Fast Idle when hot

Message

Paul Kust · #1 Post by **Paul Kust** » Sat Aug 16, 2008 1:53 pm

Here is a question that I have not been able to find an answer for, I have done searches on the subject with no results. Forum and the web.

1965 356C original engine, weber carbs, correct dist rebuilt by Don Marks, Valves adjusted, timing spot on, carbs working good.
The car runs strong and idles fine when cold and warm.
The problem encountered is that when HOT, the Idle does not return to normal and tends to be about 1100 unless you slow it down by breaking with the clutch when at a stop, then it will return to normal. Any ideas on what would cause this? It does this only when it is above 85 degrees out other than that it returns to normal like it should, it's going to be 100 today. Could it be fuel volatility?

Jeffrey Fellman · #2 Post by **Jeffrey Fellman** » Sat Aug 16, 2008 2:12 pm

double check that the timing is coming back to the static timing at idle.
This is a vicious circle as a little extra advance at idle makes the engine
speed up which increases the advance which makes the idle speed up etc.....
Also double check your mixture setting when the engine is fully warm, same
situation, a little extra gas, a throttle not fully closed against the idle
stop, a little air from wherever, a little extra advance and voila high
idle.
----- Original Message -----
From: "Paul Kust" <pkust@comcast.net>
To: <356talk@356registry.com>
Sent: Saturday, August 16, 2008 1:53 PM
Subject: [356Talk] Fast Idle when hot

Here is a question that I have not been able to find an answer for, I have
done searches on the subject with no results. Forum and the web.

1965 356C original engine, weber carbs, correct dist rebuilt by Don Marks,
Valves adjusted, timing spot on, carbs working good.
The car runs strong and idles fine when cold and warm.
The problem encountered is that when HOT, the Idle does not return to
normal and tends to be about 1100 unless you slow it down by breaking with
the clutch when at a stop, then it will return to normal. Any ideas on
what would cause this? It does this only when it is above 85 degrees out
other than that it returns to normal like it should, it's going to be 100
today. Could it be fuel volatility?

------------------------
Paul Kust

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Rick Woltz · #3 Post by **Rick Woltz** » Sat Aug 16, 2008 2:17 pm

Try to swap distributors with a friend and see if the problem goes away.
Sometimes the advance of the distributor comes on a little too early. If you
prove it to be the distributor I'm sure that Don will make it right.
Rick
A59D

-----Original Message-----
From: Paul Kust [mailto:pkust@comcast.net]
Sent: Saturday, August 16, 2008 7:54 AM
To: 356talk@356registry.com
Subject: [356Talk] Fast Idle when hot

Here is a question that I have not been able to find an answer for, I have
done searches on the subject with no results. Forum and the web.

1965 356C original engine, weber carbs, correct dist rebuilt by Don Marks,
Valves adjusted, timing spot on, carbs working good.
The car runs strong and idles fine when cold and warm.
The problem encountered is that when HOT, the Idle does not return to normal
and tends to be about 1100 unless you slow it down by breaking with the
clutch when at a stop, then it will return to normal. Any ideas on what
would cause this? It does this only when it is above 85 degrees out other
than that it returns to normal like it should, it's going to be 100 today.
Could it be fuel volatility?

------------------------
Paul Kust

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Barry Wolk · #4 Post by **Barry Wolk** » Sat Aug 16, 2008 2:29 pm

I'm interested in this answer, too. I asked my mechanic the same thing. He stated that the heat of the engine changes the characteristics of fuel flow, increasing rpm. This is also the same guy that increased the size of the idle jets to make it run lean.

Something to do with today's fuel.

I'd like a layman's explanation for that, too.

Jeffrey Fellman · #5 Post by **Jeffrey Fellman** » Sat Aug 16, 2008 2:48 pm

also pop the throttles off of the balls at the carbs and see where the idle
is, you might get a surprise
----- Original Message -----
From: "Jeffrey Fellman" <pmotion@acun.com>
To: <356talk@356registry.com>
Sent: Saturday, August 16, 2008 2:40 PM
Subject: [356Talk] Fast Idle when hot

double check that the timing is coming back to the static timing at idle.
This is a vicious circle as a little extra advance at idle makes the
engine
speed up which increases the advance which makes the idle speed up
etc.....
Also double check your mixture setting when the engine is fully warm, same
situation, a little extra gas, a throttle not fully closed against the
idle
stop, a little air from wherever, a little extra advance and voila high
idle.
----- Original Message -----
From: "Paul Kust" <pkust@comcast.net>
To: <356talk@356registry.com>
Sent: Saturday, August 16, 2008 1:53 PM
Subject: [356Talk] Fast Idle when hot

Here is a question that I have not been able to find an answer for, I
have
done searches on the subject with no results. Forum and the web.

