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1994 Yamaha Virago 750 cuts out

Have a question about fixing something on a Yamaha Virago XV750? Post it here!
SteveVirago
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1994 Yamaha Virago 750 cuts out

Post by SteveVirago » Sat Oct 12, 2019 7:19 pm

I am new to the forum. I recently bought a 94 Virago 750. It starts up with no choke and runs perfect up to about 5000 rpms and then bogs and doesn't want to rev up into the higher rpm range above 6000 rpms unless in lower gears. I live on back roads so it's not a big deal but I would like to be able to rev it up without an issue. Occasionally, I can be driving along and then it will act like its running out of gas until complete fuel starvation. I have to pull over, open the gas cap for about a minute and then it will start up without any problem.

Should I be looking at anything in particular? The gas cap looks okay. The big rubber gas cap o-ring is new as of two months ago. We put a manual petcock on it about two months ago and closed off the end of the vacuum line. The tank is clean inside. Thank you for your input!

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ViragoJoe
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What Virago you Own: 1996 Virago Special XV1100SH
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Re: 1994 Yamaha Virago 750 cuts out

Post by ViragoJoe » Sun Oct 13, 2019 2:42 am

SteveVirago wrote:
Sat Oct 12, 2019 7:19 pm
I am new to the forum. I recently bought a 94 Virago 750. It starts up with no choke and runs perfect up to about 5000 rpms and then bogs and doesn't want to rev up into the higher rpm range above 6000 rpms unless in lower gears. I live on back roads so it's not a big deal but I would like to be able to rev it up without an issue. Occasionally, I can be driving along and then it will act like its running out of gas until complete fuel starvation. I have to pull over, open the gas cap for about a minute and then it will start up without any problem.

Should I be looking at anything in particular? The gas cap looks okay. The big rubber gas cap o-ring is new as of two months ago. We put a manual petcock on it about two months ago and closed off the end of the vacuum line. The tank is clean inside. Thank you for your input!
Steve,
Sounds like you may be having a venting issue. Read this article on:
Virago Fuel Systems:
https://www.viragohelp.com/virago-fuel-systems/
ViragoJoe
1996 XV1100SH Virago Special
"Never ride faster than your Guardian Angel can fly!!"
;)

SteveVirago
Posts: 13
Joined: Sat Oct 12, 2019 6:57 pm
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Re: 1994 Yamaha Virago 750 cuts out

Post by SteveVirago » Sat Oct 19, 2019 6:14 pm

I put a new gas cap on it and a new set of plugs. I'm also running sea foam through it. This evening when I took it out for a spin with the new gas cap, it ran fine up until about 5000 rpms and then bogged and hesitated up to 7500 rpms and then fully died out like I shut the key off. When I let off the throttle, it was running on 1 cylinder and making lean pops on the other. I pulled over and it idled correctly. When I took off from idle, it ran on one cylinder for a few minutes and then both. It seems to run fine if you keep it under 5000 rpms. Once you go over that, the problems start.

The bike sat before I bought it. I rinsed the tank out thoroughly and have since checked the new petcock screen. It's clean. When I open the carb bowl screws with a white rag underneath, I don't see anything dirty coming out of the carbs.

On the one hand, it seems like fuel starvation from the tank. On the other hand, I'm wondering if the main jets are tarnished or clogged up. Thanks for the input!

SteveVirago
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Re: 1994 Yamaha Virago 750 cuts out

Post by SteveVirago » Sat May 02, 2020 5:20 pm

I rebuilt the carbs. They didn't look too bad when I pulled them apart. The main jets were not clogged up. After a good cleaning and installing the rebuild kits, it does the same thing as before, bogs at 5000 rpms and higher and won't reach red line in 4th or 5th. Starts up perfect with no choke, idles perfect and runs perfect up to about 4000-5000 rpms then starts bogging with more throttle. The rubber carb vacuum boots looked good and do not have any cracks. The Intake rubber boots look good including the o-rings up against the cylinder walls.

I'm baffled. Should I be looking for a vacuum related problem since I believe that I've covered fuel starvation concerns? Forum input would be greatly appreciated!

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ViragoJoe
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Re: 1994 Yamaha Virago 750 cuts out

Post by ViragoJoe » Sun May 03, 2020 4:58 am

SteveVirago wrote:
Sat May 02, 2020 5:20 pm
I rebuilt the carbs. They didn't look too bad when I pulled them apart. The main jets were not clogged up. After a good cleaning and installing the rebuild kits, it does the same thing as before, bogs at 5000 rpms and higher and won't reach red line in 4th or 5th. Starts up perfect with no choke, idles perfect and runs perfect up to about 4000-5000 rpms then starts bogging with more throttle. The rubber carb vacuum boots looked good and do not have any cracks. The Intake rubber boots look good including the o-rings up against the cylinder walls.

I'm baffled. Should I be looking for a vacuum related problem since I believe that I've covered fuel starvation concerns? Forum input would be greatly appreciated!
I'm baffled. Should I be looking for a vacuum related problem since I believe that I've covered fuel starvation concerns? Forum input would be greatly appreciated!
Yes, definitely check for vacuum leaks. I know you said Carb boots look good. Just looking good doesn't mean they can't leak. Check all vacuum lines for leaks as well.

Also, have you checked your carburetor float levels. They may need adjusting.

