No fuel ????

[duckhead69]

Hi guys really at a loss here. I have a 1986 300 weekender twin 350 cui. The starboard motor started running ruff on way in to port last weekend on fishing tournament. Came thru channel ok then went to dock motor shut down. I cant get fuel up to carburetor now I do have spark. Did all the likely things changed water. The separator was clean when I pulled it then I did filter by the carburetor was like new. Then I pulled line that comes off the fuel tank after the filter there it was dry/or not full. So then sucked on a make shift line to pull gas from the tank to be sure the pick up tube was good. Seemed ok got gas filled in 3 foot hose. So I was sure it was fuel pump Nope not that either. Must be a obstruction some where or I am I missing a filter or Any thought pointers greatly appreciated.

 

[dwna1a]

Ok was the filter wet and have fuel? After the filter was dry and the tank has fuel, correct?

Id like to add a suggestion as well. It’s the time of year when fuel tank vents get blocked by wasp and spiders. You might want to check them as well.

 

[duckhead69]

I will check vent thanks for that great tip that's why I love this site. The filter/separator had a full filter of gas when I took it off. After dumping out to check for water. I installed anew one and it has never filled up again and 1/2 tank of fuel. The paper one bye the tank was wet but no fuel to speak of in it half a dixie cup

 

[Yendor]

You need to fill that water separating filter with gas when you reinstall it.
When the filter is full, the pump has the ability to prime itself, as it has enough suction to displace that minimal amount of air. When that filter is empty the pump cavitates because it lacks the ability to consume and displace that much air before it can draw fuel.
When I changed mine on my recently acquired 270, I didn't want to make a mess in my newly cleaned bilge, so I left about an inch empty at the top when I installed it. She had to spin for way to long before it pulled that fuel through (which it finally did). I was just about to take it apart, start over and make a mess so as not to kill a starter or the battery. With that filter empty, they really have no chance.

 

[duckhead69]

I did fill on new filter but thanks. Just thinking here at work so when I took hose off after 1st filter the one directly off the tank. Then stuck that right in can with gas it should have fired. To rule of venting problem Now only other thing is I did not reinstall the clear or yellow tube for overflow in the invent that pump fails it pumps gas back into carb to my understanding is all it does. Until I locate this tube it is off now it may use vacuum from that to get gas to carb?????

 

[Yendor]

My bad, it didn't read it that way. Sorry.

 

[Bill Curtis]

Anti-siphon valve on the fuel tank can go bad and not allow fuel to be pulled from tank. Can be removed for testing to see if that's it.

Have had to replace a couple for other people before.

 

[dwna1a]

I think I’d take it apart again and put it back together slowly. If you had fuel before and now you don’t. Be very sure those gaskets are correct and that you didn’t leave some of the old gaskets up in the frame.

please let us know how this turns out

 

[duckhead69]

Well down for a few days cut the hell out of leg last night 6 foot drop down to boat from docks wind blowing so damm hard here blew all water out. 10 stitches later I will see what I can do tonight. Bill are you talking about a check valve on tank. I don't know about a anti siphon valve may be same thing you referring too. If I pull hose off tank that goes to separator I then hooked a hose right to barb after that filter off tank. I can suck gas out But I can also blow back in so if this is the valve you are talking about it may be bad because you should not be able to do that I think back and forth like that defeats the purpose of the valve.

 

[Bill Curtis]

The anti siphon is that little "check valve".

 

[duckhead69]

update so I got a boat macanic to look at boat he tells me that cam and push rod that controls the pump that lobe is shot. Now I don't doubt what he thinks is wrong with it. But it ran and still runs so good if you pour gas in carb. SO my problem is if I put electric pump on what are thoughts on it running well. I just really hate to have to pull motor to put cam and rod in. You can cut hole in bathroom to remove cam. But may as well rebuild at this point cam lifter push rods all ride together so you see my point. I guess any one else seen this happen just pump lobe bad and have to put electric on covering old pump loc with plate re plumbing fuel lines.Any imput or thoughts on this.

 

[Flyer5]

update so I got a boat macanic to look at boat he tells me that cam and push rod that controls the pump that lobe is shot. Now I don't doubt what he thinks is wrong with it. But it ran and still runs so good if you pour gas in carb. SO my problem is if I put electric pump on what are thoughts on it running well. I just really hate to have to pull motor to put cam and rod in. You can cut hole in bathroom to remove cam. But may as well rebuild at this point cam lifter push rods all ride together so you see my point. I guess any one else seen this happen just pump lobe bad and have to put electric on covering old pump loc with plate re plumbing fuel lines.Any imput or thoughts on this.

I have never seen a SB Chev wear that lobe for the fuel pump. I have seen the pumps worn so bad the rod doesn't push far enough anymore. Not saying it cannot happen. Buuuuuuuuut.......

 

[Bill Curtis]

update so I got a boat macanic to look at boat he tells me that cam and push rod that controls the pump that lobe is shot. Now I don't doubt what he thinks is wrong with it. But it ran and still runs so good if you pour gas in carb. SO my problem is if I put electric pump on what are thoughts on it running well. I just really hate to have to pull motor to put cam and rod in. You can cut hole in bathroom to remove cam. But may as well rebuild at this point cam lifter push rods all ride together so you see my point. I guess any one else seen this happen just pump lobe bad and have to put electric on covering old pump loc with plate re plumbing fuel lines.Any imput or thoughts on this.

