Summit 600 CFM Carb

Sounds like a really nice carb, and good combos you have.  

It must be good if you can still buy a 1957 OEM design that's been improved upon 66 years after it first came out. That alone should say something right there.



Looks pretty good under the hood as well.

FordFETruck wrote

Just some feedback with the summit carbs. I own two of them. The 600 CFM variant (I would have bought the 500 CFM if they offered it back then) I bought for my truck 10 years ago. Never had a problem with it, and it had the original power valve in it for like 8 years before I swapped it out for the correct HG rating for the engine and it was still like new. I have done some tuning to it with the help of a wideband o2 AFR gauge and got it all spot on and put a Motorcraft 7 volt choke cap on it. Starts right up and runs fantastic in cold or hot weather.

I like it so much I replaced my extensively tuned 600 CFM Holley on my 64 galaxie 390 with a 500, yes 500 CFM Summit carb on that big engine. I tuned it to the application with the help of a wideband o2 AFR gauge and put a 7 volt Motorcraft choke cap on it also and I'll be darned if it didn't pick up torque and throttle response below 2000 RPM and scream just as hard to 5500-6000 as the 600 CFM Holley did. Both can sit for over a week and fire right up with just a few squirts of the accelerator. I really like both of mine.

Thanks for the feedback on the Summit carb. Interesting that you prefer the 500 CFM version over the 600. I was seriously looking at the 600 CFM version for my 351W HO. Going to have to rethink that now.  

I hope to be starting my 5.0 with new 500CFM Summit carb in a couple weeks, and I'm super stoked about it. I'm hoping that it makes my 5.0 run nice and smooth. I'll keep you posted John.

Thanks Corey, please do? I saw one on ebay, a used 600 CFM and thought about buying it and rebuilding it. Guy wanted $225 for it but the rebuild kit was $90.....OUCH! Expensive rebuild kit for this carb!  

I figured since the original Autolite 4100 1.12 my car came with (came with a 352 originally but they used the same size carb on 352 and 390 applications, ranging from 250-300 and 330HP) only flowed about 525 CFM and was very economically tuned a performance 500 CFM should do just fine and I guess I was right. I would definitely buy the 500 CFM and tune it to the application. It has more crisp throttle response off idle and better torque than the 600 does but screaming to redline doesn't seem any different than the bigger carb. Although the 600 is a very nice carb.

My 351W HO has a Comp XE250H cam, Edelbrock E street heads, about 9.2:1 static compression, 8:1 DCR, hooker long tube headers, 2.5" dual to 3" single exhaust, Weiand stealth intake with the 600 CFM Summit. It runs great but out of the box the secondary side of the carb was way rich. I'm at about 500 feet above sea level and my carb is jetted as : 68 primary jet, 69 secondary jet, 9.5" HG power valve, .035" discharge squirter, stock green acc pump cam in factory #2 position, brown secondary diaphragm spring. I had to enlarge the IFR jets from stock .046" to .049" to get rid of an off idle lean transition slot stumble - probably not required with a stock camshaft.

The 500 CFM on a 10:1 static, 8.4:1 DCR zero decked 390 with stock iron heads, stock 1964 352 4V intake, stock restrictive exhaust manifolds, Comp XE262H cam, 2.5" dual with H pipe exhaust but it's 2" for the first 6" to get hooked up to stock manifolds and despite it having that smaller carb and restrictive stock stuff it just demolishes that 351W in my truck in every way.

That carb is jetted as: 65 primary jet, secondary side did not need any tuning, 68 secondary jet, stock secondary diaphragm spring. .035" discharge nozzles and been experimenting with acc pump cams but it seems the pink cam works best for that application. Enlarged IFR jets from .046" to .048" to get rid of off idle lean transition slot stumble. Also opened up the secondary IFR jets .002" over stock size to smooth out shaking at idle without affecting low speed AFR driving on the transfer slot.

I would really prefer a 500 CFM Summit on my truck but the one I have on it works great and they are expensive so oh well. I did run a 4548 450 CFM Holley on the truck for about a year and it had very good low end response and was very free revving on the high end. In fact, I would say it was the perfect size carb for that engine and truck but it had some issues unrelated to running so I took it off.

I have that carb, it was my planned carb for my 302 roller build for my truck.  I since decided to go Sniper 4150 Stealth instead.

From what I read how ever, everyone loves the carb.  I even installed one at work on a '73 Corvette and it was one of the best running carbs I seen out of the box.  I still have mine complete with secondary quick change kit to install on it as well as a set of jets.  I havent decided if I want to go with this carb on my 351W or go with a sniper 4150 stealth on that engine as well.

Machspeed wrote

Thanks Corey, please do? I saw one on ebay, a used 600 CFM and thought about buying it and rebuilding it. Guy wanted $225 for it but the rebuild kit was $90.....OUCH! Expensive rebuild kit for this carb!

John,

I finally got my little 5.0/302 fired up and so far I'm really pleased with the simplicity of the Summit carb. I'm only running the 500CFM version below, and boy has it gone up in price! I paid something like $349 for it, and I remember being mad at the time because the price had jumped $20-$30 bucks from a few months before I bought it. Wow...but I guess everything IS crazy these days...

https://www.summitracing.com/parts/sum-m08500vs?seid=srese1&gclid=Cj0KCQjwiZqhBhCJARIsACHHEH-JHCWfutYdxlALfz9AY5xsTEXq--5m-8N_3wm71L6keZcQAnBob2oaAvYfEALw_wcB

PS: I mentioned in my project thread that with this carb the engine starts right away and almost immediately idles on its own without the choke...like really nicely.

Truck is not on the road yet...but will possibly be this weekend if some other things work out OK.
I'll keep you posted.

