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Kirkham Motorsports

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  #1 (permalink)  
Old 09-01-2017, 07:23 AM
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Default Why am i having trouble starting when warm?

The car has a small block 351w-427R.
It starts up immediately when cold. When warm, sometimes two or three attempts with a couple of seconds of cranking, unless I catch it just right with a few pumps on the gas pedal and just enough pressure on it while I start.
A new fuel pump was installed at the beginning of summer. I don't really remember having this issue before it. The mechanic says its due to the high levels of ethanol in the fuel. It took all summer, but I last week put in 5 gallons of 104 octane and filled the rest with 94 octane to see if this rectified the issue. It didn't.
I've also read it could be the starter not working well when warm.
Any thoughts or suggestions?
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Old 09-01-2017, 07:50 AM
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Quote:
Originally Posted by Midcont View Post
The car has a small block 351w-427R.
It starts up immediately when cold. When warm, sometimes two or three attempts with a couple of seconds of cranking, unless I catch it just right with a few pumps on the gas pedal and just enough pressure on it while I start.
A new fuel pump was installed at the beginning of summer. I don't really remember having this issue before it. The mechanic says its due to the high levels of ethanol in the fuel. It took all summer, but I last week put in 5 gallons of 104 octane and filled the rest with 94 octane to see if this rectified the issue. It didn't.
I've also read it could be the starter not working well when warm.
Any thoughts or suggestions?
When you write 'warm' do you mean 'hot' or normal operating temperature?

Do you have an electric fuel pump or mechanical?

At this point my guess would be vapor lock or fuel percolation. The area around the carburetor is hot enough to vaporize the fuel.

One solution is an insulating spacer between the carb and intake manifold. Electric fuel pumps seem to be less prone to this than mechanical pumps.

Probably worth a few minutes to check out this thread: Holley hot stop fuel perc issue
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Old 09-01-2017, 07:51 AM
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Vapor lock on a carburatored engine? Is there a spacer or heat shield between the carb and manifold?
Larry
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Old 09-01-2017, 08:57 AM
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On a warmed-up engine, you should only have to depress the gas pedal slightly (maybe half way at most) and turn the key (no pumping). Otherwise, you risk flooding it. If that doesn't work, then you might be boiling the fuel out of the bowls. If the starter is cranking the engine slower when warm, that could be a whole different issue (weak ground wires, thermal expansion of an older, non-high torque starter, not enough CCA from the battery, etc.).
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Old 09-01-2017, 09:04 AM
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Quote:
Originally Posted by cycleguy55 View Post
When you write 'warm' do you mean 'hot' or normal operating temperature?

Do you have an electric fuel pump or mechanical?

At this point my guess would be vapor lock or fuel percolation. The area around the carburetor is hot enough to vaporize the fuel.

One solution is an insulating spacer between the carb and intake manifold. Electric fuel pumps seem to be less prone to this than mechanical pumps.

Probably worth a few minutes to check out this thread: Holley hot stop fuel perc issue
I believe it's mechanical. Will need to verify.

Quote:
Originally Posted by LMH View Post
Vapor lock on a carburatored engine? Is there a spacer or heat shield between the carb and manifold?
Larry
It's a Rousch engine. Not modified so I doubt it.

Quote:
Originally Posted by ACademic View Post
On a warmed-up engine, you should only have to depress the gas pedal slightly (maybe half way at most) and turn the key (no pumping). Otherwise, you risk flooding it. If that doesn't work, then you might be boiling the fuel out of the bowls. If the starter is cranking the engine slower when warm, that could be a whole different issue (weak ground wires, thermal expansion of an older, non-high torque starter, not enough CCA from the battery, etc.).
Tried depressing, not halfway but maybe 1/4. I'd say its cranking as quickly warm as it does cold. It's all stock SPF components, mid 2k chassis number.
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Old 09-01-2017, 02:40 PM
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Had the same problem with my roush engine when new. Put a 1/2 inch phenolic spacer under the carb. Problem solved. No more percolation.
Also, during hot restarts, use no throttle. Should fire right up.
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Old 09-01-2017, 03:23 PM
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Quote:
Originally Posted by Midcont View Post
The car has a small block 351w-427R.
It starts up immediately when cold. When warm, sometimes two or three attempts with a couple of seconds of cranking, unless I catch it just right with a few pumps on the gas pedal and just enough pressure on it while I start.
A new fuel pump was installed at the beginning of summer. I don't really remember having this issue before it. The mechanic says its due to the high levels of ethanol in the fuel. It took all summer, but I last week put in 5 gallons of 104 octane and filled the rest with 94 octane to see if this rectified the issue. It didn't.
I've also read it could be the starter not working well when warm.
Any thoughts or suggestions?
Every older carbureted car I have ever owned exhibited this behavior to some extent including my current Cobra. My rule of thumb has always been - when cold (and I mean like first start of the day or after sitting for several hours) use one good pump and then crank with the throttle 1/4 to 1/2 open. When warm, don't touch the throttle just turn the key. Some cars like just a LITTLE throttle on a warm start but not much and if you pump it warm you will almost always flood it and it will take a bit of cranking to get the extra fuel out (and a nice black cloud when it finally fires). My old 390 Galaxie was like this, my small block Camaro, my F-150 with the 351W...all of them.

If the starter is cranking quick when warm it's not your starter.
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Old 09-01-2017, 04:13 PM
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By all of the replies so far, your starter sounds fine.

What carburetor have you got?

