Hard starting when hot - vapor lock?
 

Our SPF MKIII has had this issue since it was new. Once it gets up to temp, if you let it sit for more than a couple of minutes, it struggles to start back up unless you let it fully cool down. We have found a rather annoying work around of leaving the hood open in this situation. It has a windsor/dart based 427 small block with a 850 mighty demon (phenolic spacer) and a rear mount electric pump with no return line. Headers are ceramic coated.

Is this vapor lock? Is it a common problem with these cars?? We are thinking about running a bypass style regulator to address this but are concerned the problem is in the float bowls and not in the fuel lines. Anybody been down this road before??? Looking for some ideas...

Have you pulled the air cleaner to check if you are getting fuel in the carb?

No, but judging by the behavior of the engine before and after it starts in this situation it seems very obvious it is struggling to get enough fuel. Car runs and starts great under all other scenarios although we are getting intermittent weird noises/vibrations at low engine speeds that we have narrowed down to either the fuel pump or regulator.

BTW, we are in Michigan so ambient temps are not that high. Normally around 80 and rarely over 90. This also means we are not able to go out and reproduce this scenario anytime soon. I was hoping this would be a common problem with a proven solution but maybe that is not the case.

Depending on the type of ignition system your running it could be related as well. Timing and ignition can sometimes mimick the fuel issues as well. Not likely but just dont rule it out.

Put some cardboard in front of the radiator and get the motor hot...you might be able to reproduce the problem in the garage.

I used to have the same problem with my SPF. I wasn't starving for fuel, the heat under the hood was boiling the fuel in my carb when I shutoff and flooded the engine through the vents. If I held the throttle open and cranked, it would eventually start with a big cloud of black smoke. Now, at least 25 seconds before I shutoff the engine, I turn off my electric fuel pump and drain the carb by letting it idle. I also installed an Edelbrock carb insulating gasket. With my 557, I don't have enough hood clearance to use a wood spacer. No more problem. Worth a try.
Eric 1151

When you say hard to start, I assume it cranks normally, but just won't fire?

I had a similar problem. I resolved it, after a good deal of frustration, by replacing a large diameter air cleaner with a much smaller diameter air cleaner during "winter gas" season.
I THINK that winter gas is more gaseous than summer gas and it was evaporating in the fuel bowls due to air cleaner trapped heat after a drive.
Mike

On cars I have worked on with problems similar to yours, the fuel problems went away when we installed a Mallory 4309. We install the bypassing regulator after the carb. This keeps the carb and the fuel in the carb much cooler. Also if you have a fuel log or worse a fuel filter bolted to the engine (like the original 427 cars) you will have vapor lock problems.

http://www.jegs.com/i/Mallory/650/4309/10002/-1

I feel you are dead on. What do you suggest with a mechanical fuel pump? Thicker gasket between carb and manifold?

I have been through some of what your are experiencing with my own carbuerated cars and those of other rodders. MOst of thetime it is vapor lock. It could also be the carb or timing. I have found what Tom K is suggesting is rigt on as to the fuel pump and the location of the regulator. I would add that the return line will help your car run better CONSISTENTLY, so even if ithis is not the exact problem, I would encourage you to put one in with a high end fuel regulator with an accurate fuel pressure gage installed.

Answering a few questions would help give you some suggestions.

Have you checked your fuel pressure? If so what is it?

Do you have a fuel regulator. Is it adjusted to the proper fuel pressure for your carb. Too much fuel flowing to the carb at start up is just as bad as too little.

How old is your electric fuel pump and what brand is it? Is it mounted correctly? Some units need to be mounted so that the unit is horiz vs vertical. Also they need to be mounted on the chasis rail so that the incoming fuel line is at a certain distance from the fuel tank and cannot have a point in it that is lower than the inlet of the electric fuel pump. If installed incorrectly they will cavitate for awhile causing a hard start problem. That's why it's a good idea to know what your fuel pressure is at the carb or fuel log at strat up and while running.

Have you noticed that when the car is off and sitting for a while, and you first open the fuel cap, that your hear a slight sucking sound for a split second, like there is a vacumn in the tank? We have found a couple of SPF cars that had a problem with the gas tank venting properly. It caused a vacumn in the tank especially on hot days and caused problems for the fuel pump.

What size is the fuel line?

Have your floats in your carb been adjusted to the proper height?

What is your vacumn at idle?

Have you adjusted the idle circuit lately?

What type of fuel does the area of Michigan have that you live in when you experince this problem? Oxygenated or not? We have found that some oxy fuels in Arizona, boil at 140F. That means that they can boil in the fuel lines and/or float bowls on a med warm day. Different parts of AZ have different oxy fuels and other parts don't have oxy fuels.

What type of fuel log are you using?

Have you checked ALL of the the fuel filters? Besides an inline unit, sometimes there is one in the fuel logs and the inlet of the carb.

What is your initial timing?

