Stall during acceleration

[Jfreakman84]

Hello all,

Finally got my boat to start when I wanted it to... https://forums.iboats.com/threads/mercruiser-4-3-not-starting-when-hot.759153/
Rebuilt the carb and still had the issue, finally wrapped the fuel pump and line in heat reflective tape. That seemed to do the trick.

However, now that I rebuilt the carb, I get a full stall whenever I jam the throttle forward. If I ease the throttle it runs like a top. I've confirmed the idle is set correctly both in the driveway and in the water. New spark plugs and it still does it. It seems like when I jam the throttle its pushing too much fuel and causing the engine to flood.

Is there something I can do to fix this or do just need to deal with easing the throttle?

 

[Bondo]

Ayuh,..... Sounds like an accelerator pump problem,......
'n I'd guess it's goin' lean, not rich,.....

 

[flashback]

Pull the flame arrestor and have someone drive the boat while you observe the carb. When they hammer down you should see a generous spray of fuel..

 

[Jfreakman84]

Pull the flame arrestor and have someone drive the boat while you observe the carb. When they hammer down you should see a generous spray of fuel..

I do, coming from the jets in top of the carb

 

[Jfreakman84]

Ayuh,..... Sounds like an accelerator pump problem,......
'n I'd guess it's goin' lean, not rich,.....

It seems like it's working normally? Whenever I hammer down I see gas squirt out like normally

 

[Jfreakman84]

Pull the flame arrestor and have someone drive the boat while you observe the carb. When they hammer down you should see a generous spray of fuel..

It also seems like whenever I do that it's "backfiring" into the flame arrestor. When the flame arrestor is on I hear a coughing sound coming from it

 

[Scott06]

It also seems like whenever I do that it's "backfiring" into the flame arrestor. When the flame arrestor is on I hear a coughing sound coming from it

Thats a lean sneeze , would make sure the accelerator pump linkageis adjusted so there is no slop which creates a lag when hitting throttle. you may want to recheck float level. Have you measured fuel pressure and what do the spark plugs look like ?

 

[Jfreakman84]

Thats a lean sneeze , would make sure the accelerator pump linkageis adjusted so there is no slop which creates a lag when hitting throttle. you may want to recheck float level. Have you measured fuel pressure and what do the spark plugs look like ?

I'll check the accel pump linkages on Monday. Float levels were set when I rebuilt the carb but I guess I can recheck them, which way do I need to go with them? Spark plugs were new, I'll pull some on Monday as well. How do I measure fuel pressure?

 

[stresspoint]

sounds to me like the timing is not advancing , use a timing light to check if the mechanical advance is working , it may just need some lube.

 

[Silvertip]

If this is a 4-bbl carb, you may have mucked up the "timing" of the secondaries opening. Air valve secondaries use airflow to open those jets and there is an adjustment that determines when that happens. Misadjustment creates exactly the situation you describe. If this a 2-bbl then ignore this. The secondaries should open gradually as rpm rises. If they don't open at all or if they flop open then the spring is broken or misadjustment is the cause. You need a manual.

 

[Jfreakman84]

Thats a lean sneeze , would make sure the accelerator pump linkageis adjusted so there is no slop which creates a lag when hitting throttle. you may want to recheck float level. Have you measured fuel pressure and what do the spark plugs look like ?

Scott, checked this today. Linkage is tight and no lag. Accel pump seems to be working right and I see solid squirts of gas when throttle is advanced. Don't have a Schrader valve on my fuel line to measure pressure so I'll have to figure something else out but the pump is working fine. Spark plugs look ok, no burn or oil or white dust, but they're pretty new.

 

[Jfreakman84]

If this is a 4-bbl carb, you may have mucked up the "timing" of the secondaries opening. Air valve secondaries use airflow to open those jets and there is an adjustment that determines when that happens. Misadjustment creates exactly the situation you describe. If this a 2-bbl then ignore this. The secondaries should open gradually as rpm rises. If they don't open at all or if they flop open then the spring is broken or misadjustment is the cause. You need a manual.

I'm not sure how that would happened, I was very meticulous but anything is possible. The secondaries look like they're working right? Do you have a link for a manual? The one I used to adjust the idle was the one on this site (I think I found it here anyway). As far as rebuilding it, I followed the instructions that I got with it and watched multiple YouTube videos (I know I know but it was the best option, I don't have a dedicated carb place around me and the boatyard wanted $300 to look at it. The carb itself is just the Weber 4bbl carb that was on the boat when I got it, from what I can tell it's very common.

