Fuel starvation - '82 90HP

[interalian]

Hi all, got the boat on the lake this evening as promised to the Mrs (by the end of July - yes, I'm a deadline driven guy). Started and idled out fine, water pump working properly, temperature good on both heads. Brought it on plane OK, but after a few seconds of high (not full) throttle it ran out of gas.

Pumping the bulb brought the power back, but it didn't keep up with demand a second or third time either. Had to come back across the lake with the Mrs squeezing the lemon all the way.

Back on the driveway, I took apart the fuel pump and I can't see any reason it doesn't work (see pic). All the rubber parts are supple, no evidence of any leaks. Yes, I had the pump off the block while I rebuilt the carbs and didn't replace its gasket, but that looks fine too. When I did the carbs, I set the floats parallel to the carb bodies, but the original floats were set a bit lower - it ran like that for many years. It's certainly not flooding.

Thoughts? I'd rather not just throw parts at it. Pretty sure all the lines are sealed.

 

[interalian]

Oh, and the fuel line is not the original - was replaced a few years ago. Bulb works, didn't go flat.

 

[Macca1500s]

I've experienced something similar, but uneven idle and then a cruising speed fuel starvation, in my case the bulb was sucked flat, i disconnected the fuel line blew back into the tank, re connected and away it went, for awhile anyway, but then happened again and then at slow speed running rough on what seems like two cylinders,

turned out to be crap in the fuel tank getting picked up and blocking supply.

I've just today removed the tank, flushed it out ,I'm planning while I'm there to replace the fuel line from tank (in the bow) to filter , filter to bulb, bulb to motor already done.

can i suggest you check your tank pickup and filter

macca

 

[racerone]

Where are the springs for the pump ?------The pump is driven by a positive pulses from crankcase compression.------Cylinder compression is not the same thing.---Cylinder compression test can be helpful here.

 

[interalian]

Where are the springs for the pump ?------The pump is driven by a positive pulses from crankcase compression.------Cylinder compression is not the same thing.---Cylinder compression test can be helpful here.

Both pump springs are there, under the nylon caps - just can't see in the picture. The metal check valves are aligned and making good contact with the plastic center piece.

Compression is 110-120, checked after the run on the still warm motor. It was lower when I tested in June but the battery wasn't fully charged and the motor hadn't been run for 4 years.

I'm thinking there's nothing wrong with the pump and will explore the tank and lines. I do have two tanks so will open the empty one, check for crud, transfer fuel through a fine mesh funnel and see. The hose O rings will be inspected as well.

 

[interalian]

Checked tanks - surgically clean. Gas is fresh. Got a tiny bit of sediment - photo shows total from two tanks:




Pulled the output hose and found this:



This hose is cracked in a number of places so I'll fab up a replacement today using a 90 and some 5/16" fuel line. I have no way to pressure test the hose, but was able to hold vacuum on it with a hand pump (not that it proves it's sound). The feed line to the pump inlet was replaced earlier as I saw it leak under pressure when priming using the bulb.

Checked for crank case pulses - good puffs but didn't read at all on the compression tester. Pressure probably too low to register anyway.

Thoughts? (TIA)

 

[interalian]

Couldn't find a 90. Trying a sweep of regular line - hope it doesn't kink. I pulled it out of the little nitch in the motor pan to permit a smoother sweep.



Any thoughts about running the motor with the plastic air horns off? I'd like to leave access to the pump on a test run.

 

[oldboat1]

circling around back a little, but the fuel pump diaphragm looks to me like it should be replaced. A new one would not have a set in it -- should be flat and flexible.

 

[interalian]

True enough. I suppose 33 years under spring tension is a long time. Test running in the morning. Can't get a pump rebuild until Tuesday at the earliest - long weekend...

 

[emdsapmgr]

Having to constantly prime the fuel hose bulb to keep the engine going indicates it is starving for fuel. That can be a weak fuel pump, or a restriction on the fuel system. I've seen fuel hoses go bad-the ball valves can malfunction if the hose bulb is not oriented such the arrow is not pointing in generally "upward". That engine uses bulk 5/16" hose from the tank to the engine. Some of the hoses under the cowling are special and may be smaller in size. They have actual part numbers assigned by the factory. These are heated and bent to still flow fuel around tight radius corners. Bulk hose will kink and can cause a restriction. You may want to check to be sure the hoses are not kinking-esp the one from the pump to the manifold. Your 82 has the pump screen as the only filter-you might opt to add a white in-line filter in the fuel hose. Am not a fan of the ty-wrap clamps. Over time the hoses can loosen up under the clamps. Could wind up with an air/fuel leak. You will have better luck with the Bombardier Snap-clamps.

 

[interalian]

All good now. The bulk hose between pump and manifold will work until I can get the proper formed one. See clips:

https://youtu.be/AlzcA4U0N60

https://youtu.be/jyzGYhxsdiA

I'm only hitting 4000 or so indicated, but I'm not sure the tach is accurate. Bear altitude in minde, we're at 3400 feet. My semi-calibrated ear says it's running faster than 4000 - what do you think? Didn't have GPS to check true speed.

 

[emdsapmgr]

Make sure the tach is on the correct setting, usually the pointer should go to #6.

 

[interalian]

Tach has never been touched in 30 years. That said, if there is a switch (and it's been a long time since I crawled under the dash), maybe it needs some exercise.

 

[oldboat1]

well, your motor sounds smooth, whatever the actual rpms. Grounding issues with the panel (other gauges or switches) might cause the tach to show an rpm change or fluctuation (have a Trojan inboard that has done that).

 

[interalian]

Yeah, it ran pretty nice today. Going out again tomorrow to pull some kiddies around on a tube.

I'm trying to find the opportunity to check WOT timing (28 degrees according to the sticker), but the Mrs doesn't have the required patience. Need to take a drinking buddy out to operate the helm. The timing has never been set since new, nor has anything ever been changed to make me suspect it's other than the way the factory set it. Aside from wear?

 

[oldboat1]

the life of a tinkerer.... all good.

 

[emdsapmgr]

Do you have any indication that the battery is being charged properly by the engine?

 

[interalian]

I'm assuming the question pertains to the tach, no?

Volt meter shows a tick over 12V with the motor off, and after running a while it's at 14 or so. I'd say the thing is charging OK. When I did compression tests in June, I just pulled the battery out of the garage and slapped it in the boat without charging it first. I put the C-Tek on it last week for an overnight charge.

 

[interalian]

Well, 4 hours on the lake today, 3 happy kids, 2 tanks of gas (~40L - always been a pig on gas), and 1 vindicated mechanic (me). Ran like a top the whole time too. Not bad for a 'free' boat.