GS450 fuel air mixture to weak

[Darren GS450T]

Hi, I am still having problems with my 1982, GS450 runing weak, I have stripped and cleaned carbs, fitted new air filter but still weak, back fires when of choke and plugs are white, I think you can lift the needle to richen it, ticks over fine but will not rev unless I put my hand over air intake, I have looked at threads on here but cant seem to get the answer I an Looking for. Please help. Darren (uk)

[Steve]

You say you have to put your hand over the intake. Does that mean your filter is off for testing?
If so, that's most of your problem. The air filter needs to be installed for proper running.

As far as being too lean, is the bike stock as far as air filter and exhaust systems? Raising the needle mightl help some in the mid-range, but at idle, you really want to turn the idle mixture adjustment screws. On the 450, they sit horizontally, above the outlet of the carbs. Not sure if yours would be been sealed like ours in the US were, but remove the caps, if necessary, turn the screws in until they seat lightly, then back them out three full turns. When the bike is running better and fully warmed up, adjust those screws by turning them in slowly, listening for highest engine speed. There won't be much difference, but there will be one setting that makes the engine happiest. Do that for both carbs, you will be set.

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[Darren GS450T]

Thanks Steve, the air box and filter are in place, engine and exhausts are standard, I put my hand over air box inlet (under seat, when fitted), I cant see any adjustment screws, I will look again tonight, I think they must be blanked off. Thanks. Darren

[Steve]

It appears that you are still running lean. There is a possibility that you have an air leak at your intake boots, where they connect to the head. There is an o-ring there that is a prime suspect.

I don't have a picture of a 450 carb, but here is one on an 850. The difference is that the adjustment screw on the 850 is vertical, the one on the 450 is horizontal, pretty much in the same location.


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[terrylee]

air

Have 450T myself, screws are on side of carbs. (outside) under metal plugs. I have same problem myself and cleaned carbs. got new o-rings everywhere and new filter. Hope to put all back on later today and hope all this solves the problem. Also doing valve adjust. terrylee

[Darren GS450T]

Hi, I have just tried removing the blanking plugs, do I need to carefully chisel them out? A big problem for me is that the bike is a restoration project, it came complete, but with what looks like a whole other GS400 in spare parts, I wonder if the previous owner has put the 400 carbs on for some reason, how would I know the difference in 1982 GS450T carbs and a later GS400 carb set up??? The spare carbs have metal needle retainig parts with a much thinner needle, the ones fitted to my bike have plastic neddle retainig parts with a thicker needle, the plastic ones seem to be more modern? HELP!!!

[terrylee]

Blanks

If the blanks have a small hole in middle ,screw in a small screw and wiggle and pull and they should come out. If no holes, drill with small bit and do same. Just be careful and don't drill to deep. Sorry not sure about different carbs., but I'm sure someone on here does. terrylee

[terrylee]

Put carbs. back on and airbox with new filter and had some problems with reving up, until I adjusted air mix. screws some. Turns out I had a airbox rubber seal that was smashed, replaced, so now no need to put hand over end of top of airbox to get it to rev. Still have to do vavle adjust. and sync., hope this will make everything alright. Not trying to steal thread, just hope this will help with your air problem. terrylee

[cdnoel]

air mixture screw.

Having problems my self with air screw plug that was removed in the wrong fashion. The small screw method is the best. If you have no screw small enough drill out the hole larger untill you can get the smalest sheet metal screw possible threaded in and pull them that way. If you drill the plug out compleetly like the previous owner of my bike did you will need a new carburetor. Another helpfull bit of advice is.... Righty Leaney, Lefty Ritchey. It's bass ackwards I know, but it helps me remember.

[Steve]

Another helpfull bit of advice is.... Righty Leaney, Lefty Ritchey. It's bass ackwards I know, but it helps me remember.

Nothing backwards about that at all.

Virtually all threaded controls (read that as screws) operate the same way: turn them left, they allow more of what they are controlling, turn them right, they allow less.

In the case of the CV-type carbs on his 450, the screw actually contols how much of a pre-set mixture is admitted to the air stream at idle and low throttle openings. So, it follows convention: turning LEFT allows more of the mixture (yes, it makes it richer) and turning it RIGHT allows less of the mixture (making it leaner).

In the case of earlier VM carbs, there are two screws for adjustment. They follow the same convention, but they control different things.
The screw on the bottom controls GAS, so turning it LEFT makes it richer.
The screw on the side controls AIR, so turning it LEFT makes it leaner.
Try applying your "lefty/righty" logic on those screws.

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