Mercury ,1973, 150HP, in-line 6 outboard problems

[dandel]

My 1973 Mercury 1500 (150HP Inline 6) is surging and bogging down at top speed. It only seems to occur at top speed. The primer bulb does not seem to stay hard on its own and I can't keep it hard by manually pumping. It also is a very difficult to start and takes some time to idle properly. Once its warm it runs great and also runs strong pulling tubes at about 3/4 speed. <br /><br />I haven't cleaned the carbs, replaced plugs, or cleaned fuel tank yet but that seems the next step. Any other suggestions? <br /><br />Gotta luv the old Keikehaffers! Is that Keekhifer or Kikeheffer?

 

[Kenny Bush]

Re: Mercury ,1973, 150HP, in-line 6 outboard problems

I would clean those carbs, check timing, and change plugs. Run it and see if any change. You may also want to check your compression just to make sure your powerhead is "balanced".

 

[RICKRICK1]

Re: Mercury ,1973, 150HP, in-line 6 outboard problems

Bushcat has the right ideas and you might want to overhaul the fuel pumps while your at it.

 

[schmoedog]

Re: Mercury ,1973, 150HP, in-line 6 outboard problems

Ya might want to start at the tank and fuel line and bulb. Any small leak will make the bulb soft.

 

[mikesangelonly]

Re: Mercury ,1973, 150HP, in-line 6 outboard problems

i just had the same problem with my 115hp my timing belt jumped time so i redone it and it runs good so i would check the timing first

 

[Blindo the Frog]

Re: Mercury ,1973, 150HP, in-line 6 outboard problems

I reckon Schmoedogs on the right lines. If the non-return valve in the bulb is buggered (like it was with mine), then you will be getting a fuel & air mix going through which would make it tricky to start and spluttery whilst idling. At greater speeds, though the fuel would be forced through quicker and so the non-return valve would be irrelevant.

 

[what200]

Re: Mercury ,1973, 150HP, in-line 6 outboard problems

They all are hard to start. Check fuel pump or better yet get a small electric pump and set at 4 psi. Makes starting much easier.

 

[dandel]

Re: Mercury ,1973, 150HP, in-line 6 outboard problems

thanks for guidance fellas,<br /><br />I'll start from the tank and track back to the carbs and check compression this weekend.

 

[skier]

Re: Mercury ,1973, 150HP, in-line 6 outboard problems

I think that the L6 Mercs are easy to start. Pump the bulb, Turn the key on, Push and hold the choke, Advance the timing, Crank it until it fires then let go of the key and choke.<br /> Works every time.<br /><br />Craig

 

[dandel]

Re: Mercury ,1973, 150HP, in-line 6 outboard problems

Drained all old gas from the tank, cleaned carbs, changed sparked plugs, looked for any leaks in fuel system, and checked compression this past weekend.<br /><br />Compression checked out per manual, and the motor starts much better now. Intially going from idle into gear is a little rough also I'm still losing rpm at WOT. I can run at 4500 rpm without a miss but once I go any higher the rpm will fluctate rapidly. I haven't rebuilt fuel pump yet but I plan on doing that next, any other suggestions?<br /><br />Thanks in advance!

 

[mellowyellow]

Re: Mercury ,1973, 150HP, in-line 6 outboard problems

double check the floats are working properly.<br />(squeeze bulb and look for gas spilling out carbs)<br />make sure o-rings on quick connect male and female<br />are good.

 

[jdkzrt]

Re: Mercury ,1973, 150HP, in-line 6 outboard problems

Did you clean carbs, or re-build them? If you had them apart you should have replaced the needles and seats (easy and cheap to do once you are in there). Sounds to me like this is where your problem is. Also, on an old engine, rebuildind the fuel pump is never a bad idea (you don't want to risk a lean out condidtion @ full throttle IE: burn down)

 

[mellowyellow]

Re: Mercury ,1973, 150HP, in-line 6 outboard problems

ditto what JDK said!

 

[dandel]

Re: Mercury ,1973, 150HP, in-line 6 outboard problems

I did not remove the carbs and rebuild I only used carb cleaner. Now that you mention it I have noticed gas coming out of the carbs when starting which points to a stuck float or needle valve issue. <br />Since the season is coming to a close is there any harm continuing to run the motor up to 4500 rpms before it starts to fluctuate? I don't want to cause additional harm by continuing to run.

 

[Fouled Plug]

Re: Mercury ,1973, 150HP, in-line 6 outboard problems

If one of those sticky needles sticks closed at 4500 RPM and you lean out a cylinder, there will be harm indeed! Take an afternoon, drop the carbs and soak 'em at least. The new needles and seats would be a great idea. An ounce of prevention.....

 

[briannh1234]

Re: Mercury ,1973, 150HP, in-line 6 outboard problems

My L6 had just one carb doing the gas out the front thing .. My engine siezed after running for 15 minutes. The engine is at the machine shop now, costing me time and money. Wish I had cleaned my carb's.

 

[jdkzrt]

Re: Mercury ,1973, 150HP, in-line 6 outboard problems

Sorry to hear that B1234.<br />This would be a good time to add- <br />"unhook your fuel line and drain the gas from the carburator float bowls when you you put your boat away for the winter ---- in addition to using fuel stabilizer"<br />(this is an old snowmobilers tip)

 

[dandel]

Re: Mercury ,1973, 150HP, in-line 6 outboard problems

Can anyone describe to me the best way to "soak" the carbs? I was going to do a re-build just because I'm not familar with any other process. Is there a certain brand of de-carb that is better than another. Anyone that can walk me thru this would be appreciated!<br /><br />Thanks again in advance!

 

[dandel]

Re: Mercury ,1973, 150HP, in-line 6 outboard problems

I did forget to mention the last time I was out I tried to pump the bulb at WOT to see if I could get a reaction but it had no response. Also after the motor is warm and at idle it can be difficult to get back into gear without having the idle bar at full just before I put the throttle wide open. Not sure if this info helps or just confuses?

 

[dandel]

Re: Mercury ,1973, 150HP, in-line 6 outboard problems

Just ran the boat this last weekend without rebuilding carbs to test to see if there is a fuel restriction. Ran motor at WOT and waiting for motor to bog down. When it started to bog down I hit the choke and the motor proceeded to fall on its face for a second before re-bounding. This seems to me like not a fuel restriction issue. I spoke with a local Mercury mechanic and he agreed he thought this is more of a compression/timing issue. Any other ideas out there?