New carb - can't get RPMs down from 2500

[brian]

I'm noticing a lack of and insulator plate under the carb.

 

[Pin_Head]

Yes, that carb needs an OEM insulator that is about 3/4 invh thick. You are going to have linkage issues without it.

I guarantee that your enginewon’t run at 2,500 RPM with both throttle plates closed.

 

[Vae Victus]

@Pin_Head
Did you see the photo below of the two spacers? Those were on the vehicle with the Weber carb. Wonder if i can use one of those, or is an insulator necessary for a 2bbl carb?

Is it the height that is needed or what purpose does the spacer/insulator have? I don't understand.

Also, with a spacer under the carb, I have clearance issues with the darn brake master circuit. Poop.

 

[Dizzy]

Like Pin_Head said, be observant of the throttle plate positions. If you have the idle speed screw hitting the shop floor, my guess is that something is hanging up one of these two shafts. I wonder if there is a compression spring in the housing of the secondary diaphragm? Like in Pin_Head's YouTube video, you can put a paperclip on the arm of the diaphragm, at the opening of the diaphragm, to see if it moves from a closed position. If it doesn't with no throttle, then I would like to see where the throttle positioner screw (a.k.a. 'idle-speed-screw') is at no throttle.

 

[Pin_Head]

Aluminum isn’t a very good insulator, but if you have enough gaskets, give it a try.

 

[Vae Victus]

Aluminum isn’t a very good insulator, but if you have enough gaskets, give it a try.

So it's the insulation that is important as well as the spacing?

Sounds like it's best to find a proper insulator. I have one for the frame off project truck.

 

[stoshzack]

I had this happen to me one time on a carb install. I rebuilt the carb linkage incorrectly and had one of the butterfly plates jammed open (I believe). If you do not have the correct height, my guess is that one of those butterfly plates is also jammed open.

 

[Vae Victus]

I had this happen to me one time on a carb install. I rebuilt the carb linkage incorrectly and had one of the butterfly plates jammed open (I believe). If you do not have the correct height, my guess is that one of those butterfly plates is also jammed open.

Yep, must be the case. I didn't realize I needed that spacer. Will try that and see. Will have to remove the master cylinder to allow it to fit.

One step forward two back. Such is the life of old vehicles.

 

[ginmtb]

I remember reading about the Trollhole carb issue - that was a one batch issue from what I understand. Sorry can’t really add anything more than that @Solace in Solitude

 

[David70FJ40]

Having somewhat of the same problem on my 40. Replaced the Weber for a Holley and now it will not idle below 1100. I do have the insulator installed and will replace the PCV and grommet today.

 

[David70FJ40]

Blocked off the PCV hose and it started right up and the RPM came down. Ran a lot smoother. I need a new grommet and the Toyota PCV isn't available in the US.

 

[Vae Victus]

Blocked off the PCV hose and it started right up and the RPM came down. Ran a lot smoother. I need a new grommet and the Toyota PCV isn't available in the US.

SOR has metal ones I think. Land Cruiser Brake Booster, Check Valve and Hose 7/70-1/98

 

[Vae Victus]

Great news. Sourced an F carb from Mark's Off-road, and finally got it idling.

Having two issues, thought I'd ask:
1. Idle screw isn't long enough to engage the throttle mechanism before it is tightened all the way down. Do I need a different idle screw or should I bend the little pad the screw engages up a little bit to give me some adjustment room?

2. Throttle mechanism sticks open after using the pedal. Some spring somewhere doesn't close it back to idle after release. I can do it manually on the carb just fine. F carb, cable has a barrel stop on the end. Any input on how to get this to return to idle? Stronger spring in the accelerator pump?

 

[Dizzy]

I'm fairly certain that you need a return spring on the throttle shaft.

 

[Vae Victus]

Thanks for the response. Are you talking about one of these two springs? (In the second pic I'm assuming there's a spring under that boot).

 

[emac]

I think you need a throttle return spring like this:

 

[Vae Victus]

Ahhh

 

[thebigredrocker]

I wouldn’t think you’d have to bend the tab for the idle speed screw to reach. There are two other screws you may need to back out so the speed screw can be in charge of the main butterfly’s position.

Looks like the carb side spring bracket is missing. Couple more pics for ya Vae Victus

 

[Vae Victus]

Wonderful photos! Been looking for some photos all night, and you delivered them right to me! Thank you! Looks like I'm going to make a couple of brackets!

 

[thebigredrocker]

I took some measurements of that return bracket Baseline adjustments on a Trollhole carb ('77)

I can take measurements of the other bracket if needed.