Super Rocket Carb

[worntorn]

I did a leakdown test and it appears the top end is as new. I suspect major work was done about 542 miles ago, that is what the odometer reads. Or that may have been when the speedo was last repaired!
Either way the leakdown tester says the Super Rocket has essentially the same numbers as my all new 1360 Vincent engine and significantly better numbers than the other bikes here, all of which are in good shape.
The stroke measures 84 mm as it should.

The Carb was full of crud from the ethanol gas which would have been the only thing available for the last few years in both Texas and California. It's amazing the bike ran at all and it actually ran very sweetly up to midrange rpm.   I believe the crud occluded the flow of gasoline into the bowl so much that there was insufficient fuel for higher rpm. Every thing inside of the Carb has hard white lumps bonded on, especially the passages.
The mainjet is a 240, does that sound about right for sea level to 1000 ft ( Mk1 concentric)?

I might abandon this Carb as I have a near new 32 mm Concentric here on the shelf. The intake port on the bike measures 30.5 mm, so 32 would leave a nice shoulder like Roland Pike used for an extra couple of horses on the late Goldstars. Got to be a square shoulder or it doesn't work, no one knows why! This was an accidental discovery brought about when the parts boy mistakenly brought back a 1 5/16" tt Carb when the request was for a 1 5/32". The extra power with the bigger Carb disappeared when they tried blending the intake to meet up flush. Also rounding the shoulder saw the power go away.

Glen

[muskrat]

Stranger things have happened, Glen.
I'd only go the 32 if the ex pipes/mufflers are made to breath a bit easier.
I run a 932 on my A7 plunger. But it's got a '57SS top end, 357, A10 valves, straight through pipes and no air filter .
Cheers

[chaterlea25]

Hi Glen,
To the best of my knowledge the original size jet with a Monobloc carb on the SR was a 420
I know this seems huge but thats what the book says
Modern (crap) fuel is completely different to 1963 stuff and jetting needs to be altered to suit it

I have read the Gold star story, that was with GP or TT carbs fitted though
there are also conflicting articles written about carburation probems where theres a step obstruction in the inlet tract
It can especially ruin low speed running

HTH
John

[worntorn]

For some reason the Monoblocks use a much bigger mainjet than similar sized Concentrics fitted to the same engine. When Norton switched from Monoblocks to Concentrics on the 650ss they reduced from something like  380 mainjets to 220. It must be due to the difference in Carb design, more venturi effect with the Concentric.
 I'll just have to play with the mainjet sizes to see what works, start rich and work down.

If the step doesn't work out, the 928 will get cleaned and reinstalled. The step works well with the Dellortos fitted on my project bike, the throttle response from idle is very sharp.
I have Siamesed pipes and a freeflowing Gold star muffler on order for the SR. The existing pipes and mufflers are in rough shape, plus the mufflers are the restrictive type.

Glen

[a101960]

To the best of my knowledge the original size jet with a Monobloc carb on the SR was a 420
I know this seems huge but thats what the book says

I agree John. My Monobloc 389 (1 5/32) is set up with Main jet 420, pilot 25, slide 3, and needle 106. I also run on the highest octane that I can get, which happens to be Tesco's Premium unleaded 99 octane. Premium is marginally more expensive but my engine loves it, so it is well worth the little extra per litre that it costs. I also always add Redex to my petrol.

[worntorn]

Short of aircraft fuel, 94 octane Chevron Supreme is it around here for high octane.
It is ethanol free though, so I run it in all the bikes, even though some only require regular fuel. I used to run the lowest octane possible (just enough octane to avoid pinking) since low octane fuel contains more energy and make more power, contrary to common thinking. The addition of ethanol to most of our fuels changed that.

Glen

[worntorn]

Well that awakened it!
Definitely feels worthy of the name "Super Rocket" now.
It idles better and runs perfectly up to as high as I dare go without functioning tach. It cruises along at 80mph on about 1/2 throttle and accelerates nicely from there when opened up. Not neck snapping acceleration from 80, but all one could ask for from a 50 year old 650.

I can't say that the 32 mm is better on there than a 28 mm as the 28 was clogged. For now I'll leave the 32 on there but I had to transfer the needle, needle jet and mainjet from the 28 in order to get it running well. The nice thing is that the 32 mm slide and body are new, no wear.
The port measures 30.5 mm, however the insulating spacer measures only 26 mm so that has to be cut out to at least 30.5 mm.
For now I have left the spacer out, will deal with it shortly.



