engine and drivetrain Idle and backfire issue

[doslucero]

I have a 76' 2002 with a 32/36 carb.   The car starts fine but when you step on the gas, it wants to die.  In order to rev the engine up, the gas pedal must be pushed slowly.  I took apart the carb twice. I replaced carb gaskets, parts and checked the float.  I replaced the solenoid with a regular secondary idle jet.  That secondary jet must be unscrewed a little to have the car idle right.  This doesn't seem right.  I checked for vacuum leaks and didn't find any.  I have a water choke.  There was emissions on the car but everything was blocked off when I got it.  Sucked on the vacuum hose coming from the distributor to the carb and it did move the distributor components a little.  At this point, I'm not sure what else could be causing this idle/ running issue.  When I'm driving the car, it does this same dead spot when I step on the gas,  it happens the most going into second gear.  It also backfires sometimes when I step on the gas to fast.  Any suggestions would be greatly appreciated.  It also runs rich.   

 

Roberto  

[percy]

First, when did the engine first exhibit these symptoms and what, if any, work was performed on the engine.  (Toby is always curious.)

 

Second, have you insured the ignition is spot on.  To paraphrase MikeS and his father-in-law, make sure you do not have any ignition issues and that includes setting your points correctly and properly adjusting the ignition timing.

 

That said, and assuming you do not have a weak condenser or coil, or plug gaps that are too wide - or narrow - as alluded to above, your problem is most likely the carb setup.

 

If you have to jury-rig the idle jet by leaving it loose in the carb body, something is wrong.  Try putting things back the way they were and please state what jets, as in sizes, are currently in the carb.  (I am confused when you describe being able to swap idle jets because the primary side that receives the solenoid-jet assembly is a dimensionally inconsistent with the non-solenoid jet assembly - they have different threads.)

 

When you describe needing to slowly depress the pedal, to accelerate, it sounds like your "accelerator pump" is not functioning properly.    When you open the throttle, can you see a jet of fuel squirt from the accelerator pump noZzle down the carburetor throat?     If not, have you replaced the accelerator pump diaphragm?    Or could you have possibly left something out, like a spring or damaged the diaphragm?

 

If you do see the jet of fuel from the pump noZzle, then your symptoms also suggest the possibility of an the idle jet port being clogged, or more likely an idle jet that is too small or possibly your primary main jet may be too small.  They do work in concert..

 

 

 

 

I am NOT suggesting you use these jet or emulsion tube numbers, but it may be helpful to identify each jet you are currently using in your setup. 

 

 

Is it possible your solenoid-jet assembly is not seated properly?  Got "O" rings?  And - if the assembly is over-tightened, this can result in a distorted jet.  Is yours tweaked?  Doesn't happen often, but I have seen one or two examples. 

Edited February 10, 2016 by percy

[dbmw2002]

I've had five 2002s everyone one of them got a brand-new redline Spanish build weber carburetor you'll be amazed what about $400 will do for the car. There will be several questions why didn't I already do this why cant I rebuild a carburetor and make it work as good. Why didn't I get a 38 38.

Just make sure when you mount it an absolutely flat clean perfect manifold you will have time to enjoy the rest of the car and it will be money well spent

[avoirdupois]

I've had five 2002s everyone one of them got a brand-new redline Spanish build weber carburetor you'll be amazed what about $400 will do for the car. There will be several questions why didn't I already do this why cant I rebuild a carburetor and make it work as good. Why didn't I get a 38 38.

Just make sure when you mount it an absolutely flat clean perfect manifold you will have time to enjoy the rest of the car and it will be money well spent

 

 

You may be correct in assuming there is something internally wrong with the OP's current carburetor.    Still, the carb setup problem, if that is the current problem,  might be as simple as changing jets, or readjusting the floats or choke..   Unless you know the unpublished details of the subject car and its carburetor, how do you know the carburetor isn't relatively new?    With respect, despite your apparent good luck with new carburetors - five times over,   purchasing           a    new   carburetor    is    not      much of a    guarantee that the jetting is appropriate for all applications, including this one, or that it will fix the current problem.

 

 

Regarding the issue at hand, is the choke fully disengaged?

