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Loss of power, backfires, running on one cyl. (SOLVED)

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Loss of power, backfires, running on one cyl. (SOLVED)

PostAuthor: RusXV1k » Sun Jun 05, 2011 1:47 am

Hi folks,
I've got a 1985 XV1000 that I've had for a couple of years now, and it has run well until recently. This spring,
when I got it out on the road, it would sometimes lose power, backfire, and then "chug" along, running sometimes
on just the rear cylinder.
I decided to get serious, and read the tech material in this forum, and lots of other google-searched stuff, and
learned about the carb issues (I have the Hitachi carbs), and the MCV/AIS mods, etc. I held off for a while, as it
would often start easily, run quite badly (no power, chugging), but once it had warmed up, it would zoom along
just fine, full power, smooth running, etc. But about 2 weeks ago, it became a consistant problem. Everytime
I started it, it would run badly for at least the first 10 minutes of riding. Did not improve. I spent a fair bit of
time fiddling about with the idle mixture screws. But I could get only temporary improvement, sometimes it would
run ok, other times, chugged and appeared to run on only rear cylinder.
I ran a tank of fuel system cleaner thru the bike a few days ago. Didn't seem to solve the problem.
So, I decided to check and clean the carbs. And also remove the MCV ("mixture control valve") stuff.
And I've done that. I removed the Hitachi carbs, disassembled and cleaned them, and confirmed that the
float valve was working ok, all the passageways were clean, etc. Cleaned all the parts in alcohol, confirmed all the
little passages in the Hitachi carbs were open, the black rubber diaphram had no holes, etc. Reassembled it all.
Also, removed the MCV stuff, and ensured that the small black hose from the pressure sensor just above the two
coils just behind front fork, was attached to the smaller nipple on the front carb-boot. Capped off the larger one,
as per the various MCV removal instructions.
Got it all back together, filled gas tank, and bike started no problem, but still does not run well on front cylinder.
Basically, there is little change. The rear cylinder runs fine, But the front cylinder seems to be too lean. It will
run ok on idle, and up to 2500 rpm, but any throttle application above 2500, and the bike "chugs", loses power badly,
and misfires. And it will backfire, sometimes with real drama... Seems like a carb problem, but I was thinking
maybe it could be the TCI?
Any suggestions much appreciated. When I took the carbs off, I did not drill out the bung to remove the choke
tube. Oh, and I've also tried many settings of the idle jet (or pilot jet?) - the little downward-pointing brass
screw beside the carb-bowl. This has virtually no effect on engine operation - anywhere from closed to out 6 turns
and the result remains the same - idle is ok, but power dies above 2500 rpm, with backfire, chugging, misfireing, etc.
I also switched the spark plugs - had no effect. Front cylinder plug is black and wet when I remove it.
Frustrating and annoying problem. Any help or suggestions much appreciated.
- RusXV1K
Last edited by RusXV1k on Wed Jun 15, 2011 2:23 pm, edited 1 time in total.
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Re: Loss of power, backfires, running on one cyl.

PostAuthor: packman » Sun Jun 05, 2011 7:39 am

Had similar problems with my 86 XV700 a few years ago & my problem was a crack in one of the carb holders. Really hard to detect & was not a constant problem but did get progressively worse until I replaced the carb holders. Not sure if you can switch the coil wires & see if the problem moves to the rear cylinder. More knowleagble members may be better qualified to advise. May want to check the coils with a multimeter to rule them out. I have some extra coils if that is the problem & you need them. Good luck.
Packman
([strike]86 YAMAHA XV700 WRECKED[/strike]), 93 YAMAHA XV 750 & 2006 HONDA 750

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Re: Loss of power, backfires, running on one cyl.

PostAuthor: RusXV1k » Sun Jun 05, 2011 12:06 pm

Thx for the suggestion, Packman. I will check that today. In fact, I will go thru all the small hoses and
connectors to make sure the vaccum circuit is tight, as well as the main carb holder boot.
And here is a dumb question.. Since the TCI can have bad capacitors (so I have read), I want to look
at it. Where the heck is it? And any special issues related to removing it? I found all the material
on the Hitachi carbs really useful. Anything similar for the Transistor Controlled Ignition device?
- RusXV1k
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Re: Loss of power, backfires, running on one cyl.

