The oil cooler is too small. That much hp should have a cooler with a 3x12 core inside. Total length of about 18 in. I agree that there is something wrong causing the low idle vacuum. First make sure the carb is right, the needle and seat doesn't leak, the float bowls aren't set too high, the idle mixture screws are between 1/2 and 2 turns out. Then make sure the ignition system is working correctly, 16min. degrees of initial timing and 34-36 total. Last check the inner workings of the engine with compression and leakdown tests. I still don't think it's water temp related. Like I said, I run a crossover with a 120 thermostat and I don't foul plugs. These engines aren't rocket science but they can be frustrating.

I did a compression test, prefect. I will do a leakdown.
Cooler, I would like a termosate setup. With cold lake water it is HARD to get oil temp, and then once it is hot.........

Vacuum, I will look at.
Carb is coming off, and I am going to build it to HP 500 specs with 2 sizes bigger jets........ does that make sense?

RT

If your AF numbers were correct on the dyno there's no need to change your jets, in fact you'll just make the engine run richer which may exacerbate your problem.

I'd start with getting a visual down the venturi and see if fuel is leaking past the booster at idle before going any further.

When you say fouling plugs, do you mean they're just darker in color or do they actually foul and misfire? It takes a fairly decent amount of fuel to foul a plug.

You could always put a #6 heat range plug in, I think I read that you're running a #7.

But the dyno had dyno headers, no flame arrestor, no pullies.

When I say fouled, I mean......... NO FIRE. Put new plugs in it will run fine for a bit. IF you idle more than a few min they are toast. If you run at 3000 or more they slowly go to toast.
The boat goes from 80- 60's in about an hour, new plugs back to 80...... always the front 2 plugs...... always.

RT

Dyno headers run leaner than manifolds, the engine will be slightly richer in the boat. Also, running without the flame arrester will make it run slightly leaner than with because it restricts airflow to the carb. The pullies are just a tiny bit extra load on the engine and carbs pull more fuel when they are put under a load. So if you jet up you'll be even richer...

If you're fouling plugs that quickly you're dumping fuel, has nothing to do with water temps....

A V6-14 module on a V8 engine will give about 10* of advance, all in by 2500rpms.

Your problem is being caused by the low vacuum. The low vacuum is making the carb powervalves open and making it run rich at idle. You need to figure out why you have such low vacuum.

Fix the problem, not the issues caused by it.

Been trying to say that for the beginning...you say it much simpler than I can... :drink:

what sort of vacuum should I have on a 9.8-1 compression 502 with Edlebrock oval port aluminum heads, a Victor Jr. intake and a Crane 741 with an 850 holley?

1. make sure you are checking the vacum in the right place on the carb. 2. what block is this mark 4 mark 5 mark6 if it is a 5 or 6 i hope you used the head gaskets that block off the front water passages in front of the cly. bore if you don;t the water will not move through the block like it should. i built a pair of 496's ,not the merc 496 used the 741 no thermostat at all i used the air gap with 1050's idles at 800 never loads up and made 640 at 5800

Thats basically my motor RBT has described. Odds are its the Vacuum leak. Should be 10-12 inches of vac. If it has a vacuum leak that bad then the carb might be adjusted over rich to compensate for the leak just to keep it running and therefore taking out the coldest plugs. If thats really the correct vac reading from the manifold and the intake gaskets are not leaking then I would try a different carb, just to see. Was it a new carb? I have had used carbs that just never ran right no matter what I did, swapped out to a new one (or different) and problem was gone.I run NGK #7 in my motor with no problem.#9 fouls out with extended idle. Make sure to try plugs that are a bit warmer. BTW What was the compression PSI when you checked?
So try warmer plugs, make sure there is no vac leak, buy or borrow a carb.

I run those Ngk plugs but 1 size colder -8, no fouling problems. A vacuum leak that big would be instantly noticable. You wouldn't be able to idle below 1200 rpm's. It sounds like the engine runs well in the upper rpm's, just not at idle. Probably too much fuel at idle and then the opening power valve just making it worse.

Not sure on the head gaskets, I did not put them it. I am a 2 -stroke guy.
All I know is they are Cometic, the block I belive is a Gen 6. I have a Mallory 130 gph fuel pump at 4.5 psi.
The motor idles at 800 as solid as a rock, start easily. It just eats plugs.
Interestingly, the intake never fit right, and had to be machined to make it seal.........

RT

99% sure but LOOK FOR VAC LEAK AT FRONT OF INTAKE.....

and dang it listen to Mike 280 and panther.... they know yer problem.. stop bein ignorant about 4 strokes just cause ya play with a lapptop and 2 strokes... tunin a carb is highschool mechaniics class basics... even a retarded Special ed student can do it....

