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1982 Suzuki GS450 Ignition timing system

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mr72:
If there's a rip in the diaphragm, you have to fix that FIRST. Even a tiny pinhole will make the entire carb not work correctly.

Pod filters may make this harder to tune. It slows the air velocity, which is why you need bigger jets... slower, higher pressure air means we have to add more fuel per unit over time to achieve the same mixture as with the faster, lower pressure air.

To me, this sounds like it's running too rich on the main jet. I should say, this is precisely how my GS500 ran when it was too rich on the main jet. At first I thought my problem was ignition, and I was wrong.

Phelicks:
For the diaphragm, I couldn't see any holes in the wall of it, just the ridge portion that goes in the carb groove and some rips. I do have a replacement pair, but I want to be sure I need to replace them because it looks like a pain to change.

For the jet issue, I tried everything, stock jets on the main and pilot, +1 pilot with stock main jet, +1 pilot with +2 main jet and yesterday I tried +1 pilot with +4 main jet. The plugs on the 2nd setup looked a little lean so I decided to put a bigger main.

The story was the same for the last two setup, bogs down like the engine just want to stop completly and it won't rev past the different "walls" in each gears.

Phelicks:
Well well well, thank you mr72 for giving me doubts and thinking about my choice of main jet all night long  :icon_confused:. This morning I got to work and put the original main jet (117.5) and leaving the +1 pilot jet (45) and the bike ran alort better reving out in first gear, but not quite in 2nd, 3rd and the other gears.

So now i'm confused, because in my mind my "pod" setup would let more air in, looks like im wrong about that  :dunno_black:. I'm saying "pod" because I made my own setup with some plumbing rubber and a foam filter that is oiled. So now it looks like i'm restricting the air flow making the stock jet too rich. Should I order new jets to take more fuel out at wot or could I play around with the needle height?

mr72:
Yeah it's a common misconception that a "less restrictive" air filter "lets in more air". The bike was getting plenty of air with the stock filter. The amount of air is a function of the displacement, and the rate at which it consumes that air is a function of the rpm, within reason anyway.

So the air filter doesn't "let in" air. It just filters it. By filtering it, it may be adding some resistance which will decrease the air PRESSURE for an instant, and that lower pressure air as it comes through the carburetor doesn't require as much fuel as higher pressure air that would come through if there was less restriction. But this isn't like creating lower density or higher density air, it just changes the time over which the air comes in.

You have to put in bigger jets with the pod filters because the air is moving slower at any given instant, so it pulls less fuel from the jet. So the jet has to be bigger to supply the same amount of fuel to the lower velocity air.

Once you switch the intake, you have to go through a lot of trial and error with needles, shims, jets, and even stuff like the slide return spring to get it to run right. Or someone else has done that work for you and you can put together a tried and true setup.

FWIW I think 45 sounds like a real big pilot jet. But I'n no pro on GS450 carbs by any means.

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