[kvinmn]

The PO of 68 KAT put a bunch of work into the 390 engine rebuild - .040 over, 10:1 pistons, true roller timing chain, port matched heads, Performer RPM intake and a Demon 750.

I replaced the 750 with a 625 Demon with vacuum advance and drivability has improved immensely. However, it still seems to run rich (wet black crap on the garage floor!).

I'm wondering if it will always be running rich because the *%%&$# PO put in a 'RV' cam. The only specs I can find on anything called an 'RV' cam indicates it is just mildly more performance oriented than the stock cam. We ( a local Cougar buddy) were discussing this and I wanted to get a bit more feedback from other learned individuals on this fabulous site!!!

Anyone???

 

[modifiedmark]

kvinmn, the cam dosent have any thing to do with your "rich" problem. Face it, when you purchase an aftermarket carb its a fit all and the manufature dosnt know what its going to end up being used on.

Its still up to you to "fit" it to your engine. That means it could be jetted too rich for your "mild" engine. You need to pay attention to your engine to see if it is indeed rich. You need to "read" the plugs to see what its doing. Black sooty plugs all the time is a sure sign of a overly rich condition where a white plug is a sign of a lean mixture.

Check it out and see where your at and dont forget to check the power valve to make sure you have one that meets your engines vacume requirements. I would suggest if you find black plugs to go ahead an replace both primary and seconday jets to a smaller size. Many only suggest dropping one size at a time but it just depends on your situation.

A example is I just put a new Eldebrock 600 on my truck a while ago and it didnt run too bad but I dont drive it much to really check it out. Well the more I drove it the more I realized it didnt seem right as it was kinda doggy and checked the plugs after a longer drive and found it a little on the lean side. A 4% richer primary mixture made a world of difference along with the next step stronger step up spring. Now I'm going to richen up the secondarys to match.

The point is the 600 eldebrock is useally going to find its way on a 302 so thats where the factory sets it up to match the most common application. Its a little lean for the 351 but thats why the factory makes the jets and ect easy to get ahold of because there needed in alot of different applications.

The Demon on the other hand is maybe set up from the factory for a little bit more potent motor as there really aimed at the higher performance crowd and it maybe a little rich for your milder motor.

The only thing I question is the use of the performer RPM manifold with the RV cam. The RV cam is for low rpm power where the performer RPM mainifold is more for midrange and higher rpm power. There not the best combo and a regular performer manifold would be better with your RV cam or a hotter cam would be better with your RPM manifold and maybe the Demon carb.

 

[kvinmn]

Exactly MM....

My dilemma is whether to tune the existing combo (cam, intake and carb) or to change out the cam to one with a more aggressive profile and make more power.

I'm just wondering if the cam-intake mismatch is going to make it run rich no matter what I do. The new Demon has made a drastic improvement over the 750 and making it more streetable. I guess I'll try to live with it and tune the carb since I am planning on doing suspension, transmission and steering work this winter and hope to work on engine upgrades and the rear end next winter.

Ken

 

[Royce Peterson]

The wet black crap on the garage floor does not indicate a rich condition. It's normal with modern gasoline. What happens is the gasoline available today is "oxygenated". This means it has alcohol - related additives that burn partially but in a non - catalyzed exhaust they give off water vapor as part of the exhaust. When your car is hot this is water vapor and doesn't leave stains. When you park the car overnight the exhaust cools, causing water to condense in the bottom of the mufflers. When you start the car this water mixed with soot from the exhaust system is blown out and deposited on the floor.

 

[kvinmn]

Thanks again Royce, that did not occur to me. It makes sense too with the infrequent use of it. I guess I'll keep the original plan and tune the carb/intake as best as I can in the spring...

Ken

 

[ronzoni]

Ken,

Perhaps the only variable left would be to determine where the PO set up this RV cam... straight up, advanced, retarded... I can't fathom that it was set up retarded with the parts that were used... but then again there's a reason it's called "retarded", you just never know what someone has done, or why, unless you check it. I'm intending to check mine this winter, but I'm guessing it's probably staight up...

You might verify that the timing mark on your harmonic balancer in fact reads true TDC... There's a device that screws into the spark plug hole that will stop the piston from reaching the top... you do this with no spark plugs in and with a wrench on the harmonic balancer bolt... VERY GENTLY! Don't get agressive here or you can really hurt a piston top or bend something... Bad, bad, bad, it's all bad. Make a mark where the balancer stops on the timing pointer, roll the engine around the opposite direction til it stops again... make another mark on the balancer... The halfway point between the two marks on the balancer is your true TDC... I've heard of some that were off by 10 degrees or more... really messes up your ignition timing at the very least. The factory style balancers that have the outer ring on a rubber isolator are notorious for this problem... they tend to slip and retard with time.

Just something else to check.

Ron.

 

[kvinmn]

Thanks Ron...something else for me to check. The PO had a speed shop do all of the work, so i am assuming that it was done correctly. However...I won't know until I check myself...

I STILL have to mail that fuel inlet to you...I have not had a very good couple of months. I'll try to get it to you b4 the 1st of the year...

Ken

 

[cougarguy]

Kvinm if you know the speed shop go there and ask them if they still have the where tos on that engine if it was long ago they may still have what was done and what components they installed. That way you could be sure of what is going on many people say they have an rv cam and use it like coke for soda pop or colt for a pistol. at least it will be a start.

 

[kvinmn]

Way ahead of you cougarguy...

I checked it out prior to buying the car and the owner of the speed shop (in Austin TX) remembered doing the work and the car. He just couldn't recall the cam specs because the PO picked out the parts and delivered them...

To add insult to injury, I found out that my 'southern' car got to Texas by way of Ohio and Minnesota!!!

Ken

 

[cougarguy]

hey my 68 as a california car has a dso of virginia and a virginia title. lesson to all just cuase its a southwest car dont make it a southwest car it whole life.