I’ve watched a few of them but it’s been awhile and need another refresher. There’s another guy on you tube that has some food informational videos on blow through carbs I’ve been watching as well. The more I learn the more those videos make sense to me


Just rewatched it, the adjustable BRPV makes sense and is an option to play with on the secondary side. Also fuel pressure. I went from 6psi, carb builder said go to 7 and see what happens. I was richer everywhere from that, no I’m wondering if I’m still walking that fine line and should go to 8psi because last night when I drove it, it was doing the same things as before.

Base fuel pressure to maybe 8psi, adjusting the power valve in the secondary to open sooner, and researching vent tube extension lengths are my next steps I’m thinking.

 

I've never run blow through, but the BRPV and vent extensions definitely make sense to me.

 

I’m almost wondering if the secondary brpv is not adjusted properly and isn’t even opening.

 

So I understand , you have both power valves in it? You just removed some restrictors for the power valve circuit to richen it?

Its crazy but the air flowing at high speed over the top of a vent tube that isnt in the path of air flow will cause a low pressure area to the point of vacuum.


The main issue Ive had was the primary power valve wouldnt open because the air pressure to the front bowl was lower than everything else. The rear hasnt been an issue because its at the back where it gets good even pressure. Both times I had this isuse it would come into boost and go 15 afr. Once the primary pv opened it was golden. The power valves add a lot of fuel. Even though you add fuel to the pv circuits, the addition in the rear may not be enough to make up for the front not opening at all. If that is the case.

 

That thought has crossed my mind as well, is it actually the primary being the problem? My front fuel bowl leaks and mists fuel into the windshield anytime I get into boost, which also had me thinking is the primary bowl the issue? I need to data log again, but visually watching the screen fuel pressure rises 1:1, as I see 16-18psi range and I’m about 10lbs of boost.

And correct, both power valves are in and I just removed the restrictors behind them. Pictured is my vent tube extensions and where they sit in the airflow path. Side view they’re at about the “M” in extreme. #ad
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Have you blocked the original power valve vacuum source in the baseplate ?

 

did you just add the extensions or they have always been there?

 

Is this the barbed fitting usually found off the back of the base plate? If it is, the carb does not have a provision like that.

They’ve always been there. The carb builder asked if I had them on, I said yes, and he said ok good haha. Going to try and call tomorrow if I have time. He is east coast and I am west coast so narrows the communication window.

 

I watched this video on the BRPV and part of the install was blocking a hole in the bottom of the baseplate. If it is there and still open the power valve won't pressurize properly.

 

I’ll take a look at that, thanks!

 

Good video that covers that specific power valve.
Not all brpv operate and reference the same.
Gotta know what you have and how it works.

 

Installed the caltracs the other weekend, bought them awhile back but weather has been so bad to get the truck out and use the lift at work. Let’s just say getting the old bushings out is dumb! Ended up torching/burning bushing material out and then using a sawzall to cut a releif in the sleeve. After that a lot of hammer and punch work they popped out.

I had to trim the plate that bolts the leaf springs to the axle since the inside is basically touching my wheel/tire. Found this out the hard way years back when I first drove it so knew what to do this round. Basically just have to 45° the inside corners and it’s good to go.

I chose the 2 hole position plates to have more tuning ability. If I find I’m always needing the upper hole (hits harder) then I may trim the bottom one of it ever becomes an issue for clearance. I’ll test load it on a trailer or two just to know it’s going to make it.

Haven’t had a chance to test them but I can tell under acceleration it’s trying to put more power to the ground and I get less wheel hop. I also noticed my driveline has come up and rubbed on the bottom of my cab before…so knowing I’m not wrapping the axle anymore is going to be comforting. I’m going to use dykem to mark some spots of my driveline, that way upon inspections I can easily tell if it has rubbed again or not. #ad
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Cup holders installed…because “street truck”. #ad

 

So I went and switched my fuel lines around and also the placement of my regulator. This was a last ditch effort to see if my lean issue can be solved.

