Yep.......Keep in mind that a bike at idle generates very high manifold vac. When you crack the throttle vac starts to fall. At wide open throttle, there is very little manifold vac. Somewhere in there the VOES switch operates and triggers a change in spark advance. Proper spark advance is essential to an engine under load in order for it to accelerate and develop power.......

If you decide to tinker with the VOES, you can attempt adjusting it.....To adjust it, simply remove the silicon plug and use a flat tip screwdriver to tweek.

VOES is short for vac operated electrical switch.....seeing as how it's a switch, it's either on/off or open/closed...And seeing as how it's vac operated, it's triggered by manifold vac. Manifold vac is highest when throttle is fully closed and lowest when wide open.....Right?

The VOES switch is connected by a single short hose to the carb port that senses full time manifold vac. It is also electricaly connected to the ign module via a pair of wires. When manifold vac triggers the switch, it makes/breaks electrical contact that then signals the ign module to advance/retard spark timing 4 degrees. If that advance/retard doesn't happen, or if it happens at the wrong time, the scoot will stutter and not make power.

So where in the throttle position do we set the switch to operate and change timing advance? That is best done at the factory where it is then sealed with silicon, or later when on a dyno operated by a very savy tech. My experience shows me that few HD dealer dyno techs know the switch exists nor do they know it's adjustable.

 

Something that might be causing the blubbering after a minute is the vacuum operated petcock if the diaphram is leaking. If the diaphram is split, it might be sucking a bunch of raw fuel right into the intake manifold causing a very rich running condition.

If you still have the stock vacuum petcock, start and run the bike until it blubbers a bunch, then shut it off. Pull the vacuum hose that goes to the fuel petcock. If it has any gas inside the hose, then the diaphram is leaking and needs to be replaced. They're inexpensive and easy to replace.

Just another possibility to check.

Good luck.

 

Man I think you need to spend a few bucks on there bike and take to your local Indy and have them figure out whats wrong.

 

Excellent advise!

 

First, a thanks to you riders for the advice you've put up on this thread. It's cool to have this forum, and cooler to share advice and recommendations.

I was suspicious of the VOES and the vac hose earlier in this troubleshooting and checked the hose and even shorted across the switch to see if a change in the idle or bike behavior was noticeable. I was not able to get my test clips deep enough into the connector to create a 'closed switch' condition to the ign module, but when the switch was unplugged and there was no impact on the failure, I wrote the VOES out of the picture as a possible culprit for this rotten engine behavior.

Friday evening I swiped a carb off a '96 Sporty and mounted it up on the '03. I fired it up, and ran the throttle manually (didn't bother with the throttle cables for this test). Result: the bike started and ran beyond the 45-60 second mark where it has been laying down now for three weeks. I ran it this way for about two minutes --longer than the bike has run now since this whole thing started. I shut her down, reinstalled the original ign module, dressed the wires, connected the throttle cables, and took it for a short ride. The test carb has its own issues, but I know now that the 45-60 second failure thing is being caused by the original carb. I’d sure as heck have lost money on that bet, but the darn thing runs now.

This opens the next question...I’m suspicious of the bowl vent on the original carb...what sort of failure would a guy get if this vent were not breathing? I'm suspicious of this because this carb has had a few pieces chromed, and there is a question about this vent right now. The bike has run for hundreds of miles with this carb, and only failed recently so the chroming itself is not the issue, but I'm going to look into this vent before I tear the whole thing down. If it were not breathing, do we suppose that the 45-60 second issue I'm seeing could be caused by a weak or missing bowl vent? I’ll check, but it seems that a ‘fat’ situation should not arise from this. I’ll let you know what I find out.

Additionally, the vacuum petcock idea suggested by Bentwrench sounds like a real possibility here, but I’m not clear on the suggestion. Are we talking about the fuel shut-off petcock? I’m not sure I have a vac line going there. I will sure as heck check it out to see…the symptoms I get with the original carb could easily be caused by raw fuel dumping into the intake in this way…I just don’t know if there is a vac operated petcock etc on this bike, but I’ll darn sure be checking for that. Maybe this exists only on injected engines?






"I'll be Back"

 

Your 2003 bike came with a vacuum controlled petcock. the vac line on the backside of the petcock, ya gotta look close.

FYI, injected bikes don't have petcocks.

 

Thanks for that cHarley... I have an '03 FXSTI & I know it doesn't have a petcock...I thought that maybe the injected bikes used a vac operated valve system to deliver fuel in the absense of the petcock...

I will check this line...it must be pretty well hidden; I've sure not noticed it yet, but if it's there, I'll darn sure find it.

 

Injected bikes do not have a shut-off valve or petcock. There is a fuel pump in the tank.

 

OK here is the latest:

Checked for the petcock vac line as suggested. This bike has a different tank than stock, and the new tank does not have a vacume line at all on the fuel petcock. Bummer.

Tore carb down again...further this time than last & soaked it (not the soft/rubber parts). Blew out passages & reassembled. No improvement...still will run ok for 30 or so seconds then will blubber, backfire, and puff black smoke out the exhausts. No difference if tank fill cap is removed (thought maybe bad tank vent issue) Still will run ok with other carb. Everything went together well on the carb, except setting the float level. Any advice on this adjsutment would be appreciated.

I've got it narrowed down to the carb here, but still not fixed...I'm beginning to suspect a lean misfire may be what I'm getting. I did discover that when it is blubbering and running poorly that it's behavior will improve if I manually raise the slide to about 1/2 way....any comments?

 

if i were you i would re-write the problem and what you have tried and e-mail it to american iron magazine to see if they can help.