WOT sputter/popping...low RPM

T

Tinlizzy

Petty Officer 2nd Class
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May 7, 2007
Messages
121
...This is in regards to my 1971 Mercury 1150 (115 HP) outboard.

Problem: When I advance the throttle to wide open it will sputter and pop as well as only reaching 3200 RPM.

...If I back the throttle off of wide open a touch it will stop sputtering/popping and slowly climb to 3800-4000 RPM. When I do reach near the 4000 RPM mark I have tried to advance to WOT and it will start to sputter/pop and drop the RPM back down to 3200.

This motor has me about ready to sink it to the bottom of the lake :(

Here is a list of work/test I have done.

1. Rebuilt the fuel pumps and replaced the exterior fuel lines along with primer bulb. I also drained the gas tank.
2. Rebuilt the carburetors and set floats to spec. Checked the High speed jet size.
3. I have tested for spark on all of the cylinders as well as the quality. They jump a 7/16" gap.
4. Compression is 130# +/- 2# on all cylinders.
5. replaced dissy cap with new/used, as well as a new carbon button for the rotor inside of cap.
6. Checked HT wires at night for arcing, they checked OK
7. Testes coil and switch box by jumping brown term to white term, then arcing black. They tested OK.
8. Replaced the old wires on the motor.
9. Tested voltage at switch box, I have 12v at red term and 12v at white with ign. key on.
10. I have replaced the ign. switch (it was faulty)
11. When cranking I have at least 9.6v on the switch box.
12. Did a link&sync. Max advance is set to 23 deg. and primary pickup is set to 3 deg.
13. I have verified the carb butterflies are opening fully.
14. New spark plugs, L76V

It seems once the throttle engages the secondary pickup is when the sputtering/popping happens. If I hold it wide open without engaging the secondary it will run fine. Does this seem odd?

The motor idles/starts fine. When I have it WOT I tried to hit the choke as well and it dropped RPM so I know its getting fuel.

I have a 17 pitch prop.. Its on a 19' closed bow, v-hull. I have never ran this setup before.

I am completely stumped can anyone figure this one out for me :confused:

...I will buy ya a beer!
 
L

Laddies

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Re: WOT sputter/popping...low RPM

Have you checked the throttle stop that 1 or more carbs are not going by the open position
 
OldMercsRule

OldMercsRule

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Re: WOT sputter/popping...low RPM

Tinlizzy said:
...This is in regards to my 1971 Mercury 1150 (115 HP) outboard.

Problem: When I advance the throttle to wide open it will sputter and pop as well as only reaching 3200 RPM.

The pop sounds like a miss fire due to crossed wire or timming WAY OFF.

...If I back the throttle off of wide open a touch it will stop sputtering/popping and slowly climb to 3800-4000 RPM. When I do reach near the 4000 RPM mark I have tried to advance to WOT and it will start to sputter/pop and drop the RPM back down to 3200.

This motor has me about ready to sink it to the bottom of the lake :(

Don't do that, but now ya know where these old girls get their name.

Here is a list of work/test I have done.

1. Rebuilt the fuel pumps and replaced the exterior fuel lines along with primer bulb. I also drained the gas tank.

I assume yer "silver block" brass fillings don't leak then: (yet)

2. Rebuilt the carburetors and set floats to spec. Checked the High speed jet size.
3. I have tested for spark on all of the cylinders as well as the quality. They jump a 7/16" gap.

Do all the new plugs look the same after a run?

4. Compression is 130# +/- 2# on all cylinders.

VERY GOOD, it likely can be fixed!!!

5. replaced dissy cap with new/used, as well as a new carbon button for the rotor inside of cap.

If a used cap, (or even new) make sure: no cracks or any other problems that could lead to a cross fire.

6. Checked HT wires at night for arcing, they checked OK

Use an automitive spark checker to veryify each plug wire when running. Popping may mean: #1 fire at the wrong time; #2 fire at the wrong place; or #3 intermitent fire #4 bad reeds (compression seems to high for that)

7. Testes coil and switch box by jumping brown term to white term, then arcing black. They tested OK.
8. Replaced the old wires on the motor.

Plug wires too??

9. Tested voltage at switch box, I have 12v at red term and 12v at white with ign. key on.
10. I have replaced the ign. switch (it was faulty)
11. When cranking I have at least 9.6v on the switch box.
12. Did a link&sync. Max advance is set to 23 deg. and primary pickup is set to 3 deg.

I think Clams or one of the "big guns" here has said 21 degrees max!!! Please find the linc n' sync thread n' review.

13. I have verified the carb butterflies are opening fully.
14. New spark plugs, L76V

It seems once the throttle engages the secondary pickup is when the sputtering/popping happens.

Not sure what the "secondary pickup" is. Some of the others here may.

Is the distributer advancing way too much????

If I hold it wide open without engaging the secondary it will run fine. Does this seem odd?

The motor idles/starts fine. When I have it WOT I tried to hit the choke as well and it dropped RPM so I know its getting fuel.

