hard on the throttle, now it runs poor.

[cd89]

Ok, First post and I want something from you'll.... I know, selfish of me... Sorry. But I have been a lurker for a while now (if that helps??). I have an 06 gs500f all stock with a little over 18k Miles on it now. I was just out riding it and dropped a couple of gears to pass a car. I wound it up and passed and not 2 seconds later it started sputtering and bogging down. Made it home and it ran a LITTLE bit better on full choke. Sat in the driveway with it idling for a moment and noticed a rattle from the top end .... Doesn't sound good. I should say that I also checked the float height (which was slightly high) 5 miles before this. Could junk have gotten sucked into the fast jet? Could that cause a fuel-starvation induced rattle (is there such a thing?). Jumped timing? burnt valve? Haven't had any running problems prior except frame-mounted petcock issues (by-passed with shut-off valve). Just wondering what I should try to check for first... No cold-start issues. I thought I heard a ticking before but it was so inconsistent and faint that I couldn't tell if I was imagining things. Any help is greatly appreciated. 

[cd89]

I also should state that it rev's fine to high RPM while parked but has the problem under load.

[Joolstacho]

So you had done a float-height check before all this happened? You don't say whether you changed the float height though.
If it's running a little better with a little choke then it points to a lean mixture, as could a top-end rattle possibly... a lean mixture can exacerbate pre-ignition, or detonation, (which sounds like a rattle, -you mention "fuel starvation induced rattle")
If you can, do a roadtest and see if putting the choke on a bit helps at all throttle openings or just one throttle opening stage, eg wide open, or low to 1/3rd opening, or mid. That could point you towards a cause.
If it's jumped timing or burnt valve I don't think choke would make any difference. And those would cause hard cold starting probs which you don't have. And when did you do the petcock conversion? Could that be related? Has it been running well for some time since you did that?

[cd89]

Yea, I didn't change the height. I have ran the bike around 1000 miles since the fuel valve conversion with no problem.  I also did play with the choke on the way back home (10 miles). It made little difference from 1-25mph (accelerated ok). After that it started stumbling and sputtering and would slowly make it up to 50mph max. when the choke was applied it seemed to smooth out a little but still would not go faster. probably going to pull the carbs today and take a look.... thanks for the reply.

[cd89]

Ok, So I took the carbs off today and tore them apart... Was a chore. I had to drill two screw heads off and and wrench the stud off with vice grips... Replaced with allen heads. First carb (RH) was a little dirty (liquid gasket particles) so i took out the jets soaked and sprayed them, cleaned the bowls and re-assembled. The second was full of liquid gasket particles (used on both carbs... new gaskets on the way). The first thing I noticed the main jet has a small piece chipped off of the corner where the slot for a screw driver is (will this affect how it runs??) And What I think to be the culprit was A rather large (in carb terms) piece of clear plastic stuck in the main jet opening. It looks very close to the color of the fuel filter I installed...... 

I also checked the valve clearance while I had it apart. 3 are a bit too tight with the one I thought to be the one out of tolerance being on the verge.... Definitely needs shims replaced.

[cd89]

Correction, pilot jet.. Small corner of brass was chipped off and piece of plastic stuck in the PILOT jet..   I Re-read my post...

[BockinBboy]

Sounds like you uncovered quite a few issues to address.  I'd get those solved, such as cleaned carbs, new gaskets, and replaced shims - then let us know how this fares.  Too much going on right there to add anything more to the list anyway, and one or each of those could very well solves these symptoms you have described.



- Bboy

[Joolstacho]

+1  Bboy.
Ceedee... let's get those carbs thoroughly sorted -and you'll be cookin' I reckon mate.

[cd89]

So I have gotten the carbs back together. WOW what a difference at highway speed!! Definitely needed a good cleaning. However I am still having a tapping noise from the top end. It seems to be worse cold and seems to go away around 2-4k rpm. I guess my question now is could a valve job and carb sync smooth that out or does it sound like permanent damage from out of spec valves? It seems to run fine (a little rough cold) but even surprised me how quickly it started after popping the carbs back on.... Keep in mind that it didn't start until the carbs got clogged.... Just a coincidence? Thanks for any input.

[cd89]

Ok, so after starting it up and letting it run (at idle) a bit I have noticed a few things. Fist of all I was wrong about the knocking being worse when the engine is cold.... It seems to be completely random with a few tap-tap-taps here then a few there... or sometimes almost none at all... strange. Also it seems to not want to stay idling as easily when cold (needs choke longer). This may have something to do with the engine sounding as if the carbs are out of balance which I'm not going to fix until I get the valve shims in spec. The last thing I noticed is when I quickly crack the throttle a bit open a often get a hesitation and sputter (almost back-fire). It was doing that before but much less often... Any Ideas? Thanks.