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BF50a SHAKES AT IDLE + REVERSE BINDING

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Noah4200

Contributing Member
Hey guys…just been working on my motor (1996 BF50a) and cleaned my carbs and all seems to be running good. There are 2 issues i’d like to solve. Firstly my engine seems to shake a lot when idling. I’ve synced the carbs perfectly before and it didn’t make it stop. I feel like when i first got the boat it didn’t shake that badly. Would it be related to the lower shift rod adjustment? It may have started after doing my water pump and dropping the lower. At first i had the adjustment off and it was clicking in neutral but it’s quiet now. But not sure if that shift cog could make the motor shake or if it’s carburetors. I did a really through job this time so they should be clean as can be. My fuel screws are 2 turns out. I have a video of it idling i will try to link.
Secondly, it’s hard to pull the lever into reverse and just found that the shift rod is binding against the engine where the cable connects at the front of motor. Is my shift cable hooked up on the wrong side? It looks like i could pull the connection off and insert it on the outside of mechanism. Maybe a previous mechanic put it on backwards or something. I can’t even find a picture on what it’s supposed to look like. Thanks for reading :)
 

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Ok looks like it is on backwards from the manual. So just need to figure out the shaking motor. It’s not struggling to run IMO. I want to mention in addition to doing the water pump i also put an OEM flywheel brand new on the boat. The magnets were delaminating and making a tapping noise. I did timing correctly and pretty sure everything is seated well. Was just thinking what could contribute to shaking
 
Noah,
The picture makes it obvious something is not right with that cable head hitting like that.
By all means I think you should try flipping it around and seeing if it works.

As far as the shaking goes, I looked up the BF50A carb idle mixture adjustment and it states 1 turn out. You may have it too rich at idle being 2 turns out.

However, that stuff isn't set in stone IMO. It's really just a place to start...a suggestion if you will. You can always back them out farther if 1 is too lean. But I would definitely give it a try.

What's your idle rpm? Some engines "like" a little more idle rpm than others. The spec is 950 plus or minus but even a shade more than 1000 wouldn't be unheard of to smooth things out.

Aside from the carbs I think of valve lash settings and spark plug gap as important things to consider. Fresh plugs often "cure" a lot of symptoms.

If you have the ability to do a compression check....especially AFTER the valve lash is properly set....that would give you some insight and a baseline of knowledge about the "health of the engine.
 
jgmo said:
Noah,
The picture makes it obvious something is not right with that cable head hitting like that.
By all means I think you should try flipping it around and seeing if it works.

As far as the shaking goes, I looked up the BF50A carb idle mixture adjustment and it states 1 turn out. You may have it too rich at idle being 2 turns out.

However, that stuff isn't set in stone IMO. It's really just a place to start...a suggestion if you will. You can always back them out farther if 1 is too lean. But I would definitely give it a try.

What's your idle rpm? Some engines "like" a little more idle rpm than others. The spec is 950 plus or minus but even a shade more than 1000 wouldn't be unheard of to smooth things out.

Aside from the carbs I think of valve lash settings and spark plug gap as important things to consider. Fresh plugs often "cure" a lot of symptoms.

If you have the ability to do a compression check....especially AFTER the valve lash is properly set....that would give you some insight and a baseline of knowledge about the "health of the engine.
Click to expand...
jgmo said:
Noah,
The picture makes it obvious something is not right with that cable head hitting like that.
By all means I think you should try flipping it around and seeing if it works.

As far as the shaking goes, I looked up the BF50A carb idle mixture adjustment and it states 1 turn out. You may have it too rich at idle being 2 turns out.

However, that stuff isn't set in stone IMO. It's really just a place to start...a suggestion if you will. You can always back them out farther if 1 is too lean. But I would definitely give it a try.

What's your idle rpm? Some engines "like" a little more idle rpm than others. The spec is 950 plus or minus but even a shade more than 1000 wouldn't be unheard of to smooth things out.

Aside from the carbs I think of valve lash settings and spark plug gap as important things to consider. Fresh plugs often "cure" a lot of symptoms.

