Bandit Alley
MODEL SPECIFIC => SUZUKI BANDIT 250 & 400 => Topic started by: T2098 on June 19, 2015, 01:22:09 AM
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After trying unsuccessfully to get my poor '91 to run correctly in the low-end, I've finally torn the carbs off and am working on rebuilding them, along with installing:
1) Factory Pro CRB-S41-3.0 carb kit
2) K&N RU-1824 Pod Filters
3) Complete Viton o-ring kit from Thailand (http://www.litetek.co/Carb_Kit_Suzuki_GSF400.html)
Symptoms previously were:
- It was always very hard to start.
- Once started, it idled alternatingly on 2-3 or 4 cylinders unless the idle was turned up to ~2000rpm, or the choke was all the way out (even when warm)
- Snapping the throttle open below 6000rpm would give a significant bog, which was worse when cold.
- It wouldn't accept full throttle below 4000rpm (even gently!) in high gear.
Since I'm currently without a choke cable, my temporary workaround before tearing the carbs off was to take a twist tie looped around the choke plunger rod, tie it to my clutch cable, and keep twisting until the choke was propped about 1/3 of the way open. This actually made it run decently well when warm and greatly reduced the fueling issues below 6000rpm. Clearly I was running lean.
Before pulling the carbs off, I found that all 4 pilot screws were about 5 turns (!!!) out. After resetting them to factory spec of 1 5/8, the bike wouldn't even start with full choke. At that point I gave up and decided the carbs were coming off for a rebuild.
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With the float bowls off, so far I can see that the previous owner put the main jets in the wrong spot. The Japanese-spec bike is supposed to have a 102.5 in cylinders 2&3, and 105 in 1&4. Currently the bike had the 102.5 on 1&3, and 105 on 2&4. Clearly the last person working on the carbs wasn't paying much attention.
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Sounds like it wasn't getting enough fuel. I think it's just cogged up pilot jets.
The bog sounds like a problem with your needles or diaphragm
Depending on mileage, they could be worn..
What did you find when you opened them up?
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With the float bowls off, so far I can see that the previous owner put the main jets in the wrong spot. The Japanese-spec bike is supposed to have a 102.5 in cylinders 2&3, and 105 in 1&4. Currently the bike had the 102.5 on 1&3, and 105 on 2&4. Clearly the last person working on the carbs wasn't paying much attention.
Are you sure?
Usually the inner carbs have bigger jets to cool them more, not the outer ones.
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100%. I bought a copy of the JDM Bandit service manual in hardcopy for when I finally have the dreaded task of doing my valve clearances, and it's very clear that 105 is for cylinders 1&4, 102.5 for 2&3.
Tough to say why - from the service manual it seems to be a quirk of the VC models only - the later 53HP 'restricted' version was set up the same way, whereas even the JDM versions of the non-VC engine had #100 main jets in all 4 cylinders on the same 33mm carbs.
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At least my OEM needles don't appear to be appreciably worn, and the emulsion tubes (needle jets) don't look visibly ovaled either. Crazy to see just how much bigger the jets in the Factory Pro 3.0 kit are than stock for the USA-spec bikes. (the kit comes with 117.5 and 120 mains)
Part of the secret sauce might be in the needles though, which are very visibly different than the OEM ones - the Factory Pro ones have a smooth taper all the way down rather than a very abrupt step - I wonder how much this is responsible for the fact that the main jets are so much bigger (the Factory Pro needles looks like they'd block more of the flow from the main jet, even wide open):
(https://lh3.googleusercontent.com/-nBm0HHDA3yw/VYSCGJqZfGI/AAAAAAAAJWg/M9BxnP-tRwc/s800/DSC04948.JPG)
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Managed to get everything all clean now, and remarkably, even at 25,500km, my needle jets definitely still look round, so I'll be re-using them. For anyone who was ever curious, the stock markings on them are "659 P-0" (P-zero) although I've yet to find anyone other than Suzuki who sells 659-series Mikuni needle jets.
