1992 GSF400 Carb Conundrum

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Maelstrom
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Re: 1992 GSF400 Carb Conundrum

Post by Maelstrom » Sun Jan 17, 2016 9:06 am

Nice work.
Mind if I steal a few of your pics to show on the website so that customers can see where and how they fit?
The pilot screws are a fuel mixture screw so the 'n' turns out is really just a guide. You should set them by ear with the engine warmed up. You can find lots of guides on how to do that on the web.
cheers
Blair
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https://litetek.co

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Re: 1992 GSF400 Carb Conundrum

Post by lknbandit400 » Sun Jan 17, 2016 12:16 pm

LiteTekBlair wrote:Nice work.
Mind if I steal a few of your pics to show on the website so that customers can see where and how they fit?
The pilot screws are a fuel mixture screw so the 'n' turns out is really just a guide. You should set them by ear with the engine warmed up. You can find lots of guides on how to do that on the web.
cheers
Blair
Steal away, Blair. Thanks!

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Re: 1992 GSF400 Carb Conundrum

Post by lknbandit400 » Sun Jan 17, 2016 3:26 pm

To my point about uncertainty in where I should set the pilot air screw, I ran across this site. What a great idea! Makes the adjustment easy without having to remove the carbs.

http://www.factorypro.com/Prod_Pages/prods41.html

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Re: 1992 GSF400 Carb Conundrum

Post by lknbandit400 » Mon Jan 18, 2016 1:42 am

I need some help. Great news is that I borrowed two jet needles I was missing to get the pretty bandit running (the one who's carbs I've been working with on). It lives! Didn't want to fire up but I push started it and ever since it fired up with the button. Probably needs new plugs.

Anywho, I have hanging revs. When cold, I can get the bike to idle at about a thousand or a little higher/lower. Throttle response suffers if I adjust too greatly. Idle mixture screws are at 2 turns out (as a guess because the manual doesn't have a spec for my import code model). I rode it around and after warm, the bike will idle at traffic lights at 4000, and the revs don't fall when I switch gears making the changes sloppy and jerky.

Alternative problem is an air leak but I'm certain I need to optimize the air screw before diagnosing that.

Other than that, it's a great sounding engine!! Working on uploading a video...

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Re: 1992 GSF400 Carb Conundrum

Post by Maelstrom » Mon Jan 18, 2016 5:09 am

It is too lean at idle.
Try 3 or 2.5 turns out until it solves the hanging. Then you can fine tune by ear.
Carb seal kits in viton & other parts
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Re: 1992 GSF400 Carb Conundrum

Post by lknbandit400 » Mon Jan 18, 2016 2:59 pm

LiteTekBlair wrote:It is too lean at idle.
Try 3 or 2.5 turns out until it solves the hanging. Then you can fine tune by ear.
I thought it was opposite? Doesn't turning the screw in make it richer because it is further seating the needle taper?

I could be wrong. I'm at 2 turns now, and if it's too lean it makes me think I should turn it in, not out further.

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Re: 1992 GSF400 Carb Conundrum

Post by lknbandit400 » Mon Jan 18, 2016 3:03 pm

Wait - does this screw meter air or fuel? Since there's an o-ring under it I'm guessing it meters fuel. So then screwing out would indeed equal richer. If it meters air, screwing out would equal leaner...

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Re: 1992 GSF400 Carb Conundrum

Post by lknbandit400 » Mon Jan 18, 2016 11:43 pm

I answered my own question today - it must meter fuel. It's incredible how sensitive this thing is to the air mixture screw adjustment. My initial setting after rebuild was 2.5 turns. It had a hanging rev issue so I adjusted it in not knowing any better :whistle:

At 1.75 turns out the hanging revs were terrible. I knew I went the wrong direction. Today I followed Blair's instruction and went the other way, to 3 turns out. Much better :grin:

Only negative effect is a slight hesitation which happens about 1/3 throttle and usually only in second gear. First is so short you don't notice it because it only happens until you get to about 6k. From about 4-6k it want's to think about accelerating. Not saying it doesn't at all - it just noticeably loses a bit of power. Considering it's hard to ride this bike below 6k, it's no biggie but I'd like to figure that out. It may be a carb balance thing, although I'm pleased with my bench sync skills so far.

Group hug guys! Thanks for getting me this far! You fellas rock.

bighug

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Re: 1992 GSF400 Carb Conundrum

Post by lknbandit400 » Mon Jan 18, 2016 11:50 pm

@Blair

I'm getting ready to buy another o-ring kit from you. I'm curious about the fuel seal also. Do you happen to know if it's mandatory to separate the carbs to replace those seals? I'm guessing it is...

The reason I ask is that on the second GSF I recently bought, I sprung a leak somewhere. I can't tell where the fuel is coming from because the carbs are canted forward the droplets collect at the bottom fuel rail. It actually looks like it's leaking from the air screw hole so a new o-ring should help that if it is indeed the problem. Not sure why it all of a sudden spring a leak. When I say leak, I mean it all of a sudden started pouring from somewhere...

:x

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Re: 1992 GSF400 Carb Conundrum

Post by Maelstrom » Tue Jan 19, 2016 12:05 am

Sounds like you are nearly there.
Yes, the pilot mixture screws are very sensitive. Try to set them individually by ear for the best result.

Have to separate carbs to fit fuel seals. It is not that bad if you are very methodical when you separate them, take photos, that sort of thing. Watch out for the springs that try to fly off into the void. Read my guide could be useful too.
http://www.litetek.co/Guide_MikuniBDST_Rebuild.html
Carb seal kits in viton & other parts
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