engine and drivetrain In the continuing carburetor mystery....

[Mike Self]

Here's my post from last week, with updates and new discoveries...

Here's the setup: 73 2002 with Weber 32/36, manual choke, M10 with about 20k miles on a rebuild, 9.5 pistons, 284 Schrick. Carb freshly rebuilt, no obvious vacuum leaks (tested with carb cleaner and propane). Correct dwell, timing and point gap. Valve adjustment correct. No spark miss (new plugs); good plug wires. Accelerator pump delivers a nice healthy squirt of gas when I work the linkage. Choke goes completely off when the knob is pushed in.

Symptoms: horrible flat spot when accelerating. From a standing start, unless I rev to about 2k before releasing the clutch, the engine will actually stall. Boggs very badly when I shift gears----and if I let off the gas and then accelerate again. The flat spot nearly disappears if I pull out the choke partway but is still there.

Idle's a bit lopey at 900-1000 rpm.

New discoveries:

* adjusting the idle mixture screw has little or no effect on idle smoothness

* uncovering a vacuum port in the intake manifold causes the idle to jump from about 1k to nearly 2k rpm

* tailpipe is black and sooty

* increasing primary idle jet from 50 to 65 had little or no effect on either idle smoothness or the acceleration flat spot.

I'm outa ideas...

mike

[jgerock]

New discoveries:

* adjusting the idle mixture screw has little or no effect on idle smoothness

*

mike

Mike - sorry you are having continuous "gas pains". In my experience with carbs, if you adjust the mixture screw without any change, then the jet is either clogged or the circuit is clogged. Remove the jet, soak it in carb cleaner (spray can cap works great) for a few hours, then blow it out and try again.

Good luck!

[MikeinNC]

Mike

Have you plugged that jet in the top of the carb like suggested previously? Also, flat spot can be caused by incorrect timing, sounds like it may be too advanced, given the lack of effect on idle adjustment. That is my 02 cents worth

See you in 3 weeks

[eastsidebimmer]

Hi Mike, I have an extra Single Barrel Solex and manifold I can send to ya..if I recall, these babies can be fixed while stopped at a red light!

On a more serious note, I have a box full of 2 disassembled 32/36 carbs--if you need a part (or the whole box) just say the word.

-Ben

[Mike Self]

the carb is squeaky clean--no dirt in the idle jets or anywhere else...

timing has been checked and is spot on...

Anyone have a good explanation of how the power valve works--it's that long skinny thing that pokes down through the center of the float...

And Ben, I just may take you up on your offer...the Weber parts, not the 1 barrel!

cheers

mike

[TobyB]

I was actually thinking like the other Mike, too, about timing-

have you checked to make sure the advance isn't doing something

screwey? It's hard to do on a 2002 because of the stupid ball thing,

but if it's retarding or advancing when it shouldn't be, that'll ruin your

idle and launch.

I'm sure you've checked the float level and that you don't have fuel in said float.

Have you made sure the float valve's sealing? I blow air in- yes, with

my lungs.

The float valve should completely block all air... when it's closed.

The idle and progression share the 'idle' jet. Since you're not getting

any idle screw control, I'd suspect something's not working in these

circuits. It could be the throttle plate, too- it should work out that the

plate just covers the progression holes, and as soon as you start to open the

throttle, it starts uncovering them. Perversely, you might have an air leak

in there somewhere (which neuters the circuit) or a gross fuel leak.

I have a new DCOE that's misdrilled- the whole circuit on one barrel was

one- giant- air- leak...

As to the power valve, it's a main- jet helper. When the carb 'senses' little

vacuum in the primary bore, it assumes you've got the pedal on the floor

and lets the plunger in the lid of the carb drop. That drops down

onto the jet in the base of the float bowl, pushing the spring- loaded

pintle into opening it and enriching the main jet circuit.

The most common failure here is that diaphragm gets stiff, and then the

valve opens late, closes late, and sometimes gets stuck in one position

or the other. Or it leaks, and it's always on.

It's worth checking the jet and pintle too, but they seem to be pretty robust.

But that shouldn't be affecting your launch, as the main circuits shouldn't

come into play (much) (enough to kill you) at very small throttle openings.

I'd look carefully at things like the primary bore progression jet holder.

Figure out how it works and how it gets emulsion air, and make sure it

really IS getting fuel and air.

Might also try blocking the jet itself comepletely, just to confirm it's really

delivering fuel!