Does the motor smoke or use oil? Possible intake leak sucking oil from lifter vally.

nope, that is good. Just burns your eyes at idle.

any chance the valves are adjusted to tight

what does that do?

Makes it run like crap.

I don't think this your problem though since it seems to run good except at idle/low rpm.

I would suspect you would have more trouble at higher rpm if the valves were tight. More heat, and less time to close.

It would be sluggish and way down on power at higher rpms.

RBT, would you mind contacting me in the above matter. I have some thoughts around this subject and it's very hard to find correct info over here ...

/Alex

FYI, powervalves have no effect on idle quality, as they are part of the main metering system which is not active at idle. Powervalve could be an issue if its "blown", then it would leak. Are the mixture screws responsive? If not, that could indicate a blown powervalve.

Checking the valve adjust is a good suggestion, if they are too tight the valve will be held open and vacuum stuffers, probably not good for plugs either.

I suggest doing the leakdown. Myself and a buddy both run ZZ502 heads and we both had issues with poor valves sealing on NEW heads. We had very very high leakdown rates. You can just take the rockers off to make sure no valves are open when doing the test. With that low a vacuum, something is way off.

If the cam is big enough it can/will activate the powervalve depending what size PV you're running... Also if you're not running powervalves it can also draw fuel thru the main fuel metering circuit and you have to adjust the secondary butterfly so the primary isn't open as much.

??? talking about a Holley?

If your pulling from the mains at idle something is very wrong. That's why there's a idle and transfer circuit.

Yes.... check around...

Big cams with little or no vacuum activate the PV's and begin dumping fuel thru the venturi's...

big cam requires the throttle plates to be open more so the engine can idle...

It's holley 101.

Here's a Q&A taken directly from the Holley website, this is all public knowledge...

"QUESTION Why is my engine running rich and my mixture screws do not have effect?
ANSWER The first thing you need to ckeck is your float level. No fuel should run from the sight hole unless you shake the vehicle. Next check the engine vacuum at idle. (in gear if A/T) if it is 12" or more a 6.5" powervalve will usually be fine. Anything below 12" divide in half. For example 9" vacuum will use a 4.5" power valve. Another possible cause associated with performance cam shafts are exposed transfer slots. You should not see more than .025"-.030" of the transfer slot exposed past the throttle plate at idle. "

PV is not his problem. If it was, all plugs would be fouling. The low vaccum is probably b/c of the deal cylinders (fouled or something is wrong mechanically).

Should put a timing light on that wire to make sure there isnt a ignition problem after a new plug is installed.

If the knibbler pin isnt fully dampened, the fetzer valve might cause early detonation

Agreed that may not be the cause of his problem but your statement implied that powervalves don't effect idle in general and it is false... also, the front two plugs usually fowl first. If you run a big enough stick you'll run into PV problems at idle if you don't set up the carb properly... :Whatever:

We'll, I still think that PV is inactive at idle - if your pulling from the mains at idle something else is up. My motor doesnt pull from the main circuit till over 2000 rpms.

It goes by vacuum and/or load not RPMS.... You've probably never run a big enough cam or had to idle one at 1000 rpms with little/no vacuum then.... Do a google search if you don't believe me....

In the meantime here's a paragraph;
"Stock engines can have high vacuum readings (10-18 inches at idle) and the Holley power valves with higher readings like 6.5 to 10.5 will work correctly. Long duration non-stock camshafts and other performance related parts can cause a problem, because engine manifold vacuum may be lowered with these performance parts and the power valve, if incorrect, will always be open, even at part throttle, leading to an overly rich air/fuel mixture. The solution is to choose the correct power valve and to do that you need a vacuum gauge.




I give up...carry on..

Yes but the mains are activated by airflow through the venturis, not vacuum - vacuum is below the throttle blades. I agree the PV will open, but the mains should be inactive. If the mains got active, the motor would stall out fast. That Holley exerpt is not talking about idling, just overall operation which I agree with. My cam is a 231/239 .6/.6 110lsa and idles around 900 with 11" for the record.

Just have to agree to disagree

That cam is small, that's why you've never seen any problems.....

With a larger cam you have so much overlap and so little vacuum that you have to crack the throttle blades open and adjust the mixture screws further just to get the engine to idle and/or shift without stalling... If you go far enough you begin to expose the transfer slots and you begin pulling fuel thru the venturi's if you have the wrong power valve... It doesn't dump...it slowlly drips...and after 10-20 minutes you'll begin fouling plugs.

It's not rocket science it just happens when you have a big cam and you need to know how to set up the carb so that doesn't happen....whether it be proper power valve selection or by adjusting the throttle plate in the secondary...

Raise the idle speed, just because it will idle that slow doesn,t mean it should. Big cam , big intake, big heads , try raising the idle speed, thus air speed for more vacuum & fuel adtomization.