• Can't post after logging to the forum for the first time... Try Again - If you can't post in the forum, sign out of both the membership site and the forum and log in again. Make sure your COG membership is active and your browser allow cookies. If you still can't post, contact the COG IT guy at IT@Concours.org.
  • IF YOU GET 404 ERROR: This may be due to using a link in a post from prior to the web migration. Content was brought over from the old forum as is, but the links may be in error. If the link contains "cog-online.org" it is an old link and will not work.

Vulcan 800 carb problems

mattbroj

mattbroj

Member
Member
Well I've been all over the Vulcan forums and every other form of Google search to try to figure this out and i'm.having a hell of a time with it.

I'm working on a friend's 03 Vulcan 800 Classic. The bike has 16.5k miles on it and has been sitting for a little bit. It ran when we parked it a few years back and it ran a bit this year but it's been getting worse and now is not able to be ridden. It is completely stock other than de-baffled pipes. It is running the factory pilot and main jets. At the moment I can get it to fire and idle but it will not take any throttle, it just dies. I've cleaned the carb and installed a rebuild kit to the best of my (limited) abilities. It's a single Keihn CV 36mm carb so I didn't think I'd be having as many issues as I am.

With the bike running i can take the air cleaner cover off and see that the carb is pulling fuel up the vacuum needle at idle. I can't find anywhere if this is normal or not. My understanding is that the pilot should be handling fuel at idle and the main jet circuit would basically be closed until the throttle was opened. Due to this I started chasing float height issues and replaced the entire float and float needle. From there I did the Keihn recommended dry float level measuring and got that situated. No change.

Took the carb apart again to look for clogged passages and blew through everything with carb cleaner again just to be sure. Everything looked good.

Once I reinstalled everything and got it running I took the air cover off and held my hand over the carb opening to manually "choke" it and the bike will take full (strong) throttle with me metering the airflow by hand. Logically this tells me the carb is running VERY lean.

Am I missing something major? I've done the carb cleaner fogging check for vacuum leaks. I've double checked my main jet and emulsion tube orientation (guess a lot of Harley guys get that one wrong), my passages are clear, all boots and O rings are new and not folded/torn. We've tried removing the smog pump and capping all the associated ports but it doesnt change anything. The bike has had a recent valve adjustment and everything is in spec there as well. I'm at a bit of a loss.

Any help or wisdom would be greatly appreciated!
 
I would check upstream with the petcock, fuel lines, and tank. I don’t know if the bike has gravity fed fuel or a pump. Storage with gasohol can do a ton of damage and corrosion that interferes with proper fuel supply. It does not take very long for this damage to set in.
 
rlievenski4555 said:
I would check upstream with the petcock, fuel lines, and tank. I don’t know if the bike has gravity fed fuel or a pump. Storage with gasohol can do a ton of damage and corrosion that interferes with proper fuel supply. It does not take very long for this damage to set in.
Click to expand...
Good recommendation, forgot to mention that as well. Has a vacuum actuator petcock like the C10. Did a test on the petcock with the lines off and it flows freely on prime but not on run. To me it would seem that the petcock is operating properly. There are minimal fuel lines and I've had them off and blown through with air, so they're good.
 
Sounds like the petcock itself may be fine, but what about things like fuel filter or a pinched/kinked line? Simple test - unhook the fuel supply line at the carb and hold over a small clear container. Set the petcock to 'prime' and see if you get a full stream of fuel, or just a dribble. Perhaps it's getting fuel to the carb but not enough to keep up with an open butterfly?

You're correct that the pilot circuit handles 100% of the idle and just off idle fueling, and bypasses the main fuel circuit. The main circuit shouldn't come into play until about 10-20% throttle in most applications.

Does it behave differently if you very slowly open the throttle vs. quickly crack it to quarter or half throttle?

What's the choke / fast idle setup look like? You mentioned limiting air flow by hand and it seems like it runs OK, I agree that would indicate it's running lean... Are you SURE that the main jet itself as well as all of the holes around the outside of the emulsion tube are clear of gunk? Does the slide move freely up and down and 'snap' closed when it's all reassembled? Have you verified the rubber diaphragm on the slide is free of tears, completely seated in the groove, and that the hole in the slide (which allows vacuum to the top side of that diaphragm) is unobstructed?

Finally I assume you verified the main AIR jet is the correct size - make sure you didn't accidentally swap the pilot and main AIR jets - they're often pretty close in size and I've seen them labelled backwards in Clymer manuals before!

As I think you're aware, the biggest problem with bikes sitting for long periods of time (a year or more) is the fuel gelling up and clogging the tiny passages in the carb or the jets themselves. That seems the most likely culprit in this case. Did the bike run about the same before you installed the rebuild kit?
 
When you had the carb apart, did you remove the pilot jet and verify it was open and clear by pushing a soft brass or plastic brush bristle through it? I imagine the pilot jet is larger on your CVK36 than the CVK32s on the C10 (and my ZX600-C), but it's still going to be microscopic, and it's usually the first thing to get clogged from sitting on these carbs.

You're correct that the pilot circuit should be handling fuel off idle until you get up into the power band, so if it's stumbling off idle, that point strongly to an issue with the pilot circuit. Of course, other things like vacuum leaks could be a cause too. Have you checked the slide diaphragm? Uncapped vacuum port?

How does it run on the enricher?

Even if the petcock or fuel feed is not working properly, as long as you start with the carb bowl full, it should run for 30 seconds or a minute with just the fuel in the bowl. My 600 has a petcock with a full "off" setting, and I can make it a few block down the street if I start up and head off with forgetting to turn it on before it starts sputtering.
 
You must log in or register to reply here.
Top