Gyro - general thread

[vintagegarage]

Back in the day when we were racing cars with SU carburetors, we used to narrow the ends of the needles with Emory cloth to make the mixture richer at wide open throttle. Leave the top part of the needle alone so you don't affect low and mid throttle mixture. We even sometimes cut the ends off the needles if we needed super rich. Needles are easier to change than the main jet in a Gyro carb. Even if you can't find a true Gryo needle to experiment with, you could start with almost any Keihin needle, and with a micrometer and Emory cloth rework the needle to be thinner at the end than what you have now and see what happens. I'm not suggesting that you modify your existing needle if you don't have any spares, as there is no turning back and you don't want to risk a good gyro needle if they are scarce.

[motormike]

Back in the day when we were racing cars with SU carburetors, we used to narrow the ends of the needles with Emory cloth to make the mixture richer at wide open throttle. Leave the top part of the needle alone so you don't affect low and mid throttle mixture. We even sometimes cut the ends off the needles if we needed super rich. Needles are easier to change than the main jet in a Gyro carb. Even if you can't find a true Gryo needle to experiment with, you could start with almost any Keihin needle, and with a micrometer and Emory cloth rework the needle to be thinner at the end than what you have now and see what happens. I'm not suggesting that you modify your existing needle if you don't have any spares, as there is no turning back and you don't want to risk a good gyro needle if they are scarce.

That's a nifty trick, but not likely I will go to that extent.
I'll try the next bigger jet and see what happens.
Note: the P.O. has notched the rear fender assembly aft of the carb to allow removal of carb flange bolts easily.

[motormike]

Happy birthday to me.
Pic from High Valley camp and airfield, Suches, GA.
Taken by vintagegarage a few years ago.

[vintagegarage]

This was posted two weeks ago, not sure how I missed it:

https://www.youtube.com/watch?v=aUKrAM3lI30

A pretty good history of the Gyro.

[harleyracer59]

Happy birthday to me.
Pic from High Valley camp and airfield, Suches, GA.
Taken by vintagegarage a few years ago.

Happy belated bday Mike. Hope you had a good one!!!

As to your carb tuning. Remember. You can remove the slide pull the spring. Pull the needle and there’s a clip for fine tuning the carburetor. Moving the clip lower in the needle actually raises the needle making a little richer. Moving the clip up (towards the end ) lowers the needle and leans out the mixture. Might try that to see if you can find a sweet spot?

[motormike]

Continued Gyro main jet swapping.
Picked up some debris, so removed carb and did a recheck on all the circuits.
Sure 'nuff, the main jet had blockage.
Swapped in the next size larger jet.
Went from 80 to 82.
Felt a slight difference in the downhill throttle.
Going to call it an improvement since it felt like the engine did less of the "backing up".
I'm trying to find the best size that allows the throttle to be held wide open on downhill without that
sensation of backing up.
Original condition with the OEM jet left a lot of throttle play on the top end that did nothing.
The first change to 80 changed that a little.
This current change to 82 maybe a little more.
The whole idea is to try and match the amount of air being throttled to the amount of gas being metered.