Backfiring/hesitating in 03 Intruder 800

[Mfidget]

Folks,

Having an odd issue with my relatively new Intruder. I have a slow patch in my morning commute where I have to drive a sustained 30 MPH or so (no room to pass!) When I do this for a few minutes, the engine will start to ... well ... burp or stumble or hesitate -- describe it as you wish. It's like I dropped the throttle suddenly. It happens every 20-30 seconds or so until I get up to a higher speed or drop down a gear.

Is this a sign I need a tune-up, or is there an adjustment I need to do?

Thanks!

--Mike

[Uncle Bob]

Doubt it's anything major, could just be a quirk!

Could try just turning the idle screw a quarter turn or so and see if that helps otherwise you may have to drill out the plug on the air/fuel ajustement screw and fiddle with that.

Are you using regular gas 87 octane ? if you're using higher octane that could be the culprit.

[Mfidget]

Nope, 87 octane, though I was told to use 89 or higher (???)

I don't have a tach on the bike, so I'm not sure whether to increase or decrease RPM with the idle screw. All things equal, it seems to move smoother off the line with a slightly higher RPM, but I don't know if that's good or bad for the eninge. What do you think?

----Mike

[Uncle Bob]

Hard to say exactly what the problem is, doesn't sound major however. I'd just try a quarter turn at a time and try it out.

These bikes are not exactly hi-tec, plugs if not "hot" enough may be fouling at the RPM range you're in at 30mph or maybe some ajustement of the air/fuel mixture need to be done.

Might try removing the air filter and see how the bike reacts to that in similar situations. If it improves then you're running a little rich, if it gets worse then you're running lean.

You mention that it gets better when you downshift, are you lugging the engine ? If this is the case then you are actually flooding the engine.

What bike exactly do you have ? Year ,model, etc...

[Mfidget]

It's a 2003 VS800GL with about 2400 miles on it. I tried your suggestion of turning the idle adjustment. Seems better, but now it also seems like it's idling fast. Of course, I'm guessing at that, since I don't have a tach. I'll keep playing with it.

While on the subject of lugging, these kinds of slow patches seem to be right between two gear choices. If I'm in a low speed situation like above, is it better to rev higher (possibly heating up the engine) or lower (and possibly run too rich)?

Thanks for all your help!

----Mike

[Uncle Bob]

I would opt for the lower gear ( higher revs ), this would insure the fuel is burned more complety and avoid fouling the plugs. This would be less starinfull on the engine and I'm guessing would actually improve cooling.

Of course we're talking about a slight difference in RPM's here not revving the engine full throttle.