[rohrt]

My car seems to have a heck of a time starting. More so when its hot. It cranks over pretty well with the RobbMc starter but just not firing off very well. It seems to do better when cold. Once I crank over enough to get the fuel to the carb and pump it about 5 time it fires off quickly. However when it warms up it seems I need to hold the peddle down half way while cranking for 3 to 5 seconds to get it to fire.

Car is a 68 Firebird Convertible weight is around 3600lbs
455 + .060 #96heads (1971) 2.11 1.77 Ported
9.5:1 Compression Harland Sharp 1.5 Rollers
288/296 H10 110 deg lobe seperation 231 intake 239 exhaust
Stock 4bb intake 750 Q-jet 7028268 By Cliff Ruggles
Super Longbranch D ports Manifolds with 2.5" exhaust
Th400 Automatic TCI streetfight 2800RPM Stall
Daves small body HEITh400 Automatic TCI streetfight 2800RPM Stall

Is it my combo? I'm not even sure where to start.

[paint guy]

Are you running an HEI?Sometimes the modules will get"heat-soaked"and become more difficult to start when hot.

[rohrt]

Originally Posted by paint guy

Are you running an HEI?Sometimes the modules will get"heat-soaked"and become more difficult to start when hot.

Daves small body HEI. I don't know anyone else experiencing heat soak with one.

[Torment]

Fuel leaking and puddling in the manifold after you shut if off? I say that because you have to hold the throttle blades open and crank air in to start it up when it's been run - like it is mildly flooded.

[Sirrotica]

Accelerator position wouldn't have a thing to do with distributor heat soak. Having to hold the pedal halfway open to me usually signals a flooding problem or heat soak of the fuel in the carb and when warm. The gasoline actually percolates and runs out of the venturi cluster and fills the intake manifold with raw gas necessitating extra cranking with the throttle open to clear the excess gasoline from the manifold. A heavy float, or a defective needle and seat could also be causing flooding, along with too high of a float level. Any of these problems or a combination of them can cause the symptoms you describe.

If in fact it is heat soak of the fuel system heat isolator gaskets under the base of the carb help sometimes. Some of the Jap cars used to actually have a small electric fan blowing on the carb upon engine shut down to further discourage this from happening. Upon adopting fuel injection this problem went away on the newer cars but carburetor cars still suffer from it, especially in hot weather.

The reason it seems to start cold is because by sitting overnight the excess gas evaporates and you don't have the symptom when the engine is no longer flooded.

Hopefully this helps you with your detective work towards solving the problem.

[rohrt]

The heat soak seems like the most likely reason to also. Your reasoning makes sense. This is a Cliff carb so flooding due to bad needle seat or float level seems unlikely but the carb did sit for 2 years before going into service.

I guess now would be a good time to insulate the fuel line going up to the carb.

You said "heat isolator gaskets under the base of the carb help sometimes" I don't think that is what I'm using now. I think I just have a standard gasket. Maybe you can tell from the pic.

The heat soak seems like the most likely reason to also. Your reasoning makes sense. This is a Cliff carb so flooding due to bad needle seat or float level seems unlikely but the carb did sit for 2 years before going into service.

I guess now would be a good time to insulate the fuel line going up to the carb.

You said "heat isolator gaskets under the base of the carb help sometimes" I don't think that is what I'm using.

[Sirrotica]

The heat isolator gasket usually have thin sheet metal sandwiched in between composite layers to dissipate heat, yours does not have that as you say just a plain carb to manifold gasket. There are also wooden spacers that will do the same thing :
http://www.competitionproducts.com/W...ductinfo/8174/

Carburetor heat soak on Pontiacs is a common problem but sometimes takes some real effort to correct it. You might try the wooden isolator first and see if it helps.

[rohrt]

Sirrotica,

This little bit of info came from the carbshop link on the gas milage thread. Seems to say the same thing you are saying, and both hit the nail on the head.

HARD STARTING, HOT

Difficult starting of a hot vehicle from 5 minutes to an hour after the engine has been operated, can be caused by the volatility of modern fuel. If you have this problem; try using the following method to start the engine: DON’T touch the footfeed (VERY important). Crank the engine over from three to 5 seconds (different vehicles will respond to different times); and then GENTLY (so as not to activate the accelerator pump) press the footfeed approximately 1/3 of its travel. The engine should start, and may run rough. Run the engine at a high idle for about 10 seconds. This issue is caused by volatility of modern fuel. Once the engine has been shut off, the gasoline is heated by the latent heat of the engine, and percolates the fuel from the bowl into the throttle area, forming a mixture that is too rich to fire. If you push the footfeed to the floor (as has been the traditional method of “unloading” a flooded engine) the gasoline continues to flow into the engine (again due to the volatility). By not touching the footfeed, you do not open the throttle plates, and the engine will pump the overrich mixture out of the tailpipe. Once the overrich mixture has been alleviated, gently opening the throttle will allow the engine to start.