PostAuthor: RusXV1k » Sun Jun 05, 2011 2:18 pm

Ah ha! An update: I found a suggestion from another fellow via a google-search, re. the electrical
system. I got a timing light, and connected it to the front cylinder, and used a battery charger as the
timing light power. Sure enough, I have flash/flash/flash... at low speed idle, and then *nothing*
at anything above 2500 rpm. Just to confirm the test equipment, I did the same test on the back
cylinder which runs OK, and got the flash/flash/flash of the light at all rpm settings.
So, I know for sure it is an electrical problem. Carbs and vacuum system are ok. Anyone
have any suggestions re the TCI? I'm now going to start tracing thru the wiring/connecters/coils,
etc. Probably it's a bad coil or bad capacitors in the TCI. I'll post here if and when I track it down...
- RusXV1k
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Re: Loss of power, backfires, running on one cyl.

PostAuthor: packman » Sun Jun 05, 2011 4:23 pm

TCI unit is usually a blck box (sometimes gold, but my 86 had the black plastic box) fastened to the rear fender just above the battery box. It usually has 2 wiring connectors that fasten to it. It is not something most people can mess with, but you can clean the connections & possibly fix the issue as they do get corroded over time. I think there is a 6 pin & a 4 pin connector. They can be a bugger to get apart to clean the female ones, but it can be done & does make a difference. Try that before you consider looking at the TCI. Good luck.
([strike]86 YAMAHA XV700 WRECKED[/strike]), 93 YAMAHA XV 750 & 2006 HONDA 750

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Re: Loss of power, backfires, running on one cyl.

PostAuthor: anaman51 » Sun Jun 05, 2011 6:00 pm

After pulling the plastic connector block apart, you'll find that you can look down into the back side of each part of the plastic block, the side that the connectors are inserted from, to find a small tab there. If you push that tab aside with a small screwdriver, the connector can be pulled out. Slide it out the back of the box and start cleaning! I used steel wool on the male side, and emery boards cut to fit on the females. Before reinserting into the plastic block, re-crimp the wire at the back of each connector. This will help ensure good connections between the TCI and the coils.

Dan
:con: An analog man in a digital world.

'81 XV750---Mods: Battery ground modification, forward controls, four brush starter, Jardine slip-on exhaust, custom seat.

Riding my Virago is knowing pure freedom. :chop:


PLEASE RIDE SAFELY!
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Re: Loss of power, backfires, running on one cyl.

PostAuthor: zfoxfire » Wed Jun 08, 2011 3:18 pm

Just contributing my own experience with the TCI. I have had serious backfiring recently as well as a loss of power on the cylinder that also gets the pulses going to the tack. So loss of power and tach drops to zero.

I just "rebuilt" my TCI box by replacing the electrolytic capacitors and also the power transistors. It seemed to make a bit of an improvement on idle and acceleration but after 20 minutes it did it again! I'm going to go over it one more time. I'd like to clean all the parylene off the board as I plan to seal the box for moisture control instead. No serious backfire so far

Anywho, maybe its something simple like a bad soldering joint. I hope so. I may replace all the smaller transistors as well. I don't suspect a ceramic capasitor or a resistor could cause an intermittent problem. If no luck, I'll just get a replacement. I've seen aftermarkets for under $200 somewhere.

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Re: Loss of power, backfires, running on one cyl.

PostAuthor: zfoxfire » Fri Jun 10, 2011 9:02 am

Suggestion: Start the bike and disconnect the tachometer and drive around for a while. They can short and I thought I tested it before but I didn't test properly. So it looks like this was my problem all along. The bike ran flawlessly and strong for 100 miles. It acted up a few times in the end but very briefly. I reached back and touched a wire and the problem went away so I'm going to rip apart the "console" wiring and look for damage. That would explain why sometimes the tach would cut out and the bike still ran fine.

Rebuilding my TCI was a good idea still. The new caps and transistors are making the bike run really strong now.

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Re: Loss of power, backfires, running on one cyl.

PostAuthor: Buslin » Fri Jun 10, 2011 11:11 am

Wouldn't it be a good idea to see if you are getting an earth pulse from the TCI before you condemed it ?

Timing light tells you the plug lead has no power but the same result could be got from a coil thats breaking down. Or the lead is breaking down.

