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hard hot starting issues after carb replacement

 
koolblu
I love my Chevy Chevette!
Posts: 4
Joined: 02/13
Posted: 02/04/13 11:19 AM

I had used a Street Demon on my 406 SBC for a number of years w/o issues.  It developed a stumble that stumped me, so I installed a brand new Holley Street Avenger (770 cfm) last summer.  The low end responsiveness and easy of cold starting are superior to the Demon, so glad i made the switch.  The issue is starting the car when it is warm.  It acts flooded and requires a bit of cranking with the throtle wide open.  Using a 1/2" card spacer.  From a practice perspective, cannot do much about gas (use 93 octane) and its ethanol content.

The Demon was a heavy carb as compared to the Holley.  Wondering if the light construction acts like a quicker "heat sink'?  At times, i can actually hear the fuel "boiling" after i shut 'er down.
Thoughts?  

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tuffnuff
Moderator
Posts: 7841
Joined: 12/09
Posted: 02/04/13 11:48 AM

Holley makes a heat shield that stacks several insulating gaskets with aluminum "fin" spacers, similar to fins on a motorcycle engine's cylinder.,. it comes with a large aluminum base plate, to deflect engine heat.
You'll also need longer studs, to mount this.
Holley Performance Products Heat Shield Kit 108-70

www.holley.com/108-70

Smile  
When The Flag Drops.,.

tuffnuff

The Bull ***t Stops.,.
tuffnuff

P. Engineer, Engine Builder

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Serpico
I love my Chevy Chevette!
Posts: 13
Joined: 02/13
Posted: 02/04/13 03:22 PM

+1 Tuff:

I just have a question. How does it crank when its heat soaked?

Bob AKA Pepsi1  

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koolblu
I love my Chevy Chevette!
Posts: 4
Joined: 02/13
Posted: 02/04/13 07:07 PM

it cranks hard, just does not want to start.  I have a CSR mini starter on it that is wrapped in a heat shield.  Plus header tubes for cylinders #6 & 8 are also wrapped with heat cloth.  battery located in trunk with a very large diameter welding cable running to starter.  

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koolblu
I love my Chevy Chevette!
Posts: 4
Joined: 02/13
Posted: 02/04/13 07:08 PM

sounds like a better deal than the wood spacer I have on there curently.  thanks for the advice.

i am also going to try 100 octane racing fuel that likley does not have ethanol in it.  

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waynep71222
I have an SS396 tatoo
Posts: 448
Joined: 03/12
Posted: 02/05/13 09:27 AM

if you have to hold the throttle open to get it started warm or hot...

first CHECK the fuel pressure...  look at your booklet with the demon to see if its above the recommended pressure from demon and could be holding the needle and seats open allowing fuel to overfill the bowl and dribble into the intake...

if this is happening.. you could hydraulic your motor.. where enough fuel pours in that its more than can be compressed as the piston comes up and may crack your piston or damage your rings..

... with a mirror and flash light.. you can remove the air filter.. use the mirror to look down the primaries.. and see if any fuel is dripping out of the boosters when the engine is OFF...


while checking fuel pressure.. please verify that the fuel pressure is maintained after you stop cranking..  i have run into so many cars with sediment issues in the fuel system ... that the check valves in the pump are kept open slightly and the fuel can drain all the way back to the fuel tank causing extended cranking times...

i normally run a full flow fuel system test... disable the ignition system so NO SPARKS can be created..  

disconnect the fuel line at the carb.. extend it into a clean clear plastic 2 or 3 liter soda bottle...

have a friend crank the engine for 15 timed seconds...   the fuel should start flowing instantly.. each pulse should be equal to every other pulse..  each one full...

you should get almost half a quart in 15 seconds..

sediment from the fuel tank or lines can also hold the needle and seats open allowing the fuel to overflow the float bowl and out into the boosters... causing your exact issue...

i always install a decent.. fuel injection type of fuel filter before the fuel pump.. so the pump gets only clean fuel... why would the fuel pump like clean fuel... well you will spend less time pushing the car  with that cheep mod... i usually use a ford fuel filter with 5/16 fittings on either end.. all except the highest horsepower motors this will work...

i also stick super magnets in the fuel tank when i have the sending unit out...  or stick an old speaker magnet to the bottom of the fuel tank... this attracts all the Red dUST to its magnetic field.. keeps it out of the fuel system...

so far we have only spent a few bucks on a decent fuel filter and additional fuel line.. perhaps some more on magnets...

try it... you would not believe how many cars i have fixed with this ... i did one just last week...

i had a BIG speaker magnet on a friends van that would clog fuel filters as he drove it sometimes 400 miles a day... he went for months without needing to change the fuel filter.. then while under the van ... spotted the HUGE speaker magnet on the bottom of the fuel tank... wondered what's this doing here... he yanked it off... looked at it.. then remembered... put it back... but it was too late... he had freed the sediment... i only made it six blocks before the fuel filter clogged up...   changed it and did not have another clog for another 40,000 miles..  

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waynep71222
I have an SS396 tatoo
Posts: 448
Joined: 03/12
Posted: 02/05/13 09:40 AM

oh.. one of the heat shield for holley flange carbs is this one.. mr gasket 3710



holley has this 108-51

510 108 51  

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skyeking
I mow my lawn and find Chevys
Posts: 2738
Joined: 08/09
Posted: 02/05/13 04:32 PM

Hi there,
You could try lowering the fuel bowl levels by 1/2' or MORE if necessary.
You can sometimes watch the " Boiling fuel overflow into the inlet manifold
which you do NOT need. All the best....  
skyeking

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koolblu
I love my Chevy Chevette!
Posts: 4
Joined: 02/13
Posted: 02/07/13 09:46 PM

I have a filter (100 mircon) mounted just off of the gas tank sump (i added sump to stock tank) and  a 40 mircon filter just past the Holley electric pump.

Fuel pressure is monitored by Holley guage on fuel rail at carb. at idle, about 6.5 psi.  yes, I checked volume--flows like a scared........

Cranking issue started only after I ditched the Demon for a Holley carb.  turned the primary float level down from factory setting.  have less than 200 miles on this set up.  I like the Holley heat shield idea.  

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Serpico
I love my Chevy Chevette!
Posts: 13
Joined: 02/13
Posted: 02/08/13 01:10 AM

koolblu
I know I keep asking questions. But have you pulled a spark plug out to see if fuel is really fouling the plugs?

I would try getting an insulator under the carb and then see if the problem gest better or stays the same.

My thought is this. Is it really flooding?

Bob AKA pepsi1  

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skyeking
I mow my lawn and find Chevys
Posts: 2738
Joined: 08/09
Posted: 02/08/13 05:04 PM

Are you getting Air locks in the pump to carby???  
skyeking

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