SBP Shift Kit - Ratios, Speeds and Pedal-starting

Yep, I think the extra vibration 'is' detonation. I tried a mix with no octane booster today, 91 octane (or lower) and it felt almost like a bent crankshaft, with the hi-comp head. Shook heaps. Back at 98-99 it's smoother and runs better. Love the smell of the octane booster, too, reminds me of go-karts.

Not sure where you buy your engines, but ZBox 66cc have an 0.79mm stock. That's their newest 'Series 3' as Warren calls them. Yours sounds like the same jetting and not 0.7 like many sellers. I think that the earlier carb had an 0.7mm main jet and non-coated, brass/bronze slide. The later carbs all have a coated slide. Not sure where the version with a fuel tap on the carb fits in to the scheme of things. I haven't seen one yet.
Didn't get a ride today, (a layabout mate dropped in and 'made' me drink beer all afternoon), but tonight I swapped back to an 0.76 jet, from 0.72 and lean at WOT.
Adjusted chains, too, etc, for tomorrow.
Who knows, I might end up over 0.8mm too.
Tomorrow, I'm hiding the beer from visitors, they leave sooner.
I want a couple of decent rides.

One quick point - you said you didn't bother trying the next size down. Although it seems pretty good, it might get better. Best is to go, in very small steps now, until you feel that you've gone 1 size too far, then back off one.
I know these aren't competition engines, but the nearer the better. You might even get a surprise. I'm beginning to get a feeling that with reasonably good breathing, the stock 0.79 or an 0.8 might go pretty close. (Assuming our engines 'are' the same.)
Let's see where we both end up.
I've got 2 new plugs waiting to do mid-range and WOT plug chops, when I get a chance, tomorrow I hope. I'll go from there.

... Steve
 
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FWIW Zoom has Pull Starts in stock, or at least they did a week ago. My neighbor got one for his bike. He constantly complained about starting with the shift kit. Something about how cold it is at 4AM when he goes to work.
 
Sorry, I've been side-tracked for a bit.

My concern with the currently available pull-starts is that they either won't be strong enough to last long with the hi-comp head, or that the starter gearing will not be low enough to pull comfortably.

Fitted a MegaRange 13T-34T rear freewheel cluster yesterday. Still waiting for a compatible derailleur to arrive, but I can shift into 1st by hand for take-off in the meantime, so I've had a few good test-rides. Actually hit 83kph today, (52mph), on a slight downhill with a bit of a tail-wind. (Wonder if I still qualify for the 50mph club?)
Haven't calculated the exact RPM at that speed, but it's about 7500. It also happily does 5mph at about 2000RPM as predicted.

With the choke at 90% on, I can now kick-start on the centre-stand with one kick, then the 34T 1st gear allows me to take off on the clutch only, without pedalling. Exactly what I wanted, but still a little too high geared and hard to kick-start with the billet head.
The new 11T and 24T sprockets from SBP will cure that - 25% easier starting and slightly lower gearing.

Not sure what was going on with the mixture the other day, but now I've ended up pretty much where I used to be - slide needle at it's lowest and an 0.73mm main jet. It's running really well, but very slightly rich at mid-throttle and WOT. Back to my 0.72mm main jet tomorrow.

:D Overall, I'm a happy man. :D

An extra afterthought on the choke.
Many of us need one attempt at full choke, the engine coughs, then a second attempt with no choke and it runs.
Experiments have shown me that if the choke is just right, about 90% on, one attempt is enough.
It starts, then runs OK for long enough to turn the choke off without a second attempt.
Leads me to believe that if I enlarge the hole in the choke plate until it's just right, one attempt with full choke should work, most of the time. (I have a spare old carb, so I can't get into trouble.)

This HT engine mods thing never ends, does it? No sooner is one thing done than we think of something else.

... Steve
 
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Steve, had you considered using one of these for starting? Works like a champ on old, high compression pan head Harley's. Just a thought.

comprel.jpg
 
I'd love a good decompressor, but there's no room on the hi-comp head.
In fact, if it fitted, it might hit the piston when the valve is open - there's only 1.1mm between my piston and spark plug tang at TDC.
(A miniature decompressor might fit, if there's such a thing.)
The first high-compression head to come out with, or have room for, a decompressor - I'll Be There. (As Elvis once sang)

Someone suggested loosening the spark plug for starting, then tightening it when the engine's running.
 
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"I see" said the blind man! I've never seen a miniature one, but have seen them for the spark plug hole. Not sure how reliable those are, plus they are hideous looking. Those in the pic are maybe a little bigger than a zerk fitting.
 
Hi jsw5620

I've been screaming out for a compression release valve to be fitted as standard equipment from manufacturers making billet cylinder heads for 2-stroke bicycle engines.
My standard engine makes 115 PSI of compression and the engine becomes very difficult to pedal start on a cold day even when the shift kit is fitted with an easier pedal start ratio using the optional 11 tooth jackshaft sprocket and the 44 tooth standard chainwheel sprocket.

Now manufacturers hear this: please incorporate a compression release valve in your billet cylinder head: Pirate Cycles - please take note

Message to SickBikeParts: please supply an optional standard cylinder head (6mm and 8mm head stud holes) with a compression release fitted for purchasers of your shift kit.
I would dearly like to run the optional 9 tooth jackshaft sprocket and 48 tooth chainwheel sprocket but i cannot do so as the engine would be impossible to pedal start.
I'm sure people will be happy to pay an extra $40 for the convenience when ordering a SickBikeParts Deluxe shift kit.


I've found some links and a few pics:


http://www.goodson.com/store/template/product_detail.php?=3e166b94315c1efacee6d2a0139ea16d&IID=5387

http://www.hotbikeweb.com/tech/0306hb_installing_compression_releases/photo_02.html


Fabian
 

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It will probably be more than $40.

There is SOME universality in heads, but not complete.
 
Even if it's $50 or $60, it could be included in the "optional extras" section when ordering a Deluxe Shift Kit.

I would have happily paid the extra money and had it included with the kit if the website advised that "pedal starting" can be made significantly easier on standard engines that give strong compression and also if used with alternate jackshaft to chainwheel gearing.

Fabian
 
Just want to make it clear, I said that I'd love a good decompressor, much as I'd like a lot of things that would make life easier, but it's definitely not necessary for starting.
I'll be re-gearing to make it a little easier and lower my overall ratios, but I've never had trouble starting with the 142psi billet head/shift kit combo and I only weigh 50kg. (I thought it would be harder than it is.)
 
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