GAV setting "Sweet Spot" changes

stickshift

stickshift

Senior Member
For the most part, my 1915 T runs consistently and I usually don't need to mess with the GAV setting unless it moves due to vibration. There have been a handful of times however, that I had to pull to the side of the road and find another "sweet spot" so I can continue driving. My carb is a later model 1926 or 27 type, Holley I think. It runs the best about 1 1/4 turns open from fully closed. When it acts up, I need to open it another 1/2 to 3/4 turns. The GAV seems to be very sensitive and any deviation of more than 1/8 turn in either direction will cause a rough running engine. My engine never runs hot but it does seem to happen on drives that last an hour or more. Any suggestions are welcome.
 
What's the level in the fuel tank when you need to open up the GAV? I'd bet it happens when the fuel level is low- less head pressure as the level drops.
 
There is a clamp nut on the mixture needle or in your case ('26-'27) type mixture combination, a swivel - unscrew completely & pinch the opposing yokes slightly to keep from self-adjusting from vibration - that will tighten it up just a smidge. After the initial "warm-up", turn the mixture needle in (c.w.) just until the engine stumbles a little then open (c.c.w.) until it smooths back out - that's usually the sweet spot.
 
Will N said:
What's the level in the fuel tank when you need to open up the GAV? I'd bet it happens when the fuel level is low- less head pressure as the level drops.
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I live in the foothills, so I always start out on a full tank. It's never gone below 1/2 full on a drive. I ended up pulling the fuel filter that was on the T when I bought it and installing a glass type fine screen. This did help with the restriction problem I had before.


"There is a clamp nut on the mixture needle or in your case ('26-'27) type mixture combination, a swivel - unscrew completely & pinch the opposing yokes slightly to keep from self-adjusting from vibration - that will tighten it up just a smidge. After the initial "warm-up", turn the mixture needle in (c.w.) just until the engine stumbles a little then open (c.c.w.) until it smooths back out - that's usually the sweet spot."

I'll give this a try. I have noticed it sometimes tends to move on bad roads.
 
Is it a Kingston or Holley type carb? If it is the later vaporizer, you may consider going back to the older carbs. The vaporizers are very sensitive to any little problem.
 
rotorwrench said:
Is it a Kingston or Holley type carb? If it is the later vaporizer, you may consider going back to the older carbs. The vaporizers are very sensitive to any little problem.
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Here's a picture of my carb. The car had no GAV linkage when I bought it so I ordered parts for a 1915. Of course it didn't fit, so I figured out it was a late model T carb. I believe it's a Holley?
 

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Late model Holey NH - if you unscrew the mixture needle completely, you can lightly pinch the bottom of the u-joint assembly where it rotates to adjust the friction so it doesn't self-adjust.
 
Definitely not a vaporizer. Those things are set up with the float bowl down low and the throttle body up high and integrated into the exhaust manifold to warm the air coming in. The NH is easier to maintain and it is common to see them retrofitted to the 1926 & 27 models.

The 1915 model Ts used the Kingston L, the L2, and The Holley G carbs. They all had the an adjuster knob with two evenly spaced holes for what I call the pickle fork adjuster rod that fits into the two holes to act as a universal joint of sorts. The later NH uses that swivel universal joint. This link has photos.
http://www.mtfca.com/discus/message...arbs are Kingston L, Kingston L2 and Holley G.
 
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stevests said:
Late model Holey NH - if you unscrew the mixture needle completely, you can lightly pinch the bottom of the u-joint assembly where it rotates to adjust the friction so it doesn't self-adjust.
Click to expand...

I did as you suggested and it did fix the drifting issue with the gav. I took it out for a drive last Sunday and the gav position held tight, but I did get a one time occurrence of sputtering and spitting. It was similar to running out of gas, but it only lasted about 15 seconds and naturally I had a car behind me. It was on a flat stretch of road but it recovered without adjusting the gav. I think it may be a sticky float. I've never had this carb open, so maybe it's time.
 
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