Flat spot/lag when opening throttle

[GoneForTheBorder]

The drop is equal when plugs 1, 3, and 4 are pulled, now there's no drop when #2 is pulled. There's no water or debris in the plug wells. I'm thinking a new set of plugs and re-synching would be a good idea if replacing the plugs gets it firing in all 4 cylinders.

The RPMs still drop very slowly when the throttle is closed - is this normal for a 1200?

Glen

[Guest]

Boy, I can't write fast enough to keep up with you!
Let's start over.
While sitting on the bike, #1 cyl is right forward.
#2 is left forward, 3 is right rear, and #4 is left rear. I want to make sure we're on the same page when talking about affected cylinder's.
#1 was missing, now #2 is missing? And you've checked for good hot spark on all plug wires?

[GoneForTheBorder]

We're on the same page. Initially, #1 showed no RPM drop when pulled, and #2, 3, and 4 showed the same drop when pulled. After swapping plugs between #1 and #4, #s 1, 3, and 4 show the same RPM drop when pulled, and #2 doesn't show any drop at all. All wires have good spark. That's why I'm scratching my head and thinking "gremlins"!

I'm going out to pick up a new set of plugs, will install those and see if I can get it synched tomorrow.

Glen

[GoneForTheBorder]

Sorry for the delay, wasn't able to get the plugs changed for the past couple of days. Here's the status:

- Changed all 4 plugs, correctly gapped and installed.
- Started engine, immediately detected missing
- Pulled plug caps one at a time to detect missing cylinder
- Initially thought it was #1, but attached a spark plug to cap and started engine to be sure. Spark was good.
- When #2 pulled, RPMs did not drop. Attached same spark plug as used above to cap which revealed intermittent spark on #2.
- Reconfirmed that RPMs did drop when #1, 3, 4 spark plug caps pulled. It's definitely #2. The spark seemed intermittent, but I increased the gap to .060 on the test plug (not the one installed in the engine) and I can still get a spark on #2.

Now I think we're getting somewhere - but where?

Glen

[Guest]

Since you initially believed #1 to be at fault, and now can confirm #2 as definate, one could resonably assume a faulty coil. That's all #1 and #2 have in common. Since you will more than likely have to remove a lot of plastic to acces the coils you can do your resistance check on your wires at that time. Be very careful to inspect all connections at the coils for corrosion. Poor power to the coils will give weak spark. One other thing that I'm NOT sure of is the CDI unit. If it works like most, it would provide a ground to trigger the coil. If that's the case, you shouldn't have spark. Period. Make sure your coil connections are clean and tight. I said that already, didn't I? Must be important.
Good luck.

[GoneForTheBorder]

Thanks very much for the help! That should keep me busy for a while. I'll post whatever I find out.

Glen

[GoneForTheBorder]

So, after checking/cleaning all connections and ultimately replacing the coil and wires with known good items as a check, #2 gets good spark but still doesn't fire. Since that leaves mechanical issues that I'm not qualified to diagnose, it's off to our local Wing guru (Wing Nut in Fairfield, CA) next week, weather permitting. I'll post the results when we get to the bottom of the problem.

Thanks for everyone's help!

Glen

[GoneForTheBorder]

I took the bike to our local Wing guru as noted in my last post and picked it up today. He told me that all 4 carbs were constricted with fuel residue. The carb overhaul included new gaskets, float valve sets, manifold o-rings and new fuel filter. After the overhaul, the engine runs well; there is a slight hint of hesitation when cold and on choke which disappears as soon as the engine is warm. Throttle response is crisp. It feels like a brand new bike (guess it should, it only has 33K miles on it).

To summarize, I suspect that the problem was a combination of clogged carbs and intermittent coil failure. That's the only explanation I can come up with for the way the problem seemed to move from one carb to another. Eliminating the ignition problem left the carbs as the clear culprits.

Next on the agenda is changing all the fluids, cutting out the stator plug, adding turn signals to the trunk lights, and finally adding an audio/communications suite. That should keep me busy and out of trouble for a while.

Thanks to all who offered thoughtful and useful advice, especially Mike (glhonda)!

Glen