I know it is a lot to consider, but each one could influence your situation.

I would say knowing that your fuel pressure is correct is the first thing you should check out.

Thanks for all the feedback.

The fuel pressure is at 6.5 pounds as recommended by the engine builder. The regulator (Aeromotive) has a gage attached and the readings are consistent.

The electric fuel pump is two years old and also Aeromotive properly spec’ed for my set up. I have talked to the Aeromotive application engineers about my specific needs. I believe it is mounted correctly in the vertical position and on the frame below the tank. I do have a 100 micron filter between the tank and the pump where half the diameter of the filter is (barrel shape) geometrically below the pump pick up. Pump cavitation (the noise we are hearing) is a concern and this may be an element. The cavitation happens after full warm up on warm days, at low engine speed and usually in a turn – not a hard turn. You can hear it as it affects the regulator which is mounted on the firewall. I do not believe that the cavitation and the “vapor lock” (if that is what it is) are related.

I have checked the tank venting and could not detect any problems. Just to be sure I added a vent to the cap deep in the labyrinth above the gasket so as not to leak fuel. I think this can be checked off.

Fuel line is the 3/8 inch braided stainless.

Floats and carb has been inspected and tuned by a pro within a year. He believes that the problem is vapor lock as well. He theorizes that the Superformance fiberglass body is helping to insulate the heat (He wants to sell me an aluminum body).

Can’t tell you off hand what the vacuum is at idle, I have pretty bad vacuum at low engine speed – overlap I’m sure. In a hard stop with the clutch in the engine will normally stall for lack of vacuum.

I have not touched the carb settings since the pro work. The problem has existed from the beginning, before and after a number of professionals have worked on different parts of the drive train. None have worked specifically on this problem.

I’m going to guess Michigan fuel is not Oxygenated. Don’t know for sure.

The fuel log is just an Aeroquip set up with “T”s, see attachment.

I check and service both filters regularly, 100 micron before the pump and 10 micron before the carb. The problems existed before the filter installations.

Total timing is 34 degrees BTC. Don’t know off hand what the initial timing is. It was set by a very experienced professional about a year ago.

Have you tried leaving your cooling fan on for a few minutes after shutting it down? I had similar issue early on and on real hot days I let the fan run for a minute or two before I walk away to get all the heat out of the engine bay.

It appears the fuel is boiling out of the carburator on my two engines. I have always been told a non metallic spacer between the manifold and carburator will aid in reducing the symptoms. I guess as long as you have hood clearance there is no down side. All my marine engines had them and yet some of them still vapor locked.

I guess with an electric fuel pump and recirc line in reality you are using the gasoline to cool the carburator as it recirculates from the tank to the carb.

In my opinion electric fuel pump suk on a carburated engine. They are noisy, fail, require unique locations so as not to loose their prime, need additional equipment such as regulartor and a power source. I would rather deal with vapor lock then the headaches associated with a "cool" noisey electric fuel pump.

ive had the same issue on a few engines. timing was to advanced and was hard to start when hot. but that made hard starts cause the engine didn't want to turn over. haven't read if thats what is happening to you or not.

also, had one that the starter was getting heat soak. and it didn't want to start when it was hot too. also hard to turn over. i guess if your not having a hard time turning the engine over, than this isn't your problem.

another thing i would check is this, take it for a good ride, get to operating temps, and normal driving.
when you get home before you shut it off, pull the filter off the carb, and let it idle.
then, shut it off and look down the carb and see if your getting fuel leaking down the bowls. had that happen a few times in my 414w in the cobra.

This is your answer. My car does the same thing. I just put the pedal down to give it more air and it fires right up.

I chased a similar issue in my SPF all summer. I was left stranded more than once. I finally narrowed it down to the msd 6am was intermittedly working. The car would start fine cold and run for as long as you wanted until you **** it off. It wouldn't restart until it cooled down for hours. Finally the last time it just never restarted.
When it won't restart, check for spark(when hot). This drove me crazy all year. Put a new box in and it starts easier than ever before. Makes me wonder how long the box was acting up.

All good suggestions from all posts. I had simlar concerns with several of my past SPFs. One with 514 was the worst. Went to 1/2 inch fuel line, aluminum thin spacers under the carb, regulator and line off the block which fixed the concern. One car I did put a return line on which did keep the fuel moving throughout the system and keeping it cooler. That car had an Aero Automotive fuel pump and regulator also.

Thanks again for all the posts on this.

Just to clarify, it turns over fine, just refuses to fire or stumbles without fully starting when this happens. We have tried running the fan while it sits with no luck (unless the hood is open too).

Had the same trouble. Made a heat shield and all my problems solved.:)

http://s540.photobucket.com/albums/g...DSC02558-1.jpg

I had a problem with the fuel in the "squirter" boiling and squirting into the carb. My mechanic tapped a small hole in the squirter reservoir to relieve the pressure when the carb heats up. Problem solved.