XVZ1200 - Acceleration "lurches"

[Tieftoener]

Hello all,

 

Thanks in advance for your help.

 

I've got an '84 XVZ1200. I've owned it about 3 years. This season, it started doing something weird the 3rd or 4th time I had it out. As a result, I haven't been able to ride much this year.

 

It's taken me a few rides to get things narrowed down, as it was fairly intermittent.

 

When:

Under light acceleration, no problems.

Under moderate acceleration, it happens occasionally in 1st and 2nd.

Under heavy acceleration, it happens repeatedly during acceleration through 3rd gear.

I have eventually narrowed it down to a position of the throttle.

 

"What" happens: I describe it as a lurch. Although, the lurch is the result of the engine dying for a split second, followed by a quick rebound when it starts going again. When I say the engine dies, I mean all 4 cylinders loose power (not a gradual power lag).

 

My initial guess was fuel starvation, perhaps from gummed up jets, etc in the carb. But, after running 2 tanks with half a can of Sea Foam each, there was no change whatsoever. (I understand Sea Foam won't fix everything for sure... it may well be clogged.) I then started to rule this out because of discovering the quick, repeated jolts under hard acceleration later on (see below for "speed").

 

As a result, I started leaning towards an ignition problem. Its as if the coil(s) run out of spark. What strikes me as weird is that if I run the RPM's up slowly, I can get it to redline without a problem... the engine runs normal all the way up. So, it seems as if ignition is working OK under load (at high RPM).

 

So, this brings me back to a fuel problem. Are there accelerator pumps in these carbs that might be failing (I assume not)? I'm still surprised that the fuel could "recover" if there is a momentary starvation so quickly with the speed of repeated jolts.

 

To give you an idea of the "speed" of these jolts: If I rail on the throttle, I would guess it gets as "violent" as 4 times per second in the 2000-5000 RPM range, and weaning off to 1 time per second nearing redline.

 

Does anyone have any idea what this could be?

 

Many thanks in advance for your help!

 

Regards,

Scott

[Venturous Randy]

Scott, do you have any drop in the tach for that second it it doing the lurch? I don't mean because the rpm's are actually going down some, but an instantanious drop. This may indicate you have a power failure to the coils.

One thing I would suggest is to remove the airbox and on the six pin connector on the TCI, which is right under the battery box, see if you can pull the black wire with the white stripe out of the connector. It will be on the bottom right. You may need a knifeblade to undo the latch on the terminal so it will pull out. It is also easier with the connector undone. Once you have undone the black/white wire, plug the connector back up, put the airbox back on and go for a ride. This is the inhibitor wire for all the safety switches and relays like the side stand switch and kill switch so keep in mind that none of that will work.

If there is no change, then you will have eliminated all those switches and relays as contributors to the problem. If the bike runs better, then you have something in that system that is causing a problem.

RandyA

[GeorgeS]

First check the 15 Amp Ignition fuse, holder. Make sure the brass clamps that hold the fuse into position are makeing tight contact. ( this assumeing you still have the original fuse holder installed. If so, its highly reccomended to replace the entire fuse block with ATM type fuse holder )

 

Also, replace the 15 amp Ignition fuse, even if it looks good.

 

Open up, and Clean the contacts of the "" RUN-STOP "" SWITCH on the right handle bar, If this switch is going from an completly " closed position ' ie; Zero Ohm, contact. to a high resistance state, then the Voltage to the Entire Ignition system will be lost. ( Clean the Switch )

 

From that switch follow the cable to behind the head light assembly, to a Plug, Check that plug Also.

 

 

Find the " Barometric Pressure Sensor " located Forwad, and above, the Left side forward Carburator " Its hard to get to , but its there. Now, Remove the Rubber Boot covering the Electrical plug on bottom of the Sensor.

Its a 3 Pin connector, Clean the Pins, and Make Sure, there is no water or crud in the rubber boot. This item is also powered by the 15 amp Ignition fuse,

Try running the engine with this plug removed, for a few test runs.

