Weber Carburetor Question ?

[AMC86Kid]

ok so i have the Weber K490 38 DGES carb 

and as i was trying to get the timing right on the motor by turning the distributor 

i found a spot that i liked and then gas the carb a little harder it then had one huge back fire that made the engine turn off 

i turned the motor back on and it ran ruff then shut it off again what i noticed was that the throttle no long moved in proportion 

with the air flaps on top of the carb ( by the way whats the official name for those top two flaps )when the carb is warm 

but they do move in proportion when the carb is cold 

is that normal and is there any change that i damaged my carb with the back fire ?

 

 

here's how it moves when its cold 

 

 

 

after it backfired and it was warm it did not move in sync with the throttle is that normal ?

[HOrnbrod]

14 minutes ago, AMC86Kid said:

ok so i have the Weber K490 38 DGES carb 

and as i was trying to get the timing right on the motor by turning the distributor 

i found a spot that i liked and then gas the carb a little harder it then had one huge back fire that made the engine turn off

 

How are you setting the timing? With a timing light? What was the timing setting BTDC when you "found a spot that i liked"?

[Marine1Texas]

I call them air flaps. Sounds like something to do with your choke if the flap is not opening when warm. That is a auto Electric choke not a mechanical choke. I don't see it is plugged in from pictures

[Green Mesa XJ]

Butterfly valves?
The electric choke has no power so I doubt it’ll open all the way.

How did you rig timing marks?



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[AMC86Kid]

oh i havent done the timing yet with a gun i was just turning the distributor and seeing when the rpms would sound lower 

should i do the timing first and then tune the carb 

or do i tune the carb then do the timing ?

[HOrnbrod]

Base timing should be in the 10*-14* BTDC ballpark before adjusting the carb.

[Green Mesa XJ]

You shouldn’t have to really tune that carburetor. Aside from idle speed. The choke isn’t going to fully open up until it’s got power going to it.

Did you replace the distributor with vacuum advance?

For setting the timing you need a certain RPM (700?) which is not an engine on a fast cold idle. Since you have the 3.4 timing cover and no marks to work with, you can add something to mark timing like you were talking about earlier if the 3.4 has the bolt pattern for it,
possibly find a tape the fits the circumference of the Harmonic balancer and get timing marks that way,
or find TDC, Mark that then based on the picture I uploaded of 2.8 timing cover and marks take an educated guess at about where 10 degrees BTC is (or whatever you’re supposed to be set for)

Once you’re in the timing neighborhood it’ll be easier to tweak it as you drive and get a feel for it.




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[HOrnbrod]

http://www.jegs.com/i/Chevrolet-Performance/809/3991435/10002/-1 or similar.

 

[AMC86Kid]

ok i will try to get a timing tab and get it on there 

and yes i called rock auto about the vacuum advance distributor and they said that they do sell the distributor 

but without the round metal vacuum piece that the hose connects to so I'm not sure where i can get my hands on one of those pieces 

[Green Mesa XJ]

What, rockauto said that distributor was not vacuum advance? I looked it up with the suppliers the part # was for vacuum advance. In this case for that part number I don’t think rockauto knows what the hell they are talking about. They’d have to put hands on it to be sure.

 

Now if the timing tab bolts up to the 3.4 timing cover, I’d still get the TDC mark to line up with that tabs 0.

 

Edit: I mean make sure that the timing tab 0 matches the engine 0

 

 

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[HOrnbrod]

1 minute ago, Green Mesa XJ said:

What, rockauto said that distributor was not vacuum advance? I looked it up with the suppliers the part # was for vacuum advance. In this case for that part number I don’t think rockauto knows what the hell they are talking about. They’d have to put hands on it to be sure.

Now if the timing tab bolts up to the 3.4 timing cover, I’d still get the TDC mark to line up with that tabs 0.

 

Good thinking. 

[schardein]

An old trick I was taught years ago, to set ignition timing without a timing light, put a vacuum gauge on the engine and adjust your distributor to get the highest vacuum reading at idle.  Yes there are a lot of assumptions there (that you have a vacuum gauge, that the distributor is in right to begin with, that everything is close enough to correct that it will start and run).

 

I played around with the technique on Chevy 350 & 454 and found I could get it right within a few degrees.

[Marine1Texas]

^ that's is how I like to do timing as well. I would adjust timing with out advanced hooked up to highest vacuum pressure and then back off the dizzy 1 to 2 degrees.

