Weber carb rebuild

Michael and friends,

I have been monkeying with a friend's 63 Scout. It was running poorly, and so we decided to rebuild the carb (weber 32-36). The rebuild seemed to go well. The Scout started right up, idled well, no hesitation anywhere, ran smoothly. So far so good. However, the spark plugs indicated that it is running leaner than before, and it has lost some of its top-end power. The only difference I could detect between the original setup and the rebuild was the needle seat. The original was marked "250" and the new one was "200". That is the only difference I could detect. We went back with the same jets. Could that needle and seat make it run leaner and lose power? I am scratching my head on this one.

Pineneedle

Been awhile since I last scruud with the weber mixers.

My various weber references all show a 2.00 (200) needle/seat assembly for that carb version john.

I have a kit for one now in stock (empi brand) and it also contains a 2.00 seat.

The only weber of that similar series which uses the 2.50 (250) needle/seat shows to be the 38/38, a carb which has a somewhat higher flow rating for larger displacement motor apps.

As long as the fuel level in the bowl is adjusted correctly, I can see no way that the needle/seat can create the condition you describe. If the fuel bowl is being run "dry", then you would experience an extreme surging, just like running out of fuel! In actuality, the carb would be running out of fuel!

If you did not alter the main jets or air correction jets, then I'd suggest that the power valve is not being actuated when called upon. Under increasing load (drop in manifold vacuum), the power valve "opens" which enrichens the mixtures for both venturis by approximately 20%.

So test the power valve actuator/system for proper operation.

It's very possible that this carb had issues in the past and someone tried to bandaid it with a higher flow volume needle/seat...but that would not correct for faulty power valve operation.

Michael,

as usual, thanks so much for the quick and informative response. Now: I hate to be such a rookie, but how would I check the function of the power valve, and how would I check the fuel level in the fuel bowl?

The only odd symptom that has occurred post- rebuild is: when going up a hill in high, under full throttle, sometimes it will abruptly miss several times. As soon as I back off the throttle, all is well. Maybe that doesn't mean anything. She is an old girl and cranky from time to time. I should mention that the distr. Has a pertronix in it.

Pineneedle

John, tomorrow I'll tear into a weber I have here that is fresh and take some pics and do a little write-up for setting the fuel level (float height). Same for testing the power valve system.

I do have a Holley 5200 ( a weber 32/36 clone, kinda!) torn apart now that is real nasty and is not a good example for training purposes! But the weber I have should be near identical to the unit you are working with.

What you describe regarding missing under heavy load is exactly what the power valve system is designed to compensate for! And the terms for that system sometimes include "economizer" circuit...those concepts are one and the same, no matter which manufacturer's carb you are dealing with.

Stand by, I'll be back.

Let's look at analyzing the power valve system on the 32/36 weber dgv and it's variations...

Looking at the manifold side of the throttle body, you can see the manifold vacuum signal port used to actuate the power valve.

There is a near identical port on the opposite throttle bore that has a nipple for connecting any accessory that needs a manifold vacuum signal to operate. On this particular carb I have that port securely capped.

This shows the channel which is fed by the manifold vacuum signal that extends through the main body and onto the top where it meets the carb top cover.

Here is where the manifold vacuum feed interfaces with it's companion drilling in the carb top.

And through the carb top you can see the channel which transfers the vacuum signal to the power valve actuator itself.

When the engine is running at idle and manifold vacuum is highest, then that spring-loaded actuator remains retracted. Thus that complete circuit must retain manifold vacuum at all times with no "leakdown" being acceptable.

Here is the replacement power valve actuator contained in a typical rebuild kit for this carb series.

This item is nearly identical to the same part used in a Holley 1904/1906/1920 series carb and it's operational design is exactly the same.

Here is the actual power valve element. It's threaded into the fuel bowl adjacent to the primary and secondary main jets and must be submerged in liquid fuel at all times.

The purpose of this valve is to increase the liquid fuel supply to the emulsion/feed systems in the carb body in response to increasing engine load. Thus the main jets supply a relatively lean mixture for the idle/pullover and accel pump systems. When engine load conditions are increased, then a drop in manifold vacuum allows the power valve to open...increasing the liquid fuel supply by approximately 20% as compared to the main jet calibrations alone.

This item is a simple, spring-loaded needle/seat and unlike other versions used in some Holley carbs, this one does not have any internal vacuum diaphragm that can fail with exposure to fuel over time.

Using the smallest tapered "needle" tip adapter in the mityvac test kit, insert the tip into the actuator feed port in the carb top and hold firmly to create a seal, while stroking the mityvac.

If the actuator is ok, then the piston will retract in response to an increasing vacuum signal applied with the mityvac. Approximately 20"hg of vacuum can be applied with the mityvac, same as the typical vacuum level created in the intake manifold at idle.

Repeat this test several times while watching the actuator piston to detect for any intermittent operation.

