Which Carb?

[BillC 38]

Hi all,

I have a 70 428CJ 335 hp(?) Mach 1 Mustang. It currently has a Holley 750cfm manual choke and vacuum secondaries. (not original to the car). The original carb was 735 cfm.

The carb has to be rebuilt so I was thinking about buying a smaller cfm carb. The inside of my tailpipe is black with carbon even after adjustments and timing check. The Holley website shows that for my engine and a maximum 6000 rpm the recommended size should be 600-670cfm.

Considering the size of the original carb this sounds small to me. I don't plan on racing, except to give the local kids a hole shot now and then.

What do you think?

Any recommendations?

Thanks,

Bill

[Brian Conway 264]

Hello Bill;  I run a Holley 3310-1 780 cfm carb. on top of my 428.  I am satisfied with the performance and  wouldn't go smaller.  Aside from the tailpipe residue how's the car/carb run ?  If you are running rich they are remedies for that.  You mention adj. and timing.  I would start with the mixture adj. screws to lean up the mix checking the jet sizes might be a good Idea.   Might want to get the carb. rebuilt and tuned by a shop or Holley ?  I run 12 degrees BTDC.  If you go to the Holley web site you can download an owners manual for your carb.  Just a thought; If the car is running fine you might want to just leave it alone.  Brian

[BillC 38]

Hi Brian,

Thanks for your help once again. The car runs really bad. Very hard starting, uneven idle, and a very rich smell. I adjusted the air/fuel screws and have it as lean as I can. Set the float and checked the timing. I'm at 10 degrees BTDC. I'll run at 12 and see how it does. The previous owner had the car tuned at JBA Speed Shop in San Diego. (you may be familiar) before I bought It. I don't know if the jets were changed but something is wrong. BTW, there are no vacuum leaks I can find and all else seems to be OK.

I guess I'll pull it off and rebuild it.

Thanks again,

Bill

[1969_Mach1 333]

A 3310-2 carb is by no means too large for a 428.  When you rebuild it make certain the main jets and power valve are the original sizes.  Holley has a document in their tech section that lists all of the factory settings, etc. for each carb.  Holley offers a secondary metering block kit to replace the secondary metering plate.  This will give you jetting adjustments for the secondaries if it's ever needed.  Holley's are simple carbs.

 

Since the previous owner had the car tuned at JBA, is the engine stock?  Does it have an aggressive cam?

 

Use a rebuilt kit from Holley, QFT, or AED.  They come with better quality gaskets than a parts store brand.

[LoneWolf2U 136]

Rebuild the 750 and check the main jet sizes as they may have been changed and are too large for your eng spec's.

[Brian Conway 264]

Good Morning Bill.  East Coast weather is all the news out here.  Carb problems are for the most part a matter of knowing which screw to turn.  I doubt JBA would have sent the car out with a carb. issue so...  you say rich ?  choke plate not opening ?  Hard to start.... flooded ?  Did it ever run correctly ?  How much fooling around have you done ?  Any recent corrections or mods ?  Usually when I'am in up to my eye brows I go to my high school buddy, spent his whole working career as an auto mechanic,  and he unravels the mess I got myself into.  If your not the ace carb. tech and you don't have an ace in the whole maybe your first idea is not so bad ?  Call or email the HolleyTech Line tell your story and see what they have to say ?  Brian

[Max Power 74]

The size carb you are running now is virtually the same size as factory, so you are not over-carbed. You are not properly adjusted. Sometimes jet size will effect soot in the tailpipe and overall richness, but more often it is idle screw and float adjustments that are the culprit.

 

Remember,  a vacuum secondary carb is really a variable venturi carb in practice, so risk of over-carburation is very low. I would rebuild what you have.

[BillC 38]

Thank you Mach1 and Max Power. I'll take your advise and rebuild.

Bill

[BillC 38]

A 3310-2 carb is by no means too large for a 428.  When you rebuild it make certain the main jets and power valve are the original sizes.  Holley has a document in their tech section that lists all of the factory settings, etc. for each carb.  Holley offers a secondary metering block kit to replace the secondary metering plate.  This will give you jetting adjustments for the secondaries if it's ever needed.  Holley's are simple carbs.

 

Since the previous owner had the car tuned at JBA, is the engine stock?  Does it have an aggressive cam?

 

Use a rebuilt kit from Holley, QFT, or AED.  They come with better quality gaskets than a parts store brand.

As far as the previous owner says, there have been no alterations to the engine. I have most of the invoices and they don't show any modifications either. Since I'm not a carb guru, I'll send it back to Holley and let them put it back to factory specs.

Thank you for the advise.

