Home › Forum › Ask A Member › 1974 Evinrude 9.9 won’t idle at low RPMs, need help
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fleetwin.
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April 24, 2016 at 9:33 pm #35421
If the low speed needle adjustment does not change the running characteristics, I would suggest that the idle circuit is somewhat blocked, and hence the poor idle that does not change when the low speed needle is adjusted.
Agree to change the plugs also and see if that helpsApril 25, 2016 at 12:22 am #35435Thanks guys. This has been a huge help. I have a way better idea of what to do now.
April 25, 2016 at 7:15 am #35451After some "research" today with some of our 9.9/15HP experts here I found that the Champion UL81J is no longer made ,it’s now UL81C. NGK equivelent is B7HS. That’s what I’m now looking for ,but currently have BR7HS in mine. What plugs does your Bro in Laws ’75 have in there ? Just curious. Other forums I read in the past say go with NGK
So far the consensus by the experts say NGK B7HS."Some people want to know how a watch works, others just want to know what time it is"
Robbie RobertsonApril 25, 2016 at 7:31 am #35452You can take a UL81C and file the ground electrode off so it only extends half way across the center electrode and you have a UL81J The end of the filed-off electrode presents a sharp edge for the spark to jump to. Most of us know that a spark jumps to a sharp edge or point easier than to a flat one. That’s why lightning rods are pointed. The lightning prefers the pointed rod over the flat roof top.
April 25, 2016 at 1:33 pm #35459quote pugetsoundboater:After some “research” today with some of our 9.9/15HP experts here I found that the Champion UL81J is no longer made ,it’s now UL81C. NGK equivelent is B7HS. That’s what I’m now looking for ,but currently have BR7HS in mine. What plugs does your Bro in Laws ’75 have in there ? Just curious. Other forums I read in the past say go with NGK
So far the consensus by the experts say NGK B7HS.Not sure, will check this week. I had read there was an issue with the spark plug being out of production. I plan on picking up the NGK BR7HS this week and trying it out. Problem is that our motors are out at the in laws place so we only get out there once or twice a week and I didn’t even think to check what type of spark plugs they have (part of the learning curve I guess).
How do you find the NGK BR7HS works in yours? What year is it? Is it having a similar problem to mine?
April 25, 2016 at 2:21 pm #35462quote FrankR:The UL-81J is a booster gap plug. That is, the spark jumps a gap within the plug before getting to and jumping the gap at the tip. That forces the voltage up, which helps it to fire a fouled plug. I’m not familiar with the NKG’s, so not going to make a comment or choice there. Matter of fact, I don’t have up-to-date experience on those engines at all. Other guys here do. But an awful lot of these grey hairs were gotten while trying to make them run back in “the day”.
Okay….a couple of you seem to be stuck on NGK plugs. Quit drinking the Kool Aid. The engine was designed around a Champion plug. Read Frank’s post again and this time absorb it.
An auxilliary or booster gap as Frank calls it is the key word in this sentence. Does the NGK have this feature? Have you checked?
This aux gap FORCES the ignition system to produce more voltage to jump the AUX gap than is needed to jump the plug gap. This means you will have an extremely hot spark at the plug gap…..which is exactly what this engine needs as far as the ignition system goes.
Still believe your issue is fuel related and not ignition but at least this will put the ignition system to bed.
April 25, 2016 at 3:15 pm #35466I have two of these motors. A 1975 9.9Hp and a 1976 15Hp. I can tell you from experience that the UL81Cs will foul in a couple of hours of trolling and sometimes you won’t even get away from the dock with both cylinders running. As long as you don’t mind surging and bogging, surging and bogging, they work fine.
Go with the NGKs on that model of motor. Just so you know, with NGK the B6HS is a hotter plug then the B7HS. The reverse information was posted previously. Both will work fine for your motor, but the B6HS work better with the 15Hp models. I am guessing the larger carb throat in the 15Hp causes more fuel to carbon up and cause quicker fouling and therefore they prefer the hotter plug. The B7HS in a 15Hp will work but need to be changed every year. All that being said, use the NGK B6HS plug. BR6HS are fine but not needed on your motor.
OK. Really sounds like a carb problem. I would get a carb kit. Pull out that welch plug. Pull out that slow speed jet bearing (looks like a very small plastic funnel hidden well inside the slow speed jet). Soak that sucker in lacquer thinner or carb cleaner and then blow out the passages with compressed air. Do this a couple of times. Then insert a new slow speed bearing into that jet. Insert a new retainer at the outer end of that jet. The retainer will seal the needle. You do not want an air leak or you will get too much air as you have already mentioned as seeming to be the problem. One last point. Once you insert the new slow speed bearing do not use anymore carb cleaner on that area. The bearing is plastic and plastic parts do not like carb cleaner.
Now dial in the needle to lightly seated and back out 1.25 turns. Make sure the carb sync is good. As Fleetwin stated, there is an indented arrow on the throttle cam that pushes on the carbs roller. That arrow should be in the middle of the roller JUST as the carb starts to open. If it is not, it can be adjusted by the hex nuts on the starboard side of the throttle cam. YES, OMC did not make it easy to adjust. You need a thin 5/16" wrench to loosen those nuts without removing the flywheel. I filed one of mine down with a hand file, but it takes the patience of an incarcerated felon to file a wrench like that, but I had the time one day, and felt lucky that at least I was at the lake on a sunny day with a beer in my hand and not in a 6′ x 8" maximum security prison cell filing through a 1 inch hardened steel bar.
Give that a try, would be my best advice.
April 25, 2016 at 3:26 pm #35467I should add that they do sell thin wrenches at your local hardware store. It might be an easier way to go, but that being said, your carb sync is probably fine. Take a look.
April 25, 2016 at 3:49 pm #35469quote OptsyEagle:OK. Really sounds like a carb problem. I would get a carb kit. Pull out that welch plug. Pull out that slow speed jet bearing (looks like a very small plastic funnel hidden well inside the slow speed jet). Soak that sucker in lacquer thinner or carb cleaner and then blow out the passages with compressed air. Do this a couple of times. Then insert a new slow speed bearing into that jet. Insert a new retainer at the outer end of that jet. The retainer will seal the needle. You do not want an air leak or you will get too much air as you have already mentioned as seeming to be the problem. One last point. Once you insert the new slow speed bearing do not use anymore carb cleaner on that area. The bearing is plastic and plastic parts do not like carb cleaner.Thank you for that explanation. Cleaning a carb makes way more sense to me now that I am getting a better understanding of what I am looking for/how the parts work. Sometimes wading through these message boards is difficult because there is a ton of jargon and procedures used that seem pretty basic and mundane to you guys, but as a beginner it can get my head spinning.
Another thing about the spark plugs. So Pappy and FrankR talk about this booster gap. What my assumption was, was that it referred to the gap on the electrode. But the more I read, am I correct in understanding a booster gap is actually inside the spark plug and something different altogether? The reason why I ask this is because I was trying to cross reference spark plugs using:
http://www.sparkplug-crossreference.com … P_PN/UL81JReading up on the NGKs, it seems that product codes including an X will have the booster gap (and the NXG BR7HS or BR6HS don’t have that). Is that potentially why the hotter NGK works? So it seems that the cross referencing table might not be perfect matches.
April 25, 2016 at 3:57 pm #35470Yep ,getting to those 2 bolts to adjust the carb sync requires a thin wrench. I have ignition wrenches, very thin ,Craftsman brand. They work well for this and other tight spots,hood cover latch and lowest bolt on the water cover to name a couple spots right off the top of my head.
"Some people want to know how a watch works, others just want to know what time it is"
Robbie Robertson -
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