caper
Junior Member
Posts: 8
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Post by caper on Sept 26, 2005 11:13:22 GMT -4
Hi all. 81 Z-28, automatic.. I bought a 350 engine from GM (all stock). The car worked good, except obvious lack of power and top end. Car would only run about 15 s flat 1/4 mile. Put new cam (290 duration, .447 lift), intake (WIEAND), and holley 4011 carb (650 cfm, dual feed, single pump). Also put a powertrax differential posi locker in it. Now the car has no low end, and by that I mean and cant do a "burn out" anymore. When I try and burn out, the car overpowers the brakes, and inches forward, and rpm's dont go higher than 2000-2500 rpm...pathetic looking burnout. The jets in it are 60 main, 64 2nd. It seems to be running rich, as some black some comes out exhaust when accelerator is punched, and also, when idle mixture screws are turned all the way in, it doesnt stall out. You can smell the gas in the exhaust. I have a K&N 14" diameter/2.3" tall air filter, and MSD 6AL ignition. Can anyone help me out...been playing with timing etc all summer and cant get it to work the way it should. Also, it accelerates pretty fast once you get going...good power. Before the mods, it would do a huge smoke show, sitting there burning away, and you would have to watch the tach since rpms would shoot way up there...now it wont spin up... -caper
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Post by 88ss on Sept 26, 2005 16:45:40 GMT -4
By the sounds of that - you have a fuel delivery problem. If you turn your idle screws all the way in and it still runs - where is it getting the fuel from? Possible leak around power valve/blown powervalve?
How did you set the valve lash on your camshaft?
Set the total timing at 35* @3000. Tune the idle mixture with a vacuum gauge attached to full manifold vacuum. Start at 1 turn out on each side and make 1/4 turn changes on each side until you have attained your peak vacuum reading.
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Post by sam on Sept 26, 2005 19:08:58 GMT -4
447 lift and 290 duration, start out with putting in a converter you need one with that kind of duration, secondly I would bump up the carb to a 750 cfm sbc's like fuel and I would go with a dual feed as well. The intake is it a dual or single plane ? If it is a single plane I would purchase a good quality carb spacer ( Armstrong's is what I would use ) Then set up everything as Rob had said and see how it works. You said you had MSD ignition, is it just the 6al box or do you have the distributor as well.?
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caper
Junior Member
Posts: 8
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Post by caper on Sept 26, 2005 20:59:57 GMT -4
88SS, I did a rebuild on the carb this year with a holley rebuild kit, replacing power valves and accelerator pump, and cleaning it out good with varsol. I agree with fuel delivery problem. Valve lash is set at 3/8 of a turn after they stopped clacking. Will try the vacuum guage too. I tried several idle mixture settings, and dont believe that this will boost power by that much to correct the problem.
ss10: I cant remember if its dual plane or not. Distributor is stock HEI with spring advance as well as vacuum advance. The guys at msd said it will suffice because my compression is probably too low to require any more spark, as it only produces enough the cross the gap, no matter what the max voltage of the coil is...
thanks for info guys, and keep the ideas coming please...
PS: will there be another drag race this year, would love to get out...
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Post by 88ss on Sept 27, 2005 17:33:49 GMT -4
Caper in the valley eh!! What sort of Caper? I'm from Glace Bay myself.. OK - Make sure your timing is set as I stated before - that'll make that a non issue. You know that there are differences in the power valve gaskets which go with particular valves. If your powervalve has multiple small holes in the base - you need the gasket that has an inner triangle to the gasket. If your valve has 2 large slots - you need the gasket that is perfectly round in and out. Mixing these up will cause a fuel leak. That sounds like an issue you may have. If you have backfired through the carburetor - it is possible you have blown the new diaphragm. Now - is the car loading up at idle? Maybe your floats are sticking or are improper for the application (you didn't reaplace the floats did you on your rebuild) - I think someone had an issue here before that their float was hitting the metering plate/block and not operating properly causing it to load up. Those jet numbers are actually supprisingly small - with a healthy cam like that I would expect 68-70's in the front and 72-76's in the back. I think you have a fuel leak into the carburetor that is flooding your engine. Check your oil for gas smell - and if you have gas in your oil - change the oil immediately or you'll wash the cylinder bores and unseat your rings (puffing the blues!!) That duel feed didn't come original with a metering block in the rear did it? Did you add a metering block to the rear? To troubleshoot carburetor problems - I usually head over to www.holley.com - they know best what your issue is in their tech pages.
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caper
Junior Member
Posts: 8
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Post by caper on Sept 27, 2005 19:19:26 GMT -4
Hey bud. I am from Reserve Mines...the wife is from the Bay. hah! Anyhow, I know about the 2 type of powervalves with gaskets. I used the right ones. Maybe the power valve did blow because after we fired the car up immediately after the build, we heard a small popping noise (like a cap gun). I would be pissed if thats what happened. What do you mean by "loading up" at idle? I did not add a metering block to the rear, just bolted the carb right on out-of-the-box.
I was at the holley site and read everything there...twice over. I think in the spring I will try another carb if I can find someone with one laying around...like I said, there is decent power, just not out of the hole...but I am as sure as you that its a fuel delivery problem.
