Ok guys, here's a good one for ya. The engine gets flooded right as soon as I let off of the gas anywhere from half throttle to full throttle. Now this only happens when I put a load on the engine and not while cruising. To get it started again I have to keep the butterflies open and keep cranking until it fires again, then it blows out the rich mixture and is ok till I goose it again.

I've checked and changed out the 6.5 powervalve which I believe is the correct one (11.5" of manifold vac. at idle in gear), I've adjusted the accel pumps, and I have the fuel pressure set at 6 psi (I had it set at 7). I just got done changing the plugs and they were on the dark side. I also just got done setting the valve lash at .22 int. and .24 exh. The cam specs are .525/.525 lift, .248/.248 dur. and I'm using 1.5 rockers on the int. and 1.6 on the exh. The carb is a Holley 750 DP with 71 pri. and 80 sec. jets and this is sitting on a single plane Team G intake. This is all on a 383 stroker using some modded #2461 fuelies with the 2.02/1.60 valves. Also a 3500 converter with 3:70 gears.
Other than this problem, which sucks for street driving, the power is unbelievable. I also noticed that when taking off gradually the engine runs rough till around 2000 rpms then it smooths out real nice. Now is this just the normal characteristics of a "lumpy idle, high reving" engine or should I lean out the primaries? Or should I go to a 4.5 powervalve? The Holley I have is the richest one they have off the shelf, it's the #4779-6 according to the jets that were in it when I bought it from the store. I even gave my engine specs to the guys at Holley and this is what they recommended. I do have some jets to play with but how far down should I go? I have a set of #69s and #67s. I don't want to go too lean but I also don't want to have to tear into the carb a million times, so I'm asking for advice.

P.S. The video in my Sig shows the car working good but it was also alot colder outside, around 45. Lately it's been about 70 degrees.

 

check the rear float level, sounds like it may be set high, fuel sloshing (spelling) forward when you let off.

Neal

 

I did notice the other day when I took a long hair pin right turn the engine got rough and I tested this by oversteering and understeering throughout the duration of the turn. The G-force in the turn was enough for me to notice the engine running rough. I thought I checked the fuel level a couple of weeks ago but I'll do it again. Thanks.

 

OK I just got done checking the float level and actually the pri side was a little over the edge and dripping out so I lowered it. I tried it again and it still runs rough. There is a little bit of smoke that comes out the sidepipes as well once it warms up. The puddles of condensation that drips on the floor was black and sooty also. So then I changed out the 71 pri jets and put in 69s and still no change. Should I even bother trying the 67s or do I have a ring job ahead of me on my new engine?
The pass side rockers are still ticking even after I set the lash last night. I mean it's a solid lifter cam you are suppoesed to hear them right? My problem is I only hear one or two of them on the pass side and the drivers side is like a Singer sewing machine.
Since I got the engine in and running before I got it legal for the road I'm worried I didn't seat the rings properly. There was some running in the garage and some burnouts on my street before I actually got to drive her. When I first got the engine from my buddies friend I saw that the cam was already to use and was not brand new, and the crank was a GM unit, but the pistons and valves were shiny with absolutly no carbon on them. So I figured I had to break them in by driving it moderate to hard for about 20-30 miles. I didn't get to do that immediatly after the engine was running. I also had a new rear, and tranny to properly break in so I kinda took it easy. What do you guys think?

 

Here is a short video a friend made the first time it stalled. This is before I installed the air-cleaner/scoop. I also had a PCV on the drivers side valve cover. I've been running it without a PCV for the last month or so and now I'm going to re-install it, I think the vacuum will help hold back some oil from getting past the rings. For the first time 2 days ago I had to put in a half a quart.

[IMG][/IMG]

 

that carb seems awfuly big for your engine and camshaft. I think a 650 would wind you to 7,000 rpms most efficiently if you can turn it that far. Anything bigger is a waste and to hard to tune. As for the smoking, I would definitly run a pvc and a vented oil cap in the other valve cover.

 

Ok I made some very good progress tonight! I put in a 4.5 powervalve and now the rpms are smooth all the way through the rpms on a gradual takeoff. I just had to recalibrate the timing again to get rid of the hesitation when I stomp on it. And it seem to be the concensus around here from looking at recent posts that fresh engines will smoke a little when seating the rings. And more so if not using a PCV system. So I reinstalled my PCV and the smoke is less than it was. The only thing I can't tune out is one or two of the rockers from ticking. I checked the lash again and #8 exh was at .025 so I backed it down to .024 like the engine builder recommended. I also found #6 int was at 25 so I brought it down to .022. From the specs I saw in the Summit lineup for cams I think almost all of them were to be set at .022 for int and exh. My int rockers are 1.5 and the exh rockers are 1.6 ratio, is that the reason for the difference?

