Hot Start Trouble

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kiltgy
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Hot Start Trouble

Post by kiltgy » Sun Aug 09, 2015 10:21 pm

Have a '74 automatic with a 1800 and dual webber carbs.

And I also have a hot start issue.

Engine starts up just fine when cold. Drive for a while and stop. Starts back up just fine. Drive for a while. Stop. Starts just fine again. Drive it a while longer, stop, and it won't start. It cranks, but it just won't catch.

Replaced the points about 400 miles ago. Engine replaced 1000 miles ago.

Thoughts?

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Amskeptic
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Re: Hot Start Trouble

Post by Amskeptic » Mon Aug 10, 2015 12:02 am

kiltgy wrote:Have a '74 automatic with a 1800 and dual webber carbs.

And I also have a hot start issue.

Engine starts up just fine when cold. Drive for a while and stop. Starts back up just fine. Drive for a while. Stop. Starts just fine again. Drive it a while longer, stop, and it won't start. It cranks, but it just won't catch.

Replaced the points about 400 miles ago. Engine replaced 1000 miles ago.

Thoughts?
What is your starting procedure when warm?

Check dwell (44-50*)

Warm-to-hot engine starting procedure:

As soon as you start cranking the engine, slowly press accelerator to floor and leave it there until engine catches. Don't let it rev up. This is true for all carbureted engines on hot days.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

kiltgy
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Re: Hot Start Trouble

Post by kiltgy » Mon Aug 10, 2015 9:34 am

Yep. That's what I have been doing. Unfortunately it is not working. I will check the dwell when I retrieve it this morning.

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hambone
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Re: Hot Start Trouble

Post by hambone » Mon Aug 10, 2015 3:45 pm

"As soon as you start cranking the engine, slowly press accelerator to floor and leave it there until engine catches. Don't let it rev up. This is true for all carbureted engines on hot days.
Colin"
Yeah yeah? You answered my question too. Bus2 is cranky to start when hot after sitting for a spell. I will try this.
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cegammel
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Re: Hot Start Trouble

Post by cegammel » Tue Aug 11, 2015 1:46 pm

This is probably old news, but I just replaced my carb float with a hollow plastic model due to frequent hot flooding. That and a readjustment of idle seems to have cured my hot start irregularity...for now...

kiltgy
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Re: Hot Start Trouble

Post by kiltgy » Tue Aug 11, 2015 3:50 pm

Dwell is rock steady at 49. I'll go a bit easier on the gas when starting hot in the future.

Just out of curiosity, is this something that electronic ignition would help alleviate?

cegammel
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Re: Hot Start Trouble

Post by cegammel » Tue Aug 11, 2015 5:07 pm

Based on what I have read, this seemse to be an issue of air starvation, not ignition. I will say that my fuel injected, electronically IGNITED Vanagon does not have this issue...very often. I suspect that this is due more to the injectors than the ignition.

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Amskeptic
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Re: Hot Start Trouble

Post by Amskeptic » Wed Aug 12, 2015 10:51 am

cegammel wrote:Based on what I have read, this seems to be an issue of air starvation, not ignition. I will say that my fuel injected, electronically injected Vanagon does not have this issue...very often. I suspect that this is due more to the injectors than the ignition.
Seeing as my breaker points-equipped cars all start reliably enough in Hell, no, I would not assume the electronic ignition is going to fix what has been determined here to be "fuel percolation when warm" problem which afflicts all carbureted engines to varying degrees.

Flooring the accelerator simply helps to lean the mixture as best we can, it is not related to "air starvation" so much as a surfeit of fuel.

Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

cegammel
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Re: Hot Start Trouble

Post by cegammel » Wed Aug 12, 2015 11:39 am

Ah! Fuel percolation! That explains the hissing and spraying when I removed the carburetor top the other day.

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asiab3
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Re: Hot Start Trouble

Post by asiab3 » Wed Aug 12, 2015 6:09 pm

cegammel wrote:Ah! Fuel percolation! That explains the hissing and spraying when I removed the carburetor top the other day.
The way I understand it, is the fuel that expands (boils?) in the pump- to-carb hose needs somewhere to go. It can allegedly bypass the needle valve with excess pressure that the factory Pierburg pumps are designed to bleed off. I have noticed an extremely significant decrease in hot-start cranking time with mine, though ONE time it did take almost ten cranks. Of course this was parked right next to Chloe, so for all I know the bus was just nervous.
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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Amskeptic
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Re: Hot Start Trouble

Post by Amskeptic » Fri Aug 14, 2015 12:48 pm

cegammel wrote:Ah! Fuel percolation! That explains the hissing and spraying when I removed the carburetor top the other day.
Next time, look down the throat of the carburetor.
If you can see/hear dripping/hissing with fuel vapor smoke, it suggests a too-high float level among other issues.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

ainokea
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Re: Hot Start Trouble

Post by ainokea » Fri Apr 08, 2016 7:58 pm

Dual Webers, which ones? Fuel pressure regulator installed? float levels correct? Right size venturis for your application? Jetting in the ballpark? From your description I would think fuel delivery is your problem if you're running IDF's, maybe to much fuel pressure and wrong float levels, wrong size idle jets, carburetors not balanced and synchronized, to name a few problem areas. Ainokea

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