gk76a gsxr 400 restriction and running

[gsxrkev]

Hi guys, looking for a bit of advice regarding my gsxr 400, last year i had an 1990 gsxr 400 and loved it, was a true giant slayer and lived its life at 14500 rpm! However i sold it over winter to finish my streetfighter project.

I have since sold my fighter and decided to go back to a gsxr 400, i spotted a really nice 1994 model and although in ireland decided to go for it, upon riding it it immediately felt flat and no where near as rev happy as my 1990 one, after doing some google research i read about a speed limiter for japanese market and my mechanic friend also said to try for 33hp kit as many 400's had these fitted.

After a quick check last night i came across a rubber do-nut type arrangement in the plate that the air fliter mounts to that about halved the size of the air filter intake, i subsequently removed this and went a run to try it, as was wet could only manage flat in 3rd and was revving right round to redline although i believe the speed limiter only restricts in 4th, 5th and 6th gears?

also how do you tell if bike was import or uk bike as my 1990 had kph clocks and the 1994 has mph clocks?

I checked and the cdi has the 3 wires going to it and the green/yellow wire that ive heard of the resistor being fitted to to remove the limiter, does this mean it will have limiter or will i need to check the resistance on 4th, 5th and 6th to properly confirm.

i take it that it is entirely possible the rubber do-nut was 33hp restrictor but bike could still also have 180k speed limiter?

Thanks in advance for your help, and keep up the good work on a really great site!!

[Variablevalves suck]

All the 76a's are imported and will have the 180kph limit.
The MPH clocks will be from the RGV250.

The speed limit causes the bike to run on two cylinders only and is a clear missfire BUT old plugs could give similar.
You should be able to tell as it will be at the same rev/speed every time.

If you have the green/yellow wire from the gear sensor it's a simple job of putting a resitor 1K or 1.5K ohm between the cdi side and the frame , leave the gear side loose.

[gsxrkev]

thats perfect i'll just fit the resistor from the start and that should sort it out.

Any idea about the rubber donut arrangement fitted to the air intake?

thanks again

[rvf400]

[quote="blagger"]This is none of my work and ggas250 gets all the credit for this out-standing work he has done but i thought it would be a shame for this to get lost in the old forum.. I hope ggas250 doesn't mind me reposting this here...

ggas250 Qoute "Posted - 20/02/2008 : 02:46:55
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O.K. guys after suffering for quite some time with the speed restriction on my GSXR400 92' model GK76a and trying an aftermarket add on box (to no affect) I decided to do my own investigating after reading an idea on the bandit alley site regarding the neutral switch. Mine turned out to be very different than the bandit 400 one, however because my background comes from electronics it didn't take long to work out the switch. It has 4 different readings
1. 1 for gears 1st to 3rd
2. 1 for 4th gear
3. 1 for 5th gear
4. 1 again for 6th gear
Mine has now been modified to make the cdi think it never gets past 3rd gear. The bike now pulls harder than it ever did from 4th gear onwards and will pull hard into the redline even in top. No more stumbling in 5th & 6th gear at 13,500rpm (like it was starving for fuel) All for the small cost of my time approx 1.5 hrs. The biggest time taken to remove the existing putty from the switch to modify it.
I'm happy to advise any one how to do this if you drop me an email or if you aren't game to do it yourself for a very small agreed upon fee I would modify it for you if you post it to me. This worked for my GK76A with the two plug cdi which has one small plug with 3 wires and one large one with 4 wires. First race of the season I got a 1st overall in my class and the bike gave nothing away to the other 400's in the field where before I used to get left behind big time on the straights once I reached approx 180km or 13,500 rpm in the top two gears. Go the Mighty Gixxer ...






Here are the Details i recieved in an email from him.....





ggas250 Qoute
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O.K. the hardest part you have to do is remove the old sealant which is cream in colour to be able to access the circuit board. This takes some time and patience to do properly so that it is clear enough to see what you are doing and not damage the circuitry.I used a small fine bladed screwdriver to do this. For the modification stage you will need a multimeter, fine soldering iron, hook up wire and a sharp utility knife.
Next look at the contacts on the front of the switch (side that goes towards gearbox) and you will see six large contacts and two small contacts. The two small contacts are neutrals they should measure open circuit (to do measurements connect negative terminal of multimeter to green wire of the switch and positive terminal to the contacts.) 1st through to 3rd gear should measure approx 1k ohm. To work out 1st gear contact, look at how the switch sits on bike and with it in 1st gear you will soon work out the 1st gear contact. Next postion on switch will be a little nuetral contact then 2nd thru to 6th go in anticlockwise direction when looking at front of switch. Use your multimeter to work out the contact solder points on the circuit board by placing one lead on the contact point of the switch face and then with the multimeter either set to continuity or ohms find its dead short pin on the circuit board (usually directly behind the contact point) O.K. This will all sound long winded but just take your time and do one step at a time and re read this as many times as necessary, it's actually quite easy.
You will notice that gears 1st to 3rd are all linked to a resistor that sits pretty much in the middle of the circuit board this 1k ohm resistor is the one we want to connect all the switch contacts back to while disabling the normal 4th thru 6th gear links. 4th gear contact goes thru another resistor (approx 2k ohm) whose track has to be cut between pin 4 and the resistor (use sharp utility knife for this then check track is open circuit with ohm meter) 5th gear goes thru a diode which needs to be removed then cut track just after where diode was soldered. Join pins
6 to 3, 4 to 3 and 5 to 4 then just cut track behind pin 6.....ALL DONE.
Now with your ohm meter connect negative terminal to green wire and check all pin readings on front of switch they should all read approx 1k ohm except neutral which should be an open circuit. After all checks out O.K. (if it doesn't recheck everything as the readings have to be correct for this to work. The cdi has to think you are in the first 3
gears) put silastic or some kind of putty back into the switch and after it's set place switch back in bike. Test ride and enjoy the difference......... I know I did.

******* PLEASE NOTE THIS WORKED ON MY 1992 GK76A WITH CDI THAT HAS TWO 4 PIN CONNECTORS BUT ONLY 3 WIRES ON ONE OF THE CONNECTORS I HAVE NOT TESTED THIS ON ANY OTHER GSXR400'S WITH DIFFERENT CDI'S *******








as for the larger air filter i have done all of the above plus added a SV650 K&N air filter with teh small dohnut provided and spent £50 on a dyno to sort out the fuel to air ratio.
My race bike also has a stainless exhaust system and a race end can off a R6.
All up we have a good healthy 63.6 Bhp on the rear wheel and with gearing correctly its doing a great job against all the other bikes in the 400 class.
Oh and if you want to run a 520 chain use sv650 rear sprockets and GS500 front sprokets.
Gsxr750 K5 shock drops in and that sorts teh rear out for £50 and also about thte same for a new set of fork springs with fresh fluid.

what you get is a bike that revs to 15.5k and is great fun to thrash around the track or back roads.