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post #1 of (permalink) Old 03-26-2001, 05:29 PM Thread Starter
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New Carb. Backfiring???

I just installed a new Weber 38 carb on my 258, and when I really get on the gas the carb will backfire. Does anyone have some advice on how to correct this? Other than the backfire the carb was a real improvement.

'83 CJ7 Laredo,258-I6,Weber 38DGES Carb.,much much more to come.
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post #2 of (permalink) Old 03-26-2001, 06:03 PM
 
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Re: New Carb. Backfiring???

sounds like the timing is off check that first

jeep the first 4 wheel drive the only 4 wheel drive
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post #3 of (permalink) Old 03-26-2001, 06:49 PM Thread Starter
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Re: New Carb. Backfiring???

3jeepguy,

I will get a timing light and look at the timing. Another question! The distributor advance port on the Weber, my jeep has a port on the manifold that the distributor advance is hooked-up to. Should I just cap the fitting on my carb, or could I vent the vapor storage canister with this port on the carb?

'83 CJ7 Laredo,258-I6,Weber 38DGES Carb.,much much more to come.
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post #4 of (permalink) Old 03-26-2001, 08:09 PM
 
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Re: New Carb. Backfiring???

that is a confusing issue try hooking the advance up to the carb an cap the manifold and run it that way your backfire might go away the advance might not be workin quite right try that and check the timing

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post #5 of (permalink) Old 03-26-2001, 10:22 PM
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Re: New Carb. Backfiring???

Hey if your jeep never backfired before with the old carb and the timing was fine...its the carburator...its just lean if its backfiring through the intake because the motor is hot enough to fire in the intake..if its backfiring out the exhaust it rich beacause of the residual burn off after the exhaust stroke...all new carbs do need some kind of tunin' to be put on a motor...usually...check your timing also the other gentleman isnt wrong nor' am I the king but just turn the adjuster screws on the carb to richen or lean the carb out for the backfiring types I talked of...either turn them by ear untill your motor reaches the highest RPM, you will hear the motors RPM rise or stumble and die. Dieing is bad of course, so turn the screws untill the RPM's rise to the max that the idle is set at...or use a vacuum guage and hook it up to a 'direct' vacuum port and set the screws to make the most vacuum on the guage for that RPM setting on the carb...

MARK (OIIIIO) LANGMOTORSPORTS
1977/CJ7/GLASSTUB/460CIFORD/C6AUTO/4"LIFT/33'S
post #6 of (permalink) Old 03-27-2001, 05:00 PM Thread Starter
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Re: New Carb. Backfiring???

I adjusted the idle mixture screws, and I believe I did it correct, but I will do a little more adjusting then check the timming. Thanks for the info.

'83 CJ7 Laredo,258-I6,Weber 38DGES Carb.,much much more to come.
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post #7 of (permalink) Old 03-27-2001, 08:55 PM
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Re: New Carb. Backfiring???

I had the same problem with the Weber I put on my 89 YJ 258. The butterfly valve even got stuck in the closed position so that I could not get it to reopen. I sent the carb back to Weber. The Tech told me all he did was give it a good "rap". I was hoping for a replacement carb but they sent the bad one back to me with no change. Weber does not warrant their products. Check the outside of the box, it says "No Warranty What So Ever". I ended up with nothing but scrap metal for my money.

The Weber does work different in that you do not "mix" the fuel/air ratio with screws like a normal carb. Instead you have to change the jets, which you get from them.

As you can tell, I am still upset by the way Weber treated me, especially when you consider the amount of money I paid. If a manufacture will not stand behind their products, we have no other choice as consumers but to make sure everyone one knows the risk that they take in making the purchase up front.

Good Luck!
Kriss

post #8 of (permalink) Old 03-27-2001, 10:45 PM
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Re: New Carb. Backfiring???

here is a site that has alot of info on tuning a weber.
http://www.recarbco.com/technical/newtrouble.html

if its clean, I aint having fun!
post #9 of (permalink) Old 03-28-2001, 10:38 AM
brendan
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Re: New Carb. Backfiring???

It sounds as though you have your vacuum advance hooked up to manifold, not ported vacuum. The motorcraft distributor is designed to run off ported vacuum. This could be a very serious factor with the backfire.

A ported vacuum source pulls zero at idle and increases as engine speed increases. the port on the carb for ported vacuum is usually located higher up on the carb body then the throttle plates. You sound as though you know where it is is your post.

The signal to vent the charcoal can is ported vacuum, but the signal has to come after the engine is up to temperature. this means that it goes through the thermal vacuum switch near the front of the intake manifold. On a stock system, there are five vacuum lines that are routed through it. Check out the 258 emmisions primer on offroad.com for a photo.

You may very well find that the 38 is too much carb for your motor w/o an agressive cam. A jet change may be required to get it to run it's best. Good luck, Brendan

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