I have a Holley 750VS 4160 3310-6 carb. I've been reading, off and on, Dave Emanuel's "Super tuning and modifying Holley carburetors, performance, street and off-road applications." I made myself start reading from the begining to get myself familiar on how the carb works and whatnot instead of just "jumping into it" and tearing my carb apart and no know what does what. Well I haven't done anything to my carb, and I've been getting frustrated because I don't have the time to really read all the info in my book, so I jumped to the tunning section which talks about the power valves, jets and accelerator pump. This is where I'm confused.....can I or can I not change the jets on my Holley? The only thing the book said is that my carb can be adapted to a 4150 style carb which makes changing jets and power valves much easier. And somewhere along the line, don't remember if I read it in my book or read it from someone's thread/post, but, I got the impression that VS carbs' jets can't be changed. I know this sounds weird, but like I said, I picked that up from somewhere. Another thing, is it worth it for change my carb to a 4150 style? I know for the track, it's the best thing to do to optimize performance and adjustablilty. But, for an everyday street driven car, is this something I should look into? Thanks in advance everyone and please be kind....I still don't know much about carbs, that's why I'm reading and asking questions :D graemlins/beers.gif

Hello Alex,

I think I'm probably the source of your confusion....

I'll try to make it less confusing.

First, we are talking about VS carbs here, I know zilch about DPs or anything else.

Front Jets= you CAN change them.

Just go throught the steps of removing the front fuel bowl and metering block and you'll see your jets, conviniently numbered.

Rear Jets= You CAN'T change them.They don't exist in the first place. tongue.gif

At least not on MOST Vac Sec carbs. If you don't have rear metering block, you CAN"T do it. I'm not sure if you can change to a different metering PLATE or not...

I'll let the other guys handle the 4160-4150 change, I've never done it.

LXS (name?), I have the same 3310 Holley 750cfm as you do.

Enrique is correct that you can change the front jets rather easily. They are located in the primary metering BLOCK which is sandwiched between the primary bowl and the main block.

You will have a secondary metering PLATE that has drilled orifices that dictate fuel flow. You COULD (I guess) drill those holes out bigger and you might richen the carb up. Or (I guess...again) you could epoxy the holes up and drill them out to be smaller than stock. This would lean it out. I wouldn't particular recommend it.

The easiest thing to do is to buy the Holley Secondary Metering Block Kit. You get the secondary metering block, a blue non-stick gasket and some longer fuel bowl bolts. Then you will have primary and secondary metering blocks. You can jet till your hearts content. You would have a 4150 "style" carb, but it would still be a vacuum secondary. That means you only have a single accelerator pump, which is located on the driver's front corner of the carb. A double pumper will have 2 accelerator pumps, hence the name.

Anyway, I bought the kit and it's easy to install and goes for about $32 or so. Do you need it? Maybe not. Can you use it? Yes you can.

If you have any more questions just holler. Also, check into a Quick Change Secondary Spring Kit. It's cheap and super easy to tune with.

Good luck! smile.gif

To piggyback on what's been previously mentioned, your carb had a front metering block and a rear metering plate. While you can still change jets for the front there's probably not a whole heck of alot you can do for the rear since the metering plate is a preset flow from the factory. This can make re-jetting a carb tedious as you aren't able to tune the front with the rear, and from what I've seen most the time the rear metering blocks are jetted richer than the fronts.

The beauty of going to a 4150 set up is you are swapping out the metering plate for an actual metering block that you can tune with the rest of the carb. And with a metering block you can, as mentioned jet the carb till your hearts content.

I see a company is now manufacturing a metering plate that accepts jets for the secondary side. What I'm referring to is not a block and doesn't require the longer fuel bowl bolts. Something to consider. Quick Fuel Technology, Jegs sells them.

If they're not made by Holley I want no part of them. Holley parts only on my Holleys.

