pcard

While I was up in Newport last week I swapped out my carb.

My setup: 455 engine rebuilt, .030 over, cam MC2102: 280/290, 4.72/4.96, 107/117.
Pistons: KB277. I do not know the compression ratio. The displacement is now 461ci, stroke is 4.25 .
Stock heads, stock manifold, stock exhaust (dual), stock ignition system.

If you guys recall I had some issues with my carb.

The 7040251 I have I found at a swap meet for $20 and had it rebuilt. I put the 7040251 on during the restoration because it was the specified carb for the 1970 SX. I did change the secondary rods and hangars, to G hanger and CK rods, and this carb runs great at low and part throttle and WOT, good transition, good response and 14 MPG at 70 MP with 3.08 gears. However it has some issues at idle.
A. I noticed that the vacuum as measured on the carb port, and there is only ported vacuum on this carb, at idle is around 10+ inches. This should be zero.
B. After a timing test I needed to adjust the slow idle and in the process noted that my idle screws were out by 4 1/2 turns, and turning them in or out all the way had no effect on the idle. Closing in the slow idle screw stalled the engine, even with the idle screws out 6 turns.

These two items led me to conclude that the idle circuit is not functioning and the primary throttle is open so far as to expose the idle port to vacuum.

I spoke with Cliff Ruggles about this, and he concurred, with the idea that perhaps the stock idle setup not enough for my new build. He suggested that a slight modification to the idle circuit, involving opening up the idle restrictions and air bleeds, would probably fix it.

I could not send him my 7040251 because that would leave the car inoperable, a violation of the insurance agreement I have with my storage folks. But I still had the carb which was on the car when I bought it, a 7042953, which was obviously a replacement. It was originally specified for a ‘72 442 with manual trans.

The 7042953 was in bad shape so I sent it to Cliff to rebuild. I gave Cliff my engine specs and told him I wanted a “happy ending”, that is, a complete disassemble, plating, new bits, etc..
He sent it back to me in three weeks and it looks like a brand new carb, see some photos.
He replaced just about everything you can imagine: pump, jets, seats, rods, hanger, springs, bushings, float, vacuum break, connectors and fasteners, all the little plastic parts. Set up the APT for external adjustment.
He also opened up the idle fuel and air restrictions.
I put that puppy on my engine and she started up after just a few cranks. The idle was perfect right out of the box, and the vacuum on the carb port is zero at idle as it should be, and now the engine is pulling a STEADY 20 inches vacuum at idle on the manifold, which is up from a shaky 17 inches with the old carb.
I have not been able to road test it because of the weather, and can’t wait to see how it performs.

pcard

I have picture here also of my old carb showing the primary throttle plate in the ”idle” position. You can see the timed port exposed on the right side. There was is some evidence of serious leaking as well.
I have sent it off to Cliff for fixing. That will give me two assume carbs.

BILL DEMMER

that '72 carb. was calibrated way too lean, as a '72 carb. would be, for a warmed-up '70 application.


bill

72 w29 all green

pcard,

I'm sure you're relieved . Since the problems you described were with your '70 q-jet 7040251, i'm thinking Ruggles will be modifying the idle circuit on that one too along with bushing the primary throttle shaft ... unless that was already done.

Joe

pcard

Bill - the 72 is the "old" carb that Cliff Ruggles just modified and I put on last week, and is working great at idle. He changed the primaries to 42 and the jets to 70, the secondary rods to "CK" and the hanger to "K". The APT is good at first blush, I did the "tip" test.
It was the 70 carb which was giving me problems.


Joe - you are spot on, I am very relieved. I have faith that the 7042953 carb will work well on the road.
Cliff will be doing what he feels is needed to the 7040251, if he thinks it is salvageable.

72 w29 all green

Hmmm interesting choice for the primary rods (42). By the way, the CK secondary rods appear to have the exact specs of the AU rods that Olds used on most or all 455's in 1970.

allyolds68

I've got a 72 7042250 that I rebuilt with a kit from Cliff and he had me set it up almost identical to what you have. 42 Primaries (at least I'm pretty sure they are 42's, the tip was .026), 70 primary jets (both were already in the 7042250 carb), CV secondary rods (almost identical to the AU's) with a G hanger. I've got it on a 70 455. I had to adjust the secondary doors because it was a little boggy off the line but now it runs great.


The 42 Primaries & 70 primary jets were both were already in the 7042250 carb. The secondaries were originally CG's and were much too big, not allowing enough fuel, causing pinging at WOT.

pcard

I think the 7040251 had 7034849 primary rods, which were 49B double tapered. The triple taper was on the W32 carb.
The verdict is still out on what we are going to do. Cliff will examine it and pass judgment. It was obviously leaking fuel and vacuum, so there may be other forces at work.
I have no significant experience with the Q-jet and am lucky to have expert help. It is a great to learn.

pcard

Carburetor Results
I was finally able to take the car out for an extended drive to test the new carburetor. When I put the carb on the engine started right up and I did not have to adjust the idle at all. The choke needed some adjustment to the rich side, but it works well and pulls off as the car warms up. The fast idle steps down nicely, and carb idles at about 950 in Park and 600 in Drive. The vacuum on the timed port is zero at idle as it should be.
On the test drive the transition from idle to part throttle was very smooth, and acceleration is strong and constant all the way up to 3200 rpm, with no pinging at all. Acceleration up a hill at 50 mph (2200 rpm) is also strong with no hesitation or pinging. Full throttle has some giddy up.
I do not know what kind of millage I am going to get but at this point the carb is a great success.
The only negative I have is that the air horn gasket is getting very wet. I have tightened up the horn screws and front bolts but they were not that loose. I will see how this progresses. I have every confidence that Cliff adjusted the float level properly. I had the same problem with the old carb and wonder if this is an issue with fuel pressure.