Calling carb gurus HELP!!!

[kxpower?]

Hey guys I’m stumped here.

I’ll give you the TLDR first: R&R’d carbs, unclogged one pilot jet, revs will not drop below 5000 RMP when started. There is NO vacuum leak.

Bike is a 1982 GS 450 TXZ, with the BS34SS (CV) carbs. Running pods and straight pipes, 135 mains (vs 115 stock), and needles at stock height. Idle air screws are both at 1.5 turns out. Valves were adjusted a couple months ago. With this configuration it runs great at higher RPM/high load and had a really low lumpy Harley-ish idle. It has always started easy, hot or cold. But it had a pretty loud afterfire when you closed the throttle at high RPMS, and I was under the impression that upping the pilot jet by a size would help or cure the afterfire. It also had a little kind of a burble or flat spot that came and went at sustained speed, but I think that’s due to a questionable plug boot.

So I pulled the carbs and removed the pilots, and discovered that the cylinder 2 pilot was completely blocked. Air tight. The other pilot was fine, and with a little cleaning the blocked one was good to go. I replaced the old pilots with the upsize 47.5 pilots, put the bike back together, pods and all (expecting to take it on a test ride), and it fired right up as usual with choke, then revs immediately climbed to 5000. Turned off the choke and it falls flat on its face like it usually does when first started and very cold. Turned it off and backed the idle adjuster until it lost contact with the butterfly shaft, confirmed that the throttle cable was slacked, and visually verified that the butterflies were closed. Slides rise and fall nice and smooth just like always. Tried different combination of choke, throttle, mouth holding, etc., but nothing changed. Twist the throttle it revs right up, and falls right back to 5,000 RPM.

Going back to the last good configuration (except without a blocked pilot), I put the old pilots back in. Fired her up and the exact same thing happens. Revs straight to 5k. Acts just like you were holding the throttle, nice and smooth, both cylinders running fine, just free revving. It seemed to me that a vacuum leak would usually not affect both cylinders and probably wouldn’t run so nicely, but the ether squirting around the intake pipe trick didn’t turn up any leaks. Just to be sure I hadn’t screwed something up seating the carbs, I pulled the carbs back out, warmed and lubed up the boots and re-installed, once again no change.

I pulled the carbs back out and opened up the diaphragms, thinking maybe the needle had come unclipped or there was some mechanical interference but nothing was out of the ordinary.

After chasing it around a couple of weeks and failing to detect any kind of vacuum leak, I bit the bullet and bought a pair of Suzuki OE intake pipes, and installed with new O-rings. Man it sure makes putting the carbset back on a helluva lot easier...But didn't do crap for the crazy high idle.

I've messed with the idle fuel screws and everything else I've thought to put my hands on and nothing makes any difference. If I unplug one spark plug it runs on one cylinder at about 3000.

Could it be anything else going wrong? I'm really starting to think that there's something mechanically wrong with the carbs.

Sorry for the long post, I was trying to get all the details in there. What the heck is going on here?

I started a thread on a Suzuki forum earlier this month but it hasn't gone anywhere other than pointing me toward a vacuum leak. I know we've got more than a few carb experts floating around here, any of whom should be able to point me in the right direction.

THANK YOU!!!!!!

[HoneyBadgerRy]

If there is a lot of fuel on carbs at idle it can have a high floating idle. (Think turning the fuel enrichment circuit full on, on the ninjette.) Try the stock pilots and turn the mixture screws down until it idles right or dies.

[greg737]

If I unplug one spark plug it runs on one cylinder at about 3000

Interesting. Have you tried doing this with both cylinders? Have you killed the spark on cylinder #1, noting the PRMs, then put cylinder #1 back in service and then killed the spark on cylinder #2?

I ask because that sort of testing might be a way to tell if the problem is specifically isolated to one of the bike's two carbs. Might be revealing.

Also, I've worked with BST32 carbs on my GSF400. They are very vulnerable to bad o-rings or forgetting to re-install an o-ring (there are a couple of "hidden" or hard to access o-rings in the BST32 and BST33 carb family).

Another "Also", are you sure there's not something mechanically holding the throttle plates partially open? Your description of the very solid 5,000 RPM idle (and a willingness to rev higher and to do a quick return back down to the 5,000 again) sounds like two carbs obediently doing what they're being told to do. In a "no engine load" situation it wouldn't take much of a throttle plate opening to command 5,000 RPMs.

Good luck.

[chugs]

Pm @ducatiman he's quite knowledgeable about carbs.

[crazymadbastard]

Greg may be on to something. Is there slack on the carb cable? Maybe it's too tight.

[kxpower?]

Wow thanks for all the replies!

Ry, it's back on the stock pilot jet and I've tried fuel screws all the way in, to all the way out, with no change in idle speed.

