Reason for constant timing?

[MalcolmV8]

Why would a motor have constant timing from idle to WOT with no advance? A little back ground on the issue.

Buddy of mine has an older camaro with a built 496 big block. He had it professionally built by a guy/shop out in Minnesota and then picked up the engine and brought it back to Kansas City. The motor made 740 hp and 650 ft/lb on the engine dyno. See vid of it on dyno here
http://www.youtube.com/user/cobrav8281# ... FeR33C8RiA

Anyhow the problem now is we get the motor in the car and fire it up and it sounds fine in neutral but put it in gear and try drive it's like its missing like crazy. Plugs get fouled and turn all black and nasty real quick. Carb should be all tuned and perfect though as it's the carb it was tuned with at the dyno. It's a dominator 1050.

Anyhow I'm thinking something is wrong with his ignition so I check timing and it's at 42 degrees at idle. what the heck? do some more checking and the mechanical advance is locked out and it's at a constant timing all the time. According to his dyno print outs maximum hp was achieved at 36 ~ 38 degrees so we set it at 36. What's the advantage of having it set at 36 through out the entire power band? that seems limiting to me but apparently this shop that built his motor really knows their stuff.
We called up another buddy who also has a 496 in his camaro and he's running 12 degrees initial timing and 36 degrees maximum with a mechanical advance. His hits the full 36 degrees at 3000 rpm.

So I swapped out his MSD 6al box with another one and it made no difference. I'm at a loss as to what's causing the car to run so bad. You can barely drive it or get over 1500 rpms under load going up the street. It's sounds like it's missing and shuddering so bad I even thought we had spark plug wires crossed on the distributor or something. However in neutral in the driveway revving up the engine it seems to sound crisp and responsive but I think I can still hear a miss. It's hard to tell exactly because he's still running open headers and the 496 on steroids is just a tad loud.

[v8ranger]

To me, if its missing under a load, its bad wires, plugs, or cap. Under a load they would be arking. Easy enough to check, start it up after it get dark out and put it in gear and power brake it and see if you can see the arking. Or get a squirt bottle and start spraying all the electroninc stuff and see when it start messing up. Just my opinion

[MalcolmV8]

Amazingly this car is still not running right. It's been a while but we've all been so busy with work etc. I don't believe there's any arcing going on. We've checked at night.
We've since replaced the MDS box, ignition coil, plug wires, plugs, distributor cap & rotor. The only thing we haven't actually replaced yet is the distributor itself. The shop who built the motor wants us to check the distributor phasing but we haven't gotten to that yet. The procedure where you cut a hole in the cap and using a timing light to see if the rotor is at the plug terminal when it fires.
The shop has also walked us through making some carb adjustments including putting in smaller power valves but still nothing.
We'll keep at it as time allows.

Thanks

[v8ranger]

I dont know anything about dyno's and how much of a load they put on an engine, but what are the chances its jetted wrong for the street? I know when I put my supercharger on my Ranger and was trying to jet it, it would idle and rev up great, but as soon as I tried to drive it, it would buck and kick and wouldnt even go down the road 10 mph. So what are the chances its jetted to high/low?

[MalcolmV8]

Dyno puts one heck of a load on the engine but your thinking is exactly where ours has been too for a while. Unfortunately I'm such an EFI guy I know next to nothing about carbs. I mean I've tinkered with dirt bikes, quads, lawn mowers etc. and have no problem rebuilding/jetting/setting up those but car carbs are quite a bit more complex and I have absolutely no experience with them. His dominator 1050 is quite the carb too.
When this guy Bob called us from the shop in Minnesota he walked us through putting in replacement power valves in case they were blown and allowing excess fuel in the idle circuit. I believe it's a 3 circuit carb from what I've googled. Anyhow we also went from 5.5 to 4.5 power valves to reduce fuel some. The guy then walked me through adjusting some air bleed screws and had me watching certain places in the carb for fuel flow and tell him what was happening and it's supposedly where it should be. Oh yeah also checked float heights in the bowls and various things like that.

One difference from the dyno to home was that at the dyno my buddy used their headers but once the motor got home he's using his own which are not quite as big. My thinking was a smaller header is going to reduce air flow and cause a richer mixture but Bob (builder on phone) disagreed with me. Or at least thought it was a non issue.

I've been telling my buddy to purchase a wideband and stick it in the exhaust so we can see if it's running horribly rich but he's yet to get one. I wouldn't be surprised if it was because it's fouled out a couple sets of plugs something horrible. Although that could also be due to an ignition problem and not firing the plugs correctly or all the time too. Very frustrating problem.

[v8ranger]

I have to agree, I don't think the headers will make that big of a difference either. Its probably going to be something stupid that's making it run that way and you both will kick your self when you find the problem. What about the accelerator pumps? I'm just throwing things out there that I have had problems with and had the same running problems. I had my accelerator pumps set to tight, meaning, they had light pressure on them, and it was allowing gas to just run down the bowl and make it flood out after I started it and tried to drive. I thought it was running out of gas and it was just the opposite, it was flooding it out. I'm not sure if the dominators are set up similar to the holly's when it comes to those.

