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Old 10-27-2010, 04:55 PM
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Default What are the symptoms of a weak/bad fuel pump?

I have been having fits with this engine, but I have a feeling I nearly have them worked out. Its a 1988 Suzuki DT75 that came with my project boat.

Basically, its tough to start it, but that isn't what my current concern is. I primed the bulb until it was hard (still had a little squeeze to it though...?), sprayed some 2-stroke starting fluid down the carbs and it fired right up and ran for about a minute and a half at idle before it sputtered out and died.

Further attempts to start the engine produced mixed results, but the jist was this: I could only get it to run for 10-20 seconds before it would die out. It would run strong for that few minutes, and then lose power and die. Sometimes it required starting fluid, sometimes it didn't. I kept varying my starting methods; i.e, sometimes choke, sometimes no choke, etc, but always got the same results.

I tried "feathering" the throttle to keep it alive, but it didn't seem to work.

Since the carbs have been rebuilt within the last month and I am using fresh gas (less than 3 days old) would my symptoms point to a fuel pump that needs rebuilt/replaced?

Thanks guys.
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Old 10-27-2010, 06:07 PM
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What happends if you keep the bulb pumped up while running?
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Old 10-27-2010, 06:15 PM
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I didn't try that. I will give that a shot tomorrow and let you know what happens.

I was going to ask what a good way to diagnose a fuel pump was - I suppose me acting as the fuel pump would be a good way!
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Old 10-27-2010, 07:33 PM
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I suppose you could hook up a pressure gauge to the fuel pump but I think that would over kill. As in older carbed cars, if the fuel pump is shooting gas out, it's good.

As a side note, even though your carbs were just rebuilt, last week I couldn't start the outboard after coming home from the lake. It took many tries before it coughed and sputtered then started. A couple of day later, I tried it again and same routine, cranks but won't fire. In a fit of rage, got my carb cleaner and sprayed the HECK out of the venturi area of the carbs. It sputtered then started and smoked like crazy but now it starts at the flick of the key! Looks like the bowls of the carbs are the low point so all that carb cleaner probably unclogged a bunch of krap.
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Old 10-27-2010, 07:49 PM
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If the fuel pump diaphragm is cracked and you can continue to pump the bulb, the gas will pass thru the pump and into the carbs via the oil blend lines, usually draining out the front of them. Tilt the motor some before trying this..
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Old 10-27-2010, 08:51 PM
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Try running on a fresh can of fuel. Your problem may be in the existing fuel tank.

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Old 10-28-2010, 05:49 AM
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I'll try tilting the motor and priming it again, as well as spraying carb cleaner down the carbs to see if that clears anything up.

If anyone is near Cocoa FL and wants to give me a hand, there's some beer in it for ya!
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Old 10-28-2010, 09:16 PM
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Quote:
Originally Posted by the good life View Post
I suppose you could hook up a pressure gauge to the fuel pump but I think that would over kill. As in older carbed cars, if the fuel pump is shooting gas out, it's good.

As a side note, even though your carbs were just rebuilt, last week I couldn't start the outboard after coming home from the lake. It took many tries before it coughed and sputtered then started. A couple of day later, I tried it again and same routine, cranks but won't fire. In a fit of rage, got my carb cleaner and sprayed the HECK out of the venturi area of the carbs. It sputtered then started and smoked like crazy but now it starts at the flick of the key! Looks like the bowls of the carbs are the low point so all that carb cleaner probably unclogged a bunch of krap.
Update:

The motor started at the ramp today after a few tries. We motored out past the breakwater and fished for awhile. The motor started up alright and we came back into the harbor to fish in our favorite spot. We caught a few fish (released) then the motor wouldn't start. I cranked and cranked but no ignition. No gas smell either. Checked for spark at the plugs and that was okay. Pulled off air box and held butterflies open but no dice. Filled a little cap with gas from our reserve tank and splashed it into the carbs. Success, it started and we motored back to the ramp so I think it's a fuel delivery problem now.
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Old 10-28-2010, 10:24 PM
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holding the butterflys open will pour more air in - not what your trying to do - if anything put your hand over the carb
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Old 10-28-2010, 10:32 PM
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holding the butterflys open will pour more air in - not what your trying to do - if anything put your hand over the carb
The butterflies are already in the closed position when starting in neutral, so just tried to hold them open for a brief moment to eliminate that probability. The priming of the carbs tells me I have a fuel delivery problem. I changed the fuel filter a few days ago. The fact that it didn't smell flooded after many attempts leads me to suspect the pump. Once started, it ran okay, dieing once but restarted and we made back to the ramp. I'll be checking the fuel pump soon.
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Old 10-28-2010, 10:53 PM
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Just looked at an online parts catalog for Johnson outboards and discovered that there is a filter screen under the fuel pump housing cover. Aha, something to check!
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Old 10-29-2010, 01:19 PM
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Ok, here is the latest:

Today, I replaced the fuel pump diaphragms, the fuel filter and the little rubber seal that goes with the fuel filter.

