Awful mileage, no speed

Everything in-between the gas cap and the carbs. Also how the engine inhales.
DaveyG
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Joined: Sat Jun 01, 2013 4:42 pm
I ride: 1980 Yamaha XS1100 1993 Vulcan 500

Awful mileage, no speed

Postby DaveyG » Sat Jun 01, 2013 5:38 pm

My buddy (250+ lbs, 1993 500 Vulcan) has been commuting about a week since we got his bike running again (typical carb cleaning, spraying thru all the holes, ports, jets with carb cleaner, replaced hoses, adjusted A/F ratio) and he is having problems maintaining freeway speeds unless geared down to 4th gear? Also after riding about 15 minutes the idle seems to jump and stay rather high. He has filled the tank 4 times now, reporting 30-34mpg between the 4 tank refills... Seems to run fantastic though for me (150lb) and in the neighborhood, and nearby side street (up to 45-50mph) runs like a raped ape...? Strange? Ideas? Suggestions? Thanks in advance!

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Triangles
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Re: Awful mileage, no speed

Postby Triangles » Sun Jun 02, 2013 1:02 am

4th gear!?!? I didn't know you could run that low of a gear on the freeway without blowin the engine. I am going to assume you have the valves properly adjusted and that there is no issue with the spark plugs. That leaves your carbs being fubar as the culprit. There is the idle and slow speed circuit that has very tiny passages that are easily blocked by varnish in the carbs which doesn't sound like it's a problem. The main jet and jet needle control the fuel at high speed. Your buddy's MPG's should be low 40's when heavy on the throttle or at high speed and flirting with 50mpg when not. I would double check the valves and ignition system before proceeding with the carbs. Maybe a PO put the cams back in a tooth off or something. The '93 has about 50HP that is plenty of power to propel your buddy to nearly if not over triple digits.

Also after riding about 15 minutes the idle seems to jump and stay rather high.
I just reread that in your post. That is a tale tell sign of a vacuum leak. I had a similar problem on a different bike when I forgot to tighten the boot from the carb to the intake port. It would run fine but when I got on the e-way it would suck in a lot more air. When I hit about 60mph it was like the engine just ran out of power. If you have a vacuum leak you should be able to spray some carb cleaner / starting fluid where you think the leak is and verify the leak. Just be smart about it and don't burn down the bike. If it's not a vacuum leak causing the high idle you've got the idle set wrong.
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DaveyG
Posts: 5
Joined: Sat Jun 01, 2013 4:42 pm
I ride: 1980 Yamaha XS1100 1993 Vulcan 500

Re: Awful mileage, no speed

Postby DaveyG » Sun Jun 02, 2013 1:40 am

Ok thanks, I will check for leaks first. I replaced the plugs, but didn't check for spark seeing as it was running fine on both cylinders. If its not a simple vac leak I will check the valve adjustment.

DaveyG
Posts: 5
Joined: Sat Jun 01, 2013 4:42 pm
I ride: 1980 Yamaha XS1100 1993 Vulcan 500

Re: Awful mileage, no speed

Postby DaveyG » Tue Jun 04, 2013 11:00 pm

Ok, so the carb boots aren't loose, and recently it's been acting even stranger, itll run fantastic for a few minutes, gobs of power, and then it just dies. Wait a minute, then starts, runs awesome, gobs of power, then dies... Thoughts?

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Triangles
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Re: Awful mileage, no speed

Postby Triangles » Wed Jun 05, 2013 12:52 am

air vent in the gas cap isnt venting? Creates a partial vacuum as the fuel is used until it starts to starve carbs of fuel. Either that or check for lose battery terminals. The battery is necessary for proper electrical function. Weird things happen when the battery terminals come loose. If either of those don't help, good luck and let us know if you ever do figure out the problem.
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Turbojoe
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Re: Awful mileage, no speed

Postby Turbojoe » Thu Jun 06, 2013 9:55 pm

It really sounds like a couple of problems. The intermittent dieing sounds like a cap vent issue. I pulled my cap apart about 2 years ago for a look see after reading about other people having problems with the vent. Mine had quite a bit of corrosion from condensation. I soaked everything in CLR and put it all back together. Battery terminal corrosion can also be a big issue as Triangles eluded to. I took care of that problem by building a Lithium Ion pack for my bike and used an Anderson Power Pole connector. Make certain that all battery contacts are clean with NO corrosion. Low voltage will drive the ignition system absolutely nuts!

I have a 2004 EN-500 and I weigh 250#. My average mileage in the summer is in the high 50's with a high of 61mpg. In the winter for some reason mileage drops to the high 40's low 50's. Mid 30's for your bike is crazy low though. Keep working at it. Once you get her straightened out it'll be worth the effort.

Joe
The nonsensical ravings of a lunatic mind.....

2004 Vulcan 500

DaveyG
Posts: 5
Joined: Sat Jun 01, 2013 4:42 pm
I ride: 1980 Yamaha XS1100 1993 Vulcan 500

Re: Awful mileage, no speed

Postby DaveyG » Sat Jun 15, 2013 3:35 pm

Ok so after a little digging I think the biggest problem is just bad float needles. I was in the middle of chasing my tail with the a/f mixture screws (after loosening and retightening the carb boots, just for good measure) when she started leaking gas out of the airbox drain tube! So, I think that is the primary problem, at least the first to tackle, as there's no way I'm going to get the a/f dialed in while gas is spewing right up out of the main jet! So I'll get some float needles on order in a few minutes and will update once I get to that point.


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