1992 GSF400 Carb Conundrum

[SevenThreeSeven]

One more thing that I am thinking could cause the high rev is an air leak. The boots are nice and pliable so unless the carbs aren't properly seated, I have a hard time believing there's a crack. However, there ARE o-rings I have discovered under the boot/intake that could be bad. Do you think these are worth replacing while I'm waiting for the carb o-ring kit from Thailand?

It's number 19/21 in the fiche at Partzilla:

During my general refurbishment effort on my very scruffy '93 project B4 I replaced those o-rings (part number 09280-36004). I believe in replacing 20-something year old o-rings whenever the opportunity presents itself.

Warning about replacing these o-rings: The screws that hold these carb intake pipes to the cylinder head have blue threadlocker on them. They are pretty hard to remove. Do you own any real-live-honest-to-God Japanese Industrial Standard screwdrivers? In case you aren't aware, the screw heads on the B4 that look just like good-old-fashioned Phillips head screws are not good-old-fashioned Phillips head. They are Japanese Industrial Standard screw heads (abbreviated "JIS") and a good-old-fashioned Phillips head screwdriver will make a mess out of them because the Phillips head profile tends to "cam out" of the JIS screw.

A short term solution to the JIS screwdriver issue is Drywall Driver bits (purchased at Home Depot or similar store). The closest thing to a real JIS screwdriver profile is a Drywall Driver bit. While it's not an actual JIS screwdriver it's way better than date-raping JIS screws with a Phillips head screwdriver.

[SevenThreeSeven]

I've posted the BOM for the jet kit from Dynojet below - from what I remember when I first stripped the carbs, all of this is in place.

If that's pretty horrific if true, because it means that the prior owner installed a Dynojet kit including the Dynojet-provided CV springs (which were softer than the OEM Suzuki CV springs) and then he went back in and clipped these already softer Dynojet springs by several "turns" to make them even softer. Hell, why not just remove the CV slides/diaphragms altogether?

There was some real crazy carb-voodoo witchcraft going on back in the day.

[lknbandit400]

One more thing that I am thinking could cause the high rev is an air leak. The boots are nice and pliable so unless the carbs aren't properly seated, I have a hard time believing there's a crack. However, there ARE o-rings I have discovered under the boot/intake that could be bad. Do you think these are worth replacing while I'm waiting for the carb o-ring kit from Thailand?

It's number 19/21 in the fiche at Partzilla:

During my general refurbishment effort on my very scruffy '93 project B4 I replaced those o-rings (part number 09280-36004). I believe in replacing 20-something year old o-rings whenever the opportunity presents itself.

Warning about replacing these o-rings: The screws that hold these carb intake pipes to the cylinder head have blue threadlocker on them. They are pretty hard to remove. Do you own any real-live-honest-to-God Japanese Industrial Standard screwdrivers? In case you aren't aware, the screw heads on the B4 that look just like good-old-fashioned Phillips head screws are not good-old-fashioned Phillips head. They are Japanese Industrial Standard screw heads (abbreviated "JIS") and a good-old-fashioned Phillips head screwdriver will make a mess out of them because the Phillips head profile tends to "cam out" of the JIS screw.

A short term solution to the JIS screwdriver issue is Drywall Driver bits (purchased at Home Depot or similar store). The closest thing to a real JIS screwdriver profile is a Drywall Driver bit. While it's not an actual JIS screwdriver it's way better than date-raping JIS screws with a Phillips head screwdriver.

I don't have a JIS driver, but I'll get one. I have had very good luck with hand impact drivers on heads like that. When the driver bits are new, I've never had an issue removing even the worst oxidized mix-metal connections. Maybe that will work out here also.

Considering the o-rings for the carbs will take a few weeks, and I want to do this right, I might as well go ahead and get the intake o-rings and new needle spacers on order (if they are available). Unless you have some extra spacers sitting around not being used...

[lknbandit400]

I've posted the BOM for the jet kit from Dynojet below - from what I remember when I first stripped the carbs, all of this is in place.

If that's pretty horrific if true, because it means that the prior owner installed a Dynojet kit including the Dynojet-provided CV springs (which were softer than the OEM Suzuki CV springs) and then he went back in and clipped these already softer Dynojet springs by several "turns" to make them even softer. Hell, why not just remove the CV slides/diaphragms altogether?

There was some real crazy carb-voodoo witchcraft going on back in the day.

It's also a possibility that he got the Dynojet springs and decided they were too stiff, so he just cut the OEM instead. Regardless, I'm going to have a couple hundred bucks in the carbs alone getting them back to OEM so here's to hoping it works.

