Running LEAN
 

Need some help here...I have a SBC with a Performer (Weber) carb,aluminum intake and stainless marine exhaust....Motor has 42 hours on it...Well I keep up on my plugs and for about 40 hours they looked right on. Well with no changes made to the motor I started to get a slight miss on the top end and a definite miss when coming back to cruise after a W.O.T. run...When saying "cruise" I mean 32-3800 RPM's. If I bring it back far enough the miss will go away. .Usually below 3000 rpm's. Also I started getting a hesitation when going from cruise to W.O.T. I checked the plugs and they are LEAN!!!!!! What things should I look at to trouble shoot this Bit*h:D The miss and hesitation only happens under load. And again NO changes have been made to the motor to bring this on. The plugs were reading right on and then all of a sudden the symptoms started...In trying to figure this out I have upped the carb 2 steps (8%) on both the primary and secondary circuts and it did nothing....I have since went back and rejetted the carb to it's original settings. I have re-adjusted the valves (5/8 turn) and installed a new D.U.I distributor,New Taylor wires and new plugs. Still no changes. Plugs are white as a ghost....Any Ideas:confused: :confused: Thanks in advance

BH

Being that you did a jet change and saw no change in plug coloration, it could possibly be a fuel delivery problem. Maybe the pump is going bad? Clogged filter?
I am sure that when you did the jet change, you looked in the bowls for any dirt.

Did you check the fuel filters?

I put a new Fuel Filter/Water Seperator on also. Still no changes.
Have not checked Fuel Pressure though. Wouldn't this show up as rpm's increase regardless of load?

BH

anti-siphon valve at the tank fitting maybe?

An engine under load will require more fuel to run than an engine in nuetral.

I HAVE THE SAME SETUP AS YOU EXCEPT WITH A BIG BLOCK AND WAS HAVING A SIMMILAR PROBLEM LAST YEAR.IF YOU DO A FUEL PRESSURE CHECK AT THE CARB AND ARE HAVING NO SUBSTANTIAL PRESSURE DROP UNDER FULL LOAD CONDITION YOU CAN ELIMINATE PUMP,ANTI-SIPHON,FILTER,& LINE PROBLEMS.IN MY CASE I HAD PRESSURE AT THE CARB,BUT WHAT WAS HAPPENING IS ONE FUEL BOWL WAS RUNNING DRY.IF YOU PULL THE NEEDLE SEATS OUT THERE IS A FINE SREEN ON EACH SEAT.ON MINE THE SREEN ON THE NEEDLE SEAT OPPOSITE WHERE THE FUEL LINE ATTACHES WAS PLUGED.THE BOWLS ARE CONNECTED INTERNALY ON THE CARB SO BOTH BOWLS HAD SUFICIENT FUEL AT LOWER RPM BUT UNDER FULL LOAD WITH ONLY ONE NEEDLE SEAT FLOWING PROPERLY IT WOULD RUN OUT OF FUEL(LEAN).I WOULD LEAVE THE JETTING ALONE BECUSE IF IT WAS JETTED RITE IT SHOULD STILL BE JETTED OK.COOLER WINTER DAYS WILL MAKE THE ENGINE RUN BETTER(LEANER)BUT I WOULD NOT THINK THIS WOULD GIVE THE EXTEME LEAN CONDITION YOU ARE EXPERIENCING.GOOD LUCK!

power valve? What is the vacuum reading at the hesitation point? Greg

It' a Edelbrock (Weber/Carter)....It doesn't have a power valve.....Does it:confused: :confused:

BH

I THINK HP JUNKIE WAS GETTING AT ARE THE PRIMARY NEEDLES MOVING TO THE POWER STEP POSITION.IF YOU ROTATE THE NEEDLE HOLD DOWN CAPS YOU CAN SEE IF THE NEEDLES ARE RISING UNDER FULL LOAD TO THE RICH PORTION OF THE NEEDLE.IF IN DOUBT PUT THE HEAVY SPRINGS ON THE NEEDLES.IT IS VERY EASY TO CREATE A CRUISING LEAN CONDITION BY TO LIGHT OF SPRING.

When I tried going to the second step up in richness (8%) I also increased the pump shot AND tried the heavier springs (all of them). With no change. The plugs didn't change AT ALL during any of the changes....A fuel blockage or vaccum leak is starting to make sense. Can you see the "screens by looking into the carb or do you have to remove the carb to check this. Also what/where is the anti-syphon valve and what is it's purpose? What can I do to help rule out a vac leak?

