Can't Figure out Non-starting 1994 Virago 750 (Central Virginia)

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SteveVirago
Posts: 20
Joined: Sat Oct 12, 2019 6:57 pm
Location: Central Virginia
What Virago you Own: 1994 Yamaha Virago 750

Can't Figure out Non-starting 1994 Virago 750 (Central Virginia)

Post by SteveVirago » Wed Jun 09, 2021 8:21 am

Engine received honing and new rings all within tolerances, heads passed leak down test before engine reassembly and compression is good. Valve clearances have been checked and rechecked on both cylinders. Cam chain timing is spot on for both cylinders. Bike has blue spark, carbs and jets are clean and passages were also checked with compressed air. Carbs have fresh gas in them. Clear tube method looks like we have the float levels correct for it to run. Bike has new intake rubber boots. We do not see any vacuum leaks. Will only start with starting fluid or a few drops of gas in the cylinders. Both coils were checked for proper wiring on each cylinder. We think its a fuel delivery problem to the cylinders but new intake boots and clean carbs with fresh gas in them reveal that it may be something else that we can't seem to figure out or are missing with our diagnosis.

We are out of ideas and energy on why this good looking piece of junk won't start on its own. My father can usually get anything running but not this thing. I hate to see it turn into a parts bike but that's where it's headed in short order. Any suggestions?

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ViragoJoe
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Re: Can't Figure out Non-starting 1994 Virago 750 (Central Virginia)

Post by ViragoJoe » Sat Jun 12, 2021 4:41 am

SteveVirago wrote:
Wed Jun 09, 2021 8:21 am
Engine received honing and new rings all within tolerances, heads passed leak down test before engine reassembly and compression is good. Valve clearances have been checked and rechecked on both cylinders. Cam chain timing is spot on for both cylinders. Bike has blue spark, carbs and jets are clean and passages were also checked with compressed air. Carbs have fresh gas in them. Clear tube method looks like we have the float levels correct for it to run. Bike has new intake rubber boots. We do not see any vacuum leaks. Will only start with starting fluid or a few drops of gas in the cylinders. Both coils were checked for proper wiring on each cylinder. We think its a fuel delivery problem to the cylinders but new intake boots and clean carbs with fresh gas in them reveal that it may be something else that we can't seem to figure out or are missing with our diagnosis.

We are out of ideas and energy on why this good looking piece of junk won't start on its own. My father can usually get anything running but not this thing. I hate to see it turn into a parts bike but that's where it's headed in short order. Any suggestions?
Steve,
Will only start with starting fluid or a few drops of gas in the cylinders.
Sounds like a carburetion issue. If bike is firing up with the above methods then your problem would have to be Carburetion.
ViragoJoe 🇺🇸
1996 XV1100SH Virago Special
"Never ride faster than your Guardian Angel can fly!!"
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SteveVirago
Posts: 20
Joined: Sat Oct 12, 2019 6:57 pm
Location: Central Virginia
What Virago you Own: 1994 Yamaha Virago 750

Re: Can't Figure out Non-starting 1994 Virago 750 (Central Virginia)

Post by SteveVirago » Sat Jun 12, 2021 8:19 am

Thank you for responding. Agreed, we think it's a carb issue, too. Tank has fresh gas and carb bowls have gas in them. Yesterday, we pulled the plugs first to verify that they were dry. We put them back in and tried starting it with and without choke and opening the throttle. No response. We pulled the plugs back out and they were bone dry.

When we go thru the carbs, the idle jets are clean and you can see thru them. We cleaned the idle jet circuits and squirted WD40 thru them to verify that liquid is getting thru them. The idle circuits worked on both carbs and we also blew compressed air thru them. Both carbs have new rubber intake boots and fit good and snug.

We just can't seem to figure this problem out. At this point, we think we are missing something in both carbs but don't know what it is since we been thru them several times and they seem to check out okay. Is there a simple way to check the idle circuits on these carbs to make sure we have them working correctly while they are apart? We think they are clear with WD40 and compressed air but the dry plugs when trying to start the engine suggest otherwise. Any suggestions on what we might be missing would be greatly appreciated!

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ViragoJoe
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Re: Can't Figure out Non-starting 1994 Virago 750 (Central Virginia)

Post by ViragoJoe » Sat Jun 12, 2021 9:49 am

SteveVirago wrote:
Sat Jun 12, 2021 8:19 am
Thank you for responding. Agreed, we think it's a carb issue, too. Tank has fresh gas and carb bowls have gas in them. Yesterday, we pulled the plugs first to verify that they were dry. We put them back in and tried starting it with and without choke and opening the throttle. No response. We pulled the plugs back out and they were bone dry.

