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Mark Parker #836518 01/12/21 10:57 pm
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Yes, the boss is there so the stop screw can be moved over. The idle screw is not a big problem since once the left cylinder is dialed in the right carb can be adjusted to the same number of turns. Or a right angle screw driver can be used.

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Mark Parker #836520 01/12/21 11:16 pm
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Mark, Just got the new cam fitted into matts engine and went through it.
Evened out the valve seats as the inlets were around 45 thou different
as far as levels so had to cut one back a fair bit. Not such a bad thing as
the new cam needed a bit more clearance, a little work on the pistons too.
Evidence that the almost complete race he did with the split inlet rubber
had cooked the motor a bit but other than that all looks good. Putting it
back together now, new cam clocks up well and should be better.
The filling in the head seems to have held up ok but i put some porosity
sealer on as a check. Will be running it up in a couple of weeks.

Mark Parker #836559 01/13/21 4:28 am
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This is great feedback on the flat slides, Thanks Mark


71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
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Mark Parker #836578 01/13/21 2:41 pm
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Wouldn't be too hard to 3D print something like the Thunder flow optimizer for Mikuni.
I actually made some but kept running into needed revisions and eventually got distracted and shelved the project. Might revisit this season.


1966 BSA Lightning
(2) 1967 Triumph "Choppa"s
1974 Indian ME125
1960 Harley Servi-Car
1952 Harley 45" G motor in Paugho frame project
Mark Parker #836757 01/14/21 10:35 pm
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See if images work?

[Linked Image from i.postimg.cc]


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Mark Parker #836845 01/15/21 6:39 pm
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Originally Posted by Mark Parker
See if images work?

[Linked Image from i.postimg.cc]

Works just fine...is that a T'bolt head? Your carbs and David's are both 34mm with the screwed down cap but when I look at the usa-oso site it looks like that cap is available up to 30mm and then after that they have a black round plastic looking spin on cap up through the larger sizes...am I missing something? Mark R.

Mark Parker #836856 01/15/21 8:22 pm
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Looks like a T-bolt head The top is the two screw because Mark's, like mine, are probably not OEM OKOs. Compare the float and jets on mine to the one on the OKO site:
[Linked Image from live.staticflickr.com]
Mine is even different than the Chinese copy. My main jet is marked but not the same shape as the OEM.
The box does say "made in Taiwan", just does not have the flag on the front.

Mark Parker #836873 01/15/21 11:00 pm
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There are different versions. These are KOSO 34 with power jets. They are nicely made and work very well. But do not jet the same as Amals. Things effect each other quite a bit. Needles are different, to other 34 needles, but std pointy ones work with the sufficiently large mains. Me thinking rich when actually massively lean on the main jet. Seeing kit's do not quite include big enough sizes.

The manifolds are bolted on and are oval going into the head. The manifold spacing by chance is pretty exact to line up with Nick's Weber manifold. This head flows marginally more than Nick's and has slightly oversize exhausts as well, if that makes a difference. It lets the valve sit higher on a used seat.

If I do them a spare head and the manifolds are oval and at the exact angle it should be a bit better. I'd be tempted to use a std spec bottom end strengthened for rpm, even good std old pistons. Just to see what a 654 engine can do.

First picture is std 27mm port right with partly done oval on the left, it extended to the wall on the left was welded on the upper right for a mounting bolt and lower bolt hole moved down.

[Linked Image from i.postimg.cc]

With one manifold 34mm with oval end squashed in a vice because we are high tech.

[Linked Image from i.postimg.cc]

My vacuum cleaners are not precision and I'm not confident figures are exact, but the photo shows the modified little port from the other side. What it actually does by the feel of it on a stock engine would probably have upset BSA.

[Linked Image from i.postimg.cc]


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Mark Parker #836881 01/16/21 12:02 am
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Thunderbolt heads are no good eh? LOL

DMadigan #836996 01/17/21 12:29 am
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Originally Posted by DMadigan
Looks like a T-bolt head The top is the two screw because Mark's, like mine, are probably not OEM OKOs. Compare the float and jets on mine to the one on the OKO site:
[Linked Image from live.staticflickr.com]
Mine is even different than the Chinese copy. My main jet is marked but not the same shape as the OEM.
The box does say "made in Taiwan", just does not have the flag on the front.

Appears to be more than a couple copies, OKO says theirs is an improved version of the original Keihin and uses original jets, I guess that would be a plus for theirs but worth twice the price of the cheap knockoffs? I have no idea. And what happened to the original Keihin PWK carbs?

The UFO optimizer supposedly makes VM mikuni out perform flatslide per UFO site....hmmm? That would be interesting and the Mikiuni's VM are nicely made with many jetting options...and available in R & L versions too.

Mark Parker #837000 01/17/21 1:32 am
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Some race classes allow VMs so using UFOs may be something to do. These KOSO PWKs I expect flow better. They work better than I've seen with VMs though VMs last for ever. KOSOs may also though with chrome slide. TMs wear slides. Size and looks, to me, the KOSO wins.

