Tuning and Jetting My 1982 450

[pete]

That was my original plan quite a while back.

There's a mob here in Aus (http://www.wbo2.com/) that sell one in kit form to keep the price down, but has features including data logging.

That was what I was going to get, but it got postponed due to $$$ and I'll probably leave it now until after I get my Kat.

[pete]

Quick update with the current status... a while back a couple of guys commented on my still rich mid-throttle positions (one guy has a nose that works awesome with smelling rich/lean exhaust gas).

So, I took the needle back to the stock (middle) position and added a shim so it's half a notch richer than stock.

Instantly the throttle felt a lot crisper at those lower throttle positions but I still felt it was a bit rich at WOT.

So, last night I installed 142.5 main jets (down from the 145's) so I'll see how that goes.

I also counted my mixture screws last night and was surprised to find they're only 2 3/4 turns out.

[pete]

Still wasn't quite happy today so have gone to 2 1/2 turns on the mixture screws... but aside from at idle and almost closed it definitely feels more crisp on the throttle again, should be getting out on Saturday to see what WOT feels like now.

[pete]

So after Saturday's ride and the last two days' commute my mixture screws are back to 3 1/4 turns out. At 2 1/2 it was horrible when cold, very hesitant as the throttle opened to the point of stumbling and had to really crack it to get her moving until she warmed up a bit.

As for the needle and mains, they feel great! Didn't seem so soggy at or near WOT and mid throttle positions are definitely a better feel.

Looks like 1 shim up from stock and 142.5 mains are good so far.

[mikestp]

I have found that with some Mikuni float bowls the part throttle passages are half way blocked. They might actually pass some fuel even after you shoot them with carb cleaner. That small passage in the float bowl that supplies fuel to the part throttle port just past the idle position of the throttle plate, work from that point till about 2500 rpm. After that time, both the idle port and the part throttle ports are no longer measurably effective because at 2500 rpm your main jets come into play. What I usually do now on all my Mikuni rebuilds, is get a 1/64th size twist dril, set the depth to not drill through the bottom, and drill out the float bowl passage. In most cases I can feel the drill "thunking" into the lower chamber as it drills through the blockage. No metal shards have ever been seen, so I know I am drilling petrified gasoline. After reassembly the carb has taken on a whole new personality where throttle response is quick and tight with no apparent flat spots. At least not while on the centre stand. At that point I can take the bike out and test for main jet adjustments.

I have never seen a message regarding the drilling of thses passages in any forums. But after reading sooo much stuff in these forums with people searching for reasons the carbs are not working..... I have found just about 100% success rates after I drill out the passages.

[JJ]

I have found that with some Mikuni float bowls the part throttle passages are half way blocked. They might actually pass some fuel even after you shoot them with carb cleaner. That small passage in the float bowl that supplies fuel to the part throttle port just past the idle position of the throttle plate, work from that point till about 2500 rpm. After that time, both the idle port and the part throttle ports are no longer measurably effective because at 2500 rpm your main jets come into play. What I usually do now on all my Mikuni rebuilds, is get a 1/64th size twist dril, set the depth to not drill through the bottom, and drill out the float bowl passage. In most cases I can feel the drill "thunking" into the lower chamber as it drills through the blockage. No metal shards have ever been seen, so I know I am drilling petrified gasoline. After reassembly the carb has taken on a whole new personality where throttle response is quick and tight with no apparent flat spots. At least not while on the centre stand. At that point I can take the bike out and test for main jet adjustments.

I have never seen a message regarding the drilling of thses passages in any forums. But after reading sooo much stuff in these forums with people searching for reasons the carbs are not working..... I have found just about 100% success rates after I drill out the passages.

Can you please post a picture of the passages you are drilling? I have never needed to drill any part on any motorcycle carburetor to make it work correctly.