Logo
FULL SITE MENU

Honda B100 won’t start.

T

tinsel

New member
Hi. I have. A probably 70s B100 unit with points. I got it not working as a project. I’ve tried a few things and I still can’t get her to start. I’m hoping someone here can offer some advice.

When I got the unit it had no spark so I assumed fixing that and a carb cleaning would get her fired up. Spark was pretty easy. She’s pop just needed a points adjustment and a new condenser. The carb cleaning was pretty straightforward as well. Also replaced the fuel lines. Fuel pump was still good. She has decent compression. A little low at 130 psi.
Unfortunately she’ll pop a bit but not start even with starter fluid.

I was worried about the timing after removing the cam shaft pulley but I followed the service manual to a tee. I checked with an dmm and the points start to open at the firing mark. I also checked with an endoscope the T mark on the flywheel does coincide with the pistons reaching the top of their travel. Both valves in both cylinders are moving. It is very sooty in there though.

A this point I’m thinking valve adjustment but after that I’m stumped.

Another note, she had melted her impeller housing which may indicate the engine overheated at some point but I’m not sure.

If you’ve made it this far, I appreciate you.
 
Did you check valve clearances?
It's got...
Spark
Fuel
Compression
Is timed correctly.

It should start.

130 psi is low but most of those old girls will easily run on that. Usually the valves are too tight but if somebody has them loose, it might not be breathing enough air

I suspect weak spark may be your issue otheewise.

But first, tilt her up to get the cylinder head as near horizontal as you can. Remove the plugs and squirt a bit (just a bit) of engine oil in the cylinders. Pull her over a couple of times and then install the plugs and try starting again.

Hopefully the oil will bring the compression up a few psi and get her more inclined to fire cold. If she runs a bit after that, just working the valves and rings might "clear her throat". After that, you can run some Sea Foam or your favorite flavor of fuel de-carb additive. Excess carbon can mess with the spark.

I'd be looking back at spark again if it won't fire.

Did you check and lube the spark advancer in the cam pulley? Those things get dirty and rusty and can stick causing the spark to be over advanced for starting.

Where did your replacement capacitor (condenser) come from?
Have you tested it?

I don't think⁸ this one has the reed switch and magnet neutral safety switch but, if it does, check it over carefully along with the kill switch if someone has added one.
Even a bad stop button can mess up the spark.

Just some ramblings from an old man that's wrestled with a few of these old timers.

Good luck.
 
A couple of things I missed or was mistaken about....
Never.mentioned spark plugs but assumed you tried new. If not, consider it.

I wrote carbon messes up spark. WRONG! But carbon can soak up fuel and quench combustion.

Did you check ignition coil primary and secondary resistances?

Comments on the waterpump:
You say waterpump housing is melted. That can happen if the outboard is started out of the water. The pump can destroy itself very quickly that way. Hopefully the engine wasn't badly overheated as a result. But if it was, it still wouldn't damage the pump like that. The pump housing can get that melted look over time and, often, people ignore it and just replace the impeller over and over. You never know.

I should have asked....
..."compression 130"...both cylinders?

If so, that's fairly unusual. They're typically a few psi apart. That always makes me suspiciius about the gauge. Those go bad all the time. Even the "good" ones. But especially the cheap ones.

I would love to see you get her going!
 
Thanks for the info! I’m excited to get her running.

I’m checking valve clearances today and will report back. I haven’t done it before so it’ll be a learning experience.

This unit is old enough not to have the neutral safety. I checked the kill switch with a dmm and it seems to be working properly.

It looks like someone replaced the ignition coil around 2014 or so given the date stamps on the coil and wires so it’s the CDI coil. I couldn’t find any of the coils for the older points ignition online. I did read a report from someone on this forum using the CDI coil on the points model with no issues. The coil itself measures good.

I didn’t buy new plugs but someone did (ngk too). I think the points, coils and plug were replaced in an earlier repair attempt but I can’t be sure. When I got her, the points and spark gaps were totally misadjusted and the condenser was toast. I set the gaps to factory spec and I swapped in a high temp high voltage metal film capacitor with the nominal capacitance in the service manual. I got spark but it was a little inconsistent until I cleaned up the points. It seems to be good now but it’s definitely not the strongest spark I’ve seen. Pretty much impossible to see in the sun but that seems to be normal for this engine from what I’ve read.

As far as the compression I fudged a little it was 127 psi on the top cylinder and 130 on the bottom. I’ll try the oil trick too.

I’m trying to upload a picture of the impeller housing here but I can’t seem to get it working. Here’s a Imgur link instead (
https://imgur.com/a/VqfYsEJ
). The impeller inside actually looked ok but the housing was so melted I had to cut part of it off to remove the bolts. It clearly got pretty dang hot. Im really hoping however that happened it didn’t mess up the lower unit or the engine. The water tube seems fine and I can get water all the way through with a hose fortunately.

fingers crossed
 
WHEW! That's definitely the worst I've ever seen! My word!

It looks like it was run dry for some time. I can't explain why the impeller looks ok. I would think it would look horrible too! Hard to believe anyone putting a new one in that mess!
Driven by desperation I guess.

Make dang sure there isn't anything blocking water from flowing into the pump! Plastic bags or pieces of of one, can work their way into places you wouldn't think they could.

More likely though would be the little intake screen might be plugged for some reason. Algae, salt or other minerals might do that.

Yes, the spark on these can be faint and hard to see at cranking speed but you measured plenty of voltage so I don't know.

The symptom you describe of it popping a bit makes me think timing. Like the spark occuring way early or way late. But your description of how you checked that sounds right. So, again, I don't know.
Sadly, I find "I don't know" something I say regularly.

Those "new" plugs. Are they they the