Fine tuning Rigid A10

[orabanda]

Hi All,
2,800 miles up on the 51 rigid A10, so decided it was time for fine tuning on the dyno.

As a re-fresher, here is the results from my plunger A10 for comparison:



Cam is 356
Pistons are 7.25:1
Best timing is 30 degrees BTDC

This is the bike tested today:



Cam is 334
Same pistons as plunger
I had experienced two seizures on the LH pot previously. The main cause was the LH bore having been incorrectly machined; almost 0.001" less clearance than the RH bore.

I have done 1,000 miles since the last seizure.

The LH pipe had also discoloured slightly, whereas the RH had not.

For these reasons I fitted an anti-bias spacer, to provide more fuel to the LH pot.

On the first run (not shown on the graph) the bike produced only 17 HP, and was extremely rich on the main jet.

The graph shows each subsequent run in a different colour, with the fuel / air ratio (AFR) in the same colour, on the lower curve. The ideal (target) AFT is 12.5:1, throughout the rev range.

The mixture sensor was swapped from one exhaust to the other, and this showed that the RH pot was much richer than the LH pot.

The timing was checked with a strobe light.



The settings were 34 degrees RH pot, and 35 degrees LH pot.

We experimented with the timing (super easy with slotted mounting holes in the mag flange), and found that max power was achievable with timing retarded to 31/30 BTDC (RH/LH variance).

This increased the HP to 19.8 HP.

The main jet was reduced to 180, with an improvement on both pots, but they were still too rich (RH still richer than LH).

A 170 was fitted, with LH pot mixture now OK, and RH still slightly rich.

We then installed a hotter plug in the RH side (B6HS), which improved the performance to 20.7 HP, and leaned the RH mixture to an acceptable level. We did not fit a smaller main jet, as the LH pot would have become too lean. Plug in LH side is B7HS.

All this achieved in 2 hours!



Note the lean mixture just off idle. Because the type 6 Amal lacks a pilot jet,we were unable to improve this (on the Monobloc bikes not an issue)

This curve shows the (nice) torque "curve" V HP

[stephenrc45]

Fantasic!

I run a dyno in Devon, England. Most of our work is for the japanese bikes but we do do the odd classic.

My '54 plunger A10 made 21.6hp before I sold it and felt good. It ran an open carb though not using the air box. My B50 was stronger though and I'm hoping for good power out of my ZB34.

[muskrat]

Great work Richard. Shows what can be achieved with a little tuning.
What fuel are you running, 91 E10, 95 or 98?
Cheers

[orabanda]

Muskrat,
I use premium unleaded (and try not to spill it on the paintwork!).
Richard

[trevinoz]

Richard,
                The type 6 carby does have a pilot jet but it is a drilling in the jet block which makes it a bit difficult to change.
         Trev.

[Brian]

Great stuff Richard, incidently the Amal book recommends a 170 main jet for the 50 to 52 A10's.