GSXR400 Carb problems. Please help!

[Neve24]

Hi,

After having flat spots on both bottom & top end of the rev range, I sent my bike through to the local workshop & they cleaned out the carbs & changed o-rings & seals. The bike rides alot better & smoother now; the flat spot I had on high rev is gone & it seems alot better on low rev but not completely sorted. The mechanic says that the needles & nozzles need to be replaced as they are worn & these spares are no longer manufactured by Suzuki Japan.

The problem I am experiencing at low rev occurs from idle to about 3000rpm, basically if you release the clutch allowing the bike pull away only on "clutch power" & when in motion open the throttle slowly, it pulls away fine, but if you open throttle whilst releasing the clutch it stalls & feels like a flat spot, the bike is in motion but sounds starved or as if the carbs are flooding, it will jitter along until you get past 3000rpm & then run beautifully, over-reving & riding the clutch helps to get it going. This becomes annoying when needing to take off in a hurry & extremely irritating when taking off on an incline as you need to really over-rev it to get going. It often means jurking the clutch whilst over-reving to get it moving fast enough to pass the flat spot.

Please help guys, Any diagnosis or advice PLease!

[stripes1976]

its a possibility the o-rings aren't seated right. they have a habit of cutting when fitted if not done right. also could be carb balance. so many possibilitys without being able to see and hear it.

[dynomutt]

If it's happening below 3000rpm, then it's likely to be the pilot circuit that needs looking at, what size pilot jets are fitted, and what number of turns out are the pilot mixture screws set at? What air filter and exhaust combination are you running?

[stripes1976]

If it's happening below 3000rpm, then it's likely to be the pilot circuit that needs looking at, what size pilot jets are fitted, and what number of turns out are the pilot mixture screws set at? What air filter and exhaust combination are you running?

the o-rings cause this symptom! They allow fuel to be drawn up throughout the whole rev range. the pilot circuit can be perfect but the o-rings fail or emulsion tubes out of round cause rich running right the way though. There are other areas to look at but this is always the first port of call with the bds33 mikuni's or even the sp carbs the bdst35ss.
If you have a look in the archived posts and search me you will find how to's and issue's resolved there.

I bet your temperature gauge rises if sat for a while but as soon as you ride it heads for the bottom! This is the biggest cause of bore wear with the gsxr400 but is easily resolved with the right parts and set up properly

[Variablevalves suck]

If you need o'rings i supply a kit. £11 posted.
Chris.

[stripes1976]

gonna need emulsion tubes and needles by what his first post says. will need o-rings too if your changing those. while your at it swap the std float bowl screws and top screws for allen bolts.

[Neve24]

Needles & emulsion tubes are going to be a nightmare to find in South Africa & will need to be imported so I am going to try the o-rings 1st.

Can you help with the sizes as I am trying to source them locally to save cost.
From Tony sleep website I got this list, please advise if correct

ID Cross section OD Hardness Quantity
6.07mm 1.78mm 9.63mm 75°Shore'A' 4
7.65mm 1.78mm 11.21mm 75°Shore'A' 4
10mm 1mm 12mm 75°Shore'A' 4
2.5mm 1mm 4.5mm 75°Shore'A' 4

[stripes1976]

correct! i remember the original post from tony asking the same thing lol
in fact i still got all the emails that went back and forwards

[Variablevalves suck]

The 10mm ones i measured from Suzi measured 10mmX1.5mm, only the old ones measure 1mm as they go oval.

[Neve24]

I've ordered the complete set of o-rings & going to try that first if the problem still persists then I will have to do a complete carb rebuild which is going to dent my pocket.

Something new has happened yesterday. My bike cannot stand for more than 2 days without being started or it will start up with a dasterdly miss fire/flat spot & sound really horrible. I normally don't let it more than 3 days & let the bike idle & then ride the miss out. After a bit of riding it normalises. After reading about the o-rings I suspect that they become dry don't seat properly which causes this problem & a bit of riding sorts it out. I tried to start it yesterday after about a week of standing since I was extremely busy. It did the usual & started with a heavy miss fire/flat spot. I tried riding the bike but its not getting any better, now its dying at low rev & switching off. When you try to start the bike it takes full throttle to get to 2000rpm & it does not want to rev higher. I tried it again today & same story started but even open the throttle full won't let it rev pass 2000rpm but its not flooding.

Any insight?, by the way after this whole carb problem my choke doesn't work the same at all.