2 bbl carb adapters

[thinman56]

well, in my limited spare time i been trying to figure out why my motor won't rev past 4,000 rpm. my home-made adapter has been suspect because it's got kind of a 'shelf' at the bottom as opposed to the clifford adapter's tapered shape. so, i tried the clifford, and although the car does seem to run a tiny bit smoother, it still would not get past 4 grand, so the adapter is not the problem. thought i'd post a couple pics and this result, as i know there are some different shaped adapters out there. the lower profile of my adapter does allow the cool edelbrock air cleaner to fit under the hood, which the clifford does not.

cheers

 

[cfmustang]

Dumb question, but does it get past 4,000 RPM in neutral? That would rule out the transmission.

Also, is your linkage allowing the full range of the throttle on the carb (i.e. are you getting WOT)?

Sorry, if you have answered these before...

 

[MustangSix]

some things that can limit rpm other than basic mechanical design:

1. exhaust plugged

2. Not enough ignition advance

3. Not enough fuel above 4000

4. not enough air (I think this is ruled out)

5. not enough cam

6. bad fuel

7. bad ignition (not enough spark to support higher rpm, bad module, bad coil, bad wires, bad plugs)

8. not enough throttle (linkage not opening the blades far enough)

 

[Anonymous]

Try to rev it above 4000 rpm by hand at the throttle. I use an advance light with a tach readout to watch RPM.

 

[thinman56]

actually, there's a whole string about it titled 'tuning questions - kinda long'. i have tried all those things, vacuum goes to almost zero, it just maxes out, in the driveway, uphill, downhill, under load, even with the old dizzy installed. 3.5-4 psi fuel pressure all the time, 13.2 volts all the time (ran gages in the interior for road test. it's possible that 4K is all i get with the existing compression and cam. this winter there'll be more motor work, and by spring i'll have a whole new set of mysteries.

as david s. always says, welcome to the journey.....

 

[Junk-Falcon]

sounds like

 

[thinman56]

junk - the motor was rebuilt before i bought the car, so i assume it's all stock except what i've done to it. this winter i'll balance the bottom end, ARP fasteners, FSPP 264 cam, etc. thanks for feedback....

 

[Anonymous]

Ok, first post.....

I'm sure you've checked, but is the throttle plate opening all the way?
Is the fuel pressure sufficient at WOT?
Timing correct?

When I had a 200" six I ran an Offenhouser adapter with a Rochester two barrel off a '63-'64 Buick 250" aluminum V-8.
The only time I had RPM trouble was when the valves would float. It would rev right up and then fall flat on it's face.
At what RPM? No idea. No tach.

 

[pedal2themetal45]

Are you sure it opening all the way??
have some one step on the gas pedal all the way to the floor (motor off of course) and look down the carb an see if the throtal blade is streight up and down... (all thw way open) Thats where I'd start if its not popping or shaking when it at top speed or 4,000rpm per say. If its popping and sutf I'd say timming or maybe fuel starvation, vacuum advance?
Tim

 

[thinman56]

yea, the blades open all the way up. because it happens at the same rpm under all different conditions, i've been focused on air flow. valve float (springs) is the other thing i'll check this fall when i take it apart.

 

[pedal2themetal45]

So your saying if you sit in the driveway and mash the pedal to the floor and hold it there it won't go pat 4 grand??
tim

 

[Anonymous]

well, in my limited spare time i been trying to figure out why my motor won't rev past 4,000 rpm. my home-made adapter has been suspect because it's got kind of a 'shelf' at the bottom as opposed to the clifford adapter's tapered shape. so, i tried the clifford, and although the car does seem to run a tiny bit smoother, it still would not get past 4 grand, so the adapter is not the problem. thought i'd post a couple pics and this result, as i know there are some different shaped adapters out there. the lower profile of my adapter does allow the cool edelbrock air cleaner to fit under the hood, which the clifford does not.

cheers

I have a HOLLEY 2300 2bbl with the clifford adapter and have one of those " cool Edelbrock" air cleaners. Mine fits just fine.

 

[wallaka]

Every car is different.

 

[Anonymous]

Every car is different.

Isn't that the truth.

 

[thinman56]

hey, sweet 66, looks like you have the low-profile type air cleaner. check mine below, it's one of those thick foam jobs, too tall.

to answer the other questions, yea, sit in the driveway, go to full throttle, goes to 4 grand and spits and pops and vacuum goes to zero. back off and it recovers in a five or ten seconds and runs normal.

nice lookin' 66 by the way....

 

[Anonymous]

The 14" X 3" filter that came with the Edelbrock air cleaner was just a little too tall. It just barely rubbed on the bottom of the hood. So I went with a 2" filter instead and solved the problem.

 

[Stubby]

Have you tried it with out the air filter?

I would suspect the valve springs.