Carb swap for my BB

1980RS

Veteran Member
Jun 17, 2006
5,998
MN
For anyone with a 3310-1 or -2 you can take the check ball out but on most cars the sec side will come in too soon no mater what spring one uses. The trick to fix that problem is to pull out the ball, then use a philips head screw driver and smack it into the hole where the ball sits and smack it good. The reason for this is to make the ball less sensitive and make the sec side open better. You have nothing to lose by trying this mod.
 

73Motion

Member
Mar 1, 2016
48
Corsicana TX
Considering a different carb on my BB. Just getting this engine put back together and putting the car back on the road. Have a Holley 750VS carb that I went through several years ago but it has very little run time. Took it off the car yesterday to check out operation and can not seem to get the secondary blades to open.....at least using the procedure I saw on YouTube. I have the carb on an elevated stand, primaries open fully and then using compressor blew air across the vacuum hole in the front right venturi........secondary blades never moved. Going to take it apart and see what things look like but may end up just buying something different.

This car will be spending more time playing at the track and blasting around roads just for fun. Not going to spend any significant time on the highway, really just something for me to have fun with......but not a dedicated race car. Specs are +.030 454, 9.7 compression, rpm intake, Lunati Voodoo .542/.554 cam, TH350, 3.42 gear, 275/60 drag radial, currently stock converter but will be changing that to something in the range of 2400-3000 stall 11 or 10 inch converter.

Looking at 2 carbs:
ProForm 850 Street Series, mechanical secondary, electric choke
FST 850 RT-X, mechanical secondary, electric choke

Both carbs are in the $450 range.....anybody used either of these? If so results and observations. Open to other suggestions as well.

My new MJ 467 dynoed just as good and even a few hp better with my 750 over his 850. However the the barometric pressure was much better the day of the 750 dyno so not an exact comparison. That was the carb I had and wanted to use so that is what we dynoed with. The 750 is the Holley HP mechanical electric choke with a 1” phenolic spacer on the Edlebrock performer air gap intake The dyno was with aluminum spacer. I have since added the Thompson Performance Powerblast plates to the carb. It is very responsive. My setup is with 3:73 gears and a built 700r4 with a 2800 stall. I also have the 275/60 MT street radials. On the street a heavy right foot of the 607hp fries those tires uncontrollably in low gear. Needless to say it is big fun!! Good luck.
 

1980RS

Veteran Member
Jun 17, 2006
5,998
MN
My new MJ 467 dynoed just as good and even a few hp better with my 750 over his 850. However the the barometric pressure was much better the day of the 750 dyno so not an exact comparison. That was the carb I had and wanted to use so that is what we dynoed with. The 750 is the Holley HP mechanical electric choke with a 1” phenolic spacer on the Edlebrock performer air gap intake The dyno was with aluminum spacer. I have since added the Thompson Performance Powerblast plates to the carb. It is very responsive. My setup is with 3:73 gears and a built 700r4 with a 2800 stall. I also have the 275/60 MT street radials. On the street a heavy right foot of the 607hp fries those tires uncontrollably in low gear. Needless to say it is big fun!! Good luck.

Mark builds some great engines for sure. One thing to ask him is his jetting for the high altitude where he lives the same as jetting for where you live, that meaning if the jetting is let's say 84 square at Denver then where you live the jetting would be to fat of you are closer to sea level. The Thompson power blast plates really work, if they were closer to $20 each I would but more but $40 for 1 is very steeply priced.
 

75isalive

New Member
Mar 3, 2014
9
Napoleon, Mi
Considering a different carb on my BB. Just getting this engine put back together and putting the car back on the road. Have a Holley 750VS carb that I went through several years ago but it has very little run time. Took it off the car yesterday to check out operation and can not seem to get the secondary blades to open.....at least using the procedure I saw on YouTube. I have the carb on an elevated stand, primaries open fully and then using compressor blew air across the vacuum hole in the front right venturi........secondary blades never moved. Going to take it apart and see what things look like but may end up just buying something different.

This car will be spending more time playing at the track and blasting around roads just for fun. Not going to spend any significant time on the highway, really just something for me to have fun with......but not a dedicated race car. Specs are +.030 454, 9.7 compression, rpm intake, Lunati Voodoo .542/.554 cam, TH350, 3.42 gear, 275/60 drag radial, currently stock converter but will be changing that to something in the range of 2400-3000 stall 11 or 10 inch converter.