Thanks Cory! Yes, please keep me advised. As you said I keep watching the cost of this thing escalate. It seems not too long ago that these were cheap....$250ish. This price being an introductory price, which may have been further back than I think. Time eludes me these days.

I think I stated this early on in this thread but I had considered getting a used one off ebay and a kit for possible rebuild until I saw the price of the rebuild kit....$90. Are you kidding me!!! Crazy the cost of things today.  

Curious if anybody with one of the Summit (or Autolite, or Holley 4010) carbs ever had any issues with the throttle plates hanging up preventing the idle from decreasing.

My engine is running GREAT! It starts 100% perfectly, as good as any EFI. The carb seems to be very responsive, and so far the engine is looking like it is going to be good on fuel also.

I do have one nagging issue though: Idle. I can't adjust the idle below about 800-850 RPM once it is warmed up. The curb idle screw simply lifts off the throttle. I have the electric choke completely disabled...the fast idle screw is also removed, so it's not hanging up on the choke. I've done prelim check for vacuum leaks and didn't find anything. I added the thicker (0.062") carb gaskets, and have checked and torqued the carb base bolts several times. The transition slots look like they're bigger than square, but I can't adjust it any further.

With the engine cold, it idles nicely. It's when it warms up that the idle seems to creep up a bit. Once in a while, I've reached under the hood and returned the throttle by hand and the idle decreases instantly. After this I installed a return spring...not a great one, just one I had laying around. I have a proper throttle return spring/bracket kit on order arriving tomorrow.

Anyway, just wondering if anybody has any thoughts? I haven't touched the idle air mixture screws yet. It's almost perfect, but I'd love to get this idle dialed in a little better. It seems like the throttle plates are hanging up somehow, but I can't see where or how.

PS: I did not check the secondary plates...I didn't think to check them before re-installing the carb last time.

Any ideas? I was reading that a possible solution is to loosen the throttle plates and let them re-center, but I'd like to get more input on that, or other ideas first.

Edit: I also have a Holley TPS installed on this carb, and I originally thought it was an issue, but I've investigated it thoroughly and it doesn't appear to be holding anything up. When I was playing with the carb on the workbench, I had the TPS removed anyway.

I would definitely check the secondaries Cory.
The truck should die with the curb idle screw backed off the lever.
So you must be getting air from somewhere, and I know you're talented and particular enough to ferret out any vacuum leaks.
I can't say I have experience with the 4100/4010 or their clones.
Glad to hear that the old Merc is running so well!  

If the secondary throttle shaft has a stop screw like the Autolite 4100s did, it may need adjusting. Quick check, take a piece of vacuum hose and hold it near one ear, take the other end and insert it in the primary and secondary venturiis and listen to the hiss of air. If you have a loud hiss on the secondaries, then they definitely need adjusting.

Holley 4150/4160 vacuum secondaries and the Autolite 4100s use a stop screw so the throttle plates don't stick closed. The old "Teapot" Holleys had a special procedure for installing the throttle plates in the secondaries. They were slightly asymmetrical, with the long side being the one that lifted up when opening. Procedure was to take two strips of paper and put them in the back side of the secondary throttle bores and while holding the shaft closed, tighten the screws. This meant the the secondaries seated against the front of the bores so they back side wouldn't dig into the aluminum and cause them to stick.

Thanks for the tips guys. I'll check the secondaries and see what else I can find.

One thing I forgot to mention, and maybe it's nothing, but the carb seems to leak badly around the left end of the throttle plate shaft if I operate the throttle with the engine off. It did this when installed on the engine, but also on my work bench also. Not sure if that means anything or not...maybe they all do that? I don't remember my previous Holley 4160 leaking like this.

When I say that I did prelim vacuum checks, I just mean that I removed and plugged the brake booster, and I removed the vacuum tube for the wipers (truck still has original vacuum wipers...they're on the list to be electrified lol, but very low priority at the moment). I also replaced the carb base gasket (and 1" spacer gasket under that). I haven't gone around the intake and carb base yet for a proper vacuum leak test with carb cleaner or propane, etc.

If you have that big a leak around a throttle shaft, I wonder if a bushing was left out? Holley used bushings on high wear areas.

FordFETruck wrote

That carb is jetted as: 65 primary jet, secondary side did not need any tuning, 68 secondary jet, stock secondary diaphragm spring. .035" discharge nozzles and been experimenting with acc pump cams but it seems the pink cam works best for that application. Enlarged IFR jets from .046" to .048" to get rid of off idle lean transition slot stumble. Also opened up the secondary IFR jets .002" over stock size to smooth out shaking at idle without affecting low speed AFR driving on the transfer slot.

Hey FordFETruck,

I have been doing some reading, and this appears to be a somewhat common issue with the Summit carbs. Mine is working well most of the time. It starts as good as any EFI engine, and runs down the road just fine. However, if it sits off for for a little bit, or if I get stuck in the heat in stop and go traffic, it will start to idle rough. I don't know what the problem is, and I don't have an AFR gauge, but it seems to be related to the carb getting heat soaked. I watched one video where the guy was having the exact same issue, and the cure was increasing the size of the IFR jets, in his case he went from 0.046" to 0.053", and that fixed it. He says that the Summit carbs spend A LOT more time in the transition slot than other carbs, so having the IFR jets correct is critical.

So I came back to read this thread again, and sure enough you also had to increase your IFR jet size, although not as much.

I guess I should probably install an AFR gauge to confirm that the heat soak theory/engine running rough is actually due to a lean condition...but I could also try some jetting changes first.

What jets do I order? I did see a comment online that I can use Holley Emulsion Jets. If that is all that I need to do, then I'll get a few sizes ordered up to try.