If it will not hold vacuum, then the diaphragm is leaking and the actuator must be replaced with a fresh one.

Another shot of the test setup...

When replacing the actuator with a new one, start all three screws with your fingers and then push down on the piston to retract it fully. While holding in that position, then tighten the three retainer screws.

That allows full flex of the actuator diaphragm with no binding, this is a very important installation point for any similar vacuum actuator replacement.

This actuator will begin to "move" (allowing the power valve to initiate opening) at a manifold vacuum signal of approximately 12"hg.

Michael,

the photos and explanation are remarkable. I am stoked to pull the top of the carb tomorrow and check all this out. As it turns out, I even have a mityvac, so I am ready to roll. Thanks so much for taking th considerable time and trouble to help me with this.

Pineneedle

Michael,

I took the top off the carb tonight and ran the test that you have outlined above. It worked just as you described, without any bleed down.

So, where does that leave me? Could the main jets be too small? The ones in it are a 150 and a 160.

When I took the top off the carb, the bowl was about 1/3 full of gas. Does that sound about right? How do you check/set the float level? Sorry to be such a pest.

Pineneedle

The main jet numbers you posted are actually about two steps richer than what was installed in that carb when originally manufactured, so someone has been inside scruuin' with it.

Here's a page that describes the float setting for the dg-series mixers. This shows the float height and the float drop...both settings are important on any carb, not just the weber.

Have you removed the power valve from the fuel bowl and verified it opens and closes freely with no sticking?

Fuel level in any carb is critical and has a direct bearing on idle mixture settings due to the weight of the fuel in the bowl acting on the jets. And certainly if the fuel level is too low, the bowl will starve leaving the jets and power valve momentarily uncovered allowing an extreme lean condition to occur until the bowl refills.

The same condition occurs when the fuel tank(s) vent is restricted, the fuel plumbing is restricted, fuel pump is going south, fuel pump output is too "low", etc.

These carbs have many variable adjustments that can be made to calibrate for a wide range of applications. I'm certainly no expert on these as I've only played with a few of 'em and found them to be very tedious in set-up.

The primary reference I use for the weber stuff is:

"weber carburetors"
one of the hpbooks publications authored by pat braden, isbn: 978-89586-377-5.

That publication covers all the various weber mixers commonly used in aftermarket/high performance applications. It also addresses the Holley 5200 licensed variation which weber refers to as the "emissions" carb, model 32/34 dft. Many of the junkyard 5200 carbs have ended up on IH 152/196 motors (the so-called pinto and vega versions) like this one:

http://www.forums.IHPartsAmerica.co...e-I-4-engine-carburetion.html?highlight=weber

Is this the same carb we messed with in this thread?:

http://www.forums.IHPartsAmerica.com/carb-tech/1800-weber-questions.html

If so, then back then we were working from the standpoint the mixer was way too Rich...exactly the opposite condition from where we're going right now.

Michael,

well, I reassembled everything. Here is what we have: idles fine, runs smooth without any flatspots, runs really strong in first and second as you get the rpms up. The only lack is the ability to "pull" in third gear. On a grade, it just gives way and you have to downshift.

A couple of things occur to me. First, it is cold here, and I know that it is harder to push a cold machine than a hot one. Second, I have messed so much with this that I am beginning to lose track of how things were/ought to be. Maybe it isn't as bad on the top end as I imagine. I mean it runs so well otherwise. Sigh.

Finally, I have a question about the secondary barrel. When that opens up should you be able to feel it? As far as I can tell, there is no discernable increase of power or acceleration when I put the throttle all the way down so as to open up the secondary. Maybe I am expecting too much.

The bottom line is that it runs fine, all things considered whereas it would hardly run before the rebuild. My friend is happy. So count your blessings, so to speak.

Thanks for all your help, patience, and instruction. I have learned a lot about this little carburetor, and that is a good thing.

Pineneedle

That weber 32/36 carb design has a somewhat unique, mechanical linkage for control of the secondary butterfly. And it's billed as a "progressive" 2v mixer...but...it's normally mounted on a single hole manifold/four cylinder engine. It is not a true "two barrel" carb. So you must look at the entire setup as a single venturi carb or a "1v".

A true 2v carb feeds an intake manifold with a split plenum (or so-called dual plane) where one side feeds two cylinders and the other side feeds the other two cylinders. In most cases (not all) a carb setup like that has a small "crossover" passage either in the carb base or the intake flange that allows a bit of equalization across the two venturis that provides a much smoother idle quality.

So the weber opens the secondary venturi in direct command from the "cam" action provided by the throttle actuation mechanism. Because the primary and secondary sides of that carb are nearly identical and have all circuitry as found in a 1v mixer, when the secondary bore begins to open it should be indiscernible if all circuits and mixtures are correct...simply a linear increase in power produced with no "kick" at all.