Looking at 2 carbs:
ProForm 850 Street Series, mechanical secondary, electric choke
FST 850 RT-X, mechanical secondary, electric choke

Both carbs are in the $450 range.....anybody used either of these? If so results and observations. Open to other suggestions as well.
There are definitely a lot of carburetor choices. I had difficulties getting the full power out of my 406. I installed a Brawler 770 cfm, vacuum secondary, electric choke. Had to change out the factory power valve to a 3.5. A little adjusting and she screams now. Also have a TH350 with 3.42 gears.
 

73Motion

Member
Mar 1, 2016
48
Corsicana TX
Mark builds some great engines for sure. One thing to ask him is his jetting for the high altitude where he lives the same as jetting for where you live, that meaning if the jetting is let's say 84 square at Denver then where you live the jetting would be to fat of you are closer to sea level. The Thompson power blast plates really work, if they were closer to $20 each I would but more but $40 for 1 is very steeply priced.
Agree. Going to use a highly rated carb guy in my area to tune it for the exact issues you point out. I tuned with vacuum gauge to best of my ability. Plugs look good but I’m no carb guy. Will let you know the changes if any.
 

Z-28 Roadracer

New Member
Aug 23, 2014
12
Winneconne, WI
What series of 750VS carburetor do you have on now? If it's a 3310, you have about the best carburetor you can get. Chevy used a lot of them on their high performance small and big blocks. If the secondaries are not opening on a 3310, it's pretty easy to diagnose. I've had secondary diaphragms go out on me before, but you need to find the issue first. IMHO

I second that. I've got a similar set up to yours in my '69 and the 3310-2 works really good. Before I'd drop $$ on something significantly different, I'd try to borrow something from one of my friends. Or inject it.
 

1980RS

Veteran Member
Jun 17, 2006
5,998
MN
Considering a different carb on my BB. Just getting this engine put back together and putting the car back on the road. Have a Holley 750VS carb that I went through several years ago but it has very little run time. Took it off the car yesterday to check out operation and can not seem to get the secondary blades to open.....at least using the procedure I saw on YouTube. I have the carb on an elevated stand, primaries open fully and then using compressor blew air across the vacuum hole in the front right venturi........secondary blades never moved. Going to take it apart and see what things look like but may end up just buying something different.

This car will be spending more time playing at the track and blasting around roads just for fun. Not going to spend any significant time on the highway, really just something for me to have fun with......but not a dedicated race car. Specs are +.030 454, 9.7 compression, rpm intake, Lunati Voodoo .542/.554 cam, TH350, 3.42 gear, 275/60 drag radial, currently stock converter but will be changing that to something in the range of 2400-3000 stall 11 or 10 inch converter.

Looking at 2 carbs:
ProForm 850 Street Series, mechanical secondary, electric choke
FST 850 RT-X, mechanical secondary, electric choke

Both carbs are in the $450 range.....anybody used either of these? If so results and observations. Open to other suggestions as well.

So I can comment on the FST 850 after running mine for a little while on the car yesterday. The biggest gripe is you cannot change jets with what is supplied with the FST 850 as their jets will not fit through the bowl holes for the quick jet change. The run ability of the carb was good but it is very fat (rich) at idle so I think it will require some tuning to get it right, floats were a touch high but the idle mixture screws were pretty close. Do not get it in black, the finish is very poor.
 

80NastyZ

Veteran Member
Feb 8, 2007
207
Poconos P.A.
Just curious on the AED, what kind of emulsion package did they actually use, and was it a high or low set IFR ?

5 hole blocks , all .028 +/- .001 , IFR was still high .

I moved the IFR to the lower position and plugged all but 2 of the Emulsion holes .

FWIW , most of the newer Holley HP series use the same setup but with a 3 hole emulsion block , sucks to have to "fix" a new carb even before use .

TOM
 

1980RS

Veteran Member
Jun 17, 2006
5,998
MN
5 hole blocks , all .028 +/- .001 , IFR was still high .

I moved the IFR to the lower position and plugged all but 2 of the Emulsion holes .

FWIW , most of the newer Holley HP series use the same setup but with a 3 hole emulsion block , sucks to have to "fix" a new carb even before use .

TOM
You are spot on with the having to "fix" something new. On the bright side at least the FST street carbs were pretty close out of the box.
 




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