Question about the carb slides...

[greg737]

I've recently become a 1993 Bandit 400 owner (very happy and glad to be here!).

All I've done with it so far is buy it and ride it to my home.  I knew that there would be some maintenance issues to address with a 20 year old motorcycle.  While the most recent prior owner (as far as I can tell there were at least 4 before me) was showing me the bike before I bought it he said that when he'd had the carbs opened up for cleaning he noticed that somebody had messed with the holes in the bottom of the slides.

I haven't opened up the carbs yet but when I've ridden the bike it feels like the throttle response is a bit on the strange side, like the slides are either moving too fast or too slow or maybe some other odd "hitching" type of motion.

So, in anticipation of looking into the carbs I've gone on the web and found this picture of a GSF400 carb slide (Mikuni BST32) and I'm posting it here on this thread to ask you if this is what an unmodified slide from the bike looks like:



(and if the slide shown in this picture isn't unmodified please describe or show me what an unmodified slide looks like)

Thanks for your help.

Greg

[El Gringo]

Not sure if that is unmoddified (although it looks it)

You may find that the 2 air hole either side of the centre needle hole have been either enlarged or had plugs put it.

It was a common thing with dynojet kits to "improve" throttle response

Edit* That said having checked the dynojet instructions they don't list plugs/drill for the slides - although it does list different slide springs

[greg737]

Thanks for the reply El Gringo,

It sounds like I may have to do some detective work on this bike's carbs.  I'd read a couple of mentions that some of the carb tuning kits included different slide springs.  The prior owner of my bike mentioned that one of the two (normally open) holes on the slides had been "plugged" by one of the other previous owners.  Do you know what sort of carb tuning kit this indicates? 

I would really like to be able to get this bike's slides back to a point where they operate as they did in their original configuration.

I will be fuel injecting the bike.  My plan is to keep the basic structure of the bike's Mikuni carbs, modified into a "throttle body" configuration which will keep the CV slides operational.  The reason that keeping the carb bodies is very desirable in this project is that their 32mm bore size is ideal for the engine, but only as long as the CV function of the slides is preserved (without the CV effect a 32mm throttle bore size on a 100cc cylinder would be an almost un-tunable situation in the idle and off-idle acceleration areas). 

In modern fuel injected bikes the manufacturers now use an ECU-controlled secondary throttle body butterfly system, but a CV slide system works almost as well (as it did for years in the Yamaha R6 fuel injection design).

That's why the carb's slides are important to me.

[El Gringo]

Sounds like a very interesting project Greg, i'm not too sure which jet kit uses the plugs.

I believe they are used to slow the rate of the slide (i could be wrong)

The US dynojet instructions don't mention them and i don't think the factory pro stg III does either (again i could be wrong)

I can't find any instructions for the UK dynojet stg I kit.

Would you be able to tune round the slide action?

[El Gringo]

Actually Greg i've found the Euro stg1 dynojet instructions.

It does list a slide drill but for enlarging the standard plastic needle washer to take the thicker Dynojet needles - it doesn't state drilling the slide holes though

[El Gringo]

Just to drag this one up again, i stripped and rebuilt the carbs on my 400, i noticed that 1 of the 4 slide had one of its holes blocked, not a plugs but seemingly like that from the factory