Backfiring with IDF Webbers

Roukis Slammed & Awesome Dubber

77 posts · joined Feb 2003 · 12 Sep 2003, 3:05 pm

#85332

My 1776 is backfiring. What causes this?

I have noticed when I change the mixture on one particular barrell it changes slightly but never goes completely. The leaner I run it the worse.

Can it be that the valves might be too tight/lose??

It really shits me driving the thing giving everyone around me heart attacks - especially through Mascot Tunnel after work.

Bizarre Moderator The artist formerly known as blue74l

12,789 posts · joined Aug 2002 · 12 Sep 2003, 3:13 pm

#85334

Backfiring is usually caused by 2 things

1) rich mixture

2) hole in the exhaust

As you have had these carbs a while ( i am assuming it is the "peach" oval?) i would be looking at the exhaust

Does it idle ok??

Futue te ipsum!!!

Roukis Slammed & Awesome Dubber

77 posts · joined Feb 2003 · 12 Sep 2003, 3:30 pm

#85342

It idles better when running rich than lean.

It backfires on slowing down from about 2500rpm and lower.

I have played with the idle mixtures and it won't go away. I get it serviced at VW Village. It has an S&S exhaust. I'll have to check the back connecting pipes junction - I think the gasket was not in the best condition (when I get home.)

Also it has this major flat spot when you floor it - I thought it was the clutch. It happens only when you drive hard staright or right around corners but not left - can this be a float problem.

Bizarre Moderator The artist formerly known as blue74l

12,789 posts · joined Aug 2002 · 12 Sep 2003, 3:47 pm

#85349

Is this a "new" occurance or something that has always been with the car??

Just trying to work out if something has broken or a tune thing??

Backfiring is "usually" richness or holes. It can also be coils and points..... or timing - ish. As in wandering firing.

Are you running heater boxes or J pipes. I would check those stupid slip connections (viva la flange kit)

I will go one a limb and say rick backfire would be more on acceleration and a exhaust hole on decelleration??

Just pondering that last thought aloud.

2 beers on a hole in the exhaust :bounce

Futue te ipsum!!!

Roukis Slammed & Awesome Dubber

77 posts · joined Feb 2003 · 12 Sep 2003, 3:58 pm

#85350

new occurance.

No heater boxes.

It must be a hole/lose gasket because I swear I though a bit of a flame come out the exhaust when revving motor with my hand on accelerator (on deccelerating).

is flame an idicator that there is a hole?

Baja Wes V6 Baja Pioneer

3,119 posts · joined Aug 2002 · 12 Sep 2003, 4:02 pm

#85351

If you let it idle, does it slowly run richer and richer, ie starts puffing black smoke or burning your eyes?

My guess is incorrect float level in one carb, causing fuel to dribble out the overflow or just dribble out the main jet.

At higher revs the small dribble of fuel is not much compared to the air flowing. But at lower revs it starts making the mixture relatively richer.

Cornering would temporarily change the float level in the carb, and momentarily stop the dribble. Weber floats are sideways so the effect would be different one way than the other.

That's my guess.

Take the air cleaners off, and let the engine idle. Use a mirror to look down the throats. See if you see fuel dribbling from the main jet spout. Use a mirror so if it backfires up the carb you don't blow your eyebrows off.

Wes - www.offroadvw.net - 200HP Quad Cam V6 in a VW Baja - with climate control... 🙂
www.taylorcycles.com.au - My DH MTB racing brothers shop.

Roukis Slammed & Awesome Dubber

77 posts · joined Feb 2003 · 12 Sep 2003, 4:10 pm

#85353

Baja,

The flat spot has been there for ages.

The backfiring only started last week.

I'm positive they are two seperate problems.

When I got the car serviced (major) they must have adjusted the float levels - how do you do this, because when I got the car back the flat spot was gone......for about 3 days then came back. I miss the days where I beat an Alfa Spider over 200m. Now I get this huge flat spot (practically stops moving) before I move to second and floor it there is no flat spot.

Bizarre Moderator The artist formerly known as blue74l

12,789 posts · joined Aug 2002 · 12 Sep 2003, 4:18 pm

#85355

Hmmm....came back

Worn linkage causing bind and unequal opening????

Ant slop in the linkage???

Still betting on a hole

Futue te ipsum!!!

Baja Wes V6 Baja Pioneer

3,119 posts · joined Aug 2002 · 12 Sep 2003, 5:10 pm

#85370

The float level can be set wrong. You check it by pulling the carbs apart basically. Turn the top upside down and measure where the floats sit.

