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Old 12-02-2010, 08:57 PM
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pro form carb conversion for blower

i have a holley 750 double pumper with pro form main body and metering plates. just purchased a weiand 177 blower and need to convert the carb. anyone have any pics or info on how to do this. called pro form but they sent me to quick fuel. thanks

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Old 12-02-2010, 09:07 PM
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A single search here for simply 'blower carb' just brought 200 entries, different search criteria will find more.

There's a lot of information in our database, surely there's something there for you, give it a try.
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Old 12-02-2010, 09:11 PM
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just getting familiar with site. tried searching before and kept getting sent to diffrent sites. just thought now that im on the site somebody might have a little more info. but thanks for the tip.
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Old 12-03-2010, 07:08 AM
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I'm talking about the search feature here on the HRB, not your browser.
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Old 12-03-2010, 10:23 AM
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A couple thoughts...

Quote:
Originally Posted by homerj55
i have a holley 750 double pumper with pro form main body and metering plates. just purchased a weiand 177 blower and need to convert the carb. anyone have any pics or info on how to do this. called pro form but they sent me to quick fuel. thanks
That carb is going to limit the boost you can use to around 5 psi. Was the carb calibrated for a good fuel delivery curve before the blower came along?
  • The fuel pump needs to be capable of supplying the engine w/enough volume at 5 psi and WOT to avoid lean out. An electric pump would be my preference. Best to use at least 3/8" fuel lines from the tank. More on pumps and regulators HERE.
  • Boost referencing the PV on a Proform throttle plate is covered HERE. Modifying a Holley throttle plate is shown HERE. Another option is to block the PV w/a plug made for the purpose and jet the 2'ndaries larger by ~8 sizes (varies by case).
  • It may need some more accelerator pump volume and/or duration.
  • Might want to use 0.110" needles and seats.
  • The Summit 1103 or 1105 cam works well w/this size blower, or so I've read.
  • Don't forget to modify the ignition timing curve to work w/the blower. The Holley Supercharger Installation Instructions and Technical Manual is HERE. It has the boost chart, pulley sizes, timing recommendations, tensioner and other part numbers, etc., for your set-up.
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Old 12-03-2010, 10:25 AM
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You want to convert to boost referenced power valve by drilling a new external vacuum passage into the power valve vac chamber and pressing in a vac nipple in the pass side of the carb body. Plug the other vac hole to the vac chamber. Connect that new vac fitting to the intake manifold under the blower.

Jet the carb up 4 to 6 jet sizes to start your tuning. 76 pri and 88sec is a good place to start. You want to jet down from `generously rich` to find the tuneup. Idle air bleeds and high speed air bleeds may need fine tuning too.

A afr meter-02sensor will help you with that.
Blower motors like lots and lots of initial base timing at idle (20++ at idle) yet modest spark advance at WOT under boost. 28 to 32deg at max advance under boost) Recurve the distributor accordingly. Distributor Vacuum advance also goes to the intake manifold under the blower and will need to be tweeked too.

Use cooler that stock non projected tip spark plugs. Start with modest max timing (yet generous initial base timing) and plenty rich jetting.
The vehicle`s fuel system must be capable of feeding the blower motor. (flow volume not pressure)
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Old 12-03-2010, 10:27 AM
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What camshaft are you using in this motorÉ
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