(https://lh3.googleusercontent.com/-qG-VEC66ukM/VYShIYPg-7I/AAAAAAAAJW0/erEwrt-YlEA/s800/DSC04980.JPG)
(https://lh3.googleusercontent.com/-FtT6dwjP_k4/VYShi5mXjiI/AAAAAAAAJXE/Evd9eHZcDmw/s800/DSC05009.JPG)
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Hooray, it runs again. Now to button everything back up.
https://youtu.be/yysZGXn8OEY
Initial setting of 2.5 turns out on the mixture screws with the stock #32.5 pilots looks to be just about right. Even without the pod filters on, off-idle pick up is way better than before, even with the choke off and the bike still rather cold. With the previous mixture screw settings of 5 (!) turns out, the bike would only accept throttle slowly from idle with the choke off, even when completely warm.
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I've had such a crazy pilot screw setup too. it was maybe 3.5 turns out. The bike started on first crank but the mixture was so rich that everything other than slow throttle caused it to heavy misfire and slowdown. Then black huge smoke flown out of silencer and engine began to accelerate. Now I'm on stock 1 1/4 turns and it is maybe slightly leaner that it should but definitely better response to throttle than before. I guess I am on opposite side of mixture hill.
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Good to hear you got it running.
I use the Dynojet needles on my VVC and run same jets across all 4 cylinders, its been on the dyno and fuel is spot on.
Be carful comparing jets from different companies as the rate differently so a mikuni 110 can be different to factorypro etc, if you need to change them slightly get same make.
One of the problems with the b4 is the pilots are linked to the main emulsion tube and then rely on the rubber plug to make this happen, this eventually goes hard or worse is lost by previous owners and causes major headaches with fueling.
A little fine tuning and you should be there. :congrats:
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Sorry to jump on this thread, the little rubber plugs, are they still available do you know, one of mine was lost by a previous owner and the others arent great. Cheers
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13357-34C00 is the part number.
You in the US, UK?
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Thanks, I can be in either, I live in the UK but my Mum lives in the states.
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Speak to Robinsons then they supply most of the shops anyway.
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Thank-you for the advice Chris and everyone else. :)
It's running like a champ now - after swapping to the 195F thermostat, it idles much happier and off-idle pickup is definitely better. It's funny, I'd read some threads before about people not wanting to run individual/pod filters on the Bandit 400 due to intake resonance, noise, etc. being too unbearable, even when wearing a helmet.
Some of this might be due to the very sedate cams the VC model uses in the low RPMs, but if I didn't know the pod filters were there because I installed them, there'd be no way I'd know the difference. I've run other bikes with individual filters before, and my VTR250 Interceptor (V-twin) and GSX400e (parallel twin) both got almost unbearably noisy with intake resonance/"honk" without the airbox - the Bandit does not.
It is noticeably noisier/angrier above 9k or so when the VC switchover happens, but I consider that a good thing - if I'm revving it above 9k, I'm obviously trying to give it the business, and so a little extra intake noise is no biggie. When cruising around though on the low cam though, it's quiet as can be.
Fun facts from the JDM Service Manual:
Advertised duration on the 'high' intake cam is 292 degrees on the '91 VC model, same as the '91 USA 49-state or Japanese non-VC model, with 7.5mm lift
Advertised duration on the 'low' intake cam is only 232 degrees with 5.8mm lift though, which is part of why it's so gentle and tractable at low RPMs.
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You getting there for sure! These are great bikes, once you set the carbs up! When you have some spare cash, order the Long Boy air mix screws from Factory Pro. They make adjustments much easier! Also, sync up the carbs. The cheap way is to try the "Bench Sync" method.
https://www.youtube.com/watch?v=2nwP6R1P58A
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Details and pics for the Ti pipe..please!
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I actually had the bike dynoed and it's spectacularly rich everywhere - more so in the midrange peaking at 15% CO on the Factory Pro dyno, tapering down to 7% CO or so near redline. I ordered a brand new set of US-spec emulsion tubes from Suzuki that just arrived, so i'm going to try installing those this weekend as the Factory Pro needles were designed with those in mind. If that still doesn't work, I might just utter some expletives, go back to stock jetting and airbox and sell the K&N individual filters and the Factory Pro Config 30 kit to someone with a USDM bike and the 32mm carbs it was meant for. :)
The Ti pipe is from Beet and was bought from Yahoo! Japan auctions using www.buyee.jp - a very convenient broker/buyer service that bids on stuff for you and re-ships it from Japan to wherever in the world.
Ended up being pretty expensive - $400ish USD when all was said and done, but it's gorgeous, weighs nothing, and sounds fantastic.
