mercruiser 5.7 bogs down a 2600 rpms

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jay904

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l have a 1986 sea ray with a 1986 260 5.7 thunderbolt lV ignition sbc mercruiser with a rochester 4 barrel quadrojet carb,l have rebuilt the carb,new wires,plugs,dist cap & rotor,changed fuel filters, cleaned flame arrestor , checked the timeing also checked to see if it was advanceing 24deg and it was,had the boat out with flame arrestor off put throttle full forward to see if secondaries where opening on carb and they were, but it seemed like the fuel was puffing a little up thru the carb instead of being sucked down the barrel on the secondaries, l am at wits end trying to figure out why l have no power and bogging down at 2500-2700 rpms, anybody out there tell me what l should for or check
 
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jay904

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Re: mercruiser 5.7 bogs down a 2600 rpms

yep l checked that too,l'm now thinking weak coil ,not a hot enough spark
 
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sea flower

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Re: mercruiser 5.7 bogs down a 2600 rpms

Don't waste any time on anything else. You have a bad carburetor. Rebuild it again.
Probably got something in a jet hole. Happenned to me. everything you're writting I did. Carburetor.. take it for what's it's worth......remove it and clean it. takes about 3 hours done right. you've done it once already
 
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FreeBeeTony

FreeBeeTony

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Re: mercruiser 5.7 bogs down a 2600 rpms

jay904 said:
seemed like the fuel was puffing a little up thru the carb instead of being sucked down the barrel on the secondaries
Click to expand...

I had a problem similar to this and it ended up being an intake valve being stuck open at higher RPM's......mine was "bogging" at 3200 RPM's
 
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John_S

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Re: mercruiser 5.7 bogs down a 2600 rpms

FreeBeeTony said:
I had a problem similar to this and it ended up being an intake valve being stuck open at higher RPM's......mine was "bogging" at 3200 RPM's
Click to expand...

"puffing a little up thru the carb"

I was heading down same thought path, make sure the mechanicals are in good order. Compression and vacuum checks.
 
FreeBeeTony

FreeBeeTony

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Re: mercruiser 5.7 bogs down a 2600 rpms

FWIW.......my engine showed good compression. The problem didn't appear until 3200 RPM's, that's when I would loose a cylinder. I found it by shorting out the plug wires at the dist cap when the problem was happening........was able to determine which cylinder was not "contributing".......
 
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John_S

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Re: mercruiser 5.7 bogs down a 2600 rpms

FreeBeeTony said:
FWIW.......my engine showed good compression. The problem didn't appear until 3200 RPM's, that's when I would loose a cylinder. I found it by shorting out the plug wires at the dist cap when the problem was happening........was able to determine which cylinder was not "contributing".......
Click to expand...


That might be hard to detect with vacuum gauge at 3200 rpm too, but think you would see some indication.
 
FreeBeeTony

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Re: mercruiser 5.7 bogs down a 2600 rpms

If I remember correctly I tried using a vacumm gauge during my troubleshooting but didn't really see anything........it was normal at idle.
 
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jay904

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Re: mercruiser 5.7 bogs down a 2600 rpms

l forgot to add ;;;l was thinking maybe a bad intake valve also but in neutral the engine runs perfect up to 4000 rpms,problem only happens in gear under a load ,l don't think its the prop because it only has a 16" pitch 4 1/2 diam 4 blade prop on it got me stumped
 
FreeBeeTony

FreeBeeTony

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Re: mercruiser 5.7 bogs down a 2600 rpms

reving it in neutral will tell you nothing.......however, when I did that I did notice the fuel coming out of the carb while I operated the throttle from the carb.
 
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John_S

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Re: mercruiser 5.7 bogs down a 2600 rpms

jay904 said:
l forgot to add ;;;l was thinking maybe a bad intake valve also but in neutral the engine runs perfect up to 4000 rpms,problem only happens in gear under a load ,l don't think its the prop because it only has a 16" pitch 4 1/2 diam 4 blade prop on it got me stumped
Click to expand...

Running in neutral does not find many problems. If you have a consistant valve issue, the vacuum test should find it. Tony's issue was something that only started to happen at a particular rpm.
 
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Aloysius

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Re: mercruiser 5.7 bogs down a 2600 rpms

If you've got vortec heads, you have to change the intake manifold to match the votec bolt pattern.
 
CAPTKEV85

CAPTKEV85

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Re: mercruiser 5.7 bogs down a 2600 rpms

I am having the same problem too. 1985 sea ray 260 mercruiser at the same rpms, my carb was rebuilt last year from previous owner. but I am going to rebuild again.
 
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Aloysius

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Re: mercruiser 5.7 bogs down a 2600 rpms

Angle of the center bolts.
 
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