Carb tuning and frustration...

[gregnash]

Ok I am finally breaking down as I really want to figure this out.
This time last year when I rebuilt my topend I also rebuilt the carb. Since then I have had an on-going issue with tuning the carb so that it will HAPPILY idle below 1k rpm.

Used the proper kit from Kurt at Cruiser Outfitters and replaced the secondary diaphragm at that time with a NAPA one. BeBe runs great but just will not hold a consistent idle down around 650rpm like she used to.
Now this isn't saying that I cannot get her to idle down at 650rpm, she just won't do it happily, idling smoothly and what not.

This has finally gotten to the point where it is starting to piss me off as I know it is eating gas because it wont idle right. I spent the last two days adjusting the timing and everything per the manual but still cannot get it to idle below 1k consistently.

Anyone got thoughts or a good way to baseline a carb for tuning?
Current setup...
- truck is fully desmogged minus recurved dizzy and carb
- idle is set to right at the BB when vac advance is disconnected and plugged
- Fuel mix screw is at exactly 3 turns out from just barely seated
- idle screw seems to be just touching the arm

So at this point I am not sure where to turn next other than pulling the carb for a second rebuild to see if something is stuck/sticking or completely swapping out for a trollhole.

If video is needed I can see about putting something together.

 

[mattressking]

Do you have a vacuum gauge? Check to make sure you're holding at least 16inHg. Ideally you want to be holding right about 20inHg.

What are you using to measure rpm, gauges or clip on tach on coil wire?

 

[gregnash]

Yup... vacuum is a consistent 17inHg all the time, mind you I am at 4650' so that is supposed to be really good vacuum.
RPM is measured using the stock gauge but just remembered that I have my dads old school tach/dwell meter so going to try and hook that up tonight to see if it truly is idling high. She definitely sounds like it.

 

[NeverGiveUpYota]

Idle screw 'seems' to be? When I was really eyeballing my carb on my deck table I could finally see the seat of the screw on the plate it pushes. Are you 100% sure it's where you think it is?
And the Idle Mix screw can be pulled and carb sprayed into the hole just to be sure there isn't crud in there.
And @masonbarnard finally pulled his and was surprised to find his throttle butterfly totally locked up flat. Could be something like that is happening?
Or maybe as I also found on mine the kick plate for the secondary is bent. I've yet to mess w/ it since I'm still waiting on the manifold anyhow...
And the diz... if your not recurved would that cause the carb to be unable to fully adjust to where it could be?

 

[gregnash]

As best as I can squeeze my head back there to see. So am I 100% no, but probably 85% sure.
And that is actually a good idea, I may try pulling the mix screw all together and spray some carb cleaner down there to see if anything may be lodged.

Ultimately I have a feeling I am going to need to pull the carb and see if something jumps out at me that is either binding or bent or something else.

 

[HemiAlex]

Don't make me say it.

 

[masonbarnard]

Haha oh god

 

[HemiAlex]

Trollh....

Ah never mind.

 

[gregnash]

Trollh....

Ah never mind.

Shut it you! I don't know that it is necessarily the carb, not showing me anything that is a "smoking gun" as of yet. But yes, that is an option that is drawing ever closer. Other option is to bite the bullet, when I have more money, and go with a TBI kit from AFI.

 

[Output Shaft]

Hmmm I don't know. I drove my cruiser 250,000 miles (25 years) on the original carburetor and never touched it & it always worked fine (until the secondary diaphragm eventually dissolved).

I think once the carb is rebuilt completely and correctly you'll never have to think about it for the remaining life of the truck.

 

[NeverGiveUpYota]

Hmmm I don't know. I drove my cruiser 250,000 miles (25 years) on the original carburetor and never touched it & it always worked fine (until the secondary diaphragm eventually dissolved).

I think once the carb is rebuilt completely and correctly you'll never have to think about it for the remaining life of the truck.

Aye aye!

 

[Cruiser Jimmy]

I had to go out 5 turns for the idle mixture screw at my elevation.

Compression is even at 150psi?

 

[mwebfj60]

What level did you set the float at and was it a new float? I had trouble with a NAPA float once when it was set at the spec drop level, it would hit on that little metal bowl divider so it never would push the needle all the way closed. That caused all type of idle issues.

 

[mwebfj60]

Have you pulled the canister purge line off the port below the carb and capped that inlet? Quick easy check.

 

[NookShneer]

Check the return spring on the back of the carb. Mine was getting "lazy" and I would drive with RPM's up to 2500 and when I let off to idle the spring didn't have enough "chutzpah" to return the mechanism to idle. It made for an interesting time in Downtown Seattle rush hour traffic.

 

[jfnall]

Careful with that mixture screw. I think they are NLA. The brass is very tender.

 

[gregnash]

I had to go out 5 turns for the idle mixture screw at my elevation.

Compression is even at 150psi?

Compression was 130ish across the board when I measured back in October. I need to measure again.

What level did you set the float at and was it a new float? I had trouble with a NAPA float once when it was set at the spec drop level, it would hit on that little metal bowl divider so it never would push the needle all the way closed. That caused all type of idle issues.

Didn't touch the float when I rebuilt the carb. It was left alone and the fuel level is within normal spec.

Have you pulled the canister purge line off the port below the carb and capped that inlet? Quick easy check.

Nope that line is still connected.

Check the return spring on the back of the carb. Mine was getting "lazy" and I would drive with RPM's up to 2500 and when I let off to idle the spring didn't have enough "chutzpah" to return the mechanism to idle. It made for an interesting time in Downtown Seattle rush hour traffic.

Which spring are you talking about Nook??

Careful with that mixture screw. I think they are NLA. The brass is very tender.

Oh yeah it's head was slight jacked from the po but still works fine.

I took some time and messed with it some more tonight. Got the old RPM meter and sure enough the stock tach is about right on. I even went as far as to do like @NeverGiveUpYota suggested and pulled the screw completely and shot some carb cleaner down the hole.

I reset the mix to 3 1/4 turns out and started over again. Got it to down around 800rpm with the timing advanced only a little bit. I ran out of light so I didn't get to test run it.

 

[NeverGiveUpYota]

He's talking the horizontal spring for the throttle (both on the firewall side). Mine was missing one altogether so I picked up a box of mixed universal ones at napa and cut to fit one.

 

[NMfjCruiser]

There is a saying that 90% of carb problems are ignition related.
Just saying since you've checked the carb over so thoroughly, are you sure you are getting consistent spark at low rpm?

 

[gregnash]

There is a saying that 90% of carb problems are ignition related.
Just saying since you've checked the carb over so thoroughly, are you sure you are getting consistent spark at low rpm?

That is actually something that I have not confirmed... But why would inconsistent spark result in a higher RPM?