Triumph Bonneville Tuning Manual

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Filed Under (Triumph) by admin on 20-11-2010

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1. The Float The float bowl acts as a fuel reservoir to meet engine demand. The float is hinged on a pin in the float boss. It rises and falls with the fuel level in the float bowl. The small metal tang integrated in the plastic float supports the float valve, also known as the float needle. As the fuel in the float bowl rises, the float valve is pushed into the valve seat, until it’s high enough to shut off the fuel flow to the bowl. As fuel is used the level in the bowl drops lowering the float which pulls the float valve from its seat, and fills again. Adjusting the height of the float has a big effect on the mixture as a low or high float level makes it harder or easier for the vacuum to suck fuel into the venturi. Differing float levels cause an imbalance which may be perceived as vibration. 2. The Choke This system is referred to as the choke. But that’s a misnomer. When you pull the choke knob, what you’re doing is retracting a plunger that opens a tube connected to the starter jet, allowing additional fuel to enter the venturi just below the vacuum hose nipple. It supplements the pilot system at start up. 3. The Pilot System The primary purpose of the pilot system is to supply the mixture at idle. It continues to supply fuel throughout the entire throttle range, but after about 1/8 throttle is reached the main system starts to put out more of the total mixture, up to full throttle. By adjusting the idle with the big screw on the left side of the carburettors the position of the butterfly is altered, so exposing one or more of the four small holes that are drilled into the venturi, (leading to the pilot jet) just under the butterfly valve, letting more or less air pass the butterfly. Adjusting the pilot screw that’s under the carburettor varies the amount of air premixing with the fuel before it enters the venturi. 4. The Main System Open the throttle and the cable that’s connected to the butterfly valve turns it from vertical to horizontal, so letting more air through the venturi. This increases the vacuum effect that is transferred up through the vacuum drilling in the slide to the diaphragm valve that leads to the diaphragm chamber. The top chamber is separated from the bottom by a rubber diaphragm. The bottom chamber is open to atmospheric pressure from the airbox. When the vacuum in the top chamber rises enough, the constant ambient pressure of the lower chamber helps the diaphragm valve overcome the downward force of the diaphragm spring, so it rises from the ven- turi. As the diaphragm is raised the needle is pulled out of the needle jet, exposing a thinner portion of the needle taper which allows more fuel to rise into the venturi to meet the increased engine demand. The key parts of the main system are shown in the photo below

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Aermacchi IHRO1 Machine Specifications

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Filed Under (Aermacchi) by admin on 13-11-2010

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1. IHRO 1 caters for single cylinder thoroughbred Grand Prix racing motorcycles constructed during the period 1945-1972 inclusive, for the specific purpose of participation in Grand Prix competition during that era. Maximum capacity for any machine is 500cc, and wherever possible it is intended to run three classes, for machines up to 250cc, 350cc and 500cc. 2. Motorcycles must be presented in original, period condition, with no external updating. Period appearance seats, fuel tanks and fairings (if fitted) must be used. No external changes may be made to the appearance of any machine unless it can be proved that such a change was made in the period. Modern safety fixtures required by some federations and modifications mentioned in this document are not covered by this ruling. 3. No disc brakes are allowed. Drum brakes only may be used. 4. No alloy/magnesium wheels are allowed. Wire wheels only may be used. 5. All machines must have twin shock rear suspension: No monoshocks except Vincent Grey Flash. Suspension units must resemble period components, i.e. no external gas reservoirs etc. 6. All frames and swinging arms must conform exactly to period appearance; no box section swinging arms allowed unless fitted by the manufacturer to that machine in the period. 7. The maximum permitted rim width on either wheel is WM3. 8. No slick tyres, hand cut slicks or modern racing tyres designated by the manufacturer as being exclusively for wet weather use are permitted. Only the following rear tyres may be fitted. Any 19″ tyre. The following 18″ tyres, Dunlop 3.50×18, 3.50/3.25×18 KR124 and KR124A, Avon AM22 110/80×18 Rear Fitment and Avon AM18 120×18 9. Choice of carburettor is free, provided that this is of a period type cylindrical slide model, albeit of a later manufacture. Flat slide instruments are not permitted with the exception of Gardner carburettors. Fuel injection is not permitted except if it can be proved that particular motorcycle ran between 1945-72 with the same type of injection system fitted. A Wal Philips injector is classified under this heading. 10. The type of fuel used must conform to the ACU and FIM’s current fuel regulations for 100LL Avgas at 102 MON. See full specifications below. All machines must finish a race with a minimum of 2 litres of fuel in the tank to allow a sample to be taken for analysis. 11. The use of belt primary drives is encouraged.

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