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Mat Oxley 1986 IOM TT


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Messages - teazer

#286
Haus of Projects / Re: New project
June 30, 2021, 09:48:37 AM
EE's right.  Yamaha had issues with piston life on the 250G with it's cavernous intake ports.

Just thinking out loud, but since we are now off topic, might I suggest an RZ motor in that frame with say a stroker crank and CPI cylinder for about twice as much power as a TZ top end.  :whistle:
#287
Haus of Projects / Re: New project
June 29, 2021, 11:36:24 PM
Excellent choice.  We have an FZR in the garage.  It sounds big and mean but only makes about the same HP as our RZ350.

Didn't Yamaha go to reverse cylinders specifically to reduce piston wear with large intake ports on the 250 models which ended up with huge intakes?

It's hard to get the pipes looking good on our old downward pointing exhaust ports.  I had a set from a Kart motor years ago but they could not be fitted to a bike as you can see. On the reverse cylinder models, the exhaust ports are completely different exit angles.
#288
Turning Wrenches / Re: Needle Jet Question
June 29, 2021, 11:25:29 PM
According to an old Mikuni book, the spray tube is supposed to be called the "primary choke".  And that changes fueling from just past 1/2 way to the top end.

IIRC, the taller the Primary Choke, the more it richens up the top end. 

"The lip generates turbulence which creates a greater vacuum behind the lip where the needle is located.  At high RPMs, the increases vacuum helps to pull more fuel up from the float bowl.  The height of that lip (primary choke/spray tube) determines the amount of turbulence and consequently the amount of extra depression at the venturi exit  of the needle jet.  A taller primary choke  will create more turbulence and more suction acting on the fuel, leading to richening the mixture as revs rise.  Use of a taller primary choke allows the use of a smaller main jet to achieve the same fueling at high RPMs, but leans out the mixture in the medium throttle position."
That was basically a straight quote from an old manual.

Late model RDs with the #284 series tall primary choke and aftermarket copies are presumably designed so that at full throttle. the mixture slope is tipped to make them richer than a low primary choke at top revs. 

So if you shorten the primary choke and get the main jet right for top RPMS, it will be richer at mid revs - assuming that the main jet is actually correct for top revs.  We all tend to confuse revs with throttle position, so take care.

If your issue has an event horizon that is basically throttle position related, it most likely needs a different needle which either different slope or more likely a different position at which the taper starts.
#289
That's neat.  I cut down the side cover a little further than yours and I think I used the RD oil pump gear IIRC.
#290
I must have been asleep in class, but I just noticed that TZ water pump on the clutch cover.  How did you mount and drive that?

On the R5 side cover I fitted one in place of the oil pump, but it sits on an adapter plate.  That was a common conversion for karts back before my time. I had a pile of ex kart motors and bits a few years ago and that's where mine came from.
#291
General Chatter / Re: Oem vs restomod?
June 19, 2021, 06:14:53 PM
Busa hit the nail on the head.  My first RD400 was stock, so that's how it was rebuilt.  I had one stock GT750 that I restored. The rest were incomplete, so they were modified to a greater or lesser extend.  One was changed into a Dunstall with a few upgrades, one was more or less stock but fitted with GS mag wheels.  The others were cut and welded and tweaked to make them much lighter and easier to ride.

My RZ is stock apart from seat and pipes and I'd love one with better suspension and bigger motor etc, but I can't see myself doing that to this one. It's not perfect.  Well to my eyes it is.   
#292
Haus of Projects / Re: New project
June 18, 2021, 12:19:26 PM
But enough about part numbers,  What is the project and when do we get to see a progress report?

If it's even half as good as your last one, it should be fantastic.
#293
Turning Wrenches / Re: 1979 PE 175
June 16, 2021, 11:19:20 PM
Sounds like an issue with the "ECU"  PEI uses a proprietary timing arrangement in the ECU.  I believe that replacement CDI boxes may be available to get someone top test the system on a test jig and have them run it up to top engine revs to plot the timing curve and see if it's OK.