When we go thru the carbs, the idle jets are clean and you can see thru them. We cleaned the idle jet circuits and squirted WD40 thru them to verify that liquid is getting thru them. The idle circuits worked on both carbs and we also blew compressed air thru them. Both carbs have new rubber intake boots and fit good and snug.

We just can't seem to figure this problem out. At this point, we think we are missing something in both carbs but don't know what it is since we been thru them several times and they seem to check out okay. Is there a simple way to check the idle circuits on these carbs to make sure we have them working correctly while they are apart? We think they are clear with WD40 and compressed air but the dry plugs when trying to start the engine suggest otherwise. Any suggestions on what we might be missing would be greatly appreciated!
Steve,
WD40 is good for somethings, however, don't expect it to clean carburetors. It may clean surfaces, yet, not strong enough to budge blocked passages. Also, just because things look clean to the eye that you can see is one thing. But, it is the passages and orifices that you can't see into is where the problem may lie.

Some have good results using specifically made spray type carburetor cleaners and/or brake cleaners and compressor air to clean them. It can be hit and miss. Sometimes you get it right and other times, not so. It can take several carb cleanings to get it really clean and to work properly.

The best method is with ultrasonic parts cleaners. You don't have to run out and purchase one. YouTube has many videos where folks have made them and get great results and cleans the carburetors better than Carb/brake cleaners and compressed air.

When using Spray cleaners, do not get any on diaphragms or rubber parts too strong and caustic for them.

One example:

Ultrasonic Home Made Carb Cleaner

https://www.youtube.com/watch?v=om-yqd4R7jM
ViragoJoe 🇺🇸
1996 XV1100SH Virago Special
"Never ride faster than your Guardian Angel can fly!!"
;)


NOTE TO ALL:
:arrow: Please edit your profile to include your location.
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waspanman
Posts: 35
Joined: Tue Jul 07, 2020 4:22 am
Location: UK
What Virago you Own: 1995 535 1996 750

Re: Can't Figure out Non-starting 1994 Virago 750 (Central Virginia)

Post by waspanman » Wed Jun 16, 2021 1:54 pm

I know the educated among you will scoff, but this is so cheap and you lose nothing if it does not work, plus it takes almost no time at all.
I have a 1996 750 which belongs to my wife, which I struggled with for a long long time.
Cut to the chase, put in two NGK BPR 6ES plugs and see if that works.
Of course, it could still be carbs.
I read once "If you think it's fuel, its electrical and if you think it's electrical, it's fuel".

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ViragoJoe
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Re: Can't Figure out Non-starting 1994 Virago 750 (Central Virginia)

Post by ViragoJoe » Wed Jun 16, 2021 2:58 pm

waspanman wrote:
Wed Jun 16, 2021 1:54 pm
I know the educated among you will scoff, but this is so cheap and you lose nothing if it does not work, plus it takes almost no time at all.
I have a 1996 750 which belongs to my wife, which I struggled with for a long long time.
Cut to the chase, put in two NGK BPR 6ES plugs and see if that works.
Of course, it could still be carbs.
I read once "If you think it's fuel, its electrical and if you think it's electrical, it's fuel".
Well you have one electrical problem already. You are running a one range hotter spark plug than what your bike calls for.
Any reason you are going with a hotter plug. Yamaha designed your engine to run with NGK BP7ES or BPR7ES.
BPR6ES will just make it run hotter.
ViragoJoe 🇺🇸
1996 XV1100SH Virago Special
"Never ride faster than your Guardian Angel can fly!!"
;)


NOTE TO ALL:
:arrow: Please edit your profile to include your location.
It will aid us in assisting you!

waspanman
Posts: 35
Joined: Tue Jul 07, 2020 4:22 am
Location: UK
What Virago you Own: 1995 535 1996 750

Re: Can't Figure out Non-starting 1994 Virago 750 (Central Virginia)

Post by waspanman » Thu Jun 17, 2021 7:26 am

I have said elsewhere on this forum, with BPR 7 ES plugs, the bike ran like a dog, my local shop returned it as a non runner after 3 months of trying to fix it's issues. I changed the plugs to BPR 6 ES and it ran like a dream, changed them back' just to check, and sure enough it was crap.
I don't really care if the mechanical science doesn't stand up, this test is so cheap in both money and time, that I think it has to be worth trying.
In much the same way as some bikes need choke to start and some flatly refuse to fire with even a sniff of it. They may all be made the same, but they sure don't all behave the same.
Just my $0.02

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