I put a 1972 4.1L 250 1 barrel L6 in my 50. It runs great and has been doing good until the weather has warmed up. It starts like a dream when cold and no problem when it has time to cool down (engine temp below 170) but after an extended drive on a warm day and setting for around 15 minets to about 1 hour it will not start! It cranks OK and I can see gas in the carb when I pump the throttle and when it finally does start in doesn't seam to be flooded. I have put a 3/4" non-medal spacer between the carb and intake to help with the heat transfer upon someone's recomendiation but still no better results, I have rerouted the fuel line away from the front of the head. Been driving the truck for about 3 months without any problems with the exception of the days when the temps are over 80-85 degrees. Any suggestions would be appreciated.
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Hard start after hot soak L6
- Thread starter fielddad
- Start date
1951chevy1ton
Member
What thermostat?
I know it sounds crazy but what thermostat are you using? I had problems with a 216 engine when using a 195 Degree thermostat and hot outside temperatures.. Changed to a 180 thermostat and problem pretty well cleared up.
I know it sounds crazy but what thermostat are you using? I had problems with a 216 engine when using a 195 Degree thermostat and hot outside temperatures.. Changed to a 180 thermostat and problem pretty well cleared up.
I have went to a 160 with no change, the temps under the hood after a drive are pretty warm and as you know the temp will rise for a bit after shut down that's when the problem begins. I have tried everything I can think of just hoping some of you guys have ran across the problem. Thanks for the response!
Hot Starts
Often it's just a matter of throttle positioning ~ you never , ever want to pump the throttle on a hot engine .
Rather , holding it at part throttle and cranking it until it roars to life is usually faster , each engine wants a different throttle position ofter a heat soak ~ some want 1/2 , others want more or lees , you'll have to experiment to find the sweet spot .
The way it is tuned also greatly affects starting hot or cold .
Often it's just a matter of throttle positioning ~ you never , ever want to pump the throttle on a hot engine .
Rather , holding it at part throttle and cranking it until it roars to life is usually faster , each engine wants a different throttle position ofter a heat soak ~ some want 1/2 , others want more or lees , you'll have to experiment to find the sweet spot .
The way it is tuned also greatly affects starting hot or cold .
ccharr
Member
My truck use to vapor lock after drives on hot days, even would do it if I sat at a light to long. That problem went away after I replaced the fuel lines and put an electric fuel pump next to the fuel take and put it on a starter button. If I do not drive the truck for a week or so I give it a push of the button and she fires right up and on hot days after sitting shopping I give it a shot and it fires right up. May not be your problem but hot gas does cause vapor lock, try putting clothes pins on the line and see if that helps.
I have them on mine, I never took them off after putting on the elect. pump, it gets some good questions at the shows I take it to.
I have them on mine, I never took them off after putting on the elect. pump, it gets some good questions at the shows I take it to.
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Lakeroadster
Member
Charles,
What's the logic behind the clothes pins?
What's the logic behind the clothes pins?
morabuffalo
Member
clothes pins
Yes!!! I had not heard that for years...It works! But, you have some plastic ones...I had always heard that the wood ones work much better. I always had them on and if I did not I would vapor lock or get the stumble right before all of the time. Also, if you had enough notice that it was going to hit 120 or so, you could keep those wood ones in a little bottle soaking in water.
Now, what about the penny on the battery case? There is another I have not heard for some time!
Neat memories...rod
Yes!!! I had not heard that for years...It works! But, you have some plastic ones...I had always heard that the wood ones work much better. I always had them on and if I did not I would vapor lock or get the stumble right before all of the time. Also, if you had enough notice that it was going to hit 120 or so, you could keep those wood ones in a little bottle soaking in water.
Now, what about the penny on the battery case? There is another I have not heard for some time!
Neat memories...rod
ccharr
Member
Something that I have seen since a little boy the wood ones. The Aluminum ones are there because they work better. Somehow they work like a radiator does.
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ccharr
Member
The silver looking ones are Aluminum and work better than the wood. With the electric fuel pump inline the vapor lock is not an issue any more, for me.
The new pennies do not work as well due to their makeup and the amount of zinc v/s copper they have, you have to use those before 83.
