New carb - can't get RPMs down from 2500

[Vae Victus]

New Racer65 carb on ‘70 vehicle. The engine surges and backfires at idle.

4 of us working on this. Stumped.

Checked points, plugs, adjusted carb, etc. Getting spark, fuel, etc

What are we missing?

 

[rkymtnflyfisher]

Vacuum steady?

 

[Vae Victus]

 

[Vae Victus]

2° distributor to counterclockwise for the win.

 

[morganism]

did it hav a spacer under the old carb?

 

[JackA]

Looks like the fuel solenoid is not hooked up.

 

[Marn0]

x2 for fuel solenoid

 

[Vae Victus]

Agree but does the '70 have a fuel solenoid (F engine)? This carb is really for the 2F, and this is my first time tuning/installing a new carb.

I see the wire on the carb, but see nothing it attaches to on the F engine. (I am off to the FSM to research the answer to this)

Assume I know nothing.

 

[Vae Victus]

Vacuum steady?

Not sure - Vacuum gauge coming from Amazon tomorrow.

 

[Vae Victus]

did it hav a spacer under the old carb?

Yes, but old carb was a Weber. New carb has its own spacer... visible in first photo. Right?

 

[Vae Victus]

I will say I have it idling steady now. It's idling too high still. Tach meter on the first spark plug wire reading about 1650. Adjustments to timing screw and to mixture screw have little effect.

I'm researching the FSM tuning steps now - had 3 cruiser-heads here today, but we weren't going by the book. We were using our testosterone

 

[Solace in Solitude]

Have you lean-dropped the carb?

Eliminate vacuum leaks.

Info in HERE ... you may have to go thru it a few times to get the idle down.

I don’t know about idle solenoid on an F... but I think you should able to make the idle solenoid play, with minor electrical work.

 

[Marn0]

Try running a +12v wire from ignition to the idle solenoid. This may help. If its a 2f carb then i would assume the idle solenoid is there to help it shut down I.e stop fuel going through your idle circuit. The 1650 idle you have is probably running off the main jet, not the idle circuit

 

[ToyotaMatt]

Fuel Cut Solenoid needs Key ON B+ power

 

[Vae Victus]

Have you lean-dropped the carb?

Eliminate vacuum leaks.

Info in HERE ... you may have to go thru it a few times to get the idle down.

I don’t know about idle solenoid on an F... but I think you should able to make the idle solenoid play, with minor electrical work.

Not yet. Gotta get base idle down some first.

Thanks for the link and advice on the solenoid. I’ve done all the work on my other truck’s frame off, but I’ve not gotten to the carb setup yet - so this is new learning for me.

 

[Vae Victus]

Try running a +12v wire from ignition to the idle solenoid. This may help. If its a 2f carb then i would assume the idle solenoid is there to help it shut down I.e stop fuel going through your idle circuit. The 1650 idle you have is probably running off the main jet, not the idle circuit

Ok. Makes sense.

 

[Vae Victus]

Hooked up the solenoid wire. Ensured it has switched voltage.

Now however I have RPMs at 2500 and vacuum at 10 in Hg (too low - must be a leak. Does that cause high RPMs?).

Can’t get RPMs to drop. I’m missing something.

Photos of carb were taken before solenoid hooked up

 

[Solace in Solitude]

If you are trying setup your carb, vacuum is kinda moot when the rpms aren’t at idle (650-700).

Vacuum plays at idle rpms and when diagnosing tuning problems.

Make sure your linkage isn’t binding and that the fast idle screw is properly adjusted.

Perform the lean drop method, adjust the idle, repeat... repeat...

Read from post #3 HERE - lean drop is discussed, as well as carb adjustment screws... not sure how your’s relate to Aisan.

 

[Solace in Solitude]

While vacuum “value” doesn’t matter right now, make sure you don’t have a vacuum leak... spray fine mist water, carb cleaner, etc. around vacuum connections, brake booster, manifold gaskets, base of carb, etc.—- if idle increases, you’ve found a leak. Don’t forget the dissy vacuum advance module, if you have one.

 

[Vae Victus]

Is the fast idle screw supposed to be touching the bracket below it? It isn’t.

And with the choke in or out it never touches the bracket below. Is that normal?

I’m going to unhook the throttle cable and see if it drops the RPMs.