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New-to-me 86 XV700 with carb issues

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Re: New-to-me 86 XV700 with carb issues

PostAuthor: Flyingdog » Sat Jul 27, 2019 7:08 pm

jamesm113 wrote:Got it running!

:GJ:
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Re: New-to-me 86 XV700 with carb issues

PostAuthor: jamesm113 » Sat Jul 27, 2019 10:22 pm

Alright took it for a few rides this afternoon. 95% of the time, it runs great- smooth, accurate throttle response, from idle to wide open. No dead spots, etc. Seems to me carbs are working great and jetting is spot on.

However, there's two intermittent issues.

* At idle, it will start stumbling and eventually die. I usually have to hold it wide to get it start up again. Once it gets going, it stumbles and I have to blip the throttle to keep it running. It backfires like crazy in this state too (sounds like gunshots).

* At end of a few WOT pulls on the freeway, it started to cut out and sputter. Most power was lost. I pulled over to the shoulder and it died immediately and I couldn't get it started again, until I turned the petcock to prime, then it ran perfectly.

It's aftermarket petcock (looks like this one ebay: link), and both the fuel line & vac line are weirdly routed, I wonder if it's not getting a good enough fuel flow.

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Re: New-to-me 86 XV700 with carb issues

PostAuthor: Hellgate » Sun Jul 28, 2019 8:50 am

Did you set the float height? From what you describe they sound low.
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Re: New-to-me 86 XV700 with carb issues

PostAuthor: Jake » Sun Jul 28, 2019 9:47 am

jamesm113 wrote:I couldn't get it started again, until I turned the petcock to prime, then it ran perfectly.


Suggests a kinked or pinched vacuum line.
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Re: New-to-me 86 XV700 with carb issues

PostAuthor: jamesm113 » Mon Jul 29, 2019 1:44 am

Well today's been a fun one. Determined the rear cylinder (#1) is not firing when it gets into a rough idle state. Once the tach hits about 3k, it will all of sudden fire.

Had a friend over and we pulled the carbs twice. Reset the float levels around 19mm. Toyed with the stops on the floats so they don't go too far out. Confirmed the floats are not overflowing. We also re-cleaned the pilot circuit in #1.

We monkeyed around with the petcock some more too. Prime probably doesn't have enough fuel flow to handle extended periods of 70+mph. The petcock also requires a fair amount of vacuum to operate properly, and hooked up to #1 cylinder, it might not be getting enough. I've ordered a used OEM petcock off of ebay and a rebuild kit.

However, we could never get the #1 cylinder consistently firing between idle and 3k. When we pulled the spark plug, it was not wet.

I also noticed the tach is fluttering around a bit during these weird states. Some late night googling indicates a bad TCI could be an issue, particularity this post:
http://yamaha-virago.17922.x6.nabble.co ... l#a4714495, which says
If it fires above about 3000 RPM but misses below that or at idle, the most likely candidate is the TCI unit.

and this post kinda touches on it:
https://www.viragotechforum.com/virago-ignition-systems/

Also this one: http://viragotcirepair.com/symptoms.htm

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Re: New-to-me 86 XV700 with carb issues

PostAuthor: chrismalm » Tue Jul 30, 2019 11:59 am

With the wonky tach needle, the TCI is a likely suspect. If you have already confirmed the correct coil & plug boot resistance, and cleaned and re-crimped the TCI connectors, and the battery, alternator output and ground connections test good, you'll need to repair or replace your TCI.
I have had two failed plastic box TCIs. I have never had a bad metal box TCI. The metal box TCI can be adapted to the later model wire harness by shortening a cable and rearranging the pins in one or both plugs (don't remember exactly). I think I have a converted metal box TCI if you want to go that route.
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Re: New-to-me 86 XV700 with carb issues

PostAuthor: jamesm113 » Tue Jul 30, 2019 4:37 pm

I checked coil and boot resistance. They were close to the one spec in the clymer's manual. (Within 10%)

Did a compression test too. Was right below 150 psi on both cylinders, so I don't think it's compression.

Battery was freshly charged by a battery tender jr, and was recently replaced.

What do you mean by re-crimping the TCI connectors?

I'll test battery and alternator output. But I think I've convinced a buddy to perform a reflow on the TCI board. This post was pretty helpful in convincing me to try it out: https://viragotechforum.com/phpbb3/viewtopic.php?t=25

Of course, the plastic box is a little different, but a lot of the concepts are the same.

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Re: New-to-me 86 XV700 with carb issues

PostAuthor: jamesm113 » Tue Jul 30, 2019 8:42 pm

Alright, checked the battery voltage at rest (12.5-12.6V). When the bike is running, i measured 13.5-13.7 across the battery terminals (or between the negative terminal and the red wire), but drops to 13V when I rev it. Seems ok.

Cleaned the TCI connectors and it seems to run ok now. Except every time I rev the damn thing, the oil light comes on. Wait a minute or two for the oil to drain down into the sight window, and the oil level is OK.

I recently changed the oil with Rotella T4 15W40 (no oil filter), and put in 3.2 quarts. It was almost exactly at the full line in the sight window when I finished filling it up.

This bike feels like playing a game of whack a mole. Any insight on the oil light?

