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Dry Carb on 350/270

T

tiara2700

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I have an '88 Tiara 2700 with twin 350/270's. Starts fine, idles fine and runs fine right up to the point where I run for 20 minutes or so at speed and then cut back to troll on the port engine. It will stall, might take 5 minutes or might take an hour but it stalls every time. Won't restart unless I crank it for 10-20 seconds or so without opening the throttle. Then a pump of gas and she might. Sometimes. Sometimes we come home on 1. Starts right up the next day. Starboard engine is ok at all speeds.

Last time out my mechanic was fishing with me so he did some investigation after it cut out. Plenty of spark. Carb was bone dry. Choke was open. Definitely not flooded. Slight hiss of air when he cracked the fuel line at the carb. Spurt of gas when bumped over. Started after 10 second crank and 1 pump. Tightened the bolts, sprayed wd40, and watched it for a while with the spark arrester off. Carb was smoking a bit from the throat and vent holes. Plus it was making this faint and intermittent "ship, ship" sound if you put your ear down to it. Stb carb doesn't smoke or make any noise.

Boat has 1 tank, 2 welded-in pickup tubes, 10 micron filters, new rubber fuel lines in '13, rebuilt port carb in '14 to address and solve a flooding issue at troll. The pleated paper filters at the rear of the engines are not installed. Metal canisters but no filters.

Before the trip with the mechanic we had:
Replaced the port fuel pump
Cleared a bit of trash from the port anti-siphon
Removed the port anti-siphon altogether
Changed the big filters and the little screen in the fuel line

Next steps are to:
Add heat shield to the fuel line between the fuel pump and the carb
Eliminate the last of the metal lines up to the fuel pump and route them away from the engine
Swap carbs

There is zero smell of gas in the bilge at any time.

Thanks for making it this far on a long post.

I'd love to hear any suggestions
 
The hiss of gas (as in non-liquid) at the carb is very telling. Clear to me either a vapor lock or air getting into the fuel line. If the gas feed line remains cool to the touch on the way to the mech fuel pump, its not vapor lock. That is usually a issue with heated low pressure gas feed lines due to proximity to the exh. manifold.
That leaves air getting into the fuel line, pre-pump. I would install a temporary clear vinyl tube near the input of the fuel pump. Check for bubbles. Keep moving it closer to the tank, until no bubbles. You have a lot of opportunity to pick up air between the ASV, various used and non-used filter cans, valves, etc.
 
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tiara2700 said:
I have an '88 Tiara 2700 with twin 350/270's. Starts fine, idles fine and runs fine right up to the point where I run for 20 minutes or so at speed and then cut back to troll on the port engine. It will stall, might take 5 minutes or might take an hour but it stalls every time.
Check and see if this ignition coil is hotter than the Stbd engine's ignition coil when this occurs.

Won't restart unless I crank it for 10-20 seconds or so without opening the throttle.
Under prolonged usage with these conditions, you may shorten the life of your starter motor..... not to mention battery life.

Then a pump of gas and she might. Sometimes. Sometimes we come home on 1.
Starts right up the next day.
Both ignition coils would be cool the next day ....... so this may indicate an ignition coil issue on the Port side. Starboard engine is ok at all speeds.

Last time out my mechanic was fishing with me so he did some investigation after it cut out. Plenty of spark.
What color spark? It should be white or bluish white..... not yellowish!
If need be, swap ignition coils!
Test for voltage at both Port and Stbd systems...... they should be very close to the same.

Carb was bone dry. Choke was open. Definitely not flooded. Slight hiss of air when he cracked the fuel line at the carb.
He should have seen fuel as the line fitting was cracked loose.

Spurt of gas when bumped over. Started after 10 second crank and 1 pump. Tightened the bolts, sprayed wd40, and watched it for a while with the spark arrester off. Carb was smoking a bit from the throat and vent holes. Plus it was making this faint and intermittent "ship, ship" sound if you put your ear down to it. Stb carb doesn't smoke or make any noise.

Boat has 1 tank, 2 welded-in pickup tubes,
You may want to remove the dip-tubes/pickup-tubes and inspect/clean the screens.

10 micron filters, new rubber fuel lines in '13, rebuilt port carb in '14 to address and solve a flooding issue at troll. The pleated paper filters at the rear of the engines are not installed. Metal canisters but no filters.

Before the trip with the mechanic we had:
Replaced the port fuel pump
Cleared a bit of trash from the port anti-siphon
These are Anti-Siphon Valves! They are not expensive, so it may be worth while to replace them.

Removed the port anti-siphon altogether
Changed the big filters and the little screen in the fuel line
What type of screen is installed in the fuel line?

Next steps are to:
Add heat shield to the fuel line between the fuel pump and the carb
Eliminate the last of the metal lines up to the fuel pump and route them away from the engine
Swap carbs
Yes, with twins we have the option of swapping parts as to help eliminate or locate an issue.
Use the tried and proven P of E (process of elimination) when doing this.
Test/replace one item ONLY at a time before moving on to another item.

There is zero smell of gas in the bilge at any time.

Thanks for making it this far on a long post.

I'd love to hear any suggestions
Click to expand...
 
Thanks RicardoMarine.

I'll check the coils for sure. As I recall the spark was strong and white.

I'll put the anit-syphon back once we sort things out.

The screen I mentioned is right where the fuel line goes into the carb. Some folks call it a spring filter.
 
I'd be inclined to focus on the fuel supply given the "dry carb".....single tank infers the fuel is good....


could be the dip tube screen is lower than the other side and it accumulates the crud in the tank when the engine is running....could also be the A/S valve restricting things or an air leak anywhere up to the pump itself.....many times, a vacuum gauge on the inlet side of the pump will help steer you in the right direction...
 
Thanks makomark. We found a bit of debris blocking the anti-siphon valve early on in the saga. Second time in the life of the boat - first was a pull strip from a cigarette pack and this time it was a bit of foil with paper backing. Best guess is from the inner seal on a fuel treatment bottle. Everyone was convinced we'd solved the problem but nope. Currently running (poorly) without a ASV. So I don't think I have a screen down in the tank.
 
Twin engines.
One fuel tank
Two pick ups
To eliminate the fuel lines / fuel pickups why not switch the fuel line input to each engine?
Surely that could be done easily .....if what I read is that there are rubber fuel lines to each engine
 
It looks like the problem was air in the fuel line or vapor lock. Adding a heat shield to the fuel line between the pump and carb didn't help. Next step was to bypass the unused pleated paper filter and re-route the fuel line directly from the big filter in the stern up to the fuel pump. I moved the fuel line down to the stringer. That seemed to do the trick. So far so good on 2 trolling trips.

Thanks again for the suggestions and support.
 
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