Originally Posted by greg737

Interesting. Have you tried doing this with both cylinders? Have you killed the spark on cylinder #1, noting the PRMs, then put cylinder #1 back in service and then killed the spark on cylinder #2?

I ask because that sort of testing might be a way to tell if the problem is specifically isolated to one of the bike's two carbs. Might be revealing.

I should have pointed out that it does the same with either spark plug disconnected. No discernible difference between the cylinders. Whatever is going on affects each carb equally, which should narrow down the underlying problem.

Originally Posted by greg737

Also, I've worked with BST32 carbs on my GSF400. They are very vulnerable to bad o-rings or forgetting to re-install an o-ring (there are a couple of "hidden" or hard to access o-rings in the BST32 and BST33 carb family).

Another "Also", are you sure there's not something mechanically holding the throttle plates partially open? Your description of the very solid 5,000 RPM idle (and a willingness to rev higher and to do a quick return back down to the 5,000 again) sounds like two carbs obediently doing what they're being told to do. In a "no engine load" situation it wouldn't take much of a throttle plate opening to command 5,000 RPMs.

Good luck.

I think you're onto something here, with the O-rings. The throttle plates are closed, cable is slacked and you can see that the butterflies are closed.

So what could be allowing air around the butterfly, I guess is the question to ask here. I'm thinking the carbs may be going back on the work bench.

[HoneyBadgerRy]

If its running like that with the stock pilots and mixture screws set all the way in, its either gotta have an airleak past the butterflies, or the enrichment circuit is stuck on (maybe a bad o-ring).

Its also possible somebody drilled out the idea hole in the butterflies, JB welded it, and you knocked the JB weld off.

Anything past that, and I have no clue.

[RacinNinja]

Originally Posted by HoneyBadgerRy

If its running like that with the stock pilots and mixture screws set all the way in, its either gotta have an airleak past the butterflies, or the enrichment circuit is stuck on (maybe a bad o-ring).

Its also possible somebody drilled out the idea hole in the butterflies, JB welded it, and you knocked the JB weld off.

Anything past that, and I have no clue.

The part in bold is the issue.

There is a rubber part on the end of the choke plunger. Most likely it is hard from age or missing. Possibly the seat has goop built up causing a leak. Or, they are not seating fully.

Choke plungers are most likely your issue.

[RacinNinja]

The part in this picture where the needle comes out has a flat rubber o-ring. Check those. If they are indented or compressed at all, replace the plungers.

[kxpower?]

Originally Posted by RacinNinja

The part in this picture where the needle comes out has a flat rubber o-ring. Check those. If they are indented or compressed at all, replace the plungers.

Holy crap I've never once looked at these thank you! I'll pull it apart tonight or tomorrow, will report back with findings.

[RacinNinja]

Originally Posted by kxpower?

Holy crap I've never once looked at these thank you! I'll pull it apart tonight or tomorrow, will report back with findings.

Be sure to check the choke linkage as well to be sure it's not binding or stuck open before you take it all the way apart. Check it bit by bit.

[Linkin]

BS34SS (CV) carbs. Running pods

Constant Velocity carbs will never run right without the stock airbox, no matter what you change. If you want to remove the airbox and run pods, you might as well just shell out for a new set of carbs and appropriate jetting.

[HoneyBadgerRy]

Originally Posted by Linkin

Constant Velocity pods will never run right without the stock airbox, no matter what you change. If you want to remove the airbox and run pods, you might as well just shell out for a new set of carbs and appropriate jetting.

I disagree, pods and cv's works great.

[Linkin]

Originally Posted by HoneyBadgerRy

I disagree, pods and cv's works great.

Based on what? CV carbs are designed for constant air pressure/vacuum no matter the engine speed or speed of the bike. All your throttle cables control on a CV carb are the throttle bodies. The airbox design & piston moving down in the cylinder creates low pressure, and the airbox supplies the air at a constant rate.

You don't get that with pods. You can have extremely rich and lean spots in the rev range, and issues getting the bike to even idle do the volume of air available. Then you also have to factor in any air being forced in when the vehicle is at speed, or even being starved of air at high speed (like a blocked air filter).

The little japanese men in white coats knew well what they were doing when designing their bikes to have CV carbs and an airbox... for it to perform, no matter the speed of the bike, no matter the gear, no matter the RPM. The airbox is always at the same pressure when the engine is running no matter what, with CV carbs. That is the point, and is why you should always run with the airbox on CV's. They are designed that way.

Backyard Joe / Joe Racer who like the induction sound of pods and the idea of running pods and rejetting for more performance... I have yet to see it work 100% with CV's.

