Does anyone have a good link to a site that goes into detailed analysis of sparkplug electrode colors and their causes? I have a slight miss and am trying to figure it out. A buddy says it's a lean miss but I'm not so sure. It's not there at idle only part throttle.Some plugs are chocolate brown while others are white. My MPG SUCKS I know it's not going to be great but I didn't think it should be this bad. My engine details are as follows 455 punched 30 over Non stage1 iron heads GS 113 Cam (not sure how it was installed) Poston 10.5:1 pistons with valve reliefs Stinger S-1 (Unsure of curve)No dial back light yet S-Divider intake with light port matching & notched 1" under carb Q-jet (was told it was set up for this motor by Norm Deely) stock exhaust manifolds (soon to be opened & port matched)
Look at the intake runners for the cylinders with white plugs--If you find vacuum connections on the manifold runners feeding those cylinders, you've probably found the problem. If both inner cylinders on one side, and both outer cylinders on the other side are "problem children", half your carb isn't working properly. (assumes a 2-plane manifold) Overall, reading plugs is a poor way to judge rich/lean. Too many goofy additives in the gasoline providing (or NOT providing) coloration. In this case, though, since the plugs are not coloring evenly, you may be able to use the plug color as a guide.
Miss at cruise I had a similar problem with my car. It would kind of "chug" at about 1200-1500 RPM and surged at cruise speed. Changed points, condenser, cap, rotor, wires, even tried another carb. I re-degreed the cam and found it 4 degrees retarded. Set it back to straight up and the problem went away. I'd suggest that you degree the cam since you don't know where the centerline is. It might save you a lot of time and money messing around. Another possibility - if you have too much advance you can have part throttle surging. Borrow a dialback lignt if you have to. Make sure the advance stop bushing is in place, also check into limiting vacuum advance (or just disconnect it and see if the problem goes away).
The miss is an ever so slight sound almost like 1 valve closing a bit slow it sounds sorta like PFFP-PFFP and it goes away with a heavy foot or maybe I just can't hear it over the exhaust o No:. It pulls good from an idle but seems to flatten out over about 50mph with a heavy foot not what I would expect from . Can the cam be degreed without removing the heads to setup a piston stop ? I really don't want to tear it all apart again if I don't have to. I'll pay closer attention to which plugs are white. Thats something I had not considered. White plugs would indicate a rich condition in those cylinders if I read a few other posts correctly?? Thanks
You don't need a dial-back light. Mark your damper 1.75" clockwise from the zero mark. That is 30 degrees. You can check your total by where that mark lines up with the scale. On zero = 30, 8 = 38, etc. Easy way to check total timing. Then all you need is someone checking the tach and you can tell where and when your total is 'all in'.
White plugs would indicate LEAN, not rich. That's why vacuum fittings on the intake manifolds could be an issue--if those vacuum-driven accessories are allowing extra air into a particular intake runner, it would lean out the mixture to that cylinder. White plugs are normal for anything that's computer controlled, and unleaded gas just doesn't color plugs the way leaded stuff did years ago.
Thanks for the correction. I burn 93 octane pump gas with about 3-4 gallons of leaded 110 per tankful. I am thinking maybe I am using the wrong plugs. When I got the motor it had Champion RV17YC plugs and they are still in it. I have seen reference to other plugs people are using maybe I should be using a different plug with all the mods done to the engine
My motor had those plugs in it when I bought my GS. I've always liked them. They are a projected nose design, and offer performance advantages. I currently use NGK UR-5's. UR-4 would be equivalent to the Champion plugs. UR-5's are one step colder. THe Poston S-divider is not a popular manifold, and it requires special jetting, and possibly some milling of the divider to run it's best. I would at least get a good timing light, and figure out what your spark curve, and total timing is. That can have a huge effect on how the car runs.
I know many people say the poston intake is just so-so but it's what I have to work with at the moment The divider has been milled down about an inch and has been port matched to the heads. I do not know the setup on the carb so I will have to pop the top to see what jets,rods,hangers etc. it has. I will be looking at my timing this weekend. I'd be a happy camper if all I need to do is recurve and rejet.
