Weber 40IDA-- Float Adjustment?

[9146FAN]

Does anybody know...

Using the tube-type float gauge mounted on the side of the float bowl, can the fuel level be checked on the work bench if using the corect fuel pressure?

Or does this type of float-gauge need to used when the engine is running?

I have all new paint etc. on the engine and really don't want fuel dripping all over to check / adjust the floats.

Is there a different method to check / adjust the float level with the carbs off the engine?

Thanks for any expert help.

[Steve@Rennsport]

Hi,

I use the tube-type float gauge to measure and set correct levels with the engine running on the dyno or in the car.

I use the factory Weber tool to measure and get the float levels close when the carb is on the bench, however its no longer accurate due to changes in gasoline's specific gravity over the past 4 years.

Bottom line: Use the tube-type guage as thats FAR more accurate for today's fuels.

[steve911T]

I did it on the bench. Bought a 10' piece of fuel hose and removed the carb, sat it on the bench, hooked the line to the fuel source (car) and to the carb, turned ignition on and adjusted the float levels. Keep in mind, obviously, that the hose lines must be secured via a hose clamp or whatever due to the imminent danger of now, not only burning up your car, but maybe even your garage and house. Good luck. Steve

[1QuickS]

I've found that the floats have a little divot where the needle valve contacts it. If the divot does not match the contact point of the original needle upon installation then there can be some erratic seating of the needle. This is why I remove the divot prior to setting float levels. I've also found that no two floats have identical geometry and I've never seen any with OEM geometry; OK, maybe a couple that were close. This is why I reset the float geometry before reassembly, to help assure shims are nearly uniform and the little tab (where the divot is) is orthogonal to the needle valve when installed.

Bench setting is good as a start but a RUNNING engine is best as the vibrations help to settle out the components which WILL stick a bit and provide inconsistent readings. Also, after a rebuild and some miles accumulated the floats need to be checked as they will have settled into their new positions and new little divots will be established, all of which will change float level settings.

Paul Abbott
Performance Oriented

[9146FAN]

Thanks guys for your replies. It is clear that you guys have way more experience than I do.

My carbs are New (NOS) so they don't have any divots in the float-tabs.

Just a few more follow-up questions;

What is the measurement from the top of the float-tab yo the top of the open lower housing? I do not have the Weber tool (which I assume is a kind of metal template).

What will the running characteristics be of the engine if the float level is too high or too low?

Thanks again for the assistance.

[1QuickS]

Get a float gauge. Anything else you do is inaccurate. You will have the four floats holding fuel levels at different heights which determines when a main circuit is activated, it also controls the progression circuit; result is four different main circuit timings.

The mechanical info for the days when gasoline was leaded, etc.:
-height of float above top of throttle body = 12.5 to 13.0 mm
-tab should close float needle when it is 18mm below top of throttle body

If you want, I'd suggest initial shimming using a nominal 0.060" thick shim below each needle valve. This should get enough fuel into the bowls to start the engine without flooding the carbs. A general rule of thumb I use: the distance between the top two lines on the vial are equivalent to 0.010" shim thickness, more shim equals more fuel in the bowl.

I send a picture of my float level gauge modified to allow dumping of fuel without draining onto your hor engine. I installed a brake bleed valve in the brass plug.

Paul Abbott
Performance Oriented

[ryangray]

1QuikS (or anybody), can you be more specific about the symptoms of improperly set float heights?I seem to have an incurable rich-spot in my transition circuit (just above idle, just below about 1/6 throttle). I am wondering if this is the culprit.

Thanks so much,
RG
1973 914 powered by 2.7(s) w/ 40ida-c3's

[1QuickS]

Hi Ryan,

NOS IDA's? What size idle jets are you using? 55's would be about right for your engine at sea level.

Have you used the recommended external float gauge to check the fuel levels? If not then you are only guessing what the problem may be; you need to check/adjust fuel levels to eliminate a variable from your potential problem list.

You can catch the fuel in a little cup when draining the fuel bowls and put a shop rag down there to catch the dribbles if you're worried about fuel getting on your paint.

