HELP!!! Engine dies after a few minutes idle.

[stevoman88]

Hello,
I have a 1974 xs650 hardtail. sporty tank, new filters, carbs just rebuilt by my shop, I also have straight pipes. After about 5 minutes at idle she dies. She ran good on the highway for the most part but any time I stopped at a light she dies. At one point on the highway she started sputtering like she was in need of gas and died! I really have no idea on what to do here. She also has an oil leak on the left side by the engine fins near the spark plug. Any ideas would be appreciated.
Thanks

 

[stevoman88]

I did unscrew the gas cap and it seemed to run better. Could it be there is no vent on it and it is not getting the proper amount of air?

 

[littlebill31]

What type of carbs? Year of carbs? Did you sync them? Float adjusted correctly? Idle adjusted correctly?
The sporty tanks sometimes cause a bad vacuum. Depending on what type of petcock you have and gas cap. Is it a vacuum cap?
Another thing people forget is that the petcock on some tanks is too far forward and the tank is sitting at too steep of an angle. Therefore you have to always have the tank filled or the level drops below the petcock, even though there is a gallon or more in there. Just an FYI.

The oil leak is most likely the head gasket. Just retorque it. Usually does the trick.

 

[ippytattoo]

After reading your first post it would seem very likely that if the gas cap is not venting corrrectly it could be causing a vacuum to build in the gas tank and this will starve the carbs of fuel. As far as the oil leak goes clean the engine really well and pin point the origin of the leak. It could be coming from the cam seal on that side but you still need to clean it really well and find the source. You may find that it is coming from inside the chrome cover that goes over the end of the camshaft (breaker cover).

 

[stevoman88]

1974 Carbs with Mikes xs pods on them. Shop rebuilt and did everything on carbs. He told me they were good to go. He took the bike around locally and it drove fine. When I got on the highway and drove 10-15 minutes it started sputtering and died. After a minute I started it and it drove fine again for another 10 minutes or so. How difficult would it be to check the float level? Any directions or diagrams would really help. I think its either float level or vapor lock.
Thanks again guys.

 

[littlebill31]

You might also want to check your coil. Just in case. When coils go belly up they have a tendency to run for 10 minutes, get hot, then stop working. Then it takes a couple minutes to cool before it starts. Then it'll do it again.
In my experience the bike wouldn't go 10-15 minutes if the vacuum was bad. One reason I use clear fuel lines, so I can see it flowing.

You can either take the carbs off and check them by removing the bowls and measuring the floats. Or hook a clear tube to the bottom of the bowls (if you have a drain nipple), turn the tube upward (so it looks like a "J"), then turn the gas on and see where the level is. It should be a tad below the top of the bowl, where it mates to the carb body.

Have you read www.amckayltd.com/carbguide.pdf

 

[stevoman88]

I had thought about the coils but they are brand new from Mikes. I guess there is a potential one is bad but unlikely. I am still leaning towards float level..... Need to read up and figure out how to work on the carbs. I have never had them apart. I will check again tonight to see if it is a vapor lock. I am also gonna try and get some clear lines to check and make sure the fuel is running freely.

 

[littlebill31]

Clear lines make it a whole lot easier. You can watch to make sure it's moving freely.
It probably is floats or vacuum, I just pointed out the coils in case. Coils can fry quick. Just leaving the key on too long will do it.

 

[stevoman88]

Bill,
Thanks for the info. I will pick some clear lines up after work and put them on when I get home. Ill update after I see whats going on. To test should I just watch the fuel pass through and see if it is easily moving through? If it starts to die at all i will try and open the fuel cap to see if it helps it at all. Anything else you would recomend?

 

[ReycleBill]

I think you diagnosed your problem correctly when you noted that removing the gas cap made it run better-- needs a vent.

 

[stevoman88]

The issue with that is that I called TC Bros. this morning and they advised the cap I have is vented. Maybe its not getting enough air?

 

[DogBunny]

It is easy for a gas cap vent to get plugged. If the cap is new, it may be defective.

I once dropped my Sportster while rolling it around my driveway. It was down for a couple of seconds. My gas cap would not vent properly until the gas that had gotten up into it evaporated.

 

[stevoman88]

Well I have clear hoses to test tonight. I will also do a test on the gas cap and see whats going on there. Ill do the test on the carbs to see if the floats are set right as well. Ill let you guys know. Any other info you may have let me know. I really appreciate it.

 

[stevoman88]

Well I put a clear hose on it and unscrewed the gas cap. Initially gas was flowing freely. After about five minutes there was a very small stream in the bottom and that was it. The bike died about 7 minutes or so in. This would tell me its not vapor lock but rather the float valves. They must be set to the wrong level. From what I read for a 1974 xs650 it should be 24+- 1mm. Does this sound right to you guys??
Thanks again!

 

[stevoman88]

The exhaust is also shooting a flame when you rev the engine high. Would this mean that its running too rich? The main jet is too high?

 

[ReycleBill]

Well I put a clear hose on it and unscrewed the gas cap. Initially gas was flowing freely. After about five minutes there was a very small stream in the bottom and that was it. The bike died about 7 minutes or so in. This would tell me its not vapor lock but rather the float valves. They must be set to the wrong level. From what I read for a 1974 xs650 it should be 24+- 1mm. Does this sound right to you guys??
Thanks again!

What does float height have to do with gas flow? If the fuel isn't flowing TO the carb then the problem is in the tank-- low fuel, trash, water, defective petcock? The fuel line should remain full regardless of float settings.

 

[ReycleBill]

The exhaust is also shooting a flame when you rev the engine high. Would this mean that its running too rich? The main jet is too high?

One problem at a time.

 

[littlebill31]

To check your petcock, a simple dirty way, is to remove the line at the carb, put a cup under it and turn it on. Try it also at the petcock itself. It should have a nice, steady stream. As Bill say's, if fuel is not getting to the carbs, it's in the tank. The floats can cause it to die, but fuel will still be in the line.
And make sure the fuel is above the petcock in the tank. Refer back to what I said about where they are located in relation to the fuel level.
My Honda had, what I thought, was a vacuum problem. It was weird, and a total fluke, but I pinched the line off, ever so slightly, away from the petcock nipple and fuel start flowing freely again. I think it was just an air bubble or dirt, but it's worked since.
So I would try removing the line totally and turning 'er on.

 

[ReycleBill]

And if your gas smells like beer you know it's time to sleep it off.

 

[knap-sack]

I like the ideal of running line from tank and watch it empty a tank of fuel, that would rule out petcock, I have had this happen on several bikes and it was always the petcock.