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agouge888

New Weber 32/36 a little suggish

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Got the new Weber installed and it seems to work great, with one exception...it’s a little sluggish on takeoff. I know these 620’s aren’t powerhouses, but this thing is pretty sluggish. I can stomp the gas and I’m 0-60 in about 45 seconds.  Mid range seems pretty good, but off the line it’s just sluggish. It has all new gapped plugs. New points are  gapped at (19). Weird because when it’s idling and I blip the throttle...It rev’s great...very responsive, clean, and crisp. Any ideas?  

 

Thanks,

 

Andy

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 This is a progressive carb and not like the stock one. At about 2/3 throttle the secondary begins to open. Jamming it too fast, opens too much and the engine can bog. It's the nature of this carb. Try half throttle for the count of 3 and then floor the rest of the way. Experiment opening the secondary slightly slower. You'll get the feel of it and not even notice that you are driving the carb.

 

The stock carb only opens the secondary if needed. A vacuum signal does the work and if not going fast enough nothing happens. As soon as load and RPMs are sufficient the vacuum operated secondary begins opening.

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Yup.

I've looked at machining the DGV to use a separate accelerator pump for the secondary throttle, as there is the basics for one already cast into the body.

You would have to duplicate the circuit up to the discharge point, but add a separate nozzle for that throttle bore, and add a cam on the throttle shaft.

All quite doable.

But it all amounts to turd polishing a over hyped Spanish economy carb, that sells for way too much.

Good for a stock replacement, not so good far a performance build.

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Well, I wouldn't go that far....

 

Down side:

Does not accept the stock air cleaner so has no provision for ATC... the modulation of the inlet air temperature by blending cold outside air and warmed air from the exhaust manifold keeping it at around 100F all year round. Biggest advantage of ATC is it will never suffer from carb icing. Strictly controlling the air temperature makes the engine run consistent all year round with good economy.

 

Does not bolt on, needs an adapter plate and gaskets.

 

Progressive secondary. Comes in too soon forcing you to drive it progressively to avoid bogging or poor mileage.

 

Italian carburetor, not a direct replacement designed for the L series engines. Will work, but so would a lot of 2 bbl.carburetors. 

 

 

 

Up side:

Larger primary/secondary 32mm/36mm than the DCH 340 carb 30mm/34mm L16/18/20B carbs so some extra CFM available.

 

Simple, less complicated. 

 

 

 

 

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Great carb for a farm truck....

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11 hours ago, G-Duax said:

Great carb for a farm tractor....

 

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I stopped by a friends to listen to his truck that I diagnosed over the phone as having a vac leak. It has one of these carbs, and ir wouldn’t hold an idle under 1,500-1,700 rpms. Tried plugging off all the vac lines one by one and restarting it each time. When The engine warmed up the carb had a high pitch squeal that doesn’t stop. It looks to have a vac diaphragm plunger on it. Do you know if they rupture or leak they’re prone to  cause a leak and a squeal?

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I have run the Weber 32/36 on 4 cylinder Datsuns since the 70s and no they are not a performance carb.  If you wanted a performance carb you should have purchased the 38/38 Weber. 

 

First are we talking about a true Weber or a Chinese knock off.  If you have the cheap Chinese Knock off you have a great paper weight.

 

Edited by Charlie69
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ck the motor timming. like the cam position at TDC and what is the distributor timed too also..

 

Is this elelctric choke or manual? maybe choke is still on or partial ON.

 

These carbs are fine for a basic upgrade over a worn out 45 year old Hitachi. 225$ for a new carb is still cheap to keep a car running for years

Edited by banzai510(hainz)
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On 3/14/2019 at 8:22 PM, agouge888 said:

Got the new Weber installed and it seems to work great, with one exception...it’s a little sluggish on takeoff. I know these 620’s aren’t powerhouses, but this thing is pretty sluggish. I can stomp the gas and I’m 0-60 in about 45 seconds.  Mid range seems pretty good, but off the line it’s just sluggish. It has all new gapped plugs. New points are  gapped at (19). Weird because when it’s idling and I blip the throttle...It rev’s great...very responsive, clean, and crisp. Any ideas?  

