Edelbrock Electric Choke Issue

[Clem Z.]

Re: Edelbrock Electric Choke Issue

Clem,
For weekend cruising, I have a 350/345 HP GM Performance crate engine in my car (the original motor is stored on an engine stand in a warehouse). I purchased the car with this configuration. Based on my research, these are the specs. for my engine: aluminum cylinder heads similar to those used on the L98 Corvette engine, a Z28 high-rise dual-plane aluminum intake manifold, hypereutectic 9.8:1 pistons, forged crank and rods, and a single-pattern 235-degree hydraulic camshaft with 0.480-inch lift. Other information found says the motor has a hydraulic roller cam 235*/235* @ 0.050" tappet lift, 0.480"/0.480" theoretical valve lift, ground on 114* lobe separation angle, and pressed-pin flat-top hypereutectic pistons. I have limited mechanical knowledge, so I'm sure you will understand much more of what this means than I do. Do I still need the heat riser valve and, if so, where would I find it on the exhaust manifold to check it? There is a small nipple/port on the passenger side manifold that isn't connected to anything. I was also wondering if my fuel filter is located too close to the head (touching at one spot). I attached a few photos so you can see my engine set-up.

Roger (50141)

from the looks of the pictures you must not have any exhaust heat to the intake cross over because the paint is not burned off of the manifold where the heat riser crossover is located. i wonder if the heads do not have a heat riser crossover opening in them. looking in a GM performance part catalog it looks like most all corvette aluminum heads have no heat riser crossover passage because they were designed to work with electronic fuel injection and if this is the case you may be stuck with this problem till the engine reaches full operating temp.

[Stuart F.]

Re: Edelbrock Electric Choke Issue

Roger;

Regarding your PCV hose; a lot depends on your unique installation. On my 63, the hose fits onto a tube that comes from a grommet at the back of the block and causes it to make a fairly sharp bend to attach onto the PCV Valve which faces 90* from the carb base at the rear. The stock installation does not use a clamp, altough it looks like it should. I use a clamp anyway just to be certain I have a good tight seal.

I know what you mean by typical warm weather here in Florida, and I too had to deal with that with my choke. The electric unit I have on my AFB uses a temperature sensor which is meant to be mounted to one of the manifold bolts at or near one of the rear water ports. I tested the temps there and at a point on the center rear of my aluminum manifold where there is an unused tapped hole. They were very close to the same so I mounted the sensor at the tapped hole. This unit then reads the engine temperature during warm up and controls the electric choke. I don't know why Edelbrock doesn't use this design which is touted to be "solid state", as it really makes sense to correlate the action of the choke to the engine temperature rather than ambient conditions.

I see, by my other computer, you've posted some photos of your engine for Clem so I'll check them out too.

Stu Fox

[Michael W.]

Re: Edelbrock Electric Choke Issue

If nothing else, please get rid of the rubber fuel line and clamps leading to the carb and replace it with a solid steel line. That's a fire waiting to happen!

http://www.youtube.com/watch?v=47skBew4rwc&feature=player_embedded

[Stuart F.]

Re: Edelbrock Electric Choke Issue

Roger;

All things considered, it looks like you have a nice installation there. I concur with Clem's observation about the "no heat riser" situation, but have a question about your exhaust system with the cast iron manifolds; Is there a spacer used at the outlet from the R.H. manifold (often times guys install a F.I. spacer in place of the heat riser valve - as I'm about to do).

Your fuel line does seem to have quite a few contortions to get to the inlet at the rear of the carb (an AVS model, BTW). It looks well done, but may be a source of excessive heat of the fuel which could cause percolation, specially during our summer weather. The filter is, as you say, too close to the head and the transfer tube lays in the valley - altough it looks like the installer did make an effort to insulate it with standoffs.

One other question; is that an aftermarket adjustable VAC I see on the HEI distributor? I have one of those in my stock and recall it too has the "hex" shape on the can like the early 50's Delco units. The adjustment is done by inserting a hex end wrench into the tube end of the VAC to vary it's Hg values.

About your original concern (stumble/hesitation), I believe you can now work most of it out through jetting changes per the Edelbrock manual, but be careful what you do now during our cool season as it may adversely affect it's operation during the hotter months, which accounts for about 9 out of 12 months during the year, right?

Stu Fox

[Stuart F.]

Re: Edelbrock Electric Choke Issue

Michael;

Have you ever looked at other factory C-2 four barrel carburetor installations, say from 64 through 65 or 66? Many use a fuel hose from the filter to the carb. That's not to say it's the best way to go, but it's been done safely by many OEM, as well as Hot Rodders back in the day. I would say he should at least check the condition of the hose(s) and replace them with good quality material that is safe with today's corn gas.

