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1993 Mercruiser Magnum Tournament Ski - Carb/Fuel Issues


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First time poster here looking for some troubleshooting advice.

Background:  I have not been using the boat much over the last number of years.  About 5 seasons ago it had started randomly not running well.  Engine would die under load.  Not want to re-start.  Typically in a fashion that when pulling a skier would start to bog down and ultimately die.   Tried new cap. wires, coil, etc.  Thought it was an electrical issue.  It would then seem to run decent, but I always thought I had lost some top end speed.  Anyway.  Ended up the next season taking it in and they either rebuilt the carburetor or replaced it.  My memory is bad and the receipt is unclear.  I think they realized it was less expensive to replace than rebuild at that time.

Problem came back and I was suspicious that there was an electrical issue.  I ended up swapping out the Thunderbolt ignition for a GM-EST package from Michigan Motorz.  Was a straightforward install and the boat immediately ran much better.  Finished out the season, etc.  I still was lagging on top end though, but the bogging, hesitation on throttle up, etc was vastly improved.  

I didnt use the boat much for a couple of seasons, but it always seemed to start up ok, and run, though I did not do much skiing (rotator cuff issue) so I cant say how well it would have performed.

I had also done a fuel tank drain water separator filter swap etc along the way before I swapped the ignition system.

Fast forward to this season. 

1.)  Put boat in the water.  Starts right up.  Had a temp issue and sorted that out with a new raw water pump then realized the problem was actually the circulating pump.  Replaced and all is good in the temp arena.

2.) After warm-up, ran the boat for about 20 minutes, but had lost a lot of top end.  Max engine RPM was around 3400.  No missing, etc, just like that was the max speed.  I could hear a change in the air, like the secondaries were opening but maybe only a couple hundred rpm.

3.) Continued internet searches on what to root cause.  Went out and checked linkage, etc.  Could not find anything wrong.  Idled the boat up to temp yesterday.  Choke is working fine.  The secondary lock releases when the choke is open and at WOT (Engine off), the throttle blades are all open.  Was by myself so I couldn't do much more.

4.) Went out this morning with a helper.  Boat started right up.  Was idling out to warm it up.  Throttled up fine about 2800 rpm, and it started to bog down.  Did a quick swing around to get headed to the dock and it died.  Could not get it re-started.  Was trying to start, but would not stay running.  After it died at first crank there was nothing. Completely dead.  Wiggled the throttle and then it would crank (maybe I was not in neutral or could there be a switch problem?).  With the engine off, pumped the throttle and could see fuel coming into the carb.  Was able to get it started and into gear without stalling and it would run for a few seconds, but I was making my way back to the dock.  Proceeded to do that.  Engine off, pump the throttle several times.  Get it started and into gear.  Tried to accelerate slowly and it would die.  Pumped again with engine off, got it started and then was essentially trying to go to near wot and idle quickly to try and pump some fuel in.  That helped and I was able after several times to make it back to the dock.  Of course as I neared the dock, it started to run and idle better.  

5.) Being a gluten for punishment I thought lets try this again and see what happens.  Idled away, slowly powered up and although it started to take off, I could tell it was bogging  and swung back around.  Ended up dying again and I repeated the above to get back to the dock.  Covered it up and called it a day.

So I start thinking is this really a fuel problem or could something else be going wrong?  Why did it run a while back with limited top end and now wont do that?  Could I have a fuel line clog?  Could teh mechanical fuel pump be bad?(No fuel in the plastic line to the carb that I can see, but not sure that really diagnoses a fuel pump properly (Original pump as best that I know)

I was going to try and check fuel pressure but the fuel line is a hard line and I cant see where I can connect.   Do I try a temp rubber line?  Should I try and run a clean source of fuel and by-pass the tank, etc.?  Ive read there is typically some sort of anti-siphone valve of something like that?  I have no personal experience with that and not sure if all boats have it, etc.  I did at one point in teh past try running with the cap off and that made no difference, but I did not do that recently.

ok.  Sorry for the long post here, but looking for some possible suggestions on how to try and isolate.  My best route may be the mechanic, but Ive been there before and am convinced that work didn't really fix the root cause.

