Carb 4.3 Starts Fine, Only Runs Briefly

[thehemi]

We got our Bayliner 185 with MerCruiser 4.3 Carb out for season preparation. After charging up the battery we attempted to fire up the engine. It cranks quick and starts fine, but it wouldn't run for more than 3-5 seconds before sputting out. With carb cleaner I can keep it chugging along, so it definitely seems like a fuel problem.

I jumped the purple and purple/yellow wires to bypass the oil pressure switch. I can hear the fuel pump cranking after I jump the wires together. Same result, it won't run for more than 3-5 seconds, once it maybe went for 8-10 seconds.

Since it certainly seems like a fuel problem, and I've ruled out the oil pressure switch, what are some good items that I can do or check next? Replace the fuel/water separator? Is there any way to check fuel pressure on these motors? I have an external fuel pressure gauge, don't see a fuel pressure port anywhere to plug into.

Thanks!

 

[Don S]

Re: Carb 4.3 Starts Fine, Only Runs Briefly

What's the serial number of your engine. Bayliner 185 with MC 4.3 means little.

 

[thehemi]

Re: Carb 4.3 Starts Fine, Only Runs Briefly

What's the serial number of your engine. Bayliner 185 with MC 4.3 means little.

OW669146

I assume it's an O or U in front, it's wearing off.

 

[Don S]

Re: Carb 4.3 Starts Fine, Only Runs Briefly

Ahhh, you have a TKS carb.
Have you tried giving it some throttle after starting? Push in the throttle only button and give it a little throttle and see if it keeps running.

That first letter is a number 0 they are now up to 1A from your 0W

 

[thehemi]

Re: Carb 4.3 Starts Fine, Only Runs Briefly

Have you tried giving it some throttle after starting? Push in the throttle only button and give it a little throttle and see if it keeps running.

No, using the throttle only button doesn't make any difference.

That first letter is a number 0 they are now up to 1A from your 0W

Ah, thanks!

 

[Don S]

Re: Carb 4.3 Starts Fine, Only Runs Briefly

Put a jumper wire from the battery positive terminal, directly to the + terminal of the coil and see if it stays running.

 

[thehemi]

Re: Carb 4.3 Starts Fine, Only Runs Briefly

Put a jumper wire from the battery positive terminal, directly to the + terminal of the coil and see if it stays running.

I gave that a try and it didn't change anything. It would start, idle for a couple seconds, and sputter out. Was this a test to see if anything was cutting off the spark?

 

[thehemi]

Re: Carb 4.3 Starts Fine, Only Runs Briefly

Are there inline fuel pressure gauges I can use with this engine?

 

[makonnen]

Re: Carb 4.3 Starts Fine, Only Runs Briefly

Hooking up a fuel pressure guage is a bit of a painful process.

It sounds like you've got quite of a bit of mechanical know how. In any sort of diagnosis, always eliminate the easy stuff first ... most of that you've done. Its not spark - you can keep it running with a can of carb cleaner, its not cutting off oil switch - you bypassed that. BTW the engine should run "quite well" with a steady stream of carb cleaner.

Try some other easy stuff before digging deeper ... just spray the crap out of the carb bores with brake cleaner. Clean everything ... spray carb cleaner down the air ports at the top of the carb that lead to the jets and idle circuits.

Start the boat, lets it stall out, have someone slowly crank the throttle lever down, do you observe a steady stream of fuel from the accelerator pump? Repeat a few times...

Check timing

Could the plug wires be mixed up?

Could it be out of time (ie: the distributor out a tooth?)

 

[thehemi]

Re: Carb 4.3 Starts Fine, Only Runs Briefly

Try some other easy stuff before digging deeper ... just spray the crap out of the carb bores with brake cleaner. Clean everything ... spray carb cleaner down the air ports at the top of the carb that lead to the jets and idle circuits.

Start the boat, lets it stall out, have someone slowly crank the throttle lever down, do you observe a steady stream of fuel from the accelerator pump? Repeat a few times...

Bingo. After it stalls out, giving it throttle would dump fuel from the accelerator pump. I removed the carb and cleaned out the jets and passageways with carb cleaner and compressed air. Put it all back together and it fired right up!

 

[cpt ron jc]

Re: Carb 4.3 Starts Fine, Only Runs Briefly

i had somewhat the same problem,my carb.keeps getting cloged with dirt from the tank ,if you have an older boat like mine, the ethol in the fuel is eating my fiberglass tank up ,check out your fuel tank also,i switched to a 15 gallon portable with clean fuel,not to metion i switched out my carb because it was so cloged.