Fuel flow limitations of the concentric carb

[worntorn]

I have a 63 West Coast USA type Super Rocket with 9 to one CR. It came to me with a 28 mm Concentric fitted and would not rev out plus misfired quite a lot. On inspection the Carb was full of calcified ethanol crud, so I fitted a clean near new 30 mm Concentric I had on the shelf.
After playing with jetting, the bike pulls to 90 MPH (GPS) but that is it.
Also it lacks power for passing when dropped into 3 rd at 60 MPH. I have a Norton 650 SS and figure the Super Rocket should be perhaps a half step behind that, but not four steps behind.
A very knowledgeable fellow on the Norton Commando site, Jim Comstock, mentioned that the Concentric Carb is only capable of fuel flow for 30-35 HP.
This generally isn't a problem as many bikes fitted with concentrics had twin carbs and made 60 HP or less.
For a single Carb HC late Super rocket designed to make 46? HP or as some authorities claim,  50 HP,  this 30 HP fuel flow would be a problem. Jim's information comes from dyno testing on his own dyno.
I have since heard this same information repeated by an old time racer who switched to monoblocks on his Norton racing bike (70-75 hp on dyno)for the same reason, inadequate fuel flow with Concentrics. He also had a trick for increasing the fuel flow on the Concentrics but opted for the Monoblocks as he felt they were higher quality Carbs.

A friend recently gave me a newly resleeved 1 1/8" monoblock Carb and I intend to try that. I realize it is slightly smaller that the original Carb for that bike (1. 5/32l but shouldn't hamper performance much. Will report on the results here.

Glen

[Triton Thrasher]

The float needle seat can be drilled out. Mine is at 3 mm.

Banjo spigots can be drilled out a little too.

The "trick" may well have been making a hole in the wall of the well the needle sits in.

But for God's sake eliminate restriction in the taps and those silly gauzes as a cause, before you start messing around.

You are opening both taps, yes?

[worntorn]

Yes, both taps open and good flow to the carb.

Glen

[Triton Thrasher]

Hard to believe the problems aren't fixable.

People do use Mk1s with methanol.

[worntorn]

I think they are fixable, however for those of us who thought a Mk1 Concentric of equal size would be a bolt on replacement for a Monoblock, jetting adjustmemts aside, it appears they may not be, or at least could limit top end power.  As mentioned, the problem will nit show up if used in pairs on even a highly tuned old Brit bike. When these carbs came into production the sporty British parallel twins were carrying twin carbs.

I would like to change to the Monoblock for cosmetic reasons anyway, so it will be interesting to see if there is any major difference in performance.

The engine is in as new condition showing just 2% leakage on a leakdown tester.

Glen

[muskrat]

The biggest problem with concetrics is they don't like any sort of downdraught angle. To stop them flooding the fuel height has to be set very lean. Methanol bowls with larger needle & seat are available. I have a few spares if you'd like to try.
Cheers

[worntorn]

Thanks Muskrat . I think I'll try out the Monoblock first and see what happens. Just curious if anyone else here has switched from a monoblock to concentric or vise versa and noticed a difference.
It might be much like the single Mikuni conversions on Commandos. Lots of people do them and swear there is no power difference then one day learn that the bike which pulled thru the ton easily with twin carbs is now out of breath at 85 or 90.
If you only run the bike fairly gently the problem wouldn't show up.

Glen

[Triton Thrasher]

You'll get nowhere until you stop putting a letter k on the end of Monobloc.

[nimrod650]

You'll get nowhere until you stop putting a letter k on the end of Monobloc.

ear wee goe agane anuthar spelin lesan noffin beta two dew wive yor tyme

[Triton Thrasher]

You'll get nowhere until you stop putting a letter k on the end of Monobloc.

ear wee goe agane anuthar spelin lesan noffin beta two dew wive yor tyme

It's important. You'll be spelling BSA wrong next.

[nimrod650]

You'll get nowhere until you stop putting a letter k on the end of Monobloc.

ear wee goe agane anuthar spelin lesan noffin beta two dew wive yor tyme

It's important. You'll be spelling BSA wrong next.

important to who bee ess aye oaner

[worntorn]

You'll get nowhere until you stop putting a letter k on the end of Monobloc.

Not the kind of help I was looking for, thanks.
I consider it bad form to correct another poster's spelling, but in this case, I'll make an exception for you.
You need to go to the Norton site and figure out how many Ls to use in the word annealing. It took me all of 30 seconds to find your first spelling error there and you have lots more.

Typical.

Glen

[Triton Thrasher]

important to who bee ess aye oaner
[/quote]

Ok now you're in your own dream world.

Anyway I hope the change of carb does the trick.

[Triton Thrasher]

You'll get nowhere until you stop putting a letter k on the end of Monobloc.

Not the kind of help I was looking for, thanks.

You need to go to the Norton site and figure out how many Ls to use in the word annealing. It took me all of 30 seconds to find your first spelling error there and you have lots more.

Typical.

Glen

Sorry I was wrong. Please continue to add extra letters to all words.

[RichardL]

When I first saw TT's komment, I knew right away it was a light-hearted tease meant as humor. For want of a smiley face there seems a lot of angst. Let's not let our skins get so thin as to throw off the friendly tone that this growing group has been known for.  (By the way, recent opinion of grammar mavens is that it should be OK to use a preposition at the end of a sentence.) Now, if I was going to get pissy, and Lord knows I would never do that, I would ask for the occasional missing punctuation mark that would make reading so much easier, even if spelling was ignored completely. (I know, someone has just reread this post and found three punctuation errors. I am intentionally not going back to check for same, just so that you can have the fun.)

Richard L.

Edit: I didn't say I wasn't going back to correct spelling. Thumb typing is replete with typos.