How do I richen a Holley 2280 for high speed/load conditions?
This is on a '72 Valiant with milled head 9 to 1 comp, and ported exhaust manifold with 2.5" exhaust. Normal around town driving it does fine and runs really good but on the highway I hear detonation when I step on it. thank you!

http://www.slantsix.org/articles/choke- ... -info4.jpg Power valve channel restriction , clean out, if clean open it up .002 or .003

What power valve ? just vacuum or mechanical and vacuum

I do not have this carb to look at. Looking at pictures, that channel restriction is behind a lead plug.That would be a job for a machine shop. Or just a bad idea.

Thanks, Matv91, for the help! I hope not to sound too dense. Just looking for a nudge/advice in the right direction. With the old 1920 it was as easy as changing the jet. Now using a 2280 and the power enrichment valve gives me doubt. Should I up the jets in the 2280 or can the power valve be modified for more fuel???
Supposedly, my 2280 is a NOS 318 version without the vapor canister connection tube. If I can work with the 2280 it would be great...otherwise I was considering a 350 Holley 2 barrel.
The car has a stock cam and timing is set at 3 BTDC with governor slots welded for a total of 20-ish degrees.
Like I said on the highway, if I punch it it detonates....so I can't believe the 23 degrees of timing is doing this....I run premium fuel.....92 and 93 depending where I fuel up.

I'm not familiar with the 2280, but if it is the power valve, you should be able to buy a different size and swap it out after opening up the carb. There's a video on holleytv.com detailing how to size a proper valve and swap it in for the larger 2300 and the 4-barrel carbs. IIRC, the PV number you need is half of your idle intake manifold vacuum. Not sure if that'll help or if they have a separate video for the 2280.

That being said, if the problem is happening just cruising on the highway, my first inclination would also be to up the main jets.

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You can change/drill out the main jets, but I would take a reading on the plugs at cruise first to see how rich/lean they are to start with. Cruise for as long as you can (for at least 30 seconds) then cut the engine, drift to a stop, and look a the plugs. Look at them all to see if one cylinder in particular is lean.

And, I would also consider raising the float level first and see how the car reacts to get an indication if a slight enrichment will have much effect.

How is the vacuum advance set up? It could be throwing in a bunch of advance. The vacuum advance is part of the total advance picture too.

And it this actually detonation (will sound pretty violent) or just pinging (an erratic rattle)? Does it go away, or is it less, if you punch the throttle with the engine at higher RPM's, and happen more if you punch it a low RPM's?

http://slantsix.org/forum/viewtopic.php ... 80&start=0 There is adjustment for mechanical power valve if its there

2280 is much like the BBD it replaced but with short metering rods and jets, and a captured power valve, it is an emissions carb and not much is available to upgrade it...the 2300/4150/4160 are the ones that you can replace jets and change out the power valve...

You get a couple of choices here... your distributor mech. advance is either too fast and/or too much for the load when you demand it... the other choice is going with the bigger carb, but you can wash down the cylinders with excess fuel which will reduce heat in the cylinders and reduce pinging, but the aftermath will be a short life for the engine...

Reading the 78 fsm it says . The piston stem pushes the power valve needle down opening the power valve and permitting fuel to flow through the power valve,power valve channel restriction and into the main well. Based on that ,the restriction would have to be made larger to increase fuel flow. So bigger main jets Yes. 2280 jets are not the standard holley jets??

Thanks guys! for ALL the input. I should have some time in the middle of the week to tinker with it and see what I can figure out.

How do I richen a Holley 2280 for high speed/load conditions?
Dusteridot is right on about this carb. Got a feedback version of this carb 6280 to look at. You can have it for parts.I am close by. Its a solid fuel emission carb,no parts no jets etc in the after market. Only way to get parts is another carb. A wide band meter would be usefull for tinkering with the fuel curve of a carb. Carb Theory says making the main system air bleed smaller will make the top of fuel curve richer. The 6280 solid fuel carb has 2 main system air bleeds just like the bbd. Looking down the carb there are 2 philip screws,right next to and in front of those screws are the first main system air bleeds. {I think so any way not 100 percent sure.} The first air bleed is also a ant-siphon- breaker.Now in this case on this carb the bleeds are very small already.Any smaller might inter with the anti-siphon effect. So thats just another Bad idea. There not much really to do with this carb.

Sure it's not timing too advanced?

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As previous posts suggest, I think you have too much advance. Governor springs and test & tune time are cheep compared to replacing a once working carburetor turned into a doorstop.


Before you make some unreversible alteration to your carburetor a detailed graphing of timing curve has to be made. Mapping out all three timing phases base, mechanical, and vacuum advance in relation to rpm and vacuum would be a good starting place. Once that data is know, the solution most likely will be easy to see.


Once the timing curve is known and corrected if needed, and the engine exhibits surging, or stumbling under light acceleration, than we move to the carburetor side of the equation.

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