Any help would be appreciated.  I also have not run a compression check.  I was planning on doing that to see if I lost a cylinder but this mornings adventure put that on the back burner.

Thanks in advance.

 

 

 

 

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Welcome to the crew.  Nice writeup.

I think you have a fuel issue, but like you mentioned it could be mechanical.  A compression/leakdown test would help rule that out.  Is your fuel pump mechanical or electric?  If it is electric, you can remove the line to the carb and plumb it over to a jar to see what kind of flow you get.  Your engine can use up to about 30 gallons per hour at WOT, so it should only take about 15 seconds to get a pint of fuel.

I think I would just replace the pump if it is mechanical, and I would probably replace any rubber fuel line from the tank to the carb.  As it ages, it can shed chunks from the inside that end up blocking the flow.  While you have the lines apart, you could also back flush or blow any hard lines to make sure they are clear as well.

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Sounds like lack of fuel delivery.  How old are the rubber fuel and breather lines, that era rubber is not ethanol compatible.  Anti siphon valve on fuel tank vent line can cause similar symptoms.  Bad coil can fail at elevated temperatures and be fine when cool.

Did you determine an issue with the Thundervolt system?  Curious as to your thoughts on ignition system change experience.

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Thanks.  I have a mechanical pump.  I believe all of that to be original including the lines.  I think I will replace the fuel pump.  I was contemplating trying to run a clean fuel source (5 gal can) to see if there is any difference. 

In terms of the  electronic ignition change, after I first installed it, I noticed an immediate change for the better, but Id say the jury is still out at the moment until I sort this issue to make sure it is not anything related to that swap.  It was very straight forward and the boat starts and idles much better after that.  Had good take-off response, etc. until I ran into this issue.

Where would I find the anti-siphon valve and would there be a quick check to by-pass it somehow?  

Ill report back what I find.  Im also going to try and tie in a fuel pressure gage, but the hard lines are going to make that a bit of a challenge.

Thanks for the suggestions so far.

 

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Mechanical fuel pumps often have a double diaphragm so if one fails the other will either cause fuel to flow into the opaque yellow overflow hose that goes into the carb, or into the crankcase of the engine.  Check to see if you have any fuel in the yellow hose or if the engine oil level increases from being diluted with fuel.

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Thanks.  Have not noticed anything in the tube.  Also, nothing in the oil.  No gas smell of increase in level.  Not knowing if teh FP's have any kind of screen in them, Im wondering if I have a line deterioration situation and something is getting plugged and occasionally frees up so I have this intermittent problem.  Looking to try and find a replacement pump and some marine line today to see if that helps the situation.  This last situation I had really felt initially like I was running out of gas.

 

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I worked on a 2005 Moomba 10 years ago that had an odd fuel problem.  The owner said the boat would start and run for 45 minutes, then stall, and would only crank, but not start.  It would do this each day the boat was used.

The boat started and ran at the shop with no issues, but after 45 minutes the engine suddenly stalled and would not restart.  I removed the fuel line and found the rubber inside of it was swollen completely closed.  I replaced all of the fuel hoses from the tank to the fuel pump and regulator and the problem was fixed.

I left the old fuel hose on my work bench and the next morning the inside of the hose looked perfectly normal with no signs of swelling at all.

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42 minutes ago, csleaver said:

I worked on a 2005 Moomba 10 years ago that had an odd fuel problem.  The owner said the boat would start and run for 45 minutes, then stall, and would only crank, but not start.  It would do this each day the boat was used.

The boat started and ran at the shop with no issues, but after 45 minutes the engine suddenly stalled and would not restart.  I removed the fuel line and found the rubber inside of it was swollen completely closed.  I replaced all of the fuel hoses from the tank to the fuel pump and regulator and the problem was fixed.