I also wrote down exactly what I did and what happened:

Attempt #1
-Used starting fluid and the choke was closed
-It started easily and ran smoothly for 15 seconds with the choke still closed.
-After 15 seconds, I opened the choke. The engine sped up, ran for another 5 seconds or so and died.

Attempt #2
-No starting fluid
-Choke closed
-It started easily and ran smoothly for 5 seconds with the choke still closed.
-After 5 seconds, I opened the choke. The engine sped up, ran for another 5 seconds or so and died.

Attempt #3
-No starting fluid
-Choke open
-Started easily and ran for 2-3 seconds and died

Attempt #4
-Used starting fluid.
-Choke closed
-Started easily and ran smoothly for a full minute with the choke closed.
-After 1 minute, I opened the choke. The engine sped up, ran for another 5 seconds or so and died.

Attempt #5
-No starting fluid
-Choke closed
-Started easily and ran smoothly for AT LEAST 3 minutes with the choke closed.
-Sometime between the 3 and 4 minute mark, I opened the choke. The engine sped up, ran for another 5 seconds or so and died.


The pattern, which is easy to see, is that when I open the choke the engine ultimately dies. When it was running with the choke closed, it was idling fast and strong - I should also note that I had the idle speed switch set to Fast Idle.

So what would cause this? Should I just let it idle for 10 minutes or so with the choke closed to let it warm up? I was told that I should be able to let up on the choke right after the engine starts.

Or is there something else wrong, that when the engine starts sucking in more air, it can't deliver enough fuel to compensate? Like I said, the fuel pump diaphragm and filter are both brand new.

Anyway, I appreciate your helping me with this wordy posts. Thanks so much, all of you. I love boating but I don't have a lot of money, so fixing everything I can by myself is a must.
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Old 10-29-2010, 06:16 PM
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Maybe check for a vacuum leak.
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Old 10-30-2010, 11:38 PM
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Sorry to sort of hijack this topic, but maybe my problem may be similar in some ways to yours.

I took apart the fuel pump today. The screen and diaphragm looked good. I noticed I have an electronic priming solenoid also so will have to check that tomorrow with a volt/ohm meter.

I read my manual today for my 48hp Johnson and found some interesting things.

The gas tank needs to be vented so as to not create a vacuum that can overpower the pump because the pump relies on vacuum and pressure to operate unlike a four stroke that has a mechanical fuel pump. I can't remember if the vent screw was backed out or not. Something else to check tomorrow.

My fuel pump gets vacuum from the power head via a hole on the backside that looks like a gasket like material to seal up the mating surfaces. That gasket has a nice deep round groove in it so maybe it is leaking vacuum there.

New pump on order.
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Old 11-24-2010, 08:27 AM
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Well, I took the boat back to the mechanic, who rebuilt the carbs again. He said they were full of crud. I haven't gotten a chance to start it; I wanted to start it at the mechanic's but the weather was nasty so I just took it home.

I am going to fire it up tomorrow morning and see how it does. I will post the results for future reference, and for the inquiring minds that might want to know.
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Old 11-24-2010, 08:35 AM
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Update on my problematic starting issue. Your results may or may not be the same.

I changed my fuel pump and it started on about the third try from a standing cold condition, so we took it out on the lake to fish and test drive. We stopped and anchored in two spots and it started alright on each occasion but after pulling up the anchor on the third spot, cranked and no start after several tries. Turned the manual primer lever to manual start position and cranked motor and it fired after several tries so we took a fast trip around the lake to get the motor humming along. Came home to flush out motor and it started up with no problems twice. So, at this point looks like primer solenoid might be the culprit, but before more money dumping, I"ll test it out too.

Sorry to hijack but maybe my issues may help.
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