Edelbrock Electric Choke Issue

[Roger P.]

Re: Edelbrock Electric Choke Issue

Tim and Stu,
I purchased a new Edelbrock fuel filter and "carb-to-fuel pump" fuel line (carb to filter is steel, and filter to pump is braided stainless). Had the car on the lift this morning to change out the parts, but the threads on the 90* elbow at the pump were too big. I bought a smaller (1/4") threaded elbow this afternoon and will hopefully get the car back on the lift on Monday to complete the job. I also purchased a Holley choke heat sensor and will install it and make the choke adjustment next week as well. I was thinking about how to get intake manifold heat on my engine when I saw a threaded plug on the intake manifold just in front of the distributor. What is this port usually used for, and is it feasible and safe to run a choke heat tube from the port on the exhaust manifold to this port on the intake manifold to provide heat under the carb? Just thinking "out of the box" as us architects often do.

Thank you,
Roger (50141)

[Timothy B.]

Re: Edelbrock Electric Choke Issue

Hi Roger,

That plug is a vacuum port for power brakes, you can not use this to heat the plenum.

[Roger P.]

Re: Edelbrock Electric Choke Issue

Hi Roger,

That plug is a vacuum port for power brakes, you can not use this to heat the plenum.

Tim,
I believe you are referring to the plugged port on the back of the carb, however, I am talking about the plugged port on the back side of the intake manifold. As I have researched this a little further, it appears that this is a port for an EGR valve. Perhaps an EGR valve is exactly what I need to get some exhaust manifold heat under the carb?

Roger (50141)

[Stuart F.]

Re: Edelbrock Electric Choke Issue

Roger;

Can you post a photo of your manifold so we know what you're talking about. If it is an EGR tap, of course you know, that would just bleed air into the intake manifold runners and greatly upset your mixture, i.e. big vacuum leak.

Let's face it; you have a mongrel there. I don't know the answer, but surely others have dealt with later crate engines with carburetion in an early Vette.

Stu Fox

[Roger P.]

Re: Edelbrock Electric Choke Issue

Tim,
As I have researched further, of course you are correct about the plug on the top of the intake manifold. As you said, it is a vacuum port for power brakes just like the port on the back of the carb. My intake manifold is similar to the LT-1 manifold and does not take an EGR valve. I drove the car this weekend and it performed very well with almost no hesitation issues. When the engine is cold, I simply need to start out in 1st gear with a little more throttle. If I can adjust the choke to stay on longer via the heat sensor, the fast idle cam will do that for me automatically. Either way, the ignition and carb tuning have definitely helped minimize the problem. Can the heat sensor be secured to the front of one head (there are threaded taps there), or should it be secured to the top of the intake manifold?

Stu,
Although my crate engine isn't the original 327/300 that I have in storage, it was designed as a performance replacement by GM engineers for this type of application. The intake manifolds, heads, cam, pistons, valves, etc. are all stock to the engine as the General engineered it. The only variable is the carburetor; although it is very similar to the original. From what I have read and learned on this and other TDB's, the performance cam and perhaps lack of manifold heat crossover is what I believe makes the characteristics of this engine different from the stock 327/300. I have this puppy close to dialed in, so I think it's time to put down the tools and do some more cruising before the heat of the spring & summer roll in!

Thanks again guys,
Roger (50141)

[Stuart F.]

Re: Edelbrock Electric Choke Issue

Roger;

Sorry I have not sent a photo of my thermo sensor installation as yet. We're currently lacking a working digital camera.

It is no big deal; however, mine is bolted to an unused tapped boss on the top rear center of my manifold. The original instructions called for bolting it to one of the rear two bolts of the manifold to head, which ever one is convenient and will not interfere with anything. I did not like that proposition as, of course, I have complete stock ignition shielding. I set about taking temperature measurements at both the water manifold blockoff positions vs. the unused tapped boss on the manifold using my IFR gun during engine warm up. They were very close to the same temps at all locations. So, I used the tapped boss as it locates the sensor out of the way and makes for a neat stock appearing arrangement. I enclosed the wiring in a sheath which clamps to one of the carb top plate screws. You have to look close to even tell it has an electric choke, except for the lack of the choke heat tube and hose - very clean.

They also advise that you sand the copper mounting ear of the sensor and the surface to which you are mounting it so as to make a good thermal contact. That too was easier to do at the mounting boss than at one of the manifold bolts.

You should have come to the winter meet so I could show/explain the details to you.

Stu Fox

[Roger P.]

