Derestricting the fizzer

[riffer]

Even since I found out how to derestrict my FZR750R to bring it up to (nearly) OWO1 spec I've been dying to try it. I've started on the process recently and thought I'd share some of what's been happening.

Firstly, there are two types of FZR750R genesis models. The Japanese domestic model, which is restricted to 77BHP, and the USA model, which is 107BHP. I have the Japanese domestic model, and while its not too shabby, the possibility of liberating a few more horses was definitely appealing.

The Japanese model is restricted in the following way:

1. Air intake through the airbox is restricted
2. The exhaust muffler has lots of restrictions in it
3. The carbs have smaller jets
4. The digital ignitor has 5 degrees advance per 1000rpm between 1000 and 6000 rpm, instead of 10 degrees advance per 1000rpm, in the US model

First step - get the sucker breathing better. There are restrictor bungs in the airbox which are easy enough to remove. The air filter has a rubber bung in it. I removed the restrictor bungs in the airbox and replaced the air filter with a high flow one

Second step - remove the restrictions in the exhaust. I was a bit rough with this, and put a large drill down the middle of the exhaust, and drilled a few holes in the back end. Basically tried to get the air going through a bit faster. This was the zero dollar option, as I have spent about $1200 in the last couple of months fixing it after my bin, so Gini has vetoed any more $$ for things like aftermarket exhausts, etc. Obviously an aftermarket exhaust is the best option here...

[riffer]

Third step - sorting out the anaemic fuel delivery.

This was tonight's work. I've been running the bike with step one and two done, and while it's revving quicker, I'm finding I have to nail the throttle to get sprightly acceleration, and there's a flat spot around 6000-8000 (redline 11000).

SIDE NOTE: I'd turned the rubber thingies that join the airbox to the carbies around a bit to see if they fit better as I had a nasty screech on acceleration. It hadn't fixed the problem so I looked at the airbox again. Turns out on the inside of the airbox the other side of the rubber thingies has inlet pipes which point to the inside of the airbox. Turning the rubber thingies around was causing the inlet pipes to not point to the inside of the airbox, which was restricting the air again. FIXED.

I had to pull the carbs out to get at the float bowls, as there's just no room to get at the screws as the frame wraps around and over the carbies.

I discovered when I pulled the carbies out that the rubber that goes between no2 carbie (from left to right sitting on bike) and the inlet manifold is actually partially split. Awful screech found! I will have to replace that part I guess. I must have done that when I stripped and cleaned the carbies last Christmas. Shit. Never noticed at the time.

So I had to remove the float bowl covers to get at the main jets. There was one screw on no2 carbie (obviously my problem carbie) which was stripped but my trusty impact driver had that sucker out no problem.

The jets in the carbies are pretty little - 82.5's on the outsides and 80's on the insides. These have been replaced with 105's on the outside and 102.5's on the inside.

I was pleased to see that the float bowls were still lovely and clean with no mess at all inside them.

The old jets came out easily, and the new ones went in just as easy.

Then it was just a matter of putting everything back together, turning the bike on, letting the fuel pump fill the carbies, checking no petrol was leaking out of the float bowls, and checking that the idle was okay, then putting the tank back on, and starting it up again.

Dammit, it's pissing down here so I decided to come inside and type this and watch Sports Cafe.

But first reactions - the hesitation and miss has completely gone. It's possibly running a bit rich but I will have to see how it performs going over Haywards Hill to Tawa in the morning. It seems to accelerate a bit quicker but that could be because it was so wooly before I started.

The next, and final step will come when I can find (and afford) either a 1989 FZ750 or 1987/88 FZR1000 digital ignitor. The pre-89 FZ750 ignitor will not work as it has an analogue pickup and no electronics to power the fuel pump.

If anyone knows where to get one I would be grateful for the info. My finances are pretty dire when it comes to buying bike parts, but I'm sure there must be some way it can be worked out.

I will report tomorrow on how the bike is running. :spudwave:

[riffer]

Well it started okay this morning, which is always a good sign.

The power delivery is a lot smoother, and there appears to be a LOT more torque, which is probably attributable to my sorting the airbox out.

Power from 6000 onwards (when the main jet is probably starting to work) is much better, and from 9000 onwards with WOT its quite a bit quicker. I will have to watch that so I don't get a ticket.

