89- 5.8l OMC with Holley 4160 flooding problem

[Ckingk]

Hi guys Sven here from Sweden.
I recently bought my first boat from a friend its a bayliner 2755 from 89 that has flooding problem.
The engine is 5.8l OMC with 4160 Holley marine carb. The carb was rebuild by a mechanic because of this problem but it still didn’t help.

When we adjust the air&fuel mixture screws as Holley advice the engine stalls about 5 to 10 seconds and sometimes a minute after start and won’t start for like 30 minutes again cause of too much fuel. And Engine backfires as well over 2500rpm.

If we close the air&fuel screws all the way in and open secondary ports to put more air in it the engine starts and runs just fine. No backfires nothing but won’t start without opening secondary ports manually.
So I am wondering how is this possible ? When the air&fuel screws are closed carb should not send fuel right ?
What can be the problem here ? Vacuum leak or bad rebuild carb that’s leaking to the intake manifold ?
Didn’t know a thing about engines till I bought this so have a little patience with me lol what should I look for here, would appreciate all help, thanks.
Attached a video.. engine runs like this when the air&fuel mixture screws are closed. ( Screwed all the way in )

 

[Scott Danforth]

Bad rebuild

The idle mix screws only adjust idle mix. As soon as the throttle is open more than a half mm, the normal jetting and power valve take over

 

[alldodge]

Agree, bad rebuild or fuel pump has to much pressure
No more then 48 Kpa or 0.48 bar

 

[Ckingk]

Bad rebuild

The idle mix screws only adjust idle mix. As soon as the throttle is open more than a half mm, the normal jetting and power valve take over

Allright I assumed this guy didn’t know what he did when he came back with a lot gaskets and stuff that I bought for rebuild, thanks for the answer.

 

[Ckingk]

Agree, bad rebuild or fuel pump has to much pressure
No more then 48 Kpa or 0.48 bar

It’s a mechanical fuel pump not electric so there is no regulator could it still have more pressure then it should ?
Thanks for the answer.

 

[alldodge]

It’s a mechanical fuel pump not electric so there is no regulator could it still have more pressure then it should ?
Thanks for the answer.

Yes, the mechanical pumps have been known to pump to much. Doesn't happen often but does happen. Member BT had one producing 9 psi 62Kpa right out of the box

 

[Ckingk]

Yes, the mechanical pumps have been known to pump to much. Doesn't happen often but does happen. Member BT had one producing 9 psi 62Kpa right out of the box

Hmm allright this could be the case cause the fuel pump is new but same as the original one.
I will had it checked and get back when I know more, thanks for the answer appreciated.

 

[Scott Danforth]

Carb kit has lots of extra gaskets (common with carb kits)
Holleys have an easy float adjustment. Check that

 

[Ckingk]

Carb kit has lots of extra gaskets (common with carb kits)
Holleys have an easy float adjustment. Check that

I checked the float levels earlier they was at proper level and worked well. I don’t know if it can be anything else with the carb.. Maybe it’s the fuel pump, I will have the the fuel pressure checked and if it’s fine then the carb I’ll update it later if it’s resolves the problem. Thanks for the answer

 

[kenny nunez]

As Scott just mentioned about extra gaskets in the Holley kit.
There 2 different gaskets for the power valve, triangular and round. It all depends on the outlet nozzle position on the valve. If the wrong one was used that could be your problem.

 

[Redrig]

My vote is on power valve as well. I fought the same battle last year .

My Fuel screws all the way in and still running rich.

 

[Bt Doctur]

have a mechanical that worked fine one day and flooded the next. no rhyme or reason. After a carb rebuild it worked that day and flooded the next.
Put a gauge on the pump and it was 14.5 psi . Abandoned it in place and installed the Carter type electric. No more problems.

