Hesitating 20R

[Trevor]

I just brought home a rusted-out, bondo'd '76 Celica. I'm guessing it still has the original 20R; I'm not entirely sure becasue the sticker on the valve cover is missing. It idles OK, but hesitates when the gas is punched. It also backfires a little while coasting down hill (possible exhaust leak?) and diesels when the ignition is turned off. The carb appears aftermerket, but is clean. It doesn't look like any of the emissions are hooked up (but they are present under the hood).

I haven't checked the timing or vacuum yet. I'd like to address the hesitation first. Does anyone have any recommendations where to start?

 

[woody]

fuel filter is a quick obvious....otherwise, get those vacuum lines hooked, since a leak can cause a similar issue.

 

[Trevor]

Thanks Woody.

I got the thing started today (a wire fell off the starter yesterday), and heard a hissing from the carb / manifold gasket. The local Napa didn't have a Weber carb gasket, so I made my own. Unfortunately, as I was torquing down the adapter plate, it cracked and created an even bigger vacuum leak. I'm out of JB Weld, so this fix will have to wait.

Did I mention that the gas pedal fell through the floor board? That's gonna make it hard to drive.

 

[Trevor]

I finally fixed the vacuum leaks, but it still hesitates when the gas is punched. I measured 2 psi of fuel pressure at the carburator. Weber recommends 2.5 psi. I don't know if this is significant.

I checked the timing and it's dead-on. Dwell is perfect, too.

I also noticed it had a bad exhaust leak, so I pulled the manifold and found it had no gasket. It also had a broken bolt at the air injection, so exhaust was leaking through there, too. I said F-it and ordered a cheapo header from Summit.

 

[Gumby]

accelerator pump is bad.

With the engine OFF, open up the choke plate, shine a flashlight down the venturi and pump the fuel to WOT. You should see a steady stream of fuel. If not, replace your accelerator pump diaphragm.

 

[Trevor]

Uhh...After a long break from this project, I have returned. The accelerator pump shoots a decent stream when pumped. I know nothing about these carbs, but is it possible the accelerator pump isn't jetted correctly?