Maybe a CJ guy can help... - Page 2 - JeepForum.com

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post #16 of 24 Old 09-18-2011, 10:38 PM
BagusJeep
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Quote:
Originally Posted by lucdog View Post
On edit, Thanks Bagas. never heard of one of these. I must be one slow typist, took me at least 22 minutes to type this.

Bill

I hadn't either until I read the factory service manual the other day. I was just interested in the difference between ported and manifold vacuum and hey presto, there is a device.

There are also delay valves to smooth the vacuum but these look like emissions related as opposed to just getting it to run smoothly.


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1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1951 Willys CJ3A/MB/M38 - Little Willy
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post #17 of 24 Old 09-18-2011, 10:48 PM
86cj74.2L
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I've been using manifold vacuum for years. I like it.
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post #18 of 24 Old 09-18-2011, 11:06 PM
BagusJeep
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I am partial to a bit of ported myself, with cheese and crackers.

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1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1951 Willys CJ3A/MB/M38 - Little Willy
1995 Cherokee 4.0 - CHEROKEE
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post #19 of 24 Old 09-19-2011, 03:49 AM
John Strenk
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Quote:
Originally Posted by lucdog View Post
No, and I'm not 100% on this, but the engine will pull the air it needs, and 1.08 venturis are the best size. the 1.21 venturis work fine, and IIRC when air moves thru the 1.21 venturis its not at the same velosity as with the 1.08.

I'm not real sure on this either but, the velosity of the air moving thru the venturis pulls fuel from the idle circut in a siphon effect. At least this is how I understand it.

I think I would try changing your vaccume advance to straight manifold. instead of ported, see what happends.

On edit, Thanks Bagas. never heard of one of these. I must be one slow typist, took me at least 22 minutes to type this.

Bill
The difference in venturi size means you can ultimately move more air. But at lower air flow, like at partial throttle, the smaller venturi will move the air faster as it tries to get past the narrow part. This will draw the fuel out of the MAIN CIRCUIT better, more responsive feel because the metering of the fuel is better.

This is one of the main reason for going from a 1 to 2 to a 4 barrel. 4 small diameter venturis will ultimately allow more air to pass but at lower speeds it will do a better job of metering the mixture giving you better throttle response.

You can make a 1bbl flow as much as a 4 bbl but the throttle response would be sluggish.


Back to the original problem, what may be great jets for sustained RPM, doesn't always work for acceleration. You need a slightly richer mixture to accelerate properly.

The accelerator shot is great for WOT because the air flow is to slow for proper metering but as the speed starts to pick up you still need a little more fuel and this is helped by the POWER VALVE.

You need to see if this is even working, plugged or something else.

Don't forget you also may be pumping too much fuel with the accelerator pump flooding the engine in that RPM range.


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post #20 of 24 Old 09-19-2011, 07:27 AM Thread Starter
csrcn2
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Quote:
Originally Posted by John Strenk

The difference in venturi size means you can ultimately move more air. But at lower air flow, like at partial throttle, the smaller venturi will move the air faster as it tries to get past the narrow part. This will draw the fuel out of the MAIN CIRCUIT better, more responsive feel because the metering of the fuel is better.

This is one of the main reason for going from a 1 to 2 to a 4 barrel. 4 small diameter venturis will ultimately allow more air to pass but at lower speeds it will do a better job of metering the mixture giving you better throttle response.

You can make a 1bbl flow as much as a 4 bbl but the throttle response would be sluggish.

Back to the original problem, what may be great jets for sustained RPM, doesn't always work for acceleration. You need a slightly richer mixture to accelerate properly.

The accelerator shot is great for WOT because the air flow is to slow for proper metering but as the speed starts to pick up you still need a little more fuel and this is helped by the POWER VALVE.

You need to see if this is even working, plugged or something else.

Don't forget you also may be pumping too much fuel with the accelerator pump flooding the engine in that RPM range.
I was also thinking about a power valve that comes in a little earlier than the one I have. Already ordered so we shall see. I've spent plenty of time tuning the accel pump so I'm confident it is doing its job. Thanks for the input. I will get back to everyone when I get the power valve.
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post #21 of 24 Old 09-19-2011, 07:42 AM
bkeese
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Is there any play in the throttle shaft at 3/4 throttle?

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post #22 of 24 Old 09-19-2011, 07:51 AM
INKUBUS
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make you carb

make your carb i use a dodge carter and jeep carter
i use the base carburetor of the jeep carter and the jets and its run very fine without the stepper motor



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post #23 of 24 Old 09-19-2011, 11:07 AM Thread Starter
csrcn2
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Quote:
Originally Posted by bkeese
Is there any play in the throttle shaft at 3/4 throttle?
Doesn't seem to be
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post #24 of 24 Old 09-25-2011, 06:45 AM
gojeepin
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Quote:
Originally Posted by gojeepin View Post
Perhaps. The vacuum advance is going to respond to combination of butterfly position and RPMs. At lower RPMs, butterfly position is the main influence.
Quote:
Originally Posted by csrcn2 View Post
So the butterflies aren't opening fast enough? That's not adjustable is it?
You are correct about the butterflies not being adjustable... that's not what I meant. I don't think you're getting any initial vacuum advance due to the screw adjustment and the advance canister.

The mechanical advance is the amount of advance you have at a given RPM. The vacuum advance changes based on both throttle plate postition and the RPM. The same throttle plate position will give you varying amounts of vacuum based on RPM.

If you're using ported vaccum and you give the vehicle more throttle input, the vacuum increases. That will give you more vacuum and should give you a little advance.

If your vaccum advance canister is set with the preload too high, the initial vacuum at lower RPMs isn't enough to give you any advance. That could explain your "dead spot" in your acceleration.

Vibration? Bump steer? Wandering? Read the article (sticky) on Steering, suspension, and driveline.
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