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Old 10-28-2013, 05:10 PM   #1
YAHBO OP
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84 VT 500 highway crapping out issue...

Buddy of mine has the V twin Ascot...runs fine around town. At 60 mph and above, the bike shudders and craps out. Every time. Below 60, ride it all day. Above? It stalls and he has to pull off the road and wait ten minutes til it cools down and then it runs fine.

He checked the following:

Coils (new)
Carbs (cleaned)
All hoses (checked and double checked routing)

Left to do as far as easy stuff:

Plugs
Gas quality/freshness

Any ideas?
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Old 10-28-2013, 10:22 PM   #2
TrashCan
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Fuel cap venting???
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Old 10-29-2013, 05:55 AM   #3
Hughlysses
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My first guess would have been ignition coils (a notorious problem on older VT500's) but since he's installed new that's out. He did install NEW coils, right? Not used ones purchased off ebay?

Tank venting issue seems like the next most likely thing. Easy enough to check- the next time it happens, immediately pop the cap on the gas tank and see if the bike will fire up without waiting 10 minutes.

I also wonder if it could be a vacuum petcock issue. If the diaphragm is marginal in the petcock, there may not be enough vacuum at high throttle openings to keep it open (?). My 83 has the manual petcock so I'm guessing here.
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Old 10-29-2013, 08:21 AM   #4
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I had on old Suzuki that did that.
In this case the vacuum powered petcock needed replacing, it was unable to draw enough fuel at higher speeds.
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Old 10-29-2013, 09:01 AM   #5
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Quote:
Originally Posted by RedRocket View Post
I had on old Suzuki that did that.
In this case the vacuum powered petcock needed replacing, it was unable to draw enough fuel at higher speeds.
This.

Quote:
Originally Posted by Hughlysses
My first guess would have been ignition coils (a notorious problem on older VT500's) but since he's installed new that's out. He did install NEW coils, right? Not used ones purchased off ebay?
And this. Just because they were recently installed and purchased doesn't mean they're good. A lot of electrical components that fit are shit on the inside compared to the OEM stuff. Best to pull them out of the box and meter them.
I started doing this about 15 years ago with plug wires and coils when I started having "I just replaced that!" problems on cars and bikes. There's a lot of Chicom or Taiwan crap out there that isn't up to par. You may have some of it.

A tow truck will cost more than these coils, so spend coin on the best parts you can find, not eBay junk.
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Old 10-30-2013, 03:39 AM   #6
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Working on it...

Thank you for the help, gentlemen. I have relayed these ideas to my buddy and he assures me the coils are genuine Honda, it stalls with the cap open as he has experimented with the venting possibility, and that his next plan of action is replacing the petcock.

I will post up his results after the petcock replacement.
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Old 10-30-2013, 05:19 AM   #7
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Good luck, bro.
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Old 10-30-2013, 05:30 AM   #8
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Originally Posted by YAHBO View Post
Thank you for the help, gentlemen. I have relayed these ideas to my buddy and he assures me the coils are genuine Honda, it stalls with the cap open as he has experimented with the venting possibility, and that his next plan of action is replacing the petcock.

I will post up his results after the petcock replacement.
I seem to recall that the vacuum actuated petcock used on the 84 Ascot is NLA from Honda, but it'd be worth checking. Another alternative is that someone may make a repair kit. If all else fails, I'm pretty sure he can get a universal manual petcock (as used on the 1983 VT500FT) from several sources. He'll just have to plug the unused vacuum line(s).
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