Hard Start when engine is warm.

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

Asgeir

Member
Joined
Oct 22, 2022
Posts
32
Reaction score
47
Location
Nowhere, Oklahoma
First Name
Coty
Truck Year
1984
Truck Model
C10
Engine Size
383
Hello all, My 1984 C10 has a 383 in. She will start just fine when cold, but when I drive it and the engine gets warm and park it, I can come back three minutes later and it will not start. It will crank and crank but will not start, I have to set my foot on the throttle to get it started. At first I thought it was the fuel boiling off, so I put a aluminum sleeve on the fuel line and still have the issue. Can anyone help guide me as to what the next step I should take to get this fixed? Thank you.
 

Bextreme04

Full Access Member
Joined
May 13, 2019
Posts
4,315
Reaction score
5,301
Location
Oregon
First Name
Eric
Truck Year
1980
Truck Model
K25
Engine Size
350-4bbl
Maybe choke not pulling off? Carb not adjusted properly? Pics?

What carb are you running? Have you dialed in the timing and carb adjustments yet?
 

Asgeir

Member
Joined
Oct 22, 2022
Posts
32
Reaction score
47
Location
Nowhere, Oklahoma
First Name
Coty
Truck Year
1984
Truck Model
C10
Engine Size
383
Maybe choke not pulling off? Carb not adjusted properly? Pics?

What carb are you running? Have you dialed in the timing and carb adjustments yet?
I have a Holley 600 cfm that was rebuilt at a carb shop. The carb is dialed in and adjusted from the carb shop and the choke was pulled off the carb, was told I didnt need it here in this weather.
 

SirRobyn0

Full Access Member
Joined
Dec 6, 2019
Posts
6,751
Reaction score
11,380
Location
In the woods in Western Washington
First Name
Rob
Truck Year
1984
Truck Model
C20
Engine Size
305
Did the carb shop do the adjusting on the vehicle? If not, we need to start there.

It is common [especially today] with low octane ethanol fuel to boil inside carb during heat soak.
I agree with the boiling / percolation thing. Also if your heat riser is stuck shut or partially shut that will exacerbate it. If your running an aftermarket carb (or even the factory one) a phenolic heat spacer can make a big difference.
 

KnuckleBuster

Full Access Member
Joined
Jun 15, 2023
Posts
61
Reaction score
67
Location
USA
First Name
Floyd
Truck Year
1969
Truck Model
C10
Engine Size
350
So you have some mods to the fuel system. What kind of fuel line do you have? I had a truck once that had the same exact problem. It had a rubber hose (not by my hand!) from the pump to the carburetor. I replaced it with a steel line and the problem forever disappeared.
 

Asgeir

Member
Joined
Oct 22, 2022
Posts
32
Reaction score
47
Location
Nowhere, Oklahoma
First Name
Coty
Truck Year
1984
Truck Model
C10
Engine Size
383
So you have some mods to the fuel system. What kind of fuel line do you have? I had a truck once that had the same exact problem. It had a rubber hose from the pump to the carburetor. I replaced it with a steel line and the problem forever disappeared.
Some one have cut the metal line off a little above where the valve cover meets the head. The rubber line to the carb. I saw that others talked about the fuel boiling off, thats why I got the aluminum sleeve to put on the rubber hose. I got it from the fuel pump to the carb. I'm goint to check on what SirRobyn0 said about the heat spacer. I think I just stuck the Holley gasket on the intake and then carb.
 

Bextreme04

Full Access Member
Joined
May 13, 2019
Posts
4,315
Reaction score
5,301
Location
Oregon
First Name
Eric
Truck Year
1980
Truck Model
K25
Engine Size
350-4bbl
I have a Holley 600 cfm that was rebuilt at a carb shop. The carb is dialed in and adjusted from the carb shop and the choke was pulled off the carb, was told I didnt need it here in this weather.
I'd say they did a piss poor job if it doesn't restart hot without needing to do a flood clear procedure. First thing I would do is take it back and ask them to fix it. I'm guessing you paid a pretty penny for a rebuild and adjustment, so they should have it dialed in. My quadrajet starts up with just a touch of the key, hot or cold, regardless of the weather, every time. The holley should be able to do the same if they actually did the rebuild right.

I'd also question removing the choke on a 600cfm holley... if you needed more airflow, why wouldn't you just run a bigger carb? If you get down to 50 degrees or less, you will benefit from having the choke. You get snow in Oklahoma... if it isn't kept in a garage and only driven in the summer, I'd say you need it.

Holley has a whole series of videos up on their website of how to do the adjustments on their carbs. The reason people love them so much is there are very few to make and they don't need any special tools.
 