In any case, I had to winterize the boat today as weather is starting to get to the 20s at night. So I'll have plenty of time to mess with the carb this winter, along with a new boat deck, seats, exhaust work, and bilge pump.

 

[Bondo]

I'm not sure how that would happened, I was very meticulous but anything is possible. The secondaries look like they're working right? Do you have a link for a manual? The one I used to adjust the idle was the one on this site (I think I found it here anyway). As far as rebuilding it, I followed the instructions that I got with it and watched multiple YouTube videos (I know I know but it was the best option, I don't have a dedicated carb place around me and the boatyard wanted $300 to look at it. The carb itself is just the Weber 4bbl carb that was on the boat when I got it, from what I can tell it's very common.

In any case, I had to winterize the boat today as weather is starting to get to the 20s at night. So I'll have plenty of time to mess with the carb this winter, along with a new boat deck, seats, exhaust work, and bilge pump.

Ayuh,...... Yer carb is a carbon copy of the edlebrock 1409,.....
Go to the edlebrock website, they have a fantastic manual there,....
It's the Bible for these AFB carbs,.....

 

[Jfreakman84]

Ayuh,...... Yer carb is a carbon copy of the edlebrock 1409,.....
Go to the edlebrock website, they have a fantastic manual there,....
It's the Bible for these AFB carbs,.....

Thank you!

 

[QBhoy]

Does it do this when in the water, warmed up and underway?

 

[Jfreakman84]

Does it do this when in the water, warmed up and underway?

Honestly, I don't know. The last time I had it out, I didn't notice a bog when hammering down from idle. I noticed a slight hold at about 2800-3000 rpm when accelerating under full throttle but after that mark it accelerated fine. I usually don't cram the throttle anyway, and if I accelerate smoothly thru the throttle I don't notice anything different

 

[QBhoy]

Honestly, I don't know. The last time I had it out, I didn't notice a bog when hammering down from idle. I noticed a slight hold at about 2800-3000 rpm when accelerating under full throttle but after that mark it accelerated fine. I usually don't cram the throttle anyway, and if I accelerate smoothly thru the throttle I don't notice anything different

Think you will note little change when the secondary comes in around then perhaps. If you get a serious bog. When on the trailer and not up to temp. Your choke could be having an effect perhaps

 

[Jfreakman84]

Think you will note little change when the secondary comes in around then perhaps. If you get a serious bog. When on the trailer and not up to temp. Your choke could be having an effect perhaps

It's possible for sure, it's one of the old stovepipe chokes and I don't think it works well

 

[Scott06]

It's possible for sure, it's one of the old stovepipe chokes and I don't think it works well

Just make sure it is opening fully. What carb kit did u use to rebuild it? You see a lot of issues with people using cheap kits. Would get a good kit from edlebrock or mikes carb parts. Everyone on here has had to redo carb rebuilds… hardest part is getting it clean…

Id strip down and clean all passages out make sure floats are ok and not hanging up. Would also verify step up rods are moving freely and springs are in not bound up.

fuel pressure was just a sanity check suggestion. If you can run good at wot your fp is fine. for future refernce you can buy a $50 test fitting that goes in flare fitting on fuel l8ne or cobble a t with hose and barbed fitings to hook up fuel pressure guage… need 4-6psi . Too much and needle and seat gets over come and fuel comes out fuel bowl, too little and its runs lean ..

 

[Jfreakman84]

Just make sure it is opening fully. What carb kit did u use to rebuild it? You see a lot of issues with people using cheap kits. Would get a good kit from edlebrock or mikes carb parts. Everyone on here has had to redo carb rebuilds… hardest part is getting it clean…

Id strip down and clean all passages out make sure floats are ok and not hanging up. Would also verify step up rods are moving freely and springs are in not bound up.

fuel pressure was just a sanity check suggestion. If you can run good at wot your fp is fine. for future refernce you can buy a $50 test fitting that goes in flare fitting on fuel l8ne or cobble a t with hose and barbed fitings to hook up fuel pressure guage… need 4-6psi . Too much and needle and seat gets over come and fuel comes out fuel bowl, too little and its runs lean ..

I got the carb kit from carbjunkys.com. it's their specific kit for the mercruiser Weber/Edelbrock. I called to get the specific one.

I'll probably pull it apart and rebuild it next spring. It wasn't too hard to do and fairly cheap for peace of mind.

Engine runs fine at wot, so I would guess pressure is ok. It doesn't seem too high but I wouldn't actually know, $50 seems like a a small price to pay to make sure it's working right.

I will for sure check the step up rods though. I think the choke is opening all the way, but it seems... loose when it's open. Like it just flaps back and forth and isn't held open