Holley carb tuning?

[biggsie]

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


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[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?


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[cjtpilot]

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


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Yes the vacuum is on the manifold


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[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.


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[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]

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/showthr...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???


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