What size jets do I need for q-jet?
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Racer
Joined: Dec 2005
Posts: 496
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From: edinburg VA.
What size jets do I need for q-jet?
I need to rejet my q-jet on my 70 ls5.I have hooker side pipes and Lars said I need to go up at least to sizes to keep from backfiring throuh the pipes doe to lean mixture.My carb. # is 7040509 and 3226.It should have the original size in it.Is this the correct numbers for this ls5 with 4-speed?What size jets shold I buy?Also what is involved in installing them? Is this something I can do myself ? I just put on new divorce choke and it seems to work fine but I dont like how fast it idles when it is cold.Anyway to adjust this?Thanks for your help.RW
Melting Slicks
Joined: Dec 2004
Posts: 2,101
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From: Cruising somewhere in St. Louis, Missouri
That carb listing says it's from a CHEV 70 TRUCK 396 CALIF
the book says you should have carb # 7040505 for your 70 LS5 390HP MT with Evaporative Emission Control.
jim
the book says you should have carb # 7040505 for your 70 LS5 390HP MT with Evaporative Emission Control.
jim
Le Mans Master
Joined: Mar 1999
Posts: 6,744
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From: delmont pa
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Originally Posted by Ronnie wilkins
I need to rejet my q-jet on my 70 ls5.I have hooker side pipes and Lars said I need to go up at least to sizes to keep from backfiring throuh the pipes doe to lean mixture.My carb. # is 7040509 and 3226.It should have the original size in it.Is this the correct numbers for this ls5 with 4-speed?What size jets shold I buy?Also what is involved in installing them? Is this something I can do myself ? I just put on new divorce choke and it seems to work fine but I dont like how fast it idles when it is cold.Anyway to adjust this?Thanks for your help.RW
Racer
Joined: Apr 2004
Posts: 401
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From: IL
Email Lars for his latest paper (@ Corvettefaqs.com also) that lists what jets/rods are still available. If you know what size you want to start with then you could just purchase those (if still available). I ended up ordering the Edlebrock Q-Jet kit from Jeg's or Summit (I forgot which) that has 5 jets, 5 rods, a few hangers, and other parts in it. After pricing the still available jets (a $6 ea) and then the rods at a similar price it was cheaper to buy the kit since I'll be trying different size combinations down the road. Plus it won't be long when it'll be very difficult to even find this stuff, better stock up now I figure.
As far as installation, just a matter of removing the top of the carb, with care of course. The jets are just screwed into the bottom of the fuel bowl area. Lar's paper has some very good tips and instructions, read those fist. My carb was rebuilt by a major rebuiilder (auto warehouse) and during they're hot cleaning process caused the jets to "lock in" and I got one out and had to use reversible drill bits on the second one. Secondary Rods are very easy.
Only problem is the top fuel bowl gaskets are getting very hard to find seperately, now only easily available in the carb kits, about $20-$25 for the complete kit (minus float, about $7 more).
In those papers I believe it discusses choke adjustment also.
Have fun, hope this helps,
Later.
As far as installation, just a matter of removing the top of the carb, with care of course. The jets are just screwed into the bottom of the fuel bowl area. Lar's paper has some very good tips and instructions, read those fist. My carb was rebuilt by a major rebuiilder (auto warehouse) and during they're hot cleaning process caused the jets to "lock in" and I got one out and had to use reversible drill bits on the second one. Secondary Rods are very easy.
Only problem is the top fuel bowl gaskets are getting very hard to find seperately, now only easily available in the carb kits, about $20-$25 for the complete kit (minus float, about $7 more).
In those papers I believe it discusses choke adjustment also.
Have fun, hope this helps,
Later.
