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Peter Guldan Peter Guldan is offline
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Join Date: Apr 2004
Location: Memphis
Posts: 130
alloy vs plastic P factory MFI ITB's

Howdy Copbait,

Drove 2 MFI cars for about 120k back in the 70ís, loved the 71E Ė so mechanical/raw - because it still had compression, and good ign. curve., less so the 73S, the EPA had hamstrung this setup by then, still had the intake noise but nobody home until about 3,800 when port velocity finally enabled some fuel to be used and those C6ís could start doing their job.

The MFI pump was essentially bullet proof, the weak link - bushing wear at the butterfly shaft pivots bypassing air that should have gone through the bleed screws. Result - rising idle that soon slung the distributor advance weights only making it go up further. The holes wore oval as return spring tension loaded the actuation levers bearing on one side of the bushings. It was time for new ones if your screws bottomed out and even retarded static ignition setting couldnít get your idle down..not to mention lean throttle tip in causing backfires.

I was lucky with the 71E. Rolled up to Jim Watsonís country shop in Nashville back in 80 to hang out one Saturday afternoon, he immediately came out and gave me the old hand cut across the neck routine over the din of my sport muffler equipped machine idling at 1,400 and said this is your lucky day. We went in his shop, he stood on an old bucket and gingerly reached over his original 550RS Spyder into the rafters and pulled a dusty NOS set of blocks/linkages down. Unheard of in those days, the alloy ones wore out quickly, were expensive/generally unavailable and folks were already doing carb conversions at that point. The plastic ones in the 2.4 era were more durable, they just had the aforementioned new issues plaguing them: emissions which had knocked the raw edge of these powerplants.

Have generally used that experience as reference when viewing various ITB iterations since, preferring linkage types to ensure quality is present - but those very spendy - so the intro of a quality set of reasonably priced common shaft ITB's like PMO's really opens up alot of possibilities for the performance NA crowd.....but even more intriguing for turbo types.
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Cheerio,
Peter

1950 Vincent Rapide - A Red Rapide Experience -
Old 01-27-2010, 11:35 AM
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