WETTE VETTE

KAAMA, have you gotten your cranking pressures yet? I only ask because the 1350 exhaust temps with a possible rich condition could be a result of a very high dynamic compression. Another thing you should do is put a vacuum gage on one of the motors and see where it is when you are running. Short cams in large motors with efficient heads can cause a stiuation where the vacuum starts to rise substantially especially at high RPM. Your carb could be set rich in the mid range RPM due to the power valves dumping fuel and at high RPM the power valves may be pulling shut causing a lean condition, hence the higher EGT,s. I may be way off but I am just trying to give you some things to try. My Nickerson 1050 has 92's in all four corners and 4.5 power valves on the pri and sec. Seems like it should be way rich for a 496, but my transom is as clean as it was when I launched the boat after a day of hard runnin. Also I have heard of motors with a lot fo vacuum not seeing much of a difference when the jets are changed. Basically a carb is made to run properly at a certain vacuum level and if you are above where it is calibrated to run a lot more fuel will be pulled through the main jets. In this case the air bleeds need to be adjusted. Then the motor will lean out, but you may be in danger of detonation because cyl pressures will further rise. Talk to ya later. Just keep an eye on the plugs and you will be OK.
Keep up the bench racing. Winter is just starting.

KAAMA

Craig, thanks for your help again. I will give it a go in the spring. You have been an asset to this forum.

Bobby, I wouldn't mind bringing my boat down to your shop to help me solve this problem, but I am first going to try and solve it close to home. If I can't, then I may tow the boat down to your shop. BTW, with my parts combination what brand of spark plugs do you usually like to run? Thanks

razor1115

KAAMA,
What exhaust are you running? I have had a sooty transom, yet was still running lean. I was informed on big inch engines, if you run exhaust that is too small, the engine doesn't like the restriction. Too much back pressure to exhaust gases, causes black transom and loading up like an overly rich condition, when in fact it is actually too lean. Just some more input...

Zack

KAAMA

Razor, That is a good question. The tailpipes on my boat stick out about 6-7 inches from the transom. I am running with Stellings full length tubular dry stack "green" headers with 4.5"dia. tailpipes. I don't even have any mufflers. If anything, I probably don't have ENOUGH back pressure---if you can actually believe that! About a year or so ago, I personally spoke with Keith Eickert about his full length primary runner headers that are in "manifold" form that he currently sells. In our conversation he told me that the manifolds come with a 4"...NOT a 4.5"......but again a 4" tailpipe. I asked him; why not a 4.5" tailpipe? His response was; his exhaust system with a 4" tailpipe is adequate enough up to 900HP! Hmmmph,------who was I to argue with him? Therefore, I highly highly doubt that back pressure is my problem. Pretty interesting though eh?

KAAMA

Bobby Daniels,

What is the name of your business? Can you please post your business (or whatever) phone number that we might be able to get ahold of you please?

Thanks,
Mark/KAAMA