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Rough runner

RoJo smith

RoJo smith

New member
Just bought Used 18' pontoon with Honda BF50AX, 4 stroke. The serial # on the engine is BAZE-2001630.
The serial# on the transum mount is BAZL-3001909 and the Tag says Made in Japan. From that I that I think its a 1999 Model. I have a service manual.
So far I have not had it on the water, I have drained the old fuel and filled with stableized fuel, Replaced all fuel filters, changed oil and oil filter, Changed gear oil, Replaced spark plugs and gaped them to .026 in. I have, to the best of my ability, cleaned the carburator, replaceing all gaskets and o-rings (except for the pilot screw, more on that later). Have done a compression check on a cold engine and got 150psi on all cylinders.
Engine would not start without ether even then would not stay running, before carb cleaning.
Enging now starts easily but runs rough and shakes. I did not mess with pilot screw because it has limiter caps.

1. The manual says compression should be 212 +-14 @ 500rpm. I did my test with all spark plugs out just cranking the engine over. Did I do it wrong? Are my values of 150psi invalid?
2. I have not tried to syinc the carbs yet (Carb tool on the way) should I try to adjust idle before seting pilot scerws?
3. Should I just leave the pilot screw alone? Can I make adjustments to the pilot screw with the limiter cap on? Can I replace the pilot screw with one that can be adjusted?
4. When going in to adjust the valves, should I expect to replace the gasket?
 
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Hi,

Sounds like you're about to learn a WHOLE BUNCH about this outboard. Should be fun!

You "speak" about it as if it has only one carburetor. All the 50hp Hondas I know of have three cylinders and three carbs. But, I don't know if the Japanese stuff is different. AND...I have never worked on a 50 Honda so FAR from knowledgeable about them.

When you did the compression test, did you hold the throttle WIDE OPEN? If not, you might want to do the test again because that would cause your pressures to be low. Although,150 isn't horrible for a well used engine  IF the pressures are even across all three. And, adjusting the valves can often bring pressures up too.
So, take heart!

You could also do a "wet" compression test to see if it's the rings that are leaking. But I would say that's premature now unless you're really curious about it.

A cylinder leak tester could reveal some info but,.since outboard cooling systems are open, not as useful as on a.car.

As far as the carbs go, I know the later model Keihin carbs pretty well. They have a brass low speed emulsion tube that has a VERY CRITICAL little oring that HAS to be in great condition to seal properly. See item 19 in the link.



That tube is also VERY HARD to get clean..it has a fuel orifice inside the lower end that sits in the fuel and meters flow. It is VERY difficult to see and clean. Also, the tubes will develop vertical cracks ESPECIALLY if the retainer plug is overtightened
Best to inspect and clean these with a GOOD magnifying glass.
When I did several of these carb jobs a month, I would just replace the tubes and orings because they took up so much production time.

Hope you get her sorted and welcome to forum.
 
Forgot....
If you're careful removing the limiter caps on the mixture screws and not snap the head off, they will have screwdriver slots that are still usable. Even if you snap them off, you can still use them by cutting a slot in the flat.
BUT...without a slot to turn, you will need to rotate the screw using very sharp pointed picks to get a grip on them.

Even with a slot, they are a TRUE PAIN to remove because the oring acts as a "lock" preventing them from backing out. That forces you to pry them out to overcome the force of the oring. However, it's hard to tell when you've turned them enough for the threads to release. You have to turn, turn, turn, until you THINK the threads are disengaged AND THEN TURN THEM ABOUT 10 MORE TURNS to be sure. The ABSOLUTE definition of Pain In The Azz!

But to get a dirty carb truly clean you have to take them out.

Also, syncing the carbs with limiter caps on just won't work.

In this case though, it sounds like you might have a misfiring or dead cylinder so syncing typicaly won't help until you figure that out first.

I would do a cylinder contribution test before going any further to identify why it is rough.

Good luck.
 
Thanks jgmo,
I pulled it out of the barn today, It started right up with just a litte choke. Again, it ran rough, with an occasional cough.
I played around with choke and throttle, without changeing any adjustments, idle improves with higher RPM. Unfortunately the Tach dosn't work (I need to remedy that) I do know it should idle around 950 RPM. I did another compression test today with it at operating temp, all cylinders were 170 +- 5. I got your response after doing the test, so again I did it incorrectly (without throttle full open) I'll do it again, correctly next weekend. Still, I think 170 ain't bad.
I did not use a magnifying glass when cleaning and inspecting the carbs. Next time.
The Jet set #19 in your parts break out is the one with microscopic hole, if I were to just replace them would I also need to replace the main jet #20? Are they a set that need to be replaced at the same time? Thank for the advice.
 
Yes, 170 +/-5 ain't bad at all.
Says "healthy" to me.

And no, I wouldn't replace that emulsion tube (item 20) OR the main jet (item 59) as they just don't seem to erode in my experience.

Good luck.
 
It's very important to be sure to take special care with the jet set oring and don't over stretch it when putting it on the tube. Use a light lube like Vaseline on the oring before installing so that it doesn't catch, roll or bunch up when you push the tube into it's hole.

The same goes for the orings for the mixture screws. They all need to seal well or it causes trouble.

I still think you should do a power contribution test or, at least, compare spark for all cylinders before pulling the carbs back off. It might save you some work.

Good luck.
 
I'm not familiar with "power contribution test"
I did pull spark plug wires off, one at a time, with it running. Responce was simular on all cylinders. No drumatic change on any cylinder.
I will still do a proper compression test next weekend. Lubing O-rings is something I will do from now on.
 
Well, you are now because what you did, pulling the plug wires one at a time while running and noting any change in cadence  IS a power contribution test.

it can be useful for diagnosis at idle and higher rpm's

But you knew that already! :)




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