Carb ooops?

[officerbill]

Hi,
I know there is a vacuum problem, either the carbs aren't making vac, or the diaphragm in the petcock is injured. Either way the vac isn't working in the petcock ON position. (This is recent occurrence and I will fix it soon). The bike runs WELL in the PRI petcock position until tonight. I start it, it idles, a little fast but is slows after a moment, I push the choke in a little at a time, still idling about 1200 rpm, I twist the throttle to take off and sputter, sputter, dead. It restarts but will not take any fuel. It was working fine when I came home from work Friday afternoon however Friday night, no go. I'm thinking pilot circuit, but could it be related to the vacuum problem?
This is a daily ride; it was running in the C+/B- range before last weekend when I tore into her. It has not been off the road for more than a day or two here and there, so no long sitting. A friend says "thing don't usually break when they are being used, they break when they are stored." I am over due for a value shim checking party; however I don't see that having an effect on the stalling issue.
I’ve searched the forum some, but having little success finding anyone having dealt with these sorts of troubles. Thanks in advance for any and all help,
Bill

[almarconi]

I would check the compression and your valve clearances. A vacuum gauge is probably the easiest way to see if you have vacuum on each cylinder. The vacuum gauge can give you a pretty good idea of whats going on with the engine. You say you have a vacuum problem, how did you reach that conclusion?

It could be fuel related. Try removing the tank and hooking up an auxiliary fuel tank to see if it runs any better. Is the petcock original? Is the inside of your tank clean? Remove the fuel bowl drain screw and make sure you've got fuel in each bowl.

[resjudicata]

You need to diagnose the problem by excluding one thing at a time. Petcock, vacuum, carb pilot circuit.

To check whether the petcock is allowing fuel out just disconnect the fuel hose from the petcock and with a container under it move the selector to prime and see if fuel comes out. Then move the selector back to ON and pull the vacuum hose from the carb body leaving the other end connected to the petcock. Now use your mouth to suck a vacuum on one end of the hose while it is connected to the petcock. If the petcock is working then you should get fuel flow. If either of the above conditions does not allow fuel flow then you have a petcock problem.

To check vacuum, put the vacuum hose back on the correct bung of the carb body and disconnect the other end from the petcock. Now either start the bike or just run the starter and put your thumb over the petcock end of the vacuum hose. You should feel a vacuum sucking on your thumb. If you get no vacuum then check whether you have the hose installed on the right hose bung of the carb. If you are sure the vacuum hose is installed on the right hose bung then you need to check that cylinder as there is a problem with compression/vacuum.

If both of the above are working properly then you need to check/clean the pilot circuit of the carbs.

Post here with the results of the above tests.

BTW, you say the bike was running "okay" until you "tore into her." What did you do when you "tore into her?" What were you working on and what did you do specifically.

And, I disagree with your friend. More often than not, if a bike is running and then after some one touches the bike it doesn't run then it was the person who touched it that caused whatever problem it is that is keeping it from running. In other words, if your bike stops working the first thing you should look at is what you may have done to make it stop working.

Chris

[officerbill]

test results

resjudicata wrote:
To check whether the petcock is allowing fuel out just disconnect the fuel hose from the petcock and with a container under it move the selector to prime and see if fuel comes out. Then move the selector back to ON and pull the vacuum hose from the carb body leaving the other end connected to the petcock. Now use your mouth to suck a vacuum on one end of the hose while it is connected to the petcock. If the petcock is working then you should get fuel flow. If either of the above conditions does not allow fuel flow then you have a petcock problem.

Fuel flows on Prime, Fuel does not flow on Reserve or On without a little suction.

To check vacuum, put the vacuum hose back on the correct bung of the carb body and disconnect the other end from the petcock. Now either start the bike or just run the starter and put your thumb over the petcock end of the vacuum hose. You should feel a vacuum sucking on your thumb. If you get no vacuum then check whether you have the hose installed on the right hose bung of the carb. If you are sure the vacuum hose is installed on the right hose bung then you need to check that cylinder as there is a problem with compression/vacuum.

No suction. Did not have the time today for the more extencive test.

BTW, you say the bike was running "okay" until you "tore into her." What did you do when you "tore into her?" What were you working on and what did you do specifically.

