For What Its Worth

Carburetor notes 

I finished going through my carb and testing the car. Finally my 66 runs as I always thought it would. Fairly good street manners and good hard acceleration when you hit the gas. I found it was a few "little" things.

When I rebuilt it, the carb didn't look too bad, compared to most. Cleaned it, and started putting it back together. I measured all the linkages as the instructions outlined. What a mess, some measurements wrong from the factory and some way out from previous shade tree owner.

First I found the secondary's were kicking in 40% early on the throttle position. No wonder it wouldn't hold smooth speeds going down the city streets.  At about 40 it would want to lung ahead.  At the track it would fall on it's face going to WOT, wide open throttle. Opening the secondary's early, before there was enough need to cause the venturi in the secondary's to work right. Only a split second difference I know, but the effect was enormous.

Previous owner had done a number to get it to what they thought was WOT on the secondary's. The main problem was the primary WOT position. About 10 degrees short. No adjustment, just a cast stop on the body. Factory quality control isn't what it used to be. A little filling fixed it. Then adjusted the secondary's back to spec and it all went to WOT just fine.

Accelerator pump and linkage also way out. The carb just would not idle down well, It kept a high idle. The linkage to the accelerator pump was bottoming out. Just barely bottoming out so it gave enough resistance that the throttle would not always close the last little bit.

I think the electric choke rod was the only thing right.
Lastly I replaced the idle screws. Just couldn't get them to adjust smooth, 1/8 of a turn went from close to way over the hill on the adjustment. One was a little scarred from over seating, but not bad. Something just didn't look right so I got new ones. When I compared them, what a difference. The difference on the tip was dramatic.

The new ones were about twice the distance from the tip to the full diameter, a shallower or longer taper. Now the idle adjusts the way I remember carbs should adjust. Looks like another "where did it come from?" part.

Next time you ask, "how hard is it to rebuild a carb" be patient with us old guys if we take a while to answer. It isn't hard after you done a few hundred or you follow ALL the instructions in the rebuild kit and have someone with experience looking over your shoulder.  There are things they can't tell you in the instructions.

Some notes on carb rebuilding

Typical problems rebuilding carbs.

Matching Carb to engine.
Now this is a topic that can have us all talking for days.  Some things from my experience.

So you want the best, most efficient carb that gets the best power and has good street and track manners?  What is it?  It is called EFI, electronic fuel injection.  There is a very good reason car companies went to computer controlled fuel injection.  Lets face it guys, carbs are simple and cheap and don't need much computer knowledge to adjust.  We can tinker with them and still have a lot of cash left over. 


Happy Motoring, VHubbard.  June 2009

Updated Oct 2012

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