Glen

[trevinoz]

Glen,
                A 30mm carby would probably be the best option.

[worntorn]

Trev, would a new 1 5/32" Monoblock offer any  performance or other running advantage over a new 30 mm Amal Premiere?

Glen

[Rocket Racer]

Trev, would a new 1 5/32" Monoblock offer any  performance or other running advantage over a new 30 mm Amal Premiere?

Glen

An 1 5/32" was the recommended biggest carb, back in the day by Eddie Dow and other tuning literature.
The Mono blocks are a nice carb, well made and correct for the bike while a concentric isnt original fitment (if that matters to you).
The monoblocks main issue is the sidemounted float level is altered by the sidestand which alters idle mixture when idling on the sidestand. They are also more prone to swill when fitted on sidecars.
Given buying either of those two new my preference would be the monoblock, however
If you're looking for performance and bling factor (and money is no object  ) the 10TT9 was the factory go fast option but does rely on the throttle cable for idle setting.
I have dual 10TT9's on my track bike and have one for my road bike and they certainly add bling and are correct fitment. They do come up on flea bay or alternately can be bought new for a small mortgage.

[worntorn]

Thanks for that info.
I'm thinking a new Monoblock will do it, though they are about twice the price of the Amal Premieres, which are a really good Carb. The Premieres seem to have all of the weaknesses of the original Concentrics fixed.

Glen

[Rocket Racer]

Glen,
 good call. For many years monoblock or separate float carbs were out of manufacture so concentric carbs were the go (other than resleeving and building up slides) . But now we have those carbs available again new, a non original fitment makes less sense.
The big plus back in the sixties for the concentric was its cheapness, it was built to a price and prone to wear. Whereas the race carbs and the monoblock always had better quality materials.
Now of course the improved premieres are available which removes the wear problems of the early concentric, so ideal for bikes that had concentric as original fitment like the unit beesa's but less relevant to the pre unit and semi unit machines.
Tim

[Billybream]

I did the concentric conversion back in the late 60,s, can,t quite remember why now, most probably a fashion thing, still have the original monobloc, will have to try a comparison some day. The performance would not have suffered, as the old girl loved going faster then, might not have been so mindful of the economy. Now days 4000revs are enough for both of us.

[worntorn]

Tonight I had the Carb off and trimmed out the tufnol spacer and the gas deflector to match the manifold size which is 30.5 mm. This might be a bit larger than stock? The tufnol spacer was only 26 mm, barely over 1"!
The 32 mm Concentric works really well on there. With the obstruction of the small insulator and deflector trimmed away the power level is much improved. Acceleration out of corners is excellent. For all the talk of "full race 357 cam" and so on from ads of the day, this engine is a tractor engine.
It pulls better than my 650SS down low but does not have quite the top end. All in all a very nice engine.
Someone mentioned in another thread that their A10 required half or more throttle to run at 60 MPH. Obviously something is wrong there, but his comment had me noting the approximate throttle opening at speed.
At 65 MPH it isn't much, somewhere between 1/8 open and 1/4 open.
I'll mark the throttle out as others have done and report back.
The bike is also running much smoother. I ran it at 65 for ten miles or so, no numb body parts afterward.  65 is actually smoother than 60, it seems to be a sweet spot for the engine. Virtually no vibes in the bars at that speed, only a bit thru the footpegs and some thru the seat, but not bad at all.

Glen

[worntorn]

I learned a bit more about the bike this evening. The trip odometer sticks then works then sticks, so the 50 miles that burned 6.5 litres of fuel may have actually been 70 or 80 miles, no way to know.
The regular odometer does work consistently, however it measures 9 miles as 8, so I will need to add 12.5% to the odometer figures to get actually mileage covered.
This had me wondering if the speedo might be off by a similar amount, so I mounted the GPS on the bars. It turns out that the speedo is out by approximately 9 percent at 60 MPH. 60 MPH is actually a true 65 MPH. Most old Brit speeds read higher than true, so the difference is a lot.
So when I was rolling along at 85 thinking it might pull up to 90, the bike was actually running in the low 90s and headed for the ton.
No shortage of speed then.

All of this riding has exposed a problem. The mag works great cold, but after a good run, if shut off the bike will not restart until left to cool.
After doing some reading here I have ordered the Brightspark EasyCap.

Glen