Holley carb tuning?

[biggsie]

Last weekend was the 1st time out, boat ran fine but I noticed dark smoke from exhaust at slow speeds/idle and the back of the boat was all dirty from the unburned fuel. I discovered that there was no thermostat installed, ordered one and got it in. Set the mixture screws to 1-1/2 turns out and took my vacuum gauge with me on a test drive.
New t-stat worked fine, about 150-160 and holds steady. Less soot now but I think it's still a little rich. Turned in the screws all the way, no noticeable difference? What rpm to use while adjusting for max vacuum? When I adjust screws the idle changes?

Can someone explain the idle circuit of these carbs to me? I'm a motorcycle mechanic and these big holleys are foreign to me. I want to put a smaller pilot jet in but I'm pretty sure they don't have one lol.

Boat seems to run great otherwise, maybe I should just leave it alone!


Sent from my iPhone using Tapatalk

[chris young]

Yours is the 454 IIRC so the jets etc won't be the same as mine, but if you get the list number off the horn of the carb Holley will tell you which power valve and jets the carb was shipped with. Sounds like someone may have tried to re jet the carb for more power. Assuming it's the 4160 2 1/2 turns should be the initial setting on the idle screws. If you can close them all the way, and the throttle plate is closed, and it doesn't stall, you probably have either a blown power valve or the primary boosters are dripping fuel. There are no replaceable jets on the idle circuit on that carb nor switchable air bleeds. From all the reading I've done on various forums, and my own experience, it seems that these carbs are really hard to get to idle properly until you get either a wedge spacer to level the carb or adjust the front floats low enough not to flood the primary boosters. I chased that problem around all last summer and after rebuilding the carb over the winter, it actually got worse this spring. Rather than lowering the front float any further, I decided to put in a wedge spacer and everything just worked right away. (so far, I haven't had a chance to run the boat properly to get it properly tuned but it idles really well and runs up to ski speed smooth and strong)

If I had to guess, I'd say your float level is too high but that's easy to see as the boosters will be dripping fuel. It's crazy how far away from factory settings I had to adjust the floats to get that to stop on my carb, an as I said is started up again after the overhaul. The right fix is to level that carb. Check the last or second last page of the "weird heat soak" thread, I posted the Holley P/N for the wedge kit (it's actually meant for marine applications) The problem is that with any wedges I could find, none of them had a vacuum port and it would have been crazy long studs to keep the original spacer, so right now I can't tune with a vacuum gauge and I don't have any PCV. It's good for now, but I will have to drill the spacer and put in a port at some point.

BTW if you go to both the Summit pages and the Holley pages there is tonnes of good info on how to tune these carbs.

Hope this helps.

[biggsie]

Mine is a 351.

So if the floats are set too high I will see a drip (overflow) from the tubes?

Also the manifold is an Edelbrock if that makes a difference.

I had to remove a plug on the intake and install a nipple to get full vacuum for my gauge. I had no ports at all anywhere.

My valve covers are leaking and now I'm wondering about the PCV. I have a valve on the cover with a hose to the air cleaner but no vacuum to the crankcase.


Sent from my iPhone using Tapatalk

[cjtpilot]

A bad PCV will cause idle issues and keep you chasing your tail if you never think to check it. I just rebuilt my carb and ended up having my idle needles turned out 2 turns. yes adjusting your idle mixture screws will effect idle RPM. Set your screws with the idle adjustment all the way out, then after you set the mixture screws with a vacuum you can adjust the idle speed. Typically around 650-750 RPM. Which trans do you have 1:1 or 1.23:1? if you have the 1:1 then you have to adjust float level to make up for the carb sitting on an angle. Otherwise the engine and carb should set level, at least it does on a Comp.

[biggsie]

1:1
So when I adjust the screws will the idle be really low? I haven't tried to see if the engine will idle with the idle screw all the way out.


Sent from my iPhone using Tapatalk

[cjtpilot]

1:1
So when I adjust the screws will the idle be really low? I haven't tried to see if the engine will idle with the idle screw all the way out.


