olmako20

I pulled the carbs apart last night to see what jets i have been running. I am thinking that the carbs may be runing lean and making the engine run too hot. the primarys are 64 and the secondarys are 68 with a yellow spring on the vaccume. I dont know much about tuning carbs but do these numbers and springs sound about right? I want to fatten the fuel curve a little to bring down the combustion chamber temps. What would you guys recommend going to? Maybe a 68 on primary and 72 on secondary. Or is that to much of a jump. Any help is appreciated.

tinman565

First...you said carbs (plural), so I'm assuming you have more than one motor. Then you said " and making the engine run too hot" (as in one engine). If you have one engine...and its running too hot, I'd make sure your cooling system is flowing perfect (no impellar pieces stuck in any coolers..leaks..worn impellar..tight belts..etc.) Whens the last time you changed raw water impellars ? Do you have water circulation pumps on the front of the motor/motors ? Are they old ? Do you have water pressure gauges ? Whats the pressure ? If your running more than one motor, and they are both running too warm (after checking BOTH cooling systems), you could try moving up in jets. You'll be fine going up 4 numbers to 68 & 72. You may even wanna try a 74 in the back. But a 4 number move up or down on a motor thats pretty close wont hurt anything. Look at your plugs also...they can give you some indication, as well as the back of your transom if your running rich. We can change jets pretty quick, so we always kept going up in numbers till our speed dropped off...then went down 2 numbers. Good luck sir.

olmako20

Thanks for the quick reaponse. I probably should have elaborated on the setup. It's twin 350s hooked to TRS drives. Both motors seem to run hot around 180-200 at 3000 rpm. It has a sea pump hooked to a crossover. I changed the impellers at the beginning of the season and they seem to have good pressure. I don't have a pressure gauge perhaps something I will add next season. I'll try some different jets in the spring.

David Stotz

Tinman, I gotta ask, are you a sheet metal worker?
Dave

tinman565

No...lol....I just have no heart.
Old Pontiacs are often called "Tin-Indians"
"Pontiac" was an old Ottawa Indian Chief (1755)


(I'm actually a skilled trades tool & die welder at GM)

mcollinstn

olmako,

Engine coolant temp is usually not affected by fuel mixture unless it is also accompanied by the engine running poorly.

You can generally jet a motor lean enough to have it wheeze and cough, yet not see any coolant temp variation.

If your motors are running well, not backfiring, accelerate well without hesitation, not surging, not missing, start well hot and cold, run out strongly on top end, then stop looking at your fuel system.

Please advise to the character of the engines regarding how they run. What is the indicated rpm at wide open throttle, what is the boat speed. Have you owned this boat for more than one season, and is it behaving differently than last season or is this the way it has always been? What altitude is your lake? What flame arrestors are you running?

Please give us more to go on.

MC

olmako20

The engines run pretty strong and start up when cold well. They have a little more trouble starting when they are hot. It doesn't seem to hesitate when accelerating. The boat runs about 55-60 at WOT @ 4500 rpm. This is the first year I have owned the boat. I rebuilt both engines when I bought it. I am at sea level and I am running a pretty big flame arrestor so there is plenty of flow. The only reason I think it is running too lean is that I tuliped the intake valve twice on one motor. I believe this indicates a combustion chamber that is too hot. This only happened to one motor on the 1 & 7 cylinders. Both engines lost a head gasket over the season as well.

olmako20

There's alot more info on my thread in the Sutphen thread.

http://www.offshoreonly.com/forums/s...drives-12.html

JMS322

Spark plug color is going to tell you if your carb jetting is correct.

BUIZILLA

what is the carb # ??