Overtaking a car on the River Road passing lane I noticed instead of doing about 120 km/h past them, it was more like 140, so its definitely gruntier.

I don't think its giving me all the power gains I would like, but its much smoother and more fun to ride - the power's more usable.

The seat in the pants-ometer reckons its at least another 10-15hp - possibly more (at the top end) I've gotten from upjetting and opening up the airbox.

Now to find that digital ignitor...

[Cajun]

good work celticno6

[Blakamin]

Excellent!!! good to see its a happier bike now!

did you take any pictures of the proccess??

[riffer]

Excellent!!! good to see its a happier bike now!

did you take any pictures of the proccess??

No, too busy actually doing the work.

[Hooks]

Hey Simon .... now all you need to do is give it an old mans tune up and bring her up for a run over the weekend !! Let her lift her skirts and show what's really underneath !! .... be good for ya too !!!

[James Deuce]

Good on you Simon.

I'm gonna be in my Gargre all weekend I think

[geoffm]

ERD do a black box for these IIRC. "Wayne Gum - wayne (at) erd.co.nz
Put some silicone on that cracked boot for a temporary repair - an air leak will stuff things up.
Geoff

[F5 Dave]

With the inlet manifolds, they are old, they will be prone it it. With airbox mods you should make sure any entrance to the box is devoid of sharp edges. The entrance hole should be large enough but no need for excessive. On my YZF it is opened to about the size of a slightly flattened fist & I have put rubber edging around the hole. Drilling holes is a bad idea for this reason.

Most likely your emulsion tubes will be ovalised by now. If you pull the carbs again you may see the tubes from the top are worn. This is VERY common with a few miles. Surprisingly few miles on Yams it appears. Check out the Factorypro website & Exupbrotherhood. Sorry I don’t have any spare YZF ignitions, but if you rang Don at Huka Honda he might well have a spare FZR/YZF one in his personal collection. Or he might not.

Sounds like a huge increase on the mains. I would highly suspect you are running rich now. It would be a good investment to throw the bike on the dyno & use their jets to determine what you should be running. Sometimes it is hard to tell. If you have a flatspot, then it comes on -it can feel more powerful, but you are just using more throttle. I’ve fooled myself before with seat of pants dyno.

Sometimes you can seem to tune out a problem by jetting in the wrong area as they do overlap a bit but it gets too rich in an area you didn’t want to change. Read up about the emulsion tubes, it will never atomise properly if these are shagged, & the saving in gas mileage should pay for them.

Also the port on these early 5V are too big & later years they got smaller.

[riffer]

ERD do a black box for these IIRC. "Wayne Gum - wayne (at) erd.co.nz
Put some silicone on that cracked boot for a temporary repair - an air leak will stuff things up.
Geoff

Just got a pm from another kiwibiker a few minutes ago which may fix that pesky old digital ignitor problem. Watch this space...

[Blakamin]

ERD do a black box for these IIRC. "Wayne Gum - wayne (at) erd.co.nz
Put some silicone on that cracked boot for a temporary repair - an air leak will stuff things up.
Geoff

Silicon??? near fuel???...um okay.... one of the things i learnt as a young'en NOT to do!
a bit of gaffer tape maybe....

Celticno6, Cant wait to see the beast in action! might have to ride over your way after the buckets....

[riffer]

Silicon??? near fuel???...um okay.... one of the things i learnt as a young'en NOT to do!
a bit of gaffer tape maybe....

Celticno6, Cant wait to see the beast in action! might have to ride over your way after the buckets....

Let me know and I will have a fresh copy of Faster for you ...

[geoffm]

Silicon??? near fuel???...um okay.... one of the things i learnt as a young'en NOT to do!
a bit of gaffer tape maybe....

Celticno6, Cant wait to see the beast in action! might have to ride over your way after the buckets....

Silicone on the outside of the rubber boot, and only if it is age cracked and not big holes. Well known bodge if you are selling the bike (use black silicone...) It works welll, but not a permanant repair.
Geoff

[Blakamin]

Silicone on the outside of the rubber boot, and only if it is age cracked and not big holes. Well known bodge if you are selling the bike (use black silicone...) It works welll, but not a permanant repair.
Geoff

hmmm.... note to self > no buying bikes off geoffm