Well, I have messed around with my new across (1995, 31k kms) so as to get the throttle slides & needles going as well as they can, but it still seems to be a little hesitant in wanting to rev out to the 16 grand mark. 
(more of that story on my brief website au.oocities.com/ozcross250/ ). I am told that at these high revs it is really up to the main jet, and that the throttle slide/needle are at their full extension anyway, so needle settings don't mean much for high rev performance. 

Do people agree with this? Has anybody replaced their main jets with bigger ones, or drilled their mains out at all? How did it go, and what size did they take it to for the best effect?

Action Suzuki Sydney only sells 110, 112.5 and 115 size mains which is a lot bigger than the 90 that supposedly comes standard. Maybe the way to go is to drill the jets up to (I guess) 95 or 100?

There are two other factors that I can think of that might be affecting performance. One is that I have been told that if the bike is not opened up every now & again (too much low rev city riding) it carbons up & runs poorly... could this be what is wrong and what is affecting the top-end? I am a bit hesitant about taking it for a huge high-rev fang on the freeway to clear it out, if the problem is actually a lean mixture! 

The other possible factor is that the exhaust is merely choking things up - the baffle could be blocked somehow. I wouldn't really want to do the baffle mod on Krazy Ivan's site as the bike is really loud enough for me now (I like stealthy speed, not advertising to cops). Does anyone know how I can tell if the baffle's choked up?

thanks/cheers
michael 

I would still like any personal experiences or opinions from people that know the across, if possible.
thanks michael

Shane | 4agze.com | twincam16.com
When you're racing you're living, the rest is just waiting.

www.factorypro.com/tech/carbtun.html

www.carbparts.com/keihin/...r_carb.htm

(go to the first site for the link to the rest of the second)

Looking at that diagram in the 2nd link you can only blame so much on needles as you've found out. The biggest problem I have with the bike is the carbs, I'm used to the other type of slide and the across ones just seem so backward to me. So I blame the carb design for a lot of the across' general sluggishness and resistance to change throttle settings smoothly, mine feels jerky in the low revs (<8500), maybe it's just lean. I just can't get over the way fuel delivery is a function of revs, instead of the other way around. Must just be me. So all my ramblings of kicking in at certain throttle marks seem to be BS, it seems to be dependent on where the engine is ticking.

I'm not familiar with excessive low speed carboning up, or cleaning it out for that matter. Maybe not something a quick fang will solve. You really have to find out if your bike is running lean or just poorly. 

Here's a small list of what I've found a lean condition *feels* like, not exactly scientific..

-engine does not have power or pull that revs or throttle position would suggest
-symptoms of lean get better (diminish) as the engine warms up, that is to say, power increases marginally after bike has warmed up
-revs are highly responsive under little or no load (eg a hill) but have little or no power under load

I've found that jets are too expensive to buy unnecessarily, but if you go down that path, I'd probably get a set of oxytorch/carb tip/number drills from repco or wherever to drill out your existing jets. The increments are usually much smaller than genuine jet sizes and allow for better fine tuning. And if you go too far, well there's a spare for your direct cold air project

Anyway, there's plenty of dedicated carb tuning sites out there from professionals, so don't stop looking just yet.

Hey Shane, that really sucks. You need a revolving plate or something. 

Sounds like good advice & good links. I hadn't seen the second one. The stuff about "better performance when cold = too rich" in the first link is the most useful info for troubleshooting. When they talk about "standard" bikes and a specific rev range, I wish I knew what was the corresponding revs on the across. It's so unusual to me, with it's 16 grand capability!

I think I just have to keep tinkering for now. I'll probably be needing one of those drill kits soon. Before I do that I'll have to find somewhere that sells the stock 90 main jets in case I go too far with the main jet. Rich, funny how yours is jerky at lower revs, mine seems perfect in that range. Sounds like needles could be moved to fix that one, as my tinkering with needles seemed to be able to screw up & fix up that range...

Rich, the ozcross250 site is mine, I just lobbed it up quickly because I couldn't find anything specific on the common throttle slide holder failure / slide dropped problem, and had to find it out by chance. A mechanic at a local shop thought he saw me coming with that one & I might have been taken for a $$$ ride if I hadn't stumbled upon it! The site is there almost purely so that I might save someone else that fate!

