Smooth Bore Carbs staying open how to get them to close faster

[IronPawz]

I've a new bike with smooth bore carbs (I've never had these before). I heard the vacuum can keep them open and I've definitely noticed this happening. I'm happily flying up to a corner, close off the throttle and they half a second they stay open for I'm on that corner and doing a 5c moment slapping on the breaks.

I hear it is possible to add a spring to get them to shut off properly? If I open the throttle (bike off) and just release it, it snaps back as you would expect (this is not a sticky throttle though I will oil it to be sure).

What is the deal here? Any tips on getting it sorted? I am taking it to the mechanic tomorrow who will look at it for me and mentioned the spring but just interested in any comments generally. I also hear they are not the best street carbies (for a lot of commuting) and I've a standard set (engine is GSX1135EFG sitting in Suzuki Katana) but I seems there is a significant power gain with the smoothies so kind of like to hang onto that.

Cheers.

[Big Dog]

Sidecarbob was on about something like what you ask.
I'll see if I can find the thread.

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[jellywrestler]

I've a new bike with smooth bore carbs (I've never had these before). I heard the vacuum can keep them open and I've definitely noticed this happening. I'm happily flying up to a corner, close off the throttle and they half a second they stay open for I'm on that corner and doing a 5c moment slapping on the breaks.

I hear it is possible to add a spring to get them to shut off properly? If I open the throttle (bike off) and just release it, it snaps back as you would expect (this is not a sticky throttle though I will oil it to be sure).

What is the deal here? Any tips on getting it sorted? I am taking it to the mechanic tomorrow who will look at it for me and mentioned the spring but just interested in any comments generally. I also hear they are not the best street carbies (for a lot of commuting) and I've a standard set (engine is GSX1135EFG sitting in Suzuki Katana) but I seems there is a significant power gain with the smoothies so kind of like to hang onto that.

Cheers.

how do you know they are smoothbores and what brand and size are these alleged smoothbores?

[Big Dog]

Does this match what you want to know? http://www.kiwibiker.co.nz/forums/showthread.php?p=1130992673

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[IronPawz]

Does this match what you want to know? http://www.kiwibiker.co.nz/forums/showthread.php?p=1130992673

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That is my thread on the same bike. I'm lost in that conversation. I don't see anything about running on but things that might sound that way and a some concepts that I just don't really understand. Is that what is being talked about? Smoothies running on and how to prevent them?

[IronPawz]

how do you know they are smoothbores and what brand and size are these alleged smoothbores?

Fair enough I was told they are by the engineer who sold me the bike. He makes bink carbs from complete scratch. This thread on the build discusses the carbs as smooth bores.

"I have rebuilt a set of smoothbore 33mm carbs with new needle and seats, gaskets, and idle air screws etc."

http://www.thegsresources.com/_forum/showthread.php?80503-Building-a-KiwiKat&highlight=katanakid

I've this comment from him also re: track day (he has read some of the Kat thread so may even read this). I hope he doesn't mind it was a private email (I will ask in retro spec and remove this if so).

You may want to get a set of #130 Main jets and try them on the day. You may possibly get a bit more punch up the top end. I only managed 1 session at Puke, so never fine-tuned the Smoothies. You can drop the mains out by undoing the 17mm nut under the float bowls. Put a rag under the carbs to catch any fuel that runs out, and do not do it hot!!!

I'll go get a close up and post that.

[Big Dog]

Not enough of a mechanic to say yes or no.

My understanding was that under load the slides may not be closing effectively (In that example provided because of an air box mod) and he was speaking of using the method in the post to stretch the spring to increase the return pressure on the slide thereby overcoming the vacuum.

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[IronPawz]

how do you know they are smoothbores and what brand and size are these alleged smoothbores?

Smoother than a porn stars sniz?

[Big Dog]

Ah, so more no air box than air box mod.


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[IronPawz]

Not enough of a mechanic to say yes or no.

My understanding was that under load the slides may not be closing effectively (In that example provided because of an air box mod) and he was speaking of using the method in the post to stretch the spring to increase the return pressure on the slide thereby overcoming the vacuum.

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Right makes more sense thanks for the translation. I'll send the link to my mechanic who should understand it. He talked about it and should know or have a plan already so perhaps he will share and I'll add that back here also. I hope to over time get time to actually learn some things myself. I can at least get the idea to swap out jets etc I am sure (cold as he mentioned ;).

[IronPawz]

Ah, so more no air box than air box mod.

