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pasmadj
04-19-2010, 01:42 PM
Boat is a '74 S&S with a Ford 351. I replaced the carb with a rebuilt Holley 4bbl last fall. I took it out for a day just before I put it away for the winter. It idled well, started well, and had good top end.

However, out of the hole (especially when pulling skiiers), I had to goose it to coax it to not bog and die - not good at all for skiiers.

I have observed fuel spraying into the carb when I push the throttle. So, that means the accelerator pump is working fine?

Any ideas of what could be causing this, and what I might be able to do about it?

Thanks.

thatsmrmastercraft
04-19-2010, 02:46 PM
For starters why did you replace the carb?
Where you having problems prior to the replacement?
Did this bogging problem occur only after the rblt. carb was installed?
What are the condition of the plugs, points, dist cap & rotor, plug wires?
Is the timing set to spec?
Are the dist weights moving freely?
How long since you replaced the fuel filter?

Answers to these questions should give us a place to start.

dog paw
04-19-2010, 03:26 PM
Like MRMastercraft said there are alot of other things that can cause the problem your having. That said, if your replacement carb was a "fit all" rebuild you can bet it has the wrong power valve in the metering plate. I'm not sure of the valve number anymore but its not close to a "street" P valve. That will give you full throttle dump issues.

Also accel pump nozzel sizes are selectable and accel pump lever adj is critical

couple thoughts that came to mind off the cuff..... WAY to many "choices" on a Holley carb:)

03 35th Anniversary
04-19-2010, 03:45 PM
Boat is a '74 S&S with a Ford 351. I replaced the carb with a rebuilt Holley 4bbl last fall. I took it out for a day just before I put it away for the winter. It idled well, started well, and had good top end.

However, out of the hole (especially when pulling skiiers), I had to goose it to coax it to not bog and die - not good at all for skiiers.

I have observed fuel spraying into the carb when I push the throttle. So, that means the accelerator pump is working fine?

Any ideas of what could be causing this, and what I might be able to do about it?

Thanks.

This should fix it all!!!

http://www.summitracing.com/parts/EDL-2092/

pasmadj
04-19-2010, 05:49 PM
I replaced the carb because I could not get the boat to start. I would pump it like crazy, then turn it over. It would fire, but then immediately die. I couldn't even keep it running by pumping the throttle. My 'knowledgeable' friend checked the plugs, and the distributor. We also tried to run it without the fuel filter. Nothing helped. In addition, my old carb did not have j-tubes. So, I decided it was time to be safe, and take the carb out of the equation. When we replaced it, it fired right up. he made sure the timing was set top dead center, maybe a little advanced. I opened up the old carb. It was pretty bad looking. We think it was the ethanol in our gas, combined with the fact that I don't get it out as much as I used to.

pasmadj
04-20-2010, 09:58 AM
Another piece of information: Here is the carburetor I installed last fall.
http://www.nationalcarburetors.com/marine/fourbarrelholley.aspx

thatsmrmastercraft
04-20-2010, 10:16 AM
If you haven't installed new plugs, points and condenser this spring, I would do so before you do anything else. Be sure to get the dwell set at 30-32 and your timing at 10 degrees BTDC at 600 - 700 RPM. Being sure of all this is very important.

While the timing light is hooked up, watch to see that the timing advances with RPM.

Does the engine rev freely in neutral?

Have you made any adjustments to the freshly rebuilt carb from National? Their carbs normally are a bolt on and run affair.

pasmadj
04-20-2010, 12:30 PM
Thanks for your advice. When I installed the carb from National, we checked the plugs, and made sure the timing, dwell, were all as you said. It does respond well in the driveway in neutral. We did not tinker with the carb when we installed it - other than tweak the accelerator adjustment when we connected the throttle cable.

Chicago190
04-20-2010, 12:40 PM
If you haven't installed new plugs, points and condenser this spring, I would do so before you do anything else. Be sure to get the dwell set at 30-32 and your timing at 10 degrees BTDC at 600 - 700 RPM. Being sure of all this is very important.

While the timing light is hooked up, watch to see that the timing advances with RPM.

Does the engine rev freely in neutral?

Have you made any adjustments to the freshly rebuilt carb from National? Their carbs normally are a bolt on and run affair.

I thought the timing was supposed to be 10 degrees BTDC at 1000 RPMs, even on the carb boats?

thatsmrmastercraft
04-20-2010, 03:04 PM
I thought the timing was supposed to be 10 degrees BTDC at 1000 RPMs, even on the carb boats?

Its my understanding that the engines with a carb are set at idle in gear. JimN care to enlighten us.

My '77 is at its happiest at 10 degrees BTDC at 600 RPM in gear. I can do whatever I want with the throttle regardless of empty boat or loaded boat pulling skiers. That leaves it at about 700 RPM at idle in neutral.

Chicago190
04-20-2010, 06:48 PM
Its my understanding that the engines with a carb are set at idle in gear. JimN care to enlighten us.

My '77 is at its happiest at 10 degrees BTDC at 600 RPM in gear. I can do whatever I want with the throttle regardless of empty boat or loaded boat pulling skiers. That leaves it at about 700 RPM at idle in neutral.

Last post here gives us a pretty good answer: http://www.mastercraft.com/teamtalk/showthread.php?t=33740&highlight=timing

Probably makes no difference for the carb engines. EFI engines are set at 1000 RPMs because that is the RPM when the ECM is in diagnostic mode.

thatsmrmastercraft
04-20-2010, 08:50 PM
Sounds like the answer to me.

pasmadj
06-21-2010, 08:17 AM
I have a question for you knowledgeable folks. How is timing advanced during acceleration? There isn't vacuum advance on the distributor. Is there some other method that I just don't know about yet? I am learning slowly.

thatsmrmastercraft
06-21-2010, 09:22 AM
I have a question for you knowledgeable folks. How is timing advanced during acceleration? There isn't vacuum advance on the distributor. Is there some other method that I just don't know about yet? I am learning slowly.

Counter weights on springs under the base plate of the distributor. As engine speed increases, centrifugal force overcomes the tension of the spring and advances the timing.