Sent from my iPhone using Tapatalk

Yes set the idle mixture screws out 1.5 turns to start, back out idle speed screw all the way out. It should still run even if it is a very low idle. As you are adjusting the idle mixture screw to greatest vacuum the rpm will go up or down. Then you can set the idle speed screw. I actually still have my idle speed screw backed out and am @ 750RPM in neutral and 650-700 RPM in Fwd idle.

[chris young]

Interesting you have no vacuum port on the carb, I would think that motor should have PCV but maybe it's an oddball? My mistake, 1 1/2 turns is the correct starting point (I could have sworn it was 2 1/2) but I just checked the Holley video and 1 1/2 is what they say. http://holleytv.com/?p=426

Yes, if your floats are set too high you will see fuel dripping into the primaries through the booster nozzles. You'll know for sure if it continues to drip after the motor is shut down. In my case it was only one nozzle so I must have been just on the edge of having the float in the right place. BTW I just did a bunch of reading on PCV in order to determine if it was ok to run the motor for a while without it so I don't have to deal with installing a vac port right away, and it is a bad idea to use a manifold port for PCV (in case you were thinking of doing that) as the cylinders closest to the the port will run leaner than the rest.

[biggsie]

I'll have to look into the PCV thing. I have valve covers from a mercruser that say 188hp on them :/

Right side has one port with a PCV valve going to air cleaner and left side has a vented filler cap. No place to run a vacuum line to.


Sent from my iPhone using Tapatalk

[cjtpilot]

Here is what is on my 351, rh with filling port goes to flame arrester LH side goes from PCV to manifold. That's where I get vacuum from.


Sent from my iPhone using Tapatalk

[cjtpilot]

http://img.tapatalk.com/d/14/06/17/ra3yzudy.jpg


Sent from my iPhone using Tapatalk

[biggsie]

Is your vacuum port on a base plate, the carb or directly in the intake manifold?


Sent from my iPhone using Tapatalk

[CJD]

One thing I notice in the pic is your carb is filthy...inside the bores, though not so much outside. You might try running a can of cleaner around and through it before you get started.

Next, the adjustment is done in this order:

1) Set the idle screw to the idle you want.
2) Adjust the mixture screws equally to achieve the smoothest idle possible. This will likely be just below the maximum vacuum reading. Never get the screws more than 1/4 turn apart from one another.
3) Readjust the idle screw, as the engine speed will likely have increased with the mixture adjustment.

Repeat till there is no increase when adjusting step 2.

Once done, check the idle with the boat in gear in the water. Goose it and make sure it does not stumble. If it stumbles, open the mixtures 1/4 turn each and see if it gets better. If it does, repeat until you like the way it gooses. You may have to bump up the idle speed if it drops too far during the "goose" check.

If opening the mixtures does NOT help the stumble during the goose check, put them back where they were and increase the stroke on your acceleration pump...or fix it if it is not working.

Notes:

a) If you can close the idle screws all the way, but still have too fast of an idle, you have a vacuum leak or worn out throttle shaft.

b) If you close the mixture screws all the way down. and the engine still seems rich...your power valve is blown. The bowls will have to come off.

c) The jets are changed for wide open throttle mixture. The power valve controls part throttle mixture. Idle screws control mixture below about 800 rpm.

d) if your idle is above 800rpm, you are mixing the idle and transition circuits and will not get a good adjustment. Slow it down.


It's that easy. Just remember, if it does not behave like I describe...then something is unplugged, broke, dirty or worn out.

[biggsie]

Thanks CJD. Any input on the proper way to have the PCV system setup?


Sent from my iPhone using Tapatalk

[cjtpilot]

Is your vacuum port on a base plate, the carb or directly in the intake manifold?


Sent from my iPhone using Tapatalk

Yes the vacuum is on the manifold


Sent from my iPhone using Tapatalk

[cjtpilot]

One thing I notice in the pic is your carb is filthy...inside the bores, though not so much outside. You might try running a can of cleaner around and through it before you get started.