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So true, prehaps more resistant filters would help then? I think the air box room is taken up with the internal shock mounts so putting one back in is not likely (I'll go check).

[IronPawz]

Ah, so more no air box than air box mod.

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Yeah there is a very nice cross pipes welded in there for strengthening so no room for the original airbox. It is great to have the standard one to compare. Probably sell that one at some point mind.

[Big Dog]

Sounds like preloading the spring as per sidecar Bob's patented method is one option, finding a longer spring another or your mechanic may have a better answer.

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[IronPawz]

Worst case scenario at Taupo in group 4 (no stress group unless the motard hard nuts are in it again cutting everyone up in the corners) I'll just have to learn where the breaks are faster or ride more like a pussy than I do already. I'm more interested in just having a go than doing anything impressive (which is what group 4 is all about). At least I can wind it up on the straights and no one is going the other way.

Other issue is the tires have not moved in some time so as the seller said they are probably a bit stiff. If you are out in Taupo by all means stop by and have a laugh as I putter about.

[Big Dog]

So true, prehaps more resistant filters would help then? I think the air box room is taken up with the internal shock mounts so putting one back in is not likely (I'll go check).
If you are otherwise happy with three carb I'd look for a solution before I went down that road, changing your filter resistance will mess with your fuel air mix.

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[IronPawz]

Sounds like preloading the spring as per sidecar Bob's patented method is one option, finding a longer spring another or your mechanic may have a better answer.

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Yeah longer spring makes sense. I've not been able to google anything useful but the mechanic is smart and well hooked up so I'm sure if he needs to he will be asking about the community. Any open day I come home from with the bike in one bit is a winner so either way I'm going and will just try ride accordingly.

[IronPawz]

I've the 92 Gixxer for the next track days. Nut for steering head his on order, got a race battery for it last week. That bike I'll try going nuts on, get some stickies and potentially bin it. I really do not want to drop the Kat that ideally will be a daily long distance ride. So having the carbies shut off is important to me. I can see people dealing with it on the track (get on the breaks) but it would be rubbish on the daily so it needs to get sorted out of I'd have to put the standard carbs back (where is the fun in that).

[jellywrestler]

Smoother than a porn stars sniz?

smoothbores is a term referring to the inside of the carb layout, not the outside....., a lot of people refer to all slide carbs (as opposed to CV ones) as smoothbores.
is there any facility for a return cable from the handlebars?

[jasonu]

Sidecarbob was on about something like what you ask.

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That cunt...


Sorry mate I couldn't resist.

[Grumph]

smoothbores is a term referring to the inside of the carb layout, not the outside....., a lot of people refer to all slide carbs (as opposed to CV ones) as smoothbores.
is there any facility for a return cable from the handlebars?

The pics I've seen certainly looked like Mikuni 33 smoothbores. There will not be any internal springs for throttle return - they're all on the external linkage.
There are a couple of alternative spring anchor positions, someone may have backed off the return spring tension to get a lighter action.
The correct fix is as jelly says a return cable - there should be provision on the linkage for one.
The 33's don't have a rep for vacuum sticking - certainly not like the early RS flatslides.

[jasonu]

The pics I've seen certainly looked like Mikuni 33 smoothbores. There will not be any internal springs for throttle return - they're all on the external linkage.
There are a couple of alternative spring anchor positions, someone may have backed off the return spring tension to get a lighter action.
The correct fix is as jelly says a return cable - there should be provision on the linkage for one.
The 33's don't have a rep for vacuum sticking - certainly not like the early RS flatslides.

Do whatever this guy says. He knows what he is talking about!!!

[IronPawz]

The pics I've seen certainly looked like Mikuni 33 smoothbores. There will not be any internal springs for throttle return - they're all on the external linkage.
There are a couple of alternative spring anchor positions, someone may have backed off the return spring tension to get a lighter action.
The correct fix is as jelly says a return cable - there should be provision on the linkage for one.
The 33's don't have a rep for vacuum sticking - certainly not like the early RS flatslides.

Nice thanks very helpful. It is in with the man and I've passed him this thread. I will go through it again in detail and try get some schematics etc to get a handle on it.

[Katman]

The correct fix is as jelly says a return cable - there should be provision on the linkage for one.


Trouble is, if it's running the original switchblock and throttle grip it won't have provision for a return cable. (Even if there is down at the carb end).

