carb base plate for impco 425 mixer (propane)

i'v did alot of searching and reading on the net about propane conversions. i'v already bought most of the parts i need to do the conversion but still have a few
questions. i know the impco 425 will bolt to a holly base plate but witch one??? should i use a double pumper base plate or vac. secondaries base plate? ?? 650 to 800 cfm or the 800 to 1000 cfm base plate ?? does anybody know what holes in the base plate to block off if any??? any help would be great thanks david
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I thought you had to use a diffuser to run propane, not a carb.
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Does your 425 have the 2bbl base plate on it or does it have the 1bbl base plate? Either way you could put it on a spacer that is universal for the size. What is the concern you have? If it have any holes you don't need them unless you are running some sort of smog or PCV setup that you want to keep and then it's a matter of checking other installations like yours to see what is required. What engine is it for and what carb were you running before?
According to the Impco website it's a standard size.
http://www.impco.ws/download/Web-Catalog.pdf
It's a large file so be patient if you download it.
I have converted cars before and have had no trouble. If you are going to take on such a job then you must be some what used to these sort of problems. If you have no idea what you are doing then ask many more questions. I wouldn't want to see you blow yourself up.
Wiz.

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Wizard of Oz wrote:

i'm sorry guys it's all going on a 78 ford bronco with a 351m engine. it had a 670 holly truck avenger 4bbl.i'v took off the base plate and i see two lines with holes in it for vac. i guess.just wanted to know if they should be filled in or not. i'm a diesel mechanic by trade. just new to propane. thanks david
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Sorry to take so long to respond to the last post.
If it has holes for your smog controls, even though running on LPG will take care of most of the pollutants in your exhaust, you will probably need to keep them hooked up. It sounds like you have some experience working on engines so check what the holes and subsequent lines run to and are for. It could be that you could disconnect them and have no issues but if they are there they are there for a reason.
Having not worked on that particular engine and vehicle combination I can not tell from experience. The workshop manual should have a detailed diagram/schematic of the lines and from there you could tell their importance. If, on the other hand, you have disconnected the other ends of the lines because the smog gear has been removed it should be self explanatory.
You might get more information from a Bronco newsgroup. Also try looking at any Australian website dealing with LPG. We have been using a propane blend of gas for many years and one can fill up at most service stations across the country. 351's are a popular engine in Australia so conversions are plentiful and smog controls are similar.
Wiz.

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