5.7 omc stalling while shifting

[Nick_1987 5.7 OMC]

Well I’m back again…. 5.7 omc from 1987. Super clean motor. Runs mint, starts nicely. But it dies when I shift it. I don’t think it’s the switch. If I hold down the esa, the motor just stumbles continuously and does not die. I have a feeling maybe adjustment somewhere needs to be done. Just don’t know where. Any input would be much appreciated!

 

[itsathepete]

The esa shouldn't engage when going into gear, only when coming out. Verify your idle rpm with an accurate tach and check for any vacuum leaks by spraying carb cleaner around the carb base and intake. If engine increases rpm you have a vacuum leak. Check ignition timing and set to spec. Verify ignition components are in good condition and working properly, clean or replace ignition points if applicable.

 

[Nick_1987 5.7 OMC]

The esa shouldn't engage when going into gear, only when coming out. Verify your idle rpm with an accurate tach and check for any vacuum leaks by spraying carb cleaner around the carb base and intake. If engine increases rpm you have a vacuum leak. Check ignition timing and set to spec. Verify ignition components are in good condition and working properly, clean or replace ignition points if applicable.

It’s dieing coming out of gear, going into gear shifts buttery smooth.

 

[itsathepete]

I fought similar issues until I determined my tach was not accurate. By ear it sounded right but it wasn't. Once I set the idle speed properly and calibrated the tach, all was well.

 

[Nick_1987 5.7 OMC]

I fought similar issues until I determined my tach was not accurate. By ear it sounded right but it wasn't. Once I set the idle speed properly and calibrated the tach, all was well.

So what do you think my issue is? It dies when going into neutral. But it doesn’t die all the time, it’s random. I can dock one day nice and smooth no issues and then the next day stall when I get out of gear. It starts up right after but it gets nervous lol especially when you have million dollar boats around . Recently the boat started to have really small back fires at wot. My fuel line has a really small leak when it goes into the carb. Could that be the culprit for the back fires? I also rebuilt my carb. I think it needs a tune just not sure how that’s done. One more thing, the filter in the carb the really small one. I sprayed it with air to clean it out and installed it back. But I think that was not a smart move. I thing this could be restricting gas. Recently change the a fuel and water separator too. Any guidance or help is much appreciated.

 

[Lou C]

It's hard to say not seeing what it's doing but with the OMC Cobra system, the ESA will lower the idle speed from approx 600 to 450 rpm when you shift from FWD or REV into neutral. If the engine is not in good enough tune to run that slowly then it can stall. So you need to address any carb and tune up issues so it will not stall when you trigger the interrupt switch by hand when it is idling in Neutral.

 

[Nick_1987 5.7 OMC]

It's hard to say not seeing what it's doing but with the OMC Cobra system, the ESA will lower the idle speed from approx 600 to 450 rpm when you shift from FWD or REV into neutral. If the engine is not in good enough tune to run that slowly then it can stall. So you need to address any carb and tune up issues so it will not stall when you trigger the interrupt switch by hand when it is idling in Neutral.

I have done that, it will not die, even if I hold it down for 30 seconds. Should i install a new fuel line ? And can I run the carb without that filter in it, it’s a quadra jet.

 

[Nick_1987 5.7 OMC]

It's hard to say not seeing what it's doing but with the OMC Cobra system, the ESA will lower the idle speed from approx 600 to 450 rpm when you shift from FWD or REV into neutral. If the engine is not in good enough tune to run that slowly then it can stall. So you need to address any carb and tune up issues so it will not stall when you trigger the interrupt switch by hand when it is idling in Neutral.

It also used to start super easy, now I have to run the started for a few seconds before it starts.

 

[Lou C]

Well if you have the standard OMC set up, there is a large cannister filter mounted near the mechanical fuel pump and there is really just a screen filter in the carb inlet of the Quadrajet. I would fix the leak, for sure, if you have the cannister water separating filter, you probably can run without the small screen filter but I don't think that is the cause of your problem. When you did the rebuild did you clean the idle air tubes and make sure that little clip for the needle valve is not in the holes in the float arm? Because if it is, that can cause flooding because the needle valve will stick. See the pic, look at the bottom, the little clip is not in the holes...that's a common mistake on these...also, those idle tubes do get clogged over time.

