johnson seahorse ,wont go,backfires

piperdog · Apr 18, 2008

hello,just picked up an old 18 seahorse and it wont start,at the front it has a lean dial and ive put 50/1 mix in .after several pulls it backfires and the odd occasion seems its going to go but doesnt ,got spark and fuel,the previous owner did drop it ,so can the timing be out and can i check it ,any help will be great...thanks

CATransplant · Apr 18, 2008

Re: johnson seahorse ,wont go,backfires

What is the model number on your 18 hp? You can find it somewhere on the transom mount area. Without that information, it's hard to advise you. Lots of those engines require 24:1 fuel

il mix. Depends on their age.

Aside from that, see the "Waking a sleeping outboard" stickie post. If you follow that, you should get some good info about your engine and why it's not starting for you, along with many good tips. Click the link below to get to it:

http://forums.iboats.com/showthread.php?t=158086

If not, come back to this thread with the model number of your outboard and a specific list of symptoms along with what you have done to try to fix them.

Lots of helpful folks here, but they need information to work with.

Gary H NC · Apr 18, 2008

Re: johnson seahorse ,wont go,backfires

If it was dropped it may be the flywheel magnets have come loose or the woodruff key is broken.
Just a guess being we don't know much at all about the symptoms or motor..

F_R · Apr 18, 2008

Re: johnson seahorse ,wont go,backfires

piperdog said:
hello,just picked up an old 18 seahorse and it wont start,at the front it has a lean dial and ive put 50/1 mix in .after several pulls it backfires and the odd occasion seems its going to go but doesnt ,got spark and fuel,the previous owner did drop it ,so can the timing be out and can i check it ,any help will be great...thanks

Yes, do need the model # to give intelligent answers, but let me ask how you are checking the spark? Laying the plugs on the block and looking for spark jumping the gap is not checking for spark. It needs to jump a 1/4" gap in free air.

Dropping it won't get it out of time. In fact you can't get it out of time. But it can have a sheared flywheel key if somebody has been working on it without knowing what they are doing. In a way, that's sort of like getting it out of time.

If it is from the 1950-1960 era, it very well could have bad coils. They all do unless they have already been replaced.

piperdog · Apr 19, 2008

Re: johnson seahorse ,wont go,backfires

thanks for the replies,the plate says :FD-18E :C143612
i was told the coils had been changed and new spark plugs ,checked the gap ,all ok (didnt think a wrong gap could cause backfire )

piperdog · Apr 19, 2008

Re: johnson seahorse ,wont go,backfires

forgot ,ive cleaned the carb and got fuel all the way thru the system ,sparks are sparking ,any ideas about the lean control on starting ?,sometimes it backfires once ,rarely it seems to start and rev (for about a second but dies ),thats all i can say ,hope its of some use

patrickray · Apr 19, 2008

Re: johnson seahorse ,wont go,backfires

piperdog said:
forgot ,ive cleaned the carb and got fuel all the way thru the system ,sparks are sparking ,any ideas about the lean control on starting ?,sometimes it backfires once ,rarely it seems to start and rev (for about a second but dies ),thats all i can say ,hope its of some use

Hum... Theres that word again. I think I would be double checking the carb.

piperdog · Apr 19, 2008

Re: johnson seahorse ,wont go,backfires

thanks for the reply ,how does the carb create backfire ,i was under the impression it was due to timming

samo_ott · Apr 19, 2008

Re: johnson seahorse ,wont go,backfires

That's a 1964 model and can just use 50:1 mix.

Have you tried spraying a 50:1 fuel premix directly in the carb? Then try and see if it will run a few secs on the fuel you have put in it. If so it is a fuel problem. A backfire can be mistaken for a fuel sneeze.

Adjust the carb as listed in the awakening an outboard and then try the premix and see what happens.

BoatBuoy · Apr 19, 2008

Re: johnson seahorse ,wont go,backfires

Carb can't cause backfire. It's backfiring because it's firing when the exhaust ports are open. I'll as the most obvious question that hasn't been asked yet. Could the sparkplug wires be reversed? That will always cause the symptoms you describe.

freddyray21 · Apr 19, 2008

Re: johnson seahorse ,wont go,backfires

was wondering if anyone was going to suggest that. If the wires are original the top plug wire will have a metal band around it that says top. Reverse the wire and see. It will either run or back fire worse.

piperdog · Apr 19, 2008

Re: johnson seahorse ,wont go,backfires

ive checked the fuel and i can say thats okay (fuel on spark plugs ),tested the leads are on the correct plugs (by turning the flywheel ,getting a spark and checking what piston was at tdc )hve noticed that the key is broken ,but it doesnt seem to move off the mark ,all the points and other electrics seem new ,any idea of the age of this machine and also the spark plug gap ,,,do you think if i tried to fire it up by using a drill and socket on the bolt that holds the flywheel is a bad idea

freddyray21 · Apr 19, 2008

Re: johnson seahorse ,wont go,backfires

put new plugs in if you haven't already. If it has fire, fuel and compression it should run. If the plugs are wet they are not firing if you have compression.

piperdog · Apr 20, 2008

Re: johnson seahorse ,wont go,backfires

thanks again for the replies ,but i cant find any place that lists parts for this model,anyone help,thanks

BoatBuoy · Apr 20, 2008

Re: johnson seahorse ,wont go,backfires

What parts are you trying to find?

Chinewalker · Apr 20, 2008

Re: johnson seahorse ,wont go,backfires

FYI, on all Johnrude twins with the traditional points/coils/condensers magneto, the FRONT coil fires the TOP cylinder...
- Scott

tmcalavy · Apr 20, 2008

Re: johnson seahorse ,wont go,backfires

Did you say you noticed that the flywheel key is broken? Replace it and torque the flywheel down to the correct specs. Make sure the high and low speed needles on the front of the carb are set to the correct baseline, 3/4 out from lightly seated for the high speed (bottom) and 1 and 1/4 turns out from lightly seated for the low-speed. For parts, try any of the places listed on the Links page at www.aomci.org
Those are great motors, stick with it logically and you will solve its problem and have a good running, reliable workhorse.

piperdog · Apr 20, 2008

Re: johnson seahorse ,wont go,backfires

im after a plastic choke pull,an ignition cam and the flywheel key

BoatBuoy · Apr 20, 2008

Re: johnson seahorse ,wont go,backfires

These places deal in vintage parts. Since you don't know the part numbers, go to their website, get their phone number, and call. I'm sure one of them has the parts you need.

vintageoutboard.com
tcoutboard.com
americanoutboard.com
sea-way.com
lainge outboard

piperdog · Apr 20, 2008

Re: johnson seahorse ,wont go,backfires

thanks ,but being in the u.k.,it could be a bit of a hassle

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