SE on the carb

[Phil M]

While attempting my first Honda BF50A carb synchronization, I was instructed in the manual to block the three SE (Starter Enrichment) tubes by pinching them closed. I did that.
The idle speed jumped to almost 2000 rmp! I had to lower the idle speed in order to continue. Is that normal?
After the carb sync, I unblocked the SE tubes and the speed went way back down, so low the engine would not idle. I set the carb idle back up to around 1000, and then as a trial disconnected the SE tube again. The idle speed jumped up again! The diagram shows where I was connecting and disconnecting.

There is suction on the end of the tube, when it is discconnected and allowed to run open, the rpm increases significantly. It is regulated by an electronic solenoid, which I have coloured in yellow.
After running the engine for several minutes, the SE valve is hot and the valve does work like it is supposed to, but there is still suction on the end of the SE valve at that same spot.

I am trying to figure out why a SE tube would produce a dramatic idle speed increase when it is disconnected?

Any guesses?

[Whipsyjac]

Carbs are tricky, and even though I've tuned some and rebuilt a couple motors the intricacies of small carbs can still be baffling. If your source info is good printed material don't add or skip any steps. If the manual doesn't tell you to adjust the idle after pinching the hoses don't. I hate the sound of a motor revving unnecessarily but if you trust the manual just follow the instructions.

My motor trouble last year was traced to someone disconnecting a hose from the carb on my Merc 50 and putting it back in the wrong place....$3,500 because of a carb hose in the wrong place! I've done a lot of stuff, and taken some risks too when working on engines, injection, and carbs. Just be careful and if a step seems counter intuitive research it, but it's probably just a knowledge or experience gap.

I've got a weird hose issue on my wife's old car, engine surges unless you pinch off the hose. The most common(and my current) solution is to drill a hole in a penny and place that in the tube allowing a minimal amount of vacuum. The sizing of the hole changes with seasons and engine temp so you have to find what works best by trial and error. I still don't quite understand it but that's the way it is. So with your boat maybe the disconnected hose leans out your mix, or maybe it bypasses something, but whatever it does your idle with it attached is lower than disconnected so its probably best not to mess with the idle while making the adjustment unless your instructions say to do so.

I know I'm not much help but at least my post will bump the thread to the top again

Willy

[Phil M]

Carbs are tricky, and even though I've tuned some and rebuilt a couple motors the intricacies of small carbs can still be baffling. If your source info is good printed material don't add or skip any steps. If the manual doesn't tell you to adjust the idle after pinching the hoses don't. I hate the sound of a motor revving unnecessarily but if you trust the manual just follow the instructions.

My motor trouble last year was traced to someone disconnecting a hose from the carb on my Merc 50 and putting it back in the wrong place....$3,500 because of a carb hose in the wrong place! I've done a lot of stuff, and taken some risks too when working on engines, injection, and carbs. Just be careful and if a step seems counter intuitive research it, but it's probably just a knowledge or experience gap.

I've got a weird hose issue on my wife's old car, engine surges unless you pinch off the hose. The most common(and my current) solution is to drill a hole in a penny and place that in the tube allowing a minimal amount of vacuum. The sizing of the hole changes with seasons and engine temp so you have to find what works best by trial and error. I still don't quite understand it but that's the way it is. So with your boat maybe the disconnected hose leans out your mix, or maybe it bypasses something, but whatever it does your idle with it attached is lower than disconnected so its probably best not to mess with the idle while making the adjustment unless your instructions say to do so.

I know I'm not much help but at least my post will bump the thread to the top again

Willy

You made some good points. The manual says nothing about an increase in rpms when the SE tubes are pinched, hence my suspicion about something is wrong. I am hoping someone who has done a carb sync will reply.
And yes, one of the hoses could be put back incorrectly after dismantling the three carbs. It does seem like that happened, but I cannot see the other side of the carbs to verify.
The BF50A runs okay. It could be better.

[Spector]

Are you using a vacuum gauge? Not familiar with the honda but just did my Yamaha F60 this weekend. Just hook up the hoses to the manifold and dial it in.

http://youtu.be/KdYnxBOn00Q

[Catigale]

It might be worth looking on some other fora for Honda synching tips?

[Phil M]

Yes, videos on YouTube helped me actually do the carb syncing with the sync tool that measures the vacuum on each carb. None of the videos, or nowhere can I find that the engine idle speed is supposed to jump dramatically when the SE (starter enrichment) tubes are pinched off, as they are supposed to be pinched off to accurately measure each carb.
I have looked on the web with no results about this particular aspect of syncing Honda carbs. So maybe I'm looking for something that is not there.