Have the instruments mounted, the regulator/rectifier instead of the zener, ignition swapped over and set up negative earth, motor starts. Tomorrow wire in the instruments. Gauge jumps around on rubbers. Found a push bike magnet to connect to a spoke. I hope the polarity works.

All I have to do is wire in + and - and I'm guessing 'speed' on that main plug is the rpm trigger seeing the speed wire has it's own plug already plugged to the sensor.

I'm guessing trigger side of the coil for rpm. There is a high beam light probably worth wiring in at some stage.

[Linked Image from i.postimg.cc]

I'll tidy this up when it all works.


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Mark Parker #837075 01/17/21 5:30 pm
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im going to try the UFOs

i have a morgo with 34mm VMs on it and even though the mixture is correct on the slide there is still a slight lag in throttle rezponse from the bottom. wasnt there with 32mm

ive alwayz been curious and now ill test it and see


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Mark Parker #837092 01/17/21 7:36 pm
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Kevin, your engine might just need more timing off idle...This is the dual plug ?


79 T140D, 89 Honda 650NT ,61 A10 .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
Mark Parker #837100 01/17/21 8:44 pm
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you know, i forgot, you're completely right.

this 72 T120 originally ran 38 BTDC. now im running twin plugs and a Boyer at 30 BTDC, and so the timing at idle is 8 degrees retarded. no way to modify an ordinary Boyer for more advance off-idle that i know about.

any ideas?


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Mark Parker #837109 01/17/21 9:50 pm
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it's why I have points in my 79 so I could modify the mechanical advance. the only suggestion is to advacne the timing just for a test to see if it sharpens up the low speed response.


79 T140D, 89 Honda 650NT ,61 A10 .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
Mark Parker #837113 01/17/21 10:14 pm
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i don't even need to test to know that, but i will as soon as the stinking snow goes away.

i do have a pazon dual-plug ignition that i was saving for the day when i give up on the ARD in my LSR machine. it has a curve designed to accommodate the increased retard needed by the dual plug head.

maybe i'll put that in the morgo, swap the Boyer into the bitsa A65, and take out the overkill pazon smartfire from the A65 and save it for something where it would constitute an advantage. it's way too sophisticated for that cheap and cheerful machine.

i was going to put that smartfire into the trackbike project but got a nice ARD for a very reasonable price from a member here.


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Mark Parker #837256 01/19/21 3:49 am
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My goodness the instructions. The pulse setting: 1 to 9 isn't the tach, I think its the number of magnets you put on the wheel for the speed sensor. The tach I think is stroke either 2stroke 4stroke 1stroke the last one puzzling, except it should be cylinders. 4 stroke is set to '0' etc. frown so 4cyls is what I use because of the wasted spark. I wonder how many gauges get sent back because people cannot get them working?

The rev counter is nice. Past 4,000 is vibration, it's pretty fierce wide open and feels abusive because of the vibes. 7,000 comes up fast and makes you think my gosh, hope everything is locktited on. If it was smooth or if you watched from somewhere else it may seem like it likes it. It feels terminal as revs, noise and vibes build. Gearing is sooo short. Does anyone know if earlier 42T QD bits fit?

Ben said he revved his 90 to 9,000, I've revved one to about 8,500. BSA experimented and found a good balance factor for high rpm, but didn't change it on these keeping smoothness at lower rpm.

Sensible and well expressed last line Kevin, could not agree more.


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Mark Parker #837265 01/19/21 9:15 am
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"The pulse setting: 1 to 9 isn't the tach, I think its the number of magnets you put on the wheel for the speed sensor."
Ive fitted a few magnet driven speedos to pushbikes, usually its one magnet and an input for the wheel circumference, maybe thats what the 9 choices are?

IIRC Allan Gill has an early 42 tooth QD fitted to one of his A65s.


71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
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Mark Parker #837345 01/20/21 3:25 am
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The beauty and the ease and the smoothness of a 90degree 750.



Setting up the rev-counter but the battery is dead. I fitted a modern rec/regulator wired it -earth in the hope it was not the old alternator but no. Pulled the cover and it stank.

Anyway this video is me trying to get home on a half dead battery with no charging. I put it into 2nd early so it would have something to pull against and you can hear when it goes onto the main jet. It sounds so busy. Not on the main long enough to see much but the noise changes and it gets light at the front.



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Mark Parker #838917 02/03/21 10:16 am
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Seems happy enough to rev to 7,300, and pulls well. I can probably try 8,000 or more. Though it pulls fine from down low and it seems pointless in a way.

An interesting test may be a 1/4 mile with someone who can get off the line (and have the throttle on the stop). A '71 Lightning did a 14.3 and they seem to be changing at 7,000. This feels fairly strong in that range, it likely revs higher but I don't think it needs to.


Last edited by Mark Parker; 02/03/21 10:19 am.

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