Fuel Problem: Vapor Lock?

[ohekk]

I'm bringing this up from another thread hoping to find a cure!

Having a problem with what seems like vapor lock.

Runs good at highway speed but when I get into town or run slower, engine temp climbs to 200-205. soon afterward it will stall and will not restart until after a 15 minute cooling off period.Then it will fire right up.

Note: also happens after I stop and shut 'er down...I get a couple of miles down the road and it'll stall.

It's getting both frustrating and embarrassing.

Thought maybe it was a bad coil. replaced coil.

last time I took a small bottle of gas and dumped a little in the carb...fired right up!

Stewart Warner Fuel pump - 6 PSI
3/8 alum fuel line insulated tank to carb

Could be this $#@%&*&$ reformulated gas the EPA makes us burn!!!!

have not tried the racing fuel suggested a not real practical where I live.

any other ideas?

Thanks
Tom "OHekk" Hekkers

[chopper]

Difficult to say without knowing what type of carb, cam, distributor, ignition, etc you're running. However, just off the top, I would be surprised if the coolant temperature you're seeing (205 degrees F) would be enough to cause vapor lock. It sounds like you feel it's a fuel starvation problem. If it is, when the car stumbles, check to see if your accelerator pump can squirt some gas into the carb. If not, the bowls are empty and I'd go from there. I'd probably be more apt to look at the fuel pump to see if it's running a little weak after it runs for a while and heats up. If there is fuel in the float bowls, the problem is more likely ignition related. You may then want to check your ignition system to see if the spark is getting weak as a result of overheating of the ignition box or similar problem. Where is your ignition system located? If it's under the hood, it may be overheating. I have mine (MSD) mounted under the dashboard on the passenger side, to keep it out of the hot underhood environment. What type of distributor are you running? I originally had a Mallory Unilite optical pickup distributor, and had random problems similar to what you describe. The Unilite optical modules can't take the vibration and heat of the engine and I got random problems. I eventually trashed it and went to an MSD billet. Just a couple of ideas. This type of problem is difficult to track down. I wish you luck.

[Bob Putnam]

Tom,

Are you using an electronic ignition system? Where is the module located?

[BJGreen]

When the problem first appears, unscrew the sight plug from the fuel bowl and check that it just barely runs out. Fuel bowling in the system or needle and seat problems will cause a large quantity of fuel to pour out. Careful of getting fuel on the hot motor. Also, open the gas tank and see if it is highly pressurized.

If no fuel pours out, watch the accelerator pump discharge nozzles in the carb when you work the linkage. You should get a good quantity of fuel squirted out.

The roadside procedure for checking a Mallory Unilite module is at
http://www.centuryperformance.com/mallory/unitest.asp

The procedure for MSD is at
http://www.msdignition.com/

While this may not do you any good, I suggest these procedures because I have experienced similar problems with my own cars and the problem has tended to be one of these.

Good luck.

[ohekk]

Thank you all... I don't want to mislead anyone...this problem I'm having is NOT with my Cobra (ready for paint but not on road yet) but with my 34 Ford Roadster.

Running a Chrysler 392 Hemi,Isky cam, Weiand 2x4 intake with a pair of Edlebrock 500 CFM carbs 10-1 compression

Stock Delco dual point distributor,external ballast resistor and MSD coil.

I've replaced points,condensers and now the coil.

When it stalls, there's a strong blue spark at the coil wire. accelerator pump only results in a sputter of fuel.
as stated earlier, I poured a little gas down the carb and it'll fire but won't continue to run until the obligatory 15 min cool down.

So...I think we've narrowed it down to fuel related.

also it's been persistant, I've tried 3 different electric fuel pumps,insulated the lines but no change. Different brands of gas and different octane levels.( Have NOT tried the racing gas mix yet as suggested in another thread)
I've never had to before in any of my other carbureated cars but should I consider a fuel return line ?

Any other ideas?

