Silly question: At 5K rpms,

[Guest]

What circuit is the carbs running through (needle or main jet)?

84 Katana 750

[tkent02]

Depends on throttle position, not RPM.

[TheCafeKid]

Depends on throttle position, not RPM.

Indeed. You can be spinning 6-7k but still be in the pilot circuit. Or you could be well on your way to full main... The easiest way to discover WHAT circuit you're having whatever problem in is to mark your throttle with tape from closed to WOT in 1/8 turn increments ive found. Some may say 1/4 turn, but if you're having a problem in transition between two circuits rather than a circuit itself, the 1/8 will be a bit more revealing.. Give that a shot, then let us know what youre dealing with! Curious minds want to know!

[Steve]

Are you doing 5K RPM in neutral or up a hill in fifth gear?

In neutral, you are likely still on the pilot circuit, in fifth gear you will be wide open, on the main jet.

.

[Smokinapankake]

Flat, mostly level terrain. Throttle cracked open enough to maintain 55 - 65 mph.

Plug chops show lean condition.

At those speeds, the bike kind of "surges" as if it were running out of gas. This makes sense (academically, anyway) as they are lean.

Over the winter I tore the carbs down, cleaned as per the GSR manual, replaced o-rings, and bench synched but have yet to vacuum synch as I haven't had much time. Valves were adjusted less than 1000 miles ago.

Airbox, not pods, with stock exhaust headers. Mufflers, however, were cut off because they were rattling (and non-serviceable) and replaced with cheapy aftermarket items. I think this may have something to do with my problem. I've got a set of 88-ish Katana 600 exhaust on the way that I'm thinking of replacing the cheapys with. As I understand it the 88-96 ish Katana 600 and 750 used the same exhaust so airflow and back pressure should be similar to what was original to my 84?

Been looking for a 4-1 header for 2 years now with no luck.

[Nessism]

Shimming the needle works wonders on these lean GS bikes. Pull the carb slides and then remove the needle (long nose circlip pliers required). Take off the plastic spacer on top of the needle clip and replace with a stack of small washers roughly 1/2 the height of the spacer. Put everything back together and try the bike. It should run better. If you still need a little richer mixture remove another washer. I've done this trick on several GS's and all of them responded positively.

Good luck.

[TheCafeKid]

I agree with Ed. Ive done it to a couple of stock bikes and it helps A LOT!! One question: Does it seem to get a little better once the bike warms up? No change? Worse? At least for me, Ive found that at minimal throttle openings, sometimes its hard to discern between what I would consider a "lean stagger" vs a rich flatspot that you sort of gravitate around at small openings...

[Smokinapankake]

I've tried raising the needle as it has multiple notches on the needle by lowering the clip one notch. Made the surging worse but I did not plug chop to verify if I was rich or lean, so I went back to original stock setting.

Maybe one notch difference is too great?

TCK, it seems to be about the same warm or cold, but I would have to say that if it is worse in one, it would be worse when warm.
I'd wondered if I was in a transition phase whereby if I whack the throttle it would be better, but it seems fairly consistent from about 50 mph on up.

Been fighting various issues on this thing for 2 years now, and if I could find a reasonably priced 4-1 header I'd go the whole pods / jet kit / exhaust route.

[Dave8338]

when you feel the surge what happens if you add a little choke?

I too, had to raise the needles 1/2 notch to rid the problem of a "surge" that was only noticeable, once the outside temps dropped into the 40's.

[Steve]

Been fighting various issues on this thing for 2 years now, and if I could find a reasonably priced 4-1 header I'd go the whole pods / jet kit / exhaust route.

Just think ... you go "the whole route", you get to play with jetting problems ALL OVER AGAIN.

.

[Smokinapankake]

Nnnoooooooo!!!!!

[TheCafeKid]

If its actually worse when warm, you may be rich in the pilot. Ive been playing with my pilot set up even with the DJ kit in my 1100ES. A quarter turn on the adjustment screws makes a bigger difference than one might think. Also, from MY experience, one whole notch can make a HUGE difference in MPG, as well as smoothness. EX: I was running my ES in the third clip from the bottom. It ran well, better up top than down low, and i was getting 37-42mpg even when putting the whip to it. I dropped the needle to the 4th clip from bottom (leaner) and noticed a little studder on the transition from pilot to needle, but was getting 47-50mpg and still had good looking plugs. (I purposely leaned it because i was headed for altitude on our recent trip to WV) Now that im home, I have TWO shims in the needle (the DJ washer, and another stock washer, which is apparently equal to a half clip) and Im spot on, no studder and STILL getting 45 or better unless im REALLY beating on her. even then im better than 40mpg...What have I learned? Basicly what looks to the eyes like a small adjustment actually has a bigger effect than it would appear. Now to your problem...Like i said if it actually IS worse when warm, thats a sign of richness, but what you need to do is figure out WHERE its rich. Is it just off pilot into the needle? or is it the pilot circuit itself? The only way that *Ive* figured out how to tell is by marking the throttle like I said earlier in the thread, and then only adjusting one or the other at a time. Start with the pilot screws, since they're easiest. Back em off a half turn, see if it gets better or worse or no change. Then try adding a half turn, and compare. If there is no change there, then move to the needles. As has been pointed out on here before () Im no carb expert. But all i can offer is what info I have gleened based on months and months of asking questions, seeking advice from those who do this WAY more often than I and pulling whats left of my already thin hair out. I tell ya what, if you'd like to discuss this further, let me know, I will give you my phone number, and I will try to help as much as I can...

TCK

[Smokinapankake]

TCK,

PM sent.

I've been fighting this thing for way too long.

Thanks!