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Hard Starting When Hot

3K views 15 replies 5 participants last post by  67CamaroRS/SS 
#1 ·
I have read all the previous posts about hard starting and I can't seem to find an answer. I have a 70-72 350 with Pertronix distributor, Crane Hi-6 ignition, Optima battery, initial is 16*, total is 36*, PowerMaster Torque XS mini starter, Accel header plugs(equivalent to R45ts), Edelbrock Thunder series 650, Accel 8.8mm wires, and an Edelbrock Performer RPM cam #7102. It starts absolutely beautifully when it's cold, but if it's hot and I shut it off for over 5 minuted, then it wants to crank for about 5 seconds before it starts. I also have to give it a lot of pedal to start. If I shut it off for under 5 minutes it will start up fine. I don't know what to do. I swapped plugs out from the Accels to AC's(R44ts) and it seemed to start when I did the swap so naturally I swapped them back thinking that was the problem and it seemed to help until today when my club was taking pictures. It had sat for some time after a 30 minute drive to the location and it didn't want to fire over right away. I have even tried to dial in less initial, but then the car seems sluggish. I tried more initial(around 20*), but it didn't seem to like that much initial off the line. It started fine when cold, but I didn't leave it at 20* long enough to see if it would start hot because of how it performed. I never had this problem until I made the initial switch in plugs, but now that I switched back, it stopped and then started again. Could it be that the Accel plug was a R45ts equivalent and I installed R44ts's? The reach was off by a bit. The Accel's have .460" and the AC's are a little less. I can't remember exactly what the AC's are. I don't think the reach really matters that much unless it is a "Race Car". Should I try to run around 17*-18* initial? Any suggestions will be appreciated and I am up for whatever. If it is in my power to perform. Thanks.
 
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#2 ·
The reach can be determined pretty easily. Stick a bent piece of wire in the hold and put your thumb nail on the gasket flange of the plug hole, then measure. You need to have the proper reach. If it's too short, you are likely to have starting problems.
 
#3 ·
I went by the part number given to me by AC Delco. I typed in my vehicle and engine and they told me to use R44ts. Now both Autolite and Champion show their respective plugs to be .460" reach, but I thought if I typed in my vehicle and engine then AC should be able to tell me the correct plug.
 
#4 ·
The Ac plug reach is .4375". I don't understand why Ac calls for a plug that has .4375" and Autolite/Champion/Accel call for .460"? Would the idle mixture screws have something to do with it?
 
#5 ·
When I put the Accel plug back in(.460 reach)it stopped with the hard start for a while, but then it started again, which leads me to believe that it's not the plug reach. It's not evaporating the fuel. I know this because I got it hot, went for a long/hard drive, came home and let it sit for around 20 minutes, pulled the air cleaner off and watched fuel squirt as I moved the throttle linkage. I don't know what else to try. I even hooked a vacuum gauge to manifold vacuum and re-adjusted the idle mixture screws. What if the carb mount gasket is leaking? I don't think it is. I sprayed carb cleaner around the base and the rpm's didn't increase. Does anyone have any other suggestions? Thanks in advance.
 
#6 ·
Charlie,

I know you mentioned that this all started with the plug change, but this does sound like the classic Edelbrock carb issue that a lot of folks battle, me included. The best explanation I have heard is that when the engine is hot and allowed to sit for about 5 minutes, the heat that has been transfered into the carb causes the gas to "percolate" into somewhat vaporish fuel. When you try to start it, it acts like a rich/flooded condition that only allows the car to start by opening up the throttle.

Edelbrock offers these special gaskets for the issue. From what I have gather from posts here, these gaskets have helped some, but not others.

Good luck in getting it resolved.

Jon


Straight from Edelbrock web page... the part numbers are edelbrock numbers.
"Heat Insulator Gaskets
Designed to help prevent fuel percolation in Performer Series and Thunder Series AVS carburetors exposed to extreme underhood temperatures. Use #9265 with open plenum manifolds such as Torker II and Victors. #9266 features a divided center which is designed to seal the carburetor to dual-plane manifolds including Performer, Performer RPM and most RPM Air-Gap manifolds. All gaskets come with extended carb studs."
 
#7 ·
Jon, if I was experiencing fuel percolation, wouldn't there be no fuel when you pull back on the throttle linkage? What I mean is, after it gets hot(like normal)and I turn it off, after waiting 5 or more minutes and I manually pull back on the throttle linkage at the carb itself, not by pressing on pedal, I can see fuel squirt out of the two nozzles inside the venturies. If it was fuel percolation, wouldn't there be no fuel coming out of the nozzles inside the venturies when I pull back on the throttle linkage? I am just asking because by there being fuel coming out of the nozzles, doesn't that mean there is still fuel in the bowl ready to be burned at start up? Am I off here? This thing has me stumped. I have tried everything else. I guess I can try one. They don't cost that much.
 
