My recently acquired '98 Superhawk suddenly started running very poorly. Has 8000 miles on it (had 7900 when I bought it). Ran great until recently. It suddenly started stalling at low rpm. Then it slowly started stalling at even higher RPM's. Now is only running on one cylinder

So far I have done the following.

1. Removed the gas tank and inspected for flow. Seems ok.
2. Removed air filter and inspected carbs. Front slide when closed seems to have a smaller gap than the rear carb. Air filter looks good. No visible lines crimped.
3. Pulled spark plugs and inspected - seemed to be normal.
4. Hmm. maybe bad gas. So I spit and sputtered my way to the nearest Sunoco station and filled up. Rode about 15 miles up and back the interstate. Ran even worse - max speed about 70 and definitely seems to be running only on one cylinder now.
5. Back home - pulled plugs again - definitely one plug looks good but the back plug is not firing and smells of gas.

My conclusion - not getting spark to the back plug. Since my manual says replace plugs at 8K miles I am going to try that next.

(I carefully checked the vacuum line to the gas tank to prevent PVLIR syndrome.)

Any other suggestions? I really don't want to dive into the carbs; my history with cleaning carbs is spotty, so I'll probably rely on my local dealer if necessary.

The only other contributing factor I can remember is that I rode the bike home from work on Wednesday in the rain. Not a very heavy storm, but a steady drizzle. It may have started missing then ??

Frustrated in South Florida and was planning a nice ride on my holiday,

Sparky

 

I'd check the plug wires and coils before carbs.

 

If the problem started while riding in the rain, a good possibility is that you have a leak to ground from a plug wire or the coil.
On a car you would check it by attaching a jumper wire from a long narrow screwdriver to ground, then run the tip of the screwdriver along the wire and around the coil while looking for a spark jumping to the screwdriver. Of course this won't work on the SH too well since everything is pretty much buried.
You would have to visually inspect the plug wires and coil for burn marks which appear as gray areas and carbon tracks.
Good luck

 

If you have a way to check carb sync that might not be a bad idea. Are the lines going to the tank and petcock hooked up correctly? That's a VERY easy mistake to make and cause all kinds of issues.

 

I checked the fuel tank and petcock lines carefully. I am fairly certain they are in the correct locations.

I bought and installed new plugs. No improvement.

I checked the rear spark plug wire resistance. Seems to be OK. Was going to check the coil resistance but the primary wires are to difficult to disconnect.

I am 90% sure at this point there is debris in the rear carb and needs to be cleaned. I will take to a dealer tomorrow and let them go thru it.

It probably needs to have a professional tuning anyway. It was backfiring slightly on deceleration before this problem althought it was not enough to worry me.

I just don't like working on carbs. Some people fear snakes and spiders. I fear carburetors. I can rebuild an old BMW's carbs with my Swiss Army knife and a pair of pliars. But not these babies.

Guess I am getting old and lazy.

Thanks for the suggestions.

 

Double check for PVLIR (the bottom line on the petcock doesn't get a vacuum tube connected to it, even though it looks like it should, it is the back one that does)

 

Like so, as seen from the back.