Author Topic: 1970 350 quadrajet questions. 7040208  (Read 184 times)

Offline Chris_Oz

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1970 350 quadrajet questions. 7040208
« on: December 03, 2019, 05:15:36 PM »
Hello all,

I would like some advice on which way to go with repairing or replacing my Qjet.

BACK STORY:

STOCK 1970 Chev C20 pick-up, 350 sbc, manual and stock other than a HEI distributor, 34 deg total mech and 18 deg of vacuum, manifold vacuum.
Carb id 7040208, correct year, but mine is a Cali truck and manual, not Auto

Truck was rich and flooding.
Had 75 jets and 39/26 rods, which is federal spec for that carb and year.
Very rich at cruise. Float was fuel soaked and not shutting off, so time for a rebuild.

Rebuild done and carb running fine, 20inHG vacuum at idle, still rich on stock jetting so I fitted some 71 jets and 45/26 rods, as this is the spec from a chev 68-69 350 truck.
Runs much better everywhere, now has 21inhg at idle and 16-17inHG at 55mph on flat driving, I have the heaviest (strongest) power piston spring in, it starts to lift at 11-12in hg, I cant get an accurate reading at idel when its fully raised, but on road it feels like its all the way up at 9-10 inHG, if I go lighter on the spring, it has a slight hesitation on light roll in throttle.

Pretty happy with the tune and how it drives, it is a play toy, not hauling loads or working hard, gets used as a daily drive and weekend cruiser, so reasonable fuel economy is a factor.

Now the bad part.

The fuel inlet is stripped, it was weeping before the rebuild, it had a very slight wetness, but is now stripped out and I am in 2 minds what to do.
I am in AUSTRALIA, shipping to send out for a repair both ways, with tax and import charges will cost me more than a new carb, so its not a viable option.
The fuel inlet fitting I have only has 0.280

Offline Chris_Oz

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Re: 1970 350 quadrajet questions. 7040208
« Reply #1 on: December 03, 2019, 06:03:06 PM »
The carb has just over 0.500
« Last Edit: December 03, 2019, 06:09:31 PM by Chris_Oz »

Offline Chris_Oz

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Re: 1970 350 quadrajet questions. 7040208
« Reply #2 on: December 03, 2019, 06:08:08 PM »
I have no idea what is going on.

It wont allow me to post a whole message, shows in preview, but only posts the first bit.


Offline Chris_Oz

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Re: 1970 350 quadrajet questions. 7040208
« Reply #3 on: December 03, 2019, 06:10:34 PM »
, the carb has just over 0.500

Offline Chris_Oz

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Re: 1970 350 quadrajet questions. 7040208
« Reply #4 on: December 03, 2019, 06:11:18 PM »
, the carb has just over 0.500

Offline Chris_Oz

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Re: 1970 350 quadrajet questions. 7040208
« Reply #5 on: December 03, 2019, 10:22:39 PM »
The fuel inlet fitting I have only has 0.280

Offline Cliff Ruggles

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Re: 1970 350 quadrajet questions. 7040208
« Reply #6 on: December 04, 2019, 05:05:48 AM »
The specs from the 1969 carb do NOT apply to your 1970 carb.

Even with the smaller metering rods it is too lean on the primary side.

Your 1970 model uses large MAB's near 1/8" and the 1969 and older units use very small MAB's.  They are calibrated in a completely different way.

Not sure why you are using manifold vacuum to the advance, most of those used ported vacuum.  Those tiny cammed truck engines don't need a lot of timing at idle and it can make the exhaust stinky (simulates a rich condition) if you put too much timing in them.

If the carb has a distributor port on the main casting in the front on the drivers side use it for the distributor VA.

If you would have called the shop I could have explained all this and set you up with a good kit and tuning parts for what you are doing. 

If you were running "rich" with the stock set-up there is a fundamental issue someplace.

