BF50 idles rough, but runs OK?

Engine seems to run ok, but idle can be low at times. On cold starts I have to hold choke for about 3-5 minutes to warm up or motor will die. After motor is warm idle will usually hold, but motor seems to shudder.

1. I recently took carbs apart and cleaned them, and synced carbs but vacuum seems low at around 5in Hg. - what could be causing low vacuum?

2. I'm suspecting timing is off... how do check timing? sorry I searched but apparently couldn't find my answer.

Thanks
Andrew

Do something easy first, I would run the motor with Sea Foam, a few hours at high RPM, so maybe use it a few times and don't run it at low RPM. The high RPM will heat up your intake and valve/intake systems and the Sea Foam and the high temps will clean out the valve train and fuel system.

Also, use an ethanol free gasoline if possible.

If this doesn't change anything, then come back and ask for further advice, but do this first.

Thanks for replying I will try a can of sea foam in the tank at high rpm, but I still would like to verify my timing is correct. I know carbs are clean, plugs are recent, fuel and water separator are recent, oil is fresh, and carbs are synced.

The motor always runs high rpm (4000-5500ish RPM). Problemis I do a lot of idling when I take boat out to spearfish( when anchoring near rocks while anchored for safety for instance). I will try not to idle so much next time out and fish a different/safer location where I can shut down.

To check timing.....

Align the arrow next to the T on the cam with the arrow next to the T on the top of the cylinder head. Then look for the T with a mark next to it on the outside of the flywheel. That mark should align with the alignment mark on the port side engine hanger boss. All marks should align.

If the mark on the flywheel is 180 degrees out, just rotate the flywheel 180 degrees to get everything lined up.

It may be possible that your low vacuum is due to a low idle. Idle should be 950 plus/minus 50. I usually set it close to 1000 rpms.

Mike

Also......make sure to set the idle mixture screws to the proper setting. Depending on the carburetor number, the number of turns out is 1 or 2 1/8.

hondadude said:

To check timing.....

Align the arrow next to the T on the cam with the arrow next to the T on the top of the cylinder head. Then look for the T with a mark next to it on the outside of the flywheel. That mark should align with the alignment mark on the port side engine hanger boss. All marks should align.

If the mark on the flywheel is 180 degrees out, just rotate the flywheel 180 degrees to get everything lined up.

It may be possible that your low vacuum is due to a low idle. Idle should be 950 plus/minus 50. I usually set it close to 1000 rpms.

Mike

Also......make sure to set the idle mixture screws to the proper setting. Depending on the carburetor number, the number of turns out is 1 or 2 1/8.

Click to expand...

My idle was around 1000rpms when vacuum was checked...

I may have a problem with the idle mixture screws - mine appear to be unadjustable. There seems to be like a "wall" in the way giving them limited turnability if that makes sense. Also, two of the heads of the idle screws broke off so I'll have to get an easy out to remove and replace those. (this picture is old and only one idle screw is broken, currently two are broken off, and sorry I couldn't figure out how to rotate the image - the top of the motor is to the left of the picture)

It appears that you did not remove them, so they are hopefully set correctly.

One way to get out the broken one is to take a center punch and punch a hole near the edge and then another on the opposite side, near the edge. Use some penetrating oil around the screw to help lubricate the o ring. Then take two small picks...and stick them in each hole and it should ultimately rotate out.

As far as the vacuum is concerned...I never pay attention to the value....I just want them to be the same.

One other variable could be valve clearances out of adjustment.



Mike

Thanks so much for your advice.

I’ll try that center punch idea for the broken idle screws.
ive never worked on internals of engines , but am mechanically inclined. Is it a difficult procedure to adjust valves? Special tools required?

if you look close there is like a wall that prevents the idle screws from being adjusted- and that is why I broke them trying to turn them resulting in the heads snapping off.

maybe I need a different type of idle screws?

The EPA has Honda put a limiter cap on the screws so they are not tampered with.

A different screwdriver will not help.

Mike

No, the limiter thing is the carb itself, not the screws.

Not a different screwdriver, I meant different idle screws. I saw that there are different types when I ordered them.

The plastic silver cap on the screw on the top carburetor is a cap put onto the screw with loctite. The screw itself is brass. The new screws consist of the brass screw, o ring and separate cap.

The manual says to break off the cap and remove the screw. After the carb is cleaned, a new screw should be installed to the proper turns and then the cap should be put on the screw.

The new screws have a small slot in them for a small screw driver. Once the screws are adjusted properly, the cap is supposed to be put on with loctite.

Techs can be fined heavily by the EPA if they/we do not adjust properly and install the caps before the boat is delivered to a customer. That is why I am explaining the way it "should be done".

I have never been checked by the EPA, even though we service several of their motors. In any case, we always install as the book says, if for no other reason, to keep the customer from getting "tinkeritis".

Mike

As for the valve clearances. Here is a video, that goes in great detail on the adjustments. It is on a Honda 40, which is essentially the same as your 50. The specs and measurements will be the same for your motor. https://www.youtube.com/watch?v=aVBWNAhs3XU

Mike

Thanks again Honda Dude, you’re awesome! Since my idle screws broke from trying to turn them I don’t think I adjusted them back when I was trying to tinker with them. When I do install the new ones- how do I break off the caps without breaking the screws?(like I did before as seen in picture) Pull the caps off?