Loading up at idle
 

Ever since I got my current boat, I've had idle issues on both engs (468's).
The engs will idle at 800 RPM in neutral, but when drives are put in gear, the RPMS drop to 500-600 RPMs and die after abt 10-20 seconds if I don't catch them.
After idling thru a No Wake zone for a few mins, the issue is even worse.

I've dipped/rebuilt the carbs, replaced power valves, played with the mixture screws, adj'ed fuel press and adj'ed float levels many times (while on the water) but issue is still present.

The carbs are the Holley 4010/4011 series and only have idle mixture adjustments for the front barrels.
The heads are Merlins with the big rectangle ports and they also have the matching Merlin intakes.

I'm pretty sure the fuel is falling out of suspension due to low charge velocity thru the runners at idle.

Assuming the root cause is slow charge velocity, would modern carbs (i.e. QF 800/850's) really help much?
Anything else I could try?

These old carbs work great everywhere except at idle.

What is the timing at idle ?

Increase the idle to 900rpms. The drives will still be fine.

Need to check the timing.

If I set the idle speed screw to 900 rpm on the trailer, both engs will idle too high once they have cleared their throats. It takes a while for the idle to drop back down.
The way it is now; I set them to 650-700 rpm on the trailer with the idle speed screw. After a good run, they idle at abt 800-900 for a bit then start dropping.

You need to set float levels with the boat in the water if you have not been doing that way. The angle of the engines changes.

Set idle rpm when warmed up and in the water also.

put a timing light on it drop in gear in water, see if timing is backing off and causing stall, depending on cam etc, locking the advance and setting about 32 deg will help idle quality

x 100 on getting ignition straightened out before carb work.

That said, those 4010 carbs never did too well, thus why Holley dumped them.Not much adjust ability (tune ability)

When setting up the carb, like all Holley's, it is very important to also set the secondary throttle blade's opening when closed at idle. They have an idle circuit too, but it's fixed since no idle mixture screws. Set blades so the transfer slots are square typically .020"-.030"

Thx for all the replies!!

I'm not able to get the boat on the water today but I did check a few things mentioned.

The timing results were surprising.
The port eng was found set to 35 degs and does not change between idle and ~3k rpm.
The starboard eng at idle was found at ~40 degs (jumps around a few degs) and seems to increase a few degs more at 3k rpm.:picard1:
Does the MSD ign need to have a jumper installed/unplugged or something to check base timing?

I'm running a 6AL's, MSD Blaster coils and MSD distributors:.

[ATTACH=CONFIG]559150[/ATTACH]

Pulled both carbs.
The secondary transfer slots were not visible at all on either carb:

[ATTACH=CONFIG]559136[/ATTACH]

[ATTACH=CONFIG]559137[/ATTACH]


Transfer ports with throttle held partially open:

[ATTACH=CONFIG]559139[/ATTACH]


After adjustment of stop screw for secondary's:

[ATTACH=CONFIG]559140[/ATTACH]

When adjusting the transfer ports, I first backed off the primary and secondary idle screws, loosened all the throttle plate screws 1/4 turn and snapped the throttles shut a few times to center the butterflies and re-tightened the butterfly screws. They seem to be closing all the way without any binding. Next, I adj'ed the secondary idle screws to provide a square shape on the transfer slots (~.030" exposed).

The engs both idle well but the idle speed is too high now on both engs. When first started, they idle at 900-1000 rpm. When warm they are at 1100-1200 rpm.
This is with the throttles disconnected, idle speed screw backed off all the way, idle mixture screws at 1.5 turns out and throttle held closed by hand just to make sure.

Checked for vacuum leaks but none found. The only vacuum hoses are the PCV hoses. When they are pinched off, the idle speed drops some (~100 RPM) but not enough.

I did discover that when the PCV valve is pulled from the valve cover, there's a loud air rushing sound, like there's a significant vacuum in the crankcase. Looked at the other valve cover and it had a PCV valve (that can't be right!?) which connects to the bottom of the flame arrestor/air cleaner.
I pulled both PVC valves from one eng and placed palms over valve cover openings to check for an internal vacuum leak, but didn't get a vac or a press build-up.

In regards to the carbs; only thing I can think of is to re-adj the secondary idle screws so the transfer port is closer to .015"-.020" of exposed port.

Thoughts??

Many marine engine run an open elbow that looks like a PCV at the valve cover. This is connected to flame arrestor.

