48 IDA fuel level

[Eljaro]

The Weber tuning manual says that the fuel level inside the main well should be less than 5-6mm below the nozzle bottom edge. It explains how to measure this parameter with the help of a Vernier Caliper and a Flashlight.
On anothe hand there is a procedure with special tools on how to adjust the correct float height, which is 5.5mm for the float (not the central ridge) above the lower carburetor body.
If the float level is adjusted to these 5.5mm the fuel level in the well will be somewhere between 10.5 and 12mm, which is not what it should be according to the Weber Tuning Manual.
I am having problems with slight intermitent hesitations or misses when driving with the engine between 2500 and 4000 rpm at a steady speed. It is subtle but clearly can be felt as if the engine would be slightly breaking and going again.
I have checked my ignition, changed the 6AL box and bought a new distributor pickup, even made a new shielded cable from the AL6 to the distributor, with no success.I even have a ground cable going from the engine direct to the ground terminal on the battery.
Under the timing light the timing fluctuates at those engines speeds slightly, maybe 2 or 3 degrees retarding over the 36º set for maximum. The belt also starts to slack up .
I have tried everything up to now with no success.
I suspect that maybe this has to do with the fuel level and some improper aireation of the mixture. I tried to rise the fuel level to reach those 6mm below the nozzle hole in the well but I started getting gasoline dripping out of the pump jets.
The engine idles great, does not backfire or sneeze, accelerates fantastically and goes generally very well.
Only this hitch with this stop and go feeling when driving a steady speed above the idle circuit speed range.
What should the fuel level really be? Any suggestion as to what is causing this missing at medium engine speed?

[carmine]

Hello Eljaro.
If i remember correctly in the weber book by John Passini he states a measurement of 5-12mm below nozzel edge.
Have you checked what your air fuel ratio guage reads at the 2500-4000 rpm.

[DMXF]

Fuel level relative to the AV passage is the primary parameter. The measurement in many manuals referencing the top of the float is a secondary parameter derived from the AV passage method intended to be easier to measure. If the fuel level is too high, fuel would come out of the venturi. If fuel is coming out out of the pump jets, then it sounds to me like the check valves may be bad in the jets. If you have more modern made webers or newer jets in older carbs, that may be the cause, because there have been many problems with new weber part quality (leaks, etc), incl with needle valves.

[Snakebit]

I would look elseware for the problem. If the float levels are close, there should be a steady supply of fuel with the fuel pressure set to just under 3 psi. At a steady run, I don't see where an intermittant skip would be float related.

[Rick Parker]

From my experience of Weber carb tuning (Small block) if the engine accelerates well, idles well, but has an intermitant "Skip" (for lack of a better word) while at cruise it is related to the emulsion tubes and the cruise A/F mix. With foot to the floor and low vacuum, the E tubes have little to do. While at varying degrees of part throttle and higher manifold vacuum the fuel is being emulsified at varying rates within in the main well.
Is this constant when a certain RPM and light throttle is reached??? Is it heard in the pipes, more than felt? If so, bring it to that RPM in 4th gear, for instance 2500-2800 RPM; then apply VERY VERY light throttle while attempting to accelerate slightly. If the symptom stops, (listen to the pipes) it can be remidied by a slightly different E tube. (Eliminating some of the small lower holes). In my case going from F7 to F16 solved this symptom without any resulting jet changes.

Eljaro you have admitedly done an unusual amount of experimentation with E Tube modifications, perhaps you are overworking one system in lieu of another???

I don't think the fuel level change is causing your concern. If so, it would be apparent throughout the entire RPM range, with more dramatic symtoms.
You might also check the distributor cap for ionization or carbon tracking.

[rokndad]

Stefan,

Our KC 427 FE engines are almost identical from what I recall, and I was running the F15 emulsion tube and also experienced some of that hesitation and stumbling at cruise which was driving me crazy. A/F ratios were in the high 13's and I though everything was good, since it accelerated like a striped ape.