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Re: Loss of power, backfires, running on one cyl.

PostAuthor: RusXV1k » Wed Jun 15, 2011 2:20 pm

Hi all. Thanx to everyone for suggestions. It appears problem
is defn. electrical, and seems to be the TCI circuit related to
the timing advance. I would lose front cyl. spark everytime,
at around 2000 rpm. Figured it might be related to the timing
advance circuit - little box above the two coils on front forks.
(confirmed it was not coils, by swaping in another coil - first
to rear cyl to confirm old external coil was good - then into
front cyl, to confirm loss of spark was not coil related - bike
looked like an electrical experiment - but I knew coil not the
problem when that diag. was done)
Oh, I also disconnected and removed TCI, and cleaned all
electrical connectors, and confirmed physical integrity of
the TCI box and all its wires. (long process - made every
connector shine like a new penny...) Was not problem,
but I note neutral light shines a bit brighter.
Anyway, simply disconnecting the electrical connector to
the vaccuum advance circuit solved the problem. With the
vacuum advance *electrical* connection *NOT* connected,
I had spark on the front cyl at all rpm!
Surprising. Note the vacuum line is still connected, so I am
not getting air sucked into front port. Also, I removed the
MCV vacuum circuit - the whole thing, and plugged the
other vacuum hole on the front cyl carb port.
I needed to clean up the fouled front plug to get a good
clean spark, but once that was done, I found that the bike
runs just great!
I sometimes get a little bit of a hiccup under heavy
acceleration, when the engine is still cold - but I get *NO*
backfiring!
The bike runs just wonderful - though sometimes, only
when cold (first four minutes running) a little bit of
miss on the front under heavy acceleration - sorta
consistant with not having timing advanced...
Probably the utter failure of the timing advance
circuit is due to a bad capacitor on the TCI. And my
fix is a bit of a kludge. But I've changed the oil and
filter, and run the bike for many days now, and it
continues to run really well.
Oh, I also put a tiny shim in the main needle valve
when I cleaned the front carb. Bike seems to start
best at half to three qtr choke now. And my XV1000
has 65,000 km on it. My dual Hitachi's seem quite OK.
It was an electrical issue,solved by removing the
timing advance electrical connection to the sensor.
This winter, I will trace down the TCI, or just
get another, maybe. Thanx again to those who
made suggestions and comments. When the Virago
runs well, it is a real joy to ride.
- Rus.
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My "Loss of power, backfires, running on one cyl."

PostAuthor: kyron » Sun Aug 07, 2011 10:48 am

I moved this post to its own thread (posting in a "solved" thread won't get me much help ;)
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Re: Loss of power, backfires, running on one cyl. (SOLVED)

PostAuthor: Danl » Thu Nov 22, 2012 5:13 pm

Check your stator this bike runs hot and is tough on the stator. The problem only shows up after the bike is hot.....the stator is bad.
Another way is watch your neutral light whens the bike is running and turn on the directional or hazard lights. If the neutral or head light is flickering thats another sign the stator is bad.

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Re: Loss of power, backfires, running on one cyl. (SOLVED)

PostAuthor: Bane » Wed Jun 05, 2013 2:11 pm

Reviving an old thread.
I have an '85 XV1000 as well that is experiencing similar problems.

Never had the chugging unless the plugs were fouled.
ALWAYS backfires since I picked it up 3 years ago, to the point where I've grown so accustomed to it, I don't mind it at all (neighbours might disagree after long late night cruises, lol)... Not the cartoon explosion backfire, just a lot of loud popping on downshift or throttle cut.

Today definitely know it cut to one cylinder. As I was on the highway, you can imagine my concern!
Thought it might be carbs or a poor ground (which i suspect is still an issue regardless).

Last night before this started acting up I also notice that my headlight brightens when i'm sitting at idle and just rev the motor a bit.

Will definitely check out both the vaccuum advanced circuit and the stator.

Are both original posters still active here in case I have any questions?
Thanks,

James
___________

'85 xv1000 - mine
'09 Honda DN-01 - wifey's
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Re: Loss of power, backfires, running on one cyl. (SOLVED)

PostAuthor: Quarinteen » Wed Nov 22, 2017 1:04 am

I believe I have a similar issue. How do you test with a battery charger?

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