Rex's Speed Shop in the UK can probably test it and tell you if it's OK.
#294
Turning Wrenches / Re: Needle Jet Question
June 15, 2021, 10:14:14 AM
That indicates that it was marginally rich with cold dense air and has become too rich with warmer less dense air.  Try O-8 needle jets to clean that up.

The idle is now too lean, so try going up two sizes in the pilot jet.

Needle jet size doesn't usually have that much impact on idle but circuits do overlap.  Try that and see what changes.
#295
Turning Wrenches / Re: spark plug heat range
June 14, 2021, 09:47:31 PM
plug color is a measure of how hot the plug got on a particular run. That is affected by load, Air:fuel ratio, compression, pipes and so on. You appear tho have changed a lot of things at once, so it's hard to tell which of them reduced plug temperature.

If you check plugs at part throttle it tells us a little about plug temperature and nothing about jetting.

You said it makes less power when you could reasonably expect it to make more.  Is it really making less power or is it just smoother than it used to be?  A bike that comes on the pipe hard feels powerful even if it makes less power but simply has a bigger hole in the power curve.

If it does in fact make less power it is probably jetted wrong or ignition timing is off. 

Where you read plug temperature as it relates to heat range is the side electrode.  How does that look?
#296
Turning Wrenches / Re: Needle Jet Question
June 14, 2021, 09:41:21 PM
At what revs and/or throttle position are you seeing/feeling that difference?

In theory, the needle and needle jet are there to moderate the main jet. Normally the pilot jet and pilot air jet/adjustment control idle and just off idle.  As the throttle is cracked open, the cutaway becomes the main control system and from there up to say 3/4 it's all about the needle and needle jet.  Main jet does impact all the way down but main jet has to be set of full throttle operation and the needle jet spray bar height and main air jet control the fuel slope.

What the heck is a fuel slope?  Well we tend to conflate revs and throttle opening and that's understandable, but we usually get things wrong because of that.  At full throttle the air:fuel ratio changes as revs rise.  Two strokes typically require a richer mixture at full throttle & full revs than a 4 stroke, so the air jet or spray bar are used to change how much richer or leaner it gets aas revs rise.  That's what they mean by changing the fuel slope.

That's also why people say to get idle right first and then main jet at full revs.  After that the needle and needle jet are used to tweak that fuel slope at lower throttle openings.

In this case, it sounds like a wrong cutaway or wrong needle jet taper or the point at which that taper starts.

Which is why I asked where is the issue in terms of throttle opening.
#297
RZ350 front end with RD350 wheel or even better FZR400 front end with RD350 wheel slotted between the legs.

Or maybe go for a GSX600 Katana front end with RD350 wheel
#298
eBay/FB Marketplace/Craigslist watch / Re: GT750
June 10, 2021, 04:57:27 PM
That's my Dunstall. 

Racer1 perhaps on that fugly bike.  Pipes could be J&R Power Pipes.  Interesting time capsule though.
#299
Forget the leathers.  That pipe is pure bike porn.
#300
Haus of Projects / Re: New project
June 10, 2021, 04:30:46 PM
Correct, 750 motors run backwards. 
I want to say that originally only the OW31 works motors had TZ350g (3g3 casting) 6 port but I read somewhere that they were standard on later monoshock production bikes. 409-70 and 409-71 share the same RD type 4 transfer ports plus boost port.  Not sure what the later 6 port barrel casting number is but they may have been used on E and F models, but I have zero experience or documentation on those.  If someone has a set of those or E/F parts book, that would be interesting.

According to the parts books 409-71 (4 ports) was introduced on the D model in production December 1976, so a 77 model as we would know them.

On a twin the intake port becomes imprinted on the piston skirt. OK for low mileages and race motors that are often apart, but not ideal for a daily driver.