I use a fuel hose on my L-76 63 too as I needed to raise my carb up the thickness of a penolic spacer and two gaskets in order to lower the heat at the carb. The OEM chrome steel piece wouldn't make that stretch.

Stu Fox

[Roger P.]

Re: Edelbrock Electric Choke Issue

Clem, Stu, and Michael,
As always, I can count on you guys to give me useful information from your respective experiences. Michael, a fire is always a concern of mine -- certainly don't want anything to do with what I saw in that video! The Corvette specialist mechanic actually changed the fuel inlet line to what I have now because he didn't like what was there before as he didn't think it was safe. Go figure. I guess the line and filter should be changed to a set-up similar to what Paul shows in his photo. With regard to my cold engine stumble on acceleration issue, I guess it becomes a tuning trial & error exercise until the issue resolves itself. I already paid a mechanic to tune the carburetor (including engine timing, etc.), and although he installed smaller jets in the carb, he left me with this issue. I will test for vacuum leaks first. Then I will change the springs on the metering rods to stronger springs. If those things don't fix the problem, do I continue to play around with this 750 cfm carb, or should I replace it with a 600 cfm carb? If my engine doesn't have a heat riser, is there a way around that? Do I need one here in hot South Florida? BTW, my carb sits directly on a gasket without a heat spacer. What should I do next?

Roger (50141)

[Michael W.]

Re: Edelbrock Electric Choke Issue

Michael;

Have you ever looked at other factory C-2 four barrel carburetor installations, say from 64 through 65 or 66? Many use a fuel hose from the filter to the carb. That's not to say it's the best way to go, but it's been done safely by many OEM, as well as Hot Rodders back in the day. I would say he should at least check the condition of the hose(s) and replace them with good quality material that is safe with today's corn gas.

I use a fuel hose on my L-76 63 too as I needed to raise my carb up the thickness of a penolic spacer and two gaskets in order to lower the heat at the carb. The OEM chrome steel piece wouldn't make that stretch.

Stu Fox

Stu,

I'll forward your message to the fellow that lost his C3 in the fire. I'm sure it'll make him feel much better. Sure wish I knew you back in the mid 70's when I had a rubber fuel line burst and spray fuel on a hot engine. Guess I imagined the whole thing. OEM set ups are one thing, self-engineered systems are another.

There again, almost 84% of people say there was no ill effects to playing Russian Roulette.

[Clem Z.]

Re: Edelbrock Electric Choke Issue

fuel proof rubber lines are not a problem as long as the metal line that the hose is slid over had a enlarged diameter on the end so the clamped hose can not slip over the enlarged diameter because of the clamp

[Clem Z.]

Re: Edelbrock Electric Choke Issue

Clem, Stu, and Michael,
As always, I can count on you guys to give me useful information from your respective experiences. Michael, a fire is always a concern of mine -- certainly don't want anything to do with what I saw in that video! The Corvette specialist mechanic actually changed the fuel inlet line to what I have now because he didn't like what was there before as he didn't think it was safe. Go figure. I guess the line and filter should be changed to a set-up similar to what Paul shows in his photo. With regard to my cold engine stumble on acceleration issue, I guess it becomes a tuning trial & error exercise until the issue resolves itself. I already paid a mechanic to tune the carburetor (including engine timing, etc.), and although he installed smaller jets in the carb, he left me with this issue. I will test for vacuum leaks first. Then I will change the springs on the metering rods to stronger springs. If those things don't fix the problem, do I continue to play around with this 750 cfm carb, or should I replace it with a 600 cfm carb? If my engine doesn't have a heat riser, is there a way around that? Do I need one here in hot South Florida? BTW, my carb sits directly on a gasket without a heat spacer. What should I do next?

Roger (50141)

the smaller jets could cause your lean problem when the engine is cold. i would install the jets the carb came with stock. carbs are jetted for sea level running and the only time most need to be leaned out is when you go up in altitude. i believe most all of fla. is very close to sea level.

[Roger P.]

Re: Edelbrock Electric Choke Issue

the smaller jets could cause your lean problem when the engine is cold. i would install the jets the carb came with stock. carbs are jetted for sea level running and the only time most need to be leaned out is when you go up in altitude. i believe most all of fla. is very close to sea level.

