lagg on take off and high rpm

[T-stone]

So i have done some work on my 1972 240z, put a cam in it, and headers.

I was told that you cant set the timing with a timing light if you have a modded cam, so i set it as best i could.

i have been driving it for around a month now, but it feels like it has a loss of power. when i put fresh plugs in it, it runs like a champ. however after a while it starts to feel laggy, when starting off if i dont have around 2 rpm it will bog and stumble to get up to speed.

while driving it does good but some times it will jult like all 6 cylinders have no spark.

also when at high rpm it will spudder and start to miss fire.

i have a new msd coil for the car but am waiting on the resister to get here,

im thinking it could be the coil, or i could just be off on the timing, also the carbs could have a slight of hand to do with it.

need some help

[FastWoman]

What do your plugs look like? I bet they're fouling. Maybe you're running too rich?

Are you blowing smoke (not steam) out the exhaust, and if so, what color is it?

[T-stone]

Plugs do look fouled,6-4 are dark brown/black 3-1 are black and charred looking.

when i first crank the car i have alot of white smoke, it stops after engine warms up

[FastWoman]

Well, the white smoke is probably steam (normal).

Do your plugs look oily at all? (I suspect not, but if so...)

You're probably just running (way) too rich. The fact that 4-6 look different from 1-3 suggests they're also out of balance. Unfortunately carbs aren't my thing, so that's about all I can say with an ounce of intelligence.

[T-stone]

plugs are dry and chalky looking, i have noticed water and black sutt on the ground from exhaust.

i have not see this in a while

i do need to equalize carbs, but im not entirely sure how to set mixture how it needs to be

[FastWoman]

Hmmmm... Well, my fuel injected '78 was running quite lean when I got it, and the mix burned poorly enough that I saw a lot of soot on my plugs and around the tail pipe. It was confusing, because the plug appearance suggested rich running. However, I suppose if the mix gets lean enough, all bets are off on plug appearance. My exhaust blew very hard, with occasional hard puffs. I had lots of steam and moisture as well. Engine vacuum was quite low -- around 14 in Hg. When I richened the mix, the idle picked up quite a lot, as did the engine vacuum. After I adjusted down the idle, the engine ran smoothly. Exhaust wasn't nearly so labored and was very smooth. Moreover, plug appearance returned to normal (well, after replacing the fouled plugs). So maybe your engine has an extremely lean condition. One test would be to take off your air cleaner and manually lift the SU pistons just a bit to see if the RPMs pick up (PRETTY sure about this). That would richen the mix. You might also pull off a vacuum line somewhere to see if RPMs drop (leaner = worse, or so the theory would go).

Lean running could be from fuel starvation (e.g. insufficient pump, clogged filter, clogged float valve) or maladjustment. Dunno... I really don't know carb stuff very well. They're magical thingies!

[Dobber]

I would go ahead and put the timing light on it. ( have not heard that one before ) At least its far better than a guess. There are many links for tuning S.U. carbs. Sounds like yours are out of wack alright. I trust you don't have any choke issues?

[Dobber]

Are you sure that the timing chain did not slip a tooth on the crank when you took it off the cam? If engine was running ok before you did the swap chances are your carbs are at least in the ball park. If this cam is just one step up from stock, ( mild ) your timing should not be so far out that you can't ball park it with a light. I would be willing to bet that the chain has slipped.

[T-stone]

I have set the cam timing dead on im sure of that.

im running a su carb setup from another z, had a 280 motor

original carbs were not working right.

specs on cam- valve lift .480 duration 274 camlift .325 duration 215

Also has a 6-1 2.5 inch header

msd blaster coil

new plug wires

new distributor cap and rotor

im looking for some information on setting for a modded cam, i know that the stock setting wont work as well.

setting for carbs and timing

the car runs great with new plugs but they foul out very quick.

how well do point distributors work with this type of set up

how much different should the carbs be set for the added fuel and air consumption

[Bruce Palmer]

By fouling out do you mean the plugs black and sooty? If so that's a rich condition and more than likely accompanied by a blubbery running condition.

Do you know what needles are in your carbs?

SUs are a variable venturi and supply air and fuel in direct relation to what the engine is pulling in. Not a whole lot of compensation tuning you can do. At X cfm of engine draw, the carbs will supply X cfm of air and fuel and all one can do is find that sweet spot between rich and lean.

[T-stone]

plugs are black and wet with a clear liquid

plugs are not oily but have a dry chalky look when allowed to dry out

[FastWoman]

What sort of clear liquid? Gasoline?