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carb tuning questions
i need some help getting my carb tuned right. 351 W with a holley hp 650 sitting on a victor jr intake. it has always run overly rich. based on some advice from a friend i changed jetting and p.v. went from 68 to 66 primary jets. (haven't looked at the secondaries yet) and changed p.v. from 8.5 to 6.5.
I just bought a nice little A/F meter from F.A.S.T., got it hooked up here are the readings i get : at idle with idle screws turned out 3/4 turn A/F is about 13.6-13.8 as soon when i rev up the A/F goes to 10 (3-4 K rpm) when throttled down A/F jumps to 18 ( high as the gauge reads)for a second or two then back to 13.6. This is all in the garage no load test yet. I clearly need to change something, any help would be appreciated. i just noticed this should have gone under holley tuning! |
If your carb has screw-in airbleeds, I'd change the outer airbleeds to a larger size.
You also need to eliminate the accelerator pump, and wind the engine speed up with the speed screw while testing idle/progression A/F ratio. |
it does have adjustable airbleeds,thanks for the tip, will work on that soon!
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the first thing I do to a Holley that is running rich is lower the float level. Set to the factory spec. is almost always too high in my experience.
Z. |
This may help: Untitled Document.
Also, be certain your ignition system is healthy and your timing is correct; ignition first or you'll never get the carb tuned correctly. |
last time i ran it when i shut it down gas continued to run out of one of the squirters for a long time. now i need to change oil. the float may be set too high but it still should have shut the flow off, wondering if it is stuck some how.
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i think that those pv have to be looked at. the right size depends on your vacuum/cam. to me you have to get that right before the other stuff.
the 6.5 sounds to high unless you have a pretty mild cam. that could account for that 10a/f (but i would have guessed you hit 10 sooner than 3-4k - more like 1500-2500). does it bog pretty good when you accelerate? |
right now i am dead in the water. was running the car in my garage, revved it up to see when the secondaries were kicking in and bam the motor sounded like a bunch of rocks in a garbage disposal. thought maybe a push rod bent ,checked out the valve train and on first look every thing seems o.k. after sitting a couple of days i cranked it over again no obvious noises so i fired it up ran nice and quiet for 15 seconds or so then the noise started again sounded like a huge hole in the exhaust ( thought maybe i was lucky and my header had cracked) but it is clearly coming from inside the block. i have never seen or heard a bad rod but i think that might be the case, maybe a broken rod bolt or bent rod ? not sure but right now i feel like it has SOME MAJOR PROBLEM
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If you over rev'ed the engine, it is likely that you stretched the rod bolts enough to allow the rod bearing to turn. When the rpm came down, the notch in the bearing was not aligned, as the bolts spring back to the normal position. This makes a tight spot on the crank and the bearing spins in the rod. Shortly after the spinning, the gap increases dramatically as metal is ground up. The large gap then causes the knocking sound.
If so, don't skimp on good rod bolts, when you put it back together. |
The PV is usually 1/2 manifold vacuum at idle. It can be really difficult to see if the secondaries are opening by revving the engine with no load. You may have lucked out without destroying the engine. Pull the pan first to see what's going on.:CRY:
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i am hoping for the best but am not feeling lucky right now. the carb has mechanical secondaries so i was watching the a/f gauge as the secondaries opened I was told by rhe engine builder i could easily go up to 6500 rpm, i have the rev limiter set at 6000rpm guesss that was too much
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my 351C got over revved to 7200 once. seemed ok at first but after about 10 minutes it started losing power and 10 minutes more it died on me and would not really run.
turns out that it bent 2 pushrods and destroyed a spark plug - replaced those and it was fine. |
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DO NOT rev any engine to high rpm under no load. |
yeah, i am learning the hard way. as soon as it happened i knew i had made a big mistake!
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might be you just floated and bent a valve if you can hear it out the exhaust.
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thats a good thought, thanks
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