[IronPawz]

I rode this bike in this morning to get it started for certification. With fresh gas it stopped all forms of hesitation with mild roll on (I never really opened it up mind low profile ride). No issue in the shut off not under power so that is good (it is road ride able). Idle is a bit lumpy but it is ok. After riding the standard Kat most of last week and yesterday this bike is fantastic in terms of power from down low, ride comfort, handling, breaking all so much better.

The throttle is really heavy is my only issue. So mechanic is looking at that as part of the mix (saw wrist just holding it at road speeds and I ride 10+ hours a week, the old Kat was ok on the wrist). I wonder if some riding (given it sat a long time) will also free this up. The owner did mention it happens (sticks open, known for the carb and get on the breaks). He also mentioned it was never fully tuned but it was rebuilt and only did around 1500kms from the build of the bike in general.

So mechanic / builder is looking to soften the throttle and improve the return. I can confirm the clippons are setup for push pull but looking there the carbs do not cater for this. Bike made me smile the whole ride and I might have failed to resist the detour over Paekakariki. The front wheel is so pointy it was trying to steer in (under gentle riding). I was wondering why when the mechanic pointed out the tire.

Grateful for all comments here, I'll be taking those details to google also and trying to understand it better. I trust these are smoothies based on the engineer that created the bike and his thread and character (good decent guy has a wire wheel Kat sitting in the shed along with a sweet 90's GSXR1100) he builds Bink carbs from scratch so I trust his skills. Still if there is anything better images I can put up I will (bike in shop probably till Wednesday now).

[Katman]

The throttle is really heavy is my only issue.

That's slide carbs for you.

[Grumph]

The throttle is really heavy is my only issue.

You may have a quick action throttle if there's provision there for a return cable. That does make them heavy. They're not usually bad, have a look at the cable for kinks.

If there's no provision on the carb bank then someone's cut it off. The bits are available.

Not exactly IronPawz are you....That's a mans bike you've got.

[jellywrestler]

Not exactly IronPawz are you....That's a mans bike you've got.

that's what the women up there call him after he did community service ironing their clothes.....

[IronPawz]

That's slide carbs for you.

Fly by wire conversion? On a standard carb it would seem simpler than fuel injection.

Are there ways to make is easier generally? I like those carbs but I'm not sure I could really live with it all week they are really heavy. Even then they don't shut off. Am I hoping to much for something that is essentially a racing setup..

[IronPawz]

You may have a quick action throttle if there's provision there for a return cable. That does make them heavy. They're not usually bad, have a look at the cable for kinks.

If there's no provision on the carb bank then someone's cut it off. The bits are available.

Not exactly IronPawz are you....That's a mans bike you've got.


You might say so but I ride about 70 minutes each way twice a day five times a week, rain - hail - shine - winter / summer etc, and then I do every track day available from Taupo and Manfield and then I get out on some pretty epic rides with friends or visiting family. I'm no weekend around the bays type.

Maybe I should change it to iron arse limp wrist but it seems a lot of typing. I'm past 30 and by the end of a long week (especially if the weekend has rides) I have limits. So I want to bend a 'real man's bike' into a heavy commuter that is going to take some mods.

[IronPawz]

You may have a quick action throttle if there's provision there for a return cable. That does make them heavy. They're not usually bad, have a look at the cable for kinks.

If there's no provision on the carb bank then someone's cut it off. The bits are available.

Not exactly IronPawz are you....That's a mans bike you've got.

Good point on the cable mechanic is checking it all over. It is 1/4 turn so maybe that can be changed. I think the clippons etc are all early GSX-R. My daily ride currently is a CBR1000RR so I'm use to sports bikes but that is pretty mild on the wrist and also 1/4 turn.

I'll ask about the return cable I know they are there on the bars but not sure if attached.

[IronPawz]

that's what the women up there call him after he did community service ironing their clothes.....

As long as they don't call me late for dinner or make me burn my Y fronts in solidarity.

I'd be interested to see how the average back / butt / wrists would be feeling after my week on the Blade let alone this bike (the clutch is a little heavy too but I don't use it much it is fine).

There is a lot of splitting and highway in my day so you are constantly changing speed or sitting at very specific speeds. Having really precise throttle requirements on the blade was an issue initially but I got use to that so perhaps I will harden up (I'm riding that Kat bike regardless it is after all my dream bike).

There is always a possible GSX-R engine conversion...

[Grumph]

There is always a possible GSX-R engine conversion...

You've already got the best engine Suzuki ever made...

