Hard starting when hot - vapor lock?

[tcrist]

This may be a long shot but years ago my Grandfather had the same issue with an older car that he had. Found out that the coil was loosing spark when it was hot. Changed the coil and never had that problem again.

Just a thought,

[Rick Parker]

This is a fuel related problem. The floats are probably just a little too high and when the carb heat soaks after shutdown the fuel expands, percolates and drips out of the venturi boosters, and onto the throttle plates, probably the primary side. It drips past the throttle plates because they are slightly open (idle position). Then the moment you tip the throttle any additional fuel that has collected on the throttle plates and not evaporated pours into the plenum in raw liquid form and creats a massivly over rich condition that wets the plugs and takes several seconds of cranking to overcome. To verify this, bring it to full operating temp, shut it down and pull the air cleaner and watch for dripping fuel within a very few minutes. Take corrective measures. This can also happen with Webers. Fuel levels are critical and can play tricks on you.

[Ronbo]

Haven't heard it mentioned, but you could use freeze spray and cool different (suspect) items down to narrow down the culprit.

I also have one of those Snap-on air powered choke testers that's pretty handy for this type of stuff. Don't ask me how it works but you put shop air in and it blows hot air out one end and cold air out the other with no moving parts.

OK, did a little digging. Snap-on no longer sells it but here is one: http://www.exair.com/en-US/Primary%2...es%20Home.aspx

[nxfedlt1]

Its the poor vapor point of the fuel causing it to boil out. I took the advice from above and watched it come out of the bowls. I had the same problem and here is what I did:

- mix race fuel to try and negate the effects of our ethanol 91 octane fuel
- run the fan before and after I turn it off to move the hot air
- oddly, changing to an AGM battery greatly helped over the stock junker that came in mine

[tcrist]

Ronbo,

Pretty neat looking tool. Don't know how it works but as long as it does, who cares if I know or not.

[madmaxx]

Thanks Rick Parker!!!!

I checked my float levels, primary was just at bottom of hole, lowered by 3/16 of a turn, secondaries were high lowered by 3/8 of turn. Both are now below bottom of hole by 1/8" inch. Ran it up to 6K a couple time as usual excellent power. Tested about 5 times yesterday and fired right up even after sitting 30 minutes. Gave about 1/4 gas pedal and cranks up great. While it sat I would sniff the hood scoop LOL and never got a whiff of gasoline. In the last week between PatrickT tip and yours I have improved cold and hot start characteristics 100%.

[Zoom This]

Randy did the same thing by same mechanic as I did. Had the very same problems with my 418W when the car was new 7 years ago. Crappy hard starting and gasoline odor in garage when parked. Had the carb drilled in metering block to relieve pressure when motor was hot, mitigating gas drooling into intake manifold making motor hard starting when hot. Bad for rings too with gasoline wash down on cylinders. I added a phenolic 1/2 inch spacer under carb also. That fixed the flooding condition forever. Running the motor for about a minute with electric fuel pump off will help your issue also by draining the carb.

[cdog]

Originally Posted by Eric 1151

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.

I do this for my 521. If it sits less than 10 minutes or so, I make sure to hold the throttle open for about 30 seconds when I get in. It will fire up, but does shoot out some smoke. It only happens in the heat.

When I drove it in VERY hot temps, say 110+ in Vegas, it really didn't want to idle and had significantly more trouble starting. Idling in traffic it did not like. If I moved to Vegas, I guess I'd need to address this.

My 14" air cleaner doesn't leave much room for a carb spacer. Maybe 1/4"? I guess I could look at doing that. Or lowering the floats.

[Learjockey1]

I have Holley's, but check to make sure the little bendable rod that connects the primary shaft linkage to the secondaries is adjusted so it completely closes the secondary butterfly shaft when the carb primaries go to idle. If not adjusted correctly the secondaries are left a little open causing a lean starting condition with the engine hot. I do not believe you will not see this adjustment in any rebuild book or instructions. I never did, I noticed it when rebuilding the carbs. This fixed my problem a few months ago but never I came back on the thread to mention the fix.

[601HP]

Originally Posted by Rick Parker

This is a fuel related problem. The floats are probably just a little too high and when the carb heat soaks after shutdown the fuel expands, percolates and drips out of the venturi boosters, and onto the throttle plates, probably the primary side. It drips past the throttle plates because they are slightly open (idle position). Then the moment you tip the throttle any additional fuel that has collected on the throttle plates and not evaporated pours into the plenum in raw liquid form and creats a massivly over rich condition that wets the plugs and takes several seconds of cranking to overcome. To verify this, bring it to full operating temp, shut it down and pull the air cleaner and watch for dripping fuel within a very few minutes. Take corrective measures. This can also happen with Webers. Fuel levels are critical and can play tricks on you.

I had exactly the same issue in the past. When the engine was hot it would only start with the pedal fully to the floor, and it was still difficult to start.

After I lowered the floats in both carbs, the problem disappeared. That was about 1,000 miles ago.

I hope your fix is as easy.

David

[BAsque1]

Wow this is the perfect description of what I am experiencing (still) with my car. It is equiiped with a 427 FE s/o. I have installed the following:
1. Brand new high torque starter
2. 1/2' phenolic spacer (not higher due to hood clearance) the carb is a Holley 770cfm.
3. Removed all-together the useless and faulty fuel pressure regulator, not needed if you run a mechanical pump which delivers 7lbs consistently.
4. New 100 micron in line-filter element.
5. Added water-wetter to the coolant so as to reduce the working temp to 212 degrees.
6. The tank is vented
7. Spark plugs changed
8. Timing is fine.
9. Cooling fans are left on until they turn off themselves via thermostat when engine is turned off.
10 Always use octane booster with every fill up.

However, all this said if I run the car for at least 1 hr and turn it off it will be difficult to start, engine turn fine but it is starved for gas.
Also it is a pain in the rear if I come to a light stop, and must keep the idle above 800rpm to preclude stalling.
I am stomped with this. I am in NY and summers could be 90+ at times. I used to have a similar problem with 123 GT Volvo in Puerto Rico years ago but it was solve by installing a cool can whioch I ran with dry ice and/or isopropyl alcohol.

I don't know what else to do, I have a very professional mechanic who has been analysing this case with me and we are getting very frustrated with this. Has anyone come up with any new thoughts which might work?

My next thing to do is cover the gas lines near the engine and carb with heat insulation material and installing a cool can. Will have to carry an ice cooler in the trunk to replace the ice when melted :-((
Tks guys
Lou

[Rick Parker]

Are you sure that fuel is not percolating out of the fuel bowls from heat soak and onto the throttle plates thus creating an overly rich condition making it hard to start? Just a thought?

[BAsque1]

Originally Posted by Rick Parker

Are you sure that fuel is not percolating out of the fuel bowls from heat soak and onto the throttle plates thus creating an overly rich condition making it hard to start? Just a thought?

IT could be, however, if it is a hot day and at a slow cruis or at a traffic stop the car would stall and it is a pain to start. I just got back from a show tonight and someone suggested to install a fan shroud on my electric fans so as to redirect more the air towards the engine.
At this point I try anything
Tks
Lou

[PANAVIA]

The other think I do is insulate any hard metal fuel line with the space fibreglass mylar stuff - keeps the fuel cool if you are using a mechanical pump

[DSM351]

I'll tell you I had a terrible time, until I set my idle at 1000-1200 RPM, solved a ton of problems.
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