Low RPM Bog/Stumble

[Lucien Harpress]

After three months I finally got the bike in a rideable condition. There is just one thing that still kind of bugs me. At low RPMs (1100-2000) when you give it some throttle, it bogs down quite a bit, starts farting out the tailpipes, and struggles to get going. Once you get to 2.5K or 3K, she's off like a rocket, smooth and pretty as can be.

In addition, this problem tends to go away a bit after it's been running for about 10 minutes (but can crop up again occasionally).

I have yet to do a proper mixture screw adjustment or carb sync (but I've never taken the carbs apart, so the sync should be rather close). Could doing so solve the problem I'm having?

(Also, please don't say gummed pilot jets. I've been through these carbs four times- trust me, there isn't any crud left in there.)

[CatatonicBug]

When you start it, are you pulling out the choke lever? If you are, there is a chance that the enricher (choke) circuit is clogged a bit. Did you clear out the ports in the bottom of ther float bowls?

I still say it's the pilot circuit though...

[tw1980]

Sync the carbs and then worry about the mixture screws.If it tends to mess up when hot you're rich.If when cold you're lean.If the problem crops up intermittently with out provocation and has no pattern I'd start checking for vacuum leaks.

[Ken Talbot]

I have yet to do a proper mixture screw adjustment or carb sync (but I've never taken the carbs apart, so the sync should be rather close).

Bad assumption. If it has not been sync'd and had the mixture screws properly set, it needs it. Taking off after it gets to 2.5 or 3.0 is an indication your bottom end is dead. You should be able to easily torque your way to a nice get-away with no more than 1.5. And, if you've never had the carbs off, there is a very good chance you've lots of deposits plugging up all those low-speed circuits. Once you get it all cleaned and sync'd, you'll think you've got a whole new bike!

[CatatonicBug]

And, if you've never had the carbs off, there is a very good chance you've lots of deposits plugging up all those low-speed circuits.

I think he meant that he has not taken them off the rack and separated them. He has already taken them out and cleaned them 4 times...

Ken is right though, just because you have not taken them off the rack does not mean they are not in need of a sync. Every time you adjust ANYTHING on these carbs, you need to re-sync.

[Lucien Harpress]

Alright. I guess what I was most curious about was if this was a common problem that could be solved with your average sync/idle screw adjustment.

Ports on the carb bowls and pilot circuits are all as clean as a whistle. Once I get a day off I'll sync the carbs and check around for vacuum leaks.

[dbeardslee]

Lucien - I just had a similar issue with Betsy. After replacing the carb boots, adjusting the valve clearances, replacing pickup coil wires, redoing the wiring harness, and no less than 15 trips into the carbs the culpret was finally identified - bad ignition coils. At less than 2k the alternator isn't putting out its full 14.2v, and the 12 I was getting from the battery wasn't enough to make the coils fire reliably. It was backfiring through the carbs, and doing all kinds of wierd stuff below 2.5k. If you have the original coils then you also have high tension wires that are 30 years old. Have you tested yours with a digital multimeter? Might not be a bad idea to make sure all the electrical connections are clean also - particularly the ones with the red/wht wire. Corroded or dirty connections can also cause the condition you describe.

[Hawkins]

the culpret was finally identified - bad ignition coils..

Was it OEM coils or Mikes XS coils? I'm having pretty much the same problem, but was hoping it wasn't coils because they are relatively new ones I bought from Mikes a couple of years ago. I recall reading something recently about problems with Mikes XS coils, but haven't been able to find the post via search.

Seems like an endless cycle of troubleshooting and frustration with these bikes - by the time you chase one thing down, something else comes up, and sometimes things recently replaced are crapping out. IMO, currently available replacement parts are nowhere near the quality of the OEM gear - we are replacing quality (but worn out) Japanese parts with Chinese junk, but what choice do we have?

[dbeardslee]

Hawkins - They were black Mikes XS coils with around 7k miles on them that crapped out on me, but you can experience problems with the stock ones and original wires. Cleaning the electrical connections is critical, and I mean clean them. Take the connectors apart and really hit them good. On mine I got over a full volt back at the TCI by cleaning and replacing old connectors. I'd get a tenth of a volt here, two tenths there - it adds up. On the parts - a lot of the ones that are available are actually better than the originals - hot coils, kevlar clutch plates, oregon motorcycle parts regulator/rectifiers, iridium plugs - the list goes on and on. Just depends on what you buy, and how much your are willing to spend. Once you get them all straightened out these bikes are still pretty bullet-proof - IMHO. Even the new ones develop problems from time to time.

[Hawkins]

You have a point, there is a range of quality available, and all machines are subject to problems. I'm just on another low in the XS wave. If I had sprung for Accel coils maybe I wouldn't be suspicious of them as I now am of the Mikes XS coils. Are the green Mikes coils a direct fit as well? Are they supposed to be any better?

On connectors, do you have a source for good quality OEM style connectors? All I can find in these parts is spade connectors. I would gladly swap out all the key ignition and charging connectors if I could get new ones.

Thanks.

[Hawkins]

hey, how did you determine the coils weren't up to scratch?

[slow mo]

hi lucien

this may or may not be your problem ,,but i would look at the pick-up coil wires these are a usual suspect on xs11s,, ride safe,, slow mo!!

[dbeardslee]

how did you determine the coils weren't up to scratch?

By replacing everything else, until coils were all that was left . Either they were getting hot and failing, or they had issues with voltage - or a combination of both. I tested them with a DMM and they looked OK, so naturally they were the last thing I replaced. I got rid of them in favor of the Mikes green coils and haven't had a problem since. They're not really a direct fit - you either have to fab some brackets or drill some holes - but they're pretty close. Here's how they fit on mine - green monster details.

If you need anymore info on the coils, pm me. I don't want to hijack Lucien's thread any more than we already have .

[Hawkins]

Yeah, sorry Lucien, but maybe the discussion helped?

[Lucien Harpress]

Well, at the very least it gives me something to look at if a good sync or screw adjustment doesn't solve my problem.

Discussion's good anyway- I really can't do much of anything until I get a proper sync in, so might as well talk about SOMETHING until I get that done!