Its also possible that a defect inside this electrical item, can be dropping or shorting out the Voltage supply to the TCI ( Ignition system )

 

 

Find the Cable from the Ignition system pick up coils located under the left engine case cover. ( If you loos the signal from the pick up coils to the TCI the engine will quit ) . This " Might " be your problem. There is a 5 wire plug, located just about under you left knee as you sit on the bike, Open the Plug, and clean the contacts with contact cleaner. Inspect the 5 sets of male , female pins, make sure they are makeing GOOD contact. This plug pass's low voltage signals from the pick up coils to the tCI to fire the System.

 

 

If all this fails, the Remove the TCI from under the Air cleaner box.

Remove the cover from the TCI Unit.

Put the unit in OVEN at 110 deg. F. for 2 hours to DRY OUT THE MOISTURE THAT IS!!! IN THE UNIT. (( This is a very common problem with these units ))

 

Now, there are two plugs on the box, one has six wires the other 8 wires,

Follow the 14 contact to the circuit boare, and useing a 15 Watt Pen soldering iron and Rosin Core Solder, Resolder all these 14 conect points to the Circuit board of the TCI unit.

 

Also, at the Right front corner of your engine crankcase, find the Black neg battery cable, where its grounded to the engine case. Remove the Corroded Bolt, and Clean the threads, clean the stud on end of cable, ( the #6 wire black cable ) and then use a Propane torch , and Resolder the Stud to end of cable.

You might have a bad ground.

 

 

Next. --- Under the Upper, left side fairing, on the upper frame member, there is a MAIN GROUND STUD--- Find this. Its hard to get to. There are about 4 black wires connected there. These wires provide Ground Return for All electrical systems on the entire bike. CLEAN ALL THOSE WIRE ENDS, and resolder the studs to the black wires.

 

Find the Main wire cable ( 3 #14 wires from Stator to Voltage regulator ) left side of bike, above the left foot peg. Open the plug, check for BURNT PINS, DAMAGED PINS, PINS THAT ARE NOT MAKEING GOOD CONTACE. This is a known high failure rate point !!!!!!!!!!! IF PLUG IS HIGHLY DAMAGED, CUT IT OUT AND SPLICE THE WIRES TOGETHER, AND SOLDER THE NEW SPLICES !!!!!!!!!!

 

Find the Lagre Plug comeing FROM---- the Rectifyer/Regulator Unit. 2 red wires, and 2 black wires going thru it. AGAIN open and inspect and clean the contacts.

 

At this point, you should have found something wrong.

 

Consider alll these item's to be a witch hunt, Good luck

[6m459]

Hi,

 

The problem you describe sounds very much like the intermittent, heat related misfire under load at 3k rpm's and above, that I have been experiencing for the last couple of seasons. It started small and got worse over the course of a couple of seasons.

 

Recently I could stand it no more so, having satisfied myself that other areas like those enumerated in the previous post were not my problem, I set to and dug the TCI box out of its stock location and relocated it on top of the air box as per VR.org lore and advice . I found that the TCI connections were a bit crusty so I gave them a rudimentary clean up.

 

Seems to have the problem 90% fixed. I still get a brief band as the engine comes up to operating temperature. Its quite abrupt and goes away completely now by the time the temperature is up. I think more cleaning / tightening of connections and possibly a look inside the TCI box for cracked broken or cold solder joints, will eventually rid me of the problem completely. I am encouraged.

 

Moving the TCI box is not a 5 minute job. It took me both days of a weekend, by the time I got things back together. Now that I have it relocated for better accessibility, I can work on the TCI and its connections at my leisure.

 

I think that changing the fuse box is another area that you should definitely look at regardless of its involvement in your current problem. The OEM one is a piece of junk and needs to be replaced with a more modern one that accespts ATC type fuses. See other posts on how others have tackled this.

 

Hope this is of some interest & good luck!

 

Cheers,

 

Brian H.

[Tieftoener]

Hey folks,

 

Thanks again for all your help. I only got one notification for randya's post, so I'm just now getting to see all the other help flooding my way

 

Unfortunately, the bike is in storage far away (100 miles) so getting to it is a pain. I did get to go on Tuesday and managed to get the air box off to get at the TCI. What a pain... (my first time).