[BillC 38]

Good Morning Bill.  East Coast weather is all the news out here.  Carb problems are for the most part a matter of knowing which screw to turn.  I doubt JBA would have sent the car out with a carb. issue so...  you say rich ?  choke plate not opening ?  Hard to start.... flooded ?  Did it ever run correctly ?  How much fooling around have you done ?  Any recent corrections or mods ?  Usually when I'am in up to my eye brows I go to my high school buddy, spent his whole working career as an auto mechanic,  and he unravels the mess I got myself into.  If your not the ace carb. tech and you don't have an ace in the whole maybe your first idea is not so bad ?  Call or email the HolleyTech Line tell your story and see what they have to say ?  Brian

Hi Brian,

Yeah, the east coast was nailed pretty hard but luckily we only got clouds with occasional showers here I'm Maine. Not good cruise-in weather! I need to move to California so I don't have to keep heading to Florida every winter to escape the snow and cold.

I've heard JBA is a great shop. I'm sure it was fine when it left them. I don't know what happened.

Yes, it's running very rich. I've adjusted the air/fuel mixture and checked the float level. All appears OK. Anything else to do is beyond my experience level so I'm sending it to Holley and have them overhaul and put everything back to original configuration.

Once again, Thanks for all the help. I'll let you know how I make out when I get the carb back.

Bill

[Raven R code 281]

I believe my stock carb on my R code is a holly 650. Seems to provide enough octane to make me fly along the highway. On the flip side, my Q code has the original holly 735. I always thought about running the 735 but wondered if I would gain anything.

[Brian Conway 264]

No I think Florida would be a better choice.  California was a great place once.  Now not so much.  I think I's try the tech site first.  Who knows they may say the 750 is not the right carb for the 428 ?   Brian

[1969_Mach1 333]

The 3310-2 is a common universal carb.  Nothing rare about that one.  Have you compared pricing of a new Holley 750 cfm vacuum secondary carb vs. having Holley rebuild your existing carb.  Of course the new version of the 3310-2 will be something like 3310-11 for example.  And there are the street avenger series.  I haven't used one of those but other members here seem to like them.  A rebuild by Holley might be more costly if during the rebuild Holley also recolors the carb.  And maybe needs to replace a worn base plate or install bushings in the existing base plate to repair worn throttle shaft holes.  Just a thought.

[Brian Conway 264]

FWIW;  the 3310-1 is not the same as any other series 3310-2 and up carb.  The 3310-1 is a far superior carb and does not belong in the same class as the others which by the way are 750 cfm's.  There are other pronounced differences but not the topic here. Brian

[1969_Mach1 333]

I agree, the 3310-1, 780 cfm vacuum secondary carb is superior to the 3310-2 and later 750 cfm carbs.  Although, I think the differences are not that drastic.

 

3310-1:  Down leg boosters, primary and secondary metering blocks.

3310-2 and newer:  Straight leg boosters, primary metering block and secondary metering plate.  Holley offers a secondary metering block kit to replace the secondary metering plate.  The straight leg boosters dropped the cfm rating from 780 to 750 and also probably improved low speed drivability.

 

There are probably some air bleed and emulsion bleed differences between the them to accommodate the different types of boosters.  Beyond these, all other aspects are identical.

 

On a stock motor for general driving, a down leg booster carb would not be my first choice.  They have a greater tendency to cause low speed drivability issues than carbs with straight leg or annular boosters.

[Alan_Mac 48]

Hi Brian,ope this helps 

Yeah, the east coast was nailed pretty hard but luckily we only got clouds with occasional showers here I'm Maine. Not good cruise-in weather! I need to move to California so I don't have to keep heading to Florida every winter to escape the snow and cold.

I've heard JBA is a great shop. I'm sure it was fine when it left them. I don't know what happened.

Yes, it's running very rich. I've adjusted the air/fuel mixture and checked the float level. All appears OK. Anything else to do is beyond my experience level so I'm sending it to Holley and have them overhaul and put everything back to original configuration.

Once again, Thanks for all the help. I'll let you know how I make out when I get the carb back.

Bill

Just my 2 cents.  ethanol in pump gas accelerates deterioration of the float needle tips causing them to not fully seat at idle. Hence the motor runs rich and erratic at idle. That is why I switched to pure gas awhile back. So the fix maybe replacement of the float needle valves and then an idle mixture adjustment.  now if your A/F mixture off idle hasn't been measured through the RPM range you may have the wrong jets installed.  Holley cant fix that problem for you since it needs to be done while running your car.  I use an air fuel ratio meter from innovate to dial in my carb.   I hope this is helpful. 

[BillC 38]

Just my 2 cents.  ethanol in pump gas accelerates deterioration of the float needle tips causing them to not fully seat at idle. Hence the motor runs rich and erratic at idle. That is why I switched to pure gas awhile back. So the fix maybe replacement of the float needle valves and then an idle mixture adjustment.  now if your A/F mixture off idle hasn't been measured through the RPM range you may have the wrong jets installed.  Holley cant fix that problem for you since it needs to be done while running your car.  I use an air fuel ratio meter from innovate to dial in my carb.   I hope this is helpful.

