4100 slight surge

4100 slight surge

Bob P.
Bob P.

August 8th, 2010, 2:45 pm #1

I have a 66 T-Bird 390 with a c5sf-a i installed. The car runs great except for a slight little surging at speeds above say 50. Set the primary float at 7/8 and secondary at 3/4 wet. Primary jets are 48 f with a h-k booster. When i pulled the booster i noticed the outer tubes are not in tight if it matters. I have a plain h booster if loose tubes are a problem also a set of 54 jets, Don't know if thats to much of an increase or if jets are even the cause? Any suggestion? Thanks Bob
Quote
Share

Lee
Lee

August 12th, 2010, 1:02 am #2

on my big Merc w/390. The carb came stock with 49 primaries and 60 secondaries. Also, the pri. booster should be a KD. Sounds like a lean surge so I would go with some 50F in the front(54s probably too big) and recheck. The newer oxygenated fuels contain less energy per volume than the "old" fuel the carb was designed for so going up 2 jet sizes might just be the ticket for you.
Quote
Share

Bob P.
Bob P.

August 12th, 2010, 11:11 am #3

Lee, Thanks for the response. I'll order a set of 50f. Also i could pull out the outer brass tubes on th primary H-K booster pretty easy. Does that matter? I put a little lock tight on them whem i put them back. I have a Plain H booster. Could this be used if needed. Thanks Again BOb
Quote
Share

WerbyFord
WerbyFord

August 12th, 2010, 4:26 pm #4

The tubes help form the emulsion of fuel and air. If they are loose, air could leak in at the top and lean the mix out like an added air bleed. A loctite seal should hold em I suppose.

As far at the "H", the fastest 4100 carb I have runs an "H" booster, but it is a stock c3af-t. Would the "H" run the same in the c5sf-a carb? Well, those 1.12 carbs are all the same, except for the little holes, that is......

So if the remaining holes in the c5sf-a body are "close" to the holes in the c3af-t body then it should work. Easy enough to try!
Quote
Share

Lee
Lee

August 12th, 2010, 5:56 pm #5

IIRC, the "H" is a sec. booster N/M
Quote
Share

WerbyFord
WerbyFord

August 12th, 2010, 6:48 pm #6

This "H" came from my c3af-r carb, but the c3af-t has an "H" in front also, with a "BA" in the secondary.

Maybe the "H" was used in the secondary of the super-rare double-pumper 4100? (LOL)
Quote
Share

Bob P.
Bob P.

August 12th, 2010, 9:54 pm #7

Yes, I did pull the H booster out of a c3 primary.
Quote
Share

Lee
Lee

August 13th, 2010, 3:05 am #8

as in '65 and '66...which cover the Mustang, Falcon, Comet and Fairlane only. The "H" was used in the sec. for certain 289s only. Looks like the "H" really had some staying power/versatility.

I just took a look at my 4300(C8AF-B)...don't remember where I got it...and noticed it has secondary throttle plates about 1/8" bigger than the primaries. Is this true of all non-D 4300s? ...or is it a "D"? Also, did all 4300s have manual secondary throttle plates and a vacuum operated "choke" plate on top?
Quote
Share

WerbyFord
WerbyFord

August 13th, 2010, 3:09 am #9

I have a 66 T-Bird 390 with a c5sf-a i installed. The car runs great except for a slight little surging at speeds above say 50. Set the primary float at 7/8 and secondary at 3/4 wet. Primary jets are 48 f with a h-k booster. When i pulled the booster i noticed the outer tubes are not in tight if it matters. I have a plain h booster if loose tubes are a problem also a set of 54 jets, Don't know if thats to much of an increase or if jets are even the cause? Any suggestion? Thanks Bob
Ok I had my c5sf-a on the car today. It was surging and transition gasping on our 289 Stang and I am trying to sort it out on a 250-4v 6cyl.
With G3G (maybe that means G?) primary and AB (VB or upside-down A B) secondary boosters:
It runs very lazy when floored, I feel like getting out to push to help it accelerate. Surges a little at cruise about 40mph or 2000, same with or without vac adv.
Not sure if these G3G and AB boosters are stock or not.

So, I pulled the H primary and B secondary boosters from a good c3sf-b carb and put them in the c5sf-a.
Now the c5sf-a:
Accelerates pretty good to the floor. That is just seat of the pants, no timeslips yet. One problem solved.
But, it surges worse than ever. Other problem worse.

I will play with it more but just as a caution, if you try the H booster it maybe worse!

I show a KD booster as stock for the c5sf-a, but yours is a KH????
Quote
Share

Lee
Lee

August 13th, 2010, 3:26 am #10

Yep...KD pri, BA sec for C5SF-A N/M
Quote
Share