Next, the adjustment is done in this order:

1) Set the idle screw to the idle you want.
2) Adjust the mixture screws equally to achieve the smoothest idle possible. This will likely be just below the maximum vacuum reading. Never get the screws more than 1/4 turn apart from one another.
3) Readjust the idle screw, as the engine speed will likely have increased with the mixture adjustment.

Repeat till there is no increase when adjusting step 2.

Once done, check the idle with the boat in gear in the water. Goose it and make sure it does not stumble. If it stumbles, open the mixtures 1/4 turn each and see if it gets better. If it does, repeat until you like the way it gooses. You may have to bump up the idle speed if it drops too far during the "goose" check.

If opening the mixtures does NOT help the stumble during the goose check, put them back where they were and increase the stroke on your acceleration pump...or fix it if it is not working.

Notes:

a) If you can close the idle screws all the way, but still have too fast of an idle, you have a vacuum leak or worn out throttle shaft.

b) If you close the mixture screws all the way down. and the engine still seems rich...your power valve is blown. The bowls will have to come off.

c) The jets are changed for wide open throttle mixture. The power valve controls part throttle mixture. Idle screws control mixture below about 800 rpm.

d) if your idle is above 800rpm, you are mixing the idle and transition circuits and will not get a good adjustment. Slow it down.


It's that easy. Just remember, if it does not behave like I describe...then something is unplugged, broke, dirty or worn out.

That pic was taken before I removed the carb and rebuilt it, and yes it was filthy! Lol I was surprised the boat ran.


Sent from my iPhone using Tapatalk

[chris young]

Mine is original (I'm pretty sure it is, I'd have to check the manual to be sure) and the aft end starboard side valve cover holds the PCV and connects to a 1" spacer below the carb. The port side oil filler cap has a hose which goes to the flame arrester.

I can post up a pic tomorrow

[chris young]

http://i.imgur.com/uFykK6k.jpg (http://imgur.com/uFykK6k)
http://i.imgur.com/GOpMKnW.jpg (http://imgur.com/GOpMKnW)

I don't have a really good view of the system overall, but you can see where the PCV hose goes to the spacer in one pic, and where it leaves the valve cover in the other.

Another note, the main jets control the fuel mixture for idle all the way up to WOT. The main jets are where the fuel is supplied to be mixed with air from the idle bleeds and then that mixture passes by the idle mixture screws. The power valve only comes in to play when you are going to high power, and it's job is to open in order to richen the mixture at high throttle.

[CJD]

The holes in the main jets do feed the idle circuit, but the holes in the jets are very large in relation to the amount of fuel used at idle. If you make a small jet change, say one or two number sizes, then the affect on the idle circuit is pretty negligible.

If the power vlave is blown, it screws up most of your low end mixtures. It's easy to spin your wheels adjusting, just to find out the valve needs to be replaced.

[cadunkle]

You're running rich, it's pulling fuel from somewhere. Most likely high float level or blown power valve.

Check my post here: https://forum.supraboats.com/showthread.php?8915-smokes-at-idle for a rundown on how to set float level and idle mixture. Note you will want to set timing before doing this and verify afterwards. 10* is good and safe though up to 16* may have a little more power out of the hole but can run into detonation issues depending on engine and octane. If you have a 4160 you will not have externally adjustable floats which sucks, but you'll just have to pull the bowls and check float height. If higher than spec, set to spec for your carb (Holley list number, check their charts) or just lower a bit at a time until you get no fuel dripping from boosters at idle or after shutdown. Just bend the tab a little at a time like most bike carbs. Spec is just a starting point as these engines are mounted at steep angles and may or may not have angled spacers. If you don't have a wedge spacer and can fit one under the doghouse, get one and it'll make carb tuning easier. The more angled down towards rear the lower the primary float level will need to be and the higher the secondary level will need to be. The float being level and in the middle of the bowl is a good starting point if unsure of spec and not externally adjustable.