I stock the correct power piston spring as well.  Trying to get the PP up really quickly is a crutch fix for trying to overcome a lean condition as the jets are too small and primary metering rods too large for that carb number.

That carb also has an APT system in the baseplate.  I would try to use it.  We make an external APT screw if you can get the factory one out.  It usually takes a little work with a propane torch and penetrating oil, but once you get it out fine tuning becomes much easier without taking the top off the car IF you have the correct parts inside.

Anyhow, we've been having some issues with the website far as getting logged on and posting, sorry for the issues but if you want help with the carb call the shop and I'll get you set up with what you need......Cliff

Offline Kenth

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Re: 1970 350 quadrajet questions. 7040208
« Reply #7 on: December 04, 2019, 05:21:16 AM »
I

Offline Chris_Oz

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Re: 1970 350 quadrajet questions. 7040208
« Reply #8 on: December 04, 2019, 11:34:21 AM »
The specs from the 1969 carb do NOT apply to your 1970 carb.

Even with the smaller metering rods it is too lean on the primary side.

Your 1970 model uses large MAB's near 1/8" and the 1969 and older units use very small MAB's.  They are calibrated in a completely different way.

Not sure why you are using manifold vacuum to the advance, most of those used ported vacuum.  Those tiny cammed truck engines don't need a lot of timing at idle and it can make the exhaust stinky (simulates a rich condition) if you put too much timing in them.

If the carb has a distributor port on the main casting in the front on the drivers side use it for the distributor VA.

If you would have called the shop I could have explained all this and set you up with a good kit and tuning parts for what you are doing. 

If you were running "rich" with the stock set-up there is a fundamental issue someplace.

I stock the correct power piston spring as well.  Trying to get the PP up really quickly is a crutch fix for trying to overcome a lean condition as the jets are too small and primary metering rods too large for that carb number.

That carb also has an APT system in the baseplate.  I would try to use it.  We make an external APT screw if you can get the factory one out.  It usually takes a little work with a propane torch and penetrating oil, but once you get it out fine tuning becomes much easier without taking the top off the car IF you have the correct parts inside.

Anyhow, we've been having some issues with the website far as getting logged on and posting, sorry for the issues but if you want help with the carb call the shop and I'll get you set up with what you need......Cliff

Thanks for the reply,

I live on the east coast of Australia, I have only just found your page and site, I appreciate your time to reply.

I don't know where to go with this carb now, The fuel inlet is stripped and I think its not really worth fixing. Shipping to and from the US is out of control, we pay import tax and duty on every item we buy or import, even if it was ours and we sent away for repairs, we are taxed when it comes back in.

I have a 1976 carb off a Pontiac Lemans, 400ci auto. 17056264, i got it off the original car owner and its dirty but all there.
I understand these are higher CFM, but given the way a Qjet works, should it be ok?

I have a milling machine and lathe and would love to repair my 704 carb if I could buy a tap/insert and helicoil kit at a reasonable cost.

Again, thanks for the advice, if this carb ever goes back on, I will use ported vacuum.
I have a 625cfm street demon on it at the moment (had spare on the shelf)and to be honest, it is running pretty well, it was rich out of the box, like they all are, but 2 sizes smaller on the primary jets and its getting 15mpg and goes fine.

I just want my Qjet back, so it is factory again.

Offline Chris_Oz

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Re: 1970 350 quadrajet questions. 7040208
« Reply #9 on: December 04, 2019, 02:06:11 PM »
Hi again,

I also was able to get the Power Piston adjustment screw to move. I let it soak for a couple days in penetrating oil and it moved fine, I counted out the turns and reset it to the same when I re assembled it. It still had the factory plug/cover over it, so I would hope it was in its factory position.

It has a spring steel U shaped item it pushes on and moves the power piston up in its bore.
seems to work but limited with the movement as far as I can tell.