Webers are also sensitive to fuel pressure. You should use an electric pump with a regulator to keep the pressure low. The stock mechanical pump has been known to force fuel past the webers sensitive float needle.

Wes - www.offroadvw.net - 200HP Quad Cam V6 in a VW Baja - with climate control... 🙂
www.taylorcycles.com.au - My DH MTB racing brothers shop.

Roukis Slammed & Awesome Dubber

77 posts · joined Feb 2003 · 15 Sep 2003, 8:47 am

#86328

There was a gap in the extractors (between joins) that I closed up.

Backfiring still there!!!!

How do you adjust float levels?? Is it by pouring more fuel into float chamber then raising the depth??

I'll take it to VW village tomorrow -

I'll get them to fix the backfiring and the flat spot. Without these two problems it puurrrs like a dream.

Thanks for your help everyone.

Roukis Slammed & Awesome Dubber

77 posts · joined Feb 2003 · 24 Sep 2003, 3:47 pm

#90808

Took it to a VW mechanic and said one of the vlaves was very tight. He adjusted it - still farting/backfiring when slowing down (decceleration).

He said there may be a build up of carbon that doesn't allow the valves to close hence the backfiring. He said give it a couple of hundred kays and come back ,if still tight my heads need changing.

Does anyone kwow a Webber guru on VWs that can recommend me??

Bizarre Moderator The artist formerly known as blue74l

12,789 posts · joined Aug 2002 · 24 Sep 2003, 4:17 pm

#90812

I would say either

VVDS - Boris 9789 1777

or

V Force - Richard 0408 991 247

If there was a carbon build up that wasnt allowing a valve to close you would have loss of compression and have other problems

Do you have any other problems??
What about when accelerating???

Does it pull smoothly??

I am still going to bet on an exhaust leak you cant find. I am going to guess a bit of that asbestos ring stuff has blown out or something

if it is backfiring (as opposed to popping out the carb) it means richness. It also usually does this on acceleration - too much fuel being pushed in.

Backfiring on decelleration i would said is more related to pressure build up being suddenly released (holes!)

I will be interested in the answer

Futue te ipsum!!!

Roukis Slammed & Awesome Dubber

77 posts · joined Feb 2003 · 24 Sep 2003, 4:35 pm

#90816

ok

Other problems.

Between gear changing the revs come down heaps slower than normal so I'm changing gears at say 1600rpm say.

Also it has a massive flat spot (sounds like it runs on 1 cylinder) when you floor it in 1st.

If I convert to single 40mm Webber in my 1776 would it lose heaps of power??

HELP!!!!

vassy66T1 Wow ... are U reading this?

2,120 posts · joined Jun 2003 · 24 Sep 2003, 7:39 pm

#90863

A single carb is not the greatest solution. I have had my 1776 on both single dcnf40 weber and twin 36 idf webers. The twins are smoother down low and with more power up top. It wouls be a great sacrifice to lose that.
The backfiring on deceleration (if that is what you are getting) is about rich mixture on idle combined with hole in exhaust somewhere, in my experience.
The flat spot is a problem that could come back to a number of solutions.
First I'd try the timing, advance it up a bit. Most often with my webers this has been the problem. Next thing to check would be your jetting. What is your current jets, idle, main, air? What venturi?
Lastly I would check accelerator pump adjustment, not a simple exercise, but with a technical manual, not too hard.
Send me an e-mail if you like to check your jetting. (vassy@coolcats.net.au)
cya
vassy
ps. Twin webers rule when they are set up well!!

[Edited on 24-9-2003 by vassy66T1]

vw54 Administrator Always Waiting 4 Friday

16,723 posts · joined Aug 2002 · 24 Sep 2003, 7:53 pm

#90870

Roukis

I'll take it to VW village tomorrow

I suggest that you take the car to some one who knows how Webbers work and get a tune up and have the engine gas analised.

I read it on FACEBOOK so it must be true

http://forums.aussieveedubbers.com/viewtopic.php?tid=91278&page=1#pid848630

http://forums.aussieveedubbers.com/viewtopic.php?tid=63561&page=1#pid624099

http://forums.aussieveedubbers.com/viewtopic.php?tid=4832&page=1#pid452603

http://forums.aussieveedubbers.com/viewtopic.php?tid=60650&page=1#pid574409

Bizarre Moderator The artist formerly known as blue74l

12,789 posts · joined Aug 2002 · 26 Sep 2003, 10:20 am

#91566

Roukis

U have u2u

Futue te ipsum!!!