That nonfunctioning idle screw makes me wonder, too...

hth,

t

[Mike Self]

what's truly puzzling is that the idle symptoms have persisted through a complete carb change--both were extensively gone through, jetted properly and are as the proverbial whistles. And with both carbs, turning the idle mixture screw has no effect on the idle speed or smoothness. I could believe one mis-manufactured carb, but not two!

As for the acceleration flat spot--the first carb didn't do that. But I haven't changed distributors, just checked dwell, point gap, timing etc. So that would tend to discount problems with the dizzy that we aren't noticing.

The other odd thing is uncapping the manifold vacuum port and having the idle speed double....coupled with a black, sooty tail pipe would almost make me think it was running way to rich...

Very puzzling and frustrating...

mike

[Arshloch]

It's running too rich at idle, dumping fuel in there that's why it bogs down and you have no adjustment at the idle- it probably maxed out. It might be something as simple as fuel pressure or the float needle allowing too much gas in.

A lean spot upon acceleration would be a "stumble" (and a backfire on occasion) and "bogging down" is always a richness symptom. The carb runs on idle circuit under 2000 rmp, might have to do with that or the extra fuel gets in there through somewhere else.

[vintage_car]

what about a fuel pressure regulator? If you are getting too much fuel aka black smoke and fouled plugs put one of those regulators inline and see what that does.

I know that if idle mixture screws are bottomed out to hard they will ruin and no matter what adjustment you make it won't work until those are replaced...at least at idle.

[Fishhead]

The other odd thing is uncapping the manifold vacuum port and having the idle speed double.

mike

Vacuum advance dist?

Do you have your dist. advance hose plugged into the correct port on the carb (above the throttle butterfly valve, not below the throttle valve or plugged to the manifold)?

When I had my 2bbl Weber, I had the vac advance connected below the throttle valve and it ran like crap at idle and right over idle. I moved the vac advance to above the throttle valve and it them worked like it should have and got rid of the bog over idle.

[TobyB]

I'm really starting to like the fuel pressure idea-

which means you've checked it, doesn't it?

A mech pump CAN overpower a weber-

we fixed Jenn's rough idle and poor hot- start

with a regulator in the line!

How's compression on your motor?

I'd still check the mechanical advance in your dizzy just to

completely rule it out. If a spring's failing or something's really

wrong in there, it can drive you nuts.

But yeah, sounds like gross overfuelling.

t

[PatAllen]

i had slow falling performance on my automatic 02 recently, idle was constantly going down and hard to start, i took my wonderbox and realized the dwell was totaly off, so the points needed adjustement. idle went back on perfect, but the mixture was a bit lean, performance was still below what i was used too...the base of the carb was a bit loose...

i torqued down the 4 nuts and it went all good after...

i later leaned the idle mixture a bit for more smoothness, with the help of my wide band portable oxygen sensor just thrown in the tailpipe. I made it at 12,5:1 and the idle is puuurfect.

in short , points where bad and there was a vacuum leak at the base of the carb.

[Mike Self]

1. I have a fuel pressure regulator, set to 1.5 psi

2. Pulling out the (manual) choke has no effect on the flat spot.

2a. If I accelerate very slowly, or rev the engine to about 2k rpm before releasing the clutch, the flat spot is minimal, but still noticeable.

2b. stumbling and jerking is noticeable while coasting along at lowish rpms with the throttle closed.

3. Vac advance on dizzy is working, and it's plugged into the correct port

4. Point gap & dwell are fine

5. Engine compression is great--engine has only 18k miles on a complete rebuild.

Any additional suggestions? Wanna get this solved before V@V--has the makings of a good column too...

cheers

mike

[jgerry2002]

When you check the timing with a timing light does the ball appear steady or is it bouncing around?

I've noticed as distributors age, the advance plate can stick, springs get soft and can make the motor do weird wobbly things at idle, and the off idle during transition period when you actually need a timing curve. One second you get too much advance/retard, the next second its fine.

My distributor in my '76 was doing just that, the motor had a weird lope (more like a random shake) at idle that I could never cure. After I sent it away to get rebuilt, he mentioned that the timing was moving all over the place and the advance plate was also sticking a bit.

Tii did a similar thing, idle was fine, idle would fall flat on its face, weird hesitation that was there and then vanish, and it always acted like it was getting too much timing too quickly. Sure enough, new springs and everything was much better.

When was it rebuilt last?

[Bimjam02]

your floats dont seem to be set right in my opinion. in my weber book it says that 3-5psi is the right amount and any more can overpressure your carb making you run rich, since you're sayin you're only 1.5 then it makes me think your float levels are off. it could be that your brass floats sprung a leak and they're full of fuel and extra heavy. could be way off though just offering ideas