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tex599
04-02-2012, 12:03 AM
1981, MC with the 351. boat ran great last year and the first couple of times out this year. Yesterday, the motor started to cut out and die when driving past 20 mph. Sounds like a fuel delivery issue to me. Owned the boat since last year, plan to replace plugs (don't know how long they have been in there), wire set is good. Replace distrubutor cap and rotor, again don't know how old they are. Also plan to replace the fuel filter, again don't know how old it is. Any thoughts, on where I should start trouble shooting? thanks

thatsmrmastercraft
04-02-2012, 12:06 AM
Does it still have a points ignition? If so, that may be your issue.

93Prostar190
04-02-2012, 12:17 AM
The fuel pump is my guess ..simple fix .... The old mechanical. One that crank driven.

tex599
04-02-2012, 12:20 AM
Still has points, has the old style rotor. Fuel pump, does it need to be marine specific? Can you test it?

thatsmrmastercraft
04-02-2012, 12:40 AM
How old are the points? Have you checked the point gap, or better yet, checked the dwell? Can't hardly run on bad points.

Fuel pump is marine specific (cam driven, incidentally).

There is a spec of how much volume the fuel pump should pump, but I can't remember. I'm sure someone will come up with it.

CantRepeat
04-02-2012, 07:52 AM
Dirty or clogged seats in the carb?

Sticky float bowls?

tex599
04-02-2012, 11:12 AM
I don't know how old the points are. When you refer to point gaps, are you talking about the rotor cap and rotor? What gap should they have? Thanks

thatsmrmastercraft
04-02-2012, 11:27 AM
I don't know how old the points are. When you refer to point gaps, are you talking about the rotor cap and rotor? What gap should they have? Thanks

The point gap is a measurement of when and how much the points open to create each spark. A crude measurement (point gap) can be made with a feeler gauge with the dist. cap removed and the engine rotated to the point where the points are open the farthest. To do this properly, a dwell meter is used and the points adjusted accordingly. Using a dwell meter is a much more accurate way to make this setting. Points should really be replaced every year. In their use, the surface of the points slowly becomes pitted and will lead to running issues. A points file, or your wife's/GF nail file will work in a pinch, can be used to clean the surface. Then the gap/dwell needs to be re-set.

Point gap should be .017 and dwell should be 26-31 degrees.

Conversion to an electronic ignition is the standard as it is cheap, very effective and never needs adjustment.

CantRepeat
04-02-2012, 11:29 AM
I don't know how old the points are. When you refer to point gaps, are you talking about the rotor cap and rotor? What gap should they have? Thanks

No, the gap is how far open the points are when they are on the highest part of the lobe on distributor.

http://www.earlytimeschapter.org/wpimages/wp809fda2b.jpg

thatsmrmastercraft
04-02-2012, 11:34 AM
No, the gap is how far open the points are when they are on the highest part of the lobe on distributor.

http://www.earlytimeschapter.org/wpimages/wp809fda2b.jpg

Great pic Tim.

CantRepeat
04-02-2012, 11:56 AM
Gotta love the internet, so much information for free!!

93Prostar190
04-02-2012, 12:07 PM
On my old 93 Prostar with a carb ... the fuel pump was going bad and the boat ran well at all speeds under 20 mph ... we were able to pull the kids kneeboarding, etc ... but at the speeds over 20 mph it was starved for fuel based on how open the throttle plates were ...

Just my $0.02 ... if your boat runs fine, idles fine and goes up to about 20 fine ... the old style fuel pumps would still work even though they were failing on the inside.

I do love all the information on the points but I think those symptoms would also appear at idle or on acceleration as you move form 9 mph to 14 mph and so on ....

My 2 cents .... fuel delivery issue .... willing to bet a remote beer in the interest of keeping it interesting.

93Prostar190
04-02-2012, 12:11 PM
ooops ... I meant to add this link which explains a mechanical pump (you can call SkiDim and get one.) At least it explains some of the items and pressures needed ... certainly a much different item than Fuel Injected pumps.

The old crank style pumps pulled the fuel using a diaphram ..... so 7-9 psi was in spec i recall, and it should not fluctuate too much.

http://www.73-87.com/7387garage/drivetrain/fuelpump.htm

thatsmrmastercraft
04-02-2012, 12:51 PM
On my old 93 Prostar with a carb ... the fuel pump was going bad and the boat ran well at all speeds under 20 mph ... we were able to pull the kids kneeboarding, etc ... but at the speeds over 20 mph it was starved for fuel based on how open the throttle plates were ...

Just my $0.02 ... if your boat runs fine, idles fine and goes up to about 20 fine ... the old style fuel pumps would still work even though they were failing on the inside.

I do love all the information on the points but I think those symptoms would also appear at idle or on acceleration as you move form 9 mph to 14 mph and so on ....

My 2 cents .... fuel delivery issue .... willing to bet a remote beer in the interest of keeping it interesting.