I have a 17 pitch prop.. Its on a 19' closed bow, v-hull. I have never ran this setup before.

I am completely stumped can anyone figure this one out for me :confused:

...I will buy ya a beer!
Click to expand...

When I get as frustrated as you seem to be I hire a mechanic to "tune" it since it seems you have a minor tune problem. Good luck! JR
 
T

Tinlizzy

Petty Officer 2nd Class
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Messages
121
Re: WOT sputter/popping...low RPM

Laddies, I just checked again and confirmed that all three of the butterflies are stopping at the open position.
 
T

Tinlizzy

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Messages
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Re: WOT sputter/popping...low RPM

Thanks for the reply as well JR.

All of the HT lead are on there correct spots.

My "silver block" brass fittings show no signs of leaking (yet) :)

I have not pulled the new plugs yet, but when I changed the plugs this morning to the new ones from the run last night, the old ones were appearing the same.

The power head is supposably new, according to the previous owner.

The cap does not shown any signs of a crack. I cleaned it with carb cleaner and Q-Tips.

I have checked each HT lead with a spark gap tester, and they checked OK for a 7/16" spark. Nice and blue.

You are correct JR about the 21 deg. opposed to the 23 deg. Will 2 deg. give me that much of a problem? ( I just went outside and changed it to 21 deg. I will have to try this out on sunday)

I have not changed the plug wires.

The distributor stops at the Max Spark Advance set screw. So I would not say its advancing too much. Once it stops at the max advance set screw further motion of the throttle engages the "economizer collar" which moves the secondary pickup arm. (I hope I am correct?)

..hehe the problem is finding a mechanic who will work on these old beasts!
 
L

Laddies

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Re: WOT sputter/popping...low RPM

I've been thinking about your problem for a couple hrs and a couple thing come to mind, the first is your at max spark advance a long time before wide open throttle so if the problem is a lean condition what would cause it and here are a couple ideas is the needle lever drop a 1/4 " that can cause a lean high speed problem and the other thing is did someone sell you the .065 inlet needles instead of the .078 that your engine needs for fuel deliver at high speed. The other possibility is the cap cross firing, we never clean a cap with petroleum based product either carbon tetrachloride or hot water and dish soap, the way we test a cap for cross fire is mark the flywheel in 1/6s starting with the factory timing mark then remove all spark plugs and turn the engine to number 1 at the timing mark put a 7/16" spark gap in the plug wire for 1 and the other 5 wire install plugs that are grounded the do the switch box test while doing the test if you get a spark to any plug besides the spark gap the cap is cross firing if it test good then move the flywheel to the next mark and the spark gap to the right cyl and repeat the test on all 6 cyls, if they all test OK the the cap and rotor are good sounds kinda dumb I know but with out a oscilloscope it's the only way I know to test one for sure
 
j_martin

j_martin

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Re: WOT sputter/popping...low RPM

Laddie's spot on. Be sure your high speed mix isn't too lean, and your timing isn't too advanced. If you try a pony tank of 92 octane non-oxygenated (no alcohol) gas, it would run a little better in either case. (just a test) It has a bit more fuel value (runs better lean) and higher octane (less pre-ignition)

That sort of a backfire, misfire could also point to a high voltage fault (arc-over) in the ignition. If it twer mine, I'd rig up a portable oscilloscope to check it under load.

hope it helps
John
 
OldMercsRule

OldMercsRule

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Re: WOT sputter/popping...low RPM

Glad you "big guns" weighed in to help.

I'd still be tempted to get out me wallet n' take it to a technition.

It sounds like a fairly minor problem, (but potentially fatal if not properly fixed), that I bet Laddies could fix fairly quickly, (if yer anywhere near someone like him). JR
 
T

Tinlizzy

Petty Officer 2nd Class
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Messages
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Re: WOT sputter/popping...low RPM

Ok laddies you caught my attention with the high speed jet size!

The high speed jets installed are .066 This motor requires .078's :confused:

The mercury shop manual specs for .066 up to 4000 Feet, .064 4000-7000, and .062 7000-10000. They do not even show a .078 Is the manual off on this one?
The only model I see in here that calls for a .078 jet at this altitude is the 1350 model.

Thanks for all of the superb help guys. I will wait for your reply laddies on the high speed jet size before I do any further diagnosis. Could it be that simple?? :)

(JR, I wish I lived near laddies I would have him doctor me up hehe)
 
AMD Rules

AMD Rules

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Re: WOT sputter/popping...low RPM

The jet sizes you have listed are what is shown in my manual as well. ie. .066" up to 4000 ft

The advise you have been given so far is excellent. Given that the motor overall appears healthy, and you only seem to have a problems the throttle advances, I would suggest you re-evaluate your link & sync procedure.

Maximum advance beyond 21? can damage the motor.

Did you re-confirm the piston TDC and distro alignment (ie. s the belt on properly?)
 
L

Laddies

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Re: WOT sputter/popping...low RPM

I did not mention high speed jet size! I said INLET NEEDLE SIZE but if you have never checked the size of the high speed jet that would be another thing that should be checked
 
C

CharlieB

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Re: WOT sputter/popping...low RPM

Can you manually rig the choke plates to remain in the 1/4 on position and try it again.

