Pilot air screw setting - maximum rpm method

[ianralph]

I'm seeking help to tune the pilot fuel circuit.

My bike is a '79 GS1000S with a transac 4 into 1 (not sure if this is a good pipe or not), standard air filter with the lid on, Dyna S ignition with the timing spot on, standard cams with the valve clearance all within spec, and a recently rebuilt motor. I've also replaced all the O rings in the carbs as well as the ones between the inlet manifold and the head. The needles, mainjets and needle jets are all standard and the float levels are also within spec.

I've raised the needles to 4th position from the top with the plastic spacers the right way round in response to suggestions in other posts. I did a bench synch and the pilot fuel and pilot air screws are both set to 1 1/2 turns out. The bike starts (too?)easily when cold without choke.

I'm trying to use the maximum rpm method to set the pilot air screws, but no matter which way I turn them the engine speed does not change noticeably from a 1100rpm idle when the bike is fully warmed up.

Does this lack of sensitivity to pilot air screw position indicate that the fuel screws are too far out - or something else?

Thanks is advance for any help you may be able to offer.

Ian

[Steve]

I am not the expert, I just seem to be the first to respond.

I think the usual starting point for the fuel screws is between 3/4 and 1 full turn out. The air screws are OK at 1.5 turns.

.

[tkent02]

How does it run as you ride around slowly, barely opening the throttle? Look at the plugs, are they rich after a very few minutes at very small throttle openings? Try going leaner on all four fuel screws together, then ride it again, look at the plugs again. By the way, are the carbs synched well?

[ianralph]

Thanks guys - I'll try leaning off the fuel screws to 1 turn out and then have a look at the plugs after a ride just off idle. I thought it started too easily when cold....

I haven't synched the carbs yet - the suggestion from other threads seems to be that the pilot settings should be pretty right before synching.

Thanks

Ian

[Steve]

Pilot settings should be close enough to start and run, or you will never be able to do the sync. One thing I like to do when syncing carbs is to leave the gauges hooked up after the sync, then check the mixture screws, tuning for highest rpm. Yeah, there are different methods for the VM and the BS carbs, but the can both be done with the manometer connected. Then I will double-check the sync to make sure that the tweaking of the mixture did not affect things enough to change vacuum settings.

I know, it will probably never do it, but it makes me feel better.

.

[ironsheik]

A great way to fine tune the air screws is by parking the bike with the sun behind it so the needle on the tach is casting a shadow. While you turn the screws, assuming the idle is pretty steady, you can see the needle move in slight increments as the screws are adjusted.

Josh