Johnson 1969, 20hp won't start

[Russell Huish]

Hello, can anybody help here. Rebuilt an 18hp Seahorse and that now runs fine! Was practically given a 20hp 1969 motor that ran {badly} and decided to rebuild that as well. Have replaced all electrics ie coils, condensers, points, ht leads , caps and new plugs. New impellor, plate etc. New head gasket. As thats why it previously ran badly as when I took head off the old gasket pracically fell apart and had a hole where water was getting through. Rebuilt carb with sierra parts kit. However engine will not start! There is a spark at both plugs, which also appear wet but the engine feels dead when pulling starter and only occasionally manages to backfire until my arm is dead from pulling starter and I then give up. Can't think what else to try? Oh it has also had a fuel pump from a running engine fitted but that made no differance. Help would be appreciated.

 

[1946Zephyr]

Re: Johnson 1969, 20hp won't start

Did you make sure your plug wires aren't crossed? The front coil feeds the top cylinder. The points for number one, are on the right side of the front coil.

 

[kbait]

Re: Johnson 1969, 20hp won't start

Squirt a bit of mixed gas into the carb and give it a try. If it runs for a second or 2, then you have a fuel delivery issue, or perhaps bad fuel.

 

[bktheking]

Re: Johnson 1969, 20hp won't start

First try reversing wires. Then check your compression, replacing a head gasket doesn't mean it has compression.

 

[KB1]

Re: Johnson 1969, 20hp won't start

" However engine will not start! There is a spark at both plugs, which also appear wet but the engine feels dead when pulling starter and only occasionally manages to backfire until my arm is dead from pulling starter and I then give up."

Flywheel torqued properly? Sounds like out of time/key shear to me w/wet plugs but plenty of fire/occasional backfire.

 

[Russell Huish]

Re: Johnson 1969, 20hp won't start

Thanks for your suggestions, will try reversing leads and/ or squirting gas in carb tomorrow. Am getting compression tester next week to find readings.

 

[Russell Huish]

Re: Johnson 1969, 20hp won't start

Well, had further look today and yes had ht leads to wrong plugs, doh! Swopped them around and thought it would now start - no such luck. Tried squirting some premixed fuel , still no joy. However think I know what problem is but can't explain it. I noticed that when pulling engine over that firstly it is hard to crank and secondly I think the engine is only turning one revolution or so. Took hand starter of the 18hp as that is a recon unit and it was still the same. I removed the flywheel and noticed one coil heel was rubbing on one edge so moved it in slightly and covered the scuff with some hammerite and replaced flywheel and pulled a few more times. Removed flywheel again and this time it looked fine so checked points gaps which were fine and replaced flywheel . Still no joy and engine still hard to turn over. Strange thing is turning flywheel just by hand in neutral seems to take no more effort than on the 18hp which starts first pull with the same pull start replaced! I am a bit stumped now! Thanks for your help so far.

 

[1946Zephyr]

Re: Johnson 1969, 20hp won't start

The coil faces have to match the machined edges on the mag plate perfectly. If they're not, then things won't work right. The front coil feeds number one cylinder and the points are on the right. same, facing the rear coil, facing the rear of the engine.

 

[bktheking]

Re: Johnson 1969, 20hp won't start

The coil faces have to match the machined edges on the mag plate perfectly. If they're not, then things won't work right. The front coil feeds number one cylinder and the points are on the right. same, facing the rear coil, facing the rear of the engine.

Yup, coil sounds like it's dragging on the flywheel, the coil edges have to line up perfectly with the bosses on the magneto plate.

 

[1946Zephyr]

Re: Johnson 1969, 20hp won't start

yehaaa! bktheking is my bro.

Still love that avitar. It'd be even cooler to see you at Burger King

 

[samo_ott]

Re: Johnson 1969, 20hp won't start

A dragging coil would make it a tad harder to pull but would not explain the non starting issue. did you use solid core wired? As mentioned, have you checked the compression yet? Did you use a spark tester to check spark or just hold the wire near the block? Was it s strong blue spark or a weaker yellow one? Fresh fuel? The engine should turn way more than 1 revolution when pull starting it.

