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Messages - teazer

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Haus of Projects / Re: New project
« on: Today at 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.

Turning Wrenches / Re: 1979 PE 175
« on: 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.

Turning Wrenches / Re: Needle Jet Question
« on: 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.

Turning Wrenches / Re: spark plug heat range
« on: 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?

Turning Wrenches / Re: Needle Jet Question
« on: 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.

Turning Wrenches / Re: What front end would you use?
« on: June 12, 2021, 01:36:39 PM »
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

eBay/Craigslist watch / Re: GT750
« on: 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.

eBay/Craigslist watch / Re: Kenny Roberts autographed leathers
« on: June 10, 2021, 04:52:57 PM »
Forget the leathers.  That pipe is pure bike porn.

Haus of Projects / Re: New project
« on: 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.

Turning Wrenches / Re: rd350 bottom frame crossmember
« on: June 10, 2021, 04:26:46 PM »
Good idea.  I had a TD3 years ago and decided to reinforce the frame with a front cross tube.  The fab guy did an awesome job, but unfortunately the motor was now too wide for the frame.  Funny how that works...

So I took a saw to the cross tube and watched the frame tubes spring open leaving a 3mm gap in that tube. Not sure how the welder clamped it all up, but obviously he got it wrong.

Bolt the crankcases in and then cut and weld the new cross tube.


Me overthinking things?  Puleeze..... OK. Guilty as charged.

So with absolutely no hard data to work from, I decided to browse the source of all knowledge - the might interweb and there are so many opinions and half baked theories that it's kinda hard to draw any useful conclusions.

Some believe that Iridium plugs have a different thermodynamic profile and that the same heat (number) is misleading and that while Iridium and standard are the same temp at full load they are different at light load conditions.  No data to support the theory but sounds interesting.

Others say that Iridiums improved power or smooth operating compared to Standard.

Odd incidences of Iridiums failing completely or misfiring.  Not well documented but could be there's some bad plugs out there.

Some suggestions that Iridium is mandatory in high power motors and others saying that standards must be used.  Two stroke sled manufacturers seem to like Iridiums and in some cases they want extended nose plugs and others say never use them.

The only good comment I found so far was that different applications need different plugs.

So if we discount all of the opinions, it comes down to why do some iridium plugs fail and are they actually any better in our low mileage applications, since none of us is expecting to get 100,000 miles between changes of plugs.

And in your case when the motor and jetting was set up running iridium plugs, did a simple change to standard plugs need the jetting to be revised?.   Looks like it needed a large jetting increase. When you rebuild it and set it up for standard plugs and jet it on a dyno or butt dyno, it will be interesting to see how much more main jet it likes and to see the difference if you run that setup with iridium plugs after setting it up.

Thoughtful response.  That misfire thing still doesn't sound right to me.  Doesn't mean I'm right, but let's walk through some of the possibilities.

If there's a misfire (electrical), some of the fuel and oxygen did not ignite.  That absolutely happens with most ignition systems but we mere humans can only detect that missed cycle if there are lots of them - relatively speaking.

So, on that cycle without ignition, fuel and air pass into the exhaust where they may, or may not burn.

In terms of gas analysis, we see that as a high HC level but the Air:fuel ratio which measures unburnt oxygen, doesn't really make a huge difference to the Lambda reading, and the unburnt fuel makes little to no difference to the plug color because nothing burned so no heat effect to see.  That's what we see with poor fuel atomization too.  If fuel droplets are too large, not all the fuel gets vaporised and burned.

If the spark is "weak" and lights the fire, the flame propagation rate arguably is slower because the flame kernel is smaller and less intense, so we might expect that to show up again as more unburnt fuel and oxygen passing down the pipe.

If that is the case, we should expect lower average combustion chamber temperatures and therefore lower plug tip temperatures which we read as "rich".  We know that when we read a plug, all we are really doing is to look at the temperature the plug reached, so rich jetting leads to lower combustion temps and sooty looking plugs.  "Hotter" plugs like say a B6 run higher temps and self clean at lower running loads, with the same Air:fuel ratio we read hot plugs as if they are lean and harder (e.g. B10EGV) will tend to look rich with the same A:F.

That said, if the fine wires are not generating a sufficiently strong spark, they will run cooler that they should.  We read that as rich and jet down.  If replacement plugs generate a stronger spark which creates a more complete burn, then you get the result you describe.

The problem that causes me is that fine wire plugs are supposedly deigned to fire more consistently with inconsistent combustion conditions.

Your situation suggests that Iridium plugs are not only not better, but are actually worse in a high performance two stroke.  I have not tested standard plugs back to back with say B*EGV or Iridium, but it's an interesting hypothesis.  Needs a multi gas analysis on the dyno which are not typically available on dynojet but are on eddy current dynos we were lucky to have access to a few years ago.

Left side looks much hotter than right side.  Looks like it's run lean but when it's detonating, the temperature rise tends to mask everything else.

The left appears to have eroded the front (exhaust side) and blown the particles down the pipe.  I prefer fine wire plugs on high performance motors and have never experienced that sort of meltdown with iridum or standard plugs caused by the plugs even with plugs of too low heat range - say B7s or 8s.

Working back a step or two:  If the old iridium plugs misfired, the exhaust temperature would probably be higher.  If standard plugs improved the burn, the motor should have made more power and exhaust temps should have been lower because the burn would have been more complete.

What else changed? Was it perhaps a different fill of gas that wasn't as good as prior fills?  Could the ignition timing have changed electronically for some reason?  The answer should be No F'n way, but stuff does happen. Did it happen at high revs/load and were riding conditions any different.  I'm sure you already asked yourself those questions and more, but that left piston missing the whole exhaust side ring land suggests that the problem was exhaust temperature prior to detonation.  Was air density very high that day?


Haus of Projects / Re: New project
« on: June 05, 2021, 08:52:29 PM »
TZ barrels have a number cast into the rear that represents model # 409 and year/ variant

409-70 TZ750 A/B 64mm bore 700cc

409-71 is later 66.25mm full 750cc version and so on

Haus of Projects / Re: New project
« on: June 05, 2021, 05:20:26 PM »
Interesting ports.  Is that a 40971? or later?

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