Tom
PS: you may be asking WHY are you running a STOCK distributor/ignition?...Honestly...space! the Hemi is a REALLY tight squeeze...would have cut the original fire wall

[chopper]

Is this a new problem with a car that's been running OK up until now, or is this something that began after some equipment change (new carbs, etc.)? That is, can you isolate and correlate the appearance of the problem with some modification which was performed? For example, did you recently replace something which resulted in rerouting of fuel lines under the hood, and shortly afterward notice the stalling problem? Keep in mind that the failure mode may have been added during cooler weather and is just now appearing with the onset of summer temperatures. If you can correlate it to some particular activity, it will narrow down the list of possible offending equipment.

Are both carbs manifesting the fuel starvation, or only one? Does your setup use both carbs equally throughout the rpm range or is one the "primary" carb? If either of these is true, you might swap carbs and see if that fixes the problem; this would imply the problem is in one carb and would suggest a teardown of the offending carb is in order.

Have you checked or changed your main fuel filter lately? For that matter, have you checked to ensure that there is no debris in the fuel line or around the pickup in the tank? It is possible that you may have picked up some corrosion in the fuel tank over the winter due to accumulated water in the tank, which may have led to the transfer of scale or rust throughout the fuel lines. My car had a steel log manifold installed from the previous owner and it turned out to be unprotected on the inside; when I removed it the first time I found it to be partially clogged with corrosion. I'm not all that familiar with Edelbrock carbs, but I seem to recall that they have small internal scintered bronze fuel filters which may get plugged with debris; have they been cleaned lately? As you can see, I'm trying to make sure that you have unhindered fuel flow to the carbs as fuel line blockage is one of the things which can cause this type of problem. Hope this helps.

[ohekk]

Bob,Chopper & BJ,

You've given me much to consider!

New problem? NOPE from day #1 hence the frequent fuel pump changes

New Modification? NOTTA

Plugged fuel filter? Changed new with each pump ( With arrow going in right direction

Carb set up: both primarys open simultaneously, secondaries open progressively. (NEW Carbs)

Scale in tank? New Poly tank

Starvation? I kinda ruled that out as I don't have a problem at high RPM/Speed only at low speed.
..or am I missing something?

so far my best remedy is to drive fast and avoid congestion

Thanks again guys

PS> Chopper: I'll have to check acellerator pump on both carbs...i think it's both

[Bob Putnam]

Tom,

If you aren't using them now, at this point it would be worth sticking some insulating spacers under the carbs. It certainly sounds like a perc problem, although an odd one! I still worry a bit about the ignition system, though. (Just coverin' my butt... )

[Bob Parmenter]

Tom,

Vapor lock is usually more of a problem with mechanical fuel pumps mounted to the block, an electrical fuel pump, mounted remotely, is not very likely to heat soak. Also, one of the characteristics of reformulated gasoline is a lower vapor pressure to minimize HC emissions due to evaporation.

I'll go along with brother Putnam on the possibility of percolation since the Edelbrocks are an aluminum body, which is a good conductor of heat. The confusing thing is your comment about waiting 15 minutes for cool down. Percolation in the carbs SHOULD be more of a problem after shut down, when the coolant stops circulating and the engine heat soaks. Fuel flow, which has a cooling effect, also stops. It should take considerably longer than 15 minutes if it were percolation within the carbs.

One thing you didn't mention in your listing of fuel system components is a fuel pressure regulator. I'm wondering if, at lower speeds/lower fuel consumption, you aren't oversupplying the carbs and causing a bind in the float/needle components. With some percolation after stopping, the fuel level in the carbs drops to a point where they begin functioning "normally" again. It might be worth a call to Edelbrock's tech line to see if this is a possibility. They may have some other ideas as well and can give you some trouble shooting advice.

Good luck, this is a challenging one!

[ohekk]

Ok...I installed a 3/4"(aluminum) spacer under each Carb ...Still stalls. (float bowls are dry)

I tried 50/50 blend of pump gas/Race fuel, as recommended in another thread (stalled less frequently!

