Weber 32/36 backfiring

[Anbele]

So I recently started experiencing some backfiring on my Weber 32/36 under load conditions. It only does it when I have just started the car—I won’t call it when it’s cold cuz temps have been mid 90s here in DC—but when I’ve been driving it for 15/20 minutes , it goes away and doesn’t come back till it sits again for couple of hours. Any clues? Thx.

[18Fiatsandcounting]

Sounds like your choke may not be working. If that's the case, the engine will be running lean until it warms up, and lean mixtures tend to continue burning as they travel down the exhaust manifold which is what you hear.

Which type of choke do you have on your 32/36 carb? Even when DC is 90 degrees, the engine might need a little bit of choke until it warms up. I'm surprised it takes 15/20 minutes, though. I would think several minutes at most. Everything working as it should on the cooling system?

-Bryan

[Anbele]

Thanks Bryan. I have an electric choke…the 15/20 min it’s mostly till I have no backfiring at all. In the first 5 min I get 3 to 4 bangs, then sporadically spreading apart till none. I’ve read that it might be my distributor/ vacuum set up? This just sounds a bit puzzling to me since I’ve not messed up with it and carb wasn’t doing any of this couple of months ago. My coolant seems to be ok. Needle temp stays at 190° and fan kicks in after that. Will check choke again and see what transpires…

[18Fiatsandcounting]

Thanks. Just to make sure I'm on the same page, is the backfiring through the exhaust or backfiring ("spitting back") through the carburetor? Exhaust backfiring is often a fuel mixture issue, while spitting back through the carb is often an ignition timing issue.

Since you have an electric choke, try disconnecting the wire to the choke with the engine fully cold, verify that the choke plates are fully open, then start up the car and drive. The engine will be a little balky until it warms up, but with the weather in DC like it is now, you should be OK. If the backfiring goes away, then that's a pretty good sign that it's a choke issue.

-Bryan

[Anbele]

So I went into trying the choke disconnect today…at the same time I started going over all my vacuum lines since most postings on the web referred to to bad vacuum leak as the probably cause of the backfiring. Well it turned out that my brake booster hose was collapsing under load. Every time I manually accelerated the carb, the hose walls would collapse and would became flat as a pancake. I inserted a piece of copper tubing in the section that was collapsing, and it seems to have done the trick!…although I’m still contemplating the choke probability. When I did a tuneup to the carb the choke spring seemed “tired” to me…so maybe it’s time for a new one.

[Anbele]

Well, I was wrong…the carb still backfires
So now what?…I’m baffled

[18Fiatsandcounting]

Well, I was wrong…the carb still backfires

Do you mean the "car" is still backfiring, or the "carb" is still backfiring? Totally different, and different causes. If it's backfiring through the carb, then a common cause is incorrect ignition timing.

-Bryan

[Anbele]

Hi Bryan. Yes, it’s the carb…and yes, that’s what I’ve been reading as remedy. My puzzling though is cuz I’ve never messed with the dizzy nor the timing belt. Thanks again for any input.

[18Fiatsandcounting]

OK, thanks for that. Spitting back through the carb is often due to the air/fuel mixture still burning when the intake valve starts to open for the next cycle. It can either be because of an incorrect ignition timing, or a very lean air/fuel mixture. Lean mixtures burn slower (and hotter), and if the fuel is still burning when the intake valve reopens, well, that causes the spitting.

Is your accelerator pump jet working? If not, the mixture can go way lean when you open the throttle (especially when cold) and this could cause the problem. Remove the air filter cover, engine off, and work the throttle by hand as you peer down the primary barrel of the carb (the one furthest from the engine). As you work the throttle, you should see a stream of fuel from a small jet in the center. Some carbs shoot a jet into both barrels. I can't recall for the 32/36DFEV.

-Bryan

[Jefe]

This is a reply and a question as well... (Is that OK?)
I had the same problem (coughing) but after warming up mine got a little better but did not go away. I was pretty sure my accelerator pump wasn't really working well.
For that and a couple other reasons, I rebuilt the carb. Made a huge difference! Much, much better.
(Side note, I started putting things back together the same way they were when I took it apart. Unfortunately, that is putting a lot of trust in whoever worked on it last. I just happened to have my Haynes manual opened to the carb parts blow-out page and realized that the spring had been on the wrong side of the pump diaphragm all along. No wonder it didn't work.)

My question is on the gaskets. My carb had a very thick gasket (over 1/8" thick) between the lowest plate and the center body.
It had an even thicker gasket (a good 1/4" thick) between the carb and the manifold. Was there a reason for that? I used the regular thin gasket on the manifold, but had to reuse the other one because someone had tightened the bolts to the point of warping the plate so that it needed the 1/8" thickness to seal. I have a vague memory of guys raising their carb up with multiple gaskets or even thick milled plates because they thought it would work better. Any thoughts/recollections?

[PaulC]

Thick black "gasket" between the carb and manifold is an isolator for heat i beleive.
There should be a gasket between that and the carb base.
Then between the middle and bottom section there's another tan colored isolator with a gasket on either side.
At least that's how I've set up my ADFA.

[Jefe]

Thank you PaulC, very interesting.
I wonder why they are not included in the rebuild kits.
Whoever worked on mine before did not use the regular gaskets, so the thicker isolator was destroyed when I took the carb off the manifold.

[PaulC]

Guess the isolators are supposed to be more durable than the gaskets so no need for a routine replacement.
The more expensive kits from AR have the three gaskets but no isolators. Their base spacers have both the isolators and gaskets.

[Anbele]

Back to the misfiring…still going on…and yes Bryan, I do get the shot of fuel. So I’m thinking I’m gonna have to remove the carb once again and do a complete rebuild. Last time I replaced all the diaphragm parts and gaskets but I did not touch the jets. So the saga continues.

[Anbele]

So, I’ve been driving the car even though It was backfiring for the first 3-5 minutes after starting. But then no issues at all. Till yesterday. When back form a 40+ minute drive, started backfiring when in 4th and a metal soft clanking noise was noticeable. Fortunately I was 5 minutes from home so I pulled in and listened to it while the hood was open. It sounded like something was loose in the valve chamber, around the 4th cylinder. It was late. Turned the engine off and waited till today to take a look with natural light. Removed the valve cover and fortunately did not see anything broken. But…I remove the distributor cap to inspected it and the assembly—I gues the shaft part and rotor felt kinda loose. But then again, I don’t know if this supposed to be tight. Like no movement at all…I’m gonna guess that I can move it back and forth like 3°-5°. Is this normal? If not, I might found my trouble source.