The new pennies do not work as well due to their makeup and the amount of zinc v/s copper they have, you have to use those before 83.
Clothespins & Pennies
Those aluminum clothes pins sure get the ' WTH is THAT ?! ' ' comments ! .
I have them on my Metropolitan Nash FHC (THANK YOU Charles) and I recently did a deep head gasket repair that included a new water pump and some engine re painting , the clothes pins went right back on the steel fuel pipes where they belong .
Modern fuel evaporates very easily , this is no problem on to - day's fuel injected engines but more and more it gives the Old Timers with carbys fits .
The penny is a sacrificial anode , like the ' zincs ' used on boats to prevent the propellers from corroding away unseen .
Just keeping your battery clean and dry , maybe lightly greasing the cable ends , works just as well .
Those aluminum clothes pins sure get the ' WTH is THAT ?! ' ' comments ! .
I have them on my Metropolitan Nash FHC (THANK YOU Charles) and I recently did a deep head gasket repair that included a new water pump and some engine re painting , the clothes pins went right back on the steel fuel pipes where they belong .
Modern fuel evaporates very easily , this is no problem on to - day's fuel injected engines but more and more it gives the Old Timers with carbys fits .
The penny is a sacrificial anode , like the ' zincs ' used on boats to prevent the propellers from corroding away unseen .
Just keeping your battery clean and dry , maybe lightly greasing the cable ends , works just as well .
I have had the exact same problem with my 37 Buick for 30 years and have decided there is no cure. Being obsessive I carried my fixit attemps further than you did. Finned heat dissipation block under carb, pump to carb line (with nasty asbestos sleeve) 6" above valve cover, 2# fuel regulator, shut off ball valve where fuel line enters carb so I could raise hood and stop ANY fuel flow after a long hot drive, and even a quick disconnect fuel line where I could hook the carb up to a Kool Kan with electric pump that had iced down fuel in it---nothing worked. Deciding I wasn't going to cure it I decided to live with it by building an HEI distributor to fit the Buick straight 8. With the jillion volt racing coil and the plugs gapped at 0.060 the spark if so hot it cleans the plugs and fires off the puddled fuel with minimal cranking. Just don't stand behind the tailpipe with white cloths on.
ccharr
Member
I wrapped the fuel line at first, if replacing the lines and putting ion the electric pump had not worked I was going to change out the fuel tank and install an in-tank fuel pump with return lines. So far so good.
Attachments
Thanks for all the suggestions. I have already done the closepin trick to no fix. I did rebuild the dist. to electronic ing. maybe should look at changing the plugs and widen the gap. I will also try holding the throttle instead of pumping it when hot. The fuel line has been moved a few inches and a spacer between the carb and intake has been the only alterations to this point. I will give you guys a progress report when we get it fixed!!
pmoron
Member
That might be your problem.
You shouldn't have to touch the throttle at all if the engine is hot. I'm guessing your plugs are fouled now, which would explain the stalling issue. My guess, anyway.
You shouldn't have to touch the throttle at all if the engine is hot. I'm guessing your plugs are fouled now, which would explain the stalling issue. My guess, anyway.
morabuffalo
Member
Flooded???
"It starts like a dream when cold and no problem when it has time to cool down (engine temp below 170) but after an extended drive on a warm day and setting for around 15 minets to about 1 hour it will not start! It cranks OK and I can see gas in the carb when I pump the throttle and when it finally does start in doesn't seam to be flooded."
I would go with the partial fooded thinking. Maybe check in that direction. When hot, if the floats or the little thingy that stops the gas are off a little...Ok, old age...it could cause it to "hard start". I would check those two things or even drive and just stop and see (fast) if gas might be making it down its deep throat. I think it would be like steam in the carb at that point.
Or, it might be doing the opposite, although I would think that is more unlikely, it might be draining some how back into its panza. In that case you would check to see if the line at the carb still has gas in it after a few minutes. It is much more unlikely, but when the old guy or gay just don't want to....you got to think more and more on the divergent levels.
My two cents...well, today its only about one tenth of a cent, rod
"It starts like a dream when cold and no problem when it has time to cool down (engine temp below 170) but after an extended drive on a warm day and setting for around 15 minets to about 1 hour it will not start! It cranks OK and I can see gas in the carb when I pump the throttle and when it finally does start in doesn't seam to be flooded."