Offline hiy_po

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Re: 1970 350 quadrajet questions. 7040208
« Reply #10 on: December 05, 2019, 06:12:15 PM »
Yer our government has basically made it so we only trade with China. I have tried to make purchases from US and postage and tax turn a $US5.00 into $AU75 it is insane but working for them perfectly as intended. I was trying to buy some tiny grub screws but some of the US companies I approached wouldnt even deal with me because I am in Aus and its all too hard.
If you junk that carb with its stripped out thread I may want to buy your base plate as mine is stuck solid and I may have stuffed it trying to free it.

Offline Cliff Ruggles

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Re: 1970 350 quadrajet questions. 7040208
« Reply #11 on: December 06, 2019, 05:06:33 AM »
The only heli-coil tap that I know of that's any good is a genuine Heli-Coil and are discontinued far as I know.  I purchased the Recoil tap once when I miss-placed my Heli-Coil tap and it's a useless POS.  It tried to tear out the threads and chew up the material vs a good clean operation.

I ship overseas daily, and it is getting EXPENSIVE to ship over about 2 pounds to most places, plus customers get hit with import fees on their end as well.

Still doesn't seem to slow things down, I send out orders just about every day to Australia and other Countries across the pond.  Even folks over there are tired of getting sub-standard rebuild parts for these carburetors.

Good news if you can get a Demon to work with a chit, I have never had any luck with those at all here dating clear back to when they first came out and they got sued by Holley of patent infringements.  Sure I can get them work, and clean up the "pig" rich idle/off idle by going into the metering blocks and airbleeds, but they are NOT reliable in long term service and WAY too many places to leak fuel.....Cliff

Offline Chris_Oz

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Re: 1970 350 quadrajet questions. 7040208
« Reply #12 on: December 11, 2019, 06:12:05 PM »
Hi Cliff,

The Carb I have on now is the Street Demon 625cfm its a hybrid of an AFB Carter and dare I say QJet, not the Holley copy.

It has pop up pistons and needles etc, but not the tune-ability of the QJet.
Like the "Holley" styled Demons, they are BIG FAT PIG rich just about everywhere. Cruise AFR in the 11's is normal for them, but a needle change can get them back to somewhere usable but not great.

I have been able to find and buy a close but not identical core, it is in very good condition, I would like to know if it would have similar MAB's as my current carb.

Current carb is a 7040208    (1970 Chev 350 truck)
Core carb is a     7041283    (1971 HOLDEN Sedan fitted with 350 SBC)

It does not look like it has been messed with, it is dirty and base plate is worn, but I only want the body as a donor for my carb if it would be suitable.

If you think it would be I will order a rebuild kit and marry the 2 and see how I go.

Are you still taking on repairs?
If I send you my original carb body, can you do the thread repair?

I asked around and I could not find a core for my current carb, the closest I found was a 7040502, which would suit my truck as it was a CA built and sold truck, but I dont know if its MAB's would match up either.

Thanks again

         

Offline Cliff Ruggles

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Re: 1970 350 quadrajet questions. 7040208
« Reply #13 on: December 12, 2019, 03:41:11 AM »
Not sure what you'll find in the Holden from that year I haven't worked on one over here.

All of the airhorns on the Chevy carbs from 1970-74 will have the same large MAB's.  The truck units in 75-76 will as well, 77-78 are single MAB.  Automotive from 1975-80 will have the newer castings and nothing fits your 1970.

The exception in the middle of all that were a few CA emission units around 1977-78 but they really don't apply to what you are doing.

I can repair the inlet threads but shipping is expensive.  It would be less expensive to have me find an early main casting and ship it to you.  I probably have a few in the core pile, will have to take a look when I get a moment.

I would send it over with the correct gaskets, float, N/S assembly, pump and tuning parts for what you are doing.  Then it's basically plug & play........Cliff

Offline Chris_Oz

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Re: 1970 350 quadrajet questions. 7040208
« Reply #14 on: December 12, 2019, 12:10:16 PM »
Thanks.

I like the sound of that.

Thanks again for your time