Help starting 1974 20hp Johnson

[ggant]

I recently purchased a used 20hp Johnson. When I went to look at the engine the motor ran fine and compression checked out okay. When I got the engine home I put it on a stand and ran it for a couple of minutes I then put it on the boat and now the engine will not start. I have cleaned the plugs and checked to see that both are firing. I have replaced the fuel with fresh fuel and still am having no luck with getting the motor to run. The motor hit a couple of times but now will not do anything. Any help on what to look at next would be greatly appreciated. I am wondering if something like trash in the carb could have gotten loose on the way home (had to lay it on it's side) I have also seen some post concerning the flywheel key. Where would this be located and what is it's function. Thanks for any help in advance.

 

[vmax95red6]

Re: Help starting 1974 20hp Johnson

flywheel key is what holds the flywheel to the crankshaft. located under the big nut on top of flywheel. you will need a flywheel puller to get the flywheel off. are you getting spark? if so i doubt there is anything wrong with the key.did you try spraying some fuel into the carb and see if it will kick over. did you check to see if carbs getting gas. try spraying some fuel 1st if starts rhen go to work on checking fuel line if ok clean carbs. hope this helps you. good luck

 

[Xcusme]

Re: Help starting 1974 20hp Johnson

You said that you put the motor on a stand and ran it for a few minutes....you did have it running in a tank or on muffs right??

 

[ggant]

Re: Help starting 1974 20hp Johnson

Yes I had the engine running in a tank. As far spraying fuel into the carb do you just squirt it in where the choke butterfly is? I will be heading to the library tomorrow to pick up the shop manual. Also when we ran the engine originally we were using his tank. He gave me a older tank with no fuel in it but it was clean. I am wondering though if something could have been in the line itself

 

[Solittle]

Re: Help starting 1974 20hp Johnson

Did you squeeze the primer bulb until firm?

 

[Paul Moir]

Re: Help starting 1974 20hp Johnson

To answer the question about spraying fuel down the carb's throat; yes, you spray it in where the choke plate is. There's no need to choke the engine while trying to start it this way (ie, close the choke plate), since you're enriching the fuel mix 'manually'.<br />I use a windex type spray bottle - actually a tougher carpet cleaner bottle - for this myself. Since it's dangerous to store premix that way, I empty it and run some water through it when I'm done with it.

 

[fireman57]

Re: Help starting 1974 20hp Johnson

after trying to start pull the plugs to see if they are wet. At least you will be sure that you are getting fuel. If they are not then I would suspect trash in your carb. It is not a big job to take it apart and clean it good. Pay particular attention to getting the jets cleaned out well. If your plugs are wet then you have to suspect spark. Even though you said you had spark it could be weak. Make sure that the spark is bright blue and will jump almost 1/2". If it does not then you have a bad powerpack. It could just be loose or bad connections from traveling or age. If the spark is yellow or gold it is too weak to do any good.

 

[ggant]

Re: Help starting 1974 20hp Johnson

Okay I had to take the engine to a local small engine repair guy to get it started. He replaced the points, checked the lower unit and rebuilt the carb. I then took the engine out to test it. It was still hard to start I thought but I got it running. I then took the boat out she ran fine at a fast idle in gear but when you tried to accelerate through the midrange the engine would die. If you went quickly through the midrange to w.o.t. the motor ran fine flat out. I then took the motor back to him and he went through the carb again. The next time out she started much better idled fine but when I took the boat out at about half throttle she would die. Upon restart the engine runs much rougher than before and still will not run past half throttle. I took it back to him again and after calling him today he says he has done all he knows to do and just can't seem to get her to run. My question is what area should I look at next for the problem and what should I ask him if he has checked? With what I paid for the motor and what I have paid him so far I am at the point where I don't want to invest any more money in the engine so I can't really take it to another mechanic but I hate to give up on the engine. I know the fuel is good and I have tried two different fuel lines with the same results. Thanks for any help in advance.

 

[G DANE]

Re: Help starting 1974 20hp Johnson

Instead of just replacing points, it would have been nice to know how the sparks were. Try to pull both plug booth from plugs, take one spark wire at a time, put a nail or screw in it and hold it 5/16" from ground ( engine block )with an insulated plier or cloth. Make someone pull starter cord. If both spark jump that gap to ground with strong blue spark, your problem is gas related, not spark related, assuming compression is good on both cylinders. I've had a problem like that, turned out to be a bad capacitor, only cost a few $, but man it was a pain untill I found out, it kept on skipping on one cylinder, when I throttled up. These had a tricky ignition system, but good and relyable, once in running order.

 

[G DANE]

Re: Help starting 1974 20hp Johnson

Another option could be he loft a piece of crud in the midrange jets in carb.

