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| Backfiring after electronic ignition ... |
| Author |
Message |
    
JR
Member
Username: jim_cc251
Post Number: 5
Registered: 09-2006
| | Posted on Sunday, May 20, 2007 - 08:36 am: | 
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I have a 1990 Marine power Chevy 350 which ran good the last two seasons. This Spring, I swapped out the points for electronic ignition and put in new plugs properly gapped and new wires. It ran great in the yard. In the water it backfires badly (sound echos from the exhaust, not the carb) under load and does not go above about 2400 rpm. At low speed it runs smooth. In neutral I can rev it high with an occasional backfire. After reading all the posts here, I will first swap out the fuel filters-- tank was stored full of E10 with stabalizer-- but I am suspicious that this is electrical. I doubt if it is an exhaust problem. I did not change the coil. I will double check the firing order and the tach wire. I can always swap the old points back in. I did not have a chance to check the timing so that will be next on my list. Any suggestions?
Thanks,
Jim |
JUST-IN-TIME
Senior Member
Username: justintime
Post Number: 1547
Registered: 09-2006
| | Posted on Monday, May 21, 2007 - 09:25 pm: |
|
check timing and then tell us
make sure #1 is at TDC |
Fastjeff
Senior Member
Username: fastjeff
Post Number: 3470
Registered: 09-2003
| | Posted on Tuesday, May 22, 2007 - 08:52 am: |
|
I'll bet you've got a couple of crossed ignition wires. Let it idle and pull one wire at a time fromthe cap. If the engine slows down, put the wire back. If it doesn't slow down, leave that one out until you find a second one, then switch the two.
Jeff |
JR
Member
Username: jim_cc251
Post Number: 6
Registered: 09-2006
| | Posted on Tuesday, May 22, 2007 - 07:58 pm: |
|
Here is the updated situation. My (ex) mechanic left me with 3 mixed up wires (2,4,8 were wrong!) and an unknown timing. The wires were an easy fix. No more backfire. At that point I could only get 3000 rpm and no high speed jets. I swapped the filters and threw some octane boost into the old gas. Not being able to find my timing light, I put on a vacuum gauge and advanced timing to max vacuum 22 inches, and then backed off the advance to 20 inches. I know this is not a timing substitute but it puts me in the ballpark. Now at least the high-speed jets open up and the tach reads 3500 (maybe not accurate it revs, actually "winds up" pretty good by ear?). I know I need to verify the real timing and find my true rpm's at wot but any sugestions are appreciated. This Chris Craft Catalina 251 goes up to 12 knots without effort and then labors to go from there to 20 knots. Maybe that is just the nature of the beast.
Thanks,
Jim |
JUST-IN-TIME
Senior Member
Username: justintime
Post Number: 1560
Registered: 09-2006
| | Posted on Tuesday, May 22, 2007 - 10:17 pm: |
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adjust timing before u find a new motor |
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