Mercury 150 HP 1550 inline 6 having issues starting and at WOT

Jacobsele

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May 12, 2015
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25
Hi,
I just got a 1978 150 HP Merc I6 this winter (along with a 1978 Checkmate Try-Mate 1).

Compression was around 136 +/- no more than 10 psi.

I have replaced all fuel lines and fittings, rebuilt carbs and fuel pumps (2) (they were all bad), primer bulb, then the basic stuff like impeller, gear oil.

The issue am having is it is really hard to start even when I prime the hell out of it and squirt some mixed fuel into carbs.

When it does start it will idle fine and run fine at cruse speed, then when I punch it to WOT it goes fine (not at the speed it should but think it's a prop issue) for about 30 - 40 sec then either bogs down or bogs down then turns off.

When I rebuilt the carbs they were bad and the float adjustments were all out of wack, I don't know the proper adjustment for the floats so I adjusted the one that had less flow to the needle.

I have also attempted the Link and Sync on a YouTobe video but I can not hear or see the spark so I cannot complete it.

Any help will be much appreciated
 

procraftguy

Petty Officer 2nd Class
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Jul 7, 2013
Messages
137
If its the electronic ignition u need the key on to get the spark from turning cap battery hooked up check ur tdc also initall should be right as cam starts to touch carb cam the two small bolts in distributer wil losen so u can make that a reality sounded like a 1977 by the way
 

Chris1956

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Mar 25, 2004
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27,035
Jacob, Technically, a 1978 1500 IL6 motor does not exist. The last one was 1977. There was a 1400 IL6 motor made in 1978 and 1979. They are identical to the 1500. A duel fuel pump IL6 may be older than 1978. You should look up the serial number at the maxrules web site.

I presume your motor has a distributor? If not it is likely 1979+1/2. Anyway your description of symptoms sounds like a fuel delivery problem. Since you rebuilt the fuel pumps, it is likely the floats are not adjusted properly. Here is how to adjust them.

Remove the carb bowl covers. Invert them. The top lever should be parallel to the bowl cover. If not bend the lower lever to make it so. Now turn covers right side up. The distance between the lever ends should be 1/4". Bend the lower lever to make it so.

You should have hard hollow plastic floats with little springs, plus stainless steel inlet needles with neoprene tips plus an all brass inlet seat. If you have the older foam floats, plastic needles and brass/rubber seats, it is time for new ones. Make sure the floats haven't cracked.
 

Jacobsele

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May 12, 2015
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25
Thanks.
It is in fact a 1973 SN: 7010714.
It does have the electronic ignition, key was on, and had a full battery.
The distributor cap and contacts were in bad shape, I will try and clean them up more or use the cap from my 115 (parts motor). I will also get new plugs but before I wanted to run sea foam through it.

I will adjust the floats soon (when I get the new ones in), the only thing I did not upgrade was the floats (still has the old foam ones).
I will also order new jets while I?m at it.

One thing that concerns me is when I replaced the fuel line I installed 1/4? fittings, do you think they need to be larger?

Thanks again everyone.
 
Last edited:

mr 88

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Nov 3, 2010
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2,115
The ftgs should be 3/8'' i.d. all the way from the tank to the motor.1/4'' will starve it or make it run lean,not good.
 

Jacobsele

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May 12, 2015
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Thanks mr 88, I just ordered some 3/8" ID fittings. They are hard to find locally and when I can find them they are an arm and a leg, lol.
 

buzzm19

Petty Officer 2nd Class
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Dec 14, 2009
Messages
152
all those carbs take 1/4 id fittings and I don't believe you can upgrade to 3/8 and even if you can run 3/8 hose you will still be defeating yourself because the gas has to go through the 1/4 id. I have drilled out brass fittings and I would say you could go 5/16 at best, hope this helps. Buz
 

Chris1956

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Mar 25, 2004
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Yes,the fittings on the carbs are usually 1/4", however, the motor needs to be fed by a 5/16" ID minimum fuel line. So run the 5/16" ( 3/8" is better but more work to adapt) fuel line up to the fuel pumps and the 1/4" after that.
 

Jacobsele

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May 12, 2015
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25
Thanks everyone. I changed the fittings/line to 5/16 (I could only find that size local). It fires up allot easier then it would not get past 2000 ish rpm. I striped the plug wires and connected them (they were kinda bad) to the distributor and it ran fine.