SirRobyn0

Full Access Member
Joined
Dec 6, 2019
Posts
6,751
Reaction score
11,380
Location
In the woods in Western Washington
First Name
Rob
Truck Year
1984
Truck Model
C20
Engine Size
305
Some one have cut the metal line off a little above where the valve cover meets the head. The rubber line to the carb. I saw that others talked about the fuel boiling off, thats why I got the aluminum sleeve to put on the rubber hose. I got it from the fuel pump to the carb. I'm goint to check on what SirRobyn0 said about the heat spacer. I think I just stuck the Holley gasket on the intake and then carb.
The metal fuel line is somewhat reflective to heat where as rubber line will soak in the heat and that is part of what Eric is saying. If after you shut it off the rubber line absorbs enough heat, it can boil the fuel in the line causing the pressure in the line to go up forcing fuel past the needle and seat, into the float bowl and into the intake. With percolation like I was talking about the heat comes up from the manifold and gets directly into the carburetor causing the fuel in the carburetor to boil and spill into the manifold. Symptoms are the same, but the solution is different.

Given that you insulated the rubber line and it didn't help, I'd lean towards it being percolation in the carburetor. However some carburetors are more prone to it than others and I do not see where you have stated which carb you are running despite a couple requests for that information.... So Edlebrocks seem to be the most prone to heat soak, Holley because of the external "hung" style float bowls are the least prone to it.
 

fast 99

Full Access Member
Joined
Dec 31, 2021
Posts
1,796
Reaction score
2,492
Location
Spokane, Washington
First Name
Brian
Truck Year
81,85
Truck Model
K20
Engine Size
350
Really question the choke removal. Not that it's bad if vehicle is used in hot climates, just that it raises questions about their ability. Really no good reason to do it.

Need to check basic things before purchasing any parts. Fuel pressure, float level, proper jets, ect. Phenolic spacers are a very good idea [have several] but won't fix a carb problem.

Although it hurts with fuel cost today, higher octane may help.
 

SirRobyn0

Full Access Member
Joined
Dec 6, 2019
Posts
6,751
Reaction score
11,380
Location
In the woods in Western Washington
First Name
Rob
Truck Year
1984
Truck Model
C20
Engine Size
305
Really question the choke removal. Not that it's bad if vehicle is used in hot climates, just that it raises questions about their ability. Really no good reason to do it.

Need to check basic things before purchasing any parts. Fuel pressure, float level, proper jets, ect. Phenolic spacers are a very good idea [have several] but won't fix a carb problem.

Although it hurts with fuel cost today, higher octane may help.
I second that concern as well. If the carb is setup so rich that it fires up cold just fine then it's running to rich, more than likely and that could be part of your hot start problem as well.

I think if it were me and I did not have the ability to tune a carburetor myself, and I don't just mean the screws on the front but jets and enrichment, then I'd take it to another carb shop, or at least a shop with a gas analyzer that could tell you if it's mixture is set at least somewhat close.

I'd hate for you to install a heat spacer to find out it's just dumping to much gas in.
 

Ricko1966

Full Access Member
Joined
Apr 11, 2017
Posts
4,595
Reaction score
6,943
Location
kansas
First Name
Rick
Truck Year
1975
Truck Model
c20
Engine Size
350
Do you have a 2 line fuel pump or a 3 fuel pump,did it originally have a 3 line pump? I'm not just asking for fun. The 3 line bypasses fuel back to the tank a 2 line has a check valve and will hold constant pressure against the needle. When the car heat soaks the fuel expands,blows the needle open and floods the car. You get back in and have to floor it to get your mixture right on a hot start.
 

Matt69olds

Full Access Member
Joined
Jan 8, 2018
Posts
2,419
Reaction score
3,749
Location
Central Indiana
First Name
Matt
Truck Year
81
Truck Model
GMC 1/2 ton
Engine Size
455 Olds
Do you have a 2 line fuel pump or a 3 fuel pump,did it originally have a 3 line pump? I'm not just asking for fun. The 3 line bypasses fuel back to the tank a 2 line has a check valve and will hold constant pressure against the needle. When the car heat soaks the fuel expands,blows the needle open and floods the car. You get back in and have to floor it to get your mixture right on a hot start.


Bingo!

Lots of people don’t understand the difference between 2 and 3 line pumps and the way they function. They cap off the 3 line and then wonder why they have this exact concern.
 

Latest posts

Forum statistics

Threads
42,984
Posts
926,006
Members
34,563
Latest member
chevyc10-1978
Top