Carter 750 float level

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fshd4it

fshd4it

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I've got a Carter 9755s (750) that I'm giving a once-over before it gets put back in service. Almost zero use, it's been sitting on the shelf for ages. It has the spring-loaded needles, float level was right on at 5/16" (per the Carter instruction sheet I found) "With only the weight of the floats on the needles". It also states "Do not press needle into seat when adjusting float lever" but when I do, gently, there's only 1/8" +/- between the float and the gasket. I've got my regulator set to 5.5 psi, but it's got me wondering how that won't overcome the spring and push the floats almost up to the gasket, which seems a bit high. Especially since the Edelbrock instructions call for a 7/16" gap, with solid needles. A I've read that float level on these carbs is pretty critical, I'd feel better with input from those more experienced than I (which won't be hard) before I put it all back together. TIA.
 
Just throwing this out there, I know he does a little Carter work on occasion, he may have a definitive answer @RRR
 
With the weight of the floats resting on the needles, they're really close to parallel. I'm going to run it like this, and keep an eye for any flooding or other strange activity.
 
I have never found the f/level to be critical with these carbs. I believe the spring loaded n/s are for off road use & I would replace them with solid n/s, more reliable. Edel ones fit, but the std ones are 0.0935", a bit small if the engine has some grunt. 0.110" would be better in that case, Edel #1466.
 
I saw them advertized for off-road use, I'm sure you're right. And they are .0935. The Carter sheet shows both types, but no mention of differing float levels, which was what got me thinking about it. With the float pressed down (or up, I guess), there's just a whisker of light between the float arm and the sheetmetal plate that sticks down from the lid. Mike's Carb is about a 10 min drive from me, could I just replace the needles? Entire assemblies probably aren't that much though.
 
The actual float level under running conditions is controlled by n/s seat & fuel pressure. Change either one or both, and FL changes. One good thing [ & about the only thing I can think of ] about the brand H carbs & clones is the sight window in the bowls for accurately setting fuel level. Carter published a chart [ which I have ] which gives you the reqd static FL adjustment change reqd with changes in fuel pressure & n/s seat. I cannot understand why the Edel carbs use such a low FL setting when they come with 0.0935" n/s; especially on the bigger 750/800 cfm models which are touted for performance. Such a small n/s size, you would expect the FL # to be smaller so that the fuel level is at the correct level in the bowls. Only reason I can think of for such a low fuel level is less fuel slosh during cornering. Another chart from Carter shows the fuel flow for n/s size/fuel pressure. For the 0935 n/s it is 48 gal/hr @ 5 psi, enough to support about 570 hp, with no margin for error. If fuel pressure drops or A/F ratio is rich, it will support less hp.

Do not adjust the floats parallel!

The float arms soldered to the float body. I have seen variations in the exact position where the arm is soldered on. So using the parallel method could be unreliable.

The n/s size needs to be balanced against sufficient fuel delivery to supply the engine & maintaining the correct f/level. A large n/s will admit more fuel, but fuel level/flooding is harder to control. A 0.110" is a good compromise for most perf engines.
 
Just another Einstein who likes to here himself talk. Set them parallel and be done with it. Should you have any trouble (highly unlikely ) report back.
 
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Carb's going on tonight or tomorrow, and I'll start getting it tuned in (to the best of my abilities, which are mostly based on searches here). No road testing for a while, still have to finish a few things on the car.
 
From memory the 9755s is a Federal Mogul Carter carb and used the short primary booster from the 625 Carter. Because the booster is shorter it wont receive the same vacuum signal and so it will achieve primary booster flow later. If you raise the float level it places the fuel level closer to the booster outlet helping it begin quicker.

Also if you go through the Carter literature you will find that they state different float heights for different needle and seat sizes. The larger the size the lower the float level.
 
I'm pretty sure this carb is circa '97 or '98, and hasn't been used since then. It's new enough to have the Weber W cast on the top. I compared the primary boosters (without removing them) to the ones in my 1406's and a Carter 625, and the main difference i saw was the end of the brass tube in the 750 booster was open on the end, while the ones in the smaller carbs had a covered/ domed end. If it makes a difference, I'll pull them and get a better look. I searched for some better Carter literature online, but haven't found much besides, or better than, general rebuild instructions. One thing I was considering, is taking a float from the 750 and one from a 1406, and seeing if they're the same physical size?
 