The bad news: after a few hours it started running like crap, I pulled the plugs and number 2 and 5 had metal attached to the plugs and the pistons were loose.

Would it be best to put new pistons, rings, baring, rods in (I don't know it it damaged the cylinder yet)?
or swap power head from my 115 hp inline 6 (if compression is okay)?

Thanks in advance
 

Jacobsele

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May 12, 2015
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Thanks, that's what I thought.
I'll just swap them and rebuild the 150 in the winter.

Well the good news is I got a good deal on a wave runner and got it running good in 3 hours so i'm not boatless yet, lol

Thanks again
 

Jacobsele

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May 12, 2015
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Here are a few pics of the number two piston, cylinder (best I could), and rings. The cylinder don't look too bad so I think I will rebuild it during winter.
I removed the 115 hp powerhead today, I attempted a compression check but it will barley turn over (battery is charged) but fairly easy to turn by hand.

I am thinking a bad starter or battery.

I will pull the 150 (bad powerhead) tomorrow and install the 115.

The bad motor I am guessing sat for a long time from the looks of it but compression tested okay when I installed it. I made the mistake of installing 1/4 fuel fittings and line at first (took it out a few times for around 10 hours each time) and it starved for fuel at WOT. I changed the fittings and line to 5/16 and it ran at WOT then just started running like crap, that is when I found the bad powerhead.

I just want to be sure this should not happen again with the 115 powerhead, if the powerhead was bad when I got it or if it's something I did.

Thanks for any input.
 

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Chris1956

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It is a bit unusual for #2 piston to go bad. Normally it is #1 and #3 that go bad. The even numbered pistons usually get more fuel from their carbs due to gravity, hence that are more resistant to overheat or lean running. You will need to find the cause for the powerhead failure, if you hope to rebuild it successfully.
 

Faztbullet

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Mar 2, 2008
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The even numbered pistons usually get more fuel from their carbs due to gravity
This is a old wifes tale as gravity has no effect on a atomized fuel charge or any type of vapor. If this was true gravity would pull clouds from the sky!!!! Likely started by someone who didn't understand principle of a wet reed engine.
 

Jacobsele

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May 12, 2015
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No Title

Thanks everyone. Looks like I found the issue, the block is cracked in two places, one spot looks as if someone attempted to put JB Weld on it, lol.
Here are a few pics.

I would not think this would be able to be repaired, what are my options? Start looking for a powerhead?
I'm in no hurry less the 115 is junk, lol
But I would like a backup motor and a project this winter.

Thanks again.
 

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Chris1956

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Fazt, I have observed that the even spark plugs on my 1500 were significantly blacker than the odd numbered plugs. As you know carbs will allow liquid and condensing fuel to enter the crankcase. Hence the need for fuel recirculation systems on 2 cycle motors. I submit that this liquid fuel under the influence of gravity feeds the lower cylinders of a pair, causing the blacker appearance..
 

Jacobsele

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May 12, 2015
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Okay.
Compression was good on the 115 powerhead, installed the powerhead and everything (carbs, distributor, etc).

I rewired (soldered new wire to what was left of the old good wire) the harness and am getting proper voltage.

I have no spark on any plug, there is no voltage to the green wire from control box to coil when cranking, there is no voltage from the white or black wire from the trigger to the control box.

It had spark on the 150 hp and I used it's components (distributor, control box, coil).

It is damn near the 4th and wanted to be on the lake by then.

Any tips or info would be helpful.

Thanks in advance
 

Chris1956

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You will not see normally voltage on the green coil wire. It is pulsed when the spark is needed, and it is likely your meter is too slow to react.

You have +12VDC on the red and adjacent white wires on the switchbox? Is the distributor wiring good? They go bad as well as the rest of the harness. Grounds are good?. You have set the timing belt per spec? Did you test for spark at the coil?
 

Jacobsele

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May 12, 2015
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Yes, I have 12+ V on the red and white wire. Distributor wiring looks good. I cleaned all the grounds before I put it together and they all ohm out.
The coil has no spark. I went by a youtube video to set the timing belt, I was not clear on this subject so it could be wrong.

Thanks
 
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