Pics and more info including weight in my other thread:
http://forums.banditalley.net/index.php?topic=13916.0 (http://forums.banditalley.net/index.php?topic=13916.0)
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Oh, and I finally scanned my dyno printouts. Factory Pro dynos are normally 'heartbreakers' at the best of times, but a completely stock '91 USA-market bike with 59HP at the crank had dynoed at 49-50HP before, so I'm definitely down on power after the carb rebuild, installing the pod filters, and the Factory Pro Config 30 kit, which is not surprising given how rich it was running.
First off is with the stock CDI module. Unfortunately even when I bought the bike, it had a hard rev limit of 11,800rpm or so in all 6 gears, which equates to exactly 180km/hr on the tach. I have a second spare '91 VC ignition module, and it does the same thing, so clearly the CDI isn't defective. Unfortnately all of my attempts to 'derestrict' the damn thing have failed, so my stock CDI dyno printouts end at ~12krpm.
38.57HP. Ugh. Stock is the curve with the higher power and ending at 12k.
(https://lh3.googleusercontent.com/-ex0uvx_NW6E/VbGoTwFCwmI/AAAAAAAAJqg/wBgOPf456aM/s1024-Ic42/91BanditVVC-FactoryProConfig30-BeetTiExhaust.jpg)
Next up is the Chinese aftermarket CDI. Given that they only made the 'unrestricted' 59HP VC Bandit 400 for one year, I'm amazed that they actually make a legitimate replacement ECU from scratch. As far as I can tell it does properly actuate the VC mechanisms when it should, and it certainly does remove the rev limit.
... unfortunately, it also makes less power than the stock CDI does at all RPMs with weak 25-year old caps does, so it's not particularly helpful. Maybe if my fueling was spot on it'd be better, but at least from this comparison it's no help on the power front - it makes .2HP more when revved to 13k and 14k than the stock CDI did at 12k, but that's still not much help. It's the dyno run on the right that goes up to 14krpm, obviously.
(https://lh3.googleusercontent.com/-PcRR0D5LB0Y/VbGoTqSK6GI/AAAAAAAAJqc/_npmi2YNrkU/s1024-Ic42/91BanditVVC-FactoryProConfig30-BeetTiExhaust-LixiandaCDI.jpg)
Having said that, 91 VC CDIs are very hard to come by, so if someone has a bike that is completely dead and can't find a spare, I can attest that they definitely do work, although they make the bike considerably harder to start from cold as well. It was about $140 shipped direct from China from aliexpress, but they sell them on eBay too.
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Also, for those not familiar with Factory Pro's 4-gas analysis, the picture below shows how CO% is related to air/fuel ratios. For my bike, the 8-9% CO reading near peak power corresponds to between 10:1 and 11:1 AFR (ew!) and the ~15% CO in the midrange from 3k-7k rpm corresponds to somewhere around 7.5:1 to 8:1 AFR (double ew!)
I'm amazed it actually runs cleanly without misfiring, but you can clearly tell that it's fluffy and 'fat' running compared to how it was before with the stock carb parts and the airbox/snorkel.
(http://www.crypton.co.za/Tto%20know/Emissions/airfuelratio5big.GIF)
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Forgive me if I miss something as I write this after only reading the last two posts but are you saying the bike is still restricted to 180 kph.
It's a very simple fix to derestrict the cdi.
Restriction is only controlled via the resistance the cdi receives from the gear sensor so you disconnect the green/yellow wire from the sensor to the CDI, connection is under the seat.
The end from the gear sensor is left loose.
Between the CDI end and the frame you fit a 1.5k ohm resistor and the restriction is gone, its that simple.
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Thanks Chris - I'm still trying to figure out what's wrong, as I've done that and double and triple checked my soldering - the bullet connector from the wire I made reads dead on 1.5k ohm to ground. Still restricted in all 6 gears.
Even if I plug the bullet connector back into the wire going to the gear selector, it still restricts in all 6, not just in the top 3 gears <sigh>
This weekend i'll try to trace the wiring from the bullet connector to the actual CDI itself, but if it's good, then I don't know what else to try, seeing as it does the same thing with two OEM CDI modules.
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There's definitely no other restriction.
Ive had mine on the dyno on more than one occasion and the resistor removes the 180 limit.