I had a -8 feed and a -10 return off the regulators instructions. I also had the regulator before the fuel log to the carburetor. I moved the regulator to the back of the fuel log to give flow priority to the carburetor, and also moved to a 10an feed and 8an return as well. Doing this on one pull it seemed to hold steady lean, but it held solid. Around 14.5-14.8afr. Now I’m only doing this for a second or two before letting out. I tried a second pull the next day and it was back to normal and back to diving into the 15’s and even flashing to 16 within 2 seconds. The hit starts fine but the longer you stay in it, the leaner it gets.

I have a Magnafuel QuickStart 300 pump, and they said I should be able to do 850-900hp with that pump. At the power level I’m estimated to be at I need 275-290lph of fuel flow. If that pump is a 300lph pump then I can see it being maxed out in my current setup. Pressure changes flow potential, older pump variables, etc.

So I have a friend with a new 600lph pump I’m going to borrow just for a test hit or two and compare to see if I can sustain afr. I’ve tried getting up the secondaries from 99 to 103, also pulled all the power valve restrictor plugs behind the power valve. I noticed this dropped a point on the afr scale for the primaries and low boost levels it seems to hold fine under part throttle. As soon as it’s full throttle it just runs out of fuel.

I feel testing a larger fuel pump is next on the list to see if I can narrow this down. I don’t feel it’s a small tweak, it’s something large that’s going to have to change.

 

Do you have the return at the pump plugged?
Can you watch fuel pressure from the drivers seat?

Also, at around 16 afr , are you getting lean sneezes. I would say if your not, the wb probably isnt reading correctly. Also, are you checking plugs to verify afr?

 

I can watch fuel pressure and have also data logged to review while I’m not driving haha. Fuel pressure stays equal 1:1 rise or just above. The return at the pump is plugged, that’s one thing Magnafuel recommended when running a boost referenced regulator.

The times it flashes really lean it does pop, kind of like a boost cut would feel but now that you me mention it I’m below my boost cut when this happens. Plugs I’ve checked and they’re ghost white all the way down, timing is dead center of the strap.

 

Got the new fuel system all setup. Welded a -12an fitting on my fuel cell for an outlet. -12 suction to a pre filter with built in shutoff valve. Then to an aeromotive eliminator fuel pump and -10an outlet. Using an aeromotive a2000 regulator as well and a -10an return back to the tank. This was a big upgrade but now am ready for anything I’m going to throw at this truck in the future. #ad
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It seemed to help with my lean issue I’ve been battling, but still wasn’t where I needed to be. I got fed up and drilled out a spare set of carb jets a 108 and saw a jump in AFR toward the rich side. So I’m 90 on the primary and 108 on the secondary at this point. I see a lot of people jetting up 10 sizes when not running a power valve. I started with a 99 jet on the secondary. This has me wondering maybe there’s been an issue with the secondary power valve this whole time.

Being a boost reference valve I figured I could test this with air pressure. I hooked up a regulator and got it up to 10psi (I’m running 10/11) and had zero flow through it. I had adjusted it to come on earlier before but apparently it needed a lot more. I backed it out quite a bit but got it cracking open around 4/5 psi. Cool this will be perfect….except now the adjustment screw sticks out too far and hits the carb main body…

Not wanting to compromise the spring it came with, I went and found a similar size spring with similar spring rate and cut it a little shorter. With this I was able to get the same calibration and gave the screw in much farther. I’ve gone out and tested since and it seems to be running too rich now which is great! I need to datalog next outing and see exactly how it’s tracking. The truck gained a lot of power having fuel on the top end and is a new animal!

 

Also got a push/pull battery shutoff installed for the drag strip. I was hoping to avoid drilling a hole in the bumper or license plate, and was able to make a bracket and have it poke right under the bumper. I made a delrin block to contain the lever and also give something slippery for it to actuate in since the lever does have a little cam over motion to it so a straight hole wouldn’t have worked. It is a little loose and may make one a little tighter, but I’m legal now so that’s all that matters haha. #ad
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Due to the room, my options for a driveline hoop were limited. We ended up having some 6” pipe that was 1/4” wall at work to meet nhra specs, and just so happens it fit pretty nicely. I tested clearance with the truck in the air and also with weight on the tires and being right next to the transmission it doesn’t alter much. Used the seat mountings bolts as a shared position to anchor it down. Should be able to remove and install the driveline without having to remove this as well. #ad
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