Miss while riding

I have a 81 XJ550 Maxim. I have had it almost a year. Last fall the engine started to miss while riding 40+ MPH. It only did this limitedly. Now it has started to do it more often and more violently. It still only does this at 40+ MPH. It idles and starts great and sounds good. When it does this I can give it more throttle and it seams to help and stop missing for a while.

Not sure where to start.

 

I just discovered that the clamp that is on the boot on the back side of the carb has slipped off on two of my carbs. I have fixed it but i need to take it for a test drive.

Would that cause the problem?

 

I fixed the boot clamp and took it for a test ride. It still has the violent miss. It will be fine for about 98% of the time. Then it looses powers and shakes. It only lasts about 3 or 4 seconds. It may repeat but sometimes it just goes away for minutes.

I am going to check the petcock to make sure the diaphragm is ok and the screen isn't clogged.

Could it be an ignition issue?

It never misses at an idle. It always starts good.

Please some advice.

 

Check the Carb Sync and clean posts. Usually losing power, missing, etc. boils down to the carbs.

Check the petcock. Try running it on prime, see if it happens.

Check your plugs - do a plug chop at 40+ mph and the rpm it misses at.

Heck, chop when it happens, if possible, see whats going on with your plugs.

That's where I would start.

 

also, if this is a fuel problem, try riding with your gas cap opened a little bit down a straight and flat road... perhaps your gas cap vent could be clogged- if those boots that slipped off arent the problem, then it must not be a lean condition... but im just offering suggestions

also try the propane test, take an unlit but runningpropand torch and poke it around the boots, see if the bike starts to rev.. then you'll know if you have leaking boots.... hmm, I dont know much about electronics.. mainly fuel... ill wait for someone to chime in..

 

Ignition ONLY at 40+ MPH?
I'm not sure. How do these bikes advance ignition timing based upon speed? Haven't seen it covered much on what I've read.

 

sorry for the ignorance but what is a plug chop?

when the boot was loose i checked the plug color and it wasn't white it was a light tan. the plugs are new i changed them this spring. it was doing this before the plug change

It does do it on PRI. However i did put a new tank cap on last fall. it wasnt new i got it off of ebay. Where is the vent in the cap?

 

i'm not exactly sure, but it's a can of worms to change it.. w2ith the locksing mechanism and springs and so on... if i had a bad cap i would think about buying a NOS one...

a plug chop is when you take it for a sping like 15 minutes, and on the home stretch have her cruising around 4500-6K rpm's then hit the kill switch and coast into the driveway and check the plugs, to see if they're a light tan, kinda like a caramel macchiato from star bucks- YUM!

 

I think i still have the old cap. I will put that on and give it a try. I can also take it for a spin with the tank low and open the cap and see what happens.

I will try that with the Plug Chop. I will also try to post a picture.

I have not taken the Petcock out yet. Is there a screen on it. could it be dirty?

 

the only screen i've seen is the one that covers the intake of gas into the petcock, which you will see instantly when you take the two bolts out and pull it off the tank...

 

Ignition timing is controlled by the TCI, it cannot be changed.

But it does sound like an ignition problem, if it's a sudden and constant miss. If it is ignition related, you will lose 2 cylinders at the same time, so you should really feel it (as opposed to a single cylinder miss from fuel problem)

If it's fuel related, i'd think it would be a more gradual loss of power, and not so much a "digital" on and off of misses.

 

one thing I forgot to add is.

it seams to miss more often when i am accelerating up to speed. When i am at speed it is less likely to happen.

What can I look for or try if its ignition?

 

Is it like it'll just miss every now and then while accelerating, or will it miss for 5 seconds at a time?

 

It will miss for about 5 seconds at a time then stop for a while. I ride 45 minutes to work on I80. If i get cruising at 70 it runs great and very seldom does it. However while i am accelerating to 70 it is more likely to happen.

 

Instead of noting the mph when this happens, make note of the rev range. Not an electronics expert, but some electronics can break down at a certain rpm. Below that range they run fine and if you can get past the "Problem" range it will be fine.
I'm comparing this to a race bike at one of the weekends I attended. The guy tried everything, carbs, plugs, coils etc. but anything over 8 grand and the bike would stumble and falter. They finally figured out it was the black box (Honda) by attaching the timing light to the bike and when the bike got near the 8 grand the timing light went nuts.
Might work, best done in low light (evening) so you can see the timing light flashing.

 

I think i found the problem. i had purchased a set of coils and a cdi pox on ebay and was ready to replace them on my bike. I take the seat off and start to disconnect the cdi connections and noticed that a few of the wires had been cut and spliced back together by the PO. One of the connections was fastened by a wire nut and the other was a crimp connections. Well the one that had the crimp connection was very loose and that circuit was the kill circuit. it went to the kill switch and the kickstand switch. I took the time and soldiered the connections together and used shrink tube to seal them. Haven't had the time to take it on a long ride yet but i road it about 5 minutes without any problems.

so it look like i have spare coils and cdi box now....

 

That would make sense if that wire was somehow shorting out to ground somehow. Something else to check if your problem isn't fixed, is the plug caps themselves. Make sure they're screwed onto the plug wire securely.

If not secure, cut off 1/4-1/2" (depending on how bad they look) from the plug wire and re-thread the spark caps back on the wire.

Let us know brackett!

 

YES!!!! the loose wire was the problem. I rode for about an hour tonight and had no problems. It ran great and solid........

The lesson learned here is to never use soldier-less crimp connections on any of the ignition circuits