I have seen two float styles used, a larger float with corrugated sides & a smaller one with plain sides. Not sure if the f/level is the same for both, but I would stick with the floats that came with the carb & set the f/level to the stated amount. If it ain't broke....

On the bullet shaped brass nozzles in the Edel pri boosters. I remember seeing Edel advertising these as giving better performance. Although they didn't state it, the impression was given that it was Edel's idea...
The original AFB on my 66 GTO had these type of nozzles, 20+ yrs before Edel started making AFBs.
 
Finally got the carb on the car last night. On startup it was pulling fuel through the boosters until I opened the choke plate about 1/3 (electric choke). Manifold vacuum was about 5" at 750 rpm. Idled for a minute or so, then died and wouldn't restart. Motor came with the car, I know almost nothing about the internals, but the cam's somewhere in the .480+" range with a good bit of duration. IIRC initial is 16-18 degrees, MSD 6al & billet non-vac advance distributor. I'll try it again later, lots of other priorities while I'm home this time.
 
I start with the floats parallel too, but I always toss the spring loaded needles in the ditch.
 
I'll pull the top, replace the sprung needles with solids, and try it again. I put the lighter (yellow) springs in for the rods, they are staying down at idle at least. Will I get into the main circuit at idle? I'm hoping I can tune some more vacuum into the engine, I just want to get it up and moving at this point.
 
That is veeeeeeery low vacuum. Try advancing the timing [ turning the dist ] with the engine idling. If rpm increases, it wants more idle timing [ your vac will have increased also ]. Depending on the type of harmonic dampener used, timing mark could have slipped & given a false indication of the timing.
 
Bewy said:
That is veeeeeeery low vacuum. Try advancing the timing [ turning the dist ] with the engine idling. If rpm increases, it wants more idle timing [ your vac will have increased also ]. Depending on the type of harmonic dampener used, timing mark could have slipped & given a false indication of the timing.
Click to expand...

Great point! metering rod carburetors DETEST low vacuum signals. It makes the metering rods bounce all to hell at idle and it's almost impossible to tune out. I agree with looking at the timing. Where do you have initial timing set?
 
Timing is 16-18° if I remember right. My fancy Craftsman timing light decided to crap out yesterday, need to find another dial back that works with MSD. I put yellow 4" springs in, so the rods are stable. I checked TDC with a piston stop and put timing tape on the balancer a while back, now need to go find my old school light.
 
Some odd numbers...
5" of vacuum at 750 rpm sounds really odd. If the low vac is due to a big cam, would have expected to see a higher idle rpm.
Is the vac gauge accurate ? Are you sure you are measuring vac at the correct place? It needs to be below the t/blades. If unsure of the correct location, use the PCV port on the carb; you may have to neck down the hose for the reading.
What can you tell us about the engine specs? Auto or manual Trans?
 
Nothing is set/adjusted at this time, didn't run it long enough. Timing/tach light died on me as well. Normally it idles about 900, automatic, don't know much about the motor, it's the only part of the car I haven't had to go through, but probably soon. Saw fuel being pulled through the primary boosters, figured I'd lower the fuel level and swap the needles to solids & see what happens. When I can get back to it, of course.
 
Rather than start a new thread, figured I'd just bring this one back around again. Why would I have fuel down in the secondary counterweight wells? Same Carter 750 AFB, the floats are set parallel after switching to solid needles, and I'm using a Holley blue pump with a dead-head regulator set to 5 psi. I noticed it after trying to start the car (this thing's still kicking my ***, I can almost write a novel about what I've done so far), so I ran the pump twice today but haven't seen any fuel pooling up yet...and there's none dripping down into the manifold if that matters. I have 3 other engines with 625 AFBs, checked them all, none seem to have this issue. They have mechanical pumps on them, however.
 
There is a LOT of BS written about fuel pressure for Carter [ & Edel ] 4 bbl carbs. I have cranked up the pressure to 12 psi as a means of richening the mixture, no problems at all, no flooding.
Your problem could be warped body or airhorn, poor gasket seal, or assuming the f/level is correct [ 1/4 - 3/8"]....& most likely: the steel needle & seats. They just never seal as well as Viton & if they leak, you get flooding. Are you using steel because of alcohol fuel? Somebody must make alcohol compatible Viton needles.
 
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