Bike sputters and dies after riding for 5-10 minutes

Detroit650

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I finally got the right cylinder to fire on my bike today. The pilot screw on that carb had to be backed out until the point that you could barely feel the spring's resistance. I didn't count the turns, but it was probably in the neighborhood of 5 turns out vs the 2 it took to get the left carb to behave nicely.

After letting it idle in the drive for a while and rapping it up a few times, everything seemed fine. So I hopped on and rode to Autozone to get some parts (5 to 10 min ride). Then rode to Lowes (5 min ride). Then to the hardware store (5 to 10 min ride) and then home (2 to 3 min ride). Everything seemed fine...

I threw on the vac gages to check the balance. They were toggling with an average of about 17" (if I remember right). The right carb seemed to have about 1" less movement in its swings.

Figuring the bike was running good enough to take my girlfriend to dinner, we hopped on and headed to town. While trying to baby it, I bogged it leaving a stop light. It started surging/ cutting out like it was running out of fuel. I tried working the throttle to keep it running, but it didn't want to come back to life. On clutch in it died, so i pushed it up on the sidewalk and started cranking it over. After cranking it over about 5 times (I only held the button for 3-4 seconds each try, then let it sit for a few seconds before trying again). It would sputter just a little bit. So I kept trying it, until it finally sputtered to life with the help of about half choke. It started running just fine again (idle, accel and cruise).

Thinking it might be a faulty fuel valve, I switched to reserve. But about 3 mins and 2 or 3 stop lights later it started bogging down while riding at about 40 mph. Again, I worked the throttle long enough to get to the next intersection, then it died when I clutched in for the turn.

Played the same game again and got it started after 10 or 15 cranks.

This time we made were already half way home. But at the next stop light, the same thing happened, and again after being patient and plenty of cranking, it sputttered back to life and got us the last few blocks home.

It sounds to me like the carbs are starving for fuel, but they got me around town earlier (and I wasn't putsing around then). Or it might be plug fouling, but it seems weird that both cylinders give out, and not just one side. I doubt it's the coil cause it starts back up without getting a real chance to cool down.

I've seen in other posts that the fuse block can cause headaches, but it seems progressive like a carb issue and not instant on/off like an intermittent electrical issue (the engine dies slowly until the clutch is pulled and then slowly comes back to life).

Thoughts?
 
I finally got the right cylinder to fire on my bike today. The pilot screw on that carb had to be backed out until the point that you could barely feel the spring's resistance. I didn't count the turns, but it was probably in the neighborhood of 5 turns out vs the 2 it took to get the left carb to behave nicely.


Thoughts?

You should have quit right here. That is not right. Just because you got it to run doesn't mean it's OK. I personally think that people have a tendency to screw with the idle mixture screws when in fact they have a carb sync problem. I start buy setting the idle mixture screws to a nominal 2 1/2 turns out AND LEAVE THEM THERE while I sync the carbs...:thumbsup:

I have 5 motorcycles with a total of 16 carbs and I do the same with all of them and they all idle and run perfectly. It's like having a bunch of kids. Once you start coddling them and trying to make each one happy there is no end to the grief. I say, give em all Oat Meal !:D (The little beggers! :mad: )
 
Hi

I had similar issue. Check that you are getting a spark when it cuts out. I had a faulty coil / plug lead combo. However it sparked fine whilst left for a while, then after a few mile spluttered and died. What ignition system are you running?

Paul
 
For the mixture screws: Are the passages clear? It shouldnt be 5 turns out..especially with one only being 2..

Are the jets clean?
Fuel lines clean?

Move onto electrical..
Strong spark on both sides?
Plugs fresh and gapped properly?

You may have fouled the plug when you were messing with the mixture screws,
And to me it sounds like a fouled plug..
 
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