[AMC86Kid]

Green Mesa XJ i think you read my post wrong here let me try to explain it better 

ok so they said that the item will look just like the picture displayed 

here's the pic :

 

however the "W/O Label" means that it comes as is but without that round golden metal thing in the top right of the pic (does anyone know what that piece is called)

i then asked them where can i get that piece because without it the distributor is useless and they then kinda told me IDK 

[Marine1Texas]

vacuum advance canister is what that is called.

[AMC86Kid]

thanks 

how do i know which one or what size i should get ?

[Marine1Texas]

So I am guessing it is the chevy 3.4 dizzy right? If it is the 3.4L GM dizzy  you can use a Adjustable Vacuum Advance Canisters like a 66952C. Now the thing to check is if the internals for your advance is there, springs/weights. If not then you need to kit was it is called a Vacuum Advance Kit. Crane 99600-1 fits stock/HEI 3.4l

[Green Mesa XJ]

Nah they (rockauto) are wrong. If it looks like the picture it comes with the vacuum advance. They got it in their catalogue wrong thinking it is without vacuum which is totally different. If it’s federal emissions “ except California “ it has to have the vacuum advance and centrifugal advance. The other designs for that description is what you have now.

They generally don’t come rebuilt without the vacuum advance if they are the vacuum advance design. It’s just one of those parts that needs to be to spec and that’ll get the distributor warranted out ever DIY screw up.
The rarest part of that distributor is the wire from ignition control module to the ignition coil.

Here is the website for that manufacture
http://www.autoline.ca/distributors.htm

This is their parts catalog
http://www.showmetheparts.com/autoline/




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[AMC86Kid]

so what do you think ?

should i just order it and see what shows up in the mail ?

if its missing the vacuum advance i can always just install it on later right 

[Green Mesa XJ]

It hard for me to say cause it’s your money. I’d hate to cause you waste it. I believe I’m correct about the part based on my experience working in auto parts and that rock autos counter jockey aren’t familiar with the parts they are selling or the at intricacies of these old carbureted setups.
I think it’s worth a punt, but it could be causing you a hassle retiring if it’s completely wrong, only thing I really hate about rock auto is the bloody return policy and cost to ship wrong crap back to them. Sometimes if the ship cost out weighs the benefit of return I keep the part which I didn’t need and was wrong. Entropy of life I guess.

BTW that vacuum timing might be worth a go. I’ve never done it but know of people who have.
If you can get it running right without a new distributor you might be better off. Again I wouldn’t touch the mixture, Weber & Holley carbs I’ve helped set up were good to go out of the box for sea level. Unless your real high altitude it shouldn’t be a problem. I know for sure on the 2.8 it was perfect out of the box.







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[schardein]

53 minutes ago, Green Mesa XJ said:

It hard for me to say cause it’s your money. I’d hate to cause you waste it. I believe I’m correct about the part based on my experience working in auto parts and that rock autos counter jockey aren’t familiar with the parts they are selling or the at intricacies of these old carbureted setups.
I think it’s worth a punt, but it could be causing you a hassle retiring if it’s completely wrong, only thing I really hate about rock auto is the bloody return policy and cost to ship wrong crap back to them. Sometimes if the ship cost out weighs the benefit of return I keep the part which I didn’t need and was wrong. Entropy of life I guess.

BTW that vacuum timing might be worth a go. I’ve never done it but know of people who have.
If you can get it running right without a new distributor you might be better off. Again I wouldn’t touch the mixture, Weber & Holley carbs I’ve helped set up were good to go out of the box for sea level. Unless your real high altitude it shouldn’t be a problem. I know for sure on the 2.8 it was perfect out of the box.







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The "highest vacuum" method is just for when you don't have a timing light or marks on the engine to go off of.  

[Green Mesa XJ]

The "highest vacuum" method is just for when you don't have a timing light or marks on the engine to go off of.  

True. Almost perfect for this situation. Although i have a feeling the ecu is jacking the electronic advance around in this jeep since the last owners have had trouble with “tuning”.

More people use vacuum reading to help set the mixture but in this case as long as the mixture wasn’t touched it ought to be set
The vacuum trick for setting timing is a good one I didn’t even remember.


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[AMC86Kid]

is it possible to get convert my current electric distributor to a vacuum advance one ?

[Green Mesa XJ]

No, you need two piece besides the vacuum.



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[Green Mesa XJ]

Sorry went to get a picture of what I was talking about and the app posted the previous post.

 

Anyhow four parts are different between the two distributors.

The casing is different with no place to mount the vacuum advance.

Ignition module is deferent.

Vacuum advance

Centrifugal advance

 

Last picture (upside down distributor)has the rotor still on it but underneath is a glimpse of the centrifugal advance

 

 

This picture is the kind of distributor you have now not a good pic but you can see some of the differences.

 

 

 

 

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