Holley 3310 idle problems

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greyhounds_amx
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Holley 3310 idle problems

Post by greyhounds_amx » Mon May 14, 2018 1:24 pm

I'm working on an older 3310-2 that I just rebuilt to replace a 80507 600cfm vacuum secondary on my '68 AMX 390. The car ran great before the carb swap, and there were no other changes to the engine.

As part of the rebuild the 3310 got a new primary throttle shaft, new Teflon bearing strips, and an automatic choke. The jets are stock size, and it's using a secondary metering block instead of the plate. Both floats are set correctly, and all of the air bleeds in the main body are clean. The engine has a mild cam and dual plane intake.

When I first fired it up I had to dial up the primary idle screw a bit to get it to idle because it was running pretty rough and eye-burning rich. The idle mixture screws made no difference in the idle speed or vacuum reading, and even screwing them in all the way had no impact.

I had an allen set screw in the secondary stop so I adjusted the secondaries open until the primary idle speed screw could be backed down all the way, but even then there was still no response from the idle mixture screws. Then I took out a little from the secondary idle screw and moved the primary idle screw back up a tad, still no improvement. After messing back and forth like that for about 1/2 hour with no improvement I shut it down and pulled the carb.

The travel of the 6.5 power valve seemed like it could be a little smoother, though it wasn't blown. I replaced it with one that felt nicer. I couldn't find anything else obviously wrong with it though. I spent some time setting the choke pull-off to 1/4" and at that point found that although the vacuum passage was drilled in the body that the base plate had a brass plug in the center hole which prevented vacuum from reaching the center cavity in the main body. So I drilled a 1/8 hole in the plug in the baseplate to let vacuum get to the center of the body.

I put it back together with fresh gaskets and once warmed up it idled just slightly better. The driver side idle mixture screw would now cause the engine to just about die if I screwed it all the way in, and seemed to work best about 1/4 turn out, but still didn't have much effect. The passenger side mixture screw still did nothing at all. It's still painfully rich. I recorded it running for a while with my cell phone looking down the primaries, and there's no fuel coming from the mains when it's idling, so I believe we can rule out the power valve.

Here's what I do know about the carb:
Marked as 3310-2, also has a large "99 CS" stamped on the body, with the C and S overlapping. I though that might be a Carb Shop stamp as they are in the neighborhood of where I bought the carb (Missouri).
Primary bleeds:
High speed = 0.028"
Idle = 0.078"
Secondary bleeds:
High speed = 0.025"
Idle = 0.028"
Metering Block Stamped 5271 5275 3
Three drilled holes per emulsion tube:
Top = 0.026"
2nd = 0.088"
3rd = 0.088"
Idle fuel = 0.088"
Idle feed restriction = 0.034"
PVCR = 0.063"
PV = 6.5
Primary jet = 72
Secondary jet = 75
Squirter = 0.025" short style

What could prevent the idle mixture screws from working, and cause it to run so rich? Is this possibly the warped metering block syndrome I've heard about? I don't have another equivalent metering block on hand to test with unfortunately.

Thanks!

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Re: Holley 3310 idle problems

Post by mag2555 » Mon May 14, 2018 1:37 pm

Look for marks on the metering block that would indicate that the hex of the power valve is butting into the block, it should not .

If it does it will keep that side of the block where the contact point is from seating as it should.

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Re: Holley 3310 idle problems

Post by grandsport51 » Mon May 14, 2018 1:48 pm

Why not install temporary plug in place power valve to test
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Re: Holley 3310 idle problems

Post by grandsport51 » Mon May 14, 2018 1:49 pm

Why not install temporary plug in place power valve to test
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Re: Holley 3310 idle problems

Post by Scotthatch » Mon May 14, 2018 1:56 pm

Did you look at the imprint on the gasket when you took it apart? Or check that the main body was flat at the screw holes? And did you check for a vacuum leak at carb base when running?

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Re: Holley 3310 idle problems

Post by pamotorman » Mon May 14, 2018 2:10 pm

check for warped metering bodies. i used this jig to straighten them check with a straight edge for flatness. after straitening the metering bodies machine the main body flat.
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Re: Holley 3310 idle problems

Post by Tuner » Mon May 14, 2018 2:38 pm

Check if the power valve is contacting the boss for the base plate screw in the cavity in the body. In some castings made in the late 70's to early 80's the cavity in the body the PV projects into is too shallow and the PV will hit the screw boss.

If the gasket faces of the body have been milled to flatten the sealing surfaces, the pins on the metering block can bottom in the holes in the body and prevent the clamping of the gasket tight between the block and body, and/or the base to body contact may be upset by interference of the lower edge of the metering block gasket flange with lumps on the base casting, such as the boss for the PCV nipple under the rear float bowl.

