GK76 Fuel tank/tap

[KiwiBiker]

Hi Guys, Ive only had the bike two weeks so bear with me if I ask some real dumb arse noob type questions

Ive just removed the fuel tank for the first time. What an arse it is getting those hoses off and back on the fuel tap with the limited slack in the hoses. Any tips greatly appreciated. In particular I struggled with getting the rear hose on to the back of the fuel tap. There's just not enough clearance to get your hands in there.

Im assuming the two large diameter hoses coming out of the tap are fuel supply lines to the carbs - one for the tap in prime and one for tap in On/Run? So is the smaller diameter hose coming out of the right hand side of the tap for vacuum then?
The guy I bought the bike off told me to switch the tap to prime for starting the bike then flick it back to 'on' once started.
Any need for this? I'm not really sure what the prime position is for...

I'll sneak in one last question and its a bit of a biggy but the bike appears to be running a bit rich (black plugs and pipe). In general where is the best place to start with this? I'm guessing jets or needle heights but I'm limited on carb knowledge.
Is it possible to work on the carbs in place or do you need to remove the bank? It's damn tight in there, looks like a bit of a mission! As you can tell, I'm used to working on singles and V twins.

Thanks in advance for any help you may wish to offer.

[willandrip]

The smaller dia pipe is the vacuum supply to the tap as you assume.
Both the larger hose supply fuel to the carbs at all times; it depends on the tap valve position to select prime/on/reserve/

A vacuum tap will not (or should not if working correctly and many aren't though) flow fuel to the carbs unless the engine is running and producing vacuum to open the tap.

This means if the bike is left for a while and the fuel evaporates from the float bowls when you come to start it and the tap is left on reserve or main tank position it will require the engine to churn on for ages until enough vacuum has been made to allow the fuel to reach the bowls before starting.

If you turn the tap to prime ; the fuel runs straight to the carbs without the engine running and the bike starts straight away.

Now Suzuki 400s are horrible little bastard things in two particular respects.
And those are flooding cylinders and rich mixture caused by faulty vacuum taps and O ring failure in the carbs.



Do not fool about with float heights and needle settings until the O rings have all been triple checked or far far better; just order the full kit off Blair Litek on here. There is absolutely reams of info on 76a carb faults and O ring problems on the web and especially on this forum. The new O rings fix about 90% of the grief providing folk have not fannied on with the jets and floats to try to compensate for the O rings

To get the carbs out ,which you will need to do; this is from memory mind and some things might not be required ;

Loosen battery box and move rearwards slightly (this is the unsure if really required bit)
Pull the two large clips out of the airbox that hold the 2 sets of inlet rubbers in.These are two huge U shaped wire clips that you just see the end of in a recess at each side of the airbox .
Loosen the clips off the carbs that hold the air box inlet rubbers.
Push the airbox rubbers into the airbox...probably best with lid off and filter out.
Undo the inlet manifold rubber clips.
I take the r/h rubber off the head completely too......it then gives you loads of space to get the carbs out..
Pull the carbs out of the l/h side.
Undo the cables at the carbs if you can....I can on mine, its only got one throttle cable and no choke cable.
You may have to take the cables off the hand controls and leave them on the carbs until you get them right out.

Hopefully someone may add to this with better tips for carb removal.

It is a bit of a fook on to get the carbs out and back in which is why I recommend the full Litek O ring kit before starting the job.
Far better to do it once and not on/off/on/off/on/off like a strobe that most do and get sick off it/damage something.

This is what most read then alter it a bit to their own method;
http://tonysleep.co.uk/info/great-gsxr4 ... ettor-saga

It is probably worth double checking tap operation when the tank is off the bike by applying suction to the vacuum line.
(you can just suck it and see )

[KiwiBiker]

Thanks muchly mate for your comprehensive reply, appreciated.

Pretty much everything you said makes sense. One thing I dont get tho is how a faulty fuel tap could make the bike run rich. I would have thought if enough fuel wasnt getting through then it would miss and fart around and run a bit lean if anything?
Or, if the vacuum function wasnt working and it was just running constantly (as in prime position) then it would just fill the carbs until the float stopped more fuel coming in and it would run fine?

I'm not going to get too finicky with this beast as Ive bought it as a track bike but if it starts fouling plugs then...

In its favor it does start well and idles nicely. The previous owner had not long had the valve clearances adjusted and carbs balanced by a suzuki dealer so thats reassuring.

[willandrip]

This is where the O rings come into the equation.

The GSXR tap is not the best vacuum tap ever made by far.....most allow fuel past to a small extent in the on/res. position

The jetholder block in the carb has an O ring that is known to fail

This allows fuel to leak straight into the cylinder as it is below the level that the float needle jet shuts at.

Fuel constantly flows into the cylinder when running or stopped.

This leads to premature bore wear eventually.

Does your bike require choke to start and run consistently at start up.?

Does the temp gauge ever get up into the very upper margin.?
Running cool is a sign of overfuelling.

Mind the thermo is another issue on these ...they open lower than is ideal and the bike runs cooler than it should for best performance and engine wear.

[willandrip]

On the plugs front......these are very fussy.

The twin electrode NGK as recommended by Suzuki is the only one that will run mine correctly at sustained rpm.

[KiwiBiker]

Its got Denso Iridium's in it. What is the number of the NGK's I should get? Cheers.

[Variablevalves suck]

As above running rich is a sure sign of bad orings, starting without chock and the temp gauge staying low are the signs.
Best advice is new orings and a warmer thermostat.

[KiwiBiker]

Thanks for the advice guys, sounds like you are both onto it. It starts without choke and I'm yet to see the temp gauge get up there, but we are just coming out of winter here to be fair

[willandrip]

A very easy test to see if the fuel tap is leaking......which I think should be performed on new acquisitions as the tap does appear a weak unit on the 76a.

Put the tap in the on/reserve position depending on fuel level and have the bike standing level.
Get a aerosol can cap and drain each bowl in turn into the cap.
Close the bowl drains and leave the bike a few days or as long as possible.

Attempt to drain the bowls after being left......any fuel whatsoever indicates a leaking tap.

The drain screws are very easily accessed on these with no removal of parts required.

Your bike tap appears to operate correctly as the PO advises use of prime position to fill bowls to replace any evaporated/leaked past the O rings fuel but it may be of help to other readers.

[KiwiBiker]

So... after another annoying run on the bike yst (started with no choke even tho cool air temp 10 -15 degrees, farted around below 6000rpm despite me cleaning plugs before hand, temp gauge hardly rose, pipe black etc etc - every thing you guys said!) I ripped the carbs off today using the Tony Sleep guide. That guy deserves a knighthood for services to GSXR owners. I also ordered the Lite Tek carb kit too. Thanks for the tip.

So other than taking off the float bowls I haven't had time to strip them yet but I wanted to ask about how to measure the float height. The picture in Tony's guide has the carbs shown lying upside down and the measured gap is to be 20mm. But when I measured mine in this position I only got 17mm which concerned me a little. Then I moved the bank of carbs to the vertical position so the little tip on the plunger wasnt pushed in but the floats still stationary and I got 20mm. So I'm assuming (hoping) this is the correct way to measure the float height. If I go much beyond vertical the floats flop over/out so i know this is not correct measuring position either.
But wait theres more... My idle mixture screws were all set at 2 turns out from seated position but Tony says 1.5. Any thoughts on that or am I getting pedantic now, which has happened before

As usual, many thanks in advance.