loading up after new top end?

[stainlesscycle]

so i replated my top end, and it's been broken in. i still need to re-shim my pv, it clatters, i could see the slop when i reassembled, just haven't gotten to it. gonna do it when i fix my kicker.

but here's the issue:

it seems to load up when i wack the throttle, and struggles to get on the pipe/rev out. i can clutch it, and zing the throttle a few times and it cleans up/will rev out. or if i hold it wide open it will eventually get on the pipe. until then, it stutters like it's rich.

my normal jetting on this motor at this elevation and temperature has been perfect in the past:


1.5 a/s, n1eg #2, 172, 42pilot.

i dropped the needle to #1, and it didn't fix it.
i leaned the a/s to 1.75 and it didn't fix it.

the plug does not look rich, nor does the bike act rich except when i transition from the pilot directly to the main. like exiting the woods onto a big straight. 1/4 throttle to 3/4-wot...

i don't want to go leaner on the main, when it eventually gets on the pipe, it's running great, it's just the getting it to that point that's the issue. yes i've changed the plug. bike runs perfect up to 1/4 throttle, and if i stay on the pipe it runs great, it's just got this big stutter in between sometimes... i thought it was jetting, but maybe it's powervalve flutter? i don't have it against the stop yet, i can hear it clunking...

any suggestions????

[Fred1956]

Make sure the power valve is working- many threads on proper preload. no preload will also cause the rattle to be worse.

[stainlesscycle]

yeah, pv is working, i know the preload procedure, just didn't do it - hadn't had a chance to get to it - was racing other bikes in the last few weeks, just through the top end on and went racing.. pv alignment changed when i put this top end back on. pv is definitely opening. also, i can hear it rattling against stop when it's fluttering.. would pv preload cause that much of a 'lag' i would think it's still opening properly, just not shutting properly..


either way, guess i gotta go in there and set it back up. maybe that will fix it.

[GMP]

PV won't do that. Sounds like bad reeds to me.

[stainlesscycle]

hadn't thought of that. haven't looked at them in about a year. might be time. 07 is vf3 right?

[Jakobi]

Lonetree had the same issue with his 09. Chased it around for weeks and it turned out the spark plug cap had untwisted a bit and would break up under high rpm. Go over the electrical agains and also check the reeds.

[stainlesscycle]

will change the cap, but its fine at top/not breaking up. it's just getting there that's causing the problems. bike starts and idles fine, which i've found is usually a good indicator of reed condition

[Jakobi]

Originally Posted by lonetree

im curious to hear what people may suggest....
my 09 GG250 2banger, with low hours, a reasonably recent topend rebuild, etc, was running great,...
so a couple of weeks ago i started to play around with my jetting, trying different needles out..
after getting some interesting results, and some brilliant bottom end responses, i was still not happy with the top end performance, in particular, if i snapped the throttle open quickly to WOT, i was seeming to be consantly running lean. after chasing jets and going to rediculously rich settings, loosing the good bottom ends i had been chasing i still couldnt get the bike to rev "cleanly" if i was really trying to keep it on the pipe- with a constant "stutter" as if it running out of fuel.
in my frustration i have gone back to my original settings with needle and jetting, (N1eg 38/178) and low and behold, now it has the same symptoms.
i can get it to run nice and crisp off the bottom, constant idle, good temps, but every time i try to keep it on the pipe, it stutters...
I've checked:
float height
changed plugs,
fuel flow out of tank,
pulled jets and cleaned, yet to pull whole carby and hit with carb cleaner and compressed air...

i will also check the reed block and reeds...

but where else do i look?
any other suggestions? what am i missing? (better not find a rag in behind my air cleaner ^rof)

Originally Posted by lonetree

so i just thought i'd report on my findings........
i pretty much did everything i was going to do, without any obvious problems. everything was clean, working, adjusted right....
dropped a brand new sparkplug in, even though i had tested several that were known to be good.
put some extra high temp copper gunk on the viton o rings...
AND, put a new air cleaner in, even though the old one wasnt very dirty...
quick squirt, problem gone.... BUT NO EXPLINATION ^cens^BGHD

about all i could find was, the sparkplug cap seemed a little loose but less than a 1/4 turn to tighten it....
and the air cleaner, had "stuck" itself in, apparently no toil will dry out if left too long... perhaps it was running super rich, but it didnt seem like it was... (nothing like pulling a choke on)
im not sure if either of these explain things, but its going now ^nana
thanks for all the suggestions..

In hindsight looks like it might of been the air filter more at fault here not letting it breath.

[stainlesscycle]

preloaded pv, of course the rattle is now gone

doesn't appear to be loading up anymore, maybe the pv was so loose it was sticking occasionally? but i won't know 100% till i race it this weekend. going to reset the needle back to #2 and see if it's fine... still have to tear into reed cage and take a look. maybe tomorrow. got some other bikes to work on.


EDIT : oi had a chance to ride it a bit more.. still loading up. going to 170 main and see if that fixes it. that seems lean for n1eg/2000'/80 degrees. gonna have to do some plug chops.


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[stainlesscycle]

170 main doesn't fix it, although it makes it a bit better.. i can duplicate the problem. i do a slow rolling start in 3rd gear and wack the throttle to about 3/4 or more.. it accelerates clean, then stutters and then finally gets on the pipe maybe 150 yards later. if i keep the revs up, it will pull clean. if i drop it back, let bike slow way down, and try again it stutters. maybe it's not jetting. gonna check reeds tomorrow.

this bike ran perfectly fine on 172 main before i replaced top end. the pv is working, and opens/closes smoothly.. i dunno what else it could be.