 

[Russell Huish]

Re: Johnson 1969, 20hp won't start

Again thanks everyone for all your input. I have used solid copper cored ht leads. Didn't use spark tester but held plugs to head. Nice blue sparks from both. Regarding petrol the 18hp starts easy on same petrol from same can so don't think prob there. Getting compression tester from ebay this week so just hoping this won't show a huge discrepancy in cylinders! Will make sure that coils are really spot on with armature bosses again this coming weekend. Thanks , Russell.

 

[Russell Huish]

Re: Johnson 1969, 20hp won't start

Well, got compression tester today and it is showing what I was afraid of. Top cylinder 85 psi, bottom cylinder 55 psi. Should have checked before spending anything. However I suppose I have two options work on engine or use all the parts to keep my 18 hp Seahorse running for the rest of my days. Many thanks to you all again.

 

[lindy46]

Re: Johnson 1969, 20hp won't start

You could try soaking the cylinders in Seafoam and see if that helps. Set motor with plug holes pointing up and see what happens. Can't hurt.

 

[bktheking]

Re: Johnson 1969, 20hp won't start

55 is too low as you know, rings and a gasket may fix, you'd need to check it all out to make sure it doesn't need to be bored out.

 

[samo_ott]

Re: Johnson 1969, 20hp won't start

Hmmm. That's not good. And with a new head gasket, you know it's not that. Not much left to do but try to soak em as mentioned. If you can loosen up the rings it will help compression. It's to bad it wont run as you could do a decarb if so. It still seems odd it wont run though as the engine can run on one cylinder as can be seen whenever one has a bad coil.

 

[1946Zephyr]

Re: Johnson 1969, 20hp won't start

One thing I would do, is pull the bypass covers and see if the pistons show any scoring. If there is any damage, you should be able to get a good visual here. Scoring would likely be caused by overheating or lack of oil. If you see any scoring on the pistons, then I would pull the head and see if there is any cylinder damage. Typically, the cylinders won't get toasted, unless you get a broken ring or a needle bearing stuck in there. These motors are tougher than shoe leather and are quite co-operative with a good tune up and a little care. There should be an abundance of people out there with a good pair of pistons, should you have the need.
No worries about loosing your money on your investment. These motors are worth the money to fix up. If nothing else, there are things that will work on your 18, partwise. If you read my post here, you would be able to see that almost anything is possible.

http://forums.iboats.com/showthread.php?t=370228

I bet your motor looks better than mine. One thing I did, was set the motor on it's back and dumped about a cup of fuel/oil mix in the carb and cranked over real slow. That got the rings and bearings all soaked up good. This loosened things up like you wouldn't believe. Once I got the rings and bearings loosened up, I was up to 100 psi evenly on the cylinders.

 

[Russell Huish]

Re: Johnson 1969, 20hp won't start

Thanks all, I was thinking of giving up but will try the cup of petrol/oil mix in the carb tomorrow and will leave it to soak. In reply to the question that it should run on one cylinder, well I thought just the same as everything else seems ok. Did double check timing/carb sync which was slightly out have since adjusted, now spot on but no differance. A puzzler!

 

[1946Zephyr]

Re: Johnson 1969, 20hp won't start

Well, these are some of the greatest motors made. I can believe that is is shot. There is just no way. If you see diescoloration on the cylinder head area, that would show that it's been overheated, but if the paint there matches the rest of the pwerhead really good, then you're okay. When these motors set for some time, then the rings will get sticky. On my old relic, I sprayed a bunch of WD-40 in the spark plug holes and freed it up and found good compression immediately. Myself, I don't find any difference from the 18's to the 20's. They're both 22 cube motors and have the same ignition systems. The difference could be in the carbs only. One other thing you could check, is the reed valves. If these have problems, then your compression readings will be low. I would look at this, after you look in the bypass covers and make sure your pistons aren't scored up.

 

[kyron4]

Re: Johnson 1969, 20hp won't start

Try soaking the cylinders with Kroil. It's a extremely light pentrateing oil that claims to soak in to 1/millionth of an inch. Good stuff, will losseen anything and breaks up carbon and gum and varnish. 100 times better than wd-40. I belive a company called Kano makes it. Worth a try.