[Drew]

You've already got the best engine Suzuki ever made...
When did he put a K5 GSXR1000 motor in? I didn't read that post.

[jellywrestler]

Fly by wire conversion? On a standard carb it would seem simpler than fuel injection.

Are there ways to make is easier generally? I like those carbs but I'm not sure I could really live with it all week they are really heavy. Even then they don't shut off. Am I hoping to much for something that is essentially a racing setup..

have you factored in the extra cost of motion lotion, those things like to drink

[jellywrestler]

You've already got the best engine Suzuki ever made...

it's a gsx not a gs.....

[Grumph]

When did he put a K5 GSXR1000 motor in? I didn't read that post.


it's a gsx not a gs.....

It's an 1135 - to get comparable torque Suzuki went to the Hayabusa....
If you've ever ridden a properly set up 1135 you'll know what I mean.

[Drew]

It's an 1135 - to get comparable torque Suzuki went to the Hayabusa....
If you've ever ridden a properly set up 1135 you'll know what I mean.
And in 2005 the gixxer trumped all. At least I thought it did. Actually falls short I now see after a bit of searching. As you were.

[Metastable]

Probably not this but just thought I'd mention it. You say it isn't a sticky throttle - fair enough, it doesn't sound like it.

I had a sticky throttle.... the butterfly valve for the air intake was sticking to the wall of the chamber when in a closed position. The previous owner kept the bike in a cement/mortar shop. Anyway - i cleaned up the air intake/valve and it worked nicely ever since. I DON'T see the valve sticking in the open position unless things are super dirty in there.... but just a thought.

[MrMarko]

It's too lean.

Put an airbox on it or you're going to have to spend some time with a jet kit a a vacuum balancer and reading spark plugs...

Or pay,,, uhhh 90 an hour they want now to do anything on a bike at these shops... i laugh and go nah i'll just do it myself.

[Grumph]

It's too lean.

Put an airbox on it or you're going to have to spend some time with a jet kit a a vacuum balancer and reading spark plugs...

Ain't necessarily so...The way the 33 smoothbores are set up, if the pilot is too big - ie running rich at part throttle - when the slide slams down, the closed throttle vacuum can pull a slug of fuel up the pilot progression holes - and it feels like it's not shutting the throttle.
They work best either with open bellmouths or the good oval K&N's.
Luckily, once the pilot is close it's possible to get them acceptable using the mixture screws - just don't expect a superb idle. They're race carbs.

[IronPawz]

Ain't necessarily so...The way the 33 smoothbores are set up, if the pilot is too big - ie running rich at part throttle - when the slide slams down, the closed throttle vacuum can pull a slug of fuel up the pilot progression holes - and it feels like it's not shutting the throttle.
They work best either with open bellmouths or the good oval K&N's.
Luckily, once the pilot is close it's possible to get them acceptable using the mixture screws - just don't expect a superb idle. They're race carbs.

Great posts. Yes that engine is great. It is so much more than the standard Kat (though it may not be what it should it seems to run fine and just does not have the stick from all areas like the 1135 does). I don't mind the idle it is functional enough, I actually like that race carb feel to it.

They have been stripped and will get a good look over. The floats where a little crushed and are being unsoldered, sorted, soldered so perhaps that is part of it (I have image of how they are). So pressure in there crushed them at some point perhaps.

I wish I had the time and skills to go further myself and I might well gain both at some point. I'm so looking forward to getting it back. The Fireblade is nice and all I just love riding the machine. I've had no change to measure the rate of fuel for general travel so be interesting to see that over time.

On the 1135 should it get a lead additive do you think? Would that be the case for the standard GSX1100E also? I think I was adding it when it was running previously (been a year or more since it was on the road).

[IronPawz]

Probably not this but just thought I'd mention it. You say it isn't a sticky throttle - fair enough, it doesn't sound like it.

I had a sticky throttle.... the butterfly valve for the air intake was sticking to the wall of the chamber when in a closed position. The previous owner kept the bike in a cement/mortar shop. Anyway - i cleaned up the air intake/valve and it worked nicely ever since. I DON'T see the valve sticking in the open position unless things are super dirty in there.... but just a thought.

It is definitely getting a clean, not used much for a good while. Only did 1500kms since it was built back in 2006 (but carbs rebuilt at that time).

[jellywrestler]

So pressure in there crushed them at some point perhaps.

more like bad handling, if the fuel pressure was enough to crush them you'd have a bomb on your hands