Failing that replace or test your power valve. Failing that check that your butterflies are not open too far at idle. Transfer slot should appear square when viewed from the bottom at your idle throttle opening. Less opening that square is alright, more will cause richness at idle. The farther closed your throttle plates the more responsive your idle mixture screws are. Turning tehm all the way in should stall the engine from an overly lean condition. If your engine wants more air at idle you can compensate some by adjusting the secondary throttle plate stop. Many nicer 4150 base plates and 4 corner idle carbs are externally adjustable, most Holleys you'll need to adjust the screw accessible from underneath the carb to open the secondaries a bit more at idle.

My money is on float level or possibly needle and seat not completely sealing. Don't leave it be just because it runs well all around or you'll be fouling plugs, not to mention wasted fuel/smell/whatever.

[biggsie]

So this weekend I removed the air cleaner and observed...,, no drips from either tube and the power valve seems to be spraying a nice stream and also not dripping. Runs good with both mixture screws all the way closed, open them and I get black smoke at idle. I'm currently not running any PCV system and am fighting a low oil psi issue.

Coming soon I will be installing a 1" spacer with PCV port, replacing my oil psi sender and testing again.

I wonder if my 2 into 1 FAE is restricting the exhaust flow enough to require smaller jets???


Sent from my brain using Tapatalk.

[CJD]

You cannot see the power valve operating from the outside of the carb. You are watching the squirts from the accelerator pump. The power valve still remains your "most likely" culprit.


edit: I realize I better expand on that a bit.

An engine that is idling or running at low load can tolerate a leaner mixture without damaging anything. When the engine is under load, the combustion temps go up, so for a safe measure, you must add extra fuel to bring them back down. If you run an engine lean under load, you will melt the aluminum pistons. If you run an engine that is coasting too rich, you foul plugs and build up carbon in the combustion chambers...not to mention you get poor gas mileage.

That is the problem. Holley's solution was the power valve. The valve is on the metering block inside the float chamber. It has a rubber diaphram that is sucked to one side by the intake vacuum. When engine load is low, the diaphram sucks a plunger to close a special fuel port. Mixture is now controlled by the idle screws (or main jets if you are cruising). When you run the engine under a heavy load, the vacuum in the manifold goes down, so the power valve diaphram relaxes and the special fuel port is opened. Extra fuel is added to the mix to richen the mixture.

Power valves are different for different applications. They are numbered similar to main jets, so you can choose at what vacuum the valve opens. Racers use a solid valve, that is always open...as they do not care about mileage, idle quality, and running at low loads. The real reason they do not like the valve is because of the rubber diaphram. The diaphram is exposed to intake vacuum, which means if the engine ever backfires...even once...the diaphram will rupture. If it ruptures, the valve stays open and even more fuel dumps through the split diaphram right into the intake.

If you have checked everything else, then it is most likely that your power valve has a ruptured diaphram. Remove the bowl and the PV is right there screwed into the metering block. you will have to read the number on it and order the same number PV replacement. Best to get 2, because, as I pointed out, one backfire and you have likely blown it.

[biggsie]

Awesome info, thanks for taking the time to write that!


Sent from my brain using Tapatalk.

[supra790]

Which Eddlebrock intake do you have biggsie ?

[biggsie]

Performer


Sent from my brain using Tapatalk.

[supra790]

If it's the 2581 it could be part of the problem. I spent all kinds of time and money rebuilding my Holley 4160 and then finally bought a brand new one which comes tuned directly out of the box and I still had similar problems at idle speed. Finally when I met a race car mechanic at the lake he immediately noticed my intake was designed to run at 1500+ rims. When I replaced it with the performer built to run at 0+ rims it runs great and I don't have any more issues at idle speeds. It's Just something else to consider ? I'm not sure if the 2185 came stock or if a previous owner changed it.

[biggsie]

Thanks, I'll check and see if there is a model #.