 

[Lou C]

Here's a couple of pix to show what's what with the design of the Quadrajet...

 

[Nick_1987 5.7 OMC]

Well if you have the standard OMC set up, there is a large cannister filter mounted near the mechanical fuel pump and there is really just a screen filter in the carb inlet of the Quadrajet. I would fix the leak, for sure, if you have the cannister water separating filter, you probably can run without the small screen filter but I don't think that is the cause of your problem. When you did the rebuild did you clean the idle air tubes and make sure that little clip for the needle valve is not in the holes in the float arm? Because if it is, that can cause flooding because the needle valve will stick. See the pic, look at the bottom, the little clip is not in the holes...that's a common mistake on these...also, those idle tubes do get clogged over time.
View attachment 364130

That’s exactly how mine looked. Needle not in the holes

 

[itsathepete]

So what do you think my issue is? It dies when going into neutral. But it doesn’t die all the time, it’s random. I can dock one day nice and smooth no issues and then the next day stall when I get out of gear. It starts up right after but it gets nervous lol especially when you have million dollar boats around . Recently the boat started to have really small back fires at wot. My fuel line has a really small leak when it goes into the carb. Could that be the culprit for the back fires? I also rebuilt my carb. I think it needs a tune just not sure how that’s done. One more thing, the filter in the carb the really small one. I sprayed it with air to clean it out and installed it back. But I think that was not a smart move. I thing this could be restricting gas. Recently change the a fuel and water separator too. Any guidance or help is much appreciated.

Not to sound condescending, but like I said, check your tach, ignition, fuel systems. If it is idling lower than your tach says, it can cause this problem. You can download a free strobe tach for a smartphone. Paint a white mark on the crankshaft pulley and use your phone to determine the rpm at idle and compare it to the gauge. Backfire thru the carb at WOT usually means lean but if its in the exhaust it's rich, or poor ignition

 

[Nick_1987 5.7 OMC]

Not to sound condescending, but like I said, check your tach, ignition, fuel systems. If it is idling lower than your tach says, it can cause this problem. You can download a free strobe tach for a smartphone. Paint a white mark on the crankshaft pulley and use your phone to determine the rpm at idle and compare it to the gauge. Backfire thru the carb at WOT usually means lean but if its in the exhaust it's rich, or poor ignition

I appreciate your time and responses. Just to clarify the boat started doing this out of no where. I have a video of the engine doing this while I was out but it doesn’t let me upload. Pretty much what it is at around 4k-4.2k rpm, the motor drop 2-500 rpm and then jumps back up. It’s a very slight stumble along with very faint pops. I’m 100% sure it’s a fuel issue. I will go tmr and replace that fuel line, I will also get a tach to read the rpm. What are spec rpms for idle?

 

[itsathepete]

What are spec rpms for idle?

500-600rpm in gear (in the water) idle mixture screw should be 3-3/4 turns out

 

[Nick_1987 5.7 OMC]

500-600rpm in gear (in the water) idle mixture screw should be 3-3/4 turns out

Ohhh I’m about 550 out of gear, which means probably to low then. So out of gear I should be what 650-800? Seems kinda high for the dog

 

[Nick_1987 5.7 OMC]

500-600rpm in gear (in the water) idle mixture screw should be 3-3/4 turns out

Also where is the idle mixture screw on the carb ?

 

[itsathepete]

Ohhh I’m about 550 out of gear, which means probably to low then. So out of gear I should be what 650-800? Seems kinda high for the dog

Also where is the idle mixture screw on the carb ?

Set it at 600 and see what happens.

 

[Nick_1987 5.7 OMC]

Set it at 600 and see what happens.
View attachment 364199

That’s not how my quadra looks, mines from 1987

 

[itsathepete]

That’s not how my quadra looks, mines from 1987

There are some variations but the idle mixture screws should be in about the same place. They may be hex head as well

 

[Lou C]

Ok do you still have points ignition? If so & the points haven’t been replaced in a while a bad condenser can cause what you’re experiencing. This happened to me once before. I usually Change points when they get pitted or it starts running bad out of the blue.