Clem,
I brought my car to the mechanic because my eyes would burn when driving. He told me the carb was running too rich, and that was why he changed the jets. Did it stumble before he re-jetted the carb? Yes, but perhaps not as much. At the time, I was dealing with other issues such as my rear suspension (and the economy), so the cold stumble problem wasn't high on my priority list. Now it is. Since a 750 has larger jets than a 600, and since it was running rich, wouldn't it make sense that he used smaller jets? Looking back at the invoice, he also changed the distributor advance springs.

Stu,
You're right about our hot, humid weather most of the year. However, other than last week, we're back to more seasonal weather now (heading to the beach with the family shortly). The vacuum advance unit on the distributor is hex shaped and was installed on the car when purchased. Should I get a small allen wrench and mess with the adjustment? Is that a possible cause for my stumble problem? I can try turning the screw one full turn to the right and/or left and see what happens, and can always turn it back to its current set position. Do we all agree that using propane to check for vacuum air leaks is safe? OMG, I have been really spoiled by fuel injection on my daily driver! Years ago I owned a Datsun 260Z which I believe had a couple of Webber carbs (or something similar). What a PITA! Always had issues with those suckers.

Thanks again,
Roger (50141)

[Clem Z.]

Re: Edelbrock Electric Choke Issue

Clem,
I brought my car to the mechanic because my eyes would burn when driving. He told me the carb was running too rich, and that was why he changed the jets. Did it stumble before he re-jetted the carb? Yes, but perhaps not as much. At the time, I was dealing with other issues such as my rear suspension (and the economy), so the cold stumble problem wasn't high on my priority list. Now it is. Since a 750 has larger jets than a 600, and since it was running rich, wouldn't it make sense that he used smaller jets? Looking back at the invoice, he also changed the distributor advance springs.

Stu,
You're right about our hot, humid weather most of the year. However, other than last week, we're back to more seasonal weather now (heading to the beach with the family shortly). The vacuum advance unit on the distributor is hex shaped and was installed on the car when purchased. Should I get a small allen wrench and mess with the adjustment? Is that a possible cause for my stumble problem? I can try turning the screw one full turn to the right and/or left and see what happens, and can always turn it back to its current set position. Do we all agree that using propane to check for vacuum air leaks is safe? OMG, I have been really spoiled by fuel injection on my daily driver! Years ago I owned a Datsun 260Z which I believe had a couple of Webber carbs (or something similar). What a PITA! Always had issues with those suckers.

Thanks again,
Roger (50141)

most of the time the carb with the same air flow use the same jets on different size engines. the 780 CFM holley used on a Z-28 302 and a 454 BBC use the same size jets. it depends on the air flow thru the carb.

[Paul L.]

Re: Edelbrock Electric Choke Issue

I'll post this because it solved a similar problem on my 1974 Q-Jet. It seems that your carb has not seen a rebuild in 20 years but this thread may be relevant to your internal rubber parts...and any rebuild kits. Just a thought. My posts are in there and my frustration with off-idle stumbles was alleviated with Viton internals as you will note.

You have not stated your Edelbrock model but the most inexpensive approach might be to simply purchase a new #1406 (<$300.00) rather than fooling about with mechanics at $75.00/hr. You may have to bend some 3/8" steel line but it is ~$6.00 for 5' at NAPA. I believe they have tube benders and flaring tools for loan as well.

http://forums.corvetteforum.com/c3-t...t-quality.html

[Timothy B.]

Re: Edelbrock Electric Choke Issue

Roger,

Slow down some... Changing metering rod springs, jets and vacuum advance adjustment is guessing. What vacuum level are you adjusting these things too??

A good test to determine if your main jets need to be changed is to drive the car at 35-45-55 MPH on a level road LIGHT THROTTLE and see if the engine surges. Ideal jetting is when the engine is leaned until this happens (surge) and then go up one jet size at a time until no more surge.

Stu has a good suggestion about the temperature sensor that grounds when the engine warms. This way the choke will stay closed longer until the engine warms to where the sensor grounds and gives the electric choke 12 volts to expand the choke spring.

If the engine does not stumble when warm the choke is opening to fast. You should be able to turn the black cover and close the choke butterfly and tension it tighter. Remember, the proper adjustment of this coil is at 68* and turned so the choke plate just closes. If you can't do that something is not connected properly.

Read the paper about the accellerator pump adjustment to make sure it's giving a shot of fuel when the throttle is moved. The purpose of the pump is to cover the lean condition the engine sees when the throttle is moved fast until the main circuit picks up. The larger venturi size of the 750 does not see the fuel signal on the 350 engine like a 600 CFM carburetor hence the delay in main circuit starting to flow fuel. The pump shot will help here but if no stumble when warm, I say choke opening too fast..

[Roger P.]

