Installed over the winter Built 2L. 10.4 to1 pistons,sport cams and 40 DCOE webers. After transplant engine fired right up.Engine pulls like a train,hit the brakes and come to a stop and the rev's jump to about 3k .Hate that! Any ideas? Things I've tried, 1st checked vacuum,it was low. Then added vacuum canister, no difference. Removed canister and installed elec. vacuum pump, no difference. Blocked engine vacuum and w/vacuum pump only,no difference.I'm starting to think this may have nothing to do with engine vacuum or brakes?Really frustrated.It's been almost a year since it went into the garage.I need to DRIVE!
Rev's jump @ stop!
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6,892 Posts
Would be good to know what model Alfa you have......
Why do you think vacume has something to do with a high idle ??
Why do you think vacume has something to do with a high idle ??
78 Alfetta gt. Engine is from same ,but don't know from what before that. As it was professionally rebuilt and modified .I thought it was vacuum related because it's only when it come to a stop. Which seems brake vacuum related(pulling all vacuum from engine)(or leak).Brake booster was just rebuilt,added vacuum pump,isolated brake system from engine vacuum. Yet the idle still jumps to 3K when I stop.Is this just a inherint problem with sport cams & high compression pistons?Or could it be something intake related?
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15,006 Posts
I have Webers and RJ racing cams and my engine idles at 700-800 rpm. Pop the hood when it is fast idling and push the Weber actuator arm and see if the butterflies will close some more. If so, then see if the linkage is hanging up on something. Or you might need an extra throttle return spring.
Then take a look at the distributor and verify that you have both springs in the centrifugal advance and that only one of them is loose when the engine is stopped.
Then take a look at the distributor and verify that you have both springs in the centrifugal advance and that only one of them is loose when the engine is stopped.
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558 Posts
Maybe this is solved already, but what comes to mind for me is floppy engine mounts (including the rear one seeing as this is an alfetta), or even not fully fastened due to an oversight in putting things back together. Too much engine movement when braking hard could be changing the throttle linkage relations enough to open the throttles, maybe ??
Just a thought
Neil
Just a thought
Neil
eedneco,You just won 1/2 the prize.The mounts are all new and tight.This got past my self and my mechanic that regularly works on his and customers race cars.Then his dad a retired mechanic said to check for the correct slack in the throttle cable.They figured out to do this on old Honda civics after doing a head job. I had set this to tot.End of Story!
stock distributor?, sounds like that or linkage, spica manifold or euro? The spica weber conversion using the spica manifold presents it's own problems in that the bent arm to acutuate the carbs from the bell crank will hang up on the carbs. I had to weld an extension to move the bent arm conection outwards away from the bellcrank to keep the arm from binding. Where is your timing set at idle? Where is it in relation to the "M" mark at 3000rmp? Do the carbs snap back onto the idle adjustment screws when released from wot? As said above are they closing all the way. Have you checked the position of the closed butterflys by looking through the plug the covers the progression holes in the weber? I know that's a lot of stuff but I seriously doubt it's a vacuum thing especially since you said you took it out of the equation.
It's all good now. There was zero slack in the throttle cable,that was the problem! As for the manifold,it is the euro style. I fabricated a bracket for the spica bell crank , this mounts to carb studs. It looks like a factory part and works great.
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