BTW, thanks for tagging along and providing insight. I'll need your help to make sure everything is "up to snuff" when all this goes back together.

FYI I didn't order dust boots for the choke plunger or fuel rail seals (not leaking a drop).

[SevenThreeSeven]

One more thing that I am thinking could cause the high rev is an air leak.

Don't get ahead of yourself diagnosing things like air leaks. I don't think you're anywhere near that level yet. (Besides, a bike with an over-rich tune on the carbs + a throttle stop screw set too far in, lifting the throttle plates too far, will generate runaway RPMs that mimic an air leak situation).

Save that sort of diagnostic work for after you've properly refurbished and sorted your carbs: cleaned internals, Litetek kit installed, bench-sync/balanced throttle plates, settings all as close as possible to Suzuki factory-spec, CV diaphragms properly installed and function-tested, carbs properly (fully) mounted into their carb-to-engine connectors with clamps tightened, throttle stop screw set to absolutely just barely lift the throttle plates, petcock problems sorted (new petcock to tank gasket installed)...

Then, and only then, if you start the bike and the idle is uncontrollable you may have an air leak. But I'm betting when you've done everything I've just mentioned you won't have an air leak.

[SevenThreeSeven]

BTW, thanks for tagging along and providing insight. I'll need your help to make sure everything is "up to snuff" when all this goes back together.

I don't mind helping. You popped up here on the forum at a good time for me to be around, I have a few days off and had decided to do little or nothing with them.

[lknbandit400]

Don't get ahead of yourself diagnosing things like air leaks. I don't think you're anywhere near that level yet. (Besides, a bike with an over-rich tune on the carbs + a throttle stop screw set too far in, lifting the throttle plates too far, will generate runaway RPMs that mimic an air leak situation).

Understood - I get it. One thing at a time. Apparently the majority of the items I will need (needles, spacers, springs, main jet) are all available fairly readily (mostly from partzilla), but they aren't cheap. At least it will all be new.

The only thing you don't know about my carb setup now, is that I have replaced the pilot air jet at the airbox side at the throat. Specification calls for a 1.45 pilot air jet, and I needed to replace mine because the heads were pretty messed up once I finally got them out. However, the only ones available are 1.5, or 1.4. There isn't a 1.45 available anymore. There are 1 or 2 on ebay, but not a full set. I'm aware that air is much thinner than fuel, so to compensate for that I'm guessing I need to go up a size or two on the pilot fuel jet. I'm just hoping that's more of a fine tune adjustment rather than a reason for the gross "rev to 9k" symptom. 1.5 is the spec for California (emissions?) so I'm hoping that it will at least be close enough until I grab the lower hanging fruit.

[SevenThreeSeven]

Specification calls for a 1.45 pilot air jet, and I needed to replace mine because the heads were pretty messed up once I finally got them out.

Okay, that's something I might be able to help you out with.

As mentioned I converted my B4 to fuel injection and in that process I ended up with a lot of parts that no longer applied to my engine. Over time I've been mailing these surplus parts out to guys who need them (people on the BanditAlley forum). I've sent B4 bits to Estonia, England, Greece, Salt Lake City and one or two other places I can't recall right now.

I'm headed down to the garage today to do some work on my project B4 so I'll take a look in my parts bin for those pilot jets.

[lknbandit400]

Specification calls for a 1.45 pilot air jet, and I needed to replace mine because the heads were pretty messed up once I finally got them out.

Okay, that's something I might be able to help you out with.

As mentioned I converted my B4 to fuel injection and in that process I ended up with a lot of parts that no longer applied to my engine. Over time I've been mailing these surplus parts out to guys who need them (people on the BanditAlley forum). I've sent B4 bits to Estonia, England, Greece, Salt Lake City and one or two other places I can't recall right now.

I'm headed down to the garage today to do some work on my project B4 so I'll take a look in my parts bin for those pilot jets.

That would be awesome. If you happen to have needles, needle spacers and stock mains I'd be willing to take those off your hands as well! Just let me know!

[SevenThreeSeven]

Okay, here's what I have left from my carbs:











Let me know what you need.

Be gentle with the brass parts, they're delicate. As mentioned, these parts are from my project B4's carbs and the bike had approximately 19,000 miles on it when I got it (just pointing out that these parts are "older" than the parts from your 3,800 mile '92 B4).

I don't have my B4's needles or spacers to give because I kept part of the needles + the spacers in my CV slides when I modified the carbs into fuel injection throttle bodies (I cut off the part of the needles that normally dangles into the emulsion tube). Because I chose to preserve the BST32 carb's original Constant Velocity feature I needed the base of each needle to continue occupying its space in the CV slide.