Presently running 100% Race fuel (oh baby! )... and NO stalls!

Ok... so maybe I found a remedy...but did I fix the problem?

Can anyone explain why Race fuel doesn't vapor lock like this EPA mandated @$#%* Reformulated corn based gas we're required to run here in SE Wisconsin?
Thanks,
Tom

PS: Watch out you California guys.. I've heard you'll be
required to run this RFG soon!!!

This winter I've got some fix'ems to do and will likely re-route the fuel line for more clearance from exhaust.

[chopper]

Just an observation on the spacers. Carb spacers generally serve two purposes: (1) to provide a longer (read: straighter) flow path to smooth out the turbulence of the air entering the venturis and (2) blockage of heat transfer between the intake manifold and carburetor. Aluminum spacers will accomplish #1 but will have essentially no effect on #2. If it is, indeed, a heat problem, you may wish to try some phenolic spacers which will help insulate the bottoms of the carbs from the intake manifold.

[Bob Parmenter]

Tom,

Re: your question on why "street" gasoline is more volatile than race gasoline; street gaso is formulated to accomplish a variety of things that it will experience in the consumers usage (read, compromises). One of the situations it needs to deal with is cold strarting, where volatility is important (although less so with FI systems). Race gas guys don't much care about cold starts for obvious reasons.
Ditto on the phenolic spacer.

[Leroy]

might just check if your fuel pump is putting out too much pressure and causing the float's valve to close,hence no fuel.
I had that problem till I installed a adjustable fuel regulator

[ohekk]

I follow the phenolic spacer reasoning but don't think it's a percolation problem.

I don't understand the fuel pressure corrolation:

If there were too much pressure, essentially shutting down the floats, why would the 15 minute "cooling of period" always work?

Just one of those things that makes you go Hhmmmmm???

For now I'm gonna run the race gas, enjoy the short crusing season here in WI, and re-route the fuel line come winter.

Thanks you guys!
Tom

PS: The Cobra is ready for paint but the whole project has
been put on the back burner due to other family
responsibilities. ("stones in the jar" as referenced from
another thread) I'm sure you understand

[ohekk]

I've been running trouble free for several years now with a 50/50 mix.

Just for the heck of it, I thought I'd try a tankful of our required reformulated gas. That's unleaded with 10% ethanol.

Lo & behold I made it about 20 miles away from home when the dreaded vapor lock occured just like before.

Yes...t's occuring at the electric fuel pump as the pump is distinctively quieter.

If I wait patiently at the side of the road for a 15-20 min cool down, it'll pump fine ( I can hear the difference in the pump) fire right up and I'm on my way.

anybody else having this problem?

OK ... now this: I've noticed some gas stations that offer "Ethanol Free" gas for "Recreational vehicles only"

I suspect this is intended for boats, ATVs and lawn mowers as I've heard that ethanol is not friendly to small engines.

I'll try some in my "Recreational vehicle" and let ya'll know.

[Tommy]

Tom,
I'm not sure the following explanation will work for your problem, but it happened to me and is worth considering.

I was running an electric fuel pump with a regulator built into the pump (Holley Red). That system regulates pressure with a spring controlled valve on the output side of the pump. When pressure in the output line exceeded the factory set 7 PSI, the valve would dump excess fuel back to the input side of the pump. Thus, when the fuel being pumped exceeded demand, a small amount of fuel would circulate continuously at the top of the pump, all the while absorbing heat from the pump. On a hot day, the combination of ambient heat and heat from the fuel pump would vaporize the fuel circulating above the pump and cause a vapor lock. It happened to me during a track day event, and I solved it temporarily by packing the fuel pump in ice. That is also a way to diagnose the problem. I solved the problem permanently by installing an unregulated pump and a separate regulator downstream from the pump. This regulator routes excess fuel back to the fuel tank.