See this Posting:
1995 XV750 carburator float specs and idle pilot screw (SOLVED)
viewtopic.php?f=41&t=1176&p=4579#p4579

They can also be checked via the hose method:
Re: float adjustment
viewtopic.php?f=44&t=368&p=741&hilit=floats%2A#p741
ViragoJoe
1996 XV1100SH Virago Special
"Never ride faster than your Guardian Angel can fly!!"
;)

SteveVirago
Posts: 13
Joined: Sat Oct 12, 2019 6:57 pm
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Re: 1994 Yamaha Virago 750 cuts out

Post by SteveVirago » Sun May 03, 2020 12:11 pm

Yes, I have the floats set at 25 mm. I checked my coils with a meter. The ohm readings check out good. However, when I checked the ignition timing this morning, which aligns properly on the "F" mark, my rear cylinder strobe light had an inconsistent blinking strobe light. The front cylinder has a consistent blinking strobe. I checked several times to make sure there was a good connection with the timing light. Front cylinder consistent blinking strobe light, rear cylinder inconsistent strobe. My next step will be to replace the rear coil.

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ViragoJoe
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What Virago you Own: 1996 Virago Special XV1100SH
"Never ride faster than your Guardian Angel can fly!!"

Re: 1994 Yamaha Virago 750 cuts out

Post by ViragoJoe » Sun May 03, 2020 12:48 pm

SteveVirago wrote:
Sun May 03, 2020 12:11 pm


Yes, I have the floats set at 25 mm.

I checked my coils with a meter. The ohm readings check out good.

However, when I checked the ignition timing this morning, which aligns properly on the "F" mark,

my rear cylinder strobe light had an inconsistent blinking strobe light. The front cylinder has a consistent blinking strobe. I checked several times to make sure there was a good connection with the timing light.

Front cylinder consistent blinking strobe light,
rear cylinder inconsistent strobe.

My next step will be to replace the rear coil.
TIMING MARKS: (XV700 thru XV1100)
TIMING MARKS XV700 THRU XV1100.png

Yamaha Virago Tuneup

https://www.viragohelp.com/yamaha-virago-tuneup/


Short Takes–Misc. Subjects/Fixes – Virago Tips
(Scroll down and read #9 Timing).
https://www.viragohelp.com/short-takes- ... rago-tips/


Trivia:

Here's another phenomenon to ponder. Just trivia, how many times does your Spark Plug fire on one complete cycle of a 4 cycle motorcycle engine or any small 4 cycle engine that depends on a flywheel for electrical power. Would you believe twice?! One occurrence of that double spark is considered or called wasted Spark.
https://www.youtube.com/watch?v=Bchzjslk3-M

NGK Spark Plugs Learning Center
https://www.ngk.com/learning-center/art ... on-systems
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ViragoJoe
1996 XV1100SH Virago Special
"Never ride faster than your Guardian Angel can fly!!"
;)

SteveVirago
Posts: 13
Joined: Sat Oct 12, 2019 6:57 pm
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Re: 1994 Yamaha Virago 750 cuts out

Post by SteveVirago » Sun May 03, 2020 5:34 pm

I typically use WD-40 to check for leaks around the carb intake boots. Everything seemed fine with the air leak check until I went back this afternoon with carburetor cleaner. That made all of the difference in the world for the leak check. Both sides are original and leaking. I will buy a set of new intake boots and hopefully resolve the issue once and for all!
The interesting thing is that the WD-40 didn't yield any idle changes before or after the carb rebuilds around the boots. Switching to carb cleaner instead of WD-40 gave me a better result for checking for leaks around the boots. Thank you for the input while I get this resolved.

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ViragoJoe
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Re: 1994 Yamaha Virago 750 cuts out

Post by ViragoJoe » Sun May 03, 2020 6:05 pm

SteveVirago wrote:
Sun May 03, 2020 5:34 pm
I typically use WD-40 to check for leaks around the carb intake boots. Everything seemed fine with the air leak check until I went back this afternoon with carburetor cleaner. That made all of the difference in the world for the leak check. Both sides are original and leaking. I will buy a set of new intake boots and hopefully resolve the issue once and for all!
The interesting thing is that the WD-40 didn't yield any idle changes before or after the carb rebuilds around the boots. Switching to carb cleaner instead of WD-40 gave me a better result for checking for leaks around the boots. Thank you for the input while I get this resolved.

Thanks for the update.


WD-40
is flammable (yet, lacks the gusto or punch). Not as highly combustible as Carburetor Cleaner and/or Starting Fluid. Main reason I suggest using Starting Fluid to find vacuum leaks. I know that it is highly combustible for it is made to start engines and to do the test outside with a fire extinguisher at the ready for safety.

I think you may have resolved your "cuts out" issue.

Let us know the out come, for it can help and assist others experiencing the same issue.
ViragoJoe
1996 XV1100SH Virago Special
"Never ride faster than your Guardian Angel can fly!!"
;)

SteveVirago
Posts: 13
Joined: Sat Oct 12, 2019 6:57 pm
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Re: 1994 Yamaha Virago 750 cuts out

Post by SteveVirago » Thu May 07, 2020 6:23 pm

I installed new K&L carb intake boots. My Bike runs 50% better gaining higher rpms but still has bog preventing redline in the higher gears when I test drove it. When I returned from the test drive, I got the carb cleaner out and found the front cylinder boot leaking. I have nothing left to work with regarding the original OEM boot clamp, it's not holding its original shape. I can't get it to stop leaking.

I don't see any OEM clamps advertised. Has anybody successfully used a radiator style hose clamp or T-clamp on these intake boots, or have something else in mind that works? Thank you for the input.

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