I suspect I have a vacuum leak going on in my 1994 Evo. I know how to test for one, but does anyone know the symptoms of one? I'd love to hear from someone who has experience with this and compare their info to the symptoms my bike is showing...
I'd rather hear some spontaneous responses before I describe what the bike is doing; If someone describes what a vacuum leak feels like in the ride and it matches my symptoms, I'm thinking I'm probably on the right track....
I've checked and/or replaced every single part of the ignition system (after 30 years it all needed freshening anyway) and just put on a new carb from Dale at Killer Motorcycle Products.

Thoughts?

Thanks
Logan

 

AIr leak the bike will act up from starting on, vacuum leak depending on where it is and the VOES setting can be at certain RPM ranges causing stuttering or misfires. This guessing game isn't going to go over well in here, warn you now.

 

Can cause all sorts of hairy running, misfiring, carb farts etc, and sometimes but not others, sometimes real bad, sometimes just a little.
On mine, source of the vacuum leak was the vacuum-operated fuel petcock. Can't remember if it was the hose or the petcock diaphragm that split. I yanked the diaphragm out and installed a blanking plate or some such, so it is now a low-tech manual petcock and no more vacuum leaks.

But, most carbutator problems are electrical. And on these, not necessarily the ignition system. If your regulator is bad and you have low system voltage, it does weird things to the electronic ignition system.

The other thing I found after years of intermittent ****les with the electrical system was the "Jesus terminal" on the starter solenoid. The heavy-duty positive battery cable goes to it, then the main ignition switch (and thus, regulator, ignition system and everything else) is connected to it by a smaller wire. That terminal can look just fine from the outside, and the nut can be tight. But after 30+ years, a thin layer of corrosion can form over the cable ends, just enough to let the bike run but enough to limit the current that can flow through there and cause problems.. A qiuick clean with some Scotchbrite and electrical weirdness is ended. Just a thought.

 

Tell us what the bike is doing.

 

Sorry, I have NO TIME for your Guessing Game. GOOD LUCK!

Bye, Bye

 

Interesting comment...is there adjustment to a VOES? Mine on that '94 is just a wire lead and a vacuum hose. Can you explain what you meant by "VOES setting"?

PeterB: Good insights and if I hadn't replaced my transmission a while back I'd be all over that "Jesus terminal" idea (love that name). But when I put the starter back in I thoroughly cleaned all the connections. Regulator is brand new.

Dan89: I guess since I managed to flame certain snarky members here, I'll go ahead and tell you that the bike cuts out intermittently, has "flat spots" on accelleration (but only sometimes) and really feels like it wants to hustle but just cant quite. I can't really explain it any better than that. One interesting thing is that, during a 99-degree day here, when the bike was REALLY good and hot, the problem disappeared. That's what I wanted to hear...that sounds very much like what's happening.

...But plenty of time to post a ****-head comment. Try reading next time. Nowhere did I ask anyone to "guess" what the problem might be. I asked if anybody could describe the symptoms of a vacuum leak. If you don't know the answer, just say so, or, better still, don't answer at all, since you have NO TIME.

Thanks all

Peace

 

First, there is an adjustment screw in the tower on the switch, manual has the procedure for setting it correctly, involves a meter and hand vacuum pump. Sets when the timing advance comes in by completing a ground at a preset point, I'd be looking over all the vacuum lines, old and hard by now. Think older cars and how vacuum was used on the distributor and carb for things.

Second, after that description I'd be looking at the ignition components, it's stock open the cover and look at the pickup, you see anything looks like pudding in the bottom, found your problem. Replace it. Aftermarket ignition we need specifics, they all act different when trouble hits.

 

I replaced my VOES two seasons ago along with the vacuum line that goes with it. So I pulled my old one out and took a look and it has a metal cap on top that's held on like a sheet-metal nut that holds an emblem on a car fender. It's not meant to be remeoved (although I could remove it) so I got into the manual (official Harley shop manual for 1994 Softails) and there's no mention of any adjustment. Diagnosis and replacement, yes...but no adjustment. Maybe newer bikes have adjustable VOES, I dunno. Gonna get into the checks for vacuum leaks; see what happens there. Pretty much at my wits end trying to diagnose why it won't run right...this is the first time in 34 years of working on bikes that I've been so utterly vexed by a problem...

Thanks again for the insights

Logan

 

Dig out the silicone plug in the round end (recess) of the VOES. You will see a screw buried under the silicone sealer plug. That is your adjustment screw. Note that most VOES have a paint mark color code on them. Just take note of what color your paint code is. That tells you the original vacuum setting of that particular VOES.

To test a voes, you pull a vacuum on it (example: 6 in/hg) and let it sit, checking it to see if the vacuum slowly drops. Good idea to test your VOES BEFORE YOU REMOVE THE SILICONE PLUG. If the gauge needle drops, you have a leak. If you test it after you remove the plug, it can leak. You will also need a means to plug it back up after your done messing with the adjustment screw. I use a a rubber cap on the end of mine with a little sealer on the cap. Removing the cap with a little sealer on it is easier than digging out all that silicone a second time.

The actual switch inside the VOES can get flakey meaning the OHM's resistance will increase with age (switch contacts oxidize) and you can get goofy ohm's resistance values when checking the switch with a meter. Zero or damn close to zero resistance when switch is closed (contacts are touching or switch is on), Should be infinite ohms when switch is open (contacts not touching or switch is off).

Bad contacts: one minute you get a couple ohms resistance, then next time you check you get 100 ohms, another could be 50 or 25 ohms, etc. If that is the case the contacts in the switch are oxidized and you will not get a reliable trigger to your VOES and it's time to replace it. See link below:

http://www.wildwestcycle.com/f_voes.html

Yes, a vacuum leak can cause the bike to run lean because there's too much air entering the engine relative to the air/fuel ratio

• Poor fuel economy
• Lack of power
• Hesitation when accelerating
• Backfiring or cough/sneeze through the carb/intake
• Overheating or hot running engine
• Strange smells due to the overheating
• Higher idle speed or wandering/surging idle speed
• engine runs on after shutting off (even a brief run on after shutting engine off)