Also, check fuel pressure at the carbs while the engine is running; it needs to be right at 3.5 psi. I've found that fuel pressure is dependent upon the voltage delivered to the fuel pump (if there isn't a fuel pressure regulator) and that voltage varies between a non-running and a running engine so fuel pressure will vary accordingly. If the fuel pressure is not constant then the fuel level in the bowls will not be constant. You may set fuel levels with the engine shut off but when running the fuel level will increase which will lead to fuel delivery being different than expected. Also, a running engine allows the fuel delivery to cycle the delivery check valves open and shut thereby eliminating (mostly) any stiction that may give false readings when floats are set staticly.

Paul Abbott
Performance Oriented

[ryangray]

Paul, thanks for the reply, sorry for the slow response. These are'nt NOS, they have been sitting on the shelf of a dude's shop for x-number of years. I did put 50's back in for idle jets...oh and I did a complete tear-down and rebuild of them last night / today. I put them on my motor when I swapped it into my 914 a month ago: It has never run right for me: that's probably an important point so thanks for asking (I am running an MSD 6aL box, and pertronix at the distributor).

Bought the float tool, measured floats, they're good. Cleaned all passages, inspected and cleaned all jets and other brass bits. Rebuild accelerator pumps, re-assembled, put back on car. No change at all. Checked fuel pressure, it's roughly 3.4. turned it down to 2.5 just to see what happened, no change. Tried three different spark plug heat ranges, no change.

I'm really out of things to check (on the carbs anyway)!Still have the dead / rich spot between just off-idle and 1/6 throttle. I did notice that in my transition circuit, I do have three progression holes in each hole. Is that normal? I though I remembered reading that this is a popular "mod". Really any input here would be great: I've been chasing this for three weeks now.

Thanks guys,
Ryan

[911pcars]

This is kinda basic, but you didn't mention checking the accelerator pump output. Does each throat display a squirt of fuel when the throttle opens? It's a quick check (with engine OFF).

BTW, Using a PMO float gauge, you can only check the float levels with the engine running, so that's not a valid method of initially setting up the floats. Reason why: If the fuel level is too high, excess fuel must be drawn from the float bowl before realizing the correct setting. Paul's nifty modified PMO gauge allows sneaking up on the desired level while on the bench.

However, if initial setup is attempted on the engine and the fuel level is not close to spec, e.g. high, excess fuel may flood the engine and create a potential fire hazard, or equally disturbing, hydro-lock a cylinder with raw fuel.

Typically, with new components (float, needle valves, gaskets), use the mechanical gauge to arrive at a ballpark setting . Thereafter, use the PMO gauge while running the engine to observe, then fine tune by adding or subtracting needle valve spacers.

Sherwood

[1QuickS]

Hi Ryan,

My web site has a picture of the stock progression holes for IDA and IDTP carbs, three holes are standard on the 40IDA3Cs but are configured differently:

Tuning the Weber Carbs

By the way, what symptoms are you experiencing that makes you believe your carbs are rich at the partial throttle position? Flat performance would indicate the idle jets are too small. When at idle is there a dull popping from the exhaust? Do the carbs sneeze under light to moderate throttle openings? These indicate lean idle jets.

You can check for progression circuit idle jet selection using the following procedure:

• set handbrake, start engine and balance carbs with engine at operating temp
• adjust both idle speed stop screws 1/8 turn "in" and balance carbs
• repeat 1/8 turn adjustments until main circuit is activated (you can look down the auxiliary venturi (use a mirror or safety glasses!) to see fuel begin delivery or just quit the procedure at 2500 to 3000 RPM)
• the speed adjustments should result in corresponding engine speed increases both up and down the rev range with screw adjustments
• there should be no faltering in engine response and should be responding smoothly
• change idle jets until the best one is found and install the next size larger for the final selection

This procedure assumes floats are set at the correct heights and the fuel pressure is 3.5 psi.

If fuel pressure is changed after float height setting then the float levels will change.