 

I pulled both connectors off and inspected them. I'm an Avionics Engineer, dealing with daily with $700 connectors and $5/ft wires... It was all I could do not to rip all the wires off the entire bike and start from scratch. 25 years have aged things extensively...

 

There were a few corroded contacts, but after some investigation and scraping, I was able to make decent connections to things with my probe/meter.

 

For what its worth, operating temperature of the bike makes no difference. I rode two-up with my wife two weekends ago on about a 100 mile (round trip) road trip. It was reliably consistent with my calibrated hand at "moderate" throttle. Dead cold or completely heat soaked - consistent results.

 

I incidentally found the Barometric Pressure Sensor, based on George's description. I was unable to disconnect it.

 

The fuse block has indeed been on my list of things to upgrade... I was just trying to find a reason to do it since the bike was working (if it ain't broke, don't fix it mentality).

 

Well, looks like you guys have given me PLENTY to work on and investigate. Thank you so much for everything. I'll keep everyone posted as I make progress.

 

1 question though - when I pulled the air box off, I was trying to trace the spark plug wires back to the coil(s). The wires disappeared under the fairing frame. Where are they (plural?) located, and what's the easiest way to get to them?

 

Regards,

Scott

[Tieftoener]

How is the TCI mounted under there? I didn't have a mirror handy with me on Tuesday.

 

Is it possible to get inside the TCI to inspect for bad solder joints?

 

Thanks,

Scott

[83VR3711]

The coils are located below and just forward of the battery. The easiest route of access is to remove the fairings, both upper and lower. Once those are removed you should have a very clear view of the coils and the wires. Good luck.

Edited August 6, 2009 by 83VR3711

[6m459]

Hi,

 

How is the TCI mounted under there? I didn't have a mirror handy with me on Tuesday.

 

There are two #3 Phillips head screws that go through tabs on either side of the TCI box, holding it to a plate which is bolted at four corners to the frame. The screws are head down so you have to reach under the plate to undo them. There isn't a lot of room for fists or tools under there though and seeing what you are doing while you work is impossible. I wound up removing the battery mount plate and then undoing the 4 mounting bolts at the corners of the TCI mounting plate, so that I could pivot it about 45 degrees off horizontal, to make more room to work. I had to use a box end wrench with a pivoting and ratcheted box end to get the bolts out, as they also are rather inaccessible. Watch out for the grounding wire on the forward port side bolt BTW.

 

Is it possible to get inside the TCI to inspect for bad solder joints?

 

Once the TCI is free of the frame, you can access small Phillips head screws at the corners holding a lid onto the TCI box. Once the lid is off you are presented with the foil side of the circuit board. That is as far in as I have been in so far. Apparently the circuit board can be removed from the box but I have yet to do this so cannot advise you as yet.

 

I understand that there are 8 or so fragile glass body diodes that, 25 years on, are good candidates for replacement with a set of 1n400x ones. I'll get round to that some day too as and when it seems appropriate or, knowing me, unavoidable.

 

Hope this is of interest.

 

Cheers,

 

Brian H.

[Marcarl]

All god technical info so far, but what gets me is that it only seems to do it under predetermined conditions, that you have discovered, in other words you can make it happen or not. That leads me to believe that you might have something to do with it. So check out what you are inadvertantly doing when this happens. Yes, you are cranking on the throttle, but what else is happening. My first thought goes to: what swings back or is pushed back so that a short is created, and when the forward pressure is released by sudden lack of power, what ever caused that to happen, now has 'swung' back out of the way and agian you have power, which then in turn starts the issue all over again. So what happens if you can duplicate this on the center stand, I know that would be entirely impossible, but you can pretend a little a see what happens. The other thing that happens is that you change position as you crank on the power, do you knees grab the bike? if so, try to emulate what your body does without cranking on the throttle, now how does the scoot react,,,,,,,got my idea?

Maybe I just provided some dumb reading, but it kept me entertained for 15 minutes.