2015 vortec 350’s repower issues

[QBhoy]

Hi

I’ll spare you all the details of what’s all been tried and replaced so far on these engines..but ask a simple question for starters.
Both engines were installed in a friend boat before he bought it. Fitted in 2015. Twin repower holly carb vortecs. It’s never really ran right. Intermittent lean running. One occasion noticed the fuel supply lines imploding sucking inwards.
The question is...am I right in thinking that vortec engines should usually have an electric fuel pump ? These don’t. They have mechanical. Can’t think of another vortec that isn’t electric. Can they run properly with mechanical?
thsnks. Ps. Fuel tank vent isn’t blocked. Last we checked.

 

[achris]

Vortec is only the heads. You can put vortec heads on an old block, and thus still have a mechanical pump.

.... One occasion noticed the fuel supply lines imploding sucking inwards....

This caught my eye. (I assume it's the line from tank to filter/pump). If it's sucked inwards, a few of reasons.
1. Anti-siphon valve failed and closed up.
2. Tank vent closed up.
3. Lines not big enough. For V8s, a minimum of 3/8" lines. My boat has 1/2" lines, and that's only a V6... I've never had a fuel supply problem
4. Lines failed with age/sunlight, chemical exposure.

BTW, never been a fan of holleys in a boat, too many fires that can be directly linked to them.

Chris......

 

[QBhoy]

Vortec is only the heads. You can put vortec heads on an old block, and thus still have a mechanical pump.

This caught my eye. (I assume it's the line from tank to filter/pump). If it's sucked inwards, a few of reasons.
1. Anti-siphon valve failed and closed up.
2. Tank vent closed up.
3. Lines not big enough. For V8s, a minimum of 3/8" lines. My boat has 1/2" lines, and that's only a V6... I've never had a fuel supply problem
4. Lines failed with age/sunlight, chemical exposure.

BTW, never been a fan of holleys in a boat, too many fires that can be directly linked to them.

Chris......

Thanks chris. Appreciated.
fuel lines we will look at next for sure. We might have been under the impression that there was no anti siphon valves perhaps. Both engines have separate feeds from the tank too. But will look or sure. Thanks again.

 

[Scott06]

Hi

I’ll spare you all the details of what’s all been tried and replaced so far on these engines..but ask a simple question for starters.
Both engines were installed in a friend boat before he bought it. Fitted in 2015. Twin repower holly carb vortecs. It’s never really ran right. Intermittent lean running. One occasion noticed the fuel supply lines imploding sucking inwards.
The question is...am I right in thinking that vortec engines should usually have an electric fuel pump ? These don’t. They have mechanical. Can’t think of another vortec that isn’t electric. Can they run properly with mechanical?
thsnks. Ps. Fuel tank vent isn’t blocked. Last we checked.

I think on some remanufactuered engines like the mercruiser 357 alpha and bravo engines they machine the block for mechanical fuel pumps. Not sure why they do that or what advantage it is vs electric

5.7L Complete Engine Package - 357 Magnum Alpha 4V (MerCruiser Applications)

Michigan Motorz has the 5.7L Complete Engine Package - 357 Magnum Alpha 4V (MerCruiser Applications) in stock. This genuine MerCruiser, 5.7L (357 ci) package is the ideal replacement engine for 5.0L & 5.7L engines. Rated at 27

www.michiganmotorz.com

you can see the mechanical pump in the 4 th photo of this engine add

 

[alldodge]

Don't about your side of the pond, but USCG Type A1 fuel line on this side can not be sucked in, its to solid. Regular auto gas line can

 

[Lou C]

I think pretty much all I/O installations have anti-siphon valves and when they stick they cause significant fuel starvation problems. So can a clogged fuel vent but I don't think that is so likely, but it for sure can happen.
The mechanical pump, I feel is more reliable than electric pumps in marine use. They are not prone to electrical connector issues (corrosion, high resistance) and are not sensitive to overheating due to fuel restrictions. They work off of the little pushrod that follows a lobe on the camshaft. The last one I replaced on mine lasted 30 years. We had cars with mechanical pumps and carbs back in the old days and fuel pumps rarely failed. In-tank electric pumps rarely fail as well because they are kept cool by fuel and push fuel forward. In a marine application they have to pull fuel from the tank due to CG regs so are under more strain.
I tried a Holley on my engine and had problems too, I think their quality control is hit or miss. I wound up rebuilding the orginal 30+ year old Rochester Quadrajet and its been fine. I seem to average 6 years between cleangings & rebuilds.

 

[QBhoy]

Brilliant reply’s guys. Can’t thank you enough