Ol No.5, aka "Thunder" is a '69, f-100, 4x4, SWB, no smog no a/c, And it has a new 390!
But I had a hard time getting the carb adjusted. Its a stock 2 bbl from the original 360 (Autolite 2100?) and would idle pretty good but was starving under load.
Finally I used a vac guage to set the idle screws and its goes down the road pretty good but I had to back the screws out 4-5 turns to get a good and fairly steady 18# or so of vacum.
EVERYTHING on this engine is either new or rebuilt, its all stock except for hi vol oil pump and generic RV type cam. There appears to be no vac leak, I'm just worried why I had to open the idle screws that much.
Sooo, do I need to get a bigger main jet? Should I look harder for a vac leak? Or should I just shut up and drive it until I get enough chips for the 4bbl.
By the way, thanks to all you guys for the great info you've contributed here, this is what the internet is REALLY all about!

Mike

P.S.: Ol No.5 is now called Thunder because the first time it fired (with a loose exhaust pipe), my wife, who was in the house visiting with her mom, said, "Oh, that sounds like thunder!" and her mom said, "No, I think that's Mikes truck!"

 

It sounds like you need bigger jets. What do your plugs look like. White means too lean. Black is too rich. Need to be a medium brown to gray.

 

I've only gone a few miles, but BEFORE I opened the idle screws they were pristine white. I think I would have seen some tan coloring, wouldn't I?

 

Yes, the plugs should be a tan or orange/brown
color, you probably need larger main jets, as
the carb came off a smaller engine.

Steve & the Rockette
'63 F100
'68 F100
'72 Capri 2L
'73 Capri 2.6L V6
'73 MG B GT 2.6L V6(Ford)
'98 Contour SVT 2.5L V6 (Mods)
'01 ZX2 (No Mods yet)

 

power valve (restriction) may need checking.
Is the float level correct.

Did you wind open the idle screws to fix idle or cruise ?

Usually when you put a big engine under a smaller engines carb it sux harder and you have to reduce main jet size.

But because it sux harder you may have the throttle in a different place and you may not be reaching the transfer slot, or you may have passed it.

I've done this before and found that the big engine just suxed so hard that there were 2 fixes a bigger cam or the right (transfer idle slots different) carb.

 

your idle circuit should be unaffected by main jet changes, you dont want the main circuit pulling fuel at idle. Also lately I've heard that with unleaded gas you need to read the plug behind the ground electrode as this is the spot to check for coloring of the plug

 

Thanks for the input guys!

OK, bear with me, The idle mix screws DON"T affect the carb when it's off idle - that's why they're called IDLE mix! - Right?

So when I adjusted the screws way out to get good vacum at idle I couldn't have improved how it runs down the road - is that right?

The only explianation then for why it now runs better at speed is while I was tinkering around with the idle mix and fidiling with plug/point gaps, timing, etc. to get a better idle, I fixed whatever was wrong to begin with!

I guess I'm back to my original question: Is my only concern to have a smooth idle with good, steady vacum, regardless of how far out the screws are?

BTW, I pulled off the top of the carb last night to check the float level wet (which was OK) and the main jets are "58"'s. The Chilton Book calls for "54"'s on a 360 OR 390!

Thanks again
Mike

 

 

>Thanks for the input guys!
>
>OK, bear with me, The idle mix screws DON"T affect the carb
>when it's off idle - that's why they're called IDLE mix! -
>Right?

wrong
They still provide fuel - why would they stop all of a sudden

>>So when I adjusted the screws way out to get good vacum at
>idle I couldn't have improved how it runs down the road - is
>that right?

wrong

>The only explianation then for why it now runs better at
>speed is while I was tinkering around with the idle mix and
>fidiling with plug/point gaps, timing, etc. to get a better
>idle, I fixed whatever was wrong to begin with!

maybe

>I guess I'm back to my original question: Is my only concern
>to have a smooth idle with good, steady vacum, regardless of
>how far out the screws are?

no - if they are out of spec somethig is wrong


>BTW, I pulled off the top of the carb last night to check
>the float level wet (which was OK) and the main jets are
>"58"'s. The Chilton Book calls for "54"'s on a 360 OR 390!

this isnt reverse idle is it ?
ie the idle screws meter air not fuel

>Thanks again
>Mike

 

>your idle circuit should be unaffected by main jet changes,
>you dont want the main circuit pulling fuel at idle.

where is the idel restriction of this carb type
what about the power valve restriction


Also
>lately I've heard that with unleaded gas you need to read
>the plug behind the ground electrode as this is the spot to
>check for coloring of the plug


doesnt unleaded produce different colours for the same conditions ?

 

[updated:LAST EDITED ON 25-Feb-02 AT 02:39 PM (EST)]OK, so opening the idle jets DOES add fuel above idle and so PROBABLY DID helped the lean condition.

Then if I SHOULD worry if I've opened the idle mix too much, could somebody tell me what the max adjustment SHOULD be, so I know how much to worry?

And while I'm getting an education, I understand what the accelerator pump does but what does the power valve do?

BTW, since I just replaced the power valve with the rebuild and cleand everything good, I wouldn't think that's a problem.

Thanks for the help
Mike

 

idle circuit works while there is vacuum under the throttle blade

idle screw adjust idle port fuel flow

idle restriction (jet) feeds idle screw and transfer slots

main jet may be working at cruise maybe not (holleys do most cruise on the idle jet ie they are WOT carbs)

main jet feed main venturi during cruise and medium throttle.

power valve restriction (jet) supplements main jet below a nominated vacuum

power valve enables the power valve jet