Bike is Warm, then dies....Frustrated

S

session101

Been Around the Block
Ok so i have a 1980 BMW R65

So far have done the following....

Tank De-rusted and Sealed professionally
New fuel lines and filter
cleaned, and rebuilt carbs
New Spark plugs
New Battery
Changed the oil and filter

Bike has Bing 32 carbs
So i get the floats full of fuel and the bike starts right up and idles great...

for about 5 mins or a little more, then just bogs out and dies.

while running i can pull on the throttle pretty good with no problems but then when its warm, i can't start it back up. and sometimes i can get it to sit, but it you even touch the throttle is dies automatically...

really frustrating, don't know what is missing and causing it to do this
 
Swapmeet Louie said:
sounds like when things get warm, they expand and it is developing a vaccum leak.
Click to expand...

Good point. 32 year old rubber carb spigots can get brittle.
 
Check the plugs too? When I bike runs great cold, and bad warm, sometimes too much fuel (aka running Rich) . Make sure your air screws are set right as these tend to be neglected little screws that make a world of difference!
 
did you ever check your floats? if they are off even by the smallest amount they can either make the fuel run rich or lean...
one of the carbs may be not filling enough so it eventually cuts out... that may be why you can idle right but then it dies, that being because it runs out of fuel in one... or the opposite, maybe too much fuel.
 
look for the easy stuff first, i think since the carbs were done, thats probably the problem.
 
After it dies, try popping the cap on the tank. Some folks accidentally seal the vent when coating it and it causes a vacuum within the tank. As the vacuum develops, fuel stops flowing to the carbs.

If this is the problem, there will be an audible hissing sound as you remove the fuel cap.
 
I ask because my 350F is acting in a similar manner. However, when I open the choke a bit, it idles and revs just fine. If I open it a lot and rev it, I get black smoke which should mean its running very rich. My thoughts are that my problem is that my mixture is too lean, and I have larger main and pilot jets on the way.
 
thanks for the attention guys,

mixture screws..not so much they are pretty good dialed it, when it idles i messed with it so that the idle seems a lot smoother, the book calls for about 1/2 turn out and the bike likes to have it about 3/4 turn out.

Floats on the carbs were set corretly, carbs were upside down on bench and the floats had to be level with the carb base.

i am curious on the vaccum, but there aren't any ports on the carb except the screw next to the air/fuel screw, When i turn on the petcock fuel doesn't leak through the lines and fill up the bowls, if my bowls are empty, i have to pull the bowl and then fuel flows and fills up the bowl. is that normal? but after i did that when i first put lines in

Similar problem on a different vehicle is that the ignition could be the problem, A heated coil does seem to overload and not want to fire correctly until it has cooled, so right now i think im going to replace the condenser, which would be my first cheapest fix, then possibly either the points or the coils next... they are 6v coils
 
Haynes manual recommends 3/4 turn, so your new setting is spot on, try working from this point, my R80 is recommended at 3/4 but runs better at 1 turn out, have you replaced/checked the rubber O rings on the pilot, these carbs are easy to work on, but they can be a bugger with the smallest of leaks or bad set up, and they need accurate balancing. Unlike a multi which will still run if one pot goes down, the boxers will cut out without any warning or coughing. The screw next to the air/fuel screw is for carb balancing. I'm pretty sure you have a carb problem, did you fit a carb rebuild kit?
 
session101 said:
thanks for the attention guys,

mixture screws..not so much they are pretty good dialed it, when it idles i messed with it so that the idle seems a lot smoother, the book calls for about 1/2 turn out and the bike likes to have it about 3/4 turn out.

Floats on the carbs were set corretly, carbs were upside down on bench and the floats had to be level with the carb base.

i am curious on the vaccum, but there aren't any ports on the carb except the screw next to the air/fuel screw, When i turn on the petcock fuel doesn't leak through the lines and fill up the bowls, if my bowls are empty, i have to pull the bowl and then fuel flows and fills up the bowl. is that normal? but after i did that when i first put lines in

Similar problem on a different vehicle is that the ignition could be the problem, A heated coil does seem to overload and not want to fire correctly until it has cooled, so right now i think im going to replace the condenser, which would be my first cheapest fix, then possibly either the points or the coils next... they are 6v coils
Click to expand...

the part above in bold... does fuel not leak after you've run it a bit and it has died? if this is the case, I would quickly check that its not the gas cap vacuum problem that Sonreir brought up. When it dies, does it struggle for a bit and then choke out? Kinda like you're running out of gas?

If the answer is yes, check for that hissing sound when opening the cap after you've run it awhile and think its about to die (like at 4min 59 seconds?). Also, if it putters out and dies. Pop the gas cap, close it again, open the choke and see if the bike starts back up soon after, maybe after giving it just a bit of throttle.

This just happened to me on my lawn tractor and that was the first thing I checked. Sure enough, the damn vent was plugged up!
 
Frog said:
Haynes manual recommends 3/4 turn, so your new setting is spot on, try working from this point, my R80 is recommended at 3/4 but runs better at 1 turn out, have you replaced/checked the rubber O rings on the pilot, these carbs are easy to work on, but they can be a bugger with the smallest of leaks or bad set up, and they need accurate balancing. Unlike a multi which will still run if one pot goes down, the boxers will cut out without any warning or coughing. The screw next to the air/fuel screw is for carb balancing. I'm pretty sure you have a carb problem, did you fit a carb rebuild kit?
Click to expand...

yeah i took apart the carbs, cleaned and put in for a full rebuild kit and replaced all the O-rings and even the floats that were a pretty penny.

I still think its with the electronics, so im going to replace the condenser and see what i got, then the coils and if that doesn't help then ill go back to the fuel side.
 
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