Every once in a while, I'll go through a short stint of some really rough engine vibration(at least MORE rough than the normal Evo-vibrations). Only lasts for a good 5-15 mins, in the middle of an all day ride, even.

Any ideas?

 

Sounds like you might be "losing" a cylinder. Do a compression and leakdown test to ensure that all is well mechanically. If it is then look at your ignition. Look at the plugs, wires, coil. pickup and wiring if you are running a single fire setup. That should give you a good list of things to look at. Check them out and then get back with the results. Hope this helps.

 

Fuel tank venting issues can cause that. They have to vent outward as well as allowing air in for the fuel to flow. If they aren't venting out, pressure can blow the fuel under high pressure into the bowl when the needle opens and create a flood situation or if they act up ocassionally on the inward vent, it'll starve.

Maybe try loosening the right cap a little as soon as it starts getting rough and see if that takes care of it in about 15 seconds or less. If so, maybe replace the venting cap.

 

Thanks all!

I'm going to try the fuel cap idea next time.

Lord, I hope that's it....I don't have the knowledge nor the tools to do the tests

 

dnlp-- try this after the easy test that tj150 suggested-- it's part of what John suggested without the need for special tools:

next time it happens pick a cylinder and removing one spark plug at a time, and with the plug lead for that cylinder attached to the plug you just removed, lay the plug base against the head or other non-insulated steel component (in order to ground it) then crank the motor while looking for spark at the plug. DO NOT turn the motor over unless the plug base is grounded, or damage to the ignition system can occur.

if you see spark between the plug electrodes while the motor is turning over, replace the plug and lead and do the same to the other cylinder.

If this is the problem you can try a different plug, then a different plug lead, then work back ( or have a shop do it) through the ignition system.

At least you will be able to help them diagnose the problem by telling them what you already know.

ALWAYS do the easiest stuff first then work back thru the harder stuff.

My money is on intermittent loss of 'fire' to one cylinder though--let us know what you find.

 

good stuff. Will put in my bag of stuff to try when it happens next

 

Also check that your engine mounts are tight.

 

dlnp-- After thinking about this last night, I recall that sometimes a coil, when it's on the way out, can start acting up when it gets hot.

Don't know when the rough running commences but if it starts acting up just at full operating temps and/or in really hot weather and/or in stop/start traffic conditions it could be the coil failing.

It's easy to change a coil for another one to test this, but check the plugs and leads first, then work back through the coil and ingintion module.
Let us know what you find please.

 

The first thing i would do is check my mounts and im sure these guys have thrown you ideas that will take you a year to go threw but i read them all and they saved me alot of things to say I LOVE THIS WEB SITE......

 

With what you are saying I say "Mechanical." I have been through the ignition and fuel problems that are intermitant. Do what the others are saying, check your motor mounts and things like that. Running rough is one thing. Feeling the "running rough" is another.