Technical question related to carbs

[stefan2519]

Hey,

I've got a GSF400 Bandit.
I recently bought a new set of 32mm Mikuni carbs from America for my bike.
After receiving the carbs, I've worked out that my bike should use the 33mm Japanese carbs.
What problems am I going to have, if any if I use the 32mm ones I've got?


Thanks, in advance.

Regards,
Stefan

[Richard-BKK]

The one millimeter is not going to be much difference, maybe you not push the engine to the maximum 59 horsepower, but that power is most of the time not needed. If the carburetors are the same Mikuni model as the original specs specify you're all in the clear.

[guzzi850m2]

Carburetors are tricky to set up correctly so I hope you know what you are doing in that regard or know somebody in the knowing.

I agree with Richard, 1mm should not make much difference and you should be able to compensate for that with bigger jets.

I had a Mikuni on my ex Harley, 42mm I think, and when the Australian mechanic finally had it set up correctly it ran very good without burning too much fuel but it took a couple of days with me going testing and coming back and give him feed back.

Good luck with it.

I can't say I miss carbs.

[mania]

I would say you will have no problems what so ever.

We routinely increased & decreased carbs a little in the past

(When carbs were popular )

Just get someone to tune the 32mm Mikunis for you to your bike.

(if your not comfortable doing it )

Meaning read the plugs & tune the main jets, needle jets & needles, set air mix etc.

No problem at all really your talking about 1mm

You can make that up with jetting changes

PS: Looking at the engine spec for that bike I see this

"Carburation, Mikuni BST33 (or BST32, depending on market) x 4"

http://www.banditalley.net/wiki/doku.php?id=gsf400

So you will be fine

Edited August 26, 2013 by mania

[Richard-BKK]

The biggest problem with four new carburetors will be to synchronize them, not easy to find a mechanic in Thailand that has much experience doing that.

[stefan2519]

Okay, good to hear.

I'm having a really hard time tunning them.

There's no adjustment on the needles or jets...........

[Richard-BKK]

Okay, good to hear.

I'm having a really hard time tunning them.

There's no adjustment on the needles or jets...........

Guess you bought the Mikuni BS carburetors from Suzuki, Suzuki presses an aluminum cap over the pilot screw that needs to be removed before you can adjust it.....

A good how-to can be found here http://www.mtsac.edu/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf

Edited August 26, 2013 by Richard-BKK

[Garry]

Okay, good to hear.

I'm having a really hard time tunning them.

There's no adjustment on the needles or jets...........

Guess you bought the Mikuni BS carburetors from Suzuki, Suzuki presses an aluminum cap over the pilot screw that needs to be removed before you can adjust it.....

A good how-to can be found here http://www.mtsac.edu/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf

Thanks for sharing Richard. A well written and photo'ed tutorial. I rarely work on carbs these days, but being an avid gear-head, its always nice to have another 'How-To' in the library (I have a bunch).

[mania]

Yes that is a well written tutorial on those Mikunis

[stefan2519]

Richard-Bkk, Thanks, for the link.
I was really thinking I'd ordered a copy set of Mikunis, I couldn't find any adjustment on them at all.
I will attempt it sometime this week, and let you know how I get on.

Regards,
Stefan

[BSJ]

It helps if you have a set of vacuum gauges. Guessing isn't a good option.

[CBR250]

It helps if you have a set of vacuum gauges. Guessing isn't a good option.

CropperCapture38.jpg

Vacuum gauges are normally essential for a good balance - but my local Thai bike mechanic tuned my 4 carbs (CB1-400) by ear. The bike runs as smooth as new, from idle to redline.

I know people have had bad experiences with some Thai mechanics (me included) but this guy is a gem with carbs on big bikes / classic bikes.

All generalizations are false. Especially this one.