Carb Backfire Problem (Video)

[Kpeters]

Was wondering if anyone ever had this problem? Under hard acceleration or heavy load like climbing an incline I get this back fire and the car will stop running until I ease off the gas.

At first the car had a problem were it wouldn't idle and the primary would drip/dump fuel like crazy all the time.

It had a 50 idle jet on the primary and a 55 on the secondary. Using c.d.'s guide I noticed the primary should be 60 and secondary 55 so as a temporary measure I swapped them. This fixed the idle and the dripping problems but completely screwed up my second stage.

Previous to this the idle was very very crappy but the car was incredibly fast and the second stage kicked in with no problems and lots of power.

I'm in the process of selecting new jets all around for the carb but it looks like this problem may be getting worse. I'm going to be using c.d.'s jetting guide to buy some new jets for it but I'm worried there may be something else going on in here.

Thoughts? Anything else I should do except from starting with the appropiate jets std.

[allbim]

The dripping problem is caused by a high float level setting or a float valve that doesn't shut off properly. It has nothing to do with jet size.

The back-fire and lack of power sounds like not enough fuel, possibly caused by low fuel pressure.

[Kpeters]

The dripping problem is caused by a high float level setting or a float valve that doesn't shut off properly. It has nothing to do with jet size.

The back-fire and lack of power sounds like not enough fuel, possibly caused by low fuel pressure.

That's very interesting weird thing is the float should be at specification at least last time I checked and the dripping stopped completely when I switched idle jet valves (ones on the sides).

Any ides if the so called power valve (one on the float chamber) may have anything to do? It's the only piece I didn't change since they are not in the kit.

[rogerspeed]

i've seen that a bad power valve cause the carb to lose fuel when sitting, (why some cars won't start right up if they sit a couple days) it's only a $12.00 part. Your current problem sounds like bad ignition timing and/or dwell asuming everything else is hoyle.

PS - the aircleaner also functions as a flame arrester(sp) it helps to limit backfire, another variable to backfire is valve timing and valve adjustment (more hoyle)

[Kpeters]

i've seen that a bad power valve cause the carb to lose fuel when sitting, it's only a $12.00 part. Your current problem sounds like bad ignition timing and'or dwell asuming everything else is hoyle

I thought exactly the same! But yesterday when the car had the inverted idle jets idle sucked but I could floor it and the car would just fly lots and lots of power.

So I'm not sure ignition/timing is the problem since a simple change in jets made all the difference.

I did inadvertently grounded the condenser with a screw driver and it sparked (forgot to turn of ignition) but afaik a condenser either works or it doesn't and it doesn't sound like the kind of problem I have,

[rogerspeed]

in tuning an '02: asuming the cam timing is correct, first cold valve adjust, then ingnition gap (dwell) and timing (advance ball strobescope). Once those are checked it's on to fuel, is the fuel pump putting out enough? is the feul pump sucking debris that intermittenly blocks the line (blow the line out from the pump to the tank [disconnnected], not from the tank towards the pump!) if the power valve is leaking it would follow that under load the engine might get not enough properly mixed fuel to operate effieciently. What ever the jets, you have to adjust both the idle and mixture screws. Too bad were on different coast. Good luck

[Hans]

could be the sound system, but is that valve train clatter I hear? If so, could be part of the issue. I spent a lot of time playing with carbs to find out my problem was not enough timing advance and a bad plug wire.

['76mintgrün'02]

+2 on the plug wires. I just replaced a set that was only a year old. It turns out two of the wires had failed. Bought a new set of 8mm wires from Kingsborne and it runs "like new."

http://www.kingsbornewires.com/category.sc?categoryId=2

I also learned that taking the time to paint the bb on the flywheel white is well worth the effort. You can do it yourself by parking on a slope and engaging the parking brake just enough to allow you to roll it in fourth gear while shining a light in the hole to find the bb. I had a wedge of firewood handy to kick under the tire, but did not need it. I spent more time looking for the bb while trying to time it, than it took to paint it white. Timing is fun now.

Tom

[c.d.iesel]

valve adjustment first - might be too tight cold

go to 0.007" cold (Go 0.006" NO-GO 0.008")

accellerator pump diaphram stiff and dead ?

float level too low ?

mechanical advance not advancing ?

[Kpeters]

It's all too weird the problem got even worse to the point were I couldn't touch the gas pedal, then I changed the plugs which had less than 10 miles on them! Bosch WRD7 for NGK BPR5 and the problem is almost gone...

Everything is new on the ignition system including the wires which are Bosch have you guys ever had problems with Bosch wires going bad in a year with almost zero engine running time?

Valves are adjusted to .08 there is clatter but not a lot most if the noise comes from a loose timing chain I need to replace.

[jimk]

Put a timing light on the coil wire and watch the lamp flash. If it is not erratic, the forget the ignition. FWIW the idle jet has nothing to do with a shortage of fuel under load, only during idle and transition loads off idle. Look at the mains and power jet for blockage.

[Kpeters]

FWIW the idle jet has nothing to do with a shortage of fuel under load, only during idle and transition loads off idle. Look at the mains and power jet for blockage.

That's the interesting thing....when I swapped them it started working fine if I put them back they way they were it screws up again.

It's not much of a problem with the transition because it actually never does it! It bogs down and back fires and won't keep revving. If I let the gas go the engine will start running again.

So bottom-line as long as I don't make the carb open second stage it's fine.

[jimk]

Refer to the Weber manual linked in another post.

http://www.lainefamily.com/images/WeberTuningManual.pdf

The picture on page 13 shows how the idle jet is out of the action during loads above transition. The various fuel circuit explanations also tell the story.

['76mintgrün'02]

This is a little embarrasing to admit, but I learned the hard way that the idle jets need to be firmly seated. I figured the O-ring would provide a seal with it screwed in rather lightly and it ran MUCH better with them in tight. One more thing you could check. Tom

[Kpeters]

Hey thanks yeah I screwed one lightly the first time and the car revved up to 3.5k when I cranked it! Certainly gave me a scare.

Well this sounds like it's going to be a long troubleshooting process! Thanks for the link to the manual much appreciated.