 

Alan,

This is very valuable information. I spoke with Holley today and they said the price to buy a new carb would be less than to overhaul my non-original carb. I bought a new carb. So now I will have a chance to overhaul the problem one and have no fear of messing it up. I will order all the necessary parts including the float needles you mentioned. Also get the correct jets, power valve etc.

There is a gas station 20 miles from me that sells pure gasoline. But I also have access to 100 octane low lead that is available at the airport I fly out of. I was surprised to see in the owners manual that the recommended minimum octane is 99.8. From now on I think I'll fill up with the aviation fuel.

Thanks for your input,

Bill

[jholmes217 65]

Unless your heads have had hardened seats installed, I'd still run a lead substitute in your gas.

 

Not my light bulb thumb.

[1969_Mach1 333]

If you are not too familiar with carb adjustments, after you get your carb I suggest watching the DVD that Holley provides with it.  The DVD has information on adjustments.  I know the carb is new and it's expected to be correct.  But, before it's installed make certain the accelerator pump adjustments are correct.  Many, many times these carbs come with the accelerator pump adjustments far from being correct.  Then you'll wonder why it has an off idle stumble.

 

One bit of info.  If you purchased a new 3310 series carb, they often need the accelerator pump nozzle size increased to #31 from the size #28 they come with.  If you have an off idle stumble this is usually the cure.

[barnett468 418]

set the gas level so it is just below the inspection hole immediately after you turn the engine off.

 

you can make your secondaries open later by installing a stiffer spring.

 

if your jets are larger than around 72 front and 76 rear they may be too big.

 

leaking power valves can cause problems . it should also be a 6.5.

 

use the blue gaskets.

[jholmes217 65]

Put Chap-stick or some other kind of lip balm on the bowl gaskets in case you need to change jets.  Old racer trick.  The gaskets don't stick and tear, so they can be reused.  x2 on what Barnett468 said about power valves.  I had a bad one a couple months ago, and I was so rich it hurt my eyes.  

 

Have you thought about the 750 cfm Summit Racing carbs?  I have one, and I like it.  Kinda a cross between a Holley and an Autolite 4100.  Uses Holley jets, power valves, needle and seats.  They have a mechanical secondary and a vacuum secondary versions.  https://www.summitracing.com/search/department/air-fuel-delivery/section/carburetors-accessories/part-type/carburetors/brand/summit-racing/universal/yes/carburetor-flange/square-bore?N=4294951509%2B4294949628%2B4294921892%2B400304%2B4294951518%2B4294921253%2B4294921888&SortBy=Default&SortOrder=Ascending

[barnett468 418]

Put Chap-stick or some other kind of lip balm on the bowl gaskets in case you need to change jets.  Old racer trick.  The gaskets don't stick and tear, so they can be reused.  x2 on what Barnett468 said about power valves.  I had a bad one a couple months ago, and I was so rich it hurt my eyes.  

 

Have you thought about the 750 cfm Summit Racing carbs?  I have one, and I like it.  Kinda a cross between a Holley and an Autolite 4100.  Uses Holley jets, power valves, needle and seats.  They have a mechanical secondary and a vacuum secondary versions.  https://www.summitracing.com/search/department/air-fuel-delivery/section/carburetors-accessories/part-type/carburetors/brand/summit-racing/universal/yes/carburetor-flange/square-bore?N=4294951509%2B4294949628%2B4294921892%2B400304%2B4294951518%2B4294921253%2B4294921888&SortBy=Default&SortOrder=Ascending

 

 

the summit carb has annular boosters and is made by holley and is the old holley shoe box carb . the casting is made overseas but holley does all the machining in the us.

 

they sometimes sell rebuilt ones pretty cheap, unfortunately, they want so much for their carbs now that you could get a quick fuel entry level carb for around $50.00 more and it is a far better carb overall except it does not have annular boosters.

[jholmes217 65]

the smmit carb has annular boosters and is made by holley and is the old holley shoe box carb . the casting is made overseas but holley does all the machining in the us.

 

they sometimes sell rebuilt ones pretty cheap, unfortunately, they want so much for their carbs now that you could get a quick fuel entry level carb for around $50.00 more and it is a far better carb overall except it does not have annular boosters.

I bought mine used on Ebay for $125 if I remember right.  Guy that sold it said it was too much carb for his small block chevy.  Changed jets to the same sizes as came in the 428 Cobra Jet carb, and it worked great.  Nice throttle response.  I don't buy new carbs.  Too many for sale cheap on Ebay and Craigslist that just need a rebuild.  I've only had one bad used carb, and I bought it more for the Edelbrock Streetmaster 390 intake manifold that it was on.  Got both for $50.  The carb became a parts carb.

[Alan_Mac 48]

+1 on the power valve replacement also

[fvike 173]

Check that you have the right size power valve for your application. Makes a huge difference.