Re: Edelbrock Electric Choke Issue

Tim, Clem, and Stu,
I hope you guys had a nice weekend. My car is running very well, but I am still having some hesitation upon acceleration until the engine warms up. Once at operating temperature, I won't say that it is perfect, but I can live with it. Considering everything that I did to tune the engine based on my research and your suggestions, it is puzzling why it can't be closer to perfect. Be that as it may, I realize it is a 46 year old carbureted car and can't be compared to today's computerized, fuel injected engines. Before I sign off on this long thread, I have one more question for you guys (and anyone else who might have the answer). I read on "eHow" that hesitation using an Edelbrock carburetor can be caused by malfunctioning secondaries. It claims that the top throttle plates should open when the throttle is snapped open and released. No matter how hard I snap the throttle, the top plates don't move at all. It goes on to say that "the bottom set open mechanically, while the top set open through a vacuum. If the top plates fail to open when the throttle is snapped open and closed, there is a vacuum leak or a bad diaphragm in the carburetor. This situation would cause a lack of power under acceleration and a dead spot when the throttle is suddenly opened." Is this information correct? If so, that must be my problem since the top plates don't move unless I push them with a screwdriver. Can this be fixed with the carburetor on the car, or does this require a complete rebuild - or a new carburetor?

Learning something new all the time,
Roger (50141)

[Timothy B.]

Re: Edelbrock Electric Choke Issue

Roger,

The lower throttle blades open mechanically in the linkage. The air door above which you are referring to opens progressively when air flow through the venturies overcomes the offset weight. The engine air demands are what controls when the door opens.

IMO, the calibration of the 750 provides enough flow in the primaries so the door does not operate at low rpm's when the throttle is opened in the secondaries. At idle, snapping the throttle is not a indicator of door operation. You probably do not have any problem there..

At this point, I don't think it's a good idea to spend any more $$ on this problem. I was pretty sure the stumble could be covered by the accelerator pump shot but the bigger problem is probably no heat in the plenum because the stumble gets better when the engine heats up.

If you know anybody that has a good 600-650 cfm carburetor I would be curious to see if that size carburetor fixes your problem.

[Stuart F.]

Re: Edelbrock Electric Choke Issue

Roger and Tim;

Let's not forget what animal you are dealing with here;
an AVS model Edelbrock carb, Not an AFB. Check your instructions closely for the proper operation of the secondary air butterflys. It is different.

I'm not sure why you are concerned about the secondaries as a cause for hesitation and/or stumble with the engine cold. Secondaries come into play when the engine is warm (choke off) and you go for a throttle up secondary dump. If you have a bog at that juncture, then you'd have a legitimate concern about the secondary air butterflys.

Stu Fox

[Roger P.]

Re: Edelbrock Electric Choke Issue

Good morning guys,
I just wanted to give you an update on my stumble issue as I find it very frustrating following a thread that ends without a solution to the problem. The stumble has been corrected by doing the following: advancing the timing, installing the largest accelerator pump nozzle (.043), installing the richest metering rods & strongest springs available, and then tuning the carb using a vacuum gauge. More than anything, it was the timing. I read a lot of information online and was lucky to find a "hot rod" mechanic who works on carbureted, high performance engines every day. He offered to communicate via e-mail to assist me. Due to the large cam (235*), it requires more timing; initial + advance = 36 to 38 degrees. My timing was about 27 degrees before I made the change. I also spoke to a tech at Edelbrock and a drag strip racer at my local speed shop and they both agreed that the timing was too low. After making the timing and carb adjustments, I now let the engine warm up in the driveway for a few minutes and she takes off without a stumble. She also has more "kick" and runs cooler, too. I understand that my total timing with the vacuum advance should be about 50 to 52 degrees, but I'm only getting 10 degrees from the vacuum advance for a total of 46 degrees. Will my gas mileage improve if I adjust or replace the vacuum can to gain the additional 5 degrees? My vacuum reading at idle is 15 in. Hg which sounds high since the strongest spring for the metering rods is specified for 8 in. Hg. Can manifold vacuum be reduced and is it necessary?

Again, many thanks to all that have helped me with this problem -- especially Tim, Stu, Clem, and Michael!!

Roger (50141)

[Clem Z.]

Re: Edelbrock Electric Choke Issue

this is why i always recommend "power timing" the engine. mark off the damper for 36 degrees and set the timing so the 36 degree mark you put on lines up with the "0" mark on the timing tab at max advance with the engine reved up till the timing mark on the damper stops moving with the vacuum advance blocked . with a stock distributor this may take 5000 RPMs. if you don't like revving the engine to 5000 RPMs remove one spring from the advance weights till you set the timing and then put the spring back on. if at idle the timing is way off your distributor needs to be looked at as something is wrong.

[Timothy B.]

Re: Edelbrock Electric Choke Issue

Roger,

I am glad you found the hesitation problem with the car. This tuning education is something all of us have been through and you never get done learning especially dealing with modified engines.

Go back and read post #33 and research the archives for discussion about vacuum advance and the selection of the proper control for your engine.