But like Rick said, it's the E-tubes that get the fuel to cylinders through the mains at cruise/steady state. Go back to your F11's or a tube you've used before in the same family. My gurgle and hesitation at cruise speeds (3,000 to 4,000 rpm) pretty much went away with the F11. I'm running 145 mains with 120 correctors. Had too much popping with the 200 correctors. Give it a try.

Tom

[Eljaro]

I have been all day trying out different combinations of emulsion tubes and jets. Since my A/F gauge only shows rich, I went out to check the combustion looking at the plugs.
I noticed that the two front cylinder plugs ( 1 and 5) read rich, and all the others lean. I did change the front main jets from 140 to 135 and the rear ones to 145 with no improvement. I changed all except 1 and 5 to 150 and still the same result.
I think the rear cylinders are getting less air than the front ones. So I proceeded to cover up the scoop and went out again, still with the 135 mains on cilinders 1 and 5 a nd 150 on the rest.
Well, the plugs have all the same dark brown color now ( it got dark so I coiuld not see the difference very well, but it was close) and the hesitation , stop and go feeling was gone also.
I will do more testing with the covered up scoop, but I think that it has to do with air flowing to fast over the Weber trumpets the feeding air uneven to the eight throats.

[rokndad]

Stefan,

Still running the F15's as well, or did you swap out to the 11's? Mine won't run at all on the F15's without exibiting that steady state hesitation. Pops like crazy with an F7. The F11's are the only ones they seem happy with.

I only notice one little slight hesitation at acceleration in 1st gear only, between 1800 and 2500 rpm and Rick Parker thinks I need to go down on my Idle Jet Holder from the 120 to a 110 or so. Just haven't gotten around to doing that. Let us know how your testing turns out.

Tom

[carmine]

Emulsion tubes that do not emulsify fuel and air very well will also give you the stop and go feeling you discribe.

Trumpets with sharp edge at outer leading edge tend to cause a lot of turbulance to incoming air entering the trumpets
That turbulance multiplied more so on the first 2 trumpets that are exposed to the scoop opening
Turn the scoop around (cowl induction) problem solved.

[priobe]

The reason why the F11 tube works well in many set ups is because the idle circuit is on the rich side, or it is just exactly the proper mixture for that setup.

One test you can do if you feel that the your fuel level is too high (depending on the etube) and you are running an electric pump is shut down the pump. If you are experiencing the problem say between 2000 - 3000.

This will lower the fuel level, uncovering the holes on say a F16, this will let you know you will need to lean out your emulsion tube or lower you fuel level.

Also, try to stick to the same diameter tube and concentrate on the hole level. By changing to a different tube say F7 to a F11 or F16 is like making multiple changes because each of these tubes are different diameter with holes placed at different heights. There is not common ground with any of the mentioned tubes, so how do you know what you have changed compared to what you came from.

This is why I posted a thread last week about emulsion tubes, which I guess was not interesting (sorry).

I have been experiementing with this for awhile now and with a 245 /250 and 680 lift camshaft, I am able to lower my idle jet to 70 (holder) and 60 fuel.

On the LM1 my reading are 18 A/R at idle and on the gas/underload I go to 2000 rpm it goes to 13.5. ( no popping)

On 2000 to 3000 I get 12.2 then goes to 11.8 above 3000.

I am experiencing no pops at all except on decelleration and then it is only 2 or 3 pops then it is fine.

Find an open road and play with your circuits.

Also,I am running a 55 exhaust valve. I also noticed that if you think you are holding the gas pedal steady to not engage the pump circuit, then you might be mistaken.
The slights movemement will engage that circuit throwing you off.

Many people say to use a blocked bypass but I prefer to tune the carbs without the aid of a pump jet. and only use the pump jet to fill in only if needed.

