Tuning for the unwary.

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hondaror
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Joined: Mon Mar 03, 2014 8:44 pm
Location: Alberta, Canada

Tuning for the unwary.

#1 Post by hondaror » Fri Sep 08, 2017 3:49 am

For a long time I've had a forum member's bike in my garage, working on it when I had free time. After many months he is now back on the road, blasting his RZ350. He has not been on the bike for the past 4 1/2 years. He is a happy guy, riding the smoker once again.

What does this have to do with tuning? Nothing.

We were chatting about the differences of our bikes after a great ride together yesterday. This is where I realized it would be a good idea to offer some information about tuning to the forum.
Many of us are well versed with regards to 2 strokes. So this blurb is nothing new. For many others, there might be some good information that helps them to decide what modifications they'd like to perform on their bike.

The bike I was working on was a ported 1990 RZ350 F2. It has V-Force 3 reeds, a Swiss cheese air box lid, JL pipes and dyno' at 48.5 horse power at the rear wheel.
My bike is a stock F1 with F2 carbs, K&N pods and Toomey pipes, dynoing at 56 hp at the rear wheel.
Both bikes are jetted the same:
Mains 260
Power jets 65 left, 60 right
Stock needles on the 5th clip, fully raised.
Pilots 27.5, too rich. On order.
The Ported F2 power pulls from 5300-11000rpm, mine from 3000-10500rpm.

So, why the differences in power? There are two ways to increase power, displacement and flow. Flow is the efficient means. All modifications for power increase come with a cost or trade off. The F2 has an air box. This is the air flow restriction that hurts the power output of the F2 compared to my bike with the pods. I'm guessing, with pods, the F2 should increase it's hp output by 8-12.

Why is power delivery different? The ported bike has had the port sizes and shapes changed for increased internal air flow. That air flow is effective in the upper rpm range, thus killing off some of the bottom end of the stock engine.
I was also asked how to get that back. Well, you can't. You'd have to buy new cylinders. Once ports are changed, they cannot be returned to stock sizes.

Why would you port the engine? People are led to believe that a ported engine is faster than a stock engine. This is not always the case. There are "tuners" that make claims of increased power, but be very careful, as many that make these claims can not follow through. A good engine tuner has access to a dyno, the "bull shit" separator. He/she also has many years of experience. Make sure you know that your porting tuner is legit.
My opinion, is not to port your engine. It's the last mod you should ever consider. A heavily ported engine is unstreetable. Port work, usually, makes the bike harder to ride. Unless the bike is for racing or track days, it's not a good mod. The guys that ride ported engines and like them, are usually above average riders, or the thrill seekers that think they are above average riders.

What are good modifications to the RZ? This is totally my opinion, let's keep that in mind. This is by no means RZ gospel, or RZ law. First of all, my question to you, is, why did you buy an RZ? To be cool? Because you like two strokes? Because someone told you about their sporty giant killer reputation?
I raced 2 stroke motocross bikes in the '70s & '80s. Parts of 9 seasons. In 1982, at the age of 19, I purchased, what any motocrosser who wanted to ride on the street would buy, an '81 RD350LC with 3200 kms. What I call, a natural transition to the street. The bike was mint, and stock. I had no issues riding. However my learning curve spiked. It took me about 3 season's to get really comfortable with the street and the bike. During this time, the bike remained pretty much stock.
In 1985 I purchased 2 TZ250s. I attended a race school and raced my TZs that season. I was 2 stroke experienced and didn't have too much trouble adapting to the Yamaha Formula II GP bikes. It was my forth season on the RD and by this time, my RD looked like a TZ with lights.
The first mod was when my tires wore out. I went oversized. Dunlop K81s. Not a good idea. It slowed the steering. Stay with stock sizes. Then DG pipes. What a gain in hp and drop in weight. Pods next coupled with jetting. That amounted to another great gain. A Harris full fairing and TZ replica seat made for the RD. I had removed mirrors, signals, all associated wiring and relays, subframe, speedo and speedo drive gear and cable, installed clip ons with the fairing, and a TZ aluminum brake arm. I also cut the bubble section of the fairing and dropped it to be like my TZ fairings. It was a cool looking street bike. Weighed well under 300 pounds.
Again, my opinion only:

Things NOT to do- :smt021
Porting-harder to ride
Shave head-increased compression results in unreliability
Larger carbs-loss of bottom end power
Oversized tires-rear, added unsprung weight & increased inertia, front, slower steering
Wider wheels & larger, stiffer front end-creates other problems, requires frame mods to handle forces

Things to do- :smt026
Replace air box with other options for breathing
Expansion chambers
Jetting
Multi piston calipers
Radial tires in stock sizes
O ring head or cylinders with combustion chamber recut
Steel braided brake lines
Fork emulators
Rear shock
Full fairing & seat kit
Fully naked
Clip ons

I'm all about performance enhancements. This advice is geared to the newer enthusiast, or those enthusiasts with limited knowledge of the RZ. A well set up stock bike is extremely fun to ride. A heavily modified race bike is very difficult to ride fast and equally as fun to ride as a well set up stock bike.
I did not talk about the second means of increasing performance, displacement. Big bore kits drastically change the characteristics of the RZ. They are expensive and are not my idea of what the RZ is, and is about. The power those kits supply, is meant for another class of bike. Be aware of what you're trying to do, and have fun!
Rory
2 1984 RZ350s
1985 RZ350
9 1986-1990 RZ350s
2000 ST2
2005 749
2005 749 with 999 engine

hablair
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Re: Tuning for the unwary.

#2 Post by hablair » Fri Sep 08, 2017 8:41 am

Good advice, you always learn something

i did, thank you for the post

evan_calgary
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Joined: Tue Nov 12, 2013 2:34 am

Re: Tuning for the unwary.

#3 Post by evan_calgary » Wed Sep 13, 2017 5:18 pm

Rory,

Bike sounded great. There is a lot in this list that is pretty much the opposite of what is preached on this forum (airbox, carbs, brakes etc..).

The guy we ran into Sunday talking about the TZR was telling me to run wider tires. Told him that was a terrible idea. Why would I want to ruin the sharp handling which is one of the most fun aspects?!

It is pointless to put modern rear wheels on these bikes. It is entirely the opposite of why they are fun (the 500 is another story).

I personally would disagree on oversized carbs and headshaving but respect your opinion. Totally agree on the fun mods and many of these that are really not that expensive.

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gammaguy21
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Re: Tuning for the unwary.

#4 Post by gammaguy21 » Thu Sep 14, 2017 11:25 am

evan_calgary wrote:Rory,

Bike sounded great. There is a lot in this list that is pretty much the opposite of what is preached on this forum (airbox, carbs, brakes etc..).

The guy we ran into Sunday talking about the TZR was telling me to run wider tires. Told him that was a terrible idea. Why would I want to ruin the sharp handling which is one of the most fun aspects?!

It is pointless to put modern rear wheels on these bikes. It is entirely the opposite of why they are fun (the 500 is another story).

I personally would disagree on oversized carbs and headshaving but respect your opinion. Totally agree on the fun mods and many of these that are really not that expensive.
I run wider tires on my TZR250 2ma. They came from a TZR250 2XT, which is a beefed up 1kt/2ma/2my.
Best modification I have done to that bike. Handles way better with modern radial tires.

Disco
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Location: Wisconsin

Re: Tuning for the unwary.

#5 Post by Disco » Thu Sep 14, 2017 4:22 pm

Rory, you mention radials in stock size. What are your preferences and experiences? Very few options out there for us, but I'm leaning that direction.

RuZty
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Re: Tuning for the unwary.

#6 Post by RuZty » Thu Sep 14, 2017 7:10 pm

hondaror wrote: Again, my opinion only:

