84 GM 305 Backfires when i use trim or tilt controls. Rebuilt carburator, No Power.

[seadoo]

ok i have been messing with this motor for a while now. It seems to no power when i give it full throttle. it will start backfiring when i use the trim controls or the tilt. its a 21' searay cuddy walkaround with a 305 gm motor. i just had the carburator rebuilt which cost alot. its a edelbrock 4 barrel 1409 carb. i checked the timing as best i can and when i raise the throttle i see it advanceing. Very strange and VERY frustating. I check all spark plugs and wires, put a new cap and rotor on. I dont know what else to check. Any help would be greatly appreciated./ it starts and idles great. I also checked compression on all the cylinders and there all about the same.
thanks for all your help

[kaz911]

Trim and Tab are electrically hungry items.

Check your alternator if it is giving out enough power. Check the 12v on the engine if it really is 12 volt. Check the ground connection on the engine if it is connected to boat ground correctly.

I had slight corrosion on starter - that made a slight short circuit to the engine (ground) and that made all kinds of funny errors.

[CliffA]

ok i have been messing with this motor for a while now. It seems to no power when i give it full throttle. it will start backfiring when i use the trim controls or the tilt. its a 21' searay cuddy walkaround with a 305 gm motor. i just had the carburator rebuilt which cost alot. its a edelbrock 4 barrel 1409 carb. i checked the timing as best i can and when i raise the throttle i see it advanceing. Very strange and VERY frustating. I check all spark plugs and wires, put a new cap and rotor on. I dont know what else to check. Any help would be greatly appreciated./ it starts and idles great. I also checked compression on all the cylinders and there all about the same.
thanks for all your help

this is a very broad list of symptoms.....so, so, so many things that can be the cause....i would suggest you first try to identify if you have an ignition related problem or a fuel delivery related problem....once that is identified you can do more specific troubleshooting to find and correct the problem....

start with the source of both the fuel supply and the ignition spark and troubleshoot each component in the path to the engine....for the fuel delivery diagnostics start with the quality of the fuel in the tank and then track it all the way to the carb...for the ignition spark diagnostics start with the level of charge in the battery and track it all the way to the spark plugs....

there is a LOT of knowledge on this forum so once you can narrow the problem down to either fuel or ignition the group can help you find the culprit....

good luck...

cliff

[seadoo]

thank you kaz911 for the advice. oviously i do not have the tools to diagnose the fuel delivery or some type of advanced electrical diagnostic tools to test ignition. i do have a brand new battery
i am getting fuel to the carb and i tested each spark plug and i am getting spark. I am going to check the ground to the engine and make sure i get a good clean contact there.i am using fresh gas as well
do you know anything about the thunderbolt ignition module? i was told that maybe that could be the problem as well but i do not know how to test it
thanks again for all your help

[kaz911]

thank you kaz911 for the advice. oviously i do not have the tools to diagnose the fuel delivery or some type of advanced electrical diagnostic tools to test ignition. i do have a brand new battery
i am getting fuel to the carb and i tested each spark plug and i am getting spark. I am going to check the ground to the engine and make sure i get a good clean contact there.i am using fresh gas as well
do you know anything about the thunderbolt ignition module? i was told that maybe that could be the problem as well but i do not know how to test it
thanks again for all your help

No all mine has been MPI's - So I don't have a any knowledge of the Thunderbolt system. But voltages are cheap and easy to "eliminate" - any $10 multimeter can help there. And since my background is electrical :-) I of course think that no boat should be without a Multimeter.

When the engine is running - the alternator should send out MINIMUM 12.8 volt at all times when engine is running. At higher RPM's it should be > 13.5 to 14.3/14.5. So stick a multimeter on the engine - The metal on the engine should be "ground" so that is where the black lead goes. The positive output you can measure directly from the alternator. Then have someone help you adjust trim and/or tabs while you measure.

So since the power part is easy to "eliminate" compared to fuel and ignition system - that is where I would start.

[seadoo]

Thanks again.Im going to start there. I'll let you know the outcome

[Sum Escape]

I had a similar issue with a 305 OMC Cobra (1988 Four Winns). Would misfire when up on plane when trying to trim it out. It ended up being a weak coil.

[seadoo]

ok so i went arountd testing with my meter and started with the starter slave solenoid. i found that, now tell me if im wrong, the yel-red wires on the solenoid are grounding out, that leads me to beleive that my starter is grounded. i will post a picture so you can see what i am talking about. both yellow-red and yel-red are touching ground. i went to the starter and touched the yel-red wire and the meter to ground and i get a solid tone. it is not the solenoid because i took the wires off and tested the terminals and no tone, just the wires alone i get tone.
thanks again for all your help....
electric 2.JPG

[CliffA]

ok so i went arountd testing with my meter and started with the starter slave solenoid. i found that, now tell me if im wrong, the yel-red wires on the solenoid are grounding out, that leads me to beleive that my starter is grounded. i will post a picture so you can see what i am talking about. both yellow-red and yel-red are touching ground. i went to the starter and touched the yel-red wire and the meter to ground and i get a solid tone. it is not the solenoid because i took the wires off and tested the terminals and no tone, just the wires alone i get tone.
thanks again for all your help....
electric 2.JPG

unless you are having problems starting the engine i would not waste time checking the starter and associated components and wiring....you did not mention anything in your initial post about difficulties in starting the engine...your problem sounds like either a fuel delivery issue or an ignition spark issue...

cliff

[CliffA]

i thought a little more about your engine's symptoms....could it be possible that the engine is running entirely off the battery and not the alternator once it is started?.....if you have an issue with the charging system the engine will run but will be using battery power to fire the spark plugs...this puts a large amount of stress on the battery...then when you attempt to engage the trim that puts additional strain on the battery, possibly enough to lower the amount of charge going to the spark plugs which could cause the backfiring since the spark plugs would not be getting a hot enough spark...one way to check this is to start the engine and disconnect the positive battery cable from the battery terminal while the engine is running...if the engine continues to run the alternator and charging system is likely OK...if the engine stalls when the battery cable is removed you have found your problem....

may be something to look at...

cliff