Vacuum to petcock

rumortoad

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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.
 
Not normal, but can work...don't think it's ideal, but depends on how well the "on" position keeps the fuel from flowing.

I'm not sure I understand your set up, but it sounds like you're saying the petcocks are traditional vacuum style, but they are not connected to the vacuum ports on the intake boots...rather they (either the petcocks or the vacuum ports on the intake boots...unclear with your description) are connected to each other?

If your petcocks are stock and have not been altered (there's a modification where you can rebuild the vacuum petcocks by switching out the internals with the opposite side petcocks and thereby block off the vacuum function) then when they are in the "on" position, they will only supply fuel when the engine is running. Thus, if the vacuum ports on the petcocks aren't connected to the vacuum ports on the intake boots, then theoretically the "on" position (or reserve) would be an "off" position for your purposes...requiring you to use "pri" (stands for Prime, not Primary).

I'm not sure why yours are set up that way, unless your bike no longer has the intake boot ports, and the PO didn't bother changing the petcocks to non vacuum type ones...or there was some other issue they needed to stop using the vacuum Function?
 
As sold 80 was single petcock, and you are not using vacuum to turn the petcock on? Some PO's will epoxy the vacuum part of the petcock shut and use them as a manual petcock. XJWMX detailed doing this, way back when. The petcock will work as you describe just left "as is" also. Running this way is a "farmer fix". Just a heads up; if the PO was a farmer fixer, you ain't found em all yet........
Running the vacuum ports together is probably a kludge also. You may have issues in at least one carb's idle circuit or the carb synch. Prepare yourself to learn how to work on motorcycles.
Check the AGE of the tires, rock hard ancient tires are an accident waiting to happen.
The front brake needs a new brake line and probably a full overhaul.
Check your charging system with a volt meter at a minimum point the headlight at a wall, does it get brighter as you rev the engine? Is the battery fresh and hold a good charge? Minor electrical problems can become major problems if ignored.
Can you smell gas when the bike is sitting?

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Welcome to XS650!
 
Running a hose from one vacuum port to the other is not a kludge. It can be used as a final step in carb tuning. Get everything else done to tune the carbs. Linking the vacuum ports just smooths things out a bit more. Only do this as a final step. It won't fix any carb issues.
You can try pulling the hose of one port, capping that port and hooking the hose to the vacuum port on the back of the petcock. Or put a tee in the hose and run another hose from the tee to the petcock. Either will let the petcock operate as it was intended. It may also show you if your petcock is in good shape.
Leo
 
Be aware that the "Prime" position flows off the reserve tube. This means you have no reserve now. When you run out of gas, you will really be completely out of gas.
 
Hi rumortoad and welcome,
what they all said, first check the tires' date-stamp, the forum search button will tell you what to look for.
Try connecting the gas tap's vacuum connection to one of the carb manifold vacuum spigots and capping off the other.
The tap may even work as it should if you do.
Or cap off both vacuum connections and buy a manual tap from MikesXS.
Certainly, operating a disconnected vacuum tap on Prime is not a good way to go.
Note that if you run out of gas you can lay the bike on it's side to get that last half-cup of gas on the tank's other side which may just get you to the next gas station.
And it might be a rare phenomenon but it happened to me.
The plastic gas filter/reserve level tower atop the gas tap can fall off to lay inside the gas tank.
You won't know until you switch to reserve and find it's already been used.
 
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The title says 80 xs65. It has two petcocks on the bike (either second one added later, or maybe wrong year on the title).
The pictures show thefollowing:
Petcock with only hose on prime side.
The tube connecting the two carbs.
The port on the back of the petcock with nothing attached.

The bike runs amazing. Last guy bought the bike with the intentions of pulling the motor and using it on his dirt track bike.

In the long run I think I will drop one petcock, and hook the vacuum on the center of the hose from the carbs, but for now I will enjoy it :D
 
I'll guess you have a 79 there. BS38 carbs, two petcock tank, 2 outlet engine breather. Does it have points ignition? The RH carb spigot has been replaced for sure, it might not be the "correct one" for your carbs. Spigots after 75 have an "angled spigot". that kinda looks like an early style "straight spigot".