It really sound like it's lean on the top end.

If this engine has been bored combined with the poor quality of todays fuel this baby could be crying for more fuel and may need jetting.

Depending on the craft and how crazy your friends are, try adding small amounts of choke and see if it picks up.
 
T

Tinlizzy

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Messages
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Re: WOT sputter/popping...low RPM

...Sorry laddies! I read too quickly...I see inlet size now :redface:

How do I determine the inlet needle size? I know the high speed jets are .066.

AMD - I am going to re-check myself yet again on the link n' sync. I will also reconfirm the TDC mark. I have not checked the distro alignment before so I will do that now.

Could there be something I am missing in the link n' sync?
 
L

Laddies

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T

Tinlizzy

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Re: WOT sputter/popping...low RPM

Ok Laddies I have done some more digging myself. And now I think I am more confused.

I remembered that I saved the wrappings from at least one of the carb rebuild kits. the part number from sierra is 18-7021 which included the needle and seat.

When i was rebuilding the carburetor, one of the needle/seat packages was different from the other two. When I went to try and install it the threads were different and would not fit into the carburetor.

Now I just had an idea to measure it, and it was 5/64" which is .078. So I have the .065's installed. As I found out the .078's would not fit the carb. According to the part number from a Mercury parts list, the correct needle/seat P/N is 1395-83181. The P/N that matches that from sierra is 18-7061 which is the .065 bore. The .078 bore is for serials 0-02933900. My serial is 3113168.

I would try the .078 but since I tried it before by accident they did not fit due to threads.

Then I decided to check the carbs to make sure they were correct. Two of the carbs are WMK-3 and the other one is WMK-3-1. Are these different carburetors? And maybe one or the other is wrong?

I do not know which carb I tried the .078 on because I was not aware of this whole issue. So maybe I have either one or two wrong carbs?

I verified the distributor alignment with the belt and flywheel and it checked OK.
I have not checked the cap for cross firing yet.

So what to do now?
 
T

Tinlizzy

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Re: WOT sputter/popping...low RPM

...I am going to check my timing again, because for some reason I have a gut feeling its wrong.

I have no timing marker on my top cowl support so I need to make a mark on the support. Let me read through the process to make sure I am thinking correctly.

On the #1 cylinder I find TDC by turning the flywheel CW. Now turning CCW go about a 1/4 turn past .464, then turn back CW to exactly .464. and scribe a mark on the cowling support at .464? Now I use this mark to set my max advance at 21 deg off of the tape on the flywheel?

Or do I mark .464, then make a mark ATDC 0deg. And time off of the 0 deg. mark? I have a feeling I did it this way.....would the motor even run if I did it this way?
 
T

Tinlizzy

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Re: WOT sputter/popping...low RPM

Is the distributor suppose to hit the max advance stop screw before it engages the economizer collar and fully open the carbs? So in other words the distributor is fully advanced with the carbs only open about 3/4 or more of the way open?
Then the economizer engages and open them the rest of the way without the distributor advancing?
 
L

Laddies

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Re: WOT sputter/popping...low RPM

I think that the difference in the WMK-3 and the WMK-3-1 is the latter is the top carb and the 3-1 is the designation for the top carb being modified with the pickup linkage. This whole thing is starting to confuse me and I'm suppose to be a mechanic, the parts manual calls for the .065 inlet to use the .078 you would have to change the top back to the early top, was the large inlet in the top carb? If it was someone may have changed it to get the larger inlet needle. Some how the inlet being smaller than the jet don't ring to me but the inlet is under pressure and the high speed deals with vacuum. The earliest carbs for that engine were Tillison and the later were Walbro I believe I still think that you are lean or have a cross firing cap. Wish I could come up with a better answer but it's tough when you can't really hear one run
 
T

Tinlizzy

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Re: WOT sputter/popping...low RPM

Ok laddies sorry for all of my mumbo jumbo. I am getting confused myself so let me try to clarify this.

All three carburetors have a .065 inlet needle bore with a .066 high speed jet.

I tried to install a .078 bore seat but they will not fit into these carbs due to the thread sizes. They all had the .065 bores before I rebuilt them. I ordered three carb rebuild kits. One out of the three rebuild kits came with the wrong needle and seat, which was the .078 bore size. I tried to install that .078 bore seat without knowing it was the wrong size, and it would not fit. I had to reuse the old needle and seat. That is how I know the .078 bore's will not fit in these carbs.

The WMK-3-1 is the top carb and the two WMK-3's are the bottom two carbs.
 
L

Laddies

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Re: WOT sputter/popping...low RPM

Thats exactly what I found the WMK-3 series use the .065 inlets and you have .066 main jets so everything is right as far as parts. I guess that if the carbs are lean then you might have main jets that are varnished, did you remove them and rod them out or just blow them out like we all tend to do when hurrying. If that was done and he float lever drop is right then you will have to go to the ign. system
 
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