BH:

Lots of good info here.
1. Vac leak can be around intake where it meets head. Spray with some starting fluid, just a quick shot. If you have a leak it will pick up rpm and or stumble a bit.
Hook a vac gauge up and observe it. A leak will make the needle bounce a bit.
2. Screens, don't now but you should pull that carb apart and inspect everything. Find a buddy with the same carb and set it up the same and re-test.
3. Your fuel pressure at running rpm should rule out the anti-siphon valve but they can stick an be erratic. It is located at the tank pickup. Looks just like a regular hose barb fitting but has a stainless ball and spring inside that serves as a check valve. It's purpose it to prevent fuel from leaking unchecked in the event of an accident or fuel line cut. Way I figure your pretty much screwed at that point anyway.
4. Winter grade fuels have different additive packages and it is really hard to get any color on the plugs. I cannot tell you much more than that, perhaps someone with more knowledge on fuel can add to this. I just know that in previous springs when jetting carbs winter fuels did not leave any color.
5. NGK plugs are easier to see color on because of the location and type of porcelain.

Good luck, I suspect you have a gummed up carb or delivery problem.

Tim T.

YOU HAVE TO TAKE THE TOP OF THE CARB OFF TO GET TO THE SREENS.ONCE YOU HAVE THE CARB TOP OFF REMOVE THE FLOAT AND NEEDLE THEN YOU CAN REMOVE THE SEAT. THE SREEN IS ATACHED TO THE SEAT.YOU GET PRETTY QUICK AT THIS IF YOU HAVE DONE MUCH MAIN JETT SWAPPING ON THESE CARBS.I LOVE IT ON A 105 DEGREE DAY.

Went and got the carb of the boat today. I brought the carb home and am planning on checking it over....What things should I look for and where...I figure I will spray it real good with carb cleaner and try and blow the passages out real good with some compressed air....I will keep you all posted and let you know if I spot anything. By the way what are the floats supposed to be set at anyone know?

Thanks
BH

BAD-HABIT
I feel your pain!!!!!!!
I had the same exact problem!
My troubleshooting consisted of the same steps.
Ended up swapping carbs from left to right and the problem followed.
While tearing down the carb for a total overhaul, (less than 1 season of running) I noticed that the bottom of the left bowl had "gold" flakes. Upon further inspection I noticed about 1/3 of the threads for the intermediate jet were missing.
I knew I hadn't stripped them out! I noticed the threads were extra deep on the "good" side of the hole.
I felt that during the MFG. process the hole had been drilled in step 1 and the tapping was done in step 2, but not aligned with the hole drilled in step 1.
I sent the carb back to Edelbrock and they sent me a "reman" carb as a replacement at no cost to me.
I just ran the boat this weakend and the backfiring in the carb is not there anymore.
But I havent been able to "tune" it yet-but- it's a whole lot better now.
I bought the carb about 1 1/2 yrs ago. So if yours is that vintage it might have been a production flaw that didn't get caught.
If all else fails contact Edelbrock. They did me right

Opie...I went through the carb and cleaned it up. Didn't really notice anything real off. The float drop was off alot but I guess that probally wasn't my problem. The float level was off about 2/16" I fixed that but Edelbrock dosen't think the amount would cause a problem to my extent. I orderd some Hi-Flow needle and seats just to make sure the bowls where filling as fast as the bowls needed them. They should come in today. I guess Im back looking at a vaccum leak or a fuel delivery problem..This is the problem child.......God it's hard to love your kids sometimes!
358/350hp roller

BH

bh, check supply line from tank to f/w separator and from there to fuel pump. any split or crack could be causing a supply problem. don't forget the simple stuff. you may have checked this already.

DID YOU CHECK THE SCREENS WHEN THE CARB WAS APPART.ALSO DO THE FUEL PRESSURE CHECK AT THE CARB FUEL INLET.YOU WILL NEED TO JERRY RIG A T-FITTING AND A GAUGE.I USED A HOSE TO THE GAUGE SEEING AS IT IS ONLY A TEMPOARY TEST SETUP AND THIS GIVES A BIT MORE FLEXABILITY.GET A FRIEND TO DRIVE WHILE YOU WATCH THE GAUGE.BE CARFUL NOT TO LOOSE YOUR SUN LOUNGE IN THE WIND.DOING THIS TEST RULES OUT FUEL DELIVERY PROBLEM!!!

Primary metering rods and springs are the power valves in this carb. Your set up should not change in the carb.
The float drop controls how much the needle valve can open, therefore how fast the fuel can come into the bowl.
All your problem sounds like a delivery problem. The fuel pressure check at the carb is where I would start.
Good Luck!!

Since my miss seems to happen at cruise am I understanding correctly that this is the point where the engine is pulling the most vaccum? If this is so wouldn't this lend itself to the miss being a vaccum leak since the engine would pull in the most air and in turn give me my miss condition at cruise? I hope to give it a run on Sunday I will let everyone know a.s.a.p

Thanks for the tips keep them coming....

BH