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Weber install: backfire from intake.


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I had some time to at least learn how to take the weber apart and document the size of the jets that are in there now. The carb comes from Redline with 140 fuel mains and the main air jets are 170/160.

 

Unfortunately, Redline sent the wrong jet kit, or at least I think they did. The smallest main fuel jet in the kit was 150.

 

At this point, I am a little discouraged. I just want my mustard wagon to live again, and really miss driving it.

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Redline suggests taking the primary main air jet (170) and moving it to the secondary. Then I am supposed to take one of the main air jets from the kit (180) and insert that into the primary.

 

This doesn't make sense to me IF the motor is running lean, but I really don't know at this point so I may as well give it a shot :)

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Redline suggests taking the primary main air jet (170) and moving it to the secondary. Then I am supposed to take one of the main air jets from the kit (180) and insert that into the primary.

 

This doesn't make sense to me IF the motor is running lean, but I really don't know at this point so I may as well give it a shot :)

 

sounds right to me, since your air is thinner, you'd want to have larger air correction sized to provide more volume....

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sounds right to me, since your air is thinner, you'd want to have larger air correction sized to provide more volume....

 

Everything I had read about up to this point suggests reducing the size of the main fuel jets rather than increasing the size of the air jet.

 

Either way, I am learning.

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Learning, is what this site is mainly about. It is a great reference for us Soob owners.

 

I have been watching the action on this thread and have noticed that the suggestion about the real problem could be with the disty position and not the carb hasn't been addressed as to yea or nea. I made a comment about it myself earlier. I hope you have made sure that this isn't the real problem and are wasting your time working on the carb. Though learning about carbs is a good thing at least.

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I see what you are saying but that is the electrical timing. The mechanical timing still could be off and since you say it happens at higher rpm's it makes me think that the disty is really the trouble. I may be wrong though.

 

Not so much at high rpms as under load (clutch engagement / getting the car moving).

 

The larger air mains were installed last night(180/170) as suggested by Redline. Although it did help smooth out the idle a bit more, the motor still bogs down under load and backfires through the intake/carb.

 

What you all are saying is starting to makes sense... I think :) I will take a stab here: If the advance is set to about 10-12 degrees now, the vac advance could then be advancing the timing too far and cause the backfire. Am I on the right track?

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If I am correct, what I think is going on is the intake valve isn't quite closed, due to the advanced disty gear position, when the ignition is firing. Since the valve isn't closed the backfire goes back through the intake. Moving the disty back on tooth position and then retiming the ignition will prove if we (the others that think the same thing) are correct about this.

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  • 2 weeks later...
Sounds like a vacuum leak to me. I've seen it many times....lean condition. Check your carb adapter, and gaskets and make sure all your vacuum ports that had hoses removed from are securly plugged.

 

Good thinking! I am wondering if the carb adapter gasket is not making a good seal because of the carb water port for the hitachi? Of course it isn't leaking though.Makes me wonder.

Shawn made the comment several times that it sounded as if it had a vac leak. I may bring another dizzy along with me tomorrow to check out the vac advace.

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Good thinking! I am wondering if the carb adapter gasket is not making a good seal because of the carb water port for the hitachi? Of course it isn't leaking though.Makes me wonder.

Shawn made the comment several times that it sounded as if it had a vac leak. I may bring another dizzy along with me tomorrow to check out the vac advace.

 

I don't think you'll find anything wrong with the distributor. American high performance cars in the late 1950's through the early 1960's never had vacuum advance from the factory. They only had centrifugal advance. However if the vacuum advance diaphragm is bad, that would create a vacuum leak but I think you are looking for a larger leak.

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...

...the suggestion about the real problem could be with the disty position and not the carb hasn't been addressed as to yea or nea. ...

 

is What I`ve Said on Page 3:

 

I Suggest you to re-Check the Ignition Timin´ Degrees... Might be...

...

 

Well... I Think that might be the Cause too... but more issues Might be involved, such like Vacuum Leaks, Wrong PCV + EGR functions, etc...

 

Good Luck! :burnout:

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Still the same problem of backfire through the carb under load. Frustrated. Beaten down. Tired. We must press on...

 

What we did tonight:

-checked everything for vac leaks (yes, everything) using carb cleaner and found none. I even took the carb off and resealed all gaskets, etc.

-vacuum tested out at 12 pounds with the meter. We changed out the cat and managed to get 14.5 on the second read.

-Jets are set to 140 / 140 fuel mains and 170 / 160 air mains.

-Checked the mechanical advance on the distrib and it is working perfectly. Currently, the engine is set to about 12 degrees when the mechanical advance is hooked up.

 

No idea where to go from here. Everything I read suggests that a backfire through the carb is a lean condition, but is it possible that it is actually running too rich? Bogging down under load, pop, pop, and starts to stall out?

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Glad to hear you made some progress at least.

 

I still feel the problem you are having is due to either the valve timing is off or the disty position is off by a tooth. Did this problem start happening after either of those areas were worked on?

 

We may be able to prove if this really is the problem by checking each cylinder while it is in the firing position. Then force air into the cylinder through the sparkplug hole, like you would on a leak down test. If you get air back up the intake you will know what to do.

 

Edit:

Looking at your last vacuum test reading of 14.5 pounds seems to confirm that there is something wrong with the valve timing or a leaky valve.

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Edit:

Looking at your last vacuum test reading of 14.5 pounds seems to confirm that there is something wrong with the valve timing or a leaky valve.

 

Don't think the valve timing is off since that was never touched. It is a low mile ea81 so I think that part is perfectly fine since it ran good with the stock hitachi. It just makes me a little sad to see Jay put so much work into his car and not having going.

 

I will have to look into the carb workings a little more cause it still seems that there is something funny about this particular weber. I have seen many people throw on a weber and with minimal effort have it screaming in no time. We did find some little metal particals in the float bowl when we removed the top portion of the carb to change out the main jets and air corrector jets back to the stock settings. I think that some of the casting/flashing may have found a way to come loose a little bit after putting some fuel through it. I will have to check all of the little ports on the carb to confirm this.

 

Any other ideas? I want this thing to go as much as Jay and Shawn do.:)

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