You certainly wouldn't be the 1st to convert from mechanical to electric.They make marinized electrics just for that. Just have to be careful on sizing for flow and pressure a,d make sure all fuel lines are CG approved.

PS: Have only seen the lobe wear down once before, but that was due to pitiful maintenance and never changing oil. Whole engine was shot, but bad fuel pump operation was what made the fool bring it in to get fixed.

 

[duckhead69]

I hear you guys that is why I asked the boat for 14 yrs has been maintained that I have owned it and previous owner. It is very clean boat inside and out. Motor maintained run great 1300 hrs not crazy on hours for year it is. I think I may get 2nd opinion on it. Thanks for the input

 

[Scott215]

Never heard that one on a Chevy

 

[duckhead69]

ok so on further investigation specs for O/A length of fuel push rod should be 5.75 mine is missing .200 on fuel armature so any idea as to why or being that Harding of pin may have gone .030 deep of penetration it failed for what ever reason. DO you think if I put new rod in I will be fine cam end shows very little wear pump side has slight mushroom like pumped seized. Any thoughts thanks

 

[DaveKamp]

There is more than one fuel pushrod used on GM Marine V8 and V6's...

Specifically, the L31 1996-2000 5.7L marine engine... it uses a slightly shorter fuel pump pushrod for marine engines set up for mechanical fuel pumps. A standard 5.7/350ci pump pushrod is LONGER than the pushrod used in the L31 5.7 "Vortec" marine engine.

You MAY just have a case where the pushrod length is incorrect.

 

[duckhead69]

THANKS FOR YOUR INPUT DAVE BUT BOAT RAN GREAT FOR 14 YRS. It failed other day on a Tournament day the push rod shows wear and new one was only .05 longer. Not enough to push rod the lobe on cam is worn I suspect. Without pulling motor I cannot tell for sure but all points in that direction. So I am installing a electric pump hoping only the eccentric/lobe is worn that actuates the pump and I can least get the rest of season in. I do have a question if any one knows out there. Can I put pump and regulator b4 the water separator or does it have to be after. There is a filter of tank then I want the pump to be spliced in there then separator then to carb with another filter b4 carb. So can I push fuel thru separator or do I have to pull fuel thru. Will it leak????

 

[DaveKamp]

Hi Duck! I wasn't challenging your conclusions, i was just bringing a point of information, as I had a different, but related scenario that enlightement of the fact would have saved me some heartache... the circumstance being that most don't realize that the FP pushrods are not all same size... and to complicate worse, the fuel pumps aren't same either.

On subject of fuel pumps... USUALLY the separator filter is BEFORE the pump, not after.

I don't think the filter separator would be under any great stress of subjected to a few psi of downstream pressure, but they're fitted with the filter's seal. If i we're the engineer designing it, i would have made it capable of safely withstanding both positive and negative, but I wasn't that guy.

As others noted above, the anti-siphon valve at tank is a minimum-pressure check valve... it's cracking pressure isn't much, but it is enough so that some pumps might not prime effectively... so if you have challenging results, don't let that scenario foil you.

The lobe wear-pushrod length just doesn't seem right to me. Loosing 50 thou of that rod isn't a nightmare, but to lose enough lobe lift to cashew your fuel flow, means the hardened cam surface has been cut through.

I'm very good at destroying things, and I've flattened a whole row of valve lobes, but I've never worn through a fuel pump lobe on a camshaft... and this is why it just doesn't seem right. if it were me (and it is a genuine pita to do in most boats) I'd cut apart a junk fuel pump, fit the body onto the block with rod in place, and measure the actual lobe lift with a dial test indicator. If it really IS a flattened lobe, then the next concern, is the other 16 lobes on that camshaft, that are under significantly more severe duty than that fuel pump... they might be very close behind.

 

[DaveKamp]

here's another goofy thing to look out for...

Fuel lines are sometimes metallic, sometimes rubber... oftentimes both.
As rubber lines age, the inner lining softens. under gentle loads, the linings often don't cause a problem, but under a bit more load, the lining can suck in, resulting in a significant restriction.

the mechanical fuel pump does its work in a 'backwards' fashion, meaning the pump rod pulls the pump diaphragm OUT (drawing fuel from the tank) and then a spring pushes the diaphragm back in, pushing the fuel to carbeurator.

if fuel flow is blocked on output, the pump's outlet flow ceases, until that pressure is gone, when it restarts. the pushrod and lever still move, but

this same thing can happen if the inlet is blocked...

Once the suction clears, operation resumes

(this same problem occurs on water tubes from gimbal to transom on outdrives)

Sometimes, metallic lines develop little fractures or corrosion pinholes, and by virtue of the pump's vaccum against the anti siphon valve, the lines won't leak, but the darned engine won't run right.

these are really frustrating, and rather than spoil any boating with the possibility of either, my choice would be to pull the lines out, and pull new in, so you KNOW those gremlins won't get you.