FZR400 3TJ race bike

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Stuart67
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FZR400 3TJ race bike

Post by Stuart67 » Mon Jun 24, 2019 8:17 pm

Hi, new to this forum and will probably be hanging around looking for advice. My son is racing a 3tj in the formula 400 class with BEMSEE and Preston and district, and I was hoping/wondering if any of you have prior experience of tuning and racing these bikes. I know the Kawasaki is the most popular bike for this class but my son gets on well with the Yamaha chassis so I'm hoping to improve things power wise to compete. He's running in the Sub 64 class and it's currently putting out 56hp on the BEMSEE Dyno so we need a few ponies to get close, any advice, tricks, tips are gratefully received and repaid in beer if I see you at a race meet 😁... Cheers!

Evilchicken0
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Re: FZR400 3TJ race bike

Post by Evilchicken0 » Tue Jun 25, 2019 5:50 pm

I don 't have a lot of tuning experience but the first things would be to ask if his bike is an SP version ??
The SP comes in the 3TJ02 model - CV carbs and 3TJ04,05,06,07 which have flatslides. Most of the flatslides have been robbed a long time ago.

The SP generally had, adjustable suspension the front was cartridge forks, the rear has a canister, Close ratio box (not that great for short circuit because of the high first gear) 9 plate clutch pack, lighter valve train and different springs (I think they're yellow), captive wheel spacers and a quick change swingarm.

56 is a reasonable bog stock engine with standard cams dialed in … so check the cam timing to find if theres anything else possibly done to the engine. Race cams could be had from Kent Cams, I imagine you need vale springs to suit it.
The oil valves on the crankshaft can be swapped out for 600 ones, they're bigger diameter so the cases need drilling and tapping.
The head can be flowed, obviously.
You can run the largest overbore pistons - but pistons are getting rare.
Use BDK Racing timing thing so you do away with the flywheel - they make a lot of other bits and do tuning but they can be slow.
Lighten and balance the crank (I guess) balance the rods and pistons too.
The barrels can be slotted to reduce the pumping pressure
Skim the head to increase compression.

A word of warning though - don't got too far, these engines do tune easily but the higher you go the more fragile they are aim for 70ish.

Stuart67
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Re: FZR400 3TJ race bike

Post by Stuart67 » Tue Jun 25, 2019 9:06 pm

Thanks for the info Evil chicken!
The bike is an RR, not SP, has CV carbs and stock cams on stock sprockets, I've stayed clear of slotting the sprockets as I'm not sure if I'd need to pocket the pistons to retain a safe clearance, perhaps you know?
The intake ports look to have had some work done on them but not sure to what extent.
I have a spare motor which is on largest oversize with what appear to be race pistons, one compression ring and an oil control ring but I'm short of some parts to get that up and running so may post a wanted as.
Regarding the timing, I've looked at the BDK ignition advancer but wondering if it's any better than just using an offset key to move the flywheel 4degrees. I know losing weight off the crank can improve mid to high rpm response but can also lose some drive off the bottom end. Jetting is stock at the moment but the AF looks good on the Dyno. Chassis wise it's stock forks with emulators in and a GSXR SRAD rear shock although I have a fox unit to try and I have a set of MAXTON modded forks (which he doesn't like) and some sp fully adjustable forks but they need new stanchions (previously been bent and straightened but have a crease and bulge just under bottom yoke).
Cheers
Stu

Evilchicken0
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Re: FZR400 3TJ race bike

Post by Evilchicken0 » Thu Jun 27, 2019 1:22 pm

Sounds like you know more about this than me.

I guess it depends on which bits you need for the engine - maybe send me an email, I live in London
If you slot the cam wheels you could put the cams into the optimum position rather than have the cam chain dictate it. You need an engine tuner.

moforockband
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Re: FZR400 3TJ race bike

Post by moforockband » Mon Jul 01, 2019 11:16 pm

400's suffer from poorly top ends, and can quickly go off. I used to race F400 and I know the Yam's were slow unless BDK ran them, god knows how they got 85hp out of them :D
I'd check that the top end is healthy. Nice compression, no carbon build up on the valves/ports, that the guides aren't worn, and also that the seats still have the triple cut left on them, and not worn to the same shape as the valve itself. This will make the head run cool/poor flow and prone to carbon up, losing power the longer it's left.
If you don't have all of the above, you'll be stuck with what hp you have unfortunately :(
Racing 400's is not cheap if you want to be at the front.

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Re: FZR400 3TJ race bike

Post by sportspromatt » Sun Jul 28, 2019 10:50 pm

Im running a sp road bike! Have you tried forcing a bit more clean air at the filters! Sorry its a basic cheap trick, you could also try turbo charging his left foot, or preloading the gears before you need them!

bendy3
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Re: FZR400 3TJ race bike

Post by bendy3 » Wed Oct 09, 2019 9:18 pm

Inlet cam to 105deg and about 3to5deg timing advance will help. You can get offset woodruff keys or file 1 down to alter timing.
You can’t go too mad as you have to stay under the hp limit!


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