 

[Ckingk]

have a mechanical that worked fine one day and flooded the next. no rhyme or reason. After a carb rebuild it worked that day and flooded the next.
Put a gauge on the pump and it was 14.5 psi . Abandoned it in place and installed the Carter type electric. No more problems.

Thanks for the reply I will have both carb and fuel pump pressure checked Tuesday this week. Will get back with the result.

 

[Ckingk]

My vote is on power valve as well. I fought the same battle last year .

My Fuel screws all the way in and still running rich.

Thanks a lot for all the reply’s guys the problem was powervalve we changed it and she works as perfect as it could be. Took her for drive today with Kenny Chesney-Boats playing on the radio.. Man what a feeling..
Peace and love

 

[Ckingk]

My vote is on power valve as well. I fought the same battle last year .

My Fuel screws all the way in and still running rich.

Thanks a lot for all the reply’s guys the problem was powervalve we changed it and she works as perfect as it could be. Took her for drive today with Kenny Chesney-Boats playing on the radio.. Man what a feeling..
Peace and love

 

[Ckingk]

1200$ Later the problem solved but the mechanic now tells me 1 or 2 cylinders are not working he checked the ignition which is all new stuff rotor cap and everything, he fixed the timing but still 1 cylinder not working he told me too much fuel can damage the spark plugs so Monday I will buy new spark plugs and if it dont work then compression test.. Wish me luck guys..

 

[Lou C]

the box makes it look like you bought a new carb rather than just replace the power valve. If one cylinder isn’t firing I’d go back and look very carefully at the distributor cap, rotor (even if new can be defective) and I’d check the ohms on the plug wires against specs. Yes it could be spark plugs fouled by running rich but then you’d expect most of them to be the same. Next thing to check is a compression test.

 

[Ckingk]

the box makes it look like you bought a new carb rather than just replace the power valve. If one cylinder isn’t firing I’d go back and look very carefully at the distributor cap, rotor and I’d check the ohms on that plug wire against specs. Yes it could be spark plugs fouled by running rich but then you’d expect most of them to be the same. Next thing to check is a compression test.

Hi yes i bought a new carb cause there is no renovation kit in Sweden for the old one I had to wait 2 months if I ordered one now so I just bought a new one.. The mechanic guy checked the distributor cap, rotor, the timing and everything else even the ohms on every plug wires and it seems to match with the omc’a specs so it should be the spark plugs cause I dont hear anything when I crank the engine it sounds normal and mechanic guy told me the same thing. So we will see.

 

[Lou C]

Hi yes i bought a new carb cause there is no renovation kit in Sweden for the old one I had to wait 2 months if I ordered one now so I just bought a new one.. The mechanic guy checked the distributor cap, rotor, the timing and everything else even the ohms on every plug wires and it seems to match with the omc’a specs so it should be the spark plugs cause I dont hear anything when I crank the engine it sounds normal and mechanic guy told me the same thing. So we will see.

Too bad you couldn’t get a Holley rebuild kit there here in the US they are very common and cost about $45 if I recall. I tried a Holley on mine and had similar problems it turned out the carb (brand new) was not assembled correctly. I actually went back and rebuilt the original 30 year old Rochester Quadrajet and it ran much better!

 

[Ckingk]

Too bad you couldn’t get a Holley rebuild kit there here in the US they are very common and cost about $45 if I recall. I tried a Holley on mine and had similar problems it turned out the carb (brand new) was not assembled correctly. I actually went back and rebuilt the original 30 year old Rochester Quadrajet and it ran much better!

Yes it sucks but even if I bought one rebuild costs 500$, I don’t have the experience to do it by myself and it’s very hard to find a good mechanic here that knows about American carbs, every single one of them says “ buy a new one “ there is like 20 boat mechanics here in the entire Stockholm, every single one of them is fully booked all the time so unfortunately I had to buy a new one to spare all the time and stuff. Yeah why not man these are good quality carbs mine looked good inside I am sure it would work fine if they rebuild it good in the beginning.