Engine almost dies when i punch it from idle ....

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79charger

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« on: April 07, 2011, 05:33:36 PM »
I put a 750 vacuum secondary Holley street avenger carb on BBF .Getting 5 psi of fuel pressure . If I punch it , It will almost die , But if i gradually floor it , it is fine .Plugs are chocolate brown . My guess is the accelerator pump ??? Any ideas ???



Your Mom

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« Reply #1 on: April 07, 2011, 06:38:40 PM »
Is it a new carb or fresh rebuilt. Hows the fuel pressure as you stomp on it.

79charger

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« Reply #2 on: April 07, 2011, 08:32:12 PM »
brand new carb . havent checked on the pressure when i stomp on it , but The fuel pump is a holley red pump and is also brand new

obnoxious001

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« Reply #3 on: April 07, 2011, 08:35:32 PM »
I put a 750 vacuum secondary Holley street avenger carb on BBF .Getting 5 psi of fuel pressure . If I punch it , It will almost die , But if i gradually floor it , it is fine .Plugs are chocolate brown . My guess is the accelerator pump ??? Any ideas ???

That's the best first guess, assuming it was running ok before you switched carbs?  Without the engine running, with the flame arrestor off, you can manually check to see if the accelerator pump is squirting fuel, either just gently pushing down the lever with your finger,, or even working the throttle.  If it does squirt a good stream of fuel, it may need a larger size nozzle.  How do you have the ignition timing set on the engine?

79charger

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« Reply #4 on: April 08, 2011, 07:19:13 AM »
 will have to check . usually i keep it around 9- 10 degrees

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« Reply #5 on: April 08, 2011, 07:45:03 AM »
I set my 460 - 33 @ 3000rpm. Idle is about 12 @ 1200 out of the water.

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« Reply #6 on: April 08, 2011, 10:52:11 AM »
will have to check . usually i keep it around 9- 10 degrees

OK, you are aware that you need to check total timing, by raising rpm until the mark stops moving while you are shining the light on it?  Depending on the distributor you are using, and what's been done to it, you can't really set the timing on an engine by only checking initial timing.

SLCKREG

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« Reply #7 on: April 08, 2011, 11:48:11 AM »
I had a simular issue when I bolted my domi on a year or 2 ago. Mine ended up getting fixed by swaping out the 6.5 pv for  4.5. Not sure if a vac secondary carb would/could have that issue....just throwin it out there.

79charger

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« Reply #8 on: April 09, 2011, 01:09:18 PM »
I had a simular issue when I bolted my domi on a year or 2 ago. Mine ended up getting fixed by swaping out the 6.5 pv for  4.5. Not sure if a vac secondary carb would/could have that issue....just throwin it out there.


So I have to have some one give the the motor throttle while holding the timing light at harmonic balancer , until what stops moving ? new to this total timing thing . I just usually set the idle to 1200 and adjust it to 10 degrees . So my timing could be off?  Why is this different for
 boats.


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« Reply #9 on: April 09, 2011, 02:47:10 PM »

So I have to have some one give the the motor throttle while holding the timing light at harmonic balancer , until what stops moving ? new to this total timing thing . I just usually set the idle to 1200 and adjust it to 10 degrees . So my timing could be off?  Why is this different for
 boats.

This is a pretty good video that MSD put out to set your timing and total timing.

1979 Sanger Superjet
BBC, 12JG

obnoxious001

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« Reply #10 on: April 09, 2011, 03:47:42 PM »

So I have to have some one give the the motor throttle while holding the timing light at harmonic balancer , until what stops moving ? new to this total timing thing . I just usually set the idle to 1200 and adjust it to 10 degrees . So my timing could be off?  Why is this different for
 boats.

The difference is within the distributor and engine, and to some degree, personal preference.  Within the distributor there is a mechanical advance mechanism that consists of weights and springs, and many times(as with an MSD distributor, or others) a bushing that limits travel.  That travel determines how much additional advance is brought in as the distributor spins, and the weights overcome the strength of the springs. 

What all that means is that you should be checking your total timing, after all of the advance is in.  I deal with mostly Chevy engines, and they tend to like 34-36 degrees total timing, on a carbureted engine, with less total advance preferred on a forced induction (blown or turbo) engine.

79charger

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« Reply #11 on: April 10, 2011, 07:07:18 AM »
The difference is within the distributor and engine, and to some degree, personal preference.  Within the distributor there is a mechanical advance mechanism that consists of weights and springs, and many times(as with an MSD distributor, or others) a bushing that limits travel.  That travel determines how much additional advance is brought in as the distributor spins, and the weights overcome the strength of the springs. 

What all that means is that you should be checking your total timing, after all of the advance is in.  I deal with mostly Chevy engines, and they tend to like 34-36 degrees total timing, on a carbureted engine, with less total advance preferred on a forced induction (blown or turbo) engine.


Thanks alot guys , I will check the timing today as soon as the ice melts off my boat.LOL

fast fred

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« Reply #12 on: April 10, 2011, 02:14:00 PM »
First off its a vaccum secondary and they really dont have two squirters like a double pumper. It is not a performance carb, its made to get better gas mileage. If you snap the throttle on a Vac Sec under a load the secondarys will not always open. You have to roll in to the throttle on a Vac Sec. And second it doesent really matter what it does on the trailer because it does not have a load on it. IMO i would put it in the water and run it check plugs and jet it. And as mentioned above timing at idle doesent mean shit unless you have a locked out dizzy. You have to check it at total and usally its 3000 rpm, it depends on the spring and weights but 3000 is usally enough. Stock Fords are normally set 27-31 degrees at total at least thats what i set them at.

Matt
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79charger

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« Reply #13 on: April 10, 2011, 06:46:21 PM »
Thanks guys total timing was way off . Too advanced . The MSD video was great . Thanks again

 


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