Chevy 350 possible edelbrock carb. problem. Need help
Hi everyone I'm new to the forum and I'm in need of some help. I recently purchased a 1922 model t with a 1978 chevy 350 30 over. I found out its got a .502 lift .298 duration crane cam. The carb is an edelbrock 1400 series 600 CFM. The previous owner bought it and drove it a couple of times in the 8 or so months he owned it. The carb is around 6 month old previous owner purchased.
I had a mechanic check it out and this is what he did. Adjusted carb choke, idle mixture and idle speed. Determine TDC for #1 cylinder. Re-mark balancer. Reset ignition timing for 35 degrees total timing at 3500 rpm. Disconnect vacuumed advance.
I'm having an idle issue. It starts good and once it warms up it idles ok, but once I go for a spin and make it to a light it starts idling low again to a point that it almost shuts off. I was getting it to idle at 1000rpm but it would drop to 500 and lower. I took the carb apart and cleaned it out and replaced the gaskets I didn't rebuild because it isn't that old. I had found what looked like a gel in there probably the ethanol from sitting or something. After that it still doing it.
Any info would be greatly appreciated I'm starting to get frustrated.
Here are a couple of videos I took one has bad lighting I apologize for that.
Edelbrock - YouTube
Rat rod bad idle - YouTube
whats your static timing set at? rehook vacuum
Just as Vinnie said, what is the base timing set at? With vacuum advance disconnected and plugged, base timing should be 12 degrees before top dead center. Once set, lock distributor. Reconnect vacuum advance to a manifold vacuum source, this is a source that pulls vacuum full time including idle.
The correct port to use on your carb with you standing in front of it will be on the front right side. When you connect the vacuum advance right away it will idle up, then lower your idle speed back down to around 700 RPM.
Next readjust the idle mixture. Without vacuum advance and with the base timing set low what happens is the throttle plates are opened so far the butterflies are off the idle slots so it's forced to pull fuel from the main boosters at idle, this is likely what's causing it to go almost dead under load as it's simply loading up. When you reset the timing and use the vacuum advance you'll find your ride will have a nice lopey idle and it'll have far better low end power. Tuning a hot rod has almost become a lost art as so many believe 12 degrees at base is all you need and they believe vacuum advance is a emissions device that hurts power and they disconnect it not realizing it's vital to tuning it correctly.
Chevy 350 possible edelbrock carb. problem. Need help
When you took it to your mechanic you said he determined TDC and remarked the balancer. Did you ask him why the original mark on the balancer was off? Did you ask him why he unpluged the vacuum advance? You definitely need to know if there is a problem with the vacuum advance. The vacuum can on the distributor could be shot, something could be broken on the plate inside the distributor not letting the advance work. When you cleaned the carburetor did you soak it or just use carb spray? Here is a Wiki article on HEI distributors to read. Read the section on the Idle transfer slot thru the example of a typical performance ignition advance curve. This is a lot of information to help you understand what is happening. Even if you don't do the work on it you will know what needs to be done.
Some set ups very similar to yours prefer ported vacuum. in fact I believe edelbrocks tuning tips state thats the most common unless you have power brakes. But there is nothing wrong with using manifold vacuum if your car runs better that way. Also, I have a lot of experienced people around me that all like to unplug the vacuum advance and use real light springs in there distributor to have timing all in as early as they can. granted they are performance junkies and not driving there cars concerned about mileage.
Im not stating the advice already givin to you is incorrect, im simply verifying that that theres many ways to go.
I would suggest pulling the carb and making sure your set to spec, and hooking up an afr gauge to make sure your safe there. I had the 1407 carb on my 355 and had to tune almost every aspect of the carb, but I think that every carb should have this done. sometimes you get lucky and it runs but most likely it could be better. Even new carbs say to open them up and look for flash, or check floats n butterflies for proper position. Remember that its just regular people putting these things together. (maybe not every carb company but for the most part). and people get stuff wrong all the time. Anyway, Im not familiar with the 1400, perhaps its a good cfm size, I heard you mention alcky so thats probly why.
I now have a demon 750 duel inlet now and chose to start off going through it and making changes right away. then bolting it up, (my timing already set, youll have to do this), then checking pressure(edies like 4.5 but If you are running mixed alcky or straight, youll have to find out, then set your idle, then fuel air screws evenlyleaving your starting point of one and a half turns out. Then your idle again, then fuel air again, then idle again. all while its warmed up and of coarse with a vacuum guage, and timing gun all correctly hooked up.:cool:
usually guys will adjust the pump shot by moving the linkage from one of three holes. depending on whether you have a bog or not from stop will prolly dictate where you put this. also the electric choke you will want to adjust according to the whether. I was able to only have to move mine about twice a year on a perfect year but the weather around me now jumps back and forth and its annoying when the choke runs longer than it should.
anyway, I hope I was able to help you out. If you just try to remember the order in which they are performed to get the correct set up, then actually performing the steps wont seem like such a big deal. Once you have it down you will be doing it multiple times a season and doing so in just minuts.
