AQ131A backfiring problem

Author Message   Richard Finkel Member Username: rfinkel Post Number: 8 Registered: 09-2007 Posted on Sunday, May 11, 2008 - 09:08 pm:    last summer, right after I had my carb rebuilt, my engine blew a connecting rod through the engine block. before parting out the boat, I found and purchased a used replacement aq131a }}motor that started and ran with some backfiring. All of the marinengine.com contributers were great!!I replaced the spark plugs, installed a Pertronix electronic ignition and and changed the oil, I installed the engine last fall, drained the engine at the fresh water pump and added pereservatives to the gas in the gas tank. This spring, the engine started after multiple tries and after priming the fuel pump with gas but it backfires frequently and often stalls after backfiring. I let the engine idle for about 30 minutes. The backfiring is less, but still too frequent. If it does't stall, the backfiring seems less when I open up the throttle (in neutral). Any help would be greatly appreciated One of the ignition wire boots seems loser at the spark plug end than the other three.Could this cause the backfiring? Could it be bad gas? Shoud I just replace the old carb with the one that I had rebuit last year from the blown engine? }}   Morten Ringvold Senior Member Username: haffiman37 Post Number: 2719 Registered: 04-2006 Posted on Sunday, May 11, 2008 - 09:27 pm:    Did the first damage (broken rod)happen after a timing belt issue? However I would have teared down the front of the engine and changed/checked timing belt and condition of gears and tensioner. You might have another case of jumping belt. Note that this is a case where You should be 110% sure, no guesswork allowed.   El Pescador Senior Member Username: el_pescador Post Number: 3129 Registered: 02-2006 Posted on Sunday, May 11, 2008 - 09:32 pm:    A few things you can check (and not necessarily in this order): 1) Make sure the timing belt is installed correctly; that is, that the three gears align with the respective marks in the block/head when #1 piston is on TDC at the end of the compression stroke. 2) Open the distributor and look at the condition of rotor and cap: if you see corrosion, either clean it or replace the parts. Also, pull the ignition leads and examine the sockets in the distributor cap for corrosion. 3) Consider removing the distributor plate under the Pertronix kit and examine the condition of the centrifugal advance weights as well as the springs. It will also be a good idea to take the distributor to a shop that can verify that the advance curve is correct (they need a special machine for that). 4) Remove the spark plugs and make sure they are clean, in good order, and correctly gapped. 5) Another thing you can do is hotwire the + of the coil with a wire running directly from the (+) of the battery; if the backfiring stops, then you have wiring problems (corroded components, loose connection, etc). 6) Remove the fuel line going to the fuel pump suction from the fuel tank and run a line from a jerrycan with fresh gas. Then, run the engine for a few minutes and see if the backfire clears: if it does, then you know you have bad gas.   Richard Finkel Member Username: rfinkel Post Number: 9 Registered: 09-2007 Posted on Monday, May 12, 2008 - 09:04 am:    Thanks for the help to both Morton Rinvold and El Pescador. In response to Morton's question: Last summer's problem(with other engine was not timing belt related per the marina mechanic) I will try what I feel competant to check next time that I can get to the boat. Today seems much to stormy. The timing and the distributer seem beyond my expertise and experience?   Richard Finkel Member Username: rfinkel Post Number: 10 Registered: 09-2007 Posted on Wednesday, May 21, 2008 - 11:19 pm:    Can the propper timing be @ 30 BTDC??? I replaced the carb with a rebuilt one from my blown engine, replaced the spark plugs and then the engine repeatedly started, sputtered and backfired and died. I checked the timing and low and behold! it showed about 10 degreea after tdc. I turned the distributer a few degrees to set timing to 6 degrees BTDC and the engine ran better but not well and sputtered out after 30 secs and immediatelty when I advanced the throttle in neutral. I then kept advancing the timing, and the engine kept stronger antil about 30 degrees btc, the limit of the distributer's leway. I did not remove the cooling tank to expose the timing marks on the top overhead cam gear. I am also unable to get the engine to stop with the timing mak at TDC, to check the position of the rotor. Should I leave things} alone with the timing at @ 30 degrees BTC or should I keep trying to get the engine to stop with the timing mark at TDC or should I remove the distributer and turn it counterclockwise a little and reinstall?? Withn the engine running strong now, is it still 110% necessary to chek the allignmnent of all of the gears(would have to remove the cooling tank) Any and all help would be gretly appreciated.   El Pescador Senior Member Username: el_pescador Post Number: 3193 Registered: 02-2006 Posted on Wednesday, May 21, 2008 - 11:29 pm:    30º BTDC is wrong. What timing light are you using? If it is one of the type you can set the advance, it may be giving you the wrong reading. To get the mark in the pulley aligned with the mark in the front casing, you may need to turn the crankshaft with a deep socket inserted into bolt 17 and a breakerbar. http://www.volvopentastore.com/CRANKSHAFT_AND_RELATED_PARTS_AQ131A/dm/cart_id.65 7400424--category_id.332888--list_time.1211426868--session_id.424092323--store_i d.366--view_id.324135   Richard Finkel Member Username: rfinkel Post Number: 12 Registered: 09-2007 Posted on Wednesday, May 21, 2008 - 11:37 pm:    I am using a basic Sears timing light left over from the college days when I worked on my fist car, a 1974 Dodge dart. Its old, but it wasn't used much. The breaker bar I have, I may not have the right deep socket. I hope to take a look on thursday or friday. Thanks for the help.   Robj Member Username: robj Post Number: 41 Registered: 09-2007 Posted on Sunday, May 25, 2008 - 10:21 am:    As suggested earlier check you timing belt. You cannot be running an engine with that much advance. Something is obviously wrong and you don't want to blow up another engine. Have a great day, Rob.

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