I left the old fuel hose on my work bench and the next morning the inside of the hose looked perfectly normal with no signs of swelling at all.

I have a riding mower that progressively got worse about running at mowing speed.  I could lower the throttle and it would idle just fine for as long as I let it.  I replaced the fuel pump and it was the same.  I blew into the fuel line from the pump end and could easily blow bubbles into the tank.  Finally, I just decided to change the fuel hose and it fully cured the problem.  I could easily blow one way through the hose, but not the other.  A chunk had come off inside and was blocking flow in only the forward direction.

After that, I don't use ethanol fuel in any small engine or any boat engine.

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Just a quick update.  In order to rule out the line from the tank to the pump, I ended up taking a few gallons of fuel in a can and running a short hose to the filter inlet.  With this set-up I was not able get the boat to run at idle.  I had to pump some fuel in with the accelerator pump and then it would fire and run for a brief period and then stall.  I decided to swap out the fuel pump.  (take note that the plunger rod is a pain if you ever do this.  I was not ready for that aspect and spent considerable time getting it in position so I could slide the new pump lever in.  There is supposedly a bolt that aligns with it, but I could not get that trick to work.  Anyway with the fuel pump swapped and the 5 gallon can, the boat started and idled fine.  I was able to take it out for a run and while it ran well, I have the same problem where it has lost top speed.  engine rpm no greater than 3400.  Im going to do a compression check and re-set the timing to make sure I don't have another issue.  Rained most of the day here, so Ill tackle the next step tomorrow.  What really puzzles me is that it runs great, accelerates well until it approaches that speed and then just falls on its face.  

1.) Compression check to try and rule out a mechanical issue

2.) Bring a helper so I can see what is going on in the carb at WOT

3.) Double check timing to make sure I am getting proper timing at idle and also at higher engine speed.  (Spec is 8 BTDC at idle). My boat tends to idle at around 500 rpm in neutral.  Does that seem correct?  I have a spec for idle speed in Forward, which was 750 - 800, but nothing in Neutral.

Thanks, Jeff

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It sounds like you are making progress.  It might be worth making sure that the inlet screen at the carb is not full of crud.  Maybe also check the float levels to make sure they are correct.  Honestly, a few seasons of sitting is probably reason enough to take the carb off and give it another bath.  You may have crud in the high speed jets on the secondaries.

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ok, im a first timer to the forum as well... I ran across this post looking for answers to very similar issues. 95 malibu echelon with the 350 Mag Tourney ski engine. I acquired the boat from a friend at a "cannot turn down" offer :) and i am having trouble cranking and starting. it had been not used for a few years. I was told it needed a high pressure fuel pump and thats it. Found a few OEMs online that were $700-800 each. I was told thru other resources (bakesonline) that the after market pumps would work fine. So i purchased one from summit. installed, it fixed nothing. I then replaced the fuel regulator and with new diaphragm that was NOT the same as what was on it. Old one looked like it was spot welded to cover up "adjustment hole". (im no mechanic so sorry about the lingo). Noticed the injectors were very rusted and spray pattern was nothing but drips, so at that point i took it to a boat mechanic.

He basically took me for a ride and told me every part i installed was crap, then ordered all new parts (which was from summit racing BTW and sure enough... he failed to fix it also. He did say that when he tested/crimped the return fuel rail going back to the high pressure pump, it would run better?

Then i discovered that the fuel line going into the inline fuel filter before the mechanical pump was not connected properly with c clamp. I fixed it and it finally started better and stayed running for a minute or so but then died. Im at a lose as to what to do next!.

Note: no clog in vent hole at tank, fuel tank drained and cleaned, mechanical pump is good, fuel separator is good. It will start fine with starter fluid but wont stay cranked.

Questions i have for the group that relates to this thread:
Should i replace all fuel lines and fuel rails going to carb?

