weber carb conversion and backfiring?

[hugginsvilleH&A]

Spike will backing the mixture screw out lean it out more ? or the make it richer? no on the vacuum guage, but hey i am always looking for a reason to purchase a new tool, your setup is what i have, stock idle with .100 main and a step up on the secondary ,

[Spike]

In makes less fuel (tighter), out makes more fuel (looser). Oddly enough, my backfire went away with a richer mix. But try and get a vacuum gauge before you start listening to me!

Poor man's economizer.

[FestYboy]

ok, here's the issue, you're trying to adjust an OFF idle condition (tip-in or part throttle) by adjusting your IDLE adjustments... this won't work because they are not related.

set your idle with a vacuum gauge. then see if your accel jet is working (it may be clogged). if it's NOT clogged, you may be dumping too much fuel during tip in (not likely) which would require a pump cam adjustment. also if the engine doesn't want to run at part throttle (push the idle speed screw WAY past idle rpm and see if it'll settle out at 1500 or so), you may have a blocked main jet or venturi or float/pintle seat issue for the bowl.

[zoe60]

I'd still see if it does better with the 140's. I know some people run 100's but mine would be deathly lean on them. since you are hitting the gas when it backfires, it seems more like a main jet problem or accelerator pump. When I had a B# my car would run fine with 140's. A little rich though.

[hugginsvilleH&A]

festyboy it is just that an off idle condition, once i rev past the initial back firing it revs smooth as silk and to the moon with no backfires, until i try and put it in gear (loaded) then its back to backfiring / spittting..... man this thing is new out of the box i would not think i would have clogged jets, i did change the main jets out , but i tend to be pretty uptight about details

a dumb question but what is more likely to cause a backfire? is it a lean condition or rich condition? or could be either? or another issue all together?

either way, gonna back up and do the vacuum gauge then timing and start over and see if i can work this thing out, I REALLY REALLY do not want to have to got back to the stock setup especially after tearing all that emissions crap out

[hugginsvilleH&A]

ok the latest to this quest, i looked thru my storage trailer and found that i did have a vacuum gauge after all, hooked everything up and it was around 16.5" after it warmed up,, tweaked with the mixture, in till it started slowing down and dropping vacuum then backed out till it smoothed out and vacuum went up to max of 18", then i bumped the idle speed up to a decent idle with electrical load, then i moved on to the disty and adjusted it till i got the vacuum to max @ 19.5" ,thats all i could get out of it, all vacuums were smooth and steady, it is improving much better than before BUT it is still backfiring when i try and drive it....i tried hooking the vacuum advance up to the manifold and plugging the carb port, and then back to the carb port, it made no difference

anyone care to analyze what in the world i am doing wrong here, all help is greatly appreciated, thanks

[bravekozak]

Here is another lost soul.

Before I went through all of that, I would throw on an Escort carb and see if the trouble disappears.

[FestYboy]

festyboy it is just that an off idle condition, once i rev past the initial back firing it revs smooth as silk and to the moon with no backfires, until i try and put it in gear (loaded) then its back to backfiring / spittting..... man this thing is new out of the box i would not think i would have clogged jets, i did change the main jets out , but i tend to be pretty uptight about details

a dumb question but what is more likely to cause a backfire? is it a lean condition or rich condition? or could be either? or another issue all together?

either way, gonna back up and do the vacuum gauge then timing and start over and see if i can work this thing out, I REALLY REALLY do not want to have to got back to the stock setup especially after tearing all that emissions crap out

have you visually inspected the accel pump jet function? and have you also verified the cam timing? 19.5" Hg isn't bad, but you should be able to crack 21" with a carb and stock cam. also, have you watched the vac gauge when blipping the throttle?

[denguy]

Isn't a backfire when gas-air mixture passes thru the cylinder without burning and then ignites in the exhaust system? We use to do it on purpose driving down the road by turning the key to off and back to on, and hoping we didn't blow up the muffler. Just kids playin. Could this be an ignition problem?

[bravekozak]

True backfire is when the valve isn't completely closed yet and the spark causes the incoming air fuel mixture to explode out through the top of the carb.

Spend the extra $80 for a rebuilt Escort carb just to rule out the carb. You can always turn around and sell it easily on the forum. I want you to be able to get some sleep without waking up in the middle of the night, screaming "Noooooooo"!

[Team Lightning]

I've seen true backfire like you described BK. It busted the number 4 piston on a low mileage B3.

[hugginsvilleH&A]

Festy when i run the throttle up by hand it would go up to in the mid/upper 20's i beleive, it seemed to not backfire when i did it by hand and slow rolled into it, but from the drivers seat and pedal it backfired everytime, i am using the bracket they sent with the carb, all rigged up to hold the factory cable (this is temporary till i make/buy another one bracket) Could that possibly bind up or something? it all looks to be functioning fine tho.

festy how do you check the accel pump jet function?

bk i read the links you posted ,,,I still need to figure the wire that is on the disty it is connected to what looks like a hall sensor maybe? 3/4" square - 1/4
" thick, it is externally on the fwd side of the disty main body, it has about 18" of wire with a ring terminal on it, does it go to the coil maybe? may have to take a pic of it to show you guys what i am talking about

will probably order a set of idle jets, one step up & down and see what happens,

also if i never mentioned it , this setup has the factory fuel pump with a fuel filter then thru a holley fuel regulator (3-4 psi) then to the carb.

[Spike]

Oh, something incredibly stupid I did.

Did you buy/make an EGR blockoff plate, or did you leave the EGR open?
..I accidentally put caps on the still-in-operation EGR, and caused a whole host of issues.

-Joe

[zoe60]

"bk i read the links you posted ,,,I still need to figure the wire that is on the disty it is connected to what looks like a hall sensor maybe? 3/4" square - 1/4
" thick, it is externally on the fwd side of the disty main body, it has about 18" of wire with a ring terminal on it, does it go to the coil maybe? may have to take a pic of it to show you guys what i am talking about"
That thing is just a capacitor to filter noise before it gets to the radio. It won't make any difference in the way the car runs. If the car idles ok and backfires when you give it gas, I really don't think changing idle jets will help any.

[hugginsvilleH&A]

spike i had made and installed a block off plate for the egr and removed all the emission stuff.

zoe thanks for the info on the cap,,,, the one thing i have yet to due is inspect the disty's insides and make sure the vacuum advance is working properly and all looks in order, that check is free so i will start there