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.
ASE Master Diesel,Heavy/Medium truck technician,ASE Master Automotive Technician.
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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?
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.
1957 WILLYS pickup,
1973 J 4000,
1978 CJ7 DD.
1979 CJ7 360, TH400/Quadratrac.
1980 CJ5 trail Jeep.
1989 YJ the CJ to YJ.