Could the fuel regulator diaphragm not be producing the correct amount of pressure? Its from autozone and could be standard setting version( fits 350 chevy)
Could i have the wrong fuel injectors installed by this mechanic? I read online ...https://skiboatpartsonline.com/TBI-Marine-Fuel-Injector-MEF-0070 ... 
Marine calibrated injectors designed for 29 PSI fuel pressure for the 5.7 Chevy engines. DO NOT use automotive injectors designed for 7 psi fuel pressure in a Marine engine.

ANY help would be appreciated. My apologies for long post but lots to explain. Im almost about to pull the plug on all this and order the Holley Sniper EFI set up and be done... i just dont have another 1500 to throw out right now...:)

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Hard to remote diagnose, although from your comments I would start with verifying fuel pressure at the throttle body so yes to that question.  Also these systems are sensitive to any air leaks between the tank and injector.

As for sniper EFI, it may not be simple plug and play.  No provision for an O2 sensor complicates any automotive aftermarket system.

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9 hours ago, mikeLF said:

Should i replace all fuel lines and fuel rails going to carb?
Could the fuel regulator diaphragm not be producing the correct amount of pressure? Its from autozone and could be standard setting version( fits 350 chevy)
Could i have the wrong fuel injectors installed by this mechanic? I read online ...https://skiboatpartsonline.com/TBI-Marine-Fuel-Injector-MEF-0070 ... 
Marine calibrated injectors designed for 29 PSI fuel pressure for the 5.7 Chevy engines. DO NOT use automotive injectors designed for 7 psi fuel pressure in a Marine engine.

An injected engine does not have a carburetor, it has a throttle body. 

You mention injectors, which leads me to believe that you have a multi-port injected (MPI) rather than throttle body injected (TBI) engine.  Your part is for a TBI engine.  Which do you have?

Depending on your system, you may need a 3 Bar (44 PSI) regulator.

This thread was specifically about a carbureted engine, so it might be best to start your own thread.  A photo would help us identify what you have.

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1 hour ago, justgary said:

An injected engine does not have a carburetor, it has a throttle body. 

You mention injectors, which leads me to believe that you have a multi-port injected (MPI) rather than throttle body injected (TBI) engine.  Your part is for a TBI engine.  Which do you have?

Depending on your system, you may need a 3 Bar (44 PSI) regulator.

This thread was specifically about a carbureted engine, so it might be best to start your own thread.  A photo would help us identify what you have.

Thank so much for the quick response. I created a new thread. 

 

it does seem to be the TBI set up.

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5 hours ago, Woodski said:

Hard to remote diagnose, although from your comments I would start with verifying fuel pressure at the throttle body so yes to that question.  Also these systems are sensitive to any air leaks between the tank and injector.

As for sniper EFI, it may not be simple plug and play.  No provision for an O2 sensor complicates any automotive aftermarket system.

im going to try and install a temporary inline fuel pressure gauge to verify. Just to clarify your response about the air leaks... are you reffering to the fuel tank in rear  OR the fuel tank cannister where the high pressure pump is? i started a new thread on this. Thanks again for response. 

 

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Had a chance to make some runs with a helper.  For reference, I am still running out of a 5 gallon can for these runs.  Trying to keep that consistent.   Also made the following check.

1.) Verified that base timing at idle is at 8 deg BTDC.  This is in Neutral with idle speed at about 750 rpm.  My idle speed in Drive drops down to about 550 rpm.  I dont know if that is too low or not.  I mention this only because the spec that I have in documentation that came with the boat has timing listed at 8 deg at idle in Drive of 750 rpm.   Curious if anyone has thoughts on this.

2.) I made several runs where I tried to video what was happening in the carb.  I personally have no experience with what this "should" look like.  I was trying to understand what was happening when the secondaries opened as that is when I seemingly dont get much performance increase.  I am going to try and post a couple of videos.  If they don't show up here, I will try to embed a you tube link.

Run1:  Short video of a run up which to me looks like the air valve is not opening up completely and the fuel spray looks marginal, but again, Im not exactly sure what this should look like. 3400 rpm max at WOT

Run2: Short video of a run up where I intervened and opened up the air valve with a screw driver(There is no mechanical connection to the throttle linkage here - essentially a counterweight type arrangement).  You might be able to hear an increase in rpm and it looks like additional fuel  (max rpm here is 3600 rpm).  When I pull the screw driver the air valve stays in place I assume due to the increased airflow, etc.