 

[Solittle]

Re: Help starting 1974 20hp Johnson

ggant - When you have a bit of time to get away from the normal maddness hit your local library & see if you can find a shop manual that is close to your motor and read up some. These older small motors are not that difficult to work on by anyone who has the slightest interest and minimum mechanical skills. Now the newer big boys are another story.

 

[ggant]

Re: Help starting 1974 20hp Johnson

Sorry it takes so long between post. I finally got to work on the engine again today. I pulled the carb apart again. The inside of the carb seemed clean but I went ahead and soaked all the parts in carb cleaner. I then reassembled using the manual. I checked the fuel pump screen and diaphram. I then proceeded to check the spark as some of you suggested. I get spark from both plug wires but neither will spark at 5/16 and the top cylinder plug wire seems to have better spark than the lower. I then decided to place the engine in a drum and see if it would run anyway. She started up fairly easily but has a definite miss at idle. The engine would always die when you tried to accelerate but this time she would open up. Upon idling back down though she still had the miss. The miss seems to go away<br />if you pump the bubble. One last thing when I tried to put the cowling on the motor dies and<br />will not start but if you remove the cowl she starts fairly easily.I guess my questions are:<br />1. Could the fuel pump be causing the miss? I am thinking of replacing it just to be on the safe side.<br />2. What would you guys do about the cowl problem and what can I do to remedy this?<br />3. Does the low spark issue need to be addressed since the engine seems to run okay except the low speed miss or could the low spark be causing this? I really appreciate all the help I have received from all of you so far.

 

[itstippy]

Re: Help starting 1974 20hp Johnson

Runs with the cover off but won't even start with the cover on?!?<br />You are bumping something when you put the cover on, creating a break or ground (check all wires including kill switch), or kinking a fuel line, or impeding the throtle linkage somehow. Look closely.

 

[fireman57]

Re: Help starting 1974 20hp Johnson

Does the engine run fine with the cowling off? If it does then you have an exhaust gasket that is bad. The exhaust coming up inside the cowling and does not have enough oxygen to burn the fuel properly. Usually this shows up at top end. When you say that you pump the bubble are you talking about the primer bulb on the fuel line? If that is the case you might look at your fuel pump. Could possibly have some junk in the screen or the diaphragm is bad. Both cheap and easy fixes. If your spark will not jump at least one half to 7/16 of an inch and is not bright blue then you need to change your powerpacks. A little more expensive (you can probably get them here at iboats cheaper) but a five minute repair.

 

[matthew hardman]

Re: Help starting 1974 20hp Johnson

you should try to replace the fuel pump diaphram first it might have a small hole in it that you cant see they are pretty cheap and usually easy to find at a local dealer

 

[ggant]

Re: Help starting 1974 20hp Johnson

The engine seems to run fairly well without the cowl on it except the occasional miss. When I spoke about pumping the bubble I meant when I squeeze the primer bulb the miss seems to go away. I think I will go ahead and replace the fuel pump next and go from there. If there is a exhaust leak where would I need to look for it?<br />Lastly is there a online source where I could purchase the fuel pump? Most of the local dealers here do not keep a lot of Johnson parts in stock. Thanks for any help.

 

[fireman57]

Re: Help starting 1974 20hp Johnson

Your local dealer should have the fuel pump rebuild kit in stock. This is a very common item and shouldn't cost much at all. I'm guessing under $20. The exhaust gasket, if I remember correctly, is under the powerhead to the lower unit. Joe Reeves, OBJ, or another pro can tell you for sure. I'm not entirely familiar with your engine. You should have a manual and it will tell you step by step how to change it if in fact it is bad. Change the fuel pump diaphragm and we'll go from there. Make sure that you get the little spring seated properly. This is an easy repair but still no reason to get in a hurry.

 

[Tinkerer]

Re: Help starting 1974 20hp Johnson

If it's running better when you press the primer bulb that indicates a fuel supply problem. It could be as simple and cheap as perished fuel lines. Pinholes and cracks can suck air instead of fuel, and it'll generally be worse at higher revs as the holes / cracks mightn't open under low revs. <br /><br />One way of testing is to remove the cowl and press the bulb until it's hard and then keep pressing it while watching to see if fuel leaks anywhere on the motor or forward of the bulb. <br /><br />If you can't get it hard so that it won't pump any more there's a leak somewhere even if you can't see it (or the needle isn't seating in the carb). Replace all the rubber lines from and to the pump and carb and see if that improves things. If not, look at the needle and seat and float level.<br /><br />Check that the cowl isn't pressing on a fuel line somewhere.<br /><br />I don't know your motor but I'm assuming it has a vacuum hose from the crankcase to the fuel pump to operate it, so make sure you replace that as well.<br /><br />I had a similar problem on a car years ago and it turned out to be a collapsed internal section of a fuel line that had a flap that was pulled out only at higher revs to let air in. Various experts failed to find it and it was only found when I replaced fuel hoses in desperation and cured the problem and then backtracked on the old hoses.