That single design concept is what makes this carb so usable on low ve (volumetric efficiency) engines with a common plenum intake that would normally be "overcarburated" at tip-in/low engine speed/cruise. That is the only reason it works so well on these IH fourbangers, it's certainly not a very sophisticated mixer but was developed back in the 50's for very utilitarian, low horsepower, eurotrash econoboxes. And it's number one application these days is on air cooled v-dub stuff where when combined with significant engine modifications involving greatly increased ve, it's a perfect mixer that allows street use of a near full-race motor spec!

The same multi-venturi design is utilized in a 4v application by having the secondary venturis operated by a vacuum setup such as the Holley concept, or using a counterbalanced "air valve" control such as the carter afb/avs series (or the edelbrock clones) or the spring-counterbalanced air valve onna rochester quadrajet. But those carbs operate on split plenum manifolds (usually dual plane) except when installed on aftermarket manifolds used only in drag race/circle track stuff.

Any multi-venturi carb/manifold combo that has a discernible "kick" when the secondary venturi(s) is fully activated (either mechanically or by vacuum/air flow) is simply not set up and calibrated for the engine which it's installed on. The secondary side should come into the picture in a very smooth, undetectable mode. You will hear an increase in air intake noise of course, along with a significant increase in power available at that throttle opening.

As long as the subject engine at test speed is not simply:

a) running out of fuel in the bowl due to low pump output or restricted fuel system plumbing.

B) jetted way too Rich (fouling plugs) or jetted way too lean (surging).

C) has a restricted air filter (resulting in super-Rich condition).

D) has a restricted/non-op fuel bowl vent system.

E) the ignition system is not optimized.

Then it will rev freely up to the point where the hydraulic-control valves "float" due to over-rev (near impossible regarding a stock IH motor). These motors are very asthmatic and tend to self-govern above about 4200rpm, they simply cannot breathe due to the design of the head/valve system.

Before sending this rig on it's way, I'd advise that yawl do the "powertime" deal described here:

http://www.forums.IHPartsAmerica.com/ignition-tech/2122-ignition-power-timing.html

Since ya installed a p-tron, I'd venture that the base timing is not optimal for this motor and it does not have enough advance. Disregard any "spec" for timing...you don't have a stock engine any longer! If you have a hill to pull in third gear, that is even better...simply go wot and listen for ping, then back the distributor advance off just a hair until the ping is eliminated under heavy load and ya got the best timing point.

Once the timing is set, then go back and adjust the idle mixture (and curb idle speed) one last time...it did change!

Also john...the ambient temperature where the vehicle being operated has nothing to do with what you May be experiencing. Once the engine is fully warmed up at any ambient (at least 20 minute run time), the ambient air temp is inconsequential regarding this deal. Yes...for a full-built race motor (drag strip app), air temp/density is very important to "tune" for, but not in the case of a 152 tractor motor-powered Scout 80!

For the record...I do run the 195f setpoint thermostat of the correct rs370 pattern in all these motors. No matter if the "small" radiator or the later version, "large" unit. These engines are not difficult to cool and the 195f stat greatly improves heater performance onna stocker.

And most importantly, that stat allows the engine oil to reach it's optimum operating temp (after a 20 minute minimum warmup).

If the engine in question happens to be the earliest version with the one-piece, cast aluminum water neck/stat housing, then that situation is different, those engines most likely have a functional heat crossover also unless they have been "updated". Those do not use the rs 370-pattern stat.

Unless the engine you are dealing with is a very early item, it does not have a functional exhaust gas crossover to pre-heat the intake manifold, that May add a bit to engine warm-up time, but is certainly of no consequence drivability-wise.

Michael,

again, many thanks. I'll tell you what. If nothing else this has made for an awesome and instructive thread. I hope maybe some other boy-idiots such as I can benefit from it.

Pineneedle

Michael,

Christmas and all the visiting family kept me away from the problem that we have been talking about, namely, the lack of top-end power with the newly rebuilt weber.

I finally was able to get back to the project, and I fell upon the solution, or at least a solution that made a big difference. By chance, the tape holding the magnets in the pertronix "wheel" (don't know the proper name) broke, scattering the little buggers through the distributor. Several went under the plate on which the pertronix sensor is mounted. So, I had to take that out and find the magnets. Success and luck, I found them all. But here is the payoff. While I had the plate out, I began poking around inside the advance mechanism. It turns out that the parts were so gunked up, springs rusty and frozen, that nothing would move except under great pressure. So, I cleaned that all up, freed the mechanism up so that the parts moved easily and the springs flexed easily. When I put it all back together, and ran it, wow! What a difference. So, it turns out, the problem was not in the carb at all. I learned a lesson there. You wouldn't think that those parts could get so fouled up, protected and all as they are. From now on, I am going to repeat this procedure on a regular basis.

Pineneedle