New rebuilt 502 installed and lacking power-Help!
08-22-2013, 10:43 AM
#12
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It might be like new or it could have color but be wet with gas. If they all look about the same color, and are dry then that is what you want. That's probably not the problem, but is an easy thing to check. Also double check the firing order, and that the wires are connected good. a friend of mine took his boat in to get tuned up this spring and it would not even get on plane. I found two spark plug wires backwards, I swap the wires around and it runs like a top.
08-22-2013, 11:01 AM
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08-22-2013, 06:56 PM
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Intake: Performer, or Performer RPM? Big difference (you need the Performer RPM, or the RPM Airgap).
Carb may not be jetted correctly.
Cam may be installed a tooth off, or in the improper position.
Timing may be off.
You should swing past 5,000 rpm with a 420 horse 502 and that prop if you ran 4400 with a vanilla 454.
"Reputable" engine builder is a nebulous term. There are guys who check everything and do it right, and there are everybody else...
Just helped a friend with a Buick nailhead motor built by "the best Buick guy in the country". He sent his motor all the way to California from Tennessee to get this guys' experience.
The motor wouldn't run right.
Ended up having way too big of a cam installed 15 degrees out of spec. Motor was supposed to be a "squish" motor, but the pistons were .090" down in the holes (and one side was milled improperly on a .020" taper). Heads did not have bowl work he promised they would have. Timing tape had been put on the balancer 5 degrees off. Oil bypass spring was left completely out of the block and it was bypassing the filter.
It didn't "act" right indeed, so I started by checking TDC to the tape. Once I found that wrong, I then pulled a valve cover and set up a dial indicator and determined the cam was advanced 15 degrees. Compression test after fixing that revealed significant difference on one bank, with pressure going up the farther back you went. I advised him to pull the heads and found crappy block work. Then when the block got pulled to send it back to the guy I checked clearances and such and found the spring missing. Everything else was "okay ish" with clearances in the normal range, etc. I just think some of these "reputable guys" get distracted by their fame, come up with "recipes" for these motors, and let minimum wage kids do most of the assembly and checking.
Don't trust your builder unless you KNOW he is top notch. I have found that you better check everything.
MC
Carb may not be jetted correctly.
Cam may be installed a tooth off, or in the improper position.
Timing may be off.
You should swing past 5,000 rpm with a 420 horse 502 and that prop if you ran 4400 with a vanilla 454.
"Reputable" engine builder is a nebulous term. There are guys who check everything and do it right, and there are everybody else...
Just helped a friend with a Buick nailhead motor built by "the best Buick guy in the country". He sent his motor all the way to California from Tennessee to get this guys' experience.
The motor wouldn't run right.
Ended up having way too big of a cam installed 15 degrees out of spec. Motor was supposed to be a "squish" motor, but the pistons were .090" down in the holes (and one side was milled improperly on a .020" taper). Heads did not have bowl work he promised they would have. Timing tape had been put on the balancer 5 degrees off. Oil bypass spring was left completely out of the block and it was bypassing the filter.
It didn't "act" right indeed, so I started by checking TDC to the tape. Once I found that wrong, I then pulled a valve cover and set up a dial indicator and determined the cam was advanced 15 degrees. Compression test after fixing that revealed significant difference on one bank, with pressure going up the farther back you went. I advised him to pull the heads and found crappy block work. Then when the block got pulled to send it back to the guy I checked clearances and such and found the spring missing. Everything else was "okay ish" with clearances in the normal range, etc. I just think some of these "reputable guys" get distracted by their fame, come up with "recipes" for these motors, and let minimum wage kids do most of the assembly and checking.
Don't trust your builder unless you KNOW he is top notch. I have found that you better check everything.
MC
08-23-2013, 09:02 PM
#16
08-27-2013, 01:38 PM
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Intake: Performer, or Performer RPM? Big difference (you need the Performer RPM, or the RPM Airgap).
Carb may not be jetted correctly.
Cam may be installed a tooth off, or in the improper position.
Timing may be off.
You should swing past 5,000 rpm with a 420 horse 502 and that prop if you ran 4400 with a vanilla 454.
"Reputable" engine builder is a nebulous term. There are guys who check everything and do it right, and there are everybody else...
Just helped a friend with a Buick nailhead motor built by "the best Buick guy in the country". He sent his motor all the way to California from Tennessee to get this guys' experience.