The more worn the points are, the larger the gap becomes, the more difficult it is for them to perform their job. While worn points make engine operation worse when worn, they will inhibit higher speed operation in the same manner that worn spark plugs, dist. cap or a rotor will.

This doesn't discount the fact that a failing fuel pump will starve an engine for fuel under load. It's just that worn points will always cause problems, and odds are if the OP can't remember when they were replaced last.....they are the problem.

In the rule of basics first, points come before fuel pump. Heck......points come before almost everything.

FWIW I still have the points in my boat. Runs like a champ...........so far. Electronic ignition is on the spring short list.

93Prostar190
04-02-2012, 01:07 PM
Tex - the advice on the points and fuel pump is good ... I agree with MrMC ... he makes good points (pun intended ;)

If the points don't look like the culprit, I wanted to mention the fuel pump since I have seen those sypmtoms before in more than 1 ski boat.

MrMC - I am with you on the points and the upgrade to electronic ignition (it was one of my favorite features on my ol 93) ... let's see where this goes. I did love the diagram as well. That is exactly the kind of data that I love being on TeamTalk for !

Tex - Keep us posted in the spirit of competition, I will lean towards the fuel delivery issue ... BUT .. you should rule the points out first .... we just want you to solve it .... MrMC and I will wager a "virtual-remote" beer in the interest of bragging rights! but we just want you back on the water with good engine performance.

tex599
04-02-2012, 05:36 PM
Really appreciate all the information and help. I am going to pull the rotor cap and take a look at the points. Not sure if I know what I am looking for or not, anyone have any thoughts? I am leaning more toward a bad fuel pump as the problem only exists at a certain speed. Bad ignition would pop up at all speeds, I would think.

tex599
04-02-2012, 05:39 PM
One other thing, what does it cost to upgrade to a electronic ignition?

thatsmrmastercraft
04-02-2012, 05:40 PM
Really appreciate all the information and help. I am going to pull the rotor cap and take a look at the points. Not sure if I know what I am looking for or not, anyone have any thoughts? I am leaning more toward a bad fuel pump as the problem only exists at a certain speed. Bad ignition would pop up at all speeds, I would think.

Inspect the points for a pitted surface and the correct point gap, at a minimum.

thatsmrmastercraft
04-02-2012, 05:41 PM
If you very gradually accelerate can you get the boat to go any faster?

02ProstarSammyD
04-02-2012, 05:46 PM
points check
voltage check at fuel pump
get a pressure gauge (free rental at advanced) and check your pressure when accelerating

I had a similar prob which coincidently ended up being a bad connection at the fuel pump.

thatsmrmastercraft
04-02-2012, 05:48 PM
points check
voltage check at fuel pump
get a pressure gauge (free rental at advanced) and check your pressure when accelerating

I had a similar prob which coincidently ended up being a bad connection at the fuel pump.

1981 MC.....back before electric fuel pumps.:rolleyes:

02ProstarSammyD
04-02-2012, 06:09 PM
Then the voltage will be fine. I fail to see your point :P

ahhudgins
04-02-2012, 06:27 PM
My neighbor had the same problem with his 79 MC a few summers ago, it died over 25 MPH. He got a fuel pump at the local Advance store and it was a quick fix.

Some people don't like to ditch the points but I would.

CantRepeat
04-02-2012, 06:33 PM
Then the voltage will be fine. I fail to see your point :P

I see what you did there. lol :D

thatsmrmastercraft
04-02-2012, 06:42 PM
I see what you did there. lol :D

Nothing slips by you, does it?:rolleyes:

CantRepeat
04-02-2012, 07:27 PM
Nothing slips by you, does it?:rolleyes:

I see what you did her!! lol :D

ted shred
04-02-2012, 11:26 PM
There should be a clear tube connected to the fuel pump. 80% of the time when they fail, this tube will have fuel in it.these pumps are dual diaphram.The engine will still run if one fails.

tex599
04-12-2012, 03:52 PM
Apologize for the delay in getting back to everyone. Checked the points, rotor it all looks good and replaced fuel filter. Took boat out and it was running fine for about the first 10 minutes, then started to act up while at speed. Felt like it was surging, if you tried to accelerate from idle it would act as if it was going to do die, but would get going. Pulled the fuel pump and waiting for the new one to show up. 90% certain that is the problem. Somebody mentioned the carb, but I think this would show up at both low and high speeds. Thoughts??

thatsmrmastercraft
04-12-2012, 05:17 PM
After reading through your posts again, a couple things come to mind. Is it possible that this is the result of a bad accelerator pump diaphragm? Simple to check by removing the flame arrestor and working the throttle (without the engine running) and look for two smooth jets of fuel.

My other thought is a bad vacuum secondary diaphragm. Pretty much need to operate the boat with the engine cover up and the flame arrestor off and look (carefully) into the carb to see if fuel is coming through the back half of the carb.