Without the gaskets, check that the metering blocks and the base will fit snug to the body with no interference so there is more than enough clearance to clamp the gaskets sufficiently.
Three drilled holes per emulsion tube:
Top = 0.026"
2nd = 0.088"
3rd = 0.088"
5271 is an original 3310 block, but the bleeds should be .026" in the angle channel and two .026" in countersunk holes that are about .088", so you may have .026" (or .028") bleeds further in the .088" holes. If they are actually .088" through into the main well you need another metering block or you need to repair that one. There should be only two .026" bleeds to the main well and the .026" to the angle channel.

The 3310-2 has straight-leg boosters and SL boosters don't need an anti-siphon bleed so a bleed in the angle channel is redundant unless necessary as a kill bleed to delay the main flow (booster) start to a higher RPM.

Original 3310 with droop-leg boosters was made with the angle channel bleed and they just kept including it in the later dash # carbs with straight-leg boosters, though straight-legs don't need it.

Except for the .088" emulsion bleeds, the specs sound like a normal 3310.

Unless there is a secondary power valve with PVCR near .062" to .067", the # 75 Secondary MJ is too small, should be 82 to 85 or thereabouts.

#72 Primary MJ may be too big.

The straight-leg 3310 doesn't usually need as large jetting as the droop-leg version, though individual engines have their own appetite ..... intake manifold type, head volume, cam, headers, etc. etc.
Last edited by Tuner on Mon May 14, 2018 3:25 pm, edited 1 time in total.

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Re: Holley 3310 idle problems

Post by Walter R. Malik » Mon May 14, 2018 2:42 pm

Sounds like it is being caused by a vacuum issue somewhere, to me. Either inside the carb or outside.
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Re: Holley 3310 idle problems

Post by aquartlow » Mon May 14, 2018 3:43 pm

Great info already given! Also make sure you have not uncovered too much of the transfer slot when setting the curb idle rpm, this pic shows a good baseline to start with and/or what it "should" look like. Good luck.
Image

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Re: Holley 3310 idle problems

Post by ZIGGY » Mon May 14, 2018 3:48 pm

greyhounds_amx wrote:
Mon May 14, 2018 1:24 pm
Marked as 3310-2, also has a large "99 CS" stamped on the body, with the C and S overlapping. I though that might be a Carb Shop stamp as they are in the neighborhood of where I bought the carb (Missouri).
Don't know that it's theirs, but C&S is in St. Charles.

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Re: Holley 3310 idle problems

Post by ZIGGY » Mon May 14, 2018 3:57 pm

P.S. - I am NOT a fan of C&S Specialties' carbs.

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Re: Holley 3310 idle problems

Post by NormS » Tue May 15, 2018 8:26 am

If you have a gasket between the main body and the baseplate that is intended for an 850, it will block off the idle mixture passages of the 3310 baseplate. That will make the idle mixture screws ineffective ,and require opening the butterflies enough to idle on the transition slot fuel .
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Re: Holley 3310 idle problems

Post by 427dart » Tue May 15, 2018 10:20 am

If you have the Idle Fuel mixture screws all the way in and it still idles..you have unmetered fuel coming from someplace.
As mentioned check the carb body and metering plates for flatness.

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Re: Holley 3310 idle problems

Post by greyhounds_amx » Tue May 15, 2018 1:16 pm

Thanks everyone for the input and ideas. Since there's no fuel coming out of the primary booster venturis while it's idling I think it's safe to rule out the power valve as the problem, and since it's an eye-burning rich condition I just wouldn't expect a vacuum leak to be the culprit either. I pulled the primary bowl and metering plate off again last night, and here's what it looks like:

Image

Image

Tuner, you were correct, the emulsion holes are way down at the bottom of the 0.088" holes and measure 0.025". Would you consider this plate to have just two emulsion holes?

I didn't see any indication of the PV hitting the main body, and I found that the metering block sits nicely flush against the body without a gasket installed, so there's not a clearance problem there. It bumps against a boss on the baseplate slightly at the lower left corner, but it doesn't effect alignment as the dowel still engages fine on the left side.

Image

The gasket impression looks pretty good too considering it was only on there a day. I suppose that block warp could still be the problem, and might explain why there was a minor improvement when I replaced the gaskets and PV.

Image

For the rear jet size I came up with 75's as they seemed to be closest to 0.081" hole the in the 134-21 metering plate. But I have no basis other than that for selecting them, so if your experience shows that a larger jet is needed in the secondary of these then I'll definitely make that change, and reduce the primary jet too. I do have a wideband on the car but need to get the poor thing to idle first before putting some miles on it.

So I'm still stumped as to what the problem could be. Tonight I'll work up a short straight edge I can drop in the metering block to check for warp. I'll check the body surface too.

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Re: Holley 3310 idle problems

Post by pamotorman » Tue May 15, 2018 1:45 pm

looks like it may be a C & S carb #99. http://www.candsspecialties.com/. maybe contact them

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