I had a few minor issues, burnt bulbs in the gagues, stalling at intersection, vibration and the normal tightening and checking. I pulled the pet cock to see if it was dirty, gave a quick once over and it seemed to be normal, tank also looked normal (not a lot of crud in it). Wanted to check and replace the fuel line to get the inline filter out. Found the vacuum line was cracked at the carb end. I cut it off and put it back on since I didn't have a line to replace it with. I reset the air valves, bench synced, reset the idle and overall cheked the carbs. I still need to get a Manometer on they for a good sync.
After all on this it ran better on Prime only, until last night when it wouldn't go. It runs and idles fast but twist the throttle and it dies. Today while checking the vacuum, it started idled and ran down the road. I could have riden to work this afternoon, but I was too chicken thinking it might not start tonight. I'm starting to wonder if the dew point pressure or just night air is the cause of the poor running? Hard to wrap around that concept thought.

And, I disagree with your friend. More often than not, if a bike is running and then after some one touches the bike it doesn't run then it was the person who touched it that caused whatever problem it is that is keeping it from running. In other words, if your bike stops working the first thing you should look at is what you may have done to make it stop working.

I believe what Dan was getting at that things gum up when not used. 'A body in motion tends to stay in motion, Phys 101.' If things stopped in the middle of a ride somewhere I'd figure something must have broke. When things work in the morning but not at night with no corrections made in the intrum, ... well I got nothing! The best idea I'm seeing is the air screws aren't set right yet. The vacuum lack has me at a loss.

Thanks for your help,
Bill

[DanTheMan]

Bill, lack of vacuum can be caused by valves being too wide open, losing compression and vacuum both. You need to do your shims, you'll find an amazing increase in runnability.

[resjudicata]

If you don't have vacuum on that line then you need to find out why. Are you absolutely sure that you have it connected to the correct spot on the carbs? There are vent lines on the carbs too that just allow ambient air pressure in the float bowls but don't carry vacuum. Only one bung on the set of carbs supplies vaccum.

If the vacuum line is connected properly then you can try something else to see if that cylinder is making vacuum/pressure. Take the airbox off and hold your hand over the carb for that cylinder and hit the starter. Only do it for a second otherwise the bike will suck your and in the carb and spit it out of the tailpipe. No really, only do it for a second because if you have vacuum then that carb will suck a bunch of gas into the cylinder quickly and at best you will foul out that plug or at worst you could fluid lock the motor (which is bad). You just want to feel if you are getting a vacuum or worse feel blow back from the mouth of the carb.

If no vacuum at the carb mouth then first check valves to see if they are just very tight. If they are so tight as to not make vacuum/pressure in the cylinder then you may find you have burned valves. I hope not but it is possible. Report back what you find.

Chris

[almarconi]

You could hook up a vacuum gauge to the sync port to see if you have vacuum on that cylinder.

[resjudicata]

You could hook up a vacuum gauge to the sync port to see if you have vacuum on that cylinder.

You can do that too. Although, he said he doesn't have a manometer yet to synch the carbs so I assumed he didn't have access to a vacuum gauge either. But, that would be easier.

I have a feeling the vacuum line is on the wrong bung. But, without seeing it I don't know for sure.

To the OP: Any chance of posting a photo of where you have the vacuum line connected?

Chris

[officerbill]

The line is connected to the same port as it has always been connected. This lack of vac is a very recent occurence. It would seem more likely to me something is plugged up. I have some time tomorrow in the day light to play before work.
I don't have a vac meter that I know of,(inheireted many of Dad's tools, not unpack them all to date.) I do have a compression meter, but where is yet another story (see album of the shop).
What is the max/min clearence for the shims in inches? Metric is like .03mm? I was going to wait until the ice was on the ground to do all of this fun stuff, but it sounds as if I need do it now.
Bill

[almarconi]

You can get a vacuum gauge from harbor freight for about $13. Have a look here, read through it and you will learn a lot about what a vacuum gauge can tell you about the condition of your engine.

http://www.secondchancegarage.com/public/186.cfm

Once you adjust the valves, you will need to sync the carbs using vacuum gauges, mercury sticks or a carbtune.

The problems you are having probably occurred over time, performance has probably degraded now to the point where it will run like crap or not at all.

[officerbill]

Had a few minutes to wrench on it today. Not enough to do any real good. No vac at the carb. Pulled the plug, not great not terrible, a little sign of not right. Work schedule this week will not allow too much time in the garage. The bad news is I have a full tank.
Later days,
Bill