Power Loss Port Engine

djmair · Post by **djmair** » Sun Jul 22, 2012 11:10 am

I was so successful in getting the correct reason for the horn blowing problem I had I thought I would try again on another issue.

I am having a problem with my port engine. I go under load for about 3/4 on an hour at 2,800 rpms and almost to the exact location I lose power from the engine. The revs drop to idling speed and when I throttle down and then back up it powers up again for a short period and then drops again. After about 3 attempts at this it will not throttle up but it will maintain speed at around 1600 rpms. At dock after this happens I can throttle up slowly but any attempt to throttle quick results in sputtering and back firing.

I have had the following done.

new electronic ignitions
new fuel pump
new coil and resistor
compression check
new fuel filters
gas additives
a mechanic who has yet to fix the problem

1985 10 meter international twin 454's

Any thoughts??

prowlersfish · Post by **prowlersfish** » Sun Jul 22, 2012 11:39 am

Fuel filter ? did you all check the one in the carb ? have you rechecked the others , may have trash in the tank . look at the check valve at the tank and also make sure the vent is not pluged

Big D · Post by **Big D** » Sun Jul 22, 2012 9:40 pm

dj, Paul just outlined the easiest and most common fuel related items to check for these symptoms. Check them out, then get back to us with your findings.

Commissionpoint · Post by **Commissionpoint** » Sun Jul 22, 2012 11:16 pm

Then there is always cracked intake and/or massive vacuum leak elsewhere. Just something to think about.

Then since you have a new distributor. Check, and recheck timing. Basic, Advance, etc.

Jerry · Post by **Jerry** » Mon Jul 23, 2012 7:54 am

It does sound like it may be fuel related.
Also check the little screen and the end of the pickup tube attached to the fuel tank sending unit.
I had one of those drive me nuts for a few weeks on my 10 Meter. It would plug up from the debris at the bottom of the tank.

djmair · Post by **djmair** » Mon Jul 23, 2012 8:49 am

prowlersfish wrote:Fuel filter ? did you all check the one in the carb ? have you rechecked the others , may have trash in the tank . look at the check valve at the tank and also make sure the vent is not pluged

I have checked and replaced all filters including the small one into the carb. I am interested in the check valve and what exactly it does. I have seen reference to this in my manual but am not familiar with it. The starboard engine luckily runs like a gem and it is off the same gas tank, can I assume this valve monitors the flow to each engine?

larryeddington · Post by **larryeddington** » Mon Jul 23, 2012 9:13 am

it is called an anti-siphon valve and prevents fuel from siphoning into bilge if a lower fuel line should break. The fuel pump can draw fuel past it but not gravity. They can get sticky. It is a ball and light spring inside.

Big D · Post by **Big D** » Mon Jul 23, 2012 8:37 pm

larryeddington wrote:it is called an anti-siphon valve and prevents fuel from siphoning into bilge if a lower fuel line should break. The fuel pump can draw fuel past it but not gravity. They can get sticky. It is a ball and light spring inside.

Larry is correct. It is mounted on top of the tank, and looks like a regular fitting that the fuel line is fastened to.

You can eliminate the vessel's fuel system and tank by running the engine on a portable tank. Just be careful. Keep the tank on deck and ventilate. If the problem persists on the portable tank, it's at the engine end.

rooferdave · Post by **rooferdave** » Tue Jul 24, 2012 1:10 am

Big D wrote:
larryeddington wrote:it is called an anti-siphon valve and prevents fuel from siphoning into bilge if a lower fuel line should break. The fuel pump can draw fuel past it but not gravity. They can get sticky. It is a ball and light spring inside.
Larry is correct. It is mounted on top of the tank, and looks like a regular fitting that the fuel line is fastened to.

You can eliminate the vessel's fuel system and tank by running the engine on a portable tank. Just be careful. Keep the tank on deck and ventilate. If the problem persists on the portable tank, it's at the engine end.

actually he states he is running both engines off the same tank so it is not a tank related problem

if you look here http://www.trojanboats.net/wforum/viewtopic.php?t=6393

you will see I have the same problem and dj read this and try what I have done, my carb swap is going to happen this week and I will report back,, we are also contemplating as nothing else seems to work is perhaps the engine is too lean and the carb is icing. I know its a stretch but I am running out of options and some of the symtoms actually support this theory

ready123 · Post by **ready123** » Tue Jul 24, 2012 6:37 am

rooferdave wrote:actually he states he is running both engines off the same tank so it is not a tank related problem

if you look here http://www.trojanboats.net/wforum/viewtopic.php?t=6393

you will see I have the same problem and dj read this and try what I have done, my carb swap is going to happen this week and I will report back,, we are also contemplating as nothing else seems to work is perhaps the engine is too lean and the carb is icing. I know its a stretch but I am running out of options and some of the symtoms actually support this theory

Two engines one tank is still two anti siphon valves!

rooferdave... what you describe sounds just like a plugging anti siphon valve. Have you removed it from your tank and cleaned it and the pickup line with screen?

I had exactly what you and djmair described and it was crud plugging the pickup/siphon over time. Low speed engine ran fine.

rbcool · Post by **rbcool** » Tue Jul 24, 2012 7:46 am

I had a similar problem with my Stbd engine, then it just wouldn't start. When I removed the check valve and reinstalled the fuel line she ran like a champ!! I replaced both check valves and no probs since

Ron

djmair · Post by **djmair** » Tue Jul 24, 2012 8:36 am

rooferdave wrote:
Big D wrote:
larryeddington wrote:it is called an anti-siphon valve and prevents fuel from siphoning into bilge if a lower fuel line should break. The fuel pump can draw fuel past it but not gravity. They can get sticky. It is a ball and light spring inside.
Larry is correct. It is mounted on top of the tank, and looks like a regular fitting that the fuel line is fastened to.

You can eliminate the vessel's fuel system and tank by running the engine on a portable tank. Just be careful. Keep the tank on deck and ventilate. If the problem persists on the portable tank, it's at the engine end.
actually he states he is running both engines off the same tank so it is not a tank related problem

if you look here http://www.trojanboats.net/wforum/viewtopic.php?t=6393

you will see I have the same problem and dj read this and try what I have done, my carb swap is going to happen this week and I will report back,, we are also contemplating as nothing else seems to work is perhaps the engine is too lean and the carb is icing. I know its a stretch but I am running out of options and some of the symtoms actually support this theory

I have looked at my tank and have 3 lines running from it. Port, starboard and generator. The fittings into the tank just look like regular over-sized nuts. Are the check valves inside these?

boatsnbars · Post by **boatsnbars** » Tue Jul 24, 2012 8:39 am

Can you swap the fuel lines from one pick up to the other? If you can and it is a check valve the other engine should now have the problem.

larryeddington · Post by **larryeddington** » Tue Jul 24, 2012 9:38 am

The anti siphon valves I have are just a small brass fitting that has the check ball and spring inside. Actually I think they are modified fittings. It is possible you may not have the valves my 78 f28 did not but will before it gets wet.

Only one sure way to check disconnect the tank and see what is actually there.

djmair · Post by **djmair** » Tue Jul 24, 2012 11:19 am

boatsnbars wrote:Can you swap the fuel lines from one pick up to the other? If you can and it is a check valve the other engine should now have the problem.

Can't swap, copper pipe. Kind of hard to get to but I am going to see if I can remove the port line.