True Tdc

[thewiz]

mechanical advance ???

Hey, Rob ... it's entirely possible that the movement you're seeing is the centrifigal part of the advance mechancism doin' it's thing. Since the advance plate is hooked to the arm on the vac advance, it may just appear that it's being moved by vacuum when, in fact, it is being moved by the weights on the inside of the plate itself .... what TC said ... hook up a vac guage.

[79XS11F]

Hey Wiz I will have to check both out tomorrow. If it's the bob weights I will guess that a new unit or springs will be needed

[randy]

The bob weights don't move the baseplate, they move the reluctor.

BTW, there are NOT "4 idle screws", those screws are the pilot screws. There is only one idle screw, the big one.

My theory is that you need to re-sync, your butterflys are too far open, at least the one on #2 is too far open.

Get her nice and hot, then do the sync. When it's synced, adjust the pilot screws for best highest idle. As the idle comes up, keep turning it down with the main screw. Then sync again. That should do it.

[79XS11F]

That's a little bit confusing Randy because #3 is fixed and in the end all the others are synced to it? Unless of course #3 is open too much. i am getting 20 cmhg on # 3 and in the end match the others to that.
Should # 3s butterfly be fully closed at the start?
What sort of numbers should I be expecting on my dial gauges?
I must admit that the engine "sounds" better with lower numbers on 1 and 2 then when I sync 1 and 2 to 3 and 4. In other words it "sounds' better out of sync.
Rob

[randy]

I assume you're using a one-guage setup? If that's true, it is very difficult to sync with one guage because each sync screw turns two carbs. As you bring one up, the other goes in the opposite direction.

If it sounds better out of sync, then you have other problems. perhaps you're syncing at too high an idle? Sync at 900-1000 RPM to be sure you're operating on the pilot circuit

[tommystinson]

Absolute values on your manometer don't matter, they would be an indication of your idle speed. If your carbs are really out of whack and you haven't done the bread tie synch first, you may need to continue to reduce the idle as you get closer. I do mine at 1100 RPM. As Randy pointed out, it's pretty much impossible to do the synchronization with less than a four gauge/column setup. "No carburetor is an island"
I'd be happy to do them for you if you're willing to ship them back and forth (as I can't say that I'm planning on a trip to The Great White North anytime soon). I do get up to Watertown quite a bit, however. I have a bevel drive screwdriver along with a carbtune II and colortune if you feel up to meeting on Rt. 81 at some point. Don't need to pull the tank to do it, which is nice. Shoot me a PM if you'd like. Tommy

[79XS11F]

Good morning guys and thanks for hanging in with me as I try to sort out what should have been a straight forward setup given that the bike is stock. Stock set up should be the easiest to do. Anyway .... I did bench sync the carbs with the wire twist tie method and I do have 4 gauges so I am looking at all carbs at the same time. I think I need to correct the vac advance issue before I go much further.
So after I get a pile of coffee into me I will work on the vac advance bounce issue. Once that is corrected I will take the bike out for a run to get it good and hot. Then I'll check the sync again. I may even run it with the gauges on the tank which would be easy to do.
QUESTION .. would the vac auto advance acting too soon have the same effect as running the engine lean. I ask because I see the headers go gold in color when the bike is at running temp but they return to normal when she cools down. These are stock pipes and headers and I do not remember this effect WAY BACK when I owned one of these bikes.
I checked the manual and it does not list a spec for how much vac there should be at the vac advance hose. They only tell you how much is required to fully advance the unit.
Rob

[79XS11F]

Thanks TC for posting that link. I will head out to the hardware store and buy a # 75 drill and see what I can get to work. Maybe I could even stick a carb jet in the line if need be
Rob

Originally posted by TopCatGr58
Hey Rob,

Another member, think it was in Australia or NZ had this same thing, was properly connected to the carb body port, but was having vacuum pot pulsating!

Turned out the PO had reamed out the hole in the carb body so that it was much larger than it was supposed to be. He put something in line to create the proper restriction, and it stopped the pulsing and worked properly!

You should be able to find it with a search.