[cgrey8]

I agree, smaller headers would likely flow more air at lower RPMs because the exhaust flow velocity is higher in a smaller pipe. It's not until you start getting to the high RPM/Loads that you max out the header pipe's flow capacity. Its at that point that a larger header would flow more. But up until then, I'd bet the smaller header would outflow the larger one purely due to higher exhaust velocities. But unless the rest of the system was a tuned exhaust, the amount more the smaller headers flowed should be negligible.

However if a swap from large to small headers is responsible, that would point me to look at the cam specs and exactly how much overlap there is. A heavy overlap cam can do weird things with AFRs at the lower RPM/Load range. In fact, they tend to fool Wideband sensors at low RPM/Loads leading you to believe you are running lean at idle when you are actually rich. The reason being the overlap, along with exhaust scavenging, pulls unburned intake air through the combustion chamber into the exhaust. The WB O2 sensor detects that unburned oxygen and wrongfully interprets/reports that as a lean burn condition. As the RPM/Load goes up, that issue goes away. Even on fairly heavy overlap cams, by ~2000 RPMs, you no longer have to worry about unburned intake air in the exhaust.

[MalcolmV8]

Prior to changing out the power valves we could see some fuel dropping at the top of the carb (air cleaner is off). Once we replaced the power valves that stopped so one of them probably was blown. They are like little vacuum actuated diagrams.

I forget the specs on the headers but they are just monsters. I think it's like 2 1/4" primaries right now if I remember right. I'll have to ask him again what the specs where.

Thanks for the tips on idle and wideband Chris. He does indeed have a very radical cam in there which I bet has a ton of overlap.

It probably is something stupid but till we find it, its just driving us nuts.

[rojam18801]

check for vaccum leak between carb and intake, most of the time at back of carb. been there done that with those big carbs....the old trucker

[MalcolmV8]

A vacuum leak can make it miss insanely crazy like a miss firing ignition? None the less I'll spray some carb cleaner back there and see if we find any.

[v8ranger]

A vacuum leak can make it miss insanely crazy like a miss firing ignition? None the less I'll spray some carb cleaner back there and see if we find any.

I wouldnt think so, not after you hit the gas. All my run ins with carb setups, it only idle's bad. You might have some hessitations, but not a miss. Thats just what I have ever run into.

[MalcolmV8]

OK guys we got to mess with his car some more yesterday. Brand new set of plugs one heat range higher since they're fouling out. We put the plugs in and fired up the car and took off driving. He tried keeping the rpms up to clean out the carb and hopefully keep the plugs from missing like crazy etc.
Didn't even ride maybe 2 minutes around the block. Maybe 3 or 4 minutes (should have timed it). Pulled plugs and they were completely pitch black and fouled like you've never seen.
In my opinion this carb is just dumping gas in there by the gallon and fouling the plugs so bad which is why its missing as though there's an electrical problem. Also when he first fired it up and backed out of drive way it died and he fired it back up and it blew weird very light smoke or something which looked like a ton of raw fuel. I have no idea what broke or changed on the carb from they dyno to taking it home but I'm almost certain that's the issue.

I know absolutely nothing about carbs other than dirt bikes etc. but I plan on pulling it off and taking it apart. I imagine there's plenty of carb people on the forum here that can tell me what's what right? perhaps walk me through jetting it etc. and checking out the setup? It's a Holley dominator 1050.

Thanks
Malcolm

[plowboy34]

Hey Malcolm I would check float adjustment before pulling the carb if you haven't already. It is not an uncommom thing in a holley. They are the best racing carb out there but they are a little finicky. You can just look down carb when engine is running and see fuel just running out. If needle valve is stuck open fuel will just run out the venturies. Sounds like it could be your problem to me.

[MalcolmV8]

Plowboy the carb is already pulled but yes we did check float levels first. We pulled the caps on the sides and level was right there. None poured out. I took carb apart and have to admit there was a ton less inside there than I was expecting. It's the 4500 series dominator. Exact model # is 8896.
I took a bunch of pics too which I'll get posted soon. I may start a new thread just on tuning this carb once I have pics so others not following this thread can jump in.
I saw jet kits at Summit that go from 60-99. He has 90 (stock 88)in the primaries (two jets) and one 92 and one 93 on the secondaries. There's also a ton of other little jets on top that I have no clue what they do. I'll post pics and get some feed back. I figured out the accelerator pump setup and it has 35 jets (stock).

Based on how simple that carb is I couldn't find anything wrong per say. Like nothing broken inside. So somehow the tune is just hosed completely from Minneapolis to KC. I think we'll purchase a jet kit and start jetting it differently and see where we go.

[v8ranger]

Make sure that the pump is not set to tight. Here is a pic of what Im talking about. There shouldnt be any presure on that when its at idle. If you have it to loose you will have a hessitation. But to much and it will flood out at idle. I have mine set so it has jut a little play in it when its at idle.