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Ke55-S Xx Coupe

Mechanical Sympathy

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It was quite interesting reading! And has given me the confidence to push past 40 degrees.

I still don't know the specs of the pistons yet - because I haven't been asked to pay for them (yet!).

I'm guessing the compression ratio has been bumped slightly by increasing the dome, which has the double effect of pushing the required advance even further BTDC, as well as making them even more resistant to ping.

I'm just shy to push the friendship, but push I must. Looks the distributor will need the mechanical advance recurved or cold starting could become problematic.

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Im wondering if your base timing is correct with that much advance.  In my experience the increase in compression would lead to more detonation, however as you say if the piston tops had a more ping resistant shape you might find the motor is happier with them in it.  As for 40 plus degrees of timing, that sounds like a bit of a worry.  Need some T motor guru to come out of retirement and chime in.

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I share your apprehension!

I'll certainly check it again tonight before advancing further.

I might even knock total advance back to 32 degrees to begin with, and work up to it.

edit: I'll leave it to the weekend and take my time going over it, and with more light. 

edit edit. I've been doing something wrong all along but I don't want to say. The temptation to go out and fix it this late is nonetheless impossible. 

Edited by Mechanical Sympathy
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I'm all over the place with this ,so I went back to basics.

Standard timing, set correctly (I don't want to talk about it) with vacuum advance connected.

Runs a little bit better. But still there's a miss/spit/bog when progressing off the idle circuit. I can advance the timing but the issue persists

I've chased vacuum leaks, idle tuning, timing issues and I'm fairly certain I can eliminate those concerns. I even discovered the air bleed screws weren't seated. Still no good.

So I think that means it comes down to jetting. I perceive the DCOE 151 is set up for a 1300cc engine.

The fellow/place I bought the carbs from was no help - doesn't stock jets and told me that a 1600 at 5700rpm is the same as a 1300 at 6000rpm.

On the face of it, I concur. But in practice.. its definitely bogging when I try to floor it or progress from the idle circuit.

The 151 DCOE comes with 

45/F9 idle jet - seems fine

30mm chokes - fine

115 main (120,125 would seem ideal for the choke size, a little bit richer)

200 air correctors (my reading suggests main + 50 is ideal = 170 air corrector, richer)

f11 emulsion tube (my reading suggests f16 or f9 for a 400cc cylinder size)

accelerator pump gives a healthy squirt - haven't looked into sizing


So I'm thinking to order/buy a pair of 120/f16/170 (main/emulsion/air) jets.

Wish there was someone knowledgeable I could ask about it!  


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The 115 main jet seems small for a 2tg. Check out here for some examples:


They are for Solex and Dellorto but would give a good starting point. 140 would be a better start. Trying out different sets of jets can cost a bit. I order from eurocarb in the UK, or UK ebay. Would be handy to have a wideband O2 sensor for tuning.

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Yeah I'm beginning to think along those lines also. I was only shooting for 6000 rpm so I hoped 30mm chokes would be streetable.   

According to the internet guides a 34mm choke means a 140 main 190 air as Bruce said above.  

Would really just have liked to get it driveable and then fine tune with an AFR when I could drive it to an exhaust shop to get a bung welded  in. But I might have to trailer it for a bung if 34mm chokes has no effect. 

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  • 3 weeks later...

Tuning kit. No more jets, I'm done.

Deal with these guys and your gear arrives in less than 24 hours.  


I've gotten through the progression with the idle jet, using  34mm chokes and F16 emulsion tubes. With the few jet sizes to hand I was able to load up the clutch on the corner of the shed slab and torque it up enough to do a skid, but the main system still bogs and spits  

With these and what I have, fresh plugs and another 10 litres of 98 - I seem to be going through a lot of those - I'll be able to have a really decent crack at finding the goldilocks zone. Just maybe not this weekend ahhh

This book has been enlightening. IMG_2975.thumb.JPG.da283fe56d7eeeb0efc3634890c91416.JPG

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Float levels fixed it, and fresh plugs. 

Set the fuel level to 5mm below the port in the emulsion well, rather than the 8mm below that they were set at ex factory. Seems to suit the F16 tube a lot better. 

Feeding it some throttle in 1st and 2nd up the street broke traction on the Jacaranda flowers. And the sound is addictive. Must.. resist.

Plug inspection suggests probably could lean it out a bit.

Leaks, tweaks, rego!


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Sounds like you have progressed towards where you need to be..well done 

May I also suggest you get a wideband. I have a bosh o2 sensor kit and autogage guage. Checked against the dyno air fuel ratio metre and surprisingly it was on the money accurate 

Edited by 7000rpm
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