1992 GSF400 Carb Conundrum

[Maelstrom]

Hi,
The top slide housing rectangular ring is used on later models of these type of Mikuni carbs. Those parts are extinct as OEM and one of our customers in Europe raised the issue that he needed them for his Bandit (he sent the picture that you included. As usual the parts book does not show them and I had the feeling that it would only be later models that needed them. However, I have not been able to find out which models do and which do not. So if you can give me exact model details of your Bandit I can start to solve the mystery. For example maybe all models prior to and including yours do not need that part. Then I could separate the Bandits.

The carbs that use those top seals also have a far more secure way to secure the needle and should lead to less wear, at least in the case of the Yamaha's.

If there is anything else I can help with just ask.

cheers
Blair

[lknbandit400]

Hi,
The top slide housing rectangular ring is used on later models of these type of Mikuni carbs. Those parts are extinct as OEM and one of our customers in Europe raised the issue that he needed them for his Bandit (he sent the picture that you included. As usual the parts book does not show them and I had the feeling that it would only be later models that needed them. However, I have not been able to find out which models do and which do not. So if you can give me exact model details of your Bandit I can start to solve the mystery. For example maybe all models prior to and including yours do not need that part. Then I could separate the Bandits.

The carbs that use those top seals also have a far more secure way to secure the needle and should lead to less wear, at least in the case of the Yamaha's.

If there is anything else I can help with just ask.

cheers
Blair

Hi Blair! Thanks for chiming in!

My GSF400 Bandit is a 1992. I will look tomorrow to see if I can find some identification on the carb body itself that will help you narrow things down. Thanks for offering this product and thanks for the quick shipping! Replacements could be quite expensive if you didn't offer your all inclusive kit.

To your point about the parts diagram, I am very surprised as well. On the fiche that I have seen, the slide holder isn't even removed from the carb and doesn't have a P/N! The slide holder o-ring isn't pictured as well which is a shame. Check out this picture of the slide holder o-rings that came out of my bike! They certainly need your replacement parts. Thanks again.

[Maelstrom]

@lknbandit400
Yes, it is a persistent problem. Many of the carb diagrams in parts books are incomplete. A lot of our kits have been made more comprehensive thanks to input from owners.

The biggest problem with NBR, what the OEM o-rings are made from, is embrittlement. When they go through wet and dry cycles they lose mass. I had some prototypes of intake rubbers made in both Viton and NBR, the ones that goes from carb to air box, and I let them soak in fuel for a few weeks and then dry out. The NBR version was hard and the viton one was unchanged.

[lknbandit400]

@lknbandit400
Yes, it is a persistent problem. Many of the carb diagrams in parts books are incomplete. A lot of our kits have been made more comprehensive thanks to input from owners.

The biggest problem with NBR, what the OEM o-rings are made from, is embrittlement. When they go through wet and dry cycles they lose mass. I had some prototypes of intake rubbers made in both Viton and NBR, the ones that goes from carb to air box, and I let them soak in fuel for a few weeks and then dry out. The NBR version was hard and the viton one was unchanged.

Interesting - there can't be much of a piece cost difference that manufacturers chose NBR. Is there? Or is Viton fairly new? I know we used them in the refined petroleum industry when I worked for a pipeline company stateside. That was about 10 years ago.

P.S. What other products do you make for the B4? Did you go to market with the intake rubbers?

[lknbandit400]

On another note, I have also placed an order to Partzilla for new carbs slide springs, lower needle spacers, main jets (102.5), and jet needles.

It wasn't cheap.

[Maelstrom]

It is much more difficult, if not impossible, to mould complex parts in Viton and it is multiple times more expensive for the raw material. I lost interest in pursuing the other rubber parts for the moment. I just don't think there would be the sales to justify the investment. I did tank rubbers (made from EPDM) for Honda CB-1's but they are not available anywhere else so I don't have to worry about competing with China, yet.

I feel your Partzilla pain. I buy OEM parts from them all the time. The shipping costs are murder because they use flat rate. Even if you just buy one o-ring it is $44. Then it takes 3 to 6 weeks to get here.
cheers

[Variablevalves suck]

Any chance I can buy the dynojet parts off you, I run one in
the vvc and have spare carbs so can make use of them.

You will be surprised how much thicker the mikuni needle is.

Blair, mikuni changed the slide holder a number of times, not sure why or if its on different bore diameters, they definitely use the same casting and then bore it differently.

I have some 91 vvc carbs that have no top seal for slide holder and I had some later vvc carbs that had no seal but had extra casting in the plastic that you could see from the top when the slide was removed, they seem to stop the slide going all the way down BUT could have been tampered with before leaving Japan.

[lknbandit400]

Any chance I can buy the dynojet parts off you, I run one in
the vvc and have spare carbs so can make use of them.

Sure. Let me hold onto them until I get the bike going properly and I'll shoot them your way.

[Variablevalves suck]

No problem.

[lknbandit400]

@litetekblair

Is there a proper installation method for these new o-rings? That may sound like a stupid question, but I want to make sure I don't do myself an injustice by "rolling" or when I should be "stretching" or vice versa. Should a silicone grease be used?