If you have the ability to do a compression check....especially AFTER the valve lash is properly set....that would give you some insight and a baseline of knowledge about the "health of the engine.
Click to expand...
Thanks for the response…the manual shows that cable elbow the other direction with the pin on the inside so i will switch that.
I attached the video of the shaking. Maybe i’m just being sensitive and they all shake like this it doesn’t seem to be as bad as others i’ve seen. I saw 2 different specs on the fuel screws 1 turn out and 2 1/2 depending on year and carb numbers. I tried 1 but was getting a sputter when trolling every 30 seconds or so and went to 2 turns and it stopped. I did the valves when i did the flywheel/belt and the compression was like 194+- 3. The previous owner did have the thermostat missing and there was moisture in the oil due to incorrect operating temperature so i cleaned it up installed a Tstat and oil change and it’s been great oil looks perfect and cooling is proper. Did new plugs too but i’ve done a TON of slow idling around the marshes so i know that’s not good even for a 4 stroke. One thing i am considering is doing a carbon cleaning by using sea foam or whatever: I’m sure there is a a lot of buildup over the years.
 
Yes! Do a "shock treatment" de-carb! Might need to do it multiple times. All the running without the stat and prolonged idling/trolling could have it badly carboned up.

A good tech I know told me that there are some pretty good, not too expensive, USB borescopes that plug into smart phones these days. You might consider getting one to take a look at valves and piston crowns. I haven't shopped for one so no recommendations yet.

I didn't think the video showed any bad shaking at all but just my opinion.

I DO think though that the idle seems a bit low and, if in the water pushing the boat, THAT might cause it to shake.

Most trollers don't like 1000 rpm idle setting but that is what makes that engine happy.

I have a 16' aluminum bass rig with a 50hp 2 stroke Merc. The guy I bought it from had a a 6hp 2 stroke kicker he used for trolling because that 50 doesn't like slow trolling either. 900 rpm minimum for it.
Heck, even my 20hp Honda wants 900+ or it will really shake.

Good luck
 
Go heavy on sea foam and give it a long run in the water at say 2500+ rpm and see if any change in idle, I’d do 30-60 minutes to rid carbs and valves of any varnish. If it helps, use sea foam in all gas for the next few trips and then once or twice a year. My old Dodge Dakota with a v6 and Holley 2 barrel would run good for about 18 months then ask for sea foam. One dose was good for another 18 months. I had the truck for 18 months and never touched a screw on the Holley.
 
NSDON said:
Go heavy on sea foam and give it a long run in the water at say 2500+ rpm and see if any change in idle, I’d do 30-60 minutes to rid carbs and valves of any varnish. If it helps, use sea foam in all gas for the next few trips and then once or twice a year. My old Dodge Dakota with a v6 and Holley 2 barrel would run good for about 18 months then ask for sea foam. One dose was good for another 18 months. I had the truck for 18 months and never touched a screw on the Holley.
Click to expand...
i’m out with my dad and i’m still getting the bogging when trying to get on plane. i was meticulous with the carb job this time and got new fuel lines and everything. Sounds amazing down low. i didn’t check the plugs through all this bc they were pretty new but we had been idling around for hours sightseeing with no planing. i’m hoping they are gunked tonight bc we still have 2 days to fish. just anchored now fishing..
 
man i bet that’s it…i bet the 2.5 turns out and idling got ‘em. Put some fresh ones in and went back to 1 turn… wish me luck tomorrow!BF6A8D06-FC56-4AE5-9BA9-E505EF5AB0BD.jpeg
 
With more thought i don’t think these plugs look bad enough to cause the symptoms. When the motor was cold the issue was only when trying to plane. But the more we idled around the worse it got to the point where it was concerning we would make it back. A few short bursts the engine would sound ok and rpm’s would go up. I’m thinking it’s something electrical like a coil. Either that or a ton of carbon buildup that’s seriously impending the combustion chambers and overheating the heads…this sucks
 
Ok!!! Huge break…did a plug drop again in the driveway and #2 made no difference. tested spark NO spark. Swapped coils…still no spark. This means CDI correct?!?!
 
