Blow Through Problem

[boosted91lx]

Alright guys Im having an issue with a blow through set-up that I cannot figure out. From a dead stop the car stumbles and sputters when you launch off the footbrake or the transbrake. It clears up about 60-70 feet out then the power is just explosive. It pulls like a train under boost but I can't get that stumble out. Its idles great and starts easy. The set-up is a 363 with Victor Jr. heads and intake and a custom solid roller cam and a CSU 750 carb. The turbo is 70mm I.T.S. putting down 20psi. The carb is currently jetted 70/94 with an AF ratio of 10.9. Timing is set at 35 degrees with the BTM taking out a total of 15 degrees under boost.

I have replaced the entire fuel system from A1000 pump and regulator to an A2000 pump and regulator, had the carb reworked, rejetted up and down, adjusted base timing up and down, and different plugs with no better bottom end results. The car just isnt responding. Im hoping its something simple, any suggestions other than fuel injection?:)

[capriracer86]

Are u running boost ref. Power valves?
Im in the prosess of doing a blow thru d-1 blower on my 64 falcon and we are going to be using a boost ref. Power valve in the primary circuit for better off idle throttle.. my dad is a engineer and has developed a better boost ref. Power valve. But have not done any real testing. Just a tought!

[boosted91lx]

Are u running boost ref. Power valves?
Im in the prosess of doing a blow thru d-1 blower on my 64 falcon and we are going to be using a boost ref. Power valve in the primary circuit for better off idle throttle.. my dad is a engineer and has developed a better boost ref. Power valve. But have not done any real testing. Just a tought!

No boost reference power valve. The carb worked perfect on my Windsor so Im stumped.

[darren]

My blow through would act exactly like that but I did not have a transbrake and it would dump rich until it built boost and then pull like hell. Since you have a brake and it used to work before that's a tough one. Do you have a wide band on the car or have you tried to read the plugs to see if you're going rich or lean during the stumble? My carb was an early CSU back before the boost referenced power valves were popular and that may have helped out. Are you leaving out on boost when you let go of the brake? If so is it the same amount of boost you were leaving on with your windsor?

[boosted91lx]

My blow through would act exactly like that but I did not have a transbrake and it would dump rich until it built boost and then pull like hell. Since you have a brake and it used to work before that's a tough one. Do you have a wide band on the car or have you tried to read the plugs to see if you're going rich or lean during the stumble? My carb was an early CSU back before the boost referenced power valves were popular and that may have helped out. Are you leaving out on boost when you let go of the brake? If so is it the same amount of boost you were leaving on with your windsor?

Im making about 6-7psi of boost with the transbrake. Wideband is at about 13.7-14.1 at idle drops to 10.1-10.3 at launch and its at about 10.7-10.9 in third on the topend. I have tried less fuel(lower jets) but that just hurt the topend numbers. I'm at a point right now where I have no clue what to try next. Maybe its time for fuel injection?

[NC STANG GUY]

Tried different size squirters? Sounds like it's just too much of a hit from the get go but as the rpms rise its able to take it/clear out. How about the little plastic accelerator pump cams? Know they make ones with different rates to them.

[nitrostangracin]

I would look into the Power valves also. What does CSU say about this?

[TrueBlue62]

do you have jet extensions ? something simple ,good luck

[boosted91lx]

Tried different size squirters? Sounds like it's just too much of a hit from the get go but as the rpms rise its able to take it/clear out. How about the little plastic accelerator pump cams? Know they make ones with different rates to them.

I ordered new cams already, Im hoping to have them in by wednesday to try. Gonna try different squirters tonight.

I would look into the Power valves also. What does CSU say about this?

Kevin at CSU wants the carb back to go through it again but that will be my last option
do you have jet extensions ? something simple ,good luck

Got the jet extensions in already.

[darren]

If you don't make any progress I'd send the carb back to CSU and let them take a look at it. They have always done right by myself and a few of my friends that have used their carbs. Just remember, if you switch to efi and start having problems you'll be paying out the nose for a tuner to try to track down issues like this. That was the whole attraction to blow through stuff for me, the ability to fix it yourself. I have not been on the site in years but turbomustangs.com used to have a great blow through tech forum with lots of good info. Have you looked over there yet? It may be called the "turboforums.com" now.

[boosted91lx]

I played with the jetting a little more last night then dropped a size on both squirters then found a sweet spot to launch on the transbrake. I'm at 70/88 on the jets and 30/32 on the squirters, leaving at 3800 rpm making 5psi of boost. AF ratio is at about 10.9-11.1 at full 20psi so I'm going to hold it there for now. There is a slight hesitation when I release the transbrake but its 10X better than it was. Thanks Guys! :thumbsup1:

[darren]

Glad to hear you're getting it whipped.

[boostedcoupe]

Sounds like a older built csu. They have changed a bit in the last couple years. I had a similar problem on my csu when we first got the car together. I sent it back to kevin and had the boost referenced power valve installed and a few other small changes. When I got it back I had to add some jet and eventually drill out the holes behind the power valve once I turned the boost up. Been running strong ever since.