Pulled the heads off and found excessive build-up of carbon. It caked the surface of the pistons, combustion chambers, and exhaust ports quite badly. However, I leaned the idle circuits out as much as recommended. Do I just need to jet the carb down? Maybe the running circuits are the problem? Also, the CR at time of disassembly was about 8.5/1. New pistons I'm installing will increase it to about 9.8/1. Would this help, maybe, without having to dink with the carb? Here are my rough specs: Engine: 302 (+ .040) Carb: Barry Grant Speed Demon 575, vacuum secondaries, factory jets (don't know jet size) Iginition: MSD 6AL, MSD Pro-Billet distributor, MSD Blaster 2 coil, timing is 34 degrees full advance in by about 3,100 RPM Intake: Weiand Stealth dual plane Cam: duration 268/280 (@ .050= 224/230), .509/.512 lift, 110 lobe separation Heads: AFR 165's, 1.90/1.60 valves Exhaust: 1.5" full length tri-y's Thanks, guys... I'm not really tuning literate, so, any advice would be great. Eric
Carbon can be the result of too much gas, not enough spark, or burning oil. Most of the time with old parts, it's all of the above.Of course short trips and driving like granny don't help none(not that you drive like granny, or do you?) After putting the pistons in it, make sure the dist, coil and plugs/wires are good. Then tune your carb. I can't help you with that, I never messed with one of those carbs. I'm sure someone around here has and would be happy to help.
If plaque is the problem...brush more...oh wait, it's carbon, not plaque! Anyhow, for my two cents, if it's running way too rich usually you'll see that the plugs are wet and the chambers will usually be washed down and nave clean spots, like around the intake valve. I've always experienced carbon from oil finding it's way past valve seals or rings. Just my experiences.
Thanks guys. The car was used as a daily-driver for about a year, so, I didn't really thrash on it that much. Pretty sedate (pronounced: granny) driving, actually. All the parts, as shown, are/were new. I'll inspect the rings and seals for oil leaks, though. I was a little suspicious of that, too. Still, I'm pretty sure a re-jetting is in order, but just thought I would get second opinions first. Any further tuning advice for would be heplful. Thanks again, Eric
Go on Barry Grant web site. They have the video on carb tuning. If you bought the carb new off a local dealer, go back an see them! Good dealer will help set up free of labor! Good luck
Even a well tuned vehicle in top shape will carbon up with commuter driving granny style short distance for a year. I might not put too much concern into the carb or looking for broken rings or whatever tangent has been mentioned. That cam is not really traffic or short trip friendly either!
What octane fuel have you ran in it during the last year? You could also bump up the spark plug heat range one notch if you stay 8.5 compression. Don't bump up if you raise compression tho.
Usually, 87 octane. Don't know if it matters, but, the commute was 60 miles/day all freeway, so, "short trips" weren't really a factor. "Spark-plug-heat-range?" :confused: I don't know what that is. However, already bought the pistons, so, upping the CR is a given at this point. Still, you have my curiosity's attention with that spark plug comment. Please, elaborate... Eric
When you install the new pistons, it helps prevent carbon buildup in the cumbustion chamber and pistons if the quench distance is kept between .035" - .040". Helps prevent detonation, too. In a carbed car you can "steam clean" the cylinders by squirting some water down the carb while the engine is running at a fast idle. It usually ruins the spark plugs so only do it just before tune up time.
Wow, I have never heard of that. If anyone takes up this idea, fine, but don't put much water! Water doesn't compress like air and will become a solid mass for your piston to run into and destroy your engine. The act of water stopping an engine in it's tracks is called hydrolock. Hydrolock in it's worst form, engine running, can bend rods, break the crank, or even damage the block. That said, a little water may not hurt at all. When I was a kid, they used to dribble tranny fluid into a running engine to clean deposits. Tranny fluid is just a very lightweight engine oil with a great deal of detergents (and red dye)... You have to be careful with that too though. Oil can hydrolock the engine, and detergents can wash out the rings just as raw gas can. Edit: Btw, spark plugs come in various heat ranges. They are rated by how fast or slow they transmit their heat to the engine. This can be used as a tuning tool. The best thing to do for performance is to use the highest heat range you possibly can without causing detonation. That is the recipe for most power, mileage, and least carbon. Lower heat range plugs can be used to run poor quality fuel, cure detonation, help overheating conditions. However they tend to foul faster, the cooler the plug. I must repeat that too hot a plug can cause problems... Over heating and detonation. So only jump up one range at a time, then when you get detonation, drop back to the next lower. Another thing you can do to help things with your new pistons is to polish the tops. It is something that everyone is supposed to do when installing pistons, but is rarely done by anyone.
Thats a great tip. I usually do this to my good customers cars before a tune up. Lot cheaper than a top end de-carb. I use a teaspoon about half full and give it about 4-5 shots of water. Make sure the motor is fully warmed up too.
I have an old plastic mustard squeeze bottle I use. Several small shots, not enough to stop the engine. Back in the 70s guys who ran water injection setups due to the crappy gas and emissions engines noticed that their piston tops and chambers were staying exceptionally clean. I sometimes use Sea Foam, too.
Wow! Seriously, great info. guys! I'll try the water application for this next build and see what happens. Ratio411... thanks very much for the clarification. AFR suggested one particular spark plug, so, I'll check that and see what other heat ranges it comes in. Thanks all, Eric
