coughing idle, 1973 - 18hp evinrude

i just rebuilt a 1973, 18 hp evinrude that was given to me in buckets. <br />got it back together and it will run but it coughs bad and dies when trying to idle. it will run decent with rpm up maybe 1000 (i don't have tach). the smoke from this thing is so thick it'll choke ya. have checked the points and are set at .020. don't have a compression tester but compression seems good with the thumb over spark-plug hole test. gas mixture is about 4oz per gal (32 to 1 ?). i heard or read that the coughing is caused by lean fuel mixture but that smoke sure seems opposite. i have done the joe reeves idle screw routine found on other posts but the screw just don't seem to affect it .... either runs and coughs or dies like no fuel at all. <br /><br />help please.... i'm getting frustrated.

Re: coughing idle, 1973 - 18hp evinrude

Fuel mix for that engine is 50:1, but 32:1 isn't causing your problem.<br />After the engine is coughing away, shut it down and pull the two spark plugs. Compare and observe their firing ends. Smoke is a good indication of too rich or missfire.<br />What you hope to learn from the spark plugs is whether this is one cylinder being affected or both. That will limit the possibilities. If there is an imbalance, trying to set the mixture screws will drive you insane. If they're the same, we could probably be looking at the carburetor for fault.<br />Another extremely telling test is to pump the primer bulb and note the changes in the engine. If there is none, we can rule out a number of components.<br />When setting the idle mix control, you'll need to let the engine run for some time before it can react properly to the changes, especially if it's been set rich.<br /><br />You ran through the carb sync routine right? Sometimes called link & sync?

Re: coughing idle, 1973 - 18hp evinrude

Thanks again paul. <br />I havent' tried pumping the primer bulb and the motor is hard to keep running long enough to do any real tweeking. I did look at the plugs and they look fairly even on the carbon-black scale. But, I could very well not be allowing time for it to react to the adjustment. <br /><br />I did do the link & sync, multitple times as a matter of fact. (throttle roller between cam marks, close throttle, tighten linkage). <br /><br />What does pumping the bulb point to ? <br /><br />The idle mixture screw seems to have a little play in it (up-down, side-side) should it. I also saw in the drawing a needle valve bearing that goes on the end of the idle mix screw. Should I be able to look in there and see it. How important is it and the rubber o-ring on the idle mix screw ? (that o-ring was dry rotted and disintigrated while trying to do adjustment... i engineered one in hopes i could see where i stand with this thing before spending more money)

Re: coughing idle, 1973 - 18hp evinrude

Sounds like you've got even cylinders then. If one were sopping wet and the other dry, it can indicate a crankcase leak, a blown fuel pump diaphram, or sometimes an ignition problem.<br />Since the cylinders are affected evenly, we can safely assume that the cause is a part common to both cylinders. Carburetor, exhaust (very unlikely), fuel supply, that sort of thing.<br /><br />The o-ring on the idle mix screw is very important as it keeps the idle fuel mixture from being contaminated with air. That area of the carb is under suction. The original o-ring is not a rubber one, since it's function is more like packing in a spigot. As a matter of fact, I've used teflon packing from the plumbing department as a 'temporary' fix. As long as when you tighten up on the packing nut the mix control is getting hard to turn, I think you're probably all-right.<br /><br />I think the "bearing" you're talking about is called a "bushing". It's just a staked threaded insert pressed into the carb body. It rarely comes out, but if your packing isn't tight it may spin and prevent movement of the needle. If you're threading the needle into something, it's present. If you can turn the needle all the way until it seats, it's functioning properly. There is normally very little movement in the needle valve, but I think that would be caused by the rubber packing. The end must be a nice sharp point.<br /><br />Pumping the primer bulb does a few things. First it effectively seals any air leaks after the bulb. So any leaks in hoses, fuel fittings, etc, won't suck air. Second it overpowers the fuel pump, so if it's weak for some reason that gets masked. If there's a tear in the fuel pump's diaphram, pumping the primer will push fuel into the crankcase making the engine run much worse or even stall. If the carburetor is flooding, it will make it a lot worse and stall the engine.<br /><br />If it does nothing, then you can be reasonably sure the fuel pump and carb float, needle & seat assy are not leaking. If you suspect a rich condition (which sure sounds like what you have) then there's a few common culprits. Other than the float/needle/seat, a very common source of troubles is the nozzle gasket. That's part #40 on the epc.brp.com website. I've made temporary ones out of thick cork gasket material but they will eventually shed particles.<br /><br />EDIT: A couple other ideas, seeing this is a basket case. You don't have the air silencer down hard over the carb's mouth like a filter do you? You can even remove it for testing, it's really not supposed to affect the mix at all. Is the choke all hooked up and working properly? Opening fully?