 

Thanks,

 

Andy

 

 If sluggish after the carb change then you don't have to look any farther. Often a change in something brings with it a problem.

 

It will rev quickly and be responsive, clean and crisp out of gear because you are only spinning up the crank and rods which weigh very little. Things are different when hauling the weight of the truck.

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4 hours ago, banzai510(hainz) said:

ck the motor timming. like the cam position at TDC and what is the distributor timed too also..

 

Is this elelctric choke or manual? maybe choke is still on or partial ON.

 

These carbs are fine for a basic upgrade over a worn out 45 year old Hitachi. 225$ for a new carb is still cheap to keep a car running for years

I was thinking the same thing. Ignition timing could probably use a bump. I would disconnect the vacuum advance and set it to around 12 at idle, but also make sure it doesn't get over 32 at high RPM.

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I do not know how long you have had your Datsun, or if you have a L-18, or a L-20-B engine.  The L-18 is factory stock, but lets be real, the engine has probably been changed, or had some work since 1974.  Your truck could also have had a L-16 engine swapped in to it.

Datsun engines in this time period are completely different than the engine in your Bronco.  Datsun engines like RPM.  If you are trying to make your Datsun engine have immediate response, in gear, it is simply not going to happen if you mash the throttle at 1,500 RPM, or even much below 2,500, even with a more torquey L-20-B.  The L-16, 3,000 minimum.  On the other hand, the L-16 will run up to 6,500 easily, and the L-20-B engine will run up to around 6,000.  The L-18 has slightly torque than the L-16, but runs closer to the L-16 RPM range.

 

What is the compression of the engine?  Should be around 160, or higher, and even in all four cylinders.

 

A carburetor measures fuel based on only one factor, "how fast is the air moving through the venturi?"  If you mash the throttle at a low RPM, the velocity of the air moving through the venturi drops so low, that the carb cannot meter the gasoline accurately going into the engine.  Also, air is light and suddenly opening the throttle causes a lot of air to rush into the manifold, and because gasoline is a heavy liquid, compared to air, almost all carburetors have an accelerator pump that mechanically squirts gasoline into the manifold, to cover the dead spot until the heavy gasoline starts flowing, and catches up with the increased air flow.

 

As mentioned, a stock Datsun carburetor has a vacuum secondary.  On a vacuum secondary carburetor, even on a V-8, the manifold vacuum is not used to open the secondary.  The secondary opens based on the vacuum developed in the primary venturi, and the primary venturi does not develop much vacuum until the RPM is up high enough to get enough air flow through the engine.  This is to allow the primary to accurately meter the gasoline, until there is enough air flow demand from the engine to have adequate airflow through the secondary of the carburetor.  A mechanical secondary Weber will have a big bogging problem if you mash the throttle, because both carb throats open if you mash the pedal, and even if you did put a accelerator pump on the secondary, the engine will not have enough RPM (and air flow) to meter the gas correctly, until the RPM gets higher.

 

Check the compression.  Adjust the valves.  Set the timing, about 10 degrees BTDC at a low idle, below 600 RPM, vacuum advance disconnected, and plugged.  If the idle is faster, mechanical advance starts to come in, and you cannot set the initial timing correctly.  

After you do all the other tune up stuff, then you can adjust the carb, AFTER the engine is warm.

 

Remember the Datsun engines like RPM.  If you want, or need quick throttle response, you have to be in the correct lower gear to get it.  You have to plan ahead to have the correct gear to have enough RPM (above 3,000, and this number is with a vacuum secondary carb) to get good throttle response.

