Cylinder popping and missing after tune-up

[emason]

Problem following tune-ups on 2000 V11 sport. Following first tune-up (valve adjust, check plugs, tps, balance) left cylinder missed and popped, wouldn’t balance, wouldn’t idle. When popping, left carb-tune rod dropped like a stone.

Went thru the whole tune up process again. This time idled and balanced. Took it for a test ride and found the problem again. When rolling off the throttle it starts missing and popping, guessing it is the left cylinder. Also, riding in first gear is the same, bucking and missing.

What could I have done to cause this? How can I find the problem?

I’ve read posts about balancing and the missing and sneezing syndrome, but can’t narrow it down.

Thanks

[docc]

Se that the connector for the TPS is not fouled on the fuel regulator.

 

Where are your air bypass screws set?

[Chuck]

If it's only the left cylinder, I'd look where I've been. Spark plug cap firmly screwed on the lead? Maybe the lead loose at the coil. Cap tight on the plug?

Left throttle body firmly attached? Simple stuff first..

[emason]

>

Found the spark plug caps loose after the first tune up. Cap is tight on the plug. Haven't checked coil lead yet.

 

>

Is the fuel regulator where the fuel enters the throttle bodies?

 

Left is one turn out, right is 3/4 turns out.

[docc]

The regulator is on the right side of the fuel tank where fuel from the injectors returns to the tank. Not at all sure that would cause your issue, but easy to check.

 

What tune-up procedure did you use?

[emason]

I used Guzziology and "TPS setup and throttle balance tuning" by dlang on this forum.

[docc]

That may be  a bit out of date. Not that any of that procedure caused your issue. Keep looking for something that got disturbed "where you've been."

 

Otherwise, this is a much more up-to-date tune-up:

 

Decent Tune-up

[fotoguzzi]

TPS not set right. it's very touchy, maybe it moved slightly as you tightened it down... go back to WG good advice there..

[emason]

Well, I will do another tune up. Practice makes perfect?

 

btw, last night I noticed that the vacuum caps have disappeared from the manifold nipples.

[swooshdave]

TPS is extremely touchy. Check and recheck.

 

Then check again.

 

The other thing to check is the valve clearances. That would cause the vacuum to disappear on your gauge.

[LowRyter]

agree about the valve settings.

 

I mentioned it on WG.  It's an easy mistake to set the left side on the exhaust stroke vs compression.  It's an easy check and a simple fix.

[footgoose]

Well, I will do another tune up. Practice makes perfect?

 

btw, last night I noticed that the vacuum caps have disappeared from the manifold nipples.

 

the manifold nipples are open? that will cause the problem

[Ian]

I would strongly suspect you have a vacuum leak. Maybe the intake rubbers are split or the cap on the vacuum nipple for balancing the throttle bodies has perished. Have a really close look at them with a bright torch

[emason]

Third tune-up shows some improvement. Re-checked valves, re-did balance, much easier following KiwiRoy’s tip. Looked to be balanced perfectly. (At a high idle and at 2 to 3k rpm) Only used white knob to balance.

 

However, test ride revealed bad surging and stumbling when starting off in first gear. Got better accelerating thru the gears, but rolling off the throttle more surging. Also surging when trying to hold a steady throttle around 3k rpm.

Spraying wd40 throttle body boots failed to affect the rpm.

 

I don’t have Guzzidiag yet. Got a pc from a friend and have the cables (I think) but have not yet committed to learning that software. It is on my to-do list.

 

Anyway, at this point it seems I need some fine tuning (I hope)

I’ll try to rebalance at a lower idle. The tps is still .157, I don’t know if I should mess with that.

Will recheck for vacuum leaks tomorrow.

Thanks all for the help, I still have a little way to go.

[docc]

If your TPS is at 157mV >totally closed

 

guzzidiag has outpaced the PC by a couple decades.

 

Download it, get the Diagnostic Cables, and see where your CO Fuel Trim is (pre)set.

 

Also, simple enough to disconnect the TPS and connect an Ohm meter. Roll the throttle gradually open and closed. There should be no *fits&starts* . . .