2001 750 dies occassionally

[2muchfun]

2001 owned since new, has 38K miles. It will be running good then begin to sputter, then cutout and die but always starts back up and runs fine. Have drained carb bowls, no water or dirt, tank removed and inspected, clean as new, petcock disassembled and inspected, all good, carb sync is right on the money, have even tried different brands and grades of fuel. My trusted independent shop also went through everything closely and found nothing wrong, however, they did suspect the pulse generator located on the left engine case behind the round aluminum "Honda" cover. It was replaced but the problem continued. This has been an intermitant problem now for a few years and it's happening more frequently. I now suspect the Electronic Control Module but at $600+ for a replacement I want get some of your feedback before taking a gamble. Thanks

[flynrider]

  Could be a fuel tank vent.    If the vent is clogged a vacuum starts to build in the tank as fuel is consumed.  Eventually, it'll stop running because fuel can't leave the tank.

  The usual way to diagnose a tank venting issue is to pop open the fuel cap as soon as it stops running.  It should restart right away and run normally until enough fuel has been used to cause a vacuum.

  I'm pretty sure that the standard tanks vent at the fuel cap.   If you have a California model, the vent is actually another tube running from the tank to an evap cannister.

[2muchfun]

Thanks for your comment. I also thought it could be the venting system but it has also passed inspection. Good call though..........

[Tryvelcro]

Actually, our California bikes have their own vent - if you're sitting on the bike, underneath the tank on the right side there should be a venting nipple with a tube that goes down to the canister near where the centerstand would be.  Make sure that tube is there and hooked up to the canister.  On our bikes that's part of the vacuum system. 

Speaking of vacuum system, check out your vacuum hoses - we have a lot more than out of state bikes, mostly on the left side underneath the tank.  There are 3 diaphragms that the hoses go into, check them all pretty closely.  I had a couple that were original and had to be replaced.  They might not be caught on inspection, but will certainly affect the running.  Also, check the "T" that leads to the petcock - those can affect your vacuum pulling fuel into the carbs & cause it to cut out.

Have you drained your crank case tube?  The one that goes down on the right side, near the right foot peg.

[Moedad]

Hey 2muchfun,

Check this thread. Is this what your bike is doing? It doesn't solve your problem, but it might be interesting to compare notes. I'm in Orange County with a CA bike also.

http://nighthawk-forums.com/index.php/topic,4267.msg51755.html#msg51755

[2muchfun]

Moedad, yeah, your symptoms were almost identical to mine. I have checked and rechecked every hose/vent/fitting ect so many times I could do it in my sleep. I may experiment with the petcock. It requires vacuum to allow fuel to flow to the carbs...maybe not quite enough vacuum to overcome the spring/diaphram due to normal engine wear(?)......thanks to all for your suggestions.

[Moedad]

Moedad, yeah, your symptoms were almost identical to mine. I have checked and rechecked every hose/vent/fitting ect so many times I could do it in my sleep. I may experiment with the petcock. It requires vacuum to allow fuel to flow to the carbs...maybe not quite enough vacuum to overcome the spring/diaphram due to normal engine wear(?)......thanks to all for your suggestions.

It's interesting that even though our bikes aren't the same age, they're in the same ballpark mileage-wise. I'm coming up on 41k. I wonder if there's some random thing with this model of CA Nighthawk that happens to some of them when the bikes get up around 40k.

[windrider]

Well, if you rule out mechanical failure of the engine, which you can since it will restart, then you are loosing fuel or spark.  Get a clear fuel filter, and some extra fuel hose, and mount the filter between the petcock and the carbs.  Go for a ride, and notice the amount of fuel in the filter.  When it dies, check the filter and see if you have fuel.  If no fuel in the filter, problem found.  If you have fuel, then I would start looking at spark problems.  Good luck.

[2muchfun]

A symptom I neglected to mention. After I restart the engine I get a fair amount of black exhaust smoke. This indicates a rich/flood condition. My reaction when it begins to cut out is to give it more throttle, but if the ignition system isn't working, then I can understand why this happens. I'm still leaning towards an ignition or ECM problem. All the wiring harnesses and grounds have also been inspected.

[Moedad]

A symptom I neglected to mention. After I restart the engine I get a fair amount of black exhaust smoke.

Hmm...mine doesn't do that.

[Brittles]

From your description of the bike sputtering then dieing I'd be leaning more towards a fuel delivery problem rather than an ignition or ecm problem. If it was the later wouldn't the bike just die immediatley and not sputter?

BTW, I'm not 100% sold on your trusted mechanic.........the pulse generator can be tested and if it was (I'm guessing it wasn't) it was either good or bad.