I would go with the partial fooded thinking. Maybe check in that direction. When hot, if the floats or the little thingy that stops the gas are off a little...Ok, old age...it could cause it to "hard start". I would check those two things or even drive and just stop and see (fast) if gas might be making it down its deep throat. I think it would be like steam in the carb at that point.
Or, it might be doing the opposite, although I would think that is more unlikely, it might be draining some how back into its panza. In that case you would check to see if the line at the carb still has gas in it after a few minutes. It is much more unlikely, but when the old guy or gay just don't want to....you got to think more and more on the divergent levels.
My two cents...well, today its only about one tenth of a cent, rod
Lakeroadster
Member
Fielddad, You are running a vented gas cap, correct?
Yes the cap is vented, thanks for the suggestion, and since last post I have changed the plugs to a hotter heat range .060 (I have electronic ignition) and still no better. My next move is to lower the timing from 8-4 degrees just to see?? I filled the tank with premium fuel 92 oct. I rebuilt the carb back 3 months ago when I first started driving it and has performed very good until the weather warmed up and that's when the hot hard start began. If I don't pump the throttle or hold it steady nothing happens if I do pump it sometimes it will spit fuel back up the carb. I can look down the carb while cranking and see a light fog of fuel vapor being pulled into the intake soooo I think it has fuel but if I don't give it some throttle I get nothing. This whole deal is making me a little frustrated. I owned a repair shop for over 20 years and don't recall ever having this problem but of course we didn't have to many carbs to work on.c
Lakeroadster
Member
How about posting up some engine photos... curious about your fuel line routing and its location to heat sources, as was previously discussed?
After I built my Model A hot rod (about 2 decades ago) I took it to Frank Johnson Carburetor & Ignition Shop that was "the place" all the guys I knew said was the best of the best to have it dyno. tuned at.
Frank (a certified "wise" been there done that older fella) went on and on about what a great job I did routing the fuel line away from heat sources....
Hard Hot Starting Problems
After I built my Model A hot rod (about 2 decades ago) I took it to Frank Johnson Carburetor & Ignition Shop that was "the place" all the guys I knew said was the best of the best to have it dyno. tuned at.
Frank (a certified "wise" been there done that older fella) went on and on about what a great job I did routing the fuel line away from heat sources....
Hard Hot Starting Problems
As for hot starting problems, the carburetor is seldom to blame. A hot start condition is usually the result of too much heat in the vicinity of the carburetor, fuel lines or fuel pump. Heat causes the fuel in the fuel lines, carburetor bowl or pump to boil. This creates a "vapor lock" condition which can make a hot engine hard to start. Replacing or rebuilding the carburetor wouldn't solve anything because the real culprit is heat. What needs to be done here is to reroute the fuel line away from sources of heat (like the exhaust manifold and pipe), and/or to insulate the fuel line by fabricating aheat shield or wrapping the fuel line with insulation.
Hot start problems can also be caused by excessive resistance in a starter, poor battery cable connections, or a faulty ignition module that acts up when it overheats.
Hot start problems can also be caused by excessive resistance in a starter, poor battery cable connections, or a faulty ignition module that acts up when it overheats.
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RidesWithYah
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I'm not familiar with the exhaust manifold on a 250.
You wouldn't happen to have a heat riser stuck?
You wouldn't happen to have a heat riser stuck?
Hot restart issues with modern gasoline is here to stay. With a carburetor we're probably looking at 3-5 psi between the pump and the carburetor. To reduce the problem of vapor lock in modern fuel injected vehicles we've seen fuel rail pressures increase from around 36 psi to 55-60 psi. So if fuel will boil at 36 psi, you probably don't stand much of a chance at 5 psi. At the tail end of carburetors, the Japanese manufacturers developed hot soak kits in warm climates to reduce this problem. The main component was a small 12 volt fan placed under the hood and aimed at the carburetor. The fan was on a temp triggered timer circuit which would turn on the fan when the ignition was turned off, and underhood temperatures were high. The fans would run for about 15 minutes and worked very well. I remember seeing them on Nissan's and possibly Honda's. Might be something to try.
John
John