340 Idles at 3200 RPM!

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Zachary

Zachary

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Hey everyone,

So I recently rebuilt my carburetor. I cleaned it out and changed out gaskets. I adjusted the floats as per the Edelbrock Manual (it's a 1407 manual choke btw) and changed out the accelerator pump. Other than those two changes and new fuel filters, everything else is the same. I also changed the location of the pump connector rod from the bottom hole on the pump arm to the top hole.

When I reinstalled the carb on the engine and hooked everything, I started it up. Right when it fires, it revs up to about 3000 RPM, then steadily builds to 3200. I tried adjusting the idle screws right on the front of the carb, but no change happened. If anyone can give me insight, that would be great. Thank you!
 
TrailBeast said:
Betcha the new pump arm location is holding your throttle open.
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I was thinking it might be that, but I wanted to check with you guys. I will look into putting it back to where it was after work. The only reason I changed it's location is because on the instructions in the rebuild kit, it had each hole labeled based on the model number of the carb. So I put the arm in the 1407 hole. If that ends up being the issue, then thank god it ends up being an easy fix. I'll keep you updated. Thanks.
 
Zachary said:
I was thinking it might be that, but I wanted to check with you guys. I will look into putting it back to where it was after work. The only reason I changed it's location is because on the instructions in the rebuild kit, it had each hole labeled based on the model number of the carb. So I put the arm in the 1407 hole. If that ends up being the issue, then thank god it ends up being an easy fix. I'll keep you updated. Thanks.
Click to expand...

If you want you can bend the rod a little to let it come down all the way.
(Just a possibility)
 
If 1407 is same hook up on accel pump as 1406 make sure the"S" hook looks like an S when looking at carb from front of car.
Pretty big jump from bottom to top hole...no?
 
4spdragtop said:
If 1407 is same hook up on accel pump as 1406 make sure the"S" hook looks like an S when looking at carb from front of car.
Pretty big jump from bottom to top hole...no?
Click to expand...

I agree that it's a big jump, but I was going by the rebuild manual. Tbh, I'm fairly new to carbs and what not. Like I said, hopefully relocating the arm will fix it.
 
Im not very familiar with them.either but never too old.to learn im doing an AFB right now, basically same as eddy. I would take Doug371 advice and unhook throttle cable too.
"S" hook should look like this.when connected properly
Zachary said:
I agree that it's a big jump, but I was going by the rebuild manual. Tbh, I'm fairly new to carbs and what not. Like I said, hopefully relocating the arm will fix it.
Click to expand...

20170220_215619.jpg
 
I bet the choke linkage has somehow got it hung up.
 
doug 371 said:
disconnect the throttle cable
Click to expand...
Would doing that just eliminate/confirm the possibility of it being the throttle cable being too tight? If it eliminates it, should I then move the pump connector rod to the original hole it was in?
 
yes...to eliminate that possibility...if you adjusted the cable with the choke set, it won't allow the throttle blades to close to idle speed...if that's the problem then readjust the throttle cable once you have the carb tuned...
 
So I currently have the pump arm in the middle hole for the accelerator pump. I disconnected the throttle cable and started it up. It still idles at about 3000 RPM. I try to set the choke using the fast idle linkage adjustment procedure in the manual, but once i bump the throttle to test that it goes back to idle, the adjustment I just did does nothing. I'm not quite sure that I'm even doing it right. Like I said earlier, my carb knowledge is next to none. The choke plate on top of the carb just falls open once I give it throttle and it just idles high. So I'm at a loss.
 
Take the carb off, Hold the primary throttles closed with one hand, and keep it closed,flip it upside down,and visually see if the throttle blades are hung open.
If they are, go to the choke mechanism and manually reposition the fast idle cam so that the throttle now closes. Again, keep the throttle closed and flip it over for inspection.If still hung open, back off the curb idle speed screw, until the throttle is completely closed. If it will not completely close, remove the S link from the pump-arm and check it again.If it still will not close check the linkrod to the secondaries; the secondaries must be closed up tight. Is it possible you installed that link-rod wrong.
You may have to reposition the fast idle cam every time you flip the carb over.
If it still won't close, I give up. Did you remove or loosen the butterfly valves?
>But when you finally get it to close all the way, you will need to readjust the curb idle speed screw. First screw in your mixture screws all the way, but lightly seating them.Next go find the transfer slots. These are right beside the idle discharge ports, with the mixture screw tips now sticking out of them. There is one vertical slot in each primary bore.
Then crank the speed-screw in to open the throttle blades just enough to expose those transfer ports; continue adjusting the speedscrew until those ports look like little squares. Now back out the mixture screws about 2 turns.
After you figure out which little bugger was the guilty one, fix it and reassemble everything. Then one final check; reposition the fast-idle cam to off,hold the throttle closed, and flip it over. The secondaries should be close up tight, and the primaries should have the Transfer ports exposed like little tiny squares.Hold the choke off and exercise the throttle arm a few times, and be sure it returns to the curb-idle screw each time.
Now it's ready to be reinstalled.

After that it is bolted back on, make sure all vacuum ports are plugged or properly hooked up, especially the PCV hose, and the vacuum booster.And that the fuel line is properly fitted and secure.
Next pop the metering rod retainer plates and make sure the rods are going up and down properly.
Make sure the choke electrical wire is hooked up and that there is power in the wire, with the ignition key in the run position. After the engine is running and you have tapped it down, you will have to adjust the fast-idle speed,to not be racing.Every engine is different and it is somewhat dependent on your timing, but I don't care for an engine warming up on the fast idle cam at much over 1200 rpm.
Good hunting!
 
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It's a common mistake for guys to put the linkage rod that goes to the choke blades on backwards. Somehow it can go both directions, but one way is wrong and will make it idle really high.
 
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