The motor wouldn't run right.
Ended up having way too big of a cam installed 15 degrees out of spec. Motor was supposed to be a "squish" motor, but the pistons were .090" down in the holes (and one side was milled improperly on a .020" taper). Heads did not have bowl work he promised they would have. Timing tape had been put on the balancer 5 degrees off. Oil bypass spring was left completely out of the block and it was bypassing the filter.
It didn't "act" right indeed, so I started by checking TDC to the tape. Once I found that wrong, I then pulled a valve cover and set up a dial indicator and determined the cam was advanced 15 degrees. Compression test after fixing that revealed significant difference on one bank, with pressure going up the farther back you went. I advised him to pull the heads and found crappy block work. Then when the block got pulled to send it back to the guy I checked clearances and such and found the spring missing. Everything else was "okay ish" with clearances in the normal range, etc. I just think some of these "reputable guys" get distracted by their fame, come up with "recipes" for these motors, and let minimum wage kids do most of the assembly and checking.
Don't trust your builder unless you KNOW he is top notch. I have found that you better check everything.
MC
Carb may not be jetted correctly.
Cam may be installed a tooth off, or in the improper position.
Timing may be off.
You should swing past 5,000 rpm with a 420 horse 502 and that prop if you ran 4400 with a vanilla 454.
"Reputable" engine builder is a nebulous term. There are guys who check everything and do it right, and there are everybody else...
Just helped a friend with a Buick nailhead motor built by "the best Buick guy in the country". He sent his motor all the way to California from Tennessee to get this guys' experience.
The motor wouldn't run right.
Ended up having way too big of a cam installed 15 degrees out of spec. Motor was supposed to be a "squish" motor, but the pistons were .090" down in the holes (and one side was milled improperly on a .020" taper). Heads did not have bowl work he promised they would have. Timing tape had been put on the balancer 5 degrees off. Oil bypass spring was left completely out of the block and it was bypassing the filter.
It didn't "act" right indeed, so I started by checking TDC to the tape. Once I found that wrong, I then pulled a valve cover and set up a dial indicator and determined the cam was advanced 15 degrees. Compression test after fixing that revealed significant difference on one bank, with pressure going up the farther back you went. I advised him to pull the heads and found crappy block work. Then when the block got pulled to send it back to the guy I checked clearances and such and found the spring missing. Everything else was "okay ish" with clearances in the normal range, etc. I just think some of these "reputable guys" get distracted by their fame, come up with "recipes" for these motors, and let minimum wage kids do most of the assembly and checking.
Don't trust your builder unless you KNOW he is top notch. I have found that you better check everything.
MC
I will have to check which intake it is but I do know it is the stock manifold that Indmar would have built the engine with so I would think it would be right.
09-04-2013, 03:18 PM
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And the latest...
I trailered my boat out to a large lake where I met my marine mechanic. We ran the boat to check the timing and then again at full throttle while he checked the advanced timing. 9 degrees and then around 33 degrees advanced. On his digital tach he read 4200 at max speed and when I backed off the throttle slightly it went up to 4550 max rpm. I talked to another guy and he suggested that I may need larger jets due to the fact that the RPM increased once I backed off the throttle. The mechanic also sprayed gas into the throttle at WOT he said if it was getting enough fuel it would bog down which it didn't. Bigger jets required??
I trailered my boat out to a large lake where I met my marine mechanic. We ran the boat to check the timing and then again at full throttle while he checked the advanced timing. 9 degrees and then around 33 degrees advanced. On his digital tach he read 4200 at max speed and when I backed off the throttle slightly it went up to 4550 max rpm. I talked to another guy and he suggested that I may need larger jets due to the fact that the RPM increased once I backed off the throttle. The mechanic also sprayed gas into the throttle at WOT he said if it was getting enough fuel it would bog down which it didn't. Bigger jets required??
09-05-2013, 08:11 AM
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Was it a new carburator? Is it a vacuum secondary carb, or double pumper? You need to pull the ends off the carb and see what jets are in it. Get the numbers off the carb and post all the numbers, because we are dealing with a lot of unknowns at this point. You could increase the timing 2-3 degrees and test to see if it makes any difference. Will it rev upto 5000+ in neutral? If not then you need to start looking for ignition problems or rev limiter. As was stated, was it timed in base timing mode?
