Throttle Linkage Adjustment

mack4759

mack4759

Member
My dad and I are new to the whole Model A scene and need some help adjusting the throttle linkage on his ‘28 Phaeton. There is no response from the throttle until it is approximately half way down in its line of travel. We have to put the pedal to the metal (or wood in this case) to be able to go anywhere, and 35mph is about our top speed. When looking at the linkage on the carburetor, while the gas pedal is completely pressed to the floor, the linkage is only half way open, so there is still plenty of travel available. We traced the throttle linkage back and found a screw by the firewall that looks like it would allow for some adjusting, but how would one go about adjusting this?

Also, we are getting some backfiring between shifts and while decelerating. Reading through some threads they suggest that it is a lean condition and that adjusting the GAV will help resolve this. Our question regarding this though is that the operators manual states “Never drive continuously with adjusting rod more than 1/4 turn open.” Will we have to continually adjust the GAV to address this issue or do we need to adjust the idle mixture screw on the carburetor?

Thanks for your help!
 

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To start with, there is no linkage adjustment. You just have two levers connected with a rod making up the pedal throttle...more stuff for the hand throttle isn't relevant here.
My guess is that the lever on your throttle assembly at the back of the engine is bent, probably from blunt force trauma inflicted during removal or installation of the engine.
I would suggest finding someone with a Model A that has full travel so you can actually figure out where the problem is and what it should look like when done.
Or...swap an undamaged throttle assembly.
 
Mack, also on repro throttle shafts you have to bend the throttle shaft arm/ball towards the fender so you get more throw
 
The welded on nut and screw is someone’s attempt at “fixing” something. What I have not a clue, but it ain’t normal. With that said, I would first check and make sure that the foot pedal is free to go as far down to the floor board as possible. Many times the shaft will hit the lower side of the hole in the floor board and you think you have reach its limit. Elongating the hole a little will allow for more pedal movement if need be. Once you have eliminated that as a possible restriction of pedal movement then I would unhook the linkage that connects the carburetor to the throttle assembly ( unhook only one end). With that, done you can press the foot pedal to the floor (or place a big rock on it to hold it in place), and then move the carburetor throttle fully open. You can then hold the loose end of the linkage to the little connecting ball and see how much gap you have to compensate to achieve full open throttle. I have avoided using the term “adjusting” but I have seen many throttle assembly arms bent in order to accommodate a different carburetor throttle arm. Therefore, you may be able to proceed with caution and re-bend the throttle assembly arm to allow for more throttle opening. But when you do you also have to make sure that the carburetor will return to partial closed for a good idle. A little bending will go a long way…

Good Luck and enjoy the hobby
 
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