LXS, as badbob71 mention about the Quick Fuel Technology metering/jet plates. I have these plates and they do accept the standard holley jets. They are a great product and work great.

I wish holley would make a product like this under the Holley name. If you have'nt noticed that it takes other companies to improve on a orginal product before the company itself makes the same product better.
Take for example the BG Demon series carb (which has improvements all over the standard holley 4150 carb). Then Holley introduced their HP series carb that has all these features standard.
Just something to make you wander about -).

You might want to take a look at the quick fuel tech meterplates. The kit comes with floats too.
This url will send you to the link.
http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=4671&prmenbr=361

If you add the rear block and have a solid type dual fuel line then you'll need another longer one. Not much money but another item on the shopping list.

The sec jet plates can be drilled with no problems and if you look the are quite a few different ones around. Another thing about them is the ease of playing the sec idle fuel volume. I have used 4160 type carbs on motors with huge cams and been able to do a lot of tuning to clear up the idle problems just by playing with the idle restrictions.

Robert is correct about the solid dual fuel line issue. Mike is also correct about other metering plates being available. I forgot to mention those points.

Mike are you talking about idle restrictors in the metering plate? If so, can you elaborate?

Thanks for pitching in guys!

can somebody give me a quick synopsis of what the jets do and why you go up or down with them. I currently have #71's in my 4150 holley.

I believe the jets control how much fuel mixture you have. You up them to richen your air/fuel mixture and you down them to lean it.

Holley does make a metering block for making it from a 4160 to what they call a 4150. A 3310 std. finish Conversion kit is #34-13, 3310 shiny is part #34-13s. Has no provision for a power valve. Comes with block,gaskets,bolts and seals. No jets. Your current plates correlation to jet size is equal to a 75 main jet. graemlins/hurray.gif

Thanks for all the responses guys!!! One more thing I'm still kinda confused about. If I do buy that conversion kit to make it easier to change jets and power valves, that's only for the front right? If so, would I also need one, or something similar, for the rear? And, if I were to try changing and tuning my carb the way it is, do I leave the rear bowl alone? All this is like one big puzzle sitting in front of me....I know I have all the answers in front of me, but, it's putting it all together to make that great big picture to finally see what everyone is talking about. Thanks a lot everyone graemlins/hurray.gif graemlins/beers.gif graemlins/thumbsup.gif

The 34-13 and 34-13s blocks are for the rear to make your carb. into one which you can change your jets as you need to. You can already change your front jets if needed.

O ok, so then the front bowl isn't and has never been a problem, just the rear is what needs to be changed. Now everything is starting to makes sense!!! Thanks everyone...and please keep the info coming graemlins/thumbsup.gif

Correct. If you remove your front fuel bowl right now, there will be 2 jets in there.

Let's make this a little bit simpler. Take a look at your carb. Lean over the driver's fender and really look at it from the side. From left to right you will see this:

Primary fuel bowl, primary metering block and then main body.

After that you only see a secondary fuel bowl. AHA! NO secondary metering block. That's cuz there's a secondary metering PLATE hidden in there that is actually bolted to the main body.

To get that extra bit of tunability, you would remove the secondary fuel bowl and then unbolt the secondary metering PLATE from the main body. Then you would install your NEW secondary metering BLOCK in it's place (with 2 jets). Finally, you would put your secondary fuel bowl back on. That's it in a simplified nutshell.

As was mentioned, you would need a slightly longer fuel line and bowl screws. The long bowl screws are included in the secondary metering block kit, but getting a new fuel line is up to you.

Good luck and feel free to ask more questions if you are still confused.

Thanks a lot Justin, and to everyone else as well!!! graemlins/thumbsup.gif Can't meet all of you at a bar, so here's the next best graemlins/beers.gif on me guys ;)

Or you could just buy a double pumper carb. That's a carb with front and rear jet's and bowls.

I know I could just buy a double pumper, but it'd be a lot cheaper to buy the kit, and have slightly better street manners then a double pumper.