What did you do today? Cobba's rebuild

[cobbadiggabuddyblooo]

No real gains by going down 2 main jet sizes and 165 shim in acc pump
It just runs a little leaner but still have the big dip in the torque curve around 5500rpm.

[cobbadiggabuddyblooo]

Ok next approach to look at is exhaust does not suit the cam profile....
The Akra works fine with the std cams and carbies /fcr's and dip was no where as bad with the Kent Yam 9 cams so the only thing that has changes since then is the Penner Higher lift longer duration cams.
Rich has gladly donated his Nojima X system for me to try and see if this makes improvements.
The Nojima and Over systems are more so designed for hi rpm compared to the Akra . The akra is tuned with gains around 4000 and 7500 and 1 reason I can find WOT by 4500rpm but I'm thinking that just as the exhaust comes off tune on comes the cams hence the mis match tuning. The Kent cams are tuned for lower mid range so they compliment the Akrapovic tuned characteristics.

Here is some info to take note of on TDMR 40 B11 carbies.
Main jet 145 (180)
pilot fuel 25 (27.5)
Needle 10E101-50
Idle air 120
Clip 2 (3) from top
Needle jet P-6
screw 2.5 turns
float level 13mm

If my suspicions are confirmed, I'll be chasing an Over system next....

[Killerwhale]

Many many MANY moons ago when MAX started this site he was the only one that had tested and did good results on different size mainjets, maybe you have something there...

[cobbadiggabuddyblooo]

Tuning a PA system is no different Killer, if you have a tuned system the subs, bottom end mid and horns are all tuned and crossed over with filters and phase aligned.
An exhaust is no different.
You get great Systems that have kick arse bottom end and top end that will tear your head off and great for rock n roll , then you have those sweet vocal PA with that tasty moist mound in the mid's that produces clarity.
Even the choice of timber and density all play their part with harmonics.

Perfect example of this is If you look at Rods dyno run you can see how the harmonics to the tuning cause little peaks at around every 1.5 k. (3-4.5-6-7.5rpm) . The H pattern standard headers are tuned for lower down torque.
The Akra system is similar with it's small balance pipe between the headers but a lot more safisticated at spreading the gains using the taper diameter on the headers. This spreads the pulse so it's not as peaky but over a wider rpm range. The longer headers aid in lower mid torque . By keeping the smaller diameter out of the head it helps with velocity and tapering to a wider diameter aids in flow at higher RPM's.

Different choice of carby jets is just like what amps you want to drive each component on an active PA system. ( either subs, low mid's hi mid's horns each with their own X over point and amp.)
Your jet needle is just like a X over and just like changing tapers or root diameter , on a system with an active X over in the drive rack at FOH , you can tweak the X over parameters on how they taper and transition between a X over point of subs to low mid's and lift or lower that or change the taper .
This is where you start to have issues with a mis matched pa and subs from a different system as they may be tuned a little different. ( just like mis matched cams and exhaust )

Just once you start to do major mods to your bike, you put something in place that's not working in harmony with your other mods, the problems become more pronounced.
Just like a mis matched PA with a different aftermarket sub cabinet, you can EQ your way around some of the problems( just like retiming your ignition) but it's a band aid solution as harmonics and phasing can create little issues further up.

Speaker cabinets are ported and flowed just like a motorcycle head too.

Suspension works on similar principals too as audio with compression , decay, gates and different tools within your drive rack to keep signal in check and good gain structure.

[cobbadiggabuddyblooo]

Dyno run today with the Nojima twin X system....

Gains all the way up-to 7300rpm then it tapers off at the top and loose 4hp at my peak at 8500rpm.
HP/torque curve improvement under 7000 buy 1-2 HP and close to 5hp gain at my 5500rpm dip.
Ignore the Air/fuel reading as it was sucking air where the can joined to the link pipe.
The Nojima has no bung for me to monitor A/F ...
Says a lot about scavenging nature of the exhaust with this cam profile.
I gained more torque under 6000rpm with the Akra/Kent Yam 9 than the Akra/Penner cams so this first combination would be a beautiful combination for a street TRX.
But I gain the best torque figures overall with the Penner/Nojima combination .
I just need to address getting peak HP back And see if jetting sorts that.
So next run will be more/fuel air mixture crammed into the chambers and if A/F is good that means a faster burn rate so back to my base -4 map once again ...

As a safe guard we did a 1/2 and 1/4 throttle run to check on fueling and all good to ride home as with traffic I use very little throttle and ride under 4500RPM.. I knew the pilot and idle circuits ran a little rich but it's still nice to know....their O2 sensor always reads higher than my gauge too as I take readings from the header not a sniffer shoved down the tail end.

[cobbadiggabuddyblooo]

Too much inconsistency from the dyno A/F readings but I can use the torque and H/P curve to see what gains I find. I know on average my own O2 sensor readings from the headers where richer than what the dyno sniffer was reading.
But 16 to 18 A/F sounds like a dodgy sensor reading..( more than likely leaky exhaust)
The bike certainly wouldn't make the gains under 7500 running that lean.
My own experience 15.8-16 with my own sensor on the Akra system the bike would stall and start to misfire at WOT.

[cobbadiggabuddyblooo]

Went over the exhaust system again today and the only join I didn't use sealant was on the can that the O2 sniffer Inplace..
So found the culprit giving the false O2 readings.
At least it's a positive in that the change of exhaust has changed the scavenging characteristics in my favour for the cam profile.
Went up in main jets from 162.5 to 165 / 167.5 to see if I get my 4 HP lost at but no real gains....