Edited February 10, 2016 by avoirdupois

[doslucero]

Thanks for the responses guys.  Here's a few answers to your questions:

 

The issue started when we noticed the solenoid (on primary jet side, my mistake in thinking it was the secondary) was loose so we tightened it and messed with a few carb settings and it got worse.  Also I can see the jet of fuel squirt into the carb.

 

Background on the car: 

Bought the car a few months back.  It wasn't running.  the weber carb was off the car.  I put the carb back together with a basic kit, installed new plugs (gapped correctly), new fuel filter (pump works fine), gas tank is clean, took the car for a short ride and it didn't exibit the current issues.  Then I installed new plug wires, adjusted valves, noticed that the solenoid was loose then the issues started.  

 

Carb details:

The 32/36 is old, but I cleaned it out really good, replaced the solenoid with a regular plug and size 60 jet.  The secondary has size 50 jet.  Not sure what the other jet numbers are without taking it apart again.  It still needs to have the primary loose to idle.  I also replaced the accelerator pump so that shouldn't be the issue.  It has a water choke, originally it had only one hose going from the manifold to the choke.  The other was blocked off.  I got a new hose and attached the 2nd choke hose from the choke to the engine block.  I adjusted the float (made sure the floats actually float).  Installed a new float filter.  I noticed that the primary bottom butterfly flap was a tiny bit open at rest which allowed some fuel to get through and stain the side of the port.  I adjusted the flap so it closes properly and doesn't block the little hole on the wall of the port.  After all this it still exhibits the idle, loose primary jet/ backfiring issues.  Also when I'm adjusting the idle mixture screw, or the secondary idle jet when the car is running, it doesn't seem to change how the car runs at all.  This doesn't seem right.  Also, all the jets are cleaned and should be working fine.  

 

My thoughts:

I don't know if the jets are the right size, probably not.  

Do you think it could be anything other than the carb?

I don't want to get a new carb until I can diagnose the problem.

 

Thanks for all the help.  

Edited February 10, 2016 by doslucero

[LimeySteve]

I'd guess the primary jet is too small, lean gives the back fire problem & accel slowly uses the acc pump to fatten up the mixture, search for the Weber recipe  on here , that jetting is universally used

[avoirdupois]

 

Also when I'm adjusting the idle mixture screw, or the secondary idle jet when the car is running, it doesn't seem to change how the car runs at all.  This doesn't seem right.  Also, all the jets are cleaned and should be working fine.  

 

 

If the idle mixture screw has no affect on engine operation, it is likely that the carb is running off of the primary rather than idle circuit.  As LS mentioned, this could be due to primary jet size, but it could also be due to throttle plate position, which you mentioned.  Also unlikely, but not impossible that you have a carb gasket that is reversed, backward or missing a perforation, so that it blocks a portion of the air feed for the idle circuit.  Not all kits are perfect, nor are those who install them.  The fact that the carb is "old" is not determinative of its ability to function, after all, your engine is probably old too.  However, there are parts on that Weber that do wear, especially the carb body that cradles the throttle shaft.  (Carbs can be overtightened and warped too.)  This in turn can cause an unwelcome vacuum leak at certain off-throttle positions.  Not saying this is your problem, but it is something to consider.  The fix is generally a bushing kit - or carb body replacement.  Do a search.

 

You wanted to eliminate other possibilities before buying a carb.  Although this is not an essential, a vacuum gauge could be helpful as an inexpensive  diagnostic tool for extraneous vacuum leaks - unrelated to the carburetor.  It can also provide feedback on mixture and ignition timing.  It is also possible you have your ignition timing too far advanced, which is why someone mentioned making sure your ignition system is A-ok.

 

 

['76mintgrün'02]

When my idle solenoid was acting up I tried to install a normal idle jet/cover, but found that the threads were completely different (as Percy mentioned above).  I was able to free up the sticking solenoid and it has been working fine.  Does the plunger move in yours, if given 12V?  This sounds like one detail you have yet to sort out.

 

There are different float settings for plastic vs brass floats.  Did you use the correct ones?

 

It is possible to install the auxiliary venturis backwards.  There is a hole on one leg, which needs to meet the hole in the carb body.  Just one thing to check.

 

Are all the vacuum ports capped?  Is the carb base down tight?

 

I would definitely check dwell and timing.

