Carb backfire and stall only when "getting on it" from idle

[EQuiNOX1216]

Hello all,
Just got a "new to me" boat.
1977 Bluewater, 19' with what should be a 185 hp chevy 305 inboard (going by this number: 990252S1).
Also says "OMC Stern drive"

The boat didn't come with a title so I can only provide information I can get from the boat itself.

I did a few searches here to find a post with this problem, with an answer, but only got kind of close.

The problem:
The engine runs perfectly except when someone yells "hit it" .
I hit the throttle from idle and it sounds like a gasp of air from the carb, and it stalls.
If I back throttle down fast enough and hit it again, it sometimes recovers and takes off like a rocket.

It has no misses at any running speed nor at idle. It runs great any other time.
The plug wires look old so I have to assume a tune up is needed.

Being the end of September, I figured I would wait another week while we enjoy one last outing this weekend before digging into the problem.

Anyone have an idea what I should check besides tune up?

 

[Bondo]

Re: Carb backfire only when "getting on it" from idle

Re: Carb backfire only when "getting on it" from idle

Hello all,
Just got a "new to me" boat.
1977 Bluewater, 19' with what should be a 185 hp chevy 305 inboard (going by this number: 990252S1).
Also says "OMC Stern drive"

The boat didn't come with a title so I can only provide information I can get from the boat itself.

I did a few searches here to find a post with this problem, with an answer, but only got kind of close.

The engine runs perfectly except when someone yells "hit it" .
I hit the throttle from idle and it sounds like a gasp of air from the carb, and it stalls.
If I back throttle down fast enough and hit it again, it sometimes recovers and takes off like a rocket.

It has no misses at any running speed nor at idle. It runs great any other time.
The plug wires look old so I have to assume a tune up is needed.

Being the end of September, I figured I would wait another week while we enjoy one last outing this weekend before digging into the problem.

Anyone have an idea what I should check besides tune up?

Ayuh,.... Rebuild the Carb, 'n replace the accelerator pump...

 

[EQuiNOX1216]

Re: Carb backfire only when "getting on it" from idle

Re: Carb backfire only when "getting on it" from idle

Thanks Bond-o.

I figured a carb rebuild was in order.
Will have to research the accelerator pump.

 

[Bondo]

Re: Carb backfire only when "getting on it" from idle

Re: Carb backfire only when "getting on it" from idle

Thanks Bond-o.

I figured a carb rebuild was in order.
Will have to research the accelerator pump.

Ayuh,... It's in the carb, but rarely comes with the "Kit"....

 

[EQuiNOX1216]

Re: Carb backfire only when "getting on it" from idle

Re: Carb backfire only when "getting on it" from idle

So I will have to learn more about this accelerator pump.

 

[EQuiNOX1216]

Re: Carb backfire only when "getting on it" from idle

Re: Carb backfire only when "getting on it" from idle

I don't know if this is related, or even the culprit, but I think the fuel pump just died.
Perhaps it was dying, losing pressure? Then died this morning?
I realize boat engines are slightly different than auto engines but the physics should still apply, no?

CLUES:
1. No fuel getting to the carb, NOR the fuel filter.
2. Engine starts and runs when I pour a little fuel into the carb directly (then dies of course).
3. 4 gallons of fuel in tank.
4. Boat was used last weekend without problems (other than the stalling issue in the original post here).

Just did a quick search for this part;
Looks like a fuel pump for 1979 MERCRUISER 305 runs about $100 plus shipping.
Anyone know a place I can get one cheaper??

Thanks.

 

[Don S]

Re: Carb backfire only when "getting on it" from idle

Re: Carb backfire only when "getting on it" from idle

3. 4 gallons of fuel in tank.

Put some gas in the tank and try it.

 

[Roadrager50]

Re: Carb backfire only when "getting on it" from idle

Re: Carb backfire only when "getting on it" from idle

You know Don I was thinking the same thing. While you are at it replace the fuel filter.

 

[888]

Re: Carb backfire only when "getting on it" from idle

Re: Carb backfire only when "getting on it" from idle

Check your anti-siphon valve on top of tank. Check/clean the filters/screens in the pump and inlet side of carburetor.

 

[EQuiNOX1216]

Re: Carb backfire only when "getting on it" from idle

Re: Carb backfire only when "getting on it" from idle

I put 4 gallons in the tank while trying to get it started that day.

 

[EQuiNOX1216]

Re: Carb backfire only when "getting on it" from idle

Re: Carb backfire only when "getting on it" from idle

::UPDATE::
Well, researching other threads on this forum I discovered that if the fuel filter canister is empty, one must fill it with fuel before trying to start the engine (presumably when changing the filter, etc.). I hadn't changed the filter, though I DID check to see if there was gas in the canister and if the filter was clogged. The canister was empty (which I thought was odd).
So after reading that post I filled the canister just to test if the fuel pump could at least send the fuel to the carb.
As it turns out, not only did it send the fuel to the carb but apparently it "PRIMED" the fuel line (??) and the engine ran in my yard for 15 minutes before I shut it off.
We decided to take it to the lake since it was such a lovely day today and ran it up and down that lake all day without a single problem.

I don't know how the fuel filter canister became empty unless it was siphoned while parked at storage and I simply ran it out of gas that morning when I started it to warm it up before going to the lake. That would explain that, I think. Maybe I need to invest in some kind of locking cap?

 

[Silvertip]

Re: Carb backfire only when "getting on it" from idle

Re: Carb backfire only when "getting on it" from idle

Or check the fuel gauge before you leave the dock perhaps.

 

[EQuiNOX1216]

Re: Carb backfire only when "getting on it" from idle

Re: Carb backfire only when "getting on it" from idle

Weird thing about the fuel gauge, most of the time the gauge doesn't register the fuel until it has been running awhile.
I don't know why that is, but when I first start it up, it ALWAYS says EMPTY, even when I know there is a full tank.
A 1/2 hour after being on the lake I notice the actual level is registering.
I usually just fill it up at the gas station on the way to the lake.
Then I know how much I have.

But that morning, I didn't know if someone had siphoned the tank or what...