97 4.3LX Mercruiser Backfiring and Stalling!!!!!!!!!!

[officerterry]

I own a 1997 4.3LX Mercruiser. Prior to purchasing went on test ride for about an hour. The boat ran great at about 50mph. Purchased the boat for a very fair price. Prior to taking the boat out the first time, I changed the spark plugs, fuel filter, and oil. While leaving the marina, the boat ran great for about 30 minutes, then it stalled out while at full speed. At the same time I heard it back fire. The boat would start right back up and idle great, but as soon as I tried to get on the throttle it would begin "sputter" and back fire out of the top of the carb. I had to slowly idle back to the marina. The gentleman I bought it from said that he thought the carb may be bad and provided me with a brand new one out of the box (same part, i.e. serial number as the old). Put it on and started it at the house with earmuffs and seem to be fine. Took the boat back on the water and the same result as the last time. 30-45min ran great, until it began to sputter and stall. Have tried everything I could find on other forums with similar issues and nothing is fixing the problem.

ITEMS CHECKED TO DATE ARE AS FOLLOWS:

1)Siphoned out the gas from the bottom of tank and it looks great
2)Oil Switch checked good
3)Fuel pump checked good
4)Spark Plugs checked good
5)Have ordered a new Distributor Cap and button, but have not put on yet
6)Have not checked the timing but the prior owner said he did not mess with it either, so don't think that should be it.

Any suggestions will be greatly appreciated, Thanks

 

[cooter2506]

Re: 97 4.3LX Mercruiser Backfiring and Stalling!!!!!!!!!!

Backfiring thru the carb is 99% of the time is a lean fuel condition. Check the ad7ult only sticky at the top of the forum for How to check your boats fuel System. It will tell you your problem.

 

[officerterry]

Re: 97 4.3LX Mercruiser Backfiring and Stalling!!!!!!!!!!

Thanks for the response. Do you mean "lean" as not getting enough fuel? After reading that sticky note post that's what it led me to believe.

 

[cooter2506]

Re: 97 4.3LX Mercruiser Backfiring and Stalling!!!!!!!!!!

Yes not enough fuel

 

[PBJMAN]

Re: 97 4.3LX Mercruiser Backfiring and Stalling!!!!!!!!!!

How's your alternator and ignition coil? Sounds like it could possibly be weak spark.

 

[officerterry]

Re: 97 4.3LX Mercruiser Backfiring and Stalling!!!!!!!!!!

Yea, I checked all fuel lines according to sticky post and they are good. I have been leaning towards the coil or I just read another post where the gentleman said that he was having same problem with his mercruiser and found the problem to be the voltage regulator. It was bad, causing the spark to jump to the wrong plugs. I may be looking into replacing it, but it cost around $60 and is on back order from wholesale marine. I may try changing the coil out first since it is only about $20. It looks to be rusted on the outside, but wires look good. I hope its one or the other because I've tried everything expect those items.

I don't know if this helps boat the boat starts and idles great. I can even open the throttle very slowly and everything's fine, but if I open up on it to quickly it will backfire and try to stall. As soon as I return to neutral it continues to idle and does not stall.

 

[mizzenmast1]

Re: 97 4.3LX Mercruiser Backfiring and Stalling!!!!!!!!!!

Hi, I have a 94 bluewater with the same exact described issue. did you finally isolate the issue?? was it electric or fuel??
mizz

 

[dg512055]

Re: 97 4.3LX Mercruiser Backfiring and Stalling!!!!!!!!!!

Check the connector to the fuel pump. I have 4.3 LX from 1997. I noticed the connector plug on the fuel pump had lost some tension in the contacts and would sometimes lose connection, causing the fuel pump to operate intermittently. I bent the contacts inside the connector with a small screwdriver and no more problem.

 

[ampcarfan]

Re: 97 4.3LX Mercruiser Backfiring and Stalling!!!!!!!!!!

Sounds like it might be a bad accelerator pump in the carb? With the engine off, remove the flame arrestor and while holding the choke open, have someone push the throttle from idle to wot quickly and look down into the carb as they are doing this. it should have a strong spray of fuel shooting into the carb. If it trickles or is not a "spray", the pump is bad.

 

[achris]

Re: 97 4.3LX Mercruiser Backfiring and Stalling!!!!!!!!!!

Check the connector to the fuel pump. I have 4.3 LX from 1997. I noticed the connector plug on the fuel pump had lost some tension in the contacts and would sometimes lose connection, causing the fuel pump to operate intermittently. I bent the contacts inside the connector with a small screwdriver and no more problem.

FINALLY!... someone got it....

There is a service bulletin or parts bulletin on those connectors, causing exactly that problem.

Chris........