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Unread 09-18-2011, 07:01 PM   #1
csrcn2
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Maybe a CJ guy can help...

I know this is the cj forum but I think someone may be able to help me. 89 YJ 258 with MC2150 and nuttered. 48 jets and 1.08 venturi. Ported vac to reman dizzy.

Problem with part throttle hesitation. Normally 1100 to 1500 rpms. If I start below and accelerate through it goes fine. Anywhere in between she wants to stall, if I pump the throttle either immediately before I know it will stall or right when it begins to she recovers and goes fine. Tried tuning the timing advanced and retarted also adjusting he advance curve with no success.

No vac leaks that I can find. Been trying to get this right for months.

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Unread 09-18-2011, 07:16 PM   #2
dzltech1
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adjust your mixture
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Unread 09-18-2011, 07:17 PM   #3
gojeepin
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It could be a problem with the carb's accelerator pump or lack of the proper timing advance.

When adjusting the timing curve, did you adjust the vacuum cansister?
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Unread 09-18-2011, 07:17 PM   #4
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get a webber or Ford 2100
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Unread 09-18-2011, 07:20 PM   #5
csrcn2
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Quote:
Originally Posted by gojeepin
It could be a problem with the carb's accelerator pump or lack of the proper timing advance.

When adjusting the timing curve, did you adjust the vacuum cansister?

Accel pump shoots two great streams of fuel, timing is 8* btdc, and I set the mixture screws with a vac gauge. And yes it was adjusted by the vac canister.
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Unread 09-18-2011, 07:21 PM   #6
csrcn2
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Quote:
Originally Posted by BlueRubiconrich
get a webber or Ford 2100
Ummm that is the Ford 2100, and i'll take a weber if ya want to buy it for me! ;b
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Unread 09-18-2011, 07:35 PM   #7
gojeepin
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Quote:
Originally Posted by csrcn2 View Post
Accel pump shoots two great streams of fuel, timing is 8* btdc, and I set the mixture screws with a vac gauge. And yes it was adjusted by the vac canister.
It sounds like you aren't getting the advance you need until the mechanical advance starts.
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Vibration? Bump steer? Wandering? Read: Steering, suspension, and driveline basics. An article on how it works and where to look for problems.

83 CJ7, 4.1L 6cyl (4.0L bored .030" over), 35" tires, T-5 transmission, Dana 300 TC, Trussed AMC 20.
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Unread 09-18-2011, 07:42 PM   #8
csrcn2
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Quote:
Originally Posted by gojeepin

It sounds like you aren't getting the advance you need until the mechanical advance starts.
So you think I need to give it more vac advance in the lower rpms? 31" tires on stock axle
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Unread 09-18-2011, 07:46 PM   #9
gojeepin
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Perhaps. The vacuum advance is going to respond to combination of butterfly position and RPMs. At lower RPMs, butterfly position is the main influence.
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Vibration? Bump steer? Wandering? Read: Steering, suspension, and driveline basics. An article on how it works and where to look for problems.

83 CJ7, 4.1L 6cyl (4.0L bored .030" over), 35" tires, T-5 transmission, Dana 300 TC, Trussed AMC 20.
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Unread 09-18-2011, 07:51 PM   #10
csrcn2
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Quote:
Originally Posted by gojeepin
Perhaps. The vacuum advance is going to respond to combination of butterfly position and RPMs. At lower RPMs, butterfly position is the main influence.
So the butterflies aren't opening fast enough? That's not adjustable is it?
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Unread 09-18-2011, 07:53 PM   #11
csrcn2
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Do you think an increased jet size might aid them?
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Unread 09-18-2011, 08:47 PM   #12
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Jets are cheap and easy to change, so you might try 50s, but I think you're okay with 48s. I want to say I'm at 10* on my timing with great response, however I am running the 2100 with 1.21 venturi.
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Unread 09-18-2011, 08:52 PM   #13
csrcn2
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Quote:
Originally Posted by Skerr
Jets are cheap and easy to change, so you might try 50s, but I think you're okay with 48s. I want to say I'm at 10* on my timing with great response, however I am running the 2100 with 1.21 venturi.
So the larger venturis means your moving more air. Correct?
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Unread 09-18-2011, 09:01 PM   #14
BagusJeep
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The ported vacuum source on the carb may not allow you to wind in enough vacuum at low load levels and this may be what you are seeing in the transition. The manifold vacuum on the other hand would give too much.

A NLVR valve was fitted to many 258s of the period and this may be what you need to smooth out the two sources. Have you got such a device in the pile of bits you took off?
nlvr-valve.jpg  
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Unread 09-18-2011, 09:21 PM   #15
lucdog
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Quote:
Originally Posted by csrcn2 View Post
So the larger venturis means your moving more air. Correct?
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
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