Thanks & regards
michael

ps Shane, it is a bummer that you can't hang onto the bike. No other way? 

I had to raise the needles after I put a hole in the exhaust baffle, but now everything below 8500 is jerky. If I took my own advice I'd say it might be lean. I'll hit the needles up again anyway just to be sure, but I might also look to the pilot jet, floats and mixture screws. On the same note, fuel consumption just went out the window with that baffle mod.

At the point of sounding like a complete retard, I still can't even understand the screws on the carb compared to what they talk of in the workshop manual. I can only find the four screws on each side of the top of the carbs, which I thought were mixture but seem to be for balancing, and the central throttle balance screw. So where are the mixture screws? 

I haven't found (or looked for) the mixture screws as yet, but one of the web essays says that they are usually sitting under machined brass or aluminium caps on all but the latest hondas. That might help?

Did you get better top end when you holed the baffle? Since my bike is not properly tuned yet, it's hard to say, but my latest fuel consumption was 7.4 litres to 100 kms. I can't complain next to the fuel consumption for a cage, but when you can get 5.1 - 6.2 fuel consumption from a hayabusa, (see www.hyp4r.com/hayabusa/sp...rmance.htm ) something's weird about fuel consumption in the across!

cheers
michael

ps you weren't being a d-@#%$, no offence taken at all. 

My consumption is almost identical to yours for general riding (thrashing) at 8000 min. Thats on standard BP, but I'd really like to check out the Mobil stuff everybody's is raving about. I think brass caps are only on late model bikes in envoronmentally tight regions like the US, where adjusting your emissions is a no-no. They would freak if they saw my friend's aussie edition RGV with half a dozen oily drip tubes pointed straight at the ground, filthy 2 stroker. 

I'm glad that replacing the holders did something - and I would expect that they usually would on any bike with a few kms on it. There just shouldn't be as much play as these rotten little plastic things allow after a bit of usage. From what I have seen you can get as much play out of worn holders as one or two jet needle positions. What a crap design (or good money spinner, depending on your point of view).

It's good to hear that your bike is right again down low, but I think that theoretically you shouldn't have to live with a decrease in mid-high end performance because of it. What if you're robbing yourself of some extra ponies that you should really have because you opened up the baffle? I could be totally wrong, but perhaps my story is now a bit like where you are at, as my low & middle revs are quite OK but I have a bit of a lack of power up in the high revs band. (mind you, God knows what my bike has been through before the past two weeks since I bought it!) 

I have leaned out the jet needle (brought it down by one position) so as to get the top end running better. But it does this mainly when the engine is colder. So that says to me that the top end is still a bit rich. The jet needle move has made my mid range too lean, but only when cold - when it's hot it's quite nice & crisp. So this says that middle range is slightly lean and maybe the optimum position for the mid range was needle position 3 -the middle. You might think then that the main jet is too large, but it doesn't really make sense to think that the stock #90 size jet has somehow "become too large".

What I may well have been doing here, I think, is compensating for something else making the top end too rich, and from reading all this carby stuff it only seems as if it can only be one of 3 things (if we count out manifold air leaks etc. ;

1 - main jet
2 - needle jet
3 - pilot fuel mixture screw & jet size & float level (one essay says this is relevant at low (1/8 ) throttle position at high engine speeds, so they say)

Number 1- as i already mentioned I think it would be crazy to be putting in lower than stock main jets on the across, #90s should be fit for the task. I trust Mr Suzuki on that one! 

Number 2 - One thing I noticed that might be important for 'acrossers' in one of the carby tune essays it is stated that needle jets (not jet needles) are prone to wearing out quickly. So this jet could actually "become too large". That is the next thing I am going to check because I think that I might just see what they have said has happened to mine, - the needle jet hole gets elongated into a oval shape. If this has happened then it might all suddenly make sense - the needle system is letting too much fuel through at top end because it's worn, and I have made that a bit better by lowering the needle, but then at the mid range it's a little bit more lean it actually should be.

Number 3 - still anyones guess until I sort out numbers 1 & 2, but less likely i think.

Then again this is all speculation at the moment & I should stop crapping on and wasting forum space! I'll let you know when I have gotten to the bottom of it. If it isn't the needle jet then I think I will be stumped for a while & will have to pull the mikunis apart altogether.