I like the wood ones but I would rather have a four hole one that is 1/4 inch.
I'm looking at getting the PHENOLIC 4 hole unit if I can find one.

I also see they make a heat shield. I have seen these before but are they worth it?

[jlwdvm]

I have a similar problem but have a pertronix ignitor 3, performer intake, and home built q-jet with well plugs and throttle shaft bushings doen by Cliff. I no longer have have a percolation problem (I could hear and see the gas boiling over into the carb) because I made a spacer out of a 1/2" piece of oak shelving with a gasket on each side. It is basically an open spacer with the divider still down the middle so it acts as an extention of the manifold. After my motor is warm and sits for about 10 minutes it has to crank for about 5-10 seconds before it will sluggishly fire (without touching the gas pedal). If I shut it down and then immediately try to start it up it fires right off. Could we be dealing with heat soak of the starter causing slower cranking rpm during hot starting? I have a stock high torque starter with headers.

[george kujanski]

Also make sure the valve in the exhaust manifold that feeds the exhaust passage under the carb is full open. In hot weather you may as well force it open permanently.

George

[Sirrotica]

Originally Posted by jlwdvm

I have a similar problem but have a pertronix ignitor 3, performer intake, and home built q-jet with well plugs and throttle shaft bushings doen by Cliff. I no longer have have a percolation problem (I could hear and see the gas boiling over into the carb) because I made a spacer out of a 1/2" piece of oak shelving with a gasket on each side. It is basically an open spacer with the divider still down the middle so it acts as an extention of the manifold. After my motor is warm and sits for about 10 minutes it has to crank for about 5-10 seconds before it will sluggishly fire (without touching the gas pedal). If I shut it down and then immediately try to start it up it fires right off. Could we be dealing with heat soak of the starter causing slower cranking rpm during hot starting? I have a stock high torque starter with headers.

It won't hurt to make a shield for the starter to keep header heat off the starter and by all means make sure all the battery to starter connections are clean and tight. Maybe a little known fact that heat does actually raise the resistance in wire and connections.

I worked in a Pontiac dealership when I was 17 and have been around Pontiacs all my life so I know that even when new these particular engines were new they need to have everything right or there was starter problems.

Another thing is the battery terminal ends should never be bolted to the cables I'm talking about the kind you find on a card in an auto parts store, they have no business on a Pontiac as there is too much resistance when using them. The terminals need to be made right on the cables and if crimp ends are used on the starter end they should also be soldered. I usually use welding cable as most of my cars have the battery relocated and don't just run 1 cable to the starter and hope that grounding the battery to the frame or sheet metal will work. You need to also run a ground cable to the engine as close to the starter mounting bolts as possible.

If you do all these things you should remove most of the pitfalls of starter heat soak and associated problems of starting a hot Pontiac engine.

[Sirrotica]

Originally Posted by rohrt

Sirrotica,

This little bit of info came from the carbshop link on the gas milage thread. Seems to say the same thing you are saying, and both hit the nail on the head.

HARD STARTING, HOT

Difficult starting of a hot vehicle from 5 minutes to an hour after the engine has been operated, can be caused by the volatility of modern fuel. If you have this problem; try using the following method to start the engine: DON’T touch the footfeed (VERY important). Crank the engine over from three to 5 seconds (different vehicles will respond to different times); and then GENTLY (so as not to activate the accelerator pump) press the footfeed approximately 1/3 of its travel. The engine should start, and may run rough. Run the engine at a high idle for about 10 seconds. This issue is caused by volatility of modern fuel. Once the engine has been shut off, the gasoline is heated by the latent heat of the engine, and percolates the fuel from the bowl into the throttle area, forming a mixture that is too rich to fire. If you push the footfeed to the floor (as has been the traditional method of “unloading” a flooded engine) the gasoline continues to flow into the engine (again due to the volatility). By not touching the footfeed, you do not open the throttle plates, and the engine will pump the overrich mixture out of the tailpipe. Once the overrich mixture has been alleviated, gently opening the throttle will allow the engine to start.

I like the wood ones but I would rather have a four hole one that is 1/4 inch.
I'm looking at getting the PHENOLIC 4 hole unit if I can find one.

I also see they make a heat shield. I have seen these before but are they worth it?

I have never bought a heat shield, but I have made my own and they helped a bunch. I would say anything you can do to keep the carb and fuel lines cooler is going to help the problem.

