1956 QD-17 Low idle miss

[OMCfan]

Greetings mates!
I am trying to diagnose a low idle miss on my QD-17. She runs strong at full throttle as I had it out yesterday and it never missed a beat. What I have noticed is an occasional low idle miss/hesitation at trolling speed. At times it will kind of chug when throttling up to fast. This is the first time I have had it out since last September. But wanted to know if this is a coil going bad, plug wire or time for a carb kit. I know the coils are not original but the plug wires do loo original.

Thanks fellows!!

 

[Crosbyman]

tried opening up the low speed needle a bit ? maybe you need to take out the carb and just clean it up.

 

[HighTrim]

I was going to say, what is the low speed needle set at? Have you tried richening it a 1/4 turn or so?

 

[OMCfan]

The low speed idle is at 4, in the middle, but I know that really does not mean much, I can try backing it off (richening) the mix and see how that works. I am not sure how far out they recommend backing off the low speed needle from all the way in. Other than this littlee hiccup she runs/starts great!

 

[HighTrim]

The setting on the plate is irrelevant, as you know. The important thing is turns out from seated. The static setting is 1.5 turns out from seated, then fine tune from there on the water. Just try turning it CCW 1/4 turn at a time and see if that helps.

 

[OMCfan]

Thanks!! I will give that a try and let you know what happens. Won't be till Thursday though.

 

[oldboat1]

The 10 will not troll quite as slowly as the smaller motors, so expectations need to be in line with what the motor can do. On the other hand, the 10 will get you to the next fishing spot pretty quickly. If up for another one in the line (and some room on the transom), consider getting a matching 3 for trolling -- amazing little motor.

You presumably adjusted the idle mix before setting the h.s. mix -- now may need to readjust the low speed side one way or the other. When you get the best setting, snug up the gland nuts enough to keep the needles in place when running. Offhand, stumbling or chugging at throttle-up sounds to me like the idle mix might be too rich, but small adjustments either way, as described.

That occasional hiccup when trolling could be a separate issue. Whatever mix you end up with, though, you might need to tweak the mix when doing prolonged trolling, then return to the original setting.

Look forward to hearing how it turns out.

 

[OMCfan]

Okay fellows, sorry for the long delay! Had the boat out fishing today and tried turning the low idle adjust 1/4 turn both to CW and CCW and still had a miss. I left my screw driver at home and could not push the carb plat back far enough to adjust it any further than a 1/4 turn either way. I am going to drop it in my test tank tomorrow and play with it more and I will let you know what I discover.

 

[OMCfan]

OK here is my amature test repot on my low idle miss.

Background:

This QD-17 I purchased and it had already been converted to run on modern single line tanks. The fuel pump that was installed is a Briggs and Stratton the fuel lines are larger in diameter than the original likely because of the larger nipple on the fuel pump. The pulse to run the fuel pump comes out of the top cover plate by the engine head.

The fuel tank and hose are new (purchased by me. The tank is plastic so no rust worries on that end and the fuel is fresh. I do not run any ethanol in my motors so this is ethanol free fuel which means you buy 91% octane mix.

Tank Test:

I started the motor and it ran better turning the low idle clock wise about a quarter of a turn. It took about 30 minutes of running before the miss went away. When trying to adjust another 1/4 turn CW the problem got worse so I backed it off and it ran better. The longer it ran the misses became fewer until at last they went away. Throttle remained at the start setting and the motor was in gear the whole time.

Observations:

I noticed slight changes in RPM while running slow. The motor would slow down on its own then return to its "baseline" then slow down slightly etc.... Another thing I did notice is that I would see occasional air bubbles coming up the tank fuel line going to the fuel pump. Obviously they put in clear fuel lines when they did the conversion. This may account for the slight RPM changes and all the clamps look tight so I do not know if this is normal or if there is a leak. I have no obvious fuel leaks in the engine hoses.

Additional check:

I am not sure as to what constitutes good water pump output, but I wanted to check it and at low speed a quart jar was filled up in 15 seconds.


