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Re: Exactly WHY is my car hard to start when warm?
[Re: BossRide]
#328180
05/26/09 09:10 AM
05/26/09 09:10 AM
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Joined: Mar 2007
Posts: 3,277
West Coast, USA
jbc426
master
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master
Joined: Mar 2007
Posts: 3,277
West Coast, USA
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I had this problem and was also baffled until I spoke with Doug Dutra, the famous slant six guru. He explained what was happening:
When you shut off a warm engine, the heat from your engine's intake manifold is boiling the fuel in your float bowl and causing it to drip into the intake etc causing an excessively rich condition. This happens because the fuel percolation drops the float and allows more fuel from the still presurized fuel line, between the fuel pump and the needle and seat to flow more fuel into the carb to bring the float level back to normal. This continues until the pressure in the fuel line between the fuel pump and the needle and seat goes to zero. In the mean while, a significant amount of fuel has now percolated out of the carb AND the pressurized fuel line between the fuel pump and the carb (until the presure is released by the process). Quite a bit of gas ends up in the intake every time you shut off a hot motor.
This is how you fix it:
#1 Use two gaskets and a sheet of aluminum to isolate the carb from the intake manifold. This will likely require longer carb studs. Be sure to check for hood clearance. (this helped a lot, but did not eliminate the problem completely)
#2 Install a fuel return line from a 3-nipple fuel filter, which is available from any autoparts store between the fuel pump and the carb, and the fuel tank. The third nipple on the 3-nipple fuel filters has a metered orifice to limit the amount of fuel it flows. I had to install a return line and a 2 fitting fuel sending unit on my 68 slant six car to complete this installation. The car had an original 5/16 fuel line, so I added a 3/8ths line as the main fuel line and used the 5/16ths line as the return. I bought a dual fitting fuel sending unit for less than $50 off ebay, ran the lines, installed the 3-nipple filter. I never had a hot start problem again.
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's
1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
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Re: Exactly WHY is my car hard to start when warm?
[Re: jbc426]
#328181
05/26/09 09:23 AM
05/26/09 09:23 AM
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Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
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that's good stuff, #1 for the heat & #2 to release the psi
live every 24 hour block of time like it's your last day on earth
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Re: Exactly WHY is my car hard to start when warm?
[Re: RapidRobert]
#328182
05/26/09 09:41 AM
05/26/09 09:41 AM
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Joined: Mar 2007
Posts: 3,277
West Coast, USA
jbc426
master
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master
Joined: Mar 2007
Posts: 3,277
West Coast, USA
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Yah, that Dutra is something else! If you don't want to spend the money on a new dual nipple fuel sending unit, you can drill and add a fitting to your existing sending unit by using those brass hardware store parts, some cheap aluminum return line and the fuel filter. The total cost is around $40 or less.
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's
1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
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Re: Exactly WHY is my car hard to start when warm?
[Re: 1_WILD_RT]
#328184
05/26/09 10:09 AM
05/26/09 10:09 AM
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Joined: Jan 2003
Posts: 10,640
S.E.Ohio
Magnumguy
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 10,640
S.E.Ohio
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Quote:
Seriously try a heat shield, it deflects most of the engine heat around the carb...In order to clear the linkage I had to trim one corner a little but it works great... Not a pretty as some other spacers but more effective & I care more about function as I like to drive my car... And if your gonna drive it it's gotta start..
Where'd you get the spacer (shield) on the right?
I wonder if you don't have your floats too high. Every Magnum I've owned (and it's been alot) would start pretty much the same hot or cold, except one of my current driver one. It will smoke black some when it starts hot, rolls over OK, but takes 2-3 seconds, but almost instant cold.
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Re: Exactly WHY is my car hard to start when warm?
[Re: RATTRAP]
#328186
05/26/09 10:28 AM
05/26/09 10:28 AM
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Joined: Jan 2003
Posts: 1,978
Southaven, MS
BossRide
OP
top fuel
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OP
top fuel
Joined: Jan 2003
Posts: 1,978
Southaven, MS
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Quote:
Prob not heat as much as your timing is off
That has crossed my mind... maybe I'll double check it... with the Holley and intake, mild cam and headers, should I set it different that the stock specs?
It was set when the engine was installed and I forget exactly what we set it at, it's been almost two years.
Funny thing, the old tired 2bbl 318 did the same thing... start great, spin over and over when hot. It acts like the gas has left the carb, and it will catch slowly, but not be skippy or stumble, just light off slowly.
The Blue Goose
My instagram: Bossride
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Re: Exactly WHY is my car hard to start when warm?
[Re: rss]
#328188
05/26/09 11:07 AM
05/26/09 11:07 AM
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Joined: Oct 2006
Posts: 4,165
Florida
cataclysm80
master
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master
Joined: Oct 2006
Posts: 4,165
Florida
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Quote:
This might make you feel better.
