Hard warm starting

[50mech]

So I got the new fuel pump and Carter yf carb installed on the 50 Plymouth. Starts when cold, starts after driving and shutting off for 3-4 minutes. If it's left for 10-20 minutes it won't start. It's still warm enough for the choke to be open. If I pull the fuel line from the carb there is still some pressure there. Only way to start it at that point is to choke it by sealing off the intake with my hand, or letting it cool much longer. Engine temps are normal.

 

I'm thinking this is due to the heat riser being stuck but thought I'd run it by you guys to see if you think I'm barking up the wrong tree or if you could throw out some other possibilities. Thoughts?

[Plymouthy Adams]

many hard HOT restarts are from two common scenarios.  One is the coil is getting hot and losing its ability to throw a hot spark...second is percolation of the carb and is often the results of todays blend of gas and high float level.  Lowering the fuel level in the bowl will help prevent percolation.   This can be verified after a run by observing the carb throat and inside the manifold for wet fuel and a highly concentrated fuel vapor easily seen by the eye as the fuel running down inside the throat of the carb to the hot manifold will cause this dense fuel vapor.    A manifold with fuel saturation due to this temp related flooding involves opening the throttle and starting the engine..this prevent drawing extra fuel into the manifold as the low starting speed of the engine prevent fuel being drawn in as the vacuum is too low for a venturi effect.   IF the engine does not start easily, and flooding is the condition, remember, every time you let up on the gas and depress it again adds fuel to the manifold through the accelerator pump on the carb.  

[50mech]

That's what has me a little confused. Open throttle won't start it.

Say the stuck heat riser is causing percolating....or just ethanol fuel.

It starts when I completely choke it with my hand. I could only only guess that draws in enough cool fuel to overcome the issue or simply gets the vacuum high enough?

 

Coil is a new pertronix and has plenty of spark during this condition.

Will check the float level though.Thank you.

[greg g]

As Tim noted, when doing a hot start slowly push the gas pedal to the floor and hold it open before engaging the starter.  I have my carbs set 3/32nds lower than factory.

[Sniper]

We know yout riser is an issue, so let's resolve that first.

 

A video on a slant six, but still relevant.  Mopar part number 4318039AC Rust Penetrant

 

 

[greg g]

Run it till you think the situation will occur, shut down and check the base of the carb.  If it's dry, shut the hood and let it sit for five minutes. Check the carb base again. If it's wet it's a perculation problem.  Can you turn the heat riser by hand?  If so rotate it as far as it will go clockwise and secure it there.

[50mech]

I'll give it another shot at WOT.

If it helps I'll drop the float level. 

 

[Plymouthy Adams]

most heat riser default in closed position that often by passes their intended use to quick heat the manifold and thus are slower to come to temp in this area.   You should have other indicators of  a stuck open heat riser.  IF your control valve is operational...once started and when cold...you should see about 1/4 inch rotation of the valve damper on sudden acceleration of the engine...

[50mech]

3 minutes ago, greg g said:

Run it till you think the situation will occur, shut down and check the base of the carb.  If it's dry, shut the hood and let it sit for five minutes. Check the carb base again. If it's wet it's a perculation problem.  Can you turn the heat riser by hand?  If so rotate it as far as it will go clockwise and secure it there.

Awesome! Will do.

It won't move by hand, probably going to gut and replace it this weekend or do a blockoff. Ill definitely try all suggestions too.

[Plymouthy Adams]

remember the terms open and close is not in relationship to the exhaust pipe as it is to the bottom of the intake for preheating that chamber....

[50mech]

Just tried it after a 20 min drive, sat for 10-15 min. wot won't get it to start, but the whole body of the carb is hot enough I can't leave my hand on it. In fact the base is hotter than the  cylinder head is. No wetness around the base, but heavy rising fuel vapor.

Edited March 2, 2020 by 50mech
Add info

[50mech]

44 minutes ago, Plymouthy Adams said:

remember the terms open and close is not in relationship to the exhaust pipe as it is to the bottom of the intake for preheating that chamber....

So when you say open, that is referring to the heating position?

[50mech]

I do have a rather slow cranking speed as well....prhaps battery or starter issue compounding the problem...?

[plymouthcranbrook]

Although often mentioned a slow cranking speed is often associated with cables that are too small and grounds that are not effective.  Several posts on this subject are around.

[50mech]

11 minutes ago, plymouthcranbrook said:

Although often mentioned a slow cranking speed is often associated with cables that are too small and grounds that are not effective.  Several posts on this subject are around.

Yes, a ground would make sense as the cranking speed is slower when warm.

[50mech]

Since it can be rust and carbon, and I have some around, I'm thinking I'll hit the riser valve with CLP

[Dan Hiebert]

For consideration - the Sisson choke may be contributing to the issue.  There can be two issues with it, one being that the gasket between it and the manifold it is mounted on has to be present, or it won't work right.  Second, and we had the same issue you do with our D24 shortly after we acquired it, the bimetal spring in the choke that determines just how much automatic choke to apply can degrade.  That spring works on the temperature from the manifold. Ours acquired a "sweet spot" where the car would not start almost exactly like yours, after sitting shut off for 10-20 minutes after getting to operating temperature.  Let it get cold again, it would start, try to start pretty quickly after shutting it off and it would start.  During that "sweet spot" time I had to have someone hold the choke open (different resolution than yours) to get it to start because the Sisson would close the choke when it needed to be open.  I didn't fix it, I replaced it with a manual choke.  If you have a different automatic choke, it could still be contributing, especially if the car will start when you cover the intake.

[Plymouthy Adams]

1 hour ago, 50mech said:

I do have a rather slow cranking speed as well....prhaps battery or starter issue compounding the problem...?

slow speeds are also voltage drop related...this induces a higher than normal current draw depriving your ignition system from the current it needs.....6 volt systems are way more problematic due to this....so be sure to check you car and for VD......

 

 

[Dodgeb4ya]

VD??

[Plymouthy Adams]

1 minute ago, Dodgeb4ya said:

VD??

VD...short for voltage drop.....the great electrical system killer...

[Dodgeb4ya]

Ohhhhhh?

[Sam Buchanan]

Wow....had me going there for a bit....was wondering if I needed to lock the garage door to keep my P15 out of trouble......

[Dodgeb4ya]

Could have really been bad if it was CV!

[50mech]

What types of penicillin mix best with gasoline?

 

Does Chrysler make penta-cyllin?

Edited March 2, 2020 by 50mech

[soth122003]

4 hours ago, 50mech said:

Just tried it after a 20 min drive, sat for 10-15 min. wot won't get it to start, but the whole body of the carb is hot enough I can't leave my hand on it. In fact the base is hotter than the  cylinder head is. No wetness around the base, but heavy rising fuel vapor.

Edited 4 hours ago by 50mech

How thick is your carb base gasket? If it is a thin one you might be getting more heat transfer than normal. I think the ones with a carb kit are about 1/8" thick. Something to look at maybe?  I've also heard of people cutting a riser/spacer out of phenolic about 1/2" thick to stop the heat transfer.

That being said, Mine has a harder time starting hot. The shop manual states to start a hot engine, press the accelerator to the floor and let up about 1/4 of the way and then start.

 

Joe Lee