Some do run a PCV. A PCV has a spring and ball inside . A PCV is connected to large vacuum port at back of carburetor.


So, check those things that look like PCV's and see if an open elbow or in fact a PCV.

Going to .020" should be fine for that circuit to work .

Most set total to 34-36 on BBC with factory heads.

Your MSD has weights and springs (mechanical advance) under the distributor cap. See if the plate is welded or if the weight / spring system works.

sounds like dist locked already, 40 is to much in a boat

I agree. 35 even sounds aggressive for a 10.25/1 static comp ratio.

Should idle great. With that much timing at idle. ? Isn't that why you lock them out. To calm big cammed motors. I'm confussed here

We weren't told about the cams.

If there is a decent cam, then those carbs are even more out of their league.

Cap the breather line coming off back of carburetor. The valve cover breather should be an open elbow both sides connected to the flame arrestor. If idle still to high back down secondary adjustment to lower idle speed. See if it will take a load and not stall after that.

Unfortunately, I don't know much abt the hyd/roller cams installed. Prev owner did say the entire valve train is Crower but he couldn't recall the cam specs.
It's nothing wild. No lope and has strong vac @ idle.

Adj'ed the timing on both engs to 34 degs.
It didn't have much of an effect on the idle quality, but makes me feel better.

I re-adjusted the secondaries some more. Wound up with the secondary transfer ports almost disappearing and now have a pretty solid idle at 775 RPMs on both engs (with normal idle speed screw backed off completely). Then adj'ed idle up to 800-825 rpm with normal idle speed screw. Both engs seem happier now. Thx for suggesting that SB!

The PCV issue still needs to be addressed. I kind of like the idea of having a PCV sys to evacuate the corrosive blow-by gasses. I'm planning on replacing the "extra" PCV valve with an elbow (hose going to flame arrestor/air filter) and hopefully will still have a solid idle in gear. If not, I'll plug off the vac port used for PCV and have both valve covers vent to the flame arrestor.

After adj'ing the starboard eng timing, I noticed it didn't seem to adv with rpm like it did before.
Wanted to pull the dist caps and see what's up with the mechanical adv mechanism but ran out of time.


It will be next week before I can lake test, but I'll let ya'll know how it turns out.

without a wideband or plug check how do you know its too much fuel and not not enough? normally a high idle after revving is LEAN, when richer they drop back easier to idle, is timing locked out? if so its easier to idle but hard on starters, what is timing at idle? I would turn mixture screws all the way in and start at 3/4 to 1 full turn out, that's normally right on the money, if carbs are old you can also have issues with things sealing like the body and flange allowing issues, many guys tighten the carbs too much and warp them...

I suggest a wideband for tuning, I cannot stress it enough it is by far the best tool I added to my boat to keep things checked out and rule out issues, without your just guyessing a lot...

if you are running a msd dist. take the cap off and check for rust !

I agree that WB02 is the way to go. I've had one installed in my street ride since the days you had to build the p/s and controller yourself then convert the 0-5v output to AFR in your head. Putting one on the boat is definitely on my short list.

These 4010's are not your normal looking Holleys.There's no float bowls and metering blocks hanging of each end which is where most over tightening issues occur with the traditional Holley carbs.

Yeah, I've heard a few stories abt that. I'll check them this weekend.

at this point I would consider those carbs door stop material, were not great in a stock app, much less a performance one, need a pair od 750 quickfuels...

Yep. Need to get a WB02 installed first, get a baseline with the old carbs and go from there. The engs where designed to use 850's but the prev went with 760's in an attempt to get some longevity out of them.

Pulled the cap (MSD Pro Billet dist) from the port eng today and guess what,, rust...
One weight was rusted and binding. Both springs were rusted and one was broke. Timing was stuck at full adv.
Disassembled and cleaned it all up.
Saw a post where CRC-400 spray was used and worked well at preventing a re-occurrence. Guess I need to pick up a can.
Need a new set of springs now.

Can't tell what color the springs were originally.
I downloaded the PDF files from MSD that show the various curves with different combinations of springs and bushings.
Saw where another member suggested starting with black bushings, a heavy sliver spring and a blue spring.
This will give me 17 deg base timing and an additional 18 degs all in at 3200 rpm (35 degs total).

I originally wanted to lock the timing at 35 degs, but the comments abt that being hard on the starter makes me want to re-enable the adv.
.
My concern now is back to idle quality at 17 degs.