Also, you could put a vacuum gauge on the carb body port and see how much vacuum it's getting? The book reports should only take about 9psi IIRC to reach full actuation and travel of advance pot!
T.C.

Found it:Goldcoast guys advance problem

[79XS11F]

WOW ... that's no SMALL hole in the carb body for the vac advance hook up I just checked it on my other carbs and I can get a twist tie through it loosely but not a piece of .023 wire for cleaning paint guns.
Rob

[79XS11F]

Vac on that advance hose is 1 and with a twist of the throttle it moved up to just under 6. So that looks to be normal. I will guess that the spring in the vac unit must be tired and not offering enough resistance to movement.
This is what I'm going to do .. tell me what you think? I will remove the vac unit and drill a small hole in the arm. I will put a spring over the arm and then put a pin in the hole to hold the spring in place. The spring will have to be just bigger then the arm itself because there not much room there. I will cut the length of this added spring until the unit works but does not bounce around at idle. It may not be doable if there is no room behind that arm. I'm not looking at it right at the moment.
Rob

[skids]

Rob, you sound as if you are going to be wasting a lot of time. If the vac/advance is bad, replace it. If the hole in the carb is too big, put an inline restrictor in it.

Originally posted by 79XS11F
Vac on that advance hose is 1 and with a twist of the throttle it moved up to just under 6. So that looks to be normal. I will guess that the spring in the vac unit must be tired and not offering enough resistance to movement.
This is what I'm going to do .. tell me what you think? I will remove the vac unit and drill a small hole in the arm. I will put a spring over the arm and then put a pin in the hole to hold the spring in place. The spring will have to be just bigger then the arm itself because there not much room there. I will cut the length of this added spring until the unit works but does not bounce around at idle.
Rob

[79XS11F]

Those units are listed as being discontinued. If you think trying to add a spring will not work then I guess I will have to restrict the vacuum hose even if the current vac reading appear to be within the normal range. When I bought the bike I noticed that PO had a piece of solid rod stuffed in the line and now I know why. He likely just blocked it to correct the same issue.
I have my doubts about the vac unit being broken because I have 3 of them here and they all behave the same way.
The engine was not very cooperative this morning when i fired her up. She was missing so I am also going to put my excel coils back on the bike. I really wanted the original appearance but it is more important that the bike run properly. I am VERY sure that the carbs are clean and I know that the jetting is stock sizes and are all original manufacturer parts. I checked every one with a magnifying glass. I added fuel filters and the carbs are not puking fuel any more.
Rob

[pggg]

The port from carb2 to the vac unit, the proper connection hole is 0.5mm, not much bigger than a full stop or decimal point on this page, the vac 'pressure' won't change, large hole or small hole - it's still the same vacuum level, the small hole gives smoother operation though. The vacuum still pulls on the timing plate at idle with the butterflys closed, the lower the revs the higher the vacuum, even more when the motor's on the 'over run' that's decelerating on closed throttle. The vac unit retards the timing when the revs are low, easier starting and better low rev response. 79, rig a restricter inside the connection hose with a 0.5mm hole thru it.

PS it's easy to sync the carbs with a single gauge - just takes practice. A 4 gauge setup is less hassle though

[randy]

Rob,

further to the restrictor-in the-line idea, if you've got an old pilot jet, shove that inside the line. that should smooth things out.

[79XS11F]

THIS BIKE HATES ME LOL LOL

So changed out the coils to make sure that the stock ones I got were not part of the issue. I fired her up and she was COLD blooded and still missing a bit. I popped off the timing cover and much to my surprise the pick up coils were not bobbing anymore ??? Go figure. So that issue fixed it's self while i was sleeping I guess.
I took the bike out for a GOOD run and got her GOOD and hot. Idle increased again since last run and there is no miss when the engine is fully warmed up. She still "buzz's" a lot while accelerating bit is not to bad at study RPM unless I am over 45 to 5 K RPMs.
I think I will leave the bike as she is until I get my color tune plugs. One way or another this appears to be a idle issue. It must be the carb idle circuits and pilot settings.
The buzz must be engine mount torque at the upper front. The bolts that I could not get torqued to the called for 48 pounds.
Rob