 

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1.  Adjust the float height and drop in your carb.  This will help, as the fuel level determines how the emulsion tubes operate, and its CRITICAL.  Google "weber float level" and look at the images section for a diagram of how and where to measure.   Use a drill bit as a guide for height.  

 

2.  Try around 12 BTDC at idle for timing.

 

3.  Where did you buy your new Weber?  Not all are real Webers - some are pure crap that look the part but dont work, no matter what you do.  Price is a good guide to good or bad.

 

4.  The diaphragm in the carb is the power valve.  It works backward from what it should, so if you can lock it from moving it will run better.  At least you'll be able to tune your mixture better instead of going len on acceleration and rich on decel.  

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I always sand the protruding rod on the power valve flat with the surface of the valve. Take it out and hit it on a belt sander, then blow it off and reinstall it. That's the easy way.

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I used to have a weber 32 36 with a tall adapter on my l20b 620 and it was very sluggish. One day I was messing with it and saw that my secondary port was dry and dirty. Turns out my accelerator cable wasnt opening my secondary at all, so I adjusted it and it made a huge difference! A whole different truck and wasnt sluggish at all anymore, it ripped! Could be a possibility with yours? 

 

You could also try getting a tall adapter, I like mine. More plenum

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On 3/19/2019 at 8:10 AM, Stoffregen Motorsports said:

I always sand the protruding rod on the power valve flat with the surface of the valve. Take it out and hit it on a belt sander, then blow it off and reinstall it. That's the easy way.

 

Intake vacuum pulls the power valve closed against a spring. When floored the vacuum drops, valve opens to enrich the high speed mixture for added power.

 

The intake vacuum is passed up into the carburetor power valve through a hollow screw at the front of the carburetor that holds the base and body together. I had one that had been apart before and the hollow screw traded with the solid one behind it. Swapped the hollow one into the correct hole and there was a huge difference when revved up and floored suddenly. Analogous to stepping into a 4bbl Quadrajet. Well not exactly...... but there was a proportional 'kick' when the secondary opened. 😁

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On 3/18/2019 at 1:55 PM, distributorguy said:

 

 

4.  The diaphragm in the carb is the power valve.  It works backward from what it should, so if you can lock it from moving it will run better.  At least you'll be able to tune your mixture better instead of going len on acceleration and rich on decel.  

 

Not following why Nissan would build it this way at all or why you think it does. The above post explains the power valve action in the 340 L20B carb.

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You do know that we're talking about a Weber, not an OEM carb, right?

 

Some early DGV's had siamesed fuel ... ports... (having a brain fart and can't think of the right word) which caused a delay in fuel delivery when the secondaries opened. Starting with the DGV 5A, the ports/chambers/whatever were individual, as in one for the primary circuit, one for the secondary. This updated design all but eliminated the characteristic bog when the secondaries opened.

 

 

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On 3/17/2019 at 5:57 AM, Charlie69 said:

I have run the Weber 32/36 on 4 cylinder Datsuns since the 70s and no they are not a performance carb.  If you wanted a performance carb you should have purchased the 38/38 Weber. 

 

First are we talking about a true Weber or a Chinese knock off.  If you have the cheap Chinese Knock off you have a great paper weight.

 

 

Charlie, have any pics identifying / differentiating the two? What happens with the Chinese one when it goes bad? 

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The Chineese Weber knockoff usually fail right out of the box.  Research has shown about 50% failure rate out of the box.  EMPI is a Weber knock off builder and seller.

 

As far as your your question, " What happens with the Chinese one when it goes bad?" The carburetor will run rough, lean, or rich, or not at all.  Changing the jets will most of the time help with either lean or rich condition.  The build quality of the Chinese Weber is poor at best.  In most cases you can not tune the Chinesse Weber to run smooth and fuel efficient.

 

Here are acouple of videos to help Identify and understand the true Webers.

 

Identifying The true Weber Carb

 

Pierce Manifolds Understanding your Weber DGV Carbureter

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