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Author Topic:   Carb Upgrade questions

Posts: 1666
From: Santa Clarita, CA
Registered: Jan 2000

posted 08-19-2001 09:54 PM     Click Here to See the Profile for cpmaverick   Click Here to Email cpmaverick     Edit/Delete Message   Reply w/Quote
I have been running a 600 DP on my Maverick for some time. I installed it when I still had a stock 1987 HO cam and stock rockers. Since then I've added a lot. Here is my combination:

1987 5.0L HO
B303 Cam
1.7:1 Crane energizer roller rockers
Weiand Stealth Intake
Ported E7TE heads with GT40 valves & Springs
Stock bottom end: shaved head & block resulting in ~10.2:1 compression, stock TRW forged pistons

I decided that with all my recent upgrades I needed a bigger carb (especially with such a light car, 3.70:1 rear and stickshift).

I obtained a 650 DP and installed it to debug everything before I make my next track trip (plan on trying both carbs). Problem is: it runs really rich.

My 600 had 70 jets front and 76 rear, and the plugs looked great (these sizes were through considerable tuning). I installed the same jet sizes in the 650. Should I really have to go smaller for the 650? Or am I perhaps missing something.

The shooters are 28s front and rear on the 650 and 28 front 32 rear on the 600.

Anyway, this might sort itself out but I am looking for some input as I learn to tune these carbs.

-Charlie Ping
1970 Maverick Grabber
[email protected]
Daily Driver

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Posts: 8826
From: Sonoma,CA,USA
Registered: Mar 2000

posted 08-19-2001 10:05 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote

Could the power valve be blown in the 650DP? The jetting should be close between the two carbs.


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Posts: 651
From: louisville, ky, usa
Registered: Jul 2001

posted 08-19-2001 11:14 PM     Click Here to See the Profile for chips67   Click Here to Email chips67     Edit/Delete Message   Reply w/Quote
it could still be running rich if the idle mixture screws are right, float levels are right and power valve isnt blown. the 650 comes with a 6.5 pv if im not mistaken (thats what mine came with) and with any kind of cam it changes idle vaccuum. with the original power valve mine also runs very rich at idle and everything else is right. what i have yet to do, and its probably the same problem you have, is check the manifold vaccuum and install the correct pv in the primary side (the only side that has a pv in a 650dp). it very easy to do and pv only costs about $6. i havent changed mine yet for 2 reasons, one is it doesnt affect my e.t. because its a stick car and never goes below 4000 rpm ever in a pass and two, im extremely lazy when it comes to doing anything that doesnt make my car quicker. you'll notice my combo is very similar to yours....a 650dp is the best carb for this sort of combo imo. was able to run 8.30's last year (1/8 mile) on bone stock '90 5.0 motor with this carb untuned and an e-303 cam.

67 coupe, 650dp and rpm intake on 5.0 with afr 165 heads, 4 speed, 4.11' so far is [email protected] in 1/8 mile with 1.89 60ft. time.

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Posts: 2419
From: Spencer, WV
Registered: Jan 2001

posted 08-19-2001 11:33 PM     Click Here to See the Profile for n2oMike   Click Here to Email n2oMike     Edit/Delete Message   Reply w/Quote
For what it's worth, the 650DP came with 67/73 jets stock. You might also want to replace the power valve in case it's blown... which will cause the car to run extremely rich at part throttle.

Good Luck!
Mike Burch
66 mustang real street
302 4-speed 289 heads
10.63 @ 129.3

[This message has been edited by n2oMike (edited 08-19-2001).]

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Posts: 1666
From: Santa Clarita, CA
Registered: Jan 2000

posted 08-20-2001 06:51 PM     Click Here to See the Profile for cpmaverick   Click Here to Email cpmaverick     Edit/Delete Message   Reply w/Quote
Thanks for the info guys. I know what a blown power valve is; this is not it. It does have a 6.5 pv, just like my 600.

Car runs really strong and I look forward to going to the track. I might lean the jets out a little, yes it had 67s in the front when I got it, but I figured since the 70s worked so well in my 600 I'd put them in the 650.

Which comes to my main question-

When upgrading a carb is it normal to have smaller jets to achieve the same AF ratio? Seems opposite but that is what I am seeing here.

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Posts: 466
From: Redwood City, Ca. USA
Registered: Jan 2001

posted 08-20-2001 08:10 PM     Click Here to See the Profile for Doc   Click Here to Email Doc     Edit/Delete Message   Reply w/Quote
If the power valve is good and the float levels are right you might have a crooked mating surface at the metering block, either the carb body or the block itself can be poor (uneven) from the factory.

I knew old people was weird! I just never realized I was gonna be one of them :)!

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