GK73a SP TPS or not to TPS question

[Mazzerdod]

Hi Guys,

New to this forum and the GSXR400 so I'm learning alot on here.

I'm working on a recently purchased 1989 GK73A SP model and plan to strip and rebuild the carbs complete with new o'rings.

However I can't find a definative yes no answer on here to my question so hope a guru could help me out.

The bike does not have a TPS mounted on the carbs is this correct? i.e. is it only the GK76a SP that has the TPS or should the GK73a also have the TPS?

Just wondering in case the bike has been fitted with non TPS carbs by previous owner.

If this is the case I will need to get a set of GK73a SP carbs with TPS because I would not be happy knowing the bike was running without it.

Thanks again for any assistance offered.

P.S I have never ridden a bike with such a long 1st gear..... talk about riding the clutch to get her moving lol!

[Variablevalves suck]

Hi,
The 73a SP does not have TPS and the yes the Suzi SP box must have the highest first gear of any 400.
Main differences of the 73a Sp are higher rpm, some seeming to have no rev limiter, so watch the revs,
Different inlet cam (exhaust is same part no. as stock), no ally spacer under the rubber inlet manifolds + bigger airbox, CR gearbox, wider wheel rims and the fully adjustable suspension.

[Mazzerdod]

Hi Fella!

Many thanks for your reply it's a great help, so the stock GK73a Carbs are the same as the GK73a SP?

I have spoken with the previous owner he is going to find the stock carbs he took off the bike.

Also you mention the airbox, I did notice when the tank was off that the previous owner appears to have applied packaging tape to two large dimameter holes in the rear of the airbox kinda to the side and above carbs 1 and 4?

They are approx 1.5 inch diameter from memory, any idea?

Should these holes be ducted somewhere?

Last question.... is it easy enough to swap the stock SP gearbox for the standard road going box?

i.e is it a cassette type box pull out push in like the old RG500's?

[Variablevalves suck]

There should be no holes in the air box so they have been cut by a previous owner.
The non SP carb bodys are the same but if i remember correctly there may be a slight difference in jetting or needle taper, i will look it up for ya and there is a dark grey 1" thick spacer on the stock inlet manifold.
I wish the gear box was cassette! you got to split the engine tho if you are mechanical enough you can leave the top end on and work from the bottom. If you take the box out i will happily deal you for a stock one.

[Mazzerdod]

I'll look out for the inlet spacers... from memory it has none and thanks for checking the jetting very kind of you, if I have this info I will make sure I use the needles and jets from the original carbs during the rebuild.

Bummer on the gearbox sounds like I will be going up a few on the rear.... or down one on the front?

However should this not work out and I decide to spill the guts out of the casing you can have them in return for the standard gearing, the bikes done 19,000km so I'm hoping also well in that department.

[Mazzerdod]

Also I have been wondering if the fork tubes from a stock gk73a will fit the SP forks.

This bike has been sat in a garage for 6 years and I don't think the fork tubes will go again without rechroming... but if I could pick up a good set of stock forks could I strip them and use the tubes in the SP fork legs?

[Variablevalves suck]

They may work, ive both sets but never compared them and the part no.s are NOT the same so may be cheaper to rechrome.
Standard carbs have 97.5 mains, 35 pilot jets and 5DH7-3 needles- SP has 5EZ54-2 which are close to the Bandit's 5EZ67's and 32.5 pilot, 102.5 main which are same as some B4's.
All the 73a's and B4's have the same exhaust cam, interesting thing is the 1988 inlet cam is the same as the 88/89 SP and the 89 stock 73a had a different cam.
What rear sprocket have you got on at present?

[Mazzerdod]

Thanks for the info now I know what to do when I rebuild the carbs and sort the front end.

I don't actually know what sprockets are on the bike so I will count the teeth front and rear to see if she is running stock SP ratio's.

Interesting how they switched the cams on the different models and excuse my ignorance but what's a B4?

Is it an abrevation for a Bandit 400?

[Mazzerdod]

Ok now she has had the carbs sorted the bike actualy pulls away much much easier now so the gearing shouldn't be such a problem.

Really pleased with the transformation A+!

And I never mentioned that I bought this bike for a good friend of mine who didn't have enough cash for his bike test and a motorcycle, he has been helping me with the house to get it ready "I have a little girl on the way" and it's my gift to him to say thanks for all the hard work.

He takes his theory test in a couple of weeks and then direct access after that so really want this bike sorted for him.... anyway....

I still have a minor hick up at road speeds she bogs trying to pull through higher rev ranges with anything more than 1/3rd throttle.

It seems to me like it is fuel starvation but I set the floats at 14.6mm interestingly though they had all been set lower than this previously and i'm wondering if the stock 14.6mm just isn't the right height for these bikes to run correctly?

I'm fairly certain it's the float heights everything else is so perfect tick over, starts on the button, rides lovely at part throttle, revs all the way to 15k when not uner load etc etc.