Mine has gotten to the point that it won't even start when warm. Nearly had it towed last week when I shut it down to fill up with gas. By the time the tow truck arrived it started and I was able to drive home. Fires up great cold, runs great, but if I turn it off and try to restart hot I can just crank away till the battery is nearly dead.
My original 1938 ford flathead does that same thing. I've been told it's caused by a bad coil that fails when it gets hot.
Check your spark next time it happens.
Tav
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Re: Exactly WHY is my car hard to start when warm?
[Re: 68Bullit]
#328190
05/26/09 11:32 AM
05/26/09 11:32 AM
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Joined: Feb 2003
Posts: 12,675
Columbia, CT
moper
I Live Here
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I Live Here
Joined: Feb 2003
Posts: 12,675
Columbia, CT
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What does the engine have for cylinder pressure? As bad as the gas is, I have yet to have an issue like this on any of mine or customers'. We have the 10% ethanol fuel, have for 4 years now at least. My truck has run at 220° before when working, and 45 minutes after parking, it turns over 2-3 times and it's fine. I find most of the issues with starting are a result of tuning or lack of cylinder pressure due to wear, or camshaft choice, or camshaft timing. Much more so than percolation issues. JMO.
Well, art is art, isn't it? Still, on the other hand, water is water! And east is east and west is west and if you take cranberries and stew them like applesauce they taste much more like prunes than rhubarb does. Now, uh... Now you tell me what you know.
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Re: Exactly WHY is my car hard to start when warm?
[Re: Rug_Trucker]
#328194
05/26/09 02:08 PM
05/26/09 02:08 PM
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Joined: Mar 2007
Posts: 3,277
West Coast, USA
jbc426
master
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master
Joined: Mar 2007
Posts: 3,277
West Coast, USA
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Quote:
Quote:
I understand the fuel boiling and evaporating out the vent tubes, but how does any fuel get into the engine to cause a rich condition? It seems something would have to force the fuel thru the jets and out the boosters.
John
Slant sixes are the worst. Fuel line is routed like crap! Even before they started adding alcohol to our fuel my 72 had to be held to the floor to start hot. This was on 50* days too!
Rerouting the fuel line worked excellent! No return line needed. My 74 slant Dart has the same problem.
Fuel injection hose with the fuel injection clamps routed over the valve cover with enough slack to pull the cover to set your valves works. It is in a sticky on www.slantsix.org in the engine section.
I have watched hot steamy gasoline boil and dribble into my hot intake many times.
Rerouting the fuel line was my first attempt at getting rid of this problem. Then I did the heat shield, which I cut out from 18 gauge sheet aluminum from Orchard Supply Hardware, and that worked for all but the hottest days. Finally, I ran the return line.
In addition to eliminating the hot starting issues, the cooler carb and fuel gave me a noticable performance improvement.
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's
1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
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Re: Exactly WHY is my car hard to start when warm?
[Re: jbc426]
#328195
05/26/09 02:56 PM
05/26/09 02:56 PM
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Joined: Jan 2005
Posts: 1,647
IL
71383beep
top fuel
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top fuel
Joined: Jan 2005
Posts: 1,647
IL
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I too experience this problem. We also have the mandatory 10% ethanol blends and have come to the conclusion that a a vapor separator is probably needed. It sucks though. Go for a cruise. Car starts and runs just fine. park for a half hour and she won't start. Pedal to floor crank and eventually she'll fire. Very frustrating. I got a separator from the last swap/show. Now I just need to cut my nice new steel braided carb supply line...  and install a return line.
'73 GK6 Challenger Rallye - 340 4-Speed
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Re: Exactly WHY is my car hard to start when warm?
[Re: moper]
#328196
05/26/09 07:10 PM
05/26/09 07:10 PM
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Joined: Aug 2007
Posts: 902
Seattle, WA
rss
super stock
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super stock
Joined: Aug 2007
Posts: 902
Seattle, WA
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Quote:
I find most of the issues with starting are a result of tuning or lack of cylinder pressure due to wear, or camshaft choice, or camshaft timing. Much more so than percolation issues. JMO.
If you are correct, then why would the car fire up instantly when cold but not start hot? Do poorly tuned cars run well cold???
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Re: Exactly WHY is my car hard to start when warm?
[Re: BossRide]
#328199
08/30/09 12:46 PM
08/30/09 12:46 PM
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Anonymous
Unregistered
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Anonymous
Unregistered
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Bump...
My '74 Fury 400 was a hot start and flooding nightmare when I went to a Thermoquad and Edelbrock intake. I swapped out the steel line for an insulated stainless mesh covered fuel line from the mechanical pump to the carb. Of course the composite body on the Thermoquad was designed to eliminate heat soak transfer to the fuel bowls but even with that, the big block generated so much heat that the only cure was to keep the fuel line cool. You not only cook the fuel in the bowls but the fuel gets cooked in the line from the pump to the carb. My only problem now is COLD starting! Always has been a bear... crank for 20 -30 seconds and then runs like cr*p for 4 minutes... IF it even starts.
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