You want to increase horsepower on your bike? Buy some Keihin FCR's. I know of a CBR250RR making over 50HP at the back wheel (40 stock on the AUS stock bikes. Jap imports are 45HP) and lifting the front with power wheelies in 1st and 2nd. The owner spent $1000 AUD or thereabouts on a set of FCR's and some basic jetting + dyno time. And then more on titanium headers and end can for weight reduction.

[HoneyBadgerRy]

Originally Posted by Linkin

Based on what? CV carbs are designed for constant air pressure/vacuum no matter the engine speed or speed of the bike. All your throttle cables control on a CV carb are the throttle bodies. The airbox design & piston moving down in the cylinder creates low pressure, and the airbox supplies the air at a constant rate.

You don't get that with pods. You can have extremely rich and lean spots in the rev range, and issues getting the bike to even idle do the volume of air available. Then you also have to factor in any air being forced in when the vehicle is at speed, or even being starved of air at high speed (like a blocked air filter).

The little japanese men in white coats knew well what they were doing when designing their bikes to have CV carbs and an airbox... for it to perform, no matter the speed of the bike, no matter the gear, no matter the RPM. The airbox is always at the same pressure when the engine is running no matter what, with CV carbs. That is the point, and is why you should always run with the airbox on CV's. They are designed that way.

Backyard Joe / Joe Racer who like the induction sound of pods and the idea of running pods and rejetting for more performance... I have yet to see it work 100% with CV's.

You want to increase horsepower on your bike? Buy some Keihin FCR's. I know of a CBR250RR making over 50HP at the back wheel (40 stock on the AUS stock bikes. Jap imports are 45HP) and lifting the front with power wheelies in 1st and 2nd. The owner spent $1000 AUD or thereabouts on a set of FCR's and some basic jetting + dyno time. And then more on titanium headers and end can for weight reduction.

Based on I have a ninja 250 with pods a yoshimira exhaust, and it runs better than it did stock. It had a Lena spot stock. I want to go efi later, but I haven't reached that point yet.

[Linkin]

Originally Posted by HoneyBadgerRy

Based on I have a ninja 250 with pods a yoshimira exhaust, and it runs better than it did stock. It had a Lena spot stock. I want to go efi later, but I haven't reached that point yet.

I never looked at my 250R's carbs (or airbox for that matter), are they variable venturi or fixed? They also have vacuum lines don't they?

I know about the lean spot on the 250 carbs though... as usual it was done for emissions reasons.

I know my FZR250R carbs (Mikuni BDST 28) don't operate correctly with the airbox off (major lean out and hanging idle as if it had an air leak) or with pods. Now that is 4 carbs vs 2 but the same principles apply. No vacuum lines on the fizzer carbs though.

[HoneyBadgerRy]

Originally Posted by Linkin

I never looked at my 250R's carbs (or airbox for that matter), are they variable venturi or fixed? They also have vacuum lines don't they?

I know about the lean spot on the 250 carbs though... as usual it was done for emissions reasons.

I know my FZR250R carbs (Mikuni BDST 28) don't operate correctly with the airbox off (major lean out and hanging idle as if it had an air leak) or with pods. Now that is 4 carbs vs 2 but the same principles apply. No vacuum lines on the fizzer carbs though.

They are classic vaccume slide venture carbs with butterfly valves. They have vacuum lines and a coasting enrichener.

[RacinNinja]

Put it on a dyno. Compare the curve to one with an airbox. You'll be surprised how much your butt dyno lies to you.

[greg737]

Here's something I've noticed with my GSF400 that I think backs up Linkin's position on this issue:

First, when I purchased my GSF400 I was told by the prior owner that it didn't run well without the airbox. He said don't even try to test ride it after/during maintenance without the airbox. And on the GSF400 forums there's a lot of agreement.

But here's the thing that seems to demonstrate the necessity of the airbox. A couple of months ago I was trying to synchronize the carbs (they're actually throttlebodies now due to my fuel injection modification) and it seemed like my Carbtune synchronizer wasn't working properly. This was only the second time I'd used the Carbtune on the GSF but I remembered it had worked fine the first time. The Carbtune synchronizer just wasn't registering anything. Then I realized I was working without the airbox installed. So I put the airbox back on and started the bike back up, the Carbtune now showed a normal engine vacuum level for each cylinder and I was able to balance them.

[HoneyBadgerRy]

Originally Posted by RacinNinja

Put it on a dyno. Compare the curve to one with an airbox. You'll be surprised how much your butt dyno lies to you.

It may make less power at 6k but it pulls smoother, and thats what matters. I'm also pretty sure it makes more peak HP, but we will find out when I dyno her. (Hopefully this week).

Edit: Also, why did you add me to your ignore list? I'm just curious, so maybe I can offend less people.

[greg737]

Edit: Also, why did you add me to your ignore list? I'm just curious, so maybe I can offend less people.