#8 ·
Charlie,
I'm by no means a carb guru, but those are just your booster squirters, I think. They are only in play when you step on the throttle, as they add a little bit of fuel to give the main fuel circuits time to catch up. On a slow, or steady throttle, or even not throttle, your carb feeds the engine through the main fuel "circuit" and the idle fuel "circuit". Within these circuits are where the fuel perculates.

That's the way I understand it. Like I said, I'm no expert so take it as you like and I may get corrected by someone who really knows.

Do a search for edelbrock and hard starting and you will see quite a few folks with this same issue.

Cheers,

Jon
 
#9 ·
Jon, I am also not a carb master and you may very well be correct. What I can't understand is that if it boils out of the circuit, that is only a very small amount and it should be replenished so quickly that you shouldn't even notice it, especially with all the extra fuel that sits in the bowls and I have pulled the carb apart when it was hot and it had plenty of fuel in the bowls. It is definately confusing. Have you had any luck with these gaskets? I will give it a try. What the heck, it can't hurt, right?
 
#10 ·
charlie, fuel percolation will not affect the accel pump at all...the pump is a diaphragm or pump with the intake of fuel being low in the bowl...even if almost empty,the accel pump will produce a stream of fuel...the percolation will create fuel vapors inside the air cleaner, and act like the car has the choke on...as a fairly simple test, try removing the air cleaner, and running the car to operating temp...turn it off, and let it heat soak...then start it with the hood open and air cleaner off...if it starts right up, then it`s prolly percolation...you can try dropping tha float level a bit to help, but i have more experience with holleys than edels, so dont know if the float adj. will work for sure...the carb spacer is also a good idea...if you use one, get a phenolic one...they seem to transmit very little heat, and usually work for me...
 
#11 ·
For some reason this morning I was reading the manual for the carb while I was waiting for my some to get up and it said that for engines with low vacuum that a softer spring for the metering rods is necessary. With the stiffer springs, the engine doesn't have enough vacuum to keep the rod in cruise mode or idle mode. The book says the following,

"If manifold vacuum is below 7HG then there is a good chance that the metering rods are in the up (rich) position. Using a weaker spring will keep the rods down at idle. If the rods are up (rich) position, this can cause the nozzles to discharge fuel at idle. This may be loading the car up with fuel causing it to "flood". Just for giggles I tried using a weaker spring this morning and it seemed to help, A LOT. I still have one step weaker to go. I have installed it and when I go out later I will see how well it reacts to the new weaker one. I will post back with the results.
 
#12 ·
I am 100% convinced that the problem I are having is due to the metering rod springs. Since changing to the lighter springs I haven't had any problems with hard starting. This is something that anyone experiencing this problem should try. Especially if you are running a large cam and have low vacuum.
 
#13 ·
I have an Edelbrock Performer carb, #1407, 750 cfm, and I was thinking of changing the metering rod springs however I purchased a Holley carb, #80457, 600 cfm and changed the power valve from a 6.5" Hg to a 3.5" Hg and also opened up the secondary valves slightly which completely fixed my problem!.....My little 327, with a radical cam profile, is only pulling 7" Hg of vacuum at idle.....My questions are: What's your vacuum reading at idle?....Did your Edelbrock carb originally have the orange, 5" Hg metering rod springs?.....And what color springs did you end up installing, was it the 3" Hg springs?
 
#14 ·
I have the Thunder series 650 #1806. My engine pulls between 7hg-8hg at idle. Yes my carb came with the orange spring(5hg) and I went with the yellow(4hg). I tried the blue(3hg), but it seemed like it wasn't stepping up to the power mode. I have since switched back to the yellow spring.
 
#15 ·
I'm glad you fixed it!....See what a little tuning and tweaking can do!!.....Is your vacuum advance working OK with the low vacuum?.....I'm running a Mallory Dual Point Distributor with the adjustable vacuum advance chamber, hooked up to full manifold vacuum, and had to adjust this also due to low vacuum.....I think my motor is happier now because it's not running rich any more and the idle quality is excellent @ 900 rpm in neutral!!:thumbsup:
 
#16 ·
I am not sure how well the vacuum advance is working. Edelbrock instructed me to hook my advance to ported vacuum. My engine idles at 750 in neutral and 600 in drive. I think I am going to have to do some testing on the vacuum advance. I have a Pertronix distributor and it does not have an adjustable vacuum unit. I am changing to the Crane distributor. It doesn't use the normal mechanical weights and vacuum canister. It comes pre-programmed with multiple vacuum and mechanical advance curves so there aren't any bushings, weights, or springs to worry about.
 
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