Hope this helps isolate your issue which is a progression circuit/idle jet selection issue...probably! ;-)

Cheers,

Paul Abbott
Performance Oriented

[ryangray]

Thanks Paul, I've spent a lot of time on your site, really good stuff. What makes me believe the dead spot is rich is the copious amount of black smoke in the dead zone, and plugs exhibiting carbon fouling. When I use the technique you describe, slowly increasing throttle opening using the idle seed screws, I do definitely get the dead zone behavior. This happens no matter which idle jets i use and no matter how i set the timing. What else could I be missing here?

[1QuickS]

OK Ryan,

I'm getting close to empty here...the only sources of fuel delivery are (assuming good condition carb bodies as in no cracks through the walls):

• from the idle mixture hole
• from the three progression circuit holes
• from the main jet via the auxiliary venturi

The mains deliver fuel through a hole in the throttle body wall, above the level of the fuel in the float bowl and into the auxiliary venturi. By physics there isn't enough air velocity through the main and auxiliary venturis at 1500 RPM to draw fuel into the engine for an engine of the displacements we have. Higher float levels would lend to an earlier main delivery. Have you checked that the auxiliary venturis are installed correctly; not inverted (had to ask) and their keeper springs hold them in intimate contact with the hole in the throttle body wall? The auxiliary venturis can have a poor fit at this interface which would have fuel seeping down the throttle body wall in additon to the fuel being delivered properly through the aux venturi. Inverting the aux venturis can be achieved if a previous owner has filed the edges of the rectangular ends to allow inverted installation.

Have you checked for blocked air correction jets for the idle circuit? A blocked air corrector will enrichen the progression tremendously. I use four fuel level gauges during my work (simultaneously) and check that after the floats have been set and the engine is shut down that the fuel levels remain as adjusted. If there is a blockage of the idle air correctors then fuel will siphon out of the fuel bowl and into your cylinder, emptying the fuel from the bowl. These jets can sometimes be blocked by a gasket that has a "dangling chad" that blocks the air hole and seals it closed; otherwise some crud can block it. You can check individual bowls for draining by moving the sight glass from bowl to bowl and letting the engine run and then let it rest to monitor fuel levels.

By the way, what size are your venturis? Idle jets? Mains? Emulsions?

Dat's all folks; Good Luck!

Paul Abbott
Performance Oriented

[ryangray]

Thanks Paul, I double checked the aux venturis: they are right-side-up. My idle air correction jets (the pressed in lead ones) appear to be clear (I cleaned them pretty well when I had the carbs apart last week). The carbs are balanced pretty well, but I am going to go through the linkage setup outlined on your website...I am reaching for anything now. If all else fails, would you advise increasing the size of the idle air jets (by reaming)?

[1QuickS]

Hi Ryan,

Give me a ring so we may discuss this off line.

Paul Abbott
Performance Oriented
530.899.8371

[ryangray]

(copied my own post from another thread below)
I have spent the last four months troubleshooting my webers on my 914-6 2.7 conversion. The symptom was a very rich spot just off idle up to about 1/5 throttle: independant of RPM. I tried a bunch of jet / venturi / timing / fuel pressure combinations and could not fix it. I even tried plugging one of the three progression holes to see if i could lean it out, it was still rich in the progression circuit. I rebuilt the carbs twice, did a ton of research and just could not figure it out. This morning, i found one sentence on a Triumph forum that solved my problem: "make sure the idle jets are seating correctly".

You are probably all familiar with the idle jets and idle jet holders. The jets slide into the holders with a friction-fit, and the holder screws into the carb body. The tapered end of the idle jet needs to seat in a cone inside the carb, or fuel will just pass around the jet.

The fix: When you put your idle jet in the jet holder, DONT PUSH IT IN ALL THE WAY! Make sure you have a good friction fit between the jet and holder. if you don't, use a small screwdriver to pry the "legs" of the jet apart just a touch. Push the jets about .1" into the holder, and install the holder into the carb. Now, when you tighten the holder down, the jet will bottom out and seat in the carb as needed. The friction fit will keep the jet in position.

If you have a rich condition at idle / progression, try this. It's easy, free, and will probably make a difference. For me, it was a total transformation.