[cobbadiggabuddyblooo]

Nice day for a winter ride today.. Mid 20's and sunny.. Went over the exhaust again to reseal all the joins and fitted the 167.5 mains.
Akra system worked flawlessly and easily rideable just off idle with just a dip at 5500 and big serge again 6000 to 8500rpm.
The Nojima has different characteristics with these cams and the overlap is evident around 3200rpm and you can hear the flat slides chattering from idle to 3500rpm and come 3700rpm it's just power on tap all the way till the red light shines bright at 8500rpm. So easy to lift the front wheel in second flip flopping up the range and answered my questioning of choice of exhaust for this cam profile.
So I feel my quest if just about finally over and I'll fit the Scotts damper and take in all I've learnt in the process.
TDMR40's , Yam9 and Akra system wins hands down for a street / odd trackday TRX. Drive ability is excellent and dealing with day to day traffic is a breeze allowing you to use throttle from just above idle.
Want to build a motor to go hard on and want to keep the revs above 3500rpm , FCR's , V2 or Penner cams and a Over/Nojima style exhaust wins the gold medal from me.
Your intake and exhaust all have to work around your camshaft choice which was fairly evident by the number of changes I slowly but surely eliminated to get the desired result.

So I was on the money with the first choice of cams and exhaust, just my 12 mths down time gave me the opportunity to question things and when I purchased the 2nd set of cams, holes started to apear.
I'm sure I could have advanced the timing more around 5500rpm with the Akra system to deal with the slower burning rich mix, but that doesn't actually fix what's causing it. But god dam when you hit 6000rpm it took off like a rocket again....
Now there is a real smooth continual take up of power until 8500 and gains all the way from 4000rpm and I couldn't be happier.
Time to just dot the i's and X the tees now and just tidy up this work in progress over the past 3 years.
Photo taken today on top of the range at Mt Mee after resealing the exhaust and fitting larger 167.5 mains. 1 final dyno run to do and I'm ready to retire.

[Tarwetijger]

8<
TDMR40's , Yam9 and Akra system wins hands down for a street / odd trackday TRX. Drive ability is excellent and dealing with day to day traffic is a breeze allowing you to use throttle from just above idle.
Want to build a motor to go hard on and want to keep the revs about 3500rpm , FCR's , V2 or Penner cams and a Over/Nojima style exhaust wins the gold medal from me.

Now that's funny you said that, as that is the exact setup I have right now (TDMR, Yam9, Akra). And it great, I'm even using it as a daily commuter right now.

So how will you be using your bike? Are you able to keep the Nojima system?

Next month I will pick up a bike with OVER exhaust (and other parts ), I 'm very curious about the difference with my current bike.

Nice picture btw!

[coxylaad]

how did you go about painting your engine Cobba, that looks really nice.

[cobbadiggabuddyblooo]

Once cleaned thoroughly, I sprayed the clutch cover centre in Silver to highlight the YAMAHA. When dry I filled the YAMAHA stamped impression with blue tack. The stuff you use to hang posters on walls. Took a little time to get all the edges nice and neat and then I sprayed the whole motor black including the cam cover. Once dry I removed the blue tack to reveille the highlighted YAMAHA in silver.
I tried play doe as a filler but it didn't really stick in place.
About a week later I got a small piece of timber wrapped in wet n dry and polished off the paint on 4 of the fins either side.
Have a look at Conrod's TRX, I got the idea from his rebuild. He has done something similar just he chose to do the the complete 7 or 8 fins on the head and barrels and I don't think he painted his cam cover black.
I just chose to highlight the ones to follow the lines of the inlet and exhaust.
I feel it gives it a bit of a retro early 2 stroke look...
Running the Akra exhaust if feels like a 2 stroke when the cams really kick in a 6000rpm too...

[dandywarhol]

Plasticote BBQ paint is the stuff and is a spot on match for 70s Yamaha 2 strokes

[dandywarhol]

I put this post in the wrong thread

[cobbadiggabuddyblooo]

Charter boat , what charter boat

Dynamic compression results..

Static compression ratio of 12.5:1.
Effective stroke is 1.94 inches.
Your dynamic compression ratio is 9.39:1 .
Your dynamic cranking pressure is 196.55 PSI.

Ramming air in over 180kph the dynamic compression will slowly rise the faster I go

[cobbadiggabuddyblooo]

A little time to think on things, my next challenge is to improve on the air box set up.
With the FCR's enclosed in the makeshift air box with the tank itself being the top this effectively pressurizes the fuel bowls.
Air is fed in either side of the frame via the top triangle sections of the frame behind the head stock and scooped up by the ramp in front of the airbox. Air is also fed through the gap between the tank and the top frame tubes.
There is a 50mm space that I can ram air directed from the front of the bike under the triple tree and over the top of the radiator and into the front section directly behind the head stock.





I'm banking on the idea to stop turbulence of the air entering under the tank, I'll build a triangle shaped air filter that will mount under the front section of the tank.







This gives a rough layout of what I'm working on but it's a work in progress.
I'll have to shape the air filter at the rear to fill the 20mm gap between the filter an to accommodate the throttle cables and bottom aluminum heat tray plus form a nice transitional piece from the air feed from the front of the fairing under the head stock.
Time for the scissors, cardboard and gaff tape and think about attempting some fibreglass work...
The race glass is fibreglass and needs a little repair so I can look at integrating a couple of small LED head lights and front ram air feed . I'll need to make the section behind the front head stock from glass too that will be fed from the front ram air.