RPM drops down at highway speed!!

[PieroBassi]

I am in the process of buying a 1979 XS1100F. The bike seems to be in relatively good condition. However, the seller is telling me that

" ... the bike twice bogged down at highway speed. When I say bogged down, I mean that it dropped RPM's and wouldn't do more than 60. This happened only twice over the 4300 miles it has been in my family and both times it just worked its way out shortly. I have had the bike since late spring and the problem has never occurred again. I assume it was something working its way through the carbs or something".

Any suggestion on what could have caused this type of malfunction?

Piero
Minneapolis

[Mike Hart]

It could have been a fuel thing, or the very common pickup coil problem. See the Battery & Electrical repair forum for more info.

[Dragonrider]

Seems likely to be a plugged fuel vent/line . . .

[Dave]

I had the same problem when I removed
and reinstalled my tank. I had pinched
a fuel line just enough to starve the
engine at hwy speeds.

Just a thought.

Dave
XJ1100J

[PieroBassi]

Thank you all for your suggestions! A venting, fuel line problem seems to be the most probable. It could be an intermittent problem with the ignition timing as well.

Thanks again,
Piero

[strom]

OK guys and gals...

My 78 starts easily (when it starts), revs OK at standstill, but if I try to ride it a bit, rpm drops to 500 and won't come up. And that's at full throttle, if I put it do 1/3 or lower, it dies. It starts right up again, but runs at 500rpm. If I let it sit for a while, it starts normally.
I cleaned the carbs twice.
I shut off the fuel this time, and we'll see if it's the TCI unit.

Is it possible that not enuff fuel gets to the carbs... they seem to fill up rather slowly.

Any ideas?

LP

[strom]

OK, carbs are fine... what are the symptoms of broken pick-up wires? And failed TCI unit?

LP

[Mike Hart]

If it revs normally under no load conditions, I doubt it is an electrical problem. Pick-up coil wire breaks are usually an intermittent cutting out of 2 cylinders (or no spark at all on all four if both are completely broken). TCI usually blows one or both power transistors (that the pickup coils send their signal to) resulting in no spark to 2 or 4 cylinders.

Could still be fuel delivery related, picks up enough gas to rev w/ no load, but can't get gas for load. Is your fuel level in the bowls okay?

Or, is something binding in the gear train? If you take out the spark plugs, can you rotate the engine while in gear by turning the rear wheel?

[strom]

I can barely turn the engine via back wheel in 1st or 2nd, didn't try any other gear... I tried with plugs in.

I found it was more of a heat issue than load.
It cuts out on 2 cyl. I got me a set of suzuki ignition coils and while the bike was running I pulled a wire... produced the same symptoms.

So, I figure it might be the coils... don't know for sure. One fails when hot. Maybe. Will try tomorrow when I put on the gas tank and give it a field test.

LP

[jgalle]

strom,

I had the same problem on my 1996 Pontiac Firebird a couple years back (I know, it's not a bike). The 3/6 Ignition Coil was burning itself out every 3 months or so. Best solution I could come up with was it was getting too much juice. Too much power or something flowing through it, and burning it up. Had to replace the coil every 3 months or so until I sold the car.

Sorry, I never took the time to trace the exact problem, but I had an electrician check my car through, and he found nothing unusual. So it may have been something else that was putting the coil through too much work...

First time it happened to me, I was going to race another car on the "drag". Needless to say, he went fast, and I didn't move

[strom]

Well, what would I do if I didn't know the guzzi folks... A friend went to Greece with his and one of the coils went. Since you can still ride a guzzi on only one cyl (OK, not faster than 80kmh), he went to an auto shop and got an auto coil... worked till he got home, but went again. Looks like they aren't made for this kind of RPM.

The coils on my XS are original... and the bike ran fine, till a bearing went and it was dissasembled and put in boxes.

When I got it, it had no battery and I rigged an auto battery charger instead of the battery to see if anything electrical worked. It did.. kinda. Till I noticed I put the positive onto the starter motor wire instead + pole on the battery.... **** happens. Do you think I might have burned sth? Like the TCI?

Mike, do you know where are these transistors and with which can they be replaced, if this is even possible?

LP

[Mike Hart]

LP, I have no idea what to tell you about the transistors, no one has come forward with that info, if they have it.

You put the charger on which wire? The solenoid +? That's okay, the batt goes direct to there anyway (well, thru the ignition), so you probably didn't fry anything. Batt chargers can have a high voltage on them if there is no load, careful there. Get a battery, man!

It cranked that way?

[strom]

Mike, the engine was in boxes then, thankfully no battery (or corroded to nothing... guess they've taken it out).

Through the ignition... TCI or ignition lock?

Dunno bout voltages... but I'll check.
Waiting for some connectors that a friend should bring in the morning, then I'll test it with suzuki coils.

LP

[Mike Hart]

ignition must be on for start button. Where did u wire the charger????

[strom]

The wire that goes to the starter motor... the fat one. I checked the diagram and it goes to the TCI among other things.
The ignition lock had no effect... on/off position. Killswitch did.
Maybe I fried sth then.


LP