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Re: New-to-me 86 XV700 with carb issues

PostAuthor: pastot » Tue Jul 30, 2019 11:49 pm

Haven't read every thread contribution but I have a brand new 85 virago 700 perfectly factory new (<2 miles on it). It also would only idle with choke on nearly full. I pulled the carbs and everything is clean. Blasted cleaner throughout the pilot circuit and got kick back on right side carb. Drilled the pilot screw covers out and found #1 pilot screw turned in all the way in. Not sure why factory would do this but I think I found my issue. Have a sure filter and carb bowl gasket to replace in a couple days and I'll know. Both pilot screws are backed out equally now to 1 1/4 turn (#2 we at 1 1/4). Mine essentially only idled on one cylinder. I can blow carb cleaner through both now.

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Re: New-to-me 86 XV700 with carb issues

PostAuthor: jamesm113 » Wed Jul 31, 2019 12:36 pm

Alright, so I cleaned the TCI connectors and had a friend who's handy with a soldering iron reflow all the solder joints in the TCI. All the gunshot backfires are completely gone.

Of course, I still get stranded on my test ride. The bike seems to cut out after long runs with prolonged throttle openings, especially at highway speeds. I'm thinking it's fuel starvation from the cheap chinese petcock and the wonky fuel line / vacuum line routings. Also, the chinese petcock's vacuum port has a significantly smaller ID than the port on the rear cylinder's intake boot, so it's very possible there's a vacuum leak and not enough vacuum is getting to petcock to supply proper fuel flow.

I have an OEM petcock from an 81 XV750 coming in from eBay, so hopefully that's the end of it. Otherwise, I'm probably out of ideas.

@pastot - Unless you are at a higher elevation, I'd suggest 2 turns out as a starting point. I'm running 3 turns out at sea level, but have an aftermarket exhaust. Whenever they put in those EPA-mandated brass plugs, they are almost always too lean.

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Re: New-to-me 86 XV700 with carb issues

PostAuthor: jamesm113 » Wed Aug 07, 2019 8:15 pm

OEM petcock arrived in rough shape. Had to clean it out and use a rebuild kit. Of course, on/reserve still flow gas without vacuum, but at least prime and on/reserve give a much better flow. Issues at highway speeds are now resolved.

Of course, a new issue has been discovered. The clutch slips at highway speeds.. joy...

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Re: New-to-me 86 XV700 with carb issues

PostAuthor: jamesm113 » Thu Aug 08, 2019 1:39 pm

Well, adjusting the clutch was fun. I followed these steps/the steps in the Clymer manual: http://viragotech.com/newtech/How%20to% ... clutch.htm

Of course, I pull the lever, so the steel balls become disengaged. I panic as I thought the balls were loose in there, and decide to pull the left side crank cover. That was a fun 3 hour detour.

In the end, I learned that if you disengage the steel balls, YOU DO NOT HAVE TO PULL THE LEFT SIDE CRANK COVER.
Simply tighten the adjustment screw and turn the adjustment screw until the steel balls engage.

I've attached pics in case anyone ends up down the same road.
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Re: 84-85 xv700 bare diagram

PostAuthor: jamesm113 » Thu Aug 22, 2019 12:38 am

Where does the wiring harness get grounded? I've been searching for it more than I care to admit...

I see the battery negative terminal meets the right crank cover & the rear brake switch's mounting bracket, but can't find the where the black wire on the main wiring harness gets grounded.
Last edited by Jake on Fri Aug 23, 2019 6:04 am, edited 1 time in total.
Reason: Post moved from "84-85 xv700 bare diagram" to this thread

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Re: 84-85 xv700 bare diagram

PostAuthor: Cusstout 1100 » Thu Aug 22, 2019 9:15 am

There's a black wire grounded to the frame/airbox hidden behind the left pod and just under and above the bottom edge of the gas tank. I think that's the one you're looking for. It's held there with a small sheet metal screw.
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Re: New-to-me 86 XV700 with carb issues

PostAuthor: jamesm113 » Thu Aug 22, 2019 6:05 pm

Well, cylinder #2 is having trouble again. Tach flutters and gets lots of misfires and loss of power. Seems to only happen when the bike is cold. After I've been riding for 5 minutes, the misfires are gone.

I tried unplugging the tach to rule out a short there, but the misfires still occurred.

Where does the wiring harness get grounded to the frame? Looking at the wiring diagrams, that seems like a likely candidate. I've already cleaned the battery negative to engine ground wire.

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Re: New-to-me 86 XV700 with carb issues

PostAuthor: jamesm113 » Fri Aug 23, 2019 1:40 am

I discovered some of the turn signals, the tail light, the gauge cluster and the headlight/turn signal switch were also partially grounded. With all of those plugged in, the frame ground lead had 5 ohms of resistance between it and the negative battery terminal.

After cleaning everything up, I'm getting 0.6 ohms of resistance between the negative battery terminal and backprobing the TCI ground input. If that's a consistent value (ie it's not relying on the ground coming from the turn signals/tail lights/cluster/etc), I doubt it's a bad ground. Next likely candidate would be new caps inside the TCI. Fingers crossed for my next ride.

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Re: New-to-me 86 XV700 with carb issues

PostAuthor: jamesm113 » Tue Sep 03, 2019 10:25 am

Needed new caps. Had the same friend who reflowed the board install the new caps. There were 10 caps to replace, 6x 1uf and 4x 4.7uf. All are 50V. I (ordered 10 of each from DigiKey.com, about $10 after shipping. Stock caps rated for 85C temps. Following Dave Denowh's advice (link: http://viragotcirepair.com/recondition.htm), I went with 105C for longer life. Hopefully it works.
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