Heat soak on the carb!! What to do????

[69wannabe]

My charger runs good most all of the time now, been driving it some lately finally got a lot of the bugs worked out but still have a carb issue after I turn it off and 20 or 30 mins pass  I have to spin it over and hold the gas down to get it to start and once it starts I have to keep it running and rev it a few times for it to run normally. I know its a heat soak issue but I have the rpm intake on there and cant run a spacer under the carb and I already have the 1215 fel pro intake gasket on there. It never was quite this bad the way it was built before just a 440 with a 750 DP holley on there. Its a 493 now with the same intake and a 850 holley DP now. The carb is pretty much right out of the box with nothing changed. It runs good besides this. I wonder if I need to make any changes in the carb and The 850 has two power valves where my 750 only had the primary one and the 850 has a 50cc pump on the back fuel bowl.  Just wondering if I need to make any changes here. The plugs actually look good when I pull and check them so i'm a little afraid to go any leaner with the jetting. Besides this my charger runs great and cruises out fine, If you got any good advise Ron I will be glad to use it. Thanks Chad

[justcruisin]

I run the RPM intake with e-heads. A half inch spacer made a big difference to how it started when hot, this is the first thing you should try. Can you run a drop base on your air cleaner?

[69wannabe]

I'm running a drop base on it already, I may could remove the hood insulation and get maybe a thicker gasket/ insulator under the carb without it putting the breather into the hood. I'm thinking of jetting it down a couple of sizes on the primaries and dropping the accelerator pump squirter down a few sizes on the primary side. When I start it in for the first time like in the mornings it stumbles and doesn't clear up even when I hold it above 1500 rpm's for several seconds. Seems really rich but after it warms up it smooths out and revs smooth. If I can get this issue dealt with I will feel better about the way it runs out!! Would like to hear any ideas Ron if you will chime in!!

[justcruisin]

The RPM manifold with no heat cross over used doesn't run well at low speed when cold. If it runs well at normal temp and your choke (if you run one) isn't staying on to long it is more likely to be running lean on cold start up than rich. If you can't run a spacer maybe try lowering your fuel levels to see if that cures your hot start issues. You may not be able to leave them at the lower level but at least you will have a direction.

[Brightyellow69rtse]

i would use the biggest phenolic spacer you can fit. my clearance is really tight so i only got a 1/4" spacer but it really makes a big difference.

[firefighter3931]

As mentioned above....you need to insulate the carb from conductive heat. The heat transferring from your manifold to the carburator is a problem. Anything you do to make the carb (and fuel) cooler will help....a lot !

I wouldn't pull any jet out of it, ethanol based fuels require richer jetting than pure gas. 

If you have ethanol-free fuel available i would try that and see if the problem persists. At any rate you should still use a spacer or carb base insulating gasket.

As for the hard "cold" starting ; that is normal and you just have to feather the gas pedal until it warms up. Once the engine warms up the fuel begins to atomize better and that's why your idle becomes stronger and smoother. With larger plenum manifolds and heavy fuel droplets the mixture is too rich. Just part of the start-up procedure with a carburated big cube monster 


Ron

[RIDELIKEHELL]

As mentioned above....you need to insulate the carb from conductive heat. The heat transferring from your manifold to the carburator is a problem. Anything you do to make the carb (and fuel) cooler will help....a lot !

I wouldn't pull any jet out of it, ethanol based fuels require richer jetting than pure gas. 

If you have ethanol-free fuel available i would try that and see if the problem persists. At any rate you should still use a spacer or carb base insulating gasket.

As for the hard "cold" starting ; that is normal and you just have to feather the gas pedal until it warms up. Once the engine warms up the fuel begins to atomize better and that's why your idle becomes stronger and smoother. With larger plenum manifolds and heavy fuel droplets the mixture is too rich. Just part of the start-up procedure with a carburated big cube monster 

My 68 has the same problem when I first start it but feathering as Ron says works nice  Good luck man I know the problem all to well


Ron

[69wannabe]