 

The rocker ratio would not matter when setting lash if you do it correctly. My rockers dont seem to make very much noise. Headers seem to make things a bit more noisy under the hood. I would have more issue with the engine cutting out like in the video. It sounds like you have that resolved. Does your car have the throttle solinoid or dash-pot to help your idle when the A/C comes on in place or is the carb/manifold conventional after-market?

 

The intake is a Team G and I don't have AC. I can't seem to be able to adjust the air screws with any good results. I thought you are supposed to have all four adjusted equally but mine won't run right unless I have the pri side at 1 1/2 and the sec at lightly seated. I can actually back off the pri a little and open up the secs to match but it's real finiky.

 

Go to this site scroll down look for lars paper how to set up a bg carb this will help you a lot!
http://lbfun.com/Corvette/Tech/vettetech.html

 

Well I read all the tech papers about carbs and timing setup. Lars is the man! I didn't know anything about the idle transfer slots having to be adjusted the same. So I took the carb off and looked at what it was set at from the manufacturer and I couldn't even see the secondary slot at all. That's why the secondary air screws had to be turned all the way in to get a decent idle.
So I set the butterflies so it makes a "perfect rounded square" and set the idle mixture screws at 3/4 of a turn out. The engine fired right up but the idle was now at 1500 rpms. I turned down the primary screw all the way but I could only get it down to 1300. So then I fabbed up a screwdriver with a 180 deg. bend in it to try and adjust the secondary screw back a little and only got it to turn a tad, now it's at 1100 rpms. So I lossened up the carb to better get at the screw again and turned it back a tad again but the rpms are still too high with the primary screw not even in effect. I also noticed that the rpms hang a little before calming down to the lowest point. If I rev it hard and fast the idle drops to 600-700 and almost stalls, but then if I rev it up to like 1500 and let it come down slow the idle is 1100 again.
I remember Lars mentioning a condition like this and I'll have to look it up to make sure but at the time I went back with my mighty vac and gauge to check the vac advance canister. I brought it down so that it only requires 8" hg to bring the advance all in at idle due to only having 11" hg of manifold vaccum and that helped when checking the timing at 2800 because it was jumping a little. I now have 36 deg at idle with no vac adv, (when it was idling at 950) and 52 deg at 3000 rpms. I havn't tested it on the road yet to see if it pings but I have a feeling that I'll be needing to stop at the airport before I ever go to the track.
It seems on my carb the idle transfer slots would be better set to look like a rounded rectangle instead. I have tested to see if there are any air leaks but this is a tight and clean engine, I made sure when I was prepping everything. It looks like I have alot of tuning to do if I want to get both idle set screws to be the same at my desired idle. OH and I found out that while doing all of this that my header bolts had loosened up around the #8 cylinder so that smoothed things out as well.

 

Well I read all the tech papers about carbs and timing setup. Lars is the man! I didn't know anything about the idle transfer slots having to be adjusted the same. So I took the carb off and looked at what it was set at from the manufacturer and I couldn't even see the secondary slot at all. That's why the secondary air screws had to be turned all the way in to get a decent idle.
So I set the butterflies so it makes a "perfect rounded square" and set the idle mixture screws at 3/4 of a turn out. The engine fired right up but the idle was now at 1500 rpms.[quote]

You were doing great up until this point. You even figured out why the secondary mixture screws didnt work.
Then you decided to : turned down the primary screw all the way. Thats not exactly what you read, at that point you should have pulled the carb and headed for a light!
Give you a little tip here, the rear transitation slot may not even come down to the butterfly on the secondaries on that carb. when there fully closed.
set the front and rear back like you did before, now at the light check and make sure the front and rear butterflys have the same amount of crack if they do just adjust both screws to about half the size crack you have now.
Now if you set them like you orginally did and the rear has a larger crack, just make it the same as the front and you should be close.

