Logo
FULL SITE MENU

Se valve issue?

W

willys_wonka

Member
Hi all, Ive got a Honda 25 I'm working on that won't start. One thing I notice is that the SE valve isn't getting power. A quick check shows it's energized by the CDI module. Am I correct in assuming that it should get 12V on startup? There's no other choke system on this engine.
 
willys_wonka said:
Hi all, Ive got a Honda 25 I'm working on that won't start. One thing I notice is that the SE valve isn't getting power. A quick check shows it's energized by the CDI module. Am I correct in assuming that it should get 12V on startup? There's no other choke system on this engine.
Click to expand...


Well, by pulling the choke valve and blocking the port with my thumb, I got her running. Strange thing is when I apply 12V to the valve nothing happens. I figured it would act like a solenoid. So no power from CDI and nothing happens when I manually add power to it. Yet this seems the source of the no-start.
 
Well, it's interesting that you can get it running that way using your thumb but, heck, I just learned a new trick from you! ,>)

You are correct that the SE valve or bystarter as it's sometimes called, gets voltage as soon as the engine starts. The power comes from a "segment" of the stator coil assembly.

But it's not a solenoid. It is actually a sort of electrically operated thermostat .

The way it operates is that when it begins getting voltage an internal coil heats up and causes the pintle valve to extend. I believe this is done by heating a wax pellet inside the valve but I've never actually opened one up so that may not be accurate. At any rate, the pintle extends and shuts off the enrichment passage, leaning the mixture out. Applying 12 volts to the coil should start the pintle to extend in about 60 seconds and it should be fully extended in around 2 minutes.... or so....depending on ambient temperature.


This means that the SE valve is defaulted to the cold start position when not powered. So, typically, when it has failed, the engine will cold start fine but then be too rich in about 3 minutes time.

But it seems that in your case the pintle may be stuck in the extended position? I don't know.
However, if it doesn't move after 1 1/2 minutes with 12 volts applied, we can assume it is probably bad.

I don't haven't worked on a 25hp and I don't have any SI for one but my 20hp wiring diagram shows the voltage to operate the SE valve is actually supplied from the voltage regulator. It comes from the stator coil on the brown wire as an ac volts signal and gets rectified through a diode in the VR to a dc volts signal. It then powers the SE coil via a brown/white wire.

The ac signal from that same segment of the stator coil is also split off to the CDI and to the tachometer as an rpm signal.

Power for the SE coil does not come from the CDI.

My 20hp manual shows that the Brown and Black/green wires from the stator harness should read 1.2 to 1.8 ohms on a good SE valve segment. The 25hp might be different but I doubt it.

I hope this helps you figure it out.
 
Last edited:
Should have said that the brown wire from the stator splits off at a splice and becomes a yellow/black wire that then feeds the VR, tachometer and CDI.

Good luck.
 
If the bystarter is getting hot to the touch after a few minutes (from the internal heating element), it's likely that it has power and it's working.

There's a fuel passage down in the bottom of that galley (directly below the bystarter) that will often fill with crud as it's a low point. That's where I would go first.

Thing is, as I generally work on only the bigger cousins of this motor (starting at 40hp), I've never seen an engine equipped with a bystarter and associated plumbing, AND a choke?

You say the 25's are set up like that (with bystarter AND choke butterfly), or have I misunderstood? What year is this motor (about)?
 
Last edited:
Alan Hicks said:
If the bystarter is getting hot to the touch after a few minutes (from the internal heating element), it's likely that it has power and it's working.

There's a fuel passage down in the bottom of that galley (directly below the bystarter) that will often fill with crud as it's a low point. That's where I would go first.

Thing is, as I generally work on only the bigger cousins of this motor (starting at 40hp), I've never seen an engine equipped with a bystarter and associated plumbing, AND a choke?

You say the 25's are set up like that (with bystarter AND choke butterfly), or have I misunderstood? What year is this motor (about)?
Click to expand...

No, what I meant to say is that it doesn't have the manual choke system but just the SE instead.
And in this unit, the CDI is the source. It has a pin labelled bystarter.
I'll check the unit today, but when I pulled it out, the needle was crudded up a bit, like it had been stuck in the port orifice. It does get warm - I noticed that yesterday - but didn't notice any movement. I have a feeling it has failed in the down position, because pulling it allowed the enrichening port to function and the engine to start.
 
There's an air passage in play there as well. So the idle fuel mixture is richer AND there's a passage that opens up allowing more air in as well (the reason for a lot of that plumbing). The idle speed dropping down as that needle closes would be another sign it's working as designed. THAT part is easily checked if the air box has been removed. If you look in the front of the carb, the top carb will have a round opening at maybe 10 o'clock. The others don't have it. You can easily put your finger over that opening with the engine running to see what the idle does. If the needle is closing as designed, there should be no change when you put your finger over that hole. If the idle does not change, there's an issue....

MOST of the problems I find with this system can be traced to a plugged jet in the fuel supply to the bottom of this galley. The passage between the float chamber and here has a jet in it, and they DO plug on occasion.
 
I think youre right about the plugged passage. With my finger blocking the hole where the valve sits and the needle passage wide open it runs fine, though too fast of course. I checked and the needle does drop over time when connected to power, but with the valve inserted engine doesn't get enough fuel.