[rohrt]

So far my thoughts are:

*Look for the regular 1/4 inch gasket that I should have but don't, then try a 1/4 phenolic spacer.
*Maybe try the heat sheild from Mr Gasket
*Insulate the fuel line to the carb
*Maybe fill the head with aluminum
*Hog out the opening of the stock intake so I have more choices of different spacers.
*Get a RAM AIR intake open the scoops.

Any other ideas that I have missed?

[Sirrotica]

Only thing not covered is go junkyard scrounging and get one of those Nissan under hood fans that they used to stop their hot soak problem (circa late 79 early 80s). The way it worked was when the ignition was turned off a relay with a timer energized and ran the fan for about 10 minutes to cool the carb and manifold down. First time I saw one I thought WTH is this but it stopped their fuel percolation problem.

I almost forgot one other thing I had to do to my fathers Econoline based RV he bought in AZ. Someone had removed the small block engine and substituted a 351/400 modified engine in it's place and the modified engine was wider they had to trim the floor around the engine to get it to fit as it's wider than the small block engine originally in there. It was so wide they sectioned the doghouse and welded a piece in to make it wide enough to cover the engine. Well being it fit so tight there was precious little room for air to get in and around the engine and they could only drive it at night as the fuel boiled going down the road and it shut the engine off.

To fix it I made a scoop below the front bumper and run a duct from the scoop up over the radiator and made a piece of sheet metal surrounding the front of the carb to shield it from the air off the fan and then I ran the fuel line inside the duct to keep the fuel cool all the way to the carb. It worked like a charm and dad picked up 1 1/2 MPG after the mod and even in the desert it never boiled the fuel again while they owned it. Picking up 1 1/2 MPG on a box with wheels was like 20% improvement over the previous mileage.

[rohrt]

Well i stoped by Sperry Engine the local machine shop we have. I saw the 1 inch phenolic spacer they had. It looked nice and was a 4 hole type.

I picked up a felpro quadrajet gasket for under the carb. The gasket is about 1/4 inch thick but not a 4 hole gasket, just open in the center. Wouldn't you think this would not flow as well as a 4 hole gasket? I'm wondering if I should stick with this or go with the 1/4 phenolic that they told me about, assuming its still a 4 hole unit?

While mentioning my heat soak issue with them they suggested the new felpro intake gasket with the asbestos heat crossover blocking material. I didn't realize they made these. That seems like a no brainer to get one them on order. My question on them is, do they hold up?

[grandville455]

If you are blocking the intake cross over. yes they work, but no they don't last!.. better off to do like i did with my old heads and use a .062 plate of aluminum or steel would work too in that area. Even tho cliff did that carb it is 2 yrs old.. it could be sticking in the needle area.. My one q-jet did exactly as urs after running and then let it sit for 10-30 minutes it would just roll until u put the foot to the floor then it would fire off..A too high of float setting will do this also.

[kate`s67gto]

Just went through similar issue. Bought a Felpro spacer 1/4" thick with the two small holes at front and open at secondaries. The gasket is all open. This has seemed to alleviate the hot starting issue after 15 minuets of heat soak to carb. Had to do this after going to a 17059272 Qjet Carb and new cam. This is when the hard start issue started. Did not experience this issue with a Edelbrock carb and old cam there was no carb spacer with it. Engine temps are the same with the Qjet as the Edel 180* rose to 200* after shut down. Fired right back up after 15 minuets of sitting. Will know better Saturday night after car sits for 2 hours or so. I hope this is the answer as i am off to Syracuse next Thursday. Hope your issue resolves easy with a spacer.

[rohrt]

Originally Posted by kate`s67gto

Just went through similar issue. Bought a Felpro spacer 1/4" thick with the two small holes at front and open at secondaries. The gasket is all open. This has seemed to alleviate the hot starting issue after 15 minuets of heat soak to carb. Had to do this after going to a 17059272 Qjet Carb and new cam. This is when the hard start issue started. Did not experience this issue with a Edelbrock carb and old cam there was no carb spacer with it. Engine temps are the same with the Qjet as the Edel 180* rose to 200* after shut down. Fired right back up after 15 minuets of sitting. Will know better Saturday night after car sits for 2 hours or so. I hope this is the answer as i am off to Syracuse next Thursday. Hope your issue resolves easy with a spacer.

That is great to hear. Thanks.

Grandville - where do I get a .062 sheet of metal? That seems pretty exact.

[grandville455]

Don't remember exactly? U could try McMaster -carr.. they have alot of different sizes of aluminum and steel

[bnorris_74]

A stainless steel putty knife sacrificed for a piece of metal large enough to cover the hole will work.