[Eljaro]

Took the car out today with the hood scoop covered. Drove with the F15 tube, then changed to the F11, which seems to be a tad better. The ride a cruising speed was smooth and the the constant brake and go feeling was gone.
All plugs were the same color, including number 1 and 5.
Water temp is a round 80ºC and oil temp 100ºC with the hood scoop covered.
TEmp used to be 75ºC and 90ºC. So the scoop does help with cooling.
Well, maybe it has to do with the emulsion tube, so I removed the duct tape from the hood scoop opening and went back on the road.
All of a sudden the car felt like a bronco wanting to throw you off. The same constant hesitation, constant braking action I noticed all along before.
Definitively it is the hood scoop which is no good for the Webers. Too much turbulence or to fast air flowing over the trumpets.
I will fabricate myself a deflector for inside the scoop to divert the incoming air downwards and I will go back to my self made emulsion tube, which otherwise seemed to have a perfect transition, which the F11 is not so good at.

I'll keep posting what comes out of this.

[Tom Kirkham]

The 289 FIA Cobras had a stone shield in the hood scoop not to keep rocks out, but to make the airflow more turbulent for the Weber carbs. Seems without the stone guard the two end cylinders would not be happy. You might want to try something similar before giving up on the hood scoop...

[Caprimaniac]

Hmm. Interesting.... If you take a look at my 48 IDF tread, you will see i've experienced the same thing: Hesitation around 4000 rpm....

As I discovered, also running a large front intake scoop, closed at the rear, the carbs were ice cold ( and so was the engine) last night running with an AF meter.

I stopped to warm the engine, oil got into 70 (centigrades) and then I took off; full throttle in 2. and 3. (7500 rpm- 180? km/h?) and then 4. .... near 4000 and started misfire/ unfire? and behave really strange. Then back in 3. and same thing happened.

I took some carboard and put in front of radiator and engine temp got up to normal. Next run, then in 3. everything worked just fine; 100% the engine ran much better than the "cold run" earlier on.

But what caused the misbehaviour? E- tubes? Icing?

Runes.

[jhirasak]

Eljaro and Runes,

I recently purchased a 48 IDA setup for a 289/302 small block and it came with carbs made in Spain. Upon first installation, I had problems with fuel flooding in the carbs after shutdown and decided to check the float levels. Upon inspection of the float needle ball height (25mm) according to the 48 IDA drawings, it was found that my carbs had different heights varying from 25mm to 25.6mm. To correct this variation, I sanded the needle seat gaskets on the offending carbs so they all were at 25mm. Next, I checked the carb top gasket to find that it measured from 3mm to 4mm depending on the location measured. If I subtract the gasket thickness from the needle ball height (uncompressed), I arrive at a float tang setting height of 24.7mm instead of 24.2mm as indicated on the drawings. Since the float setting height of 5.5mm to 6.0mm above the carb body is controlled by the float tang setting amplified by a ratio of approximately 4 to 5, I want to make sure that my assumption was correct. Anyway, I set the tangs all at 24.7 mm, reassembled the carbs, filled the bowls using the electric fuel pump, and measured the height of the gas in the main jet well as described in the Weber Tuning Manual using a vernier caliper and a light. In all of the carbs, the levels were between 42.0 to 42.7mm from the fuel to the top of the well on the carb body.

My questions to the both of you are 1) is the assumption that the tang on the float should be set to 24.7mm valid, 2) are the carbs made in Spain supposed to use the float setting dimensions given in the 48 IDA drawings, and 3) is it common to find the needle seat variations on a new set of carbs?

John

[cobra 53]

Hi John,

Not easy to explain the variation regarding different measurements.

But I think: Maybe it depends on the time the carburators are produced.

Before or after the siesta time .

Hasta luego, amigo.

Rico

[Snakebit]

Set all the floats at 5.5 to 6 mm from the top of the carb body.

[*13*]

I set mine at 6. Had them at 5.5, no noticeable difference. I had a similar hesitation but went away with main jet change. I have the rock guard. Funny thing was that I was a size above & a size under with the main jets with the same hesitation symtoms. I put the inbetween size in for the hell of it & it went away.

[Earl J]

Originally Posted by Snakebit

Set all the floats at 5.5 to 6 mm from the top of the carb body.

+1, I use the Gene Berg #GB552 Float Height Gauge tool to set the floats.

Cheers,
~Earl J

[*13*]

I second the Gene Berg gauge. They are good people too, call & order one.