Sent from my brain using Tapatalk.

[92SupraComp]

it will say performer or performer rpm

the performer is idle to 5,500 rpm

the rpm intake is 1500 to 6500 rpm

we have the performer on the family boat with a 351W and it made a noticeable difference in power, the idle is very smooth also...

[biggsie]

It's a performer. It says "Performer 351W" on one of the runners.
I'll pull the front bowl and check that diaphragm next.


Sent from my brain using Tapatalk.

[supra790]

Mine had a number stamped on the top near the back14596

[biggsie]

So I pulled the carb and disassembled it. Seems the power valve is ok, no ruptured diaphragm.

The PV is a 2.5

I forget the jet size 630's maybe?

I guess I'll have to see if the transfer slots are exposed after I re-install and tune the idle with vacuum.

Anyone know what jetting/PV sizes should be with this performer intake?


Sent from my brain using Tapatalk.

[biggsie]

Reassembled carb, set timing to 10deg btdc, and hooked up PCV to port on the new 1" spacer block.

With idle set to 750 or so I am pulling about 14" of vacuum and my mixture screws are out only 1/2 turn.

I'm thinking my PV is too small at 2.5, I may order a 3.5 and see if it makes any difference.

It is frustrating that there is no sight plug or external adjustment for the floats. I think I have them set on the low side just to be safe. We'll see if it runs out of fuel soon.


Sent from my brain using Tapatalk.

[biggsie]

Upon further investigation I have found that a small PV is ok with the vacuum I'm pulling at idle.

My guess is that I'm good to go now. If I turn in the mix screws all the way now the motor will stall. It wouldn't before. No black smoke at idle. Fingers crossed for lake test.


Sent from my brain using Tapatalk.

[CJD]

The jet size of 63.0 sounds in the ballpark. The 2.5 PV for a boat means it won"t open till the vacuum drops considerably...which, if anything, would make the mixture tend to stay on the lean side.

If you can kill the motor with the mixture screws, it does sound like you have the mixture good. What did you do that leaned it out?

If you still end up being rich with the PV functioning properly...my next thought would be the float level. If the fuel level in the float is too high, fuel will vent into the intake. Possibilities for fuel venting are the wrong setting, a carb that is tilted too much on the manifold, or fuel pressure that is so high it overpowers the needle valve.

Anyway...hope you've got it sorted out.

[chris young]

Assuming it's the same carb as my boat, the vintage and motor are pretty close, the list# indicates it was built with 66 jets and a 2.5 PV.

[biggsie]

I think the combination of timing adjustment and the addition of the PCV allowed me to lower my idle screw more which then closed off the transfer slots more.


Sent from my brain using Tapatalk.

[biggsie]

Took the boat out tonight. Ran well but seems to be lacking some power. Could be the timing adjustment.... Idle is great, no dead spots just seems a little more sluggish than before. Maybe I'll play with the timing. I have the Motorcraft duraspark electronic ignition. Timing is set at 10btdc.
Can someone explain the concept of static timing to me? I know the "brain" controls the advance but what is the advantage/disadvantage of more or less initial timing?


Sent from my brain using Tapatalk.

[supra790]

Biggsie did you ever confirm which performer intake you had ?

[biggsie]

Regular performer, not RPM.


Sent from my brain using Tapatalk.

[CJD]

I'm not sure what year you have...

With the older distributors, whether electronic or not, the initial timing setting is added to all points along the advance curve. So advancing the initial timing advances the timing at all rpm's.

With most of the modern "distributor" style ignitions, setting the initial timing only lines the rotor up with the contacts inside the distributor for the spark plugs. The advance curve has absolutely nothing to do with where you set the distributor...it is entirely controlled by the ignition module using a crankshaft position sensor. Setting the initial timing with these only optimizes the rotor position in relation to the contacts.

Then, of course, the latest round of ignition doesn't use a distributor at all. Advance is controlled by the module using a crank sensor, and is sent to individual coils for each cylinder.