 

Here is c.d.'s prescription:

 

 

c.d.iesel

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Posted 21 September 2009 - 05:45 PM

...my WEBER prescription: 
32/36 

Float Level 40mm (very important !)

ignition timing using a timing light (very important !)

throttle linkage adjusted so gas pedal to floor
='s full opening to throttle stop on the carb (very important ! )

PRIMARY 
idle 60 
main 140 
air correction 145 

SECONDARY 
idle 55 
main 170 
air correction 175 

[doslucero]

Thanks again guys.  I'll check the carb gasket to make sure it has the correct holes for the idle circuit (have not done that).  To answer your other questions,  I checked for vacuum leaks and couldn't find any.  replaced all plastic/rubber caps with new ones.  The new primary idle jet/cover threads in fine and has a rubber seal (I just cant screw it all the way in or it will starve).  This is also the same issue when I had the solenoid.  I have plastic floats set to correct level.  Aux Venturis are correct way.  The carb is tight, with new gaskets.  I also replaced the power valve near the float.  Not sure what the plunger is?  I tried to search for it.  

[percy]

The new primary idle jet/cover threads in fine and has a rubber seal (I just cant screw it all the way in or it will starve).  This is also the same issue when I had the solenoid.

 

It has been a long time since I looked closely at the various idle jet offerings, but  are you sure the tapered forward end of each jet (that fits into the carb body) is/are the same?  Or for that matter, what about the part of the carb body that receives the tapered jet end?  By leaving things loose, you are bypassing or modifying the design of that idle jet circuit.  Unclear from what you described whether the jet or the carb body has been malformed.  By way of an analogy, there is a reason for being gentle with idle mixture screws (and especially gentle with pre-emission "fine thread" screws).  If you over tighten them, the tips can bend and they can also distort the carb body making later fine adjustments "difficult" if not "very difficult" without repair. 

 

 

Different style idle jets?  Does one size fit all?

 

 

 

 

 

 

 

 

 

 

 

You never know  .  .  . 

 

Edited February 10, 2016 by percy

['76mintgrün'02]

The brass fitting on the left of the solenoid moves to the right with power.  I was referring to this as the 'plunger'.  

I realize that you are no longer using the solenoid, so moot point, I guess.

 

Dwell/timing set to spec?

 

(thanks for addressing everything I mentioned so promptly and thoroughly) 

 

edit: the brass fitting is the jet, which has the plunger inside...

Edited June 23, 2016 by '76Mintgrun'02

[Hans]

Its been said before and is still valid: most of your carb problems are electrical. I solved virtually all my DCOE tuning problems by replacing plug wires and setting timing at about 33 deg max advance at about 3000 rpm. Did you do points/dwell?

I've seen a 32/36 where the jets were switched - primary to secondary and vice versa. I think one of the U tube videos shows the same thing.

[TobyB]

If the throttle plate is open some, it'll run off the progression drillings first- the little holes on the side of the primary barrel.

They draw fuel through the 'idle' jet, thus making it really a progression jet.  The idle screw draws fuel from there, too.

 

It SOUNDS to me like something is messed up with those progression circuits, at least as far as idle's concerned.

When you cleaned it out, did you flow air through all the passageways to make sure they were open?

It doesn't take much to plug one, and then you end up with problems like this.

 

But like Hans, I too would be careful to make sure the ignition was solid.

 

As to the transition problem, how MUCH do you step on the throttle?  As in, half throttle or so?  I'm wondering if maybe the secondary

has no fuel delivery for some reason, and is acting like a big air leak....  or fuel leak.

 

As to the power valve diaphragm, it lives on the roof of the float chamber, and has a big long foot that

drops to the floor of the chamber to OPEN the valve under conditions of low vacuum.  The idea is that it

enrichens the mixture when you stand on the gas.  The diaphragm gets stiff, the thing stops behaving linearly, and

then you get problems.  But most kits have that part, as it's a consumable...

 

I don't know how much all that helps...

 

t

[2002]

Since you have emissions on the car the backfire might be a poorly functioning diverter valve (aka gulp valve) connected to the air pump.  The diverter vale is supposed to stop the flow of air into the thermal reactor exhaust manifold during deceleration.  If the diverter valve allows air to be pumped in all the time the remaining fuel in the exhaust, during deceleration, explodes and causes a backfire.  Check the vacuum line to the diverter vale and see if it is leaking when vacuum is applied.

Edited February 11, 2016 by 2002