That crane cam need a much different timing curve to idle and drive nice with a auto transmission.
You need 26deg base at idle ....a short limited travel 10deg advance curve 36 deg at max advance.
Then using ported vacuum, a 12-15deg vac advance curve. aprox 8-10deg at hi way cruise speeds.
Until you modify the mechanical curve and shorten it to allow increased stable idle timing that does not drop
below 26deg at idle it will idle like crap and stall.
You get this by limiting the mech advance curve to 10deg.
Now you can reset the carb. Use 4" rated primary power step up springs in the carb. 5psi fuel pressure
That crane cam needs a 10" high stall converter. The generous valve overlap needs a ton of timing at idle.
Depending heavily on vac advance for added advance at idle works on a manual transmission car but not a automatic car
that has to idle "in gear", under load.
vacuum drops when you idle in gear, makeing the idle timing drop and the engine stall, hunt or load up.
More base timing and a shorter advance curve is the cure. needs a high stall converter
Some people simply lock out the mechanical advacne and run locked timing 36deg BTDC
The cammed engine will love 36deg at idle.
( vacuum advance can still be used for part throttle cruise)
Locked timing + vacuum advance works very well on radical cammed auto trans cars.
Use ported vacuum.
Crane cams cam card
Thanks everyone for all the good advice. I purchased a timing light today and will be able to check the timing. I apologize for not responding sooner I had computer issues. I will be working on the car tomorrow morning.
So I'm going to try 26deg on idle if anyone thinks that's not a good idea please let me know.
One glaring thing in your video that's not a good idea is the rubber fuel line. SEt up a metal tubing line.
Unlees of course you like massive engine fires. I learned that one the hard way. Towering inferno!!!
I may be incorrect but the Edelbrock 600 carb is for stock to mildly modified motors. A sbc with a 298* duration cam is not mildly modified. This carb is not designed to work well with this type of cam and can be very difficult to tune. You may need a larger holley style carb with mechanical secondaries for this set up.
Edelbrock makes several 1400 series carbs, but the most common is the 1406, which is set lean to get good fuel mileage. It would run with your engine, but it would not be a good match for this cam.
Also, if the owner used a HP fuel pump, verify the fuel pressure stays within Edelbrock's recommendations (5 psi?). The 1400 series does not run right if the fuel pressure is too high.
Its quite easy to swap rods, jets and springs on a 1406 to tune it to run better for high performance. However, without an AFR and some other tools to see the effect of your changes it will mean a lot of experimentation before you get it right.
Instead of tuning the current carb it may be simpler in the long run to swap it out with a Holley or one of the other Edelbrock carbs that is a better match to the rest of the engine.
Thanks for letting me know about the carb. The original builder had a Holley carb i think a 750 CFM. Then the previous owner bought this carb, I thought from what I had read that the carb was not big enough but wasn't sure. I might just look into buying a bigger Holley carb before I mess with anything else.
Would a 750 CFM be good enough?
750 cfm is a good size carb for mild to moderate 350s
Thanks again everyone, I'm gonna look into getting a new Holley carb to replace the once I have then ill check on the timing and the other things you guys have recommended.
I'll post an update when I get the new carb
Mr Xiggy.. temperairily lock out the timing curve. Set the locked fixed timing at 36deg BTDC.
Now reset the carb and . Now you can fine tune from there.
This may not be the idle spark advance you end up with but it is the place to start at.
locked out at 36deg BTDC is not too much. you can fool around with it from there.
26++++ deg base at idle for a cam like that. 36 fixed /locked is not too much for a cam like that.
The timing must not drop off when you idle in gear.
if you have a auto trans and this is the cam you got, you will find the locked out mechanical timing very effective.
Wether you use the carb you got or a holley or.... will not change this.
functional vacuum advance can be retained but will need to be set up. Use ported vacuum.
Thanks f-bird I'm gonna try that tomorrow. Just curious I just picked up a timing light that is adjustable in the back. Should I have it set at 0?
How do you lock out the timing curve?
The mechanic that checked it out remarked the balancer not sure what the reason was. I'm going to determin TDC when I do should the mark be at 0?
Sorry if these are dumb questions I've never done this before and am learning as I go.
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