1965 356C original engine, weber carbs, correct dist rebuilt by Don
Marks,
Valves adjusted, timing spot on, carbs working good.
The car runs strong and idles fine when cold and warm.
The problem encountered is that when HOT, the Idle does not return to
normal and tends to be about 1100 unless you slow it down by breaking
with
the clutch when at a stop, then it will return to normal. Any ideas on
what would cause this? It does this only when it is above 85 degrees out
other than that it returns to normal like it should, it's going to be 100
today. Could it be fuel volatility?

------------------------
Paul Kust

E-mail message checked by Spyware Doctor (5.5.1.322)
Database version: 5.10490e
http://www.pctools.com/en/spyware-doctor/

E-mail message checked by Spyware Doctor (5.5.1.322)
Database version: 5.10490e
http://www.pctools.com/en/spyware-doctor/

Post generated using Mail2Forum via email.

S.J. Szabo · #6 Post by **S.J. Szabo** » Sun Aug 17, 2008 1:55 am

Mr. Kust:

Here's 2 cents out of left field……

Try this experiment: with engine hot and running at 30-40mph, shift down to second as you approach a stoplight and de-clutch after slowing, but during deceleration (using no brakes until after de-clutching and stay off the gas). If the idle is then normal (or even slower), I may have bad news for you. It may be that the brass distributor drive gear on the crank is worn and should be replaced.

Or, you can make engine braking a regular part of your driving routine. Or, a couple of light blips of the throttle can put the driven gear on the other face of the drive gear.

Keep 'em flying.

Rainer Cooney · #7 Post by **Rainer Cooney** » Sun Aug 17, 2008 7:53 am

Distributor springs. An easy way to check is to turn off the ignition switch when the car is idling and before the engine stops rotating, approx 500rpm, turn the key back on. If the engine idles OK or starts out low and creeps back up its the springs.

Mark Roth · #8 Post by **Mark Roth** » Tue Aug 19, 2008 9:14 am

Don't worry about it if all the adjustments are correct. I have Don Marks distributors and have had this situation for many years. When the engine is hot and I come to a stop, often the idle is around 1500 or so. If I let it idle by itself, the rpms will gradually come down. Or, I can blip the throttle and the idle will drop a couple of hundred rpm.

Michael Eker · #9 Post by **Michael Eker** » Tue Aug 19, 2008 11:16 am

weak distributor springs

NLA-602-650-04 Advance spring, 2 req'd. Fits 356 and 912. $2.94

http://www.stoddard.com/shop/shopdispla ... Electrical

meker

Guest · #10 Post by **Guest** » Tue Aug 19, 2008 9:52 pm

Mark,
The high idle can be caused by a dist. hanging, throttle
linkage with no free play, idle speed set too high or
mixture set a bit too lean.

Alan

Mark Roth wrote:

Don't worry about it if all the adjustments are correct. I have Don
Marks distributors and have had this situation for many years. When the
engine is hot and I come to a stop, often the idle is around 1500 or so.
If I let it idle by itself, the rpms will gradually come down. Or, I can
blip the throttle and the idle will drop a couple of hundred rpm.

------------------------------------------------------------------------

Mark Roth
65 C Cab (Black/black)
62 T-6 Notchback (Red/tan)

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Jim Breazeale · #11 Post by **Jim Breazeale** » Wed Aug 20, 2008 12:18 pm

Mark,
The high idle can be caused by a dist. hanging, throttle
linkage with no free play, idle speed set too high or
mixture set a bit too lean.

Alan

Alan

Don't forget missing/broken rubber blocks in Solex Split shaft carburators cause a high idle, also. Thank you for fixing that problem in my Cab.

Regards

Paul Kust · #12 Post by **Paul Kust** » Wed Aug 20, 2008 12:43 pm

I just have to say thank you to all of you that have replied to this tread and have contributed great ideas as to the problem.
I have been too busy to address the problem but you have given me some other directions to go in, other than the path I have been down.

You Guys are great!

And I love the way this forum is set up now, it seems more inviting