Vacuum to petcock

First post, first bike even. 1980 xs650 special with less than 5k on the odometer. Not sure if true, but I think it is. Here is my question: so I thought I had battery problems when I first bought the bike; it would stall out after a few minutes of starting. I could go about a 1/4 mile then it would bog down and die. Anyway, got multimeter and checked the charging of the battery and it was good. Next, invited father in law over (ex motorcycle mechanic) and he discovered it was the petcock with no vacuum on it. As I am told, the carbs have the vacuum connected between the two (aftermarket). So when I want to ride, I set my petcocks to primary and everything is good. When I park the bike, I set the petcock to ON for the lack of flow (no vacuum). Is this normal? So far it has worked for me.
Does your 80 still have the original head to carb flanges with brass tube ports where the intake vacuum is sourced ? rubber thick enough to not collapse under vacuum ? I really like how my vacuum petcocks control fuel flow. Check for your tubes connected.
 
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I'm currently having this same issue on my 80 xs650, do the hoses from the intake connect together and then connect to the petcock? The bike starts, runs in idle for a bit, but if I choose to hit the throttle it dies. Going to check some pilots and fuel mix screws before I try again. But I can't seem to find this info in the manual.
 
In stock form, with two vacuum petcocks...each intake manifold with a vacuum port had a hose that connected directly to the vacuum petcock (thus the vacuum ports from each manifold is not connected together)...however if the tank only has a single vacuum petcock that may be different--and it would make sense that the manifold's vacuum ports would connect together, and then T up to the single petcock....unfortunately, I don't have an XS with only one petcock so I am not completely sure about that...but I am sure someone on here will chime in to validate this. :)
 
Left side to petcock, right side capped.

oh... lol ok i'll do that. what if i joined both right and left to petcock? will that not work? or is what you said the actual way it's done lol I must knoooww!! XD
 
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oh... lol ok i'll do that. what if i joined both right and left to petcock? will that not work? or is what you said the actual way it's done lol I must knoooww!! XD

Yeah factory is one petcock, one capped vacuum port on the 80 up specials.
 
Okay so I did that and it had a harder time starting. I'll have to re-check the pilots maybe.
 
oh... lol ok i'll do that. what if i joined both right and left to petcock? will that not work? or is what you said the actual way it's done lol I must knoooww!! XD

Hi Grimmith,
what Gary said is the way those bikes left the factory.
Sure you can Tee-up two taps to feed the between carbs connection but you get 4 extra potential fuel leakage sites and you lose the ultimate fuel reserve.
The one where you lean the bike onto it's left side to get that last smidgen of gas.
 
Okay, That's what I figured, but still did it and it didn't start correctly. But even if something is wrong with the carbs, I CAN'T GET THEM APPART!! literally the 4 bolts on the mounting bracket, got one off yesterday, no sighn of anything holding it in place. The bolts are about to strip.. I even have the go fast innovations screw driver set, used knocker loose, freeze off, and even heated up the area with a pen torch incase of thread lock and nothing...… so yeah my 1980 xs650 special is for sale lol
 
Okay, That's what I figured, but still did it and it didn't start correctly. But even if something is wrong with the carbs, I CAN'T GET THEM APPART!! literally the 4 bolts on the mounting bracket, got one off yesterday, no sighn of anything holding it in place. The bolts are about to strip.. I even have the go fast innovations screw driver set, used knocker loose, freeze off, and even heated up the area with a pen torch incase of thread lock and nothing...… so yeah my 1980 xs650 special is for sale lol

Hi Grimmith,
alas that a 1980 XS650 Special with buggered up carbs won't sell worth a damn.
Better you check this list's classifieds for a replacement carb set.
You have removed your assembled carb rack to get better access?
It's been my experience that XS650 carbs need a complete annual teardown & clean out to run nice.
 
ugh....I suppose I'll have to get new carbs...I could cut off the old bolt heads and re-drill then re-tap the holes for the new bolts can't I? I feel like it would save money.
 
ugh....I suppose I'll have to get new carbs...I could cut off the old bolt heads and re-drill then re-tap the holes for the new bolts can't I? I feel like it would save money.

Hi Grimmith,
As a last resort, sure you could.
And you gotta separate the bastards to access the right-side carb's slow-running passages & enrichening system.
After the bolt heads are cut off there won't be any bolt tension but there will be an angle-iron's thickness-worth of bolt left showing
for access.
 
well hey the little bit of bolt left will be a plus in removing them. But yeah, if I try to remove them any more I'll just strip the heads, so I'll have to go to the last resort......patients and shit lol. Okay so if everything goes well with the carbs in the long run and I'm able to get the bike to run. What would it be worth? no rust anywhere, everything stock. some bolts and nuts missing for a couple parts to hold on, no major nuts or bolts. and the wiring is just to get the engine running, I don't have any lights on quite yet.
 
All depends on the buyer and their interest in a stock vs. otherwise. A running, well maintained, and clean bike vs. one that needs a lot of attention will factor in, and the buyer's knowledge of old bikes vs. just getting into it...and of course their goal with the bike (restoration or custom build, etc). Around here (Pacific Northwest), I've seen crap bikes go for a $2000+ and I've seen great bikes go for as little as $200...all based on these factors and some others of course.
 
Appreciate it man, that makes me feel better because if I get these carbs done and it runs, once I clean up the wiring and make lights work it will be almost be almost like it came off the line :D.....minus some super minor changes lol
 
Unless you are putting in new throttle shaft seals or the fuel tee leaks badly there is no reason to remove those 4 screws. Just lttfa. If the tee is leaking you only have to remove ONE carb TWO screws.
 
Well to be completely honest it was a bit of both things, it did leak from the Tee, your guy's advice worked and the seals just needed to swell up a bit and it barely drips at all. But then sometimes gas comes out of the right carb air intake, but also sometimes it doesn't....I just thought that maybe the seals were bad or something inside because it leaked like that. That led me to wanting to take the bracket off so I can check the gaskets and jets but I was only able to get one screw out, all the others are about to strip from being seized or something....so what do I do? lol
 
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Use a hand impact on the screws to break them loose. I've tackled some tough ones but they all did come apart.
 
the only one other screw will strip if I try to take it off, I tried the impact a couple times but I promise it didn't do anything except strip more. I don't know why the bolts are like this but the one I got off had no evidence of anything being used, not even thread lock, it was completely new looking. But it's good that I could only have to grind off / re-tap one bolt hole instead of all 4 since I got one bolt off.
 
The angle iron bracket does NOT need to come off to open the float bowls and get at everything inside
 
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