1989 120 Rough Idle

[quinnf]

I have a 1989 120 on a Mako 17 I just bought last weekend. Took it out for first time last weekend with new gas and oil. <br /><br />Engine runs rough at idle and low speed, but accelerates and runs fine at higher RPMs. LOTS of power! Starts readily with no coughing or sneezing, so I don't suspect a timing problem. Plugs are all the right kind and uniformly clean, but look wet. I'm beginning to think mebbe I need to look at the carbs. Wondering if low speed jet is funny or if float is set wrong.<br /><br />With this engine, are ignition or carb problems more likely to cause rough low-speed running? Any thoughts would be appreciated.

 

[Dhadley]

Re: 1989 120 Rough Idle

Youre most likely right on. Carb job. <br /><br />Describe "Plugs are all the right kind" please.<br /><br />Hows the compression?<br /><br />Good luck!

 

[quinnf]

Re: 1989 120 Rough Idle

Plugs the right kind = numbers on plugs match those the manual says it should have. Don't have either number before me right now. Two numbers were called out. One for sustained high speed, another for general use. Mine match the latter.<br /><br />Haven't checked compression yet. That didn't occur to me but now you mention it, that could explain the difference between high and low speed performance. Hmmm...<br /><br />I'll pull the carbs this weekend and clean them out and see if that helps. Meanwhile, I'll see if I can scare up a compression gauge. Not sure I really want to go there, though.<br /><br />Thanks!

 

[quinnf]

Re: 1989 120 Rough Idle

Update: Apparently it's a 1990 120, not 1989.<br /><br />Compression 125/125/125/125.<br /><br />Found one cylinder not firing because of corrosion in connector from power pack to primary terminal of one coil. Fixed that, and now spark tester shows about a 1/2" spark firing consistently on all cylinders. Still missing, so after checking timing (which cylinder is #1? Can't find that in manual), will pull carbs and clean them. Any problem using Gumout spray in this carb? I notice plastic bowl.<br /><br />When I pulled air silencer off intakes to carbs, lots of congealed green oil came out. What does that indicate?<br /><br />Thanks,

 

[93bronco]

Re: 1989 120 Rough Idle

from the back facing forward is starboard (right)<br />top is #1 bottom is #3<br />port (left)<br />top is #2 bottom is #4<br />-<br />now i believe that #2 carb feeds #1cyl, #1 carb feeds #2cyl<br />#3 carb feeds #4cyl, #4 carb feeds #3cyl.<br />so if #2 plug is wet you need to look at the carb in front of #1 cylinder. vise - versa<br />-<br />some of that oil can be caused by tilting the motor up. there should be a tube at the bottom that is used to suck it back up.<br />also could be caused by float setting or faulty needle & seat.<br />gum out is ok, dont soak them.<br />-<br />there is a torque sequence for tightening those screws.<br />dont use more than 25lbs of air to dry, try and keep the bowls together with main body.<br />it was recomended to me to use the cross flow needle & seat. but i dont have that #.<br />-<br />make sure that you put the air jets back in the rite place.<br />also check your recirculation check valves & fittings while you are at it.<br />youd be suprised of how overlooked that part of maint is.<br />just trying to help

 

[Dhadley]

Re: 1989 120 Rough Idle

The top carb feeds the top cylinder and so on. Its just that the top carb is on the port side feeding the top cylinder which is on the starboard side. The front half is an "X" design.<br /><br />Neat, huh?

 

[quinnf]

Re: 1989 120 Rough Idle

Took carbs off last night and found one of the carb base gaskets (o-ring) was folded, causing a probable air leak. That could explain why that cylinder wasn't firing very well at idle. Kits are on order. Once they're in, it's time to take her out for an Italian tune-up.