Carburetors and Intake Systems for British Motorcycles
by Jeffrey Diamond
“Mikuni” name for reference purposes only. Not affiliated with Mikuni Corporation.
This is not an actual, physical booklet, but an encrypted PDF file which you can read from any computer or lap-top using “Acrobat Reader”.
Want more performance from your classic Triumph, BSA, Norton, Royal Enfield or Matchless? Already have Mikuni carburetors, but don’t know how to adjust them? Doesn’t run “right”, and won’t respond to the changes you’ve made? Can’t make any sense of the original Japanese “instructions”? Looking for an affordable alternative to replacing or rebuilding your tired Amal Monoblocs or Concentrics? Have you heard that “Mikunis are great, but you need to be a rocket scientist to tune them”? This product will help you.
While it’s true that the Mikuni VM has many more tuning components that an Amal Monobloc or Concentric, many types and sizes can be safely removed from the list of tuning variables. In this product I show you which ones to use, and why they work.
Mikuni VM Series "Grand
Prix" carburetors have been used successfully on motorcycles for
about 25 years. I’ve learned how to select and install them on older
British pushrod models (beginning with my own 1970 Bonneville), including the T120, TR6, Thunderbird, Lightning Rocket, Thunderbolt, Commando, Atlas, Dominator, and more 500, 650, 750 & 828cc twins, as well as Gold Star, Ariel, Matchless, Norton & Velocette etc. and other 350 & 500cc singles.
These carburetors are easy to find (click here to search for them on eBay: ) and tune, relatively inexpensive, small & compact. All sizes of this type have very similar components, with almost complete interchange within family size groups. The commentary in this product is limited to 26, 28, 30, 32, 34, 36 & 38mm VM carburetors, but does not cover the other CV, HS, RS, TM, TMS, TMX or OEM and proprietary models.
This product includes specific choices of carburetor size and correct jetting for British engines, and gives you something you can really use,
along with many helpful hints, comments, observations, data, etc. I can’t include instructions for your motor - there are too many variables - but the bike will definitely start, idle, run acceptably with good throttle response, and allow you to make those final adjustments to get it running really well.
This is not like the generic manual that came with your carburetor, but begins where they leave off, and goes far beyond into fine tuning. Not an expert mechanic? You’ll still find this useful to identify what adjustments and parts you need. All parts are easily available all over the world at reasonable prices. If you’ve considered using a Mikuni, you should read this product.
I guarantee that you’ll find information in this product you’ve never seen before, and that will help you plan and complete your carburetor conversion.
Consider this: if this product saves you from making even a single mistake or bad purchase, or gives you one new idea, doesn’t that make this purchase worth while? The price is less than that of tuning components you may not need, and only a small fraction of what you will invest in the carburetors - plan more intelligently, and get better results.
Contents are 42 pages (over 30,000 words), including 20 black & white illustrations & diagrams, plus 35 data tables including 9 jetting tables containing specific trial jetting suggestions for motors based on displacement and carburetor size: 17 entries for single carburetor, 24 entries for individual carburetors. This is far more specific content on these engines than any other source. The subject matter includes:
Mikuni VM vs. Amal Monobloc & Concentric; differences in components and function.
Carburetor selection; choice of size depending on displacement, head, intake manifold, cam timing.
Tuning components; which parts can be adjusted or substituted to change mixture & when, where
the parts are located, how to remove them, what the markings & sizes mean, which jet types are
correct for each model.
Needle jets: 2-stroke vs. 4-stroke, primary vs. bleed type.
Needles sorted by length & marking; analyzing needle tapers, which needles are used in which
carburetors & why.
Adjusting mixture for hot cams, alternate exhaust systems including TT pipes, megaphones,
diagnosing and correcting mixture based on symptoms, using a vacuum gauge.
Dynamometer testing; how to prepare, tools & supplies.
Tuned length intake manifold; how to make calculations for more power, including 5 Tables of
pre-calculated manifold lengths based on cam duration, RPM, etc.
Dual carburetor conversion; how to convert your single-carburetor twin (TR6, &c.) to dual
carburetors, selecting size, how to make your own individual manifolds from common materials.
Tunnel-ram intake manifold; more power for single-carburetor racers with theory, calculations and
dimensions, including illustrations and 2 Tables of pre-set data.
Tuned “Helmholtz” resonator; add an air box for power, discusses theory, calculation and
dimensions, including 5 Tables of pre-set data.
Increased airflow with the UFO and similar devices.
Air cleaner; how to select & improve an air cleaner for more air flow.
Jetting tables; specific trial (initial starting point) jetting suggestions for motors based on displacement,
single or twin cylinder, single or dual carburetor(s), carburetor size.
Velocity stacks and ram tubes; how they work, which ones are best.
Jetting for alcohol; discusses jetting changes for methanol, ethanol, advantages, maintenance, safety.
Sample Worksheet; to prompt you to keep records of changes vs. effects
Most dimensions are given in fractional inches, decimal inches and metric for the convenience of tuners in all languages.
IBRARY has been a respected source of technical literature on older motorcycles since
1971. This information is not reprinted from other articles, magazines, or factory literature and is not available anywhere else, and not included in any of my other books; click here for other related titles: . I’ve also written booklets on Amal Concentric Tuning for British motorcycles: and Amal Monobloc Tuning for British motorcycles , and one on the Linkert Model “M” brass carburetor, used on all older Harley-Davidson & Indian models: .
Please note: this is not a repair manual. If your bike won’t start, the float bowl leaks, the spark plugs foul, &c. my product will not help you. It does not contain information on tune-ups, or explain how to remove, disassemble, clean, repair or rebuild the carburetor. If you do not already have this information please, don’t buy this product yet. If your engine is stock and you’re pleased with how it runs now, this product will not be of much use, although you might find it interesting. This is not a coffee table book, it is intended to be a research tool for those who want to make serious use of their Mikuni VM carburetors.
Total price: $9.95. This is not an actual, physical booklet, but an encrypted PDF file which you can read from any computer or lap-top using “Acrobat Reader”.
The PDF format offers advantages over a printed product: the printed text and illustrations may be zoomed much larger permitting close inspection of fine detail. You can read it anywhere (doctor’s office, train station) on your smart phone or tablet.
The file will be e-mailed to you within 24 hours of receipt of payment. There is no “hard copy”. There is no “print-out”. There is no tracking number. You must set your e-mail spam filters and preferences to accept mail from firstname.lastname@example.org. If you do not receive the file immediately, the problem is your e-mail. If you don’t understand what this is, don’t purchase it, there are no refunds.
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