Like Tree0Likes

Backire through carb

Reply
Old 05-11-2008, 03:34 PM
  #1
Registered
Thread Starter
 
Join Date: May 2008
Location: Erlanger,KY
My Boats: 1987 Mach 1 Concorde 27
Posts: 8
Question Backire through carb

Could really use some help.. I have a 1987 27' Mach 1 Concorde. Powerplant is a 454 mag 330 horse coupled with an alpha outdrive. Having wot problems. Wants to fall on its face at wot. This will not allow me to reach max rpm. Have changed plugs, prop,rebuilt carb, changed secondary metering rods. Now it will reach 4400 rpms and 49 mph. Since changing all of this it is now backfiring through the carb at wot. I am going crazy trying to figure this out. Any help would be appreciated. Thanks
embracethehorror is offline  
Reply With Quote
Old 05-11-2008, 03:46 PM
  #2
Registered
 
Join Date: Jul 2007
Location: Austin,Texas
Posts: 2,111
Default

A compression test and check for water in fuel. Would be the first things I would check.
MOBILEMERCMAN is offline  
Reply With Quote
Old 05-11-2008, 03:50 PM
  #3
Registered
Thread Starter
 
Join Date: May 2008
Location: Erlanger,KY
My Boats: 1987 Mach 1 Concorde 27
Posts: 8
Default

Already checked for water in the fuel twice this is not the problem. I agree a compression test is in order I am trying to find the time to get it done. thanks
embracethehorror is offline  
Reply With Quote
Old 05-11-2008, 04:04 PM
  #4
Charter Member # 55
Charter Member
 
Griff's Avatar
 
Join Date: Oct 2000
Location: Omaha
My Boats: .......32............. ...............Active Thunder....
Posts: 15,752
Default

Could have a bad cam lobe.
Griff is offline  
Reply With Quote
Old 05-11-2008, 05:24 PM
  #5
Registered
Thread Starter
 
Join Date: May 2008
Location: Erlanger,KY
My Boats: 1987 Mach 1 Concorde 27
Posts: 8
Default

if the cam lobe and or lobes are wore will this show up during a compression test.
embracethehorror is offline  
Reply With Quote
Old 05-11-2008, 05:40 PM
  #6
Banned
 
cuda's Avatar
 
Join Date: Sep 2001
Location: Deland, Florida
Posts: 25,191
Default

Backfire through the carb usually indicates a lean mixture, which I don't think is your problem. The second thing I'd look for would be burned valves, which will show up on a compession check. As far as losing lobe on a cam, I doubt it. Will usually happen before 21 years. 49 with that power plant on a 27 foot boat ain't bad. Btw, it's not a 454 Mag, it's just a regular 330 horse 454. That was the only year that Merc ever mated a BBC to an Alpha drive. It just has a sticker on the drive that says 454 Mag. I have one of those drives in my garage. Just a standard Alpha drive.

Best of luck!
cuda is offline  
Reply With Quote
Old 05-11-2008, 07:30 PM
  #7
Registered
 
Join Date: May 2005
Location: LOTO Performance Boat Center
My Boats: Fixing yours
Posts: 3,897
Default

Quote:
Originally Posted by Griff View Post
Could have a bad cam lobe.
I was thinking the exact same thing.
Magic Medicine is offline  
Reply With Quote
Old 05-11-2008, 07:39 PM
  #8
Registered
 
Join Date: Jul 2006
Location: Hooksett, NH
My Boats: 1987 formula 357 sr-1
Posts: 179
Default

I had this problem with a truck one time and it was the cam that was bad. good luckm .02
amazing1 is offline  
Reply With Quote
Old 05-11-2008, 07:49 PM
  #9
Registered
Thread Starter
 
Join Date: May 2008
Location: Erlanger,KY
My Boats: 1987 Mach 1 Concorde 27
Posts: 8
Default

Thanks for all of the input. Hopefully it will quit raining here sometime this week and I will be able to perform the compression test. Hopefully this will tell the tale. Much appreciated.
embracethehorror is offline  
Reply With Quote
Old 05-11-2008, 08:58 PM
  #10
Registered
 
Join Date: Mar 2006
Location: Lake Norman, NC
My Boats: '86 Donzi 22' Classic
Posts: 135
Default

Sounds like burnt intake valve. My 289 '66 Mustang would do that.

If compression test show nothing, check for leaks or rot at intake manifold gasket.
That would make a cylinder run lean, but then that should show on the spark plug.
whatabout1 is offline  
Reply With Quote
Reply

Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
tssteph
Wanted
2
07-31-2008 09:14 AM
East Coast B
General Q & A
4
07-08-2005 04:57 PM
dlbCheckmate
General Q & A
9
10-03-2003 10:11 AM
Dean Ferry
General Boating Discussion
5
05-15-2002 03:00 PM



Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -5. The time now is 11:26 AM.


Copyright 2011 OffShoreOnly. All rights reserved.