Photos would be good.
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Old 09-01-2017, 05:26 PM
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99.9%....... you need a spacer between your carb and intake. Had to put one on my old Roush 427R.... problem solved. Just make sure your air cleaner will still clear the hood if you install one.
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Old 09-01-2017, 06:10 PM
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Had the same problem with my 1955 Thunderbird, which was livable for many years. When I had to switch to 10-15% ethanol the problem became even worse. Replaced the carb with a new Edelbrock, new phenolic base plate and blocked the manifold choke heat riser passageway. Never really fixed the problem. Sold the car soon after. My ERA has a turkey pan which I feel reflects the heat from the engine and the carb.
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Old 09-01-2017, 08:18 PM
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After its warmed up, if it is turning over slower compared to when cold, your timing is to far advanced. Could be vapor lock could be heat soaking...
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Old 09-02-2017, 09:05 AM
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Aluminum intake, aluminum carb, definitely needs a phenolic spacer. Mine was boiling the fuel out of the bowls and giving me all sorts of problems. Cheap little spacer solved it. And Jeff Classic adding a whole bunch of timing really woke her up.
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Old 09-02-2017, 03:39 PM
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Quote:
Originally Posted by Midcont View Post
The car has a small block 351w-427R.
It starts up immediately when cold. When warm, sometimes two or three attempts with a couple of seconds of cranking, unless I catch it just right with a few pumps on the gas pedal and just enough pressure on it while I start.
A new fuel pump was installed at the beginning of summer. I don't really remember having this issue before it. The mechanic says its due to the high levels of ethanol in the fuel. It took all summer, but I last week put in 5 gallons of 104 octane and filled the rest with 94 octane to see if this rectified the issue. It didn't.
I've also read it could be the starter not working well when warm.
Any thoughts or suggestions?
CLICK HERE

You only need one metal heat shield and two gaskets.


Bill S.
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Old 09-03-2017, 08:24 AM
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Quote:
Originally Posted by Gaz64 View Post
By all of the replies so far, your starter sounds fine.

What carburetor have you got?

Photos would be good.
It's a Holly 4150

Quote:
Originally Posted by Phx Mike View Post
Every older carbureted car I have ever owned exhibited this behavior to some extent including my current Cobra. My rule of thumb has always been - when cold (and I mean like first start of the day or after sitting for several hours) use one good pump and then crank with the throttle 1/4 to 1/2 open. When warm, don't touch the throttle just turn the key. Some cars like just a LITTLE throttle on a warm start but not much and if you pump it warm you will almost always flood it and it will take a bit of cranking to get the extra fuel out (and a nice black cloud when it finally fires). My old 390 Galaxie was like this, my small block Camaro, my F-150 with the 351W...all of them.

If the starter is cranking quick when warm it's not your starter.
Thanks, tried this yesterday and worked. will see if the method holds.

Quote:
Originally Posted by jhv48 View Post
Had the same problem with my roush engine when new. Put a 1/2 inch phenolic spacer under the carb. Problem solved. No more percolation.
Also, during hot restarts, use no throttle. Should fire right up.
Quote:
Originally Posted by E5USMC View Post
99.9%....... you need a spacer between your carb and intake. Had to put one on my old Roush 427R.... problem solved. Just make sure your air cleaner will still clear the hood if you install one.
Quote:
Originally Posted by mrmustang View Post
CLICK HERE

You only need one metal heat shield and two gaskets.


Bill S.
Thanks guys, this will be my next step if issue persists. Question; open style or four barrel style? The carb is four barrel but either style would work?

Thanks all for replies.
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Old 09-03-2017, 03:32 PM
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Quote:
Originally Posted by Midcont View Post
Thanks guys, this will be my next step if issue persists. Question; open style or four barrel style? The carb is four barrel but either style would work?

Thanks all for replies.
Should not really matter whether open or 4 hole for a heat shield.

Just get one on there, you'll notice the difference.

Gary
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Old 09-04-2017, 02:28 PM
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I may be missing something ?
If you overheat a starter it will not give full crank.

I replaced my starter and added a stick on heat shield.
Two years no issue.
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Old 09-04-2017, 04:25 PM
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Quote:
Originally Posted by 1985 CCX View Post
I may be missing something ?
If you overheat a starter it will not give full crank.

I replaced my starter and added a stick on heat shield.
Two years no issue.
Does it ever get to 100 degrees, plus high humidity is NH? I thought your driving season was like, 6 weeks long


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Old 09-04-2017, 04:47 PM
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Good one Bill........
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Old 09-04-2017, 07:26 PM
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Quote:
Originally Posted by Phx Mike View Post
....When warm, don't touch the throttle just turn the key....
I agree with Mike. If the engine is hot, don't touch the gas pedal at all (initially). Wait until you hear the engine just start to catch on a couple of cylinders and then add just a touch of pedal.

Cheers,
Glen
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Old 09-05-2017, 05:38 AM
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Default Vapour lock: How to cure

It seems clear you need to try the spacer idea, as its simple and clearly other guys say it works.. However, if that doesn't solve it, then it means your near static fuel is most likely boiling in the line to the carb, once the engine is shut down. When it boils, AKA Vapour Lock, it creates an air pocket that can in effect, stop fuel getting to the carb.
One way to overcome, is to set your bonnet open slightly and alter your radiator fan, so it stays on longer after shutdown. Renault did this with the little 5 Turbo and it cured the hot start issues, which originated from a sometimes red hot turbocharger.
However, the bulletproof method is to have a return line back to the tank from the carb, with an in line regulator. This way cool fuel from tank is constantly circulating at idle and can't boil.
As with all fuel line fittings, monitor tightness regularly as failure of these is what causes engine fires. Metal air filter elements are better too.
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