 

I will take the carb off again and just make the cracks smaller. The first time I did it I put the carb up to a light and they were even, just that the cracks were a little to large. It's probably just a hair off of where it needed to be and then I went and tried to adjust it by listening to the idle. The problem with that is I can't verify that both slots are exactly the same. I'll try tomorrow night.
While I'm out there, I have to try and fix the fuel leak I have at my new Aeromotive fuel pressure gauge isolator. It wasn't a great fitting that they supplied but I got 98% of the leak fixed by installing a gas resistant o-ring with a precisen washer up against the isolator body. But this time I'll add some teflon on the threads too. If it's reading correctly the new gauge revealed that my fuel pressure was set a 8 1/2 psi.! So much for the cheap screw in gauge that came with the fuel rail (my buddie was right). I just hope that the regulator isn't cheap either, it is the one that comes with the Holley electric blue pump.
Knowing that the fuel pressure was sky high, now I will have to re-check the float level because I had to lower it before. I just hope I get the bugs out before Friday, I'm bringing her in to get the alignment. WOOOHOOOO!

 

I have a suggestion. In post 11, you took off the carb and adjusted the butterflies up to the transfer slots, but then you said the idle was high so you re-adjusted, on the car. I am thinking if you had less timing advance, that idle will come down. Thats a lot of advance you have there. It may be confusing the carb issue.

 

I by no means are a carb expert, I"m just trying to help cause i been working on the same carb as you have this week. I also know if i tell you something wrong there"ll be at least a dozen people to chime in and correct me!
There seems to be a order in which you tune your holley, the more tech papers you read you"ll start to see a trend. I think getting your idle set correctly with front and rear butterflys working the same is on top of the list. next you"ll need to get your idle mixture screws close keeping all 4 the same. Then at about 700rpm in gear take another vacume reading 11.5 seems a little high to me with that cam, vacume changes with every rpm increse so make sure it"s about 700 in gear. A quick call to holley tech and you"ll know what power valve you need just tell them your carb number and how many inches of vacume you have he"ll tell you the correct size power valve to install. Read how to check your accelator pump at idle and at wot. Now hit the road run 60 mph for a few miles steady speed that"ll clean up the plugs from all the burnouts, at 60 mph kill the engine coast to a stop check plug color this will tell you what primary jet size you need. After you get a nice tan color , you can do the same thing at wot usually a 1/4 mile is enough at wot to change color on the plugs. That will tell you what rear jets you need.
One last thing : teflon and gas not the best of friends! use some pipe thread sealer instead.

 

You failed to mention how much vac with car in gear and presume its a/t And also have checked cam pumps on carb what size and also accelator pump size .

 

I feel your too rich at idle powervale and also pump squirter, and also may be try 50cc accelrator and squiter with longer squit time manly for a/t.

 

I made some progress over the last week, I took the carb off again to reset the sec idle screw to be even with the pri side. But this time I went more shallow. This works better but the idle was still on the high side. I also noticed that the throttle bore on the pri side has a slight edge that keeps the butterfly from returning all the way. If I goose it a little it will come down to the screw and idle is perfect. I'm leaving it this way so that when in gear at a light or something it won't stall. And if I have to put it in gear I can just goose it a little to bring the idle back down so that there is no clunk in the rear.
In an attempt to find a shop to do my alignment I took her on the highway for a few miles on the way there and back, and then when I got home I checked the plugs and they were not even colored, so I put the stock jets back in and it runs even better. The next day I did the same test and rechecked the plugs again, still on the light side and also still has a slight bog when I floor it but is getting better. I'm going up 2 numbers higher on both sides and see how the plugs look. I don't think I need the 50cc pump because I get the slight hesitation before I get into the secondaries. I even changed the powervalve back to the stock 6.5 because I am getting 11"hg of vac in gear at idle. I'll go one step at a time and might try the 50cc pump at the end to see if there is any improvement. I also changed the pass side header gasket over to a copper one and there is no more leak now. It's funny because the drivers side has no problem. I think it has to do with the fact that the header flanges were not sqaure, and I didn't have a method of straightening them. I thought the torque from the mounting screws would be enough to properly seat it.
That's where I'm at right now and I still have to get the alignment done. Now that there is some highway time on the engine, it's starting to feel like it's breaking in. Now the stock starter has a problem turning over the engine and sometimes grinds the hell out of the ring gear. So I ordered a GM high torque mini starter and an SFI Scat flexplate. I hope to get these in before the alignment so I don't look like an idiot that can't get his vette started. Thanks so much for the carb help guys, and I will keep posting my progress as I will be using my G-Timer performance meter to record times.