15hp 1989 dying after idle

[pierretheron]

I'm running a 15hp in after a hone and new set of rings. My mixture was at 25-1, but i suspected that of fouling my plugs after a prolonged time (5-10 mins) of idle or slow speed running. The motor would not splutter, it just lost revs as if it was starving for air or fuel, and then dies.

I have since changed the mixture to between 25-1 and 50-1 (roughly 3%) and the motor still tends to die. It starts immediately again on the first pull and a few revs clear things up again.

It idles as well as can be expected, although not as well as my 1978 6hp. The 6hp also suffers from this after a few minutes idle on a 50-1 mixture.

Both these motors have had the idle mixture knob turned less than 1/4 turns until it is smoothest at idle.

Any help greatly appreciated!

 

[iwombat]

Re: 15hp 1989 dying after idle

Your mixture isn't the issue, go back to 25-1 until you're through the break in period. Seating new rings calls for some extra lubrication.

Did you rebuild the carb while you had the powerhead off?
You might try choking a little while it's at idle. If that seems to help you need to clean out your carb.

If not, then maybe on to the next idea.

 

[tashasdaddy]

Re: 15hp 1989 dying after idle

this may help. single knob

http://www.iboats.com/bbboard/bbBoard.cgi?a=viewthread;fid=28;gtid=818798;gpid=818802

 

[OBJ]

Re: 15hp 1989 dying after idle

I kind of agree with iwombat......these carbs have an idle lift tube. Where the lift tube connects to the nozzle well, is a very small hole for the fuel to come up through. Just a tiny bit of crud will partially plug/plug off the hole.

Just a little unclear......in your post you posted "It starts immediately again on the first pull and a few revs clear things up again". Does that mean it idles OK then or am I reading it wrong?

 

[Snowdrggn]

Re: 15hp 1989 dying after idle

The 1989 has the carb with the plastic plate on the top of the carb. Check to make sure it is flat, remove it nd check it with a good straight edge. If it is not flat, replace it. I have seen these cause the symptom you are mentioning. Be very careful snugging the new one down as the distort easily.

Cheers,
Snow.

 

[pierretheron]

Re: 15hp 1989 dying after idle

Fella's, thanks for the help!

OBJ: it does idle very well, but then sometimes it will loose revs and die. If you are quick, and can get your hand back on the throttle, then you can "wiggle the throttle" and catch it before it dies, sometimes. It happened about 6 times in 3 hours, only after a 5min idle. But it does idle well, just tends to die randomly. I have setup the carbs in exactly the same way as described in that post.

iwombat: I re-built the carb with a new kit, and am very sure that no crud is in there. I did not check to see that the top plastic needle plate is completely flat, will have a look when back at the sea in a weeks time. All the carb seals and gaskets are brand new.

My point is, both my 6hp and now the 15hp suffer the same issues. Could it be octane? We only have 95 here in SA.

Thanks again for you help.

 

[Boatist]

Re: 15hp 1989 dying after idle

I would start like any tune up with a compression check. Until your rings are seated compression can vary and make it hard to adjust the low speed idle. Also make sure it is heating up to 140 degrees F and not over heating. Check your spark and set the plug to a gap of .030 inches.

I also would adjust the idle a little higher until the rings are seated. As I recall the rings on this motor use compression to help the rings seal and if their not seated yet and loose compression then the rings may not seal at all and it will loose power and stall.

95 octain if it rated the same way the us does it is more than enough. Motor runs good on 87 here in the US.