CDI units very rarely fail. Could also be a pick up or ignition coil, or even a bad plug cap. You can spend a lot guessing what's wrong with an ignition system and simply throwing parts at it. If you don't have a manual I can check a wirig diagram and tell you how to diagnose.
 
iang6766 said:
CDI units very rarely fail. Could also be a pick up or ignition coil, or even a bad plug cap. You can spend a lot guessing what's wrong with an ignition system and simply throwing parts at it. If you don't have a manual I can check a wirig diagram and tell you how to diagnose.
Click to expand...
i swapped coils/caps and still no spark on that cdi output. Bad pickup i think would affect more than one cylinder
 
I’m going to check inside those little 90 degree terminal boots also on the cdi output wires. I have the service manual but there really isn’t any schematics or troubleshooting. Just ohm specs for testing individual components. Am i right though that the upper coils just energize and pulse to the CDI and it does the switching? I don’t see 3 individual pickups
 
Ok i guess the pulser coil does have 3 individual outputs so i guess it would be a lot more apt to be breaking down under heat and load then the robust CDI. It’s also cheaper and more available. So without guessing i need to be able to test pulse coil output. I’m guessing i need a DVA
 
DVA is best, check each colour to black and you should have approx 5v whilst cranking with spark plugs out. If okay then reconnect pulsar and then do a voltage test between each pair of coil wires, should be around 100 plus volts. This is a much better test than a resistance test
 
iang6766 said:
DVA is best, check each colour to black and you should have approx 5v whilst cranking with spark plugs out. If okay then reconnect pulsar and then do a voltage test between each pair of coil wires, should be around 100 plus volts. This is a much better test than a resistance test
Click to expand...
Thanks for the response. Looks like for the price of a DVA i could get a pulser coil with a 90 day warranty off ebay…might be worth just swapping it. The CDI thing sucks. They are 500-700$ for one in good shape and 260$ rebuilt (if repairable). I know they normally don’t fail but this motor is 30 years old and I had a delaminated flywheel banging coils for awhile that could have sent some crazy signals into the circuit and also a leaking cowling cover gasket that was letting moisture into the cowling….would often see water inside after rain.
 
Flywheel magnets touch coils will not damage a cdi. One cylinder out is usually pulsar coil, if you want to guess without testing, I've changed more pulsar coils than anything else on ignition Jap ignition systems
 
iang6766 said:
Flywheel magnets touch coils will not damage a cdi. One cylinder out is usually pulsar coil, if you want to guess without testing, I've changed more pulsar coils than anything else on ignition Jap ignition systems
Click to expand...
I can’t tell you how much i appreciate this response. That’s what i needed to hear. Ordering one right now! I will take the 30$ bet. It’s been a problem for over a year on and off in hindsight…Thank you!
 
ok i got the new pulser coil on and have confirmed spark. Haven’t taken it out though but i noticed when i pull the wire off the middle cylinder it doesn’t effect the running much at all. I thought it did for the first minute or two but not once warm. Even the fuel screws on 1 and 3 affect the running when turned in but 2 really doesn’t. I don’t have my compression gauge here at the moment. Is 2 just much better inherently balanced and that’s why it doesn’t effect like the other 2?
 
iang6766 said:
Compression or blocked idle jet. Are you sure you had no spark before?
Click to expand...
i think so we tried to look at the spark multiple times here was the old pulser compared to the new one. You can see the cracking and entrance for moisture and heat
 

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i feel like there is no way the carbs could be fouled i really cleaned them severely and they weren’t even dirty. My dad agrees we looked hard and did not see a spark. I realize now how faint the spark is but i can see it now in the gap and arcing onto the motor. I guess will see
 
Ok did compression and it’s 180 psi on all 3 cylinders and that isn’t turning over nearly at 500rpm so my compression is great i think! I definitely have spark and like i said my dad and i would have seen it i’ve triple checked. So i think it’s gonna run good! Will see in the next day or so. If it’s still weird then it’s CDI or middle carb issue 🤞🏼
 
ok got the boat out today and tried to plane as soon as i left the dock and it planed quickly and sounded great. Once i got above 3/4 it started bogging out every time i pulled back it would run smooth. After 10 minutes it started going downhill and wouldn’t plane anymore…by the time i was going back to the dock it was skipping a cylinder even at fast idle when headed back. Something is definitely getting worse with heat. Still had spark to the middle cylinder at the dock. I’m wondering if it’s a bad ignition coil. Possibly the middle one. They test ok in the driveway but who knows. This really sucks. Is there anyway it could still be carbs? I know the engines needs change slightly as it warms. But yeah even when cold was bogging at full throttle. I could pull it to a moderate throttle setting and it would run steady about 20mph. That makes me think carbs…but the degradation with heat makes me think ignition.
 
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