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09-17-2009, 12:50 PM
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#1
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Registered
Join Date: Dec 2004
Posts: 18
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525SC Miss/Backfire
I have a 1999 525SC in a 47 Fountain that has intermittent miss or backfire above 2500 RPM under load. If run this motor at 2000 RPM and other 2 at 3000 RPM, no miss. Have swapped coil, distributor module, etc. no change. Any ideas before I swap knock sensor and rev limiter modules? Thanks
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09-17-2009, 01:05 PM
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#2
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Boost is your friend!
 VIP Member
Join Date: Feb 2002
Location: Lake Michigan/Chain-O-Lakes
Posts: 5,121
1993 42' Fountain
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Hows the cap and rotor look?
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Saris Racing 800SC's
BMax / -2 IMCO lowers on boxes
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09-17-2009, 01:49 PM
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#3
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Charter Member # 55
 Charter Member
Join Date: Oct 2000
Location: Omaha
Posts: 7,843
32 Active Thunder
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There is no knock sensor on a 525SC and the issue won't be in the rev limiter box.
Do a complete tune up with plugs, cap and rotor. Check all the ignition wiring connections for corrosion.
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09-17-2009, 03:07 PM
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#4
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Registered
Join Date: Dec 2004
Posts: 18
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No knock sensor on a 525SC? Thought there was. Plugs, cap and rotor look good but I'll change them out as much easier to get to than the other modules. Thanks
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09-17-2009, 03:11 PM
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#5
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Registered
Join Date: Jan 2003
Location: MIDDLETOWN,DE
Posts: 1,721
320 VELOCITY
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I had the same type of problems with my 525sc engine a few years ago,it was being caused by a lean condition through the base of the carburator,sent the carbs for rebuid through Diamond Performance and replaced base gaskets and the problems went away,also as recomended on another post do a complete tune up with wires.Good luck.
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09-18-2009, 02:55 AM
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#6
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Charter Member # 55
Charter Member
Join Date: Oct 2000
Location: Omaha
Posts: 7,843
32 Active Thunder
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Quote:
Originally Posted by boatstogo
No knock sensor on a 525SC? Thought there was. Plugs, cap and rotor look good but I'll change them out as much easier to get to than the other modules. Thanks
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Almost all of the 525SC's used a TB IV ignition which does not have a knock sensor/timing retard function.
The last run of 525SC's, which you may have, does use a TB V ignition and may actually have a knock sensor.
Last edited by Griff : 09-18-2009 at 02:59 AM.
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10-03-2009, 04:14 PM
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#7
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Registered
Join Date: Dec 2004
Posts: 18
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Well, I did a cold compression test today, and found that the number no 8 cylinder intake valve is stuck in the open position. Anyone know of a way to free it up short of pulling the head and reworking the valve guide? All other cylinders are 135 to 140 PSI. Engine has 420 hrs. Could the CMI headers have an internal leak that has allowed moisture to enter the cylinder and corrode the valve stem? Thanks for any info.
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10-03-2009, 07:34 PM
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#8
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Registered
Join Date: Aug 2005
Posts: 241
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mrfixxall
Quote:
Originally Posted by boatstogo
Well, I did a cold compression test today, and found that the number no 8 cylinder intake valve is stuck in the open position. Anyone know of a way to free it up short of pulling the head and reworking the valve guide? All other cylinders are 135 to 140 PSI. Engine has 420 hrs. Could the CMI headers have an internal leak that has allowed moisture to enter the cylinder and corrode the valve stem? Thanks for any info.
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Time to pull it and fresh in it up,its a ticking bomb and here is a sign..It could get worse and eventually cost you a whole engine. |
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10-03-2009, 10:03 PM
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#9
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2005 Checkmate forsale
 Platinum Member
Join Date: Oct 2004
Location: Austin, Texas
Posts: 507
2005, Checkmate, 260 ZT
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Mine was doing this. Found broken rocker nuts. Replaced those and it was good to go.
Quote:
Originally Posted by boatstogo
Well, I did a cold compression test today, and found that the number no 8 cylinder intake valve is stuck in the open position. Anyone know of a way to free it up short of pulling the head and reworking the valve guide? All other cylinders are 135 to 140 PSI. Engine has 420 hrs. Could the CMI headers have an internal leak that has allowed moisture to enter the cylinder and corrode the valve stem? Thanks for any info.
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__________________
2005 CHECKMATE ZT 260 forsale
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10-04-2009, 07:49 PM
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#10
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Registered
Join Date: Sep 2009
Location: Hopewell, NJ
Posts: 23
24' Baja Outlaw
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Pull off the rocker and see if that is inhibiting in any way. if not it could be a bent valve
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