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Post by 88ss on Sept 27, 2005 21:21:35 GMT -4
Reserve Eh - that's cool. My wife is from the Lorway bye..
By loading up I mean is there fuel being dumped down the bowls at idle. There shouldn't be - you'll notice if you look down your carburetor with it running (watch out for flameballs!!) it will appear to be wet above the throttle plates - it shouldn't.
Did you replace the accelerator pump checkball? Did you clearance it correctly? Because if you didn't there could be fuel getting past the checkball at idle - that would also describe your situation. Did you adjust the accelerator pump arm before you started flogging it? If you didn't have the clearance set on that - you could have stretched the diaphragm beyond it's limits. Did you change pump cams? Could possibly be due to that. Lots of things to think about. I'd start with the basics. Set floats just slightly above the sight holes (small trickle out). Adjust the accelerator pump arm clearance. Adjust the idle to about 750 rpm (having this up too much allows the main jets to come in before you want them). Adjust the idle mixture screws to about 1 1/2 turns out each. If it ain't running good like that with the timing as I mentioned before - there's something gone wrong with your rebuild..
Pull out a couple of plugs and it sounds like they will be black with soot, possibly wet with gas. If they are - your going to need to replace them, for some reason - gasoline ruins traditional spark plugs.
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Post by Site Admin on Sept 28, 2005 22:45:54 GMT -4
Just a different perspective. Really all you have done is put in a new cam and carb. If you installed a reasonably compatible cam and timed it correctly that should not be an issue. Assuming the carb is not a complete basket case ( which is unlikely ) the car should perform enough to begin a burnout especially if it goes ok after the start. From your description I would be suspicious of the torque converter or the transmission. What is the possibility the transmision is not actually in 1st gear but 2nd during the burnout attempt?
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caper
Junior Member
Posts: 8
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Post by caper on Sept 29, 2005 8:19:10 GMT -4
I manually put it in 1st with the shifter...
Should also mention, the car sat for about 3 yrs after carb/cam installed. However...Carb was rebuilt 2 months ago after car was running and back on the road. If I remember correctly, the car would burn out after the mods, but not after I got it running again 3 yrs later (before & after the carb rebuild).
88ss: Where is the accelerator pump check ball? I remember a check ball being located in the center of the carb, with a small metal rod. I had a guy help me with this rebuild who raced stock all his life. He really knows his nuts, so this wouldnt have been overlooked. The arm is set properly too (small gap between arm & lever at WOT). Pump cam is the same. Floats are set OK too. RPM is about 750. Tried several settings on idle mixture screws...no change. The plugs were sooty last time I checked too...I know its running rich because of that. PS: Pm me your wifes name...maybe I know her...and when she graduated high school. cheers.
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Post by 88ss on Oct 4, 2005 17:03:23 GMT -4
OK - that's a different perspective. The car was boggy before you rebuilt the carburetor? Could be a tune up issue.. Simple plugs/wires/dist cap. Coil could be weak - check for spark..
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caper
Junior Member
Posts: 8
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Post by caper on Oct 9, 2005 18:05:41 GMT -4
new coil, dist. cap, rotor, wires, plugs. Module was removed as per MSD install. Before the carb was rebuilt it was running black smoke and you could smell the gas. the power valve and accelerator pump were both seized. Adjusted valve lash to 3/8 of a turn past when the clacking stopped. Also noticed the other day it will spin easier in reverse ?? Thought that was weird.
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caper
Junior Member
Posts: 8
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Post by caper on Jun 4, 2006 15:24:16 GMT -4
My headers were REALLY SOOTY when inspected. The oil smelled like gas when I drained it. My mains are 60 and 2ndary are 64's...on the small side. I just checked my power valves and I can suck them shut and no air passing through the diaphram. The car wont stall out when idle mixture screws are seated fully which leads me to believe that there is extra fuel being dumped in from somewhere. The only think I can think of is that the vacuum is too low to hold power valves closed at idle...but they say that 6.5" power vavles are ok for my situation. Anyone have other suggestions? Cheers.
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Post by raiderat on Jun 4, 2006 17:04:59 GMT -4
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Post by 88ss on Jun 4, 2006 23:32:54 GMT -4
My headers were REALLY SOOTY when inspected. The oil smelled like gas when I drained it. My mains are 60 and 2ndary are 64's...on the small side. I just checked my power valves and I can suck them shut and no air passing through the diaphram. The car wont stall out when idle mixture screws are seated fully which leads me to believe that there is extra fuel being dumped in from somewhere. The only think I can think of is that the vacuum is too low to hold power valves closed at idle...but they say that 6.5" power vavles are ok for my situation. Anyone have other suggestions? Cheers. Hey caper, What you are describing is a full pig rich - carb not metering your fuel situation. I would take the bowls off and check for debris. It sounds like they are not seating and allowing the fuel to dump into your carb. A float problem would act like this as well - you can test to see if they float. Or the float is binding up as was described in another poat in this forum. If you were close to Mt. Uniake, I have a known good 750 carrb you could try - to make sure your problem lies there. Kevin - that camshaft doesn't need any special compression - it's an old design, and there are many better, but it's only got 222 .050 duration. It'd make a pretty good torque cam for towing with a little more lift. (I's running one in my truck!!)
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Post by raiderat on Jun 5, 2006 9:32:36 GMT -4
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