Things NOT to do- :smt021
Porting-harder to ride
Shave head-increased compression results in unreliability
Larger carbs-loss of bottom end power
Oversized tires-rear, added unsprung weight & increased inertia, front, slower steering
Wider wheels & larger, stiffer front end-creates other problems, requires frame mods to handle forces
I agree with the principal of what you are saying, i.e.. don't try to replace a scalpel with a sharp machete, but there are some beneficial items on your 'don't' list.
-porting, depends who does it and how much but in general I would say you are right in a rideability sense.
-My bike has had a shaved head since I got it and it is nicer to ride with it, no reliability issues in 40000km. Currently running a cut, o-ringed and reprofiled head by Slinger.
-PWK 28 are larger (okay not by much) but the newer design makes these a nicer carb all around, try some.
-Tires, my last set of BT45's were stock sized and I found the front less confidence inspiring than the one size up that was on both ends before. I may be a pussy.
-I just installed an RGV rear, R6 forks. The parts that went on were same or lighter than stock. Overall the bike is down 8 lbs, but a couple of that is the centerstand. Modern tires are definitely nicer than 18" BT45's and I would wager lower inertia from the smaller diameter rim (especially compared to the hefty 31K wheels). I haven't noticed any frame flimsiness yet but it is early days. Take a look at the last steel TZ frames, visually identical design to the RZ. Sure the tubing and manufacture is probably superior, but I think bracing these frames is overkill and maybe more of an aethstetic thing, although the RGV swingarm fits that bill too. I doubt any of this makes it any faster in the hands of a skilled rider but half the fun was doing it. You are of course invited to take it for a spin next time you stop by.

hondaror
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Location: Alberta, Canada

Re: Tuning for the unwary.

#7 Post by hondaror » Thu Sep 14, 2017 9:02 pm

Disco wrote:Rory, you mention radials in stock size. What are your preferences and experiences? Very few options out there for us, but I'm leaning that direction.
The Conti's. Peter and Kelly are running them and love them. I'm going to give them a shot. They are expensive.
Rory
2 1984 RZ350s
1985 RZ350
9 1986-1990 RZ350s
2000 ST2
2005 749
2005 749 with 999 engine

hondaror
Posts: 2828
Joined: Mon Mar 03, 2014 8:44 pm
Location: Alberta, Canada

Re: Tuning for the unwary.

#8 Post by hondaror » Thu Sep 14, 2017 9:05 pm

Hi Russ,
This blurb is meant for the RZ inexperienced. So many of us like so many different things. You don't have to do too much to make them sing.
Rory
2 1984 RZ350s
1985 RZ350
9 1986-1990 RZ350s
2000 ST2
2005 749
2005 749 with 999 engine

RuZty
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Joined: Fri Oct 03, 2003 11:11 pm
Location: Southern Ontario, Canada

Re: Tuning for the unwary.

#9 Post by RuZty » Thu Sep 14, 2017 10:22 pm

Absolutely, buy one, fix the basics and flog it. Best to get to know it before you start messing with stuff.

hondaror
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Joined: Mon Mar 03, 2014 8:44 pm
Location: Alberta, Canada

Re: Tuning for the unwary.

#10 Post by hondaror » Fri Sep 15, 2017 1:05 am

That's exactly my point.
Rory
2 1984 RZ350s
1985 RZ350
9 1986-1990 RZ350s
2000 ST2
2005 749
2005 749 with 999 engine

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JonW
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Re: Tuning for the unwary.

#11 Post by JonW » Fri Sep 15, 2017 1:54 am

I like this thread, good work Rory.

Like Russ I have some of my own views on this stuff, but think for those inexperienced in RZs this is a great primer.
80 XT500 Supermoto!
81 RD350LC Resto
82 RD421LC Hybrid
82 RD350LC decapitation project
82 RD250LC JDM '251LC' YPVS
83 RZ350 Resto
84 RZ500 Resto
85 RZ350 F1 Resto
86 RZ350 F2 Resto
86 RZ350 F2 Hybrid

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hondaror
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Location: Alberta, Canada

Re: Tuning for the unwary.

#12 Post by hondaror » Fri Sep 15, 2017 12:02 pm

Thanks Jon. This is a bit of a guide for those looking to get the most of their bike on a bang for the buck bassis. This is not meant to be an attack on those who have modded their bikes far from stock. We all have preferred mods, needs, wishes. Keep those alive, and know you have fans and support out there.
I realize that I'm an above average rider with many years, and track/race experience with the mighty 2 strokes. I am hoping to expand on that experience in the future. My current daily is a simple set-up, very effective ans a hoot to ride. Just want to share that knowledge. I also want to play with the modding possibilities. The track gives opportunity to research and develope. Glyn is a perfect example, with his wealth of knowledge. Martin, MK as well.
Rory
2 1984 RZ350s
1985 RZ350
9 1986-1990 RZ350s
2000 ST2
2005 749
2005 749 with 999 engine

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