Stock 77-Flat spot in acceleration (1 Viewer)

Joined
May 22, 2002
Messages
75
Location
Sherwood Oregon
OK the vitals...

Stock 1977FJ40 with straight 6 2F motor and stock Aisan carb

If your watching Pinhead, thank you sooo much for the youtube videos on the rebuild of an Aisan Carburetor! Priceless!!

PerTronix ignition
New coil
Fairly new plugs and wires
Newly rebuilt carburetor - Hygrade kit
Slow jets were both #70 (odd??)
Primary main jet #124 (Brass)
Secondary main jet #171 (steel)
Power vlv was an 070 not sure what the kit had in it (didn't realize there was a number on it until reading about it here)
Both of the venturi's were the same (2 rings) made sure they went back to same place though. The secondary had a small dent in the edge but very small
New secondary diaphragm and tested
New power piston
New float needle seat and float adjusted to spec @ 7.5mm/1.1mm
Idle mixture screw when removed 2.5 turns out (returned to this setting and have not changed it)
New fuel filter
Installing a new air filter tomorrow(Old one you can still see light through)
Has stock charcoal canister


Since I bought her over 10 years ago she has always had a flat spot in the acceleration about 40mph. At least I could floor it and get a secondary but gas is expensive! The weird part is I could get to the flat spot I could feather the throttle slightly and it would find a sweet spot and get slightly better. Now that I rebuilt the carb I do not have secondary it seems and when I am at the flat spot if I let off slightly it accelerates a slight bit??

Starts first or second crank
idles Perfect and runs great until higher speeds then its just flat meaning little acceleration unless floored and even then not much.

I replaced things one at a time along the 10 years (don't drive it much due to this issue) and about 8 years ago bought a carb kit and finally made the leap (why did I wait so long??)

So reading threads we come to vacuum...
Bought my first vacuum gauge today and hooked it up at the manifold (thankyou edwjmcgrath!), the 3 port gizmo/fitting in the manifold. The first reading I was getting was 8!! Hmmm think per other posts this should be much higher... 15-22 perhaps...

So I cut the ends off of these three hoses and rehooked them back up (they were not too tight and could be stock hoses). The vacuum reading jumped to 15 (or dropped depending on who your talking to). At this point before we go too much farther I plan to replace them all now as there are probably about 30 connections that could be loose but my question is due to the rats nest is can I get rid of some of this stuff???

Pics below and if you see something that looks odd please chime in (How do you add more than 3 photos? Respond to my own thread?)

Can I remove a bunch of these lines that may not be required? Am sure they are there for some reason but it looks to me that the designer had a hose salesman for a brother in-law.

Can I get rid of A or B and if so what do I do with the lines that go there?
What is box C?
Seems like I read that I need to have the air filter on when checking vacuum is that right?


Thx,
Pwelco
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Joined
May 22, 2002
Messages
75
Location
Sherwood Oregon
Oops, forgot for jetting suggestions
live at 1000ft elevation and usually wheel at 3500ft

Cheers!
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Last edited:
Joined
May 22, 2002
Messages
75
Location
Sherwood Oregon
Input please??

Wanted to bring this back to the front.

I replaced all the lines, well I ran out of hose after buying 21 feet! It was all they had so probably needed 30...

In any case can anyone tell me if I can eliminate any of this vacuum hose rats nest that isn't important to the vehicle running? I would like to simplify things to eliminate vacuum leak potential.

I was able to bring the vacuum up to 16 at idle here at 1000ft but still is not rock solid. The needle moves back and forth about .5, idle mixture?

It now runs a lot better than when I had only a reading of 8, but still has this slight flat spot at about 40 but way less noticable. Any insight as of what to check next would be grand.

I also inadvertantly screwed with the wrong screw for idle instead messing with the ummm accelerator pump adjustment I believe. Can anyone tell me what I would see if that were out of wack? Perhaps limit my acceleration? It looks like it should have about 9.5mm of stroke per the manual. Any other suggestions on adjustment there would be appreciated.

Thx,
Pwelco
 

John Smith

In the garage
Joined
Jun 7, 2004
Messages
4,278
Location
Maryland
In your pictures A, B, and C are all emissions components. If you require emissions in your area, you will need all of them. Did you verify that you have all your emissions hoses hooked up correctly? I think I see at least one hose doubled back on your VSV, aka C in your picture.
 
Joined
Feb 6, 2002
Messages
15,233
Location
OC, CA
A is the vacuum surge tank for your power valve. It is operated by C, the VSV. Not sure what B is.
You want the PV to work, so either keep the OEM controls or hook it up to manifold vacuum.

You manifold vaccum sounds low. That could cause the flat spot. Did you check for vacuum leaks? Is there fuel coming out of the primary nozzle at idle?
 
Joined
May 22, 2002
Messages
75
Location
Sherwood Oregon
Good point on the line connections John, and no I have not. The one picture is not that great but the line you mention has a loop is actually a tee that continues on to ?? Will have to print out a schematic and have a look... Anyone have a link to the best schematic for this? I have found a few in here...

Hi Pin_Head you are a movie star ya know!
I didn't actually check for leaks yet by spraying something around, what is your preferred method? I did replace the hoses though. Can't believe how much hose it took!
I'll have a look at the primary at idle once I figure out where that is located exactly. I should be able to do that. Thx!!
 

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