I've got a few different spacers so i'm gonna try to fit one under there that may make a difference in the heat soak. I have a wood one that's bout 1/4 inch thick, I may try to squeeze that one under there. Ok Ron so don't change anything in the carb and just add a spacer and see how it goes?? I was going to change the power valve from a 6.5 to a 5.5 since my vacumm reading is 11hg and thought of dropping my squirter size from 31 to a 28 since it seems a little thick and I feel like a smaller size may make it a little crisper on the primary size for the rear squirter the 50 cc pump seems kinda excessive so I thought of putting a regular 30 cc pump back there and see how it ran from there. I got several old holleys laying around for extra parts so its not really gonna cost me to pick around at it. If it doesn't improve anything I can always put it back the way it came. Do you usually run two power valves or just one and if so what is the reason for two power valves?? How would you know if the rear power valve is the right one and is it supposed to be higher hg rating than the primary one?? Just some carb questions that I don't know the answers to but I don't mind experimenting to see if this work better or if it doesn't work better. The last 750 DP I had spoiled me it was such a great carb and after minor tuning it was done and I never put a screwdriver on it for three or four years. Should've kept that one!!!!

[69wannabe]

Ok, I pulled the carb and swapped the primary squirters and swapped the rear 50 cc accelerator pump for a regular 30 cc pump and managed to squeeze a heat insulator spacer under it. It was an open spacer slightly thicker than a 1/4 inch. Put it back on there and checked for any interference between the hood and the breather and it seems to be very close but still ok. Ran it for awhile til it warmed up and turned it off and let it sit for bout 15 mins and tried it and much to my surprise it started right up with no sputtering and having to rev it and get the excess fuel cleared out of it!! What a difference it did make with a 1/4 inch spacer under the carb. The engine wasn't as warm as it usually is when I drive it and park it but this is a giant improvement!!! I was just worried about my hood to breather clearance. I would have had it on there months ago if I knew it wouldn't have put the breather into the hood. I have a few of these spacers hanging on the wall. The holleys used to not heat up quite like the eldebrocks/carter style carbs did. I have always used a spacer on the eldebrock carbs just not the holleys as much. its been raining so no test drive today, maybe in a day or two I can check it out. It does seem to rev a lil better with the smaller squiters in the front of the carb and the jetting is still the same so the cruising and all should be the same too.

[firefighter3931]

It sure sounds like adding the spacer was a step in the right direction. 

Report back when you can take it out for a road test...hopefully the fuel boiling issue is resolved ! 


Ron

[69wannabe]

Its a lot better for sure, drove it today and it seems good with the smaller accelerator squirters on the primary side and it didn't die out so quickly when I was standing in it so going to the 30 cc pump on the secondary side seemed to be a good move too. It pretty much spun through 1st and mostly 2nd and grabbed and the rpms dropped to around 5000 then back up to 6000 then I shoved it into third and it was moving pretty good by then. It still had a little hesitation after I let it sit for bout 15 mins but I had really ran it hard before I parked it. It still started up good and regained its composure after just feathering the pedal a lil bit. It is a big improvement over before. It would spin over and start finally and if I didn't keep my foot on the pedal it would go dead. With the 50cc pump on there it didn't spin through second much at all. That's why I thought it may be too much  since the proform I pulled off just had 30cc pumps on front and back and it was impressive at wide open throttle. It actually started up and didn't seem to be so rich when I first started it up today. I just held it up above idle for bout 15 to 25 seconds I guess and let it idle til it warmed up. Gonna run it for awhile and let it settle in and see how it goes from there. Wish my valve train wasn't so noisy, crappy comp cam lifters I guess.

[firefighter3931]

It sure sounds like the fuel boiling issue is resolved. 

Now it's on to tuning 

What heads, cam, intake, exhaust are you using with this 493 ?

The Proform is superior to a Holley.....waay more adjustability. 


