A few tuning and workshop tips for air cooled Ducati

Carby adjustment

This is the one area that needs regular attention, particularly if the bike is used a lot.

I always carry a small screw driver under the seat.  I also slotted the heads of the carby slide adjusters to take a screw driver.

The carbys can go out of adjustment from wear, vibration, cable stretch, or contaminated fuel.

Carry out any adjustments in the following order.

Fuel contamination

Rust and paint particles are often present in old or repaired motorcycle fuel tanks, and similar vintage jerry cans.   Grit can also work it's way into the fuel system.

In line fuel filters are a good idea to catch this stuff,  paper element being the best.  The copper mesh type look good, but will not catch very fine particles.  

Heavy contamination can clog the main jets and require draining and cleaning with an air gun. If it's just a case of grit or a hair in an idle jet, raise the engine speed and unscrew the idle jet half a turn to release the obstruction, then return it to position - repeat as required. 

Before tuning an engine which has been unused for over six months, replace the fuel with fresh and drain/flush the carbys by loosening the float bowl nut.  Also check that filters in the fuel line banjo fittings are clean.

Inlet manifold gaskets

These steel/rubber laminations deteriorate with age.  Check condition and tightness.

Choke - enrichener

Ensure that the rubber seats on the enrichener slides are in good condition, and that they fully close.   The seats can compress or crack with age causing fuel seepage and an over-rich engine.

You can flip the rubber pad in the brass enrichener slide, or replace them with one cut from heavy car tire tube with a wad punch.

Idle speed

With the engine running, adjust the rear cylinder until engine speed is 1000 RPM.

Increase the front cylinder until the revs just start to rise.   Now feel the exhaust gases and power pulses for each muffler.   Back off the speed of the front cylinder until the power pulses for both exhausts feel the same, and tachometer needle fluctuation is least.

Fine adjust each cylinder until engine speed is 1000 - 1100 RPM.

Adjusting the idle mixture will alter engine speed, so repeat if required.

Idle mixture

With the engine running, adjust the rear cylinder to the point where the engine speed is highest.   Now do the same for the front cylinder.

Feel the gas temperature of each exhaust with your hand.  When idle mixture is set correctly the temperature will be at its hottest.   Any variation in temperature between cylinders indicates a difference in settings, or a possible compression or ignition problem with the cooler cylinder.

If backfiring occurs on engine over-run, screw out each needle slightly to increase fuel richness.

Main jets

Nothing to do here unless someone has played around with them.  The standard jetting is suitable for free flow exhausts and should not need replacement.

It is worth noting that the main jet for the rear cylinder is larger on some Ducati models to reduce combustion temperature and allow for heat wash from the front cylinder.   This will result in a variation between cylinder readings if vacaum guages are used for tuning.

Needles

Once again, nothing to do here normally.

Unfortunately ham fisted attempts to raise engine performance by changing mains and needle settings, can cause grief to unsuspecting tuners attempting to get the engine running correctly. 

My 750 F1 was a case in point.  It was running terribly when I bought it, massively over-rich, all due to so called tuning experts screwing with the original jetting.  

Over-rich actually makes less power, so how good were they?  But at least it won't damage the engine.  An overly lean mixture on the other hand is much more serious.

Any meaningful jetting changes are aimed at leaning out the mixture to make more heat, and hence power.   But this is an exact science, and if not done correctly can blow holes in pistons, and generally ruin things with expensive results.   Not recommended.

Air filter pods

Can they adversely affect engine performance ?  The video below looks at this.

Throttle cable adjustment

The simplest (and best) way to adjust the cables is not with a vacaum guage, but by ear.  I have a set of mercury columns but rarely use them. 

Cable adjustment is done AFTER idle adjustment has been set.  The carby slides are then in the correct position for this method. 

Oil the cables and adjust one so that it has the required  2 - 3 mm of freeplay.   The other cable (X) should have more freeplay.

With the engine OFF, open the throttle above half way and  release it letting the carby slides slam home under return spring tension.   Listen carefully.  You will hear two distinct "clicks" as the slides hit the stops.  This is because the cables are out of sync.

Repeat the exercise, reducing the amount of freeplay in cable X until only one click is heard.

Both slides are now hitting the stops at the same time.

The carbys should now be correctly synchronised.

Accelerator pumps

The engine should accelerate cleanly with no stuttering or shuddering.  Similar quantities of black smoke should appear from each exhaust.  

A visual examination of pump adjusters should show a similar number of threads exposed. 

If adjustment is required, the correct output for each carby after 20 pumps is 4 cc of fuel.

Brembo twin piston brake calipers

Caliper leaking?  Don't rush out and buy a full repair kit.

It's highly likely the single "O" ring on the transfer port between both caliper halves has lost it's strength over time.  The piston seals are probably OK.

Your local bearing company should be able to supply the "O" ring for a few cents.  It has to be Nitrile or equivalent for brake fluid use.

Specifications are:  7/32 x 13/32 x 3/32 EPDM  -  (BS107EPDM)




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2015