So I have pulled together some plots to show the effect of the main jet only change.

04 is with the 160
12 is with the 165

So the increase in jet size is worth 2bhp at the top at the expense of 2bhp in the mid range. We are now seeing the constraints of a carb.

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08 Specialized Langster

Not on this, I am just enjoying working with what I have, however I have spent time optimising inlet and exhaust on jap 4s before.

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08 Specialized Langster

Have been chatting to Tubbs on the phone and he advised to go up to the 165 main jet, even if it didn't give any more power it would help keep the rear cylinder a bit cooler.
He did recomend I got hold of one of them ignition module dooberries though.

Where ya get it?
And honestly Nick, wheelies, at your age!

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Buelling is exhillarating
But downhill bike racing is so terrifying it makes your arse grow teeth

You big FCUKing copycat

Can't remember where I got the Dynatek from... You could buy the Screaming Eagle part - 32654-98 (tres ), Black Bear will post it to you, perhaps with a discount thrown in . Check it has the 8 pin connector though.

If you want the Dynatek, it is the DD2000-HD1E8P that you want... Moorespeed will be able to get them...

Now, before we go any further, and I am no real expert on this (be guided by Tubbs and Maz); my engine has a different combustion chamber shape to yours and has quite a small squish clearance and cos of this I reckon I need less advance. Your squish clearance will be MUCH bigger, cos your motor has not been built with love and for that reason you may not get away with less advance whilst maintaining power. Erik and the Elves probably spent a lot of time tinkering with the ignition timing to get it right for your engine, and they would have used the minimum advance for best performance to ensure they steered clear of knock. Tubbs and I ran out of time on the dyno, but I think I could probably have got the same effect by taking 5deg advance off with the standard system.

I think the ignition timing for mine is pretty much OK as it appears to be insensitive to the 2.5 deg change between curves 3 and 4.

If you want to go visit Tubbs and do as I did (I would if I were you), you are welcome to try my Dynatek out before emptying your wallet further. I also have 167.5, 170 and 172.5 main jets which you are welcome to borrow.

Oh yeah, why has nobody asked me which fuel I was using?

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08 Specialized Langster

Cos it's a tuber and they run on diesel or heating oil for the cheapskates.

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I'm a Hornithologist, I get excited by exotic birds.........

Tell me about it mines got full US gearing, makes overtaking 2 up with the Mrs quite interesting

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Buelling is exhillarating
But downhill bike racing is so terrifying it makes your arse grow teeth

To answer a number of PMs, jets are:

Main 165
Pilot 20
Needle 97 with clip on #2
Accel nozzle 60

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08 Specialized Langster

I ended up with similar settings, Nick. These pulls (the blue lines) were with 165 main, 96 needle on second groove from top, 20 pilot, accel nozzle was whatever was in there (probably a 60, which is stock for Sportsters) - I've never changed it.
As you can see, the mixture was rich between 4000-6000 rpm, which shows up in the power curve and even more so in the torque curve.

The blip at about 3700rpm was a misfire (coil again). The red lines were from an earlier pre-conversion run when a coil decided to go south and wouldn't accept any throttle below 3000rpm.

After this run I reverted to the "stock" 97 needle, again on the second groove.



Since fitting the 1250 kit, I've stuck with these settings, except for increasing the pilot jet to 22.5, which cured occasional pinging below 3000rpm when hot. It runs well like this, and steady cruising at 80-90 gives reasonable mileage; but I'm sure a decent dyno session would yield more, and improve my range when riding with GB and Mo, when it drops markedly .

Thanks for posting Myles

Glad to see that you got a similar AFR characteristic as me, i.e. rich in midrange, then leaning out a bit at the top, in fact I think yours is more pronounced than mine. I saw just over half an AFR difference, you saw one AFR difference.

Were those runs with your 1250 big bore kit?

From what I can see, the N4 cams (0.49" lift I 30/49 E 52/24) are similar in grind to the S1 cams (0.497" lift I 28/48 E 52/24).

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08 Specialized Langster

Hi Nick!

No, that run was with stock bore and flat-top XB pistons that came with the heads. They have a shorter skirt and are (predictably ) lighter than stock Sporty pistons. The engine was very smooth throughout the rev range with that set-up - the XB piston weight seemed, by chance, to find a balance sweet spot with the crank.

According to NRHS, N4 cams, SE bolt-in cams and S1/X1 stock cams are all identical, and all manufactured by Andrews.

GB and I swapped bikes for a while the other week and, engine-wise at least, it's like riding the same bike. His X1's reduced primary gearing seems to have produced more or less identical overall gearing to my Sporty. Initial pick-up on the X1 may be a tad quicker (lighter crank and sorted fuel injection?) and mine may run a little stronger at the top end (better heads?), but there's f**k all in it really.

Apart from the engines, of course, they're very different bikes, and we both had "moments" on the ride - me when I hit a groove with his squared-off back tyre entering a tightish bend, which sat the bike up suddenly (GB, following me, thought I was going to ride his bike into a hedge); and GB got into a bit of a wobble on fast sweeping bends with the Sporty's wide bars ("Let go, Luke - use the Force!" ).

my buell is currently being rebuilt again (rotor /stator broke up)

its got the 1250 kit and bits and bobs and was pulling about 104-107 bhp at rear wheel

Im having new headers made with a few mods that should give a bit more even over the race headers it had on

my mate runs a dyno in notts and has buells so once built will find out for sure