Ron

[69wannabe]

The heads I am running are 346 cast irons with 214/181 valves and mild porting, I am running the comp 240/246 @ 50 degrees with 507/510 lift and an eddy RPM intake. The compression should be in the high 9's since the kit I went with dished pistons instead of flattop's. The reason I pulled the proform is because it was surgeing at cruising speeds. I jetted it up and it made the driveability worse instead of better. It worked great if you were in the throttle but if you wanted to cruise along it stumbled along until you eased your foot down on the pedal slightly and it would accelerate fine. The proform idled fine and had the power just not the driveability of the holley. The holley cruise's great when i'm just lopeing around and no stumbling and surgeing. I still have the proform and would love to have it on there since its a lil more aggressive feeling than the holley if it would just cruise like the holley does!! I got my timing set on 15 and it advances to like 34/35 and no pinging there with 93 octane!! My carb tuning skills are not the best but I will change whatever or drill or do whatever if it makes it work right!! My distributor seems ok but I am looking to improve my ignition system and hopefully get this carb dialed in and hit the road for a change!!

[firefighter3931]

If i remember correctly ; you were using vac advance  while trying to tune the Proform carb ? Then you installed the Holley carb and plugged off the vacuum advance and the surging was gone, correct ? 

Assuming this is the correct version of what transpired it's hard to blame the PF carb when the issue was in reality.... ignition related. The fact that you jetted up with negative results further reinforces this hypothesis 

Vac advance and big cams are a bad mix....plain and simple. When a member asks for solutions to a surging issue and is running a big cam i'd say that 9 times out of 10 that plugging off the vac advance fixes the problem. 

The PF carb has a more agressive fuel curve that is better suited to a big cube combo with lots of camshaft duration....that's why it felt stronger 


Ron

[69wannabe]

I had trouble with vacumm advance on a ford engine I built years ago and haven't ran a vacumm advance on anything since. Haven't ran a vacumm advance on the charger ever. Always plugged off!! The proform just had a surge in it just off idle but it accelerated nicely and ran good for the most part. I had to drill the two little holes where the power valve screws in on the 750 I had to cure a surgeing problem and I wonder if the 850 metering block may need some work in that same area also. I remember it had the same symptoms and after I enlarged them two holes it was fine. May look at that metering block tomorrow and see what it looks like.

[firefighter3931]

Ok, thanks for the clarification. I must have misunderstood what i read awhile back 

I still think the PF carb is worth dialing in when you feel like experimenting 


Ron

[69wannabe]

Hi Ron, I pulled the primary metering block off the proform today and where the power valve screws in instead of just holes it has little jets there. on the metering block that was on the 750 DP I had had tiny holes here when I called holley he said if I have an old 3310 laying around check the holes on it and I have a couple laying around so I checked it and I could actually get a 1/16 drill bit into the holes of the 3310 metering block. On the 4779 metering block I wasn't even close so instead of drilling I just used the 3310 block on my 4779 and it worked great. The guy at holley said they did this so on the 3310's they could run a smaller jet for street friendly use. And the reason for the ones on the 4779 is because this carb was popular for the chevy stroker motors and had to lean it down some. Makes since cause every ford 302 and chevy 350 have a 750 double pumper on them that I see lately. So I checked the proform and the 1/16 drill bit was slightly bigger than the jet that was in the holes behind the power valve so I just drilled them which didn't take but just a small bit of effort. This little bit may actually cure my lean surge I have just off idle. How familiar are you with these carbs Ron?? There are two of these same jets at the very top of the metering block and I wonder if they may need to be drilled too... They are the exact same jet that is behind the power valve. I am just gonna try it this way first and see how it does and go from there. Just like to get your opinion on these things since you know your stuff when it comes to getting these things right!! Thanks!!!!!

[firefighter3931]

I haven't had to do any internal mods on any proform carb and they've all run very well. 

Try decreasing the high speed air bleeds in small steps and see if that helps with your surging issue. 


Ron

[69wannabe]

Which are the high speed air bleeds?? The ones on the outside or the ones on the inside?? Can you buy an air bleed jet kit?  I drove it a bit today after replacing the old regular thermostat with a milidon  high flow thermostat. It wasn't running hot or anything I have had a couple of these hanging on the wall for awhile and decided it may help with some of the heat soak issues and help the engine run a lil cooler too. It actually cruised around nicely and the holley really runs good on there. I changed the oil and filter and went for another drive and it runs out pretty nice. I may try the proform later on when I get bored or something. It seems good for now and I may check into some of those lifters that have got to be better than the one's that are in it now. the valvetrain noise is slightly more excessive than I think it should be.