79 VINs start with 2F0
 
The tube between your carbs is a fuel cross-over, not a vacuum line. Don't be connecting the petcock vacuum line to that. As mentioned, your carb manifolds should have vacuum nipples on them so vacuum hoses can be run to the petcocks. Problem is, the replacement manifolds with the vacuum nipples for the '78-'79 BS38s are harder to come by than ones without the nipples. It's very possible the P.O. used the manifolds without the vacuum ports. The orange hose is my vacuum line running to the petcock .....

ManifoldClamp.jpg
 
Thanks for all the great info. VIN number on the title does start with 2F0, so 79?
Haven't taken the bike apart so not sure if points or electronic ignition.


The bike runs great, sometimes. The issue I am dealing with is the plugs, or ignition. It was running great, then I had one plug die on me. Replaced and started running great after a few rides. Now it's hard to keep running, also backfiring. Plugs are black but not wet. Exhaust blowing a bit of black smoke. Motor sounds "muffled". I guess I'm running rich. The plugs I bought were the NGK 8, so a little more spark there. Idle is set to about 1200. The gas is on and flowing from the back of the filters.
 
NGK plug heat ranges run "backward" an 8 is colder than a 7, get some 7's in there!

spark-plug-alternatives.jpg
 
The plug you should be running is the BP7ES, not a plain "B". The "BP" designates a projected tip. It sticks out farther and gives a better burn .....

CorrectSparkPlugs.jpg
 
Hey all. Went with the hotter plug and got no big difference. So, I tried adjusting the mixture screw on the side of the carb and syncing, but I really got it out of wack. Ended up taking the bike to local guy. My jets were 150 for some reason, he had some 145's so thats what they are now. He told me he ended up syncing the carbs using a temp gun on the head pipes. Bike runs strong and doesn't foul out the plugs now, but, as the mechanic tells me it still has a "lean hang", an air leak on the side of the carb somewhere. When I start the bike up, it stays revved up at about 4 or 5K. What he has me doing is flipping the choke open then closed which drops the idle back right.

I know he opened the top of the carbs and cleaned them but told me he never opened the side because of time involved, and cost.

I think the next step is getting personal with my carbs (long overdue).
 
Found this gem in the awesome carb guide: http://www.amckayltd.com/carbguide.pdf


- Too small of a pilot can be indicated by an idle that "hangs" after blipping the throttle or
by having the motor be slow to return to idle after running at higher speeds. Once again,
mix screw settings may help here.
 
The carbguide is the thing you need to use to get your carbs right.
Just follow the steps to tear down, clean, inspect. Once you get this far you will have a good idea of what needs to be replaced. Generally gaskets.
It appears some bone head was in your carbs before. That 150 main is way to big.On my 75 with uni-filters and a very unrestrictive exhaust running the BS34 cartbs I ran one up on tghe pilots and two up on the mains. That,s a 45 pilots and 137.5 mains. I might have been able to go with a 140 mains but it ran great.
They are now on my 81 that's bone stock and they still run great.
Leo
 
I know my bike wants to run, I just can't get it dialed in correctly.

Started pulling the carbs yesterday, loosened the right clamp on the boots and boom, the whole carb set fell out of their boots! That may have been my air leak! Well, opened the carbs cleaned them up and inspected all parts. Everything looks fantastic (except for the 145 mains). As I went to attach the carbs back to the boots I couldn't get the things to seat all the way down. Spent 30 min trying to get these things on. Once I finally did, I had the left carb sputter and blew the carb loose! I then realized I don't have the right boots. They are a general purpose 36-40 boot for Harleys.
Getting ready to order new ones tonight but had a question. Barbs or no barbs in my boots?
Also, it seems the general consensus it to buy these from jb instead of mikes, is this true?
Lastly, I have a pair of 150 main jets if anyone wants them. :)
 

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Hey everyone, long time no speak. Done a little to the bike in the time I was gone: Pulled some stuff off. Electronic ignition. Shorty's on. Wrapped pipes. Actually set the carbs to stock settings to get my plugs from fouling out. Bike runs like a beast! Done the ton a few times. Pulls hard, even at 70 mph! Just wanted to say thanks for all of the help along the way. Cheers!
 
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