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Old 04-21-2005, 14:46   #1 (permalink)
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Severe Bogging in 5.0L Engine after cam change

Hi All:

First - I hope that this is the correct forum for this question/problem.

----------------------------------------------------------------
I have an 86 5.0L engine that has the following mods:

1. Competition Cams Magnum Camshaft (.5" lift, 270 deg. Duration, power band from 1500-5000 RPM, moderately rough idle)

2. 289 Cylinder heads with 351 Windsor valves (Int & Exh) and double valve springs

3. Edelbrock Model R4B Intake manifold with 2" Riser.

4. 650 Holley Carb (DIY rebuild)

5. Holley Fuel Pump
------------------------------------------------------------------

The problem is as follows:

1. Engine ran fairly decently after initial startup but I noticed that there were some gasoline leaks in and around the carb. I corrected these and remounted the carb, only to find another leak in the rear 2-barrel ports of the Carb. I corrected this leak by re-adjusting the rear float apparatus.

2. After reinstalling the carb no other leaks were detected.

3. The engine now has a severe bog and cuts out completely (on occasion) when put into gear. Pumping the accelerator pedal to force the accelerator pump to feed more gas helps a little but for all-intents-and-purposes, the engine acts as if it is fuel starved

4. I checked the carb accelerator pump and it is working fine. I re-checked both floats and they are fine. Also, there are no apparent leaks anywhere.

5. Varying the fuel pump pressure has no effect on the problem.

-------------------------------------------------------------------

I am wondering if the engine would be so sensitive to undersized jets in the carb as to exhibit this behavior.

I suspect that the carb requires re-jetting because it did not exhibit a bog until I repaired the leak in the rear 2-barrel ports. I do not know how to calculate/estimate the correct sizing.

Could the engine timing (currently stock setting) cause the engine to exhibit this behavior under load

If there are any among you folks that have come across this problem and can offer some suggestions as to correct carb jet sizing, engine timing, or other things to look at I would MOST appreciate a response.

Thanks to all.
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Old 04-21-2005, 18:45   #2 (permalink)
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Re: Severe Bogging in 5.0L Engine after cam change

Theres a couple of things it'll be :

Lean condition
Cam timing
Ignition timing
torque convertor too small

Is that 270@50? If it is? That cam won't make power from 1500rpm.
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Old 04-21-2005, 19:03   #3 (permalink)
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Re: Severe Bogging in 5.0L Engine after cam change

Quote:
Originally Posted by bigolow
Hi All:

First - I hope that this is the correct forum for this question/problem.

----------------------------------------------------------------
I have an 86 5.0L engine that has the following mods:

1. Competition Cams Magnum Camshaft (.5" lift, 270 deg. Duration, power band from 1500-5000 RPM, moderately rough idle)

2. 289 Cylinder heads with 351 Windsor valves (Int & Exh) and double valve springs

3. Edelbrock Model R4B Intake manifold with 2" Riser.

4. 650 Holley Carb (DIY rebuild)

5. Holley Fuel Pump
------------------------------------------------------------------

The problem is as follows:

1. Engine ran fairly decently after initial startup but I noticed that there were some gasoline leaks in and around the carb. I corrected these and remounted the carb, only to find another leak in the rear 2-barrel ports of the Carb. I corrected this leak by re-adjusting the rear float apparatus.

2. After reinstalling the carb no other leaks were detected.

3. The engine now has a severe bog and cuts out completely (on occasion) when put into gear. Pumping the accelerator pedal to force the accelerator pump to feed more gas helps a little but for all-intents-and-purposes, the engine acts as if it is fuel starved

4. I checked the carb accelerator pump and it is working fine. I re-checked both floats and they are fine. Also, there are no apparent leaks anywhere.

5. Varying the fuel pump pressure has no effect on the problem.

-------------------------------------------------------------------

I am wondering if the engine would be so sensitive to undersized jets in the carb as to exhibit this behavior.

I suspect that the carb requires re-jetting because it did not exhibit a bog until I repaired the leak in the rear 2-barrel ports. I do not know how to calculate/estimate the correct sizing.

Could the engine timing (currently stock setting) cause the engine to exhibit this behavior under load

If there are any among you folks that have come across this problem and can offer some suggestions as to correct carb jet sizing, engine timing, or other things to look at I would MOST appreciate a response.

Thanks to all.
Could you have sucked some crap into the carby, maybe a small piece of gasket? This can occur after re-building a carby if it's not thoroughly cleaned out. If it ran alright to start with, then played up & leaked fuel, it could be crap in the needle+seats and/or jets.
Mal.
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