I checked by dropping a chunk of wire insulation down there (I put it beside the needle orifice so nothing was plugged) to ensure that the needle was being lifted up and not totally blocking the orifice, and then it started, but ran rough, died when putting into gear.

A rough check of the measurements shows that when cold and fully retracted, the barrel that holds the needle would only sit a few mm above the bottom of the chamber and the needle would be lifted an equivalent amount out of the orifice. Is that correct? It's not supposed to pull up further?

The upper edge of the barrel (that holds the needle) is roughly parallel with the bottom of the valve body when cold, and drops from there as it heats. The barrel can go quite a bit higher if you push up on it.

In the past, when I've needed an overly rich condition to start, it was plugged jets/passages. My only concern is that it might have dropped lower than it should be, plugging the orifice too much for that engine temperature, although clogged passages makes more sense.
 
Suggest you clean it and have another try before going much further. Pay CLOSE attention to the routing of the plumbing as it came from the factory. DO NOT re-route or change a thing! These are NOT my favorite types of carbs as they can be REALLY picky.
 
Pulled the manifold off today. Going to record all the previous settings then dismantle them and clean them. This engine has sat for years, and I'm sure I'll find a lot of gunk in them.
 
Not much to record as far as settings. You might want to take a couple of pics to make sure the fuel/vacuum/overflow/vent line routing stays the same. Did I say these are a PIA? When cleaning, pay particular attention to the brass tube that runs from top to bottom right in the middle of the carb. The idle jet is hiding on the inside of that near the bottom. Historically, that jet has caused the most headaches, bar none. It's like the size of a whisker hair, so don't try cramming anything through it. Compressed air and carb clean all that's usually required. To make matters worse, they're brittle, breaking right in half, so be careful with it! When you're done with it, you should be able to see through it lengthwise. If you can't see through it, you aren't done yet.....
 
I'm thinking throttle and mixture settings. I don't want to be balancing carbs at this point. The manual suggests removing those tubes and clean; you're suggesting leave 'em in place and clean?
 
Oh no. The tubes need to be removed to clean. There's NO NEED to be messing with those throttle setting screws. Leave them as is.

Mixture settings are locked down too, unless you want to open a can of worms getting those anti-tamper pieces off the idle mixture screws. That's a 50-50 chance of breaking the head of that screw off at the very best, assuming you use heat from a soldering gun or something to release the epoxy holding them in place. If these were older carbs, it might be worth the trouble as the screws have an o-ring that can dry out and cause a vacuum leak there. These should be fine. Suggest you leave them alone as well.
 
I think it will be more apparent when you have a carb in your hand. Once you have the big screw removed from the bottom, the only thing holding both of the tubes (there's also a larger one that doesn't go all the way to the top that needs to be removed as well) is a really tiny o-ring. I stick a screwdriver in through the front of the carb and pry the tube with the pilot jet in it down a bit. Once the o-ring clears (maybe 3/16") it'll fall out the bottom with the other tube - unless it's really gunked up. Those take a bit more persuading, but nothing difficult.
 
Well, I cleaned everything but it looked pretty clean already. The idle screws weren't capped so I pulled them and cleaned out those ports as well. Honestly, I expected to find a pile of grunge in these things, but nope.

Anything else give these symptoms? As long as the Se valve fuel port is wide open (valve removed, opening blocked) the engine runs great, just higher idle than normal, as you would expect. Put the valve in place, engine dies and can't be restarted. Past experience suggests plugged jets when you have to "choke" like hell to get the engine to run/start, but I didn't see that.

All the plumbing on those carbs gives me the willies.
 
It starts it runs, yay! It bogs at higher Rpms, oh no. It's definitely a fuel starvation problem because it's backfiring a bit and if I give it a shot of starting fluid it takes right off. There are no vacuum leaks, hoses routed correctly, filter good, new fuel pump. Squeezing the primer bulb hard doesn't get anymore fuel into the machine.
It runs quite nice at idle and low speed. You can feel it freak out as you add throttle: rpms climb climb, then suddenly it starts missing and loses power.
While cleaning I took extra care with making sure float needles and seats were clean. I eyeball float level but didn't do exact measurements as that wouldn't have changed suddenly.
I even tried tapping the sides of the carbs in case a float was stick, but no difference. Tried pulling spark boots while under load and it's system wide, no single cylinder acting up alone.
From what I had read it was always the slow and idle jets that cause the problems on these things.
 
Last edited:
Trying a different tank, no change. bypass the filter and pump, and used just the primer bulb as a pump, engine ran fine. But its a new pump, and I pulled it apart and everything looked ok. Of course adding fuel pressure by hand is probably a lot higher than through this little pump, so all that really proves maybe is I can force enough gas through the system to fill carb bowls. Everything seems to point to low fuel pressure but I can't seem to figure out why. That all 3 carbs shows low fuel at high RPM after cleaning strongly suggests problem isn't in the carbs themselves. Its not filter, pump, tank, but not enough gas is passing through...

I sure hope someone pops in with some suggestions. Ive been at this for hours and running out of options.
 
Last edited:
Back
Top