One other thing I noticed in the workshop manual today - maybe our mikunis are a bit unusual but it says that you should measure float height without the gasket on. Most carb essays mention measuring distance from the gasket surface --so that would maybe get you thinking your floats were out by a millimetre when they weren't. This might not apply to you but it's just something we acrossers should watch.

thanks for crediting me with guru  level but i still feel like a newbie in this department - at least until I have this little beast running perfectly!

cheers
michael 

I'm now thinking all my time spent on tuning the midrange was really just an attempt to clean up the first part of the throttle which in retrospect displayed more than a few signs of being lean. These old bikes I tell you, mimicking lean and rich at the same time, dodgy dodgy dodgy. One test I found for rich/lean checking was to carefully apply the choke to see if the engine responded positively (is lean) or negatively (is rich), I must be clumsy like that but I got mixed results. 

I looked at the tubes/needle holes in the carbs when I had them off and they were ok, but we now know how sensitive these things are to small variations. These suzuki parts are cheap, my pilot jets were only $10 each, so they tubes would probably only be about $20 each. 

I hate to admit it, but you could be onto something about losing a bit of punch due to the mod, or maybe I notice that I just spend more time in the high revs, just because I can, ha ha. But it definitely sounds better ...tuff 250. 

My needle holes were OK too, that'll teach me to speculate. Weird, I made the needle 1 richer (miiddle pos.) again & it ran like crap in mid with no high improvement. Set needle as lean as it would go and it's perfect low-mid revs @ hot & cold, but still that slight high rev hesitation. No other way to go I think, the next thing for me has to be a drill kit & attack the main jets. I'll let you know if I need to buy new main jets after that adventure!

safe riding
michael 

Speaking of gears, yours must be geared taller than mine, I'd be nudging 70something in 1st if I dared keep going and let it wind out, but it does get to the high 60s fine for 250 traffic drags, he he. 

I just did another mod tonight, to make the bike look heaps better IMHO. The bike has on a rack, so that holds the rear indicators, and this means that the vast amount of space of the rear fender is useless, except for doing silly things like what it was put there for, and that stupid reflector that looks like it should be on my nephews push-bike. I think it looks s#$t. So I cut it off... looks heaps better! Got the idea from the twin brothers exhaust website, where they sell fender removal kits for various bikes. The carbon pipe is that brand. 
Got the pipe from a wreckers on silverwater rd silverwater (nice guys) who pulled it off a racing kwak 250 of some sort. I figure such a pipe wasn't designed to be on that bike either! When I do the site properly I will get a .mpg sound file up as well as the exhaust note is so gnarly. Will post here to let you know when it's done.
cheers
michael

ok so here's a quicky preview, as I have to go out. here 'tis

au.oocities.com/ozcross250/tailmod2.jpg

Done the webpage, with a bit more detail.

cheers
michael. 

The only problem with my baffle mod is a slight resonance at about 10K, but surprisingly that goes away after I clear it's throat for a while above 14K. 

Speaking of attracting unnecessary attention, I've had way too many cops look and turn (pushing 2nd to 3rd, come on orrificer!), lead/follow, alert their mates in unmarked cars, and generally make themselves unwanted. Such is life, and their disappointment when they realise I'm still doing or just over the limit, mofos. 

I'd go that no. plate mod as well, but I suspect my time on the across is limited to how soon I can find a job, I want that honda! 

What honda do you want? I am presently fighting the urge to contain a desire to go for one of the big twins like a firestorm or TL1000, or even a TRX 850...for the stupid reason that it might kill me! Love the concept of ducati sound & jap reliability combined. Would probably have to get aftermarket pipes there too...

Sorry to everyone who was misled, I must have been on something strong when I thought I was in first gear at 100. I can't understand how I mistook it now. Must have been all adrenalined up with the new pipe? 

Also must have been on the same stuff later to not put some sweet redline sounds in the .ra. I had a big sample and chose a little slice that sounded nice, as it's an extremely crappy quality (high noise) little mpeg recorder that was dangling precariously off the fairing. I'll get to putting some more 'active' sound on today. Gotta get more of that chemical stuff too...

regards
michael