If anyone sees anything here that might be a clue. Let me know.  i am also going to try and check total timing at WOT condition to see where I am at.  Still not ruling out an ignition interaction.  

 

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Any reason you can't pull the carb and give it a bath?  Take it apart, dip it in a gallon can of carb cleaner, blow it with air, inspect it, put it back together, verify float levels, put it back in.  If you don't have air, use a can of spray carb cleaner.

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Timing at either idle speed should be okay, check ignition timing at around 4,000 RPM or simply make sure it maxes out at 32-33 deg BTDC.  Might be worth making sure timing marks are accurate.  Carb rebuild is easy, you can get info using Carter AFB or Edelbrock 1409, 1410 as a reference, they are all the same.

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Michigan boarder

@Vapor001The carb looks really dirty, as far as carbs go.  So I agree with the others that you should clean that up, rebuild or replace before any other steps.  Other than the compression check, did you do that?

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5 hours ago, Michigan boarder said:

@Vapor001The carb looks really dirty, as far as carbs go.  So I agree with the others that you should clean that up, rebuild or replace before any other steps.  Other than the compression check, did you do that?

Thanks all.  Will try and work on that next week.  Haven't dealt with this type of carb ever so I was a little leary.  

I still need to do the compression check.  Next on the list.  I will also check the timing at higher rpm.  Is that something best to do under load or is it ok if stationary at the dock?  Since its just rpm based, Im thinking at the dock is ok.

 

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Had a chance to get out and check a few things.

1.)  Check compression.  Cool engine.  Ran for a few minutes, but not fully up to temp.  All but 2 cylinders checked at 155. The other 2 cylinders checked between 160 - 165, so I think from what I have read, those are good checks.  Plugs all looked a nice tan color.

2.) Checked timing and from 2000 rpm on up to about 3600 rpm, it was at 26 degrees BTDC.  But here is what I find interesting.  When I go through the procedure to set timing on the electronic system that I have, the directions involve installing a shunt device that puts the distributor in a "Base Timing mode"  When the shunt is installed, the idle speed drops and then I have a digital timing light that I set to 8.0 and then adjust the distributor so that the mark ends up at TDC with the light at 8 degrees.  

3.) After disconnecting the shunt, the idle speed increases back to normal  and then when I go look at the timing, the mark is no where to be found.  if I adjust the digital light to find the mark and put it on TDC, then I am reading 20 degrees on the timing light, which to me means I am at 20 deg BTDC.  Idles great, accelerates great, but just peaks out between 3400 and 3600 rpm.

I'll be talking to the supplier of the electronic system to understand why I am seeing what I am with the timing next week as they are not around on weekends.

Will also be moving forward with either a carb cleaning or a possible replacement.  Ive seen a place on here called flyingfish carbs and I might go that route, since I am still a little unsure if the carb I have on the boat is original or not based on teh service work that was done six or so years ago.  If anyone has any other suggestions/comments, let me know and Ill post an update on what I learn from the next steps.

Thanks

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The directions to set timing with a jumper in place sound good to me.  It is the base timing you want to set.

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  • 2 weeks later...

Well ended up replacing the carburetor with one from flyingfish carbs.  Was a quick exchange.  Went our for a ride.  Idles well, much smoother on take-off, and a slight improvement on top end.  Certainly the best that is has ran in a while, but it still tops out at 3500 ish rpm.  I get about 38 mph, although I need to run a quick calibration on the speedos.  

Good compression

Timing is on

New Fuel pump

New rebuilt carb

Trying to think about what else I can check before I throw in the towel.  It is definitely usable as it is now (after I run it for a few days to make sure the intermittent nature of the problem doesn't come back).

If anyone has any other ideas, let me know

Thanks, Jeff

 

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