Any thoughts and or suggestions are welcome!!!

Thanks guys.

 

[oldboat1]

fuel pump conversion adds another layer or two of potential issues -- pulse source comes to mind (typically a bypass cover). I'm not sure what you mean by a top cover plate, but might be fine. Octane and ethanol are not on the troubleshooting radar, imo. Sounds like the water pump is doing it's job, although I don't have a metric to offer up. Check to insure the powerhead is warming up, but not too hot to touch up at the top.

Sounds like you are getting the mix right, although not sure what your idle speed is (throttle). Can't be too literal with the twist grip setting, although the start position is typically fast idle. I think the '56 has the plastic throttle stop screw, like the '57s -- might need to adjust that.

 

[OMCfan]

Hello Oldboat1,

You are correct, pulse source is the by-pass cover plate on the top cylinder. I tightened some of the fuel line hose clamps. No fuel leaks but seeing air in the line made me wonder. I did not put my hand on the top of the power head. It is warming up and I did have my hand on the area where the motor attaches on to the exhaust leg, warm enough to see the water evaporate off but not uncomfortably hot.. The water coming out was warm but not hot. My twist grip is the same as teh 1955 QD-16. In '57 they went to the white space-age grip that no one cares for.

One thing I did notice on the lake yesterday. I had to shut her down due to the misses but mostly to get rid of the shrubbery that had accumulated on the prop. I started it up and for awhile it was hesitating and would not throttle up. I had her wide open and had no power. I checked again and had just a few weeds and then started it up and it throttled up and ran just fine at full throttle.

 

[oldboat1]

Yeah, time of year I guess -- shrubbery. I had the same problem yesterday. (Not sure what to make of the missing, though, or problems throttling up. The B&S pumps are cheap, so maybe worth trying another one -- maybe with fresh lines. Maybe one of the Mikuni pumps.)

Interesting on the space-age grip. Haven't had one of the Johnsons for four or five years, but remember the grip now that your mention it. My Evinrudes have that chopped off one that is kind of clunky by comparison.

 

[OMCfan]

I may try changing out the fuel pump to a Mikuni and also the lines yet this year. Do you know what size of Mikuni would work on a 10hp? Yeah Johnson had that horrible white grip in 57 and 58 and then changed again in 59. Feels awefull on the hand.

 

[HighTrim]

I like the white grip myself! '57 and '58s are my favourite years for Johnson.

The "miss" you hear is a lean sneeze. Too much air, not enough fuel. Air is getting into the line somewhere. Try to cut back the ends, perhaps clamps on too tight. Or change fuel line all together.

 

[oldboat1]

might try a search here for prior threads on Mikuni pumps (don't know how they are sized).

 

[OMCfan]

High Trim,

Thanks, I think I am going to replace all of the fuel lines. Then I can at say that's crossed off the list. I think I found the right Mikumi pump so I may replace the pump also. When adjusting the slow speed needle it ran better when turned to lean 1/4 from center...so in the 9:00 position.

I would definitely go on the record to say the 57's and 58's are beautiful looking motors. Almost bought a 1958 18hp a month ago.

 

[HighTrim]

The BS pumps work fine as well, used them many times. I would not start changing the pump just yet, you may just be throwing parts at it. I think the pump is functioning as it should, you just have a lean condition somewhere.

 

[oldboat1]

I've taken to using plastic ties on fuel lines, particularly the smaller motors I usually mess with. The BRP ones are molded, as I understand it, but I find the regular hardware store variety work well. I use a needle nosed pliers and a bladed screwdriver to reach in and cinch them down tight.

Maybe a good approach would be to add ties to your existing clamps and see if you get any change.

 

[OMCfan]

I replaced all of the fuel lines yesterday and should be able to have time to drop it in the tank and see how it runs tomorrow. The old lines were that cheap clear plastic stuff so I replaced them all with actual fuel rated hose and new clamps.

 

[HighTrim]

Here is a '56 I had restored