Motorcycle and Scooter appreciation

Sorry, just read you have a big bore too. Maybe even 42.5 / 150 with that.

Hmm, sounds like a big jump in jets.

Kind of weird that I need to make such a huge jump. Amazing that it ran at all...trying to get my head around it.

I think that the flatslide carb (FP taper) needle had it running lean early and very rich later, and that's why the power felt different in the two positions. If the accelerator pump was still attached then that squirt woul have made up the shortfall as you nail it past the F and into the P.

Now, in the CV carb with the (CD taper) needle there's much less fuel because the needle diameter is so much wider. So, I've raised it massively to make up for that, and it runs. You must be right - larger main jet will give me that gap back that I've created raising the needle.

How much would a Dyno run be?

Not sure £100-150 if I can get to the guys. I think I will try to get the bike running nicely before I spend that money. At the moment all I'm losing is time.

Now to sound old, but how much? Is that just for one run to get an idea about fueling.

I'll shut up.

Is there a forum/group to get an idea of jetting.

People talk about reading the plug, but I haven't had that ever work.

I'm afraid of burning valves on single cylinders as I did that once.

Exactly. And it’s an hour or so away. So I don’t fancy driving a long way to spend a lot of money and get not a lot of return.

Having used it yesterday I had a look at the plug today and it’s evidently a bit white. Black on the outside but white on the electrode.

Chucked a 140 main in it, and for arguments sake dropped the needle back to middle position. Idled it a bit and guess what, same sputter. Enough you can sit on it.

Gently got it on choke and it revved on throttle. Ripped the needle out and put it back to richest condition. Revved on throttle again.

At least I know now there’ll be oodles of fuel on the throttle. In hindsight it did feel a bit lacking at WOT.

Raising the needle and introducing much more fuel much earlier, next job is to up the pilot and get it idling happy with a richer pilot jet. Ideally that allows me to drop the needle again.

After all that?

Post just arrived!

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Engine back in the bike, and all buttoned up. It works!

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Well done. Was it a lot of hours? It seemed like a lot to take on.

Congrats!!

Think about it this way, you’ve increased the pumping capacity of the engine by 10% or so, and also removed major restrictions (air box and pipe.) It’s not such a big jump at all.

Not a direct comparison but the main jets on my RD went from 120 to 230 after I ported and put pipes and filter on.

Sure, maybe that fuel economy is going through the floor after all...!

I took it round the houses, to the mechanics and back and the throttle felt almost loose. I guess it was happily drinking the petrol and producing power rather than dragging its way through a lean condition.

Going to ride it shortly to run an errand 10 miles away, and if it doesn't grenade then I'll ride it as-is on the green lanes tomorrow. That gives me next week to try to rebuild the flat slide carb with a different needle and jets. Keen to go back to the flatslide just to have maximum response vs the CV.

This is great to hear. You wouldn't be able to do that kind of maintenance on a modern car. Would rep etc.

You'll be safe on 140 I suspect, but I think you'll end up wanting bigger. Four strokes aren't quite as time-bomb like as two strokes if they're running lean. A handy trick for assessing the main jet is to get going fast, WOT, in 5th or 6th and if the engine picks up a bit when you just roll back the throttle a tiny bit, you're rich. If it doesn't, you can go richer.

Thanks for all your help.

Yea I went and did the errand, plus a long detour just to get some fuel through and it chugged along okay. Definitely smells rich, but 'pulls well'. Had one moment like a slipped clutch or bad fuelling, but could have been anything.

Overall revs reliably and once hot the idle speed is quite fast. I forgot how finicky it is to start, so I could really do with fitting the bigger pilot and getting a good start and good idle hot or cold.

On 5th/6th going WOT slowly but surely accelerates, but I haven't tried the test like you suggest.

Did you find a new (to you) gear?

Too busy bemoaning my carb problems. Congratulations and well done with that motor!

Thanks all!

Yes @lynx an old gentleman from the SOHC Facebook group had a spare in his shed.

@Airhead I was at it on and off for just over a week, but actual time spent working on the bike I think was less than 8 hours. Reckon it'd be half that if I had to do it again.

Good work, those are hefty lumps to man-handle in and out!

Very well done.

Brilliant news and top work.

That's a decent pace, well done.

Readers’ wives…

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Gonna bite the bullet and buy a Rabaconda...

Cheapest online seems to be Eurotek. Are the a kosher dealer?

StEaLtH eDiT:
I'm actually very tempted by a Baja No Pinch instead. Not the same level of awesome as owning a Rabaconda, but maybe...

Edit Edit: Learning how the Baja is a ripoff of the TMT... Maybe I need to risk the extra cost of the TMT from Estonia.

OOOOh, that's some solid filth that.