Re: Edelbrock Electric Choke Issue

Roger,

Slow down some... Changing metering rod springs, jets and vacuum advance adjustment is guessing. What vacuum level are you adjusting these things too??

A good test to determine if your main jets need to be changed is to drive the car at 35-45-55 MPH on a level road LIGHT THROTTLE and see if the engine surges. Ideal jetting is when the engine is leaned until this happens (surge) and then go up one jet size at a time until no more surge.

Stu has a good suggestion about the temperature sensor that grounds when the engine warms. This way the choke will stay closed longer until the engine warms to where the sensor grounds and gives the electric choke 12 volts to expand the choke spring.

If the engine does not stumble when warm the choke is opening to fast. You should be able to turn the black cover and close the choke butterfly and tension it tighter. Remember, the proper adjustment of this coil is at 68* and turned so the choke plate just closes. If you can't do that something is not connected properly.

Read the paper about the accellerator pump adjustment to make sure it's giving a shot of fuel when the throttle is moved. The purpose of the pump is to cover the lean condition the engine sees when the throttle is moved fast until the main circuit picks up. The larger venturi size of the 750 does not see the fuel signal on the 350 engine like a 600 CFM carburetor hence the delay in main circuit starting to flow fuel. The pump shot will help here but if no stumble when warm, I say choke opening too fast..

Tim,
I don't have a vacuum pressure gauge, so I can't answer your question. However, I assume it is within the correct range since it was tested by the mechanic when he tuned the carb, timing, etc. I already moved the linkage on the accelerator pump, so that is maxed out. The only time I get surging is sometimes in second gear when the engine is cold. When the engine is at normal operating temperature, everything works great... no stumble while accelerating in first gear, and no surging when in second gear. I agree with you that it sounds like a choke issue, but when I turned the black cover far to the right beyond the normal range to really tighten the coil (assuming it would keep the choke on a long time), two things happened. First, the choke didn't stay on much longer than before -- only 2 to 3 minutes before it was open and the idle lowered to 850 rpm. The second thing that happened was that the engine wouldn't start again once I turned it off. It just cranked and cranked until I readjusted the choke to within the normal marks on the black cap. How would I go about buying and installing the temperature sensor? That makes a lot of sense to me, too. However, I would like to check for a vacuum leak before that -- is using propane the safest and best way to do that? I also found one more item this evening that concerns me. When I went to see what color metering rod springs are currently installed (they have no color which I understand is the strongest spring), the screw securing the cover on one of the two openings was not tight. I now know why... someone stripped the threads in the top of the carb . Is this dangerous (where gas might seep out from behind the cover), and does this create either a vacuum leak or issue where that metering rod wouldn't function properly? Can I fix it by either using a slightly longer screw, or filling the screw hole with epoxy and then tapping new threads? Or as Paul suggested, should I simply buy a new 600 cfm carb and call it a day?

Roger (50141)

[Clem Z.]

Re: Edelbrock Electric Choke Issue

Tim,
I don't have a vacuum pressure gauge, so I can't answer your question. However, I assume it is within the correct range since it was tested by the mechanic when he tuned the carb, timing, etc. I already moved the linkage on the accelerator pump, so that is maxed out. The only time I get surging is sometimes in second gear when the engine is cold. When the engine is at normal operating temperature, everything works great... no stumble while accelerating in first gear, and no surging when in second gear. I agree with you that it sounds like a choke issue, but when I turned the black cover far to the right beyond the normal range to really tighten the coil (assuming it would keep the choke on a long time), two things happened. First, the choke didn't stay on much longer than before -- only 2 to 3 minutes before it was open and the idle lowered to 850 rpm. The second thing that happened was that the engine wouldn't start again once I turned it off. It just cranked and cranked until I readjusted the choke to within the normal marks on the black cap. How would I go about buying and installing the temperature sensor? That makes a lot of sense to me, too. However, I would like to check for a vacuum leak before that -- is using propane the safest and best way to do that? I also found one more item this evening that concerns me. When I went to see what color metering rod springs are currently installed (they have no color which I understand is the strongest spring), the screw securing the cover on one of the two openings was not tight. I now know why... someone stripped the threads in the top of the carb . Is this dangerous (where gas might seep out from behind the cover), and does this create either a vacuum leak or issue where that metering rod wouldn't function properly? Can I fix it by either using a slightly longer screw, or filling the screw hole with epoxy and then tapping new threads? Or as Paul suggested, should I simply buy a new 600 cfm carb and call it a day?

Roger (50141)

if the screw comes out the screw and the cover can end up in the engine or worse it could jam the throttle open at a bad time. my suggestion unless you can do the repairs yourself buy a new smaller carb