Re: coughing idle, 1973 - 18hp evinrude

The needle valve bearing(#35 in attached) usually doesn't come out. In fact, it'd be a jeweler's nightmare to get it out. If in fact, it does come out with the needle valve, then you can replace it. Otherwise don't bother.<br />

Re: coughing idle, 1973 - 18hp evinrude

basket case is right. it was looking good at first, and i was excited. now it's starting to get frustrating because it seems i'm so close but not making much headway. <br /><br />i don't have the air slencer on the carb. figured it would likely just get in the way of adjusting etc. <br /><br />choke is hooked up and seems to be at level horizontal when released. <br /><br />even though this thing seems to be running so rich, it still wants to be choked to start after it dies. <br /><br />the idle mixture screw gasket that i made is from a piece of fuel line that just fit in place of the 0-ring. but, it don't seem as tight as the original o-ring. <br /><br />from what you've said here, it sounds like you're on the edge of recommending a carb kit with new float seat, float valve, gastkets etc. <br />from the parts list it looks like the o-ring don't come in the kit. <br /><br />i'll check the other things you've mentioned too. i put a nos fuel pump on so the diaphram should be ok but i guess it could be doa. <br /><br />thanks....

Re: coughing idle, 1973 - 18hp evinrude

i swapped a fuel pump off a good/running motor. no change. <br />i squeezed primer buld while running. bulb was firm and didn't affect the motor. <br />i checked the plugs and both look evenly used.<br /><br />the engine runs fairly smooth at about 1/4 throttle (i'm guessing about 1000 - 1500 rpm) <br /><br />i'm pretty much stumped at this point. <br /><br />what if, when the original needle-valve o-ring crumbled some of the particles got into the idle jets ? (i think these are 3 tiny holes in the carb throat) <br /><br />should i invest in a carb kit and needle-valve o-ring ? <br />should this kit include the "carb plugs" so i can take out and check/clean the idle jets? <br /><br /><br />i also looked over link and sync steps again. <br />some motors have throttle cam adustment screws that it talks about adjusting (9 - 15 hp i think). i see these screws on my motor but don't suspect they were adjusted (i haven't) and i'm afraid if i adjust them will really get it out-a-whack. is anyone familiar with this ?

Re: coughing idle, 1973 - 18hp evinrude

I wouldn't reassemble a basket case like that without a new carb kit. For sure the idle jets under the plug are suspect. The kit will come with a new plug.

Re: coughing idle, 1973 - 18hp evinrude

Well folks, <br />I put a carb kit in, at least part of it. <br />Float needle, bowl gasket, forced air through the jets, and the needle valve o-ring. <br />Adjusted points, did the link and sync. <br />Fired right up and was able to adjust the idle mixture where it runs pretty good. No coughing or sneezing, idles well, runs faster rpm pretty well. <br />So far, I'm thrilled. I was getting frustrated. <br />I believe my bigest problem was the needle valve o-ring since the rest of the carb looked like new. I think it was sucking air around the needle valve causing the mixture to be too lean. <br />Even though it was smoking really bad like it was rich. I guess I'll never know which fixed it. <br />The real story waits till the weekend when I put in the lake and see how it acts. <br />It may fly to pieces. <br /><br />Thanks to all who have passed information my way on this project.

Re: coughing idle, 1973 - 18hp evinrude

weekend lake test results<br /><br />hitting on one cylinder. <br />new points and condenser sets.<br />hitting on one cylinder. <br />bad spark plug. (brand new) <br />replaced spark plugs. <br /><br />now hits on both cylinders. <br />runs pretty good. <br /><br />all the carb and condenser problems i thought i had may have been bad / doa spark plugs. because i took it to the lake once and it ran good for a few minutes. then started acting up coughing, no idle, etc. <br /><br />valueable lesson;; track your diagnostics and start with the cheapest & easiest first. <br />example: top cylinder not sparking.... swap spark plugs,, keep track of that in case you swap coil or condenser for a test you'll know if you have a bad plug.

Re: coughing idle, 1973 - 18hp evinrude

"new float seat, float valve"........Its what I'm doing on a 78 2hp Rude now. You should have done the float needle and seat FIRST.....glad you have it running. Floats and needles and seats will drive ya nuts (unless you replace them FIRST (think I'm trying to get a point across?)...Good Luck. <br />PS. Every time you get frustrated with a motor, a good idea is to stick a mirror in front of it, then look for the problem...works for me finally after all these years of throwing wrenches instead!