You're fine, honey badger. I should know, I've been banned twice (once for a whole year). Although, in my defense it was for offending the breathtakingly thin-skinned and very easily-offended Alex-S.

[HoneyBadgerRy]

Originally Posted by greg737

You're fine, honey badger. I should know, I've been banned twice (once for a whole year). Although, in my defense it was for offending the breathtakingly thin-skinned and very easily-offended Alex-S.

That seems like borderline material to get banned.

[DEFY]

[HoneyBadgerRy]

Back on topic, @kxpower? did you ever get the fuel enrichment cuircit cleaned?

[kxpower?]

Originally Posted by HoneyBadgerRy

Back on topic, @kxpower? did you ever get the fuel enrichment cuircit cleaned?

I turn my back on the thread and look what happens! Forums are so fun


Actually I'm kind of stuck at the moment, for some reason the plungers don't seem to clear the flange for the diaphragm. I know they've got to come out, (otherwise how was it ever assembled), but I really don't see how. Here's a pic.

[HoneyBadgerRy]

I reccomend starting to fully disassemble the carbs, and if you end up splitting them, then split them.

[kxpower?]

Originally Posted by HoneyBadgerRy

I reccomend starting to fully disassemble the carbs, and if you end up splitting them, then split them.

Splitting them wouldn't do any good to get the plungers out, they run smack into the casting. I'll post up when I get back in there and figure it out. Right now it's in the 70s and the Gs1000 is getting some miles

[kxpower?]

Brain fart haha the plungers are housed in a casting that's screwed to the carb body.

[HoneyBadgerRy]

Originally Posted by kxpower?

Brain fart haha the plungers are housed in a casting that's screwed to the carb body.

That why I said to start tearing them apart, sometimes when I decide to just take thing apart I notice a brain fart.

[kxpower?]

@RacinNinja: Here are my plungers, rubber has a little circle from the seat but otherwise look perfect. Can't blow through fuel or air sides of the enricher with the plunger down, so I'm taking that as they're ok?

[RacinNinja]

How do the seats look?

How deep is that groove in them? Hard to tell from the angle but the grooves look decently deep.

Did you check the linkage to be sure it wasn't holding them open before you took them out?

[kxpower?]

Originally Posted by RacinNinja

How do the seats look?

How deep is that groove in them? Hard to tell from the angle but the grooves look decently deep.

Did you check the linkage to be sure it wasn't holding them open before you took them out?

Can't really get in there to measure but grooves are a solid 20-30 thousandths.

Seats look nice and smooth, clean too. Plungers were all the way down with linkage installed.

[RacinNinja]

If it was me, I'd replace them just because of age. The rubber is bound to be hard as a rock after 30 years.

[kxpower?]

Originally Posted by RacinNinja

If it was me, I'd replace them just because of age. The rubber is bound to be hard as a rock after 30 years.

It doesn't have much give. I'll soak these in armor all a couple hours, that seems to soften up old rubber (worked wonders on air box boots for the 1000) while I mess with a couple other things.

[RacinNinja]

Originally Posted by kxpower?

It doesn't have much give. I'll soak these in armor all a couple hours, that seems to soften up old rubber (worked wonders on air box boots for the 1000) while I mess with a couple other things.

Something else.....have you checked the slide diaphragms for tears or holes?? Has it been pinched in any way from an improper install of the cap? Look them over carefully.....

[kxpower?]

Originally Posted by RacinNinja

Something else.....have you checked the slide diaphragms for tears or holes?? Has it been pinched in any way from an improper install of the cap? Look them over carefully.....

I think I might have the smoking gun, looks like they're way out of sync, going to give it a bench sync and see how it does.

Good call but the diaphragms are fine.

[kxpower?]

Well, looks like it's fixed. Lesson here: Listen to everybody's advice and BENCH SYNC YOUR CARBS!!

Purrs like a kitten at about 1200 right now.

[RacinNinja]

Originally Posted by kxpower?

Well, looks like it's fixed. Lesson here: Listen to everybody's advice and BENCH SYNC YOUR CARBS!!

Purrs like a kitten at about 1200 right now.

Good job!

[HoneyBadgerRy]

Originally Posted by kxpower?

Well, looks like it's fixed. Lesson here: Listen to everybody's advice and BENCH SYNC YOUR CARBS!!

Purrs like a kitten at about 1200 right now.

If the carbs were not synced I would think it would run at different ROM's when you pulled one plug. Hmm, oh well, you got it running and that's all that matters.

[kxpower?]

Originally Posted by HoneyBadgerRy

If the carbs were not synced I would think it would run at different ROM's when you pulled one plug. Hmm, oh well, you got it running and that's all that matters.

Yeah that's been bothering me as well. I just pulled the plug cap off, rather than unplugging the coil from the harness. My hypothesis for now is that the spark arced from the cap to the plug causing the cylinder to fire.