. for a base. Key still on, ground of meter to the three grounding wires/screw on voltage regulater hold down(this uses actual frame grounds as rest of sysyem does instead of from battery). Positive meter lead to each of the red/white stripe wire of coil plug-ins under tank(with key still on). Report the voltage first on battery(for a base voltage), then at those coil wire plug-ins for comparison(with key still on).

[BillyRok]

Voltage at the battery reads 12.20, voltage at coils read 10.65 and 10.62
The battery is new and voltage was at 13.65 after initial charge, lower now since running at idle trying to synch. I can put it back on the charger again. What do these numbers tell us?

[IanDMacDonald]

A couple options: coil relay mod, clean the connections (especially grounds), look into a single ground source straight to the battery, and/or new coils.

[motoman]

Voltage at the battery reads 12.20, voltage at coils read 10.65 and 10.62
The battery is new and voltage was at 13.65 after initial charge, lower now since running at idle trying to synch. I can put it back on the charger again. What do these numbers tell us?

Lot of areas prone to voltage drops............cruddy contacts at ignition switch is biggest one. Mine on my 81 caused a drop to 9.5v @ the coils. At this point, just have removed the switches front protective cover where wires go in and unloaded a can of pressurized electrical cleaner on a straw up in there while flippin' key on and off having lots of crud and I'm sure any lubricant wash out.. Likely gonna have to remove switch and clean correctly to find one volt of all important still missing smoke. Think there's a tip with pics for removal and dissasembly, cleaning and re-assembly. Someone else will chime in I'm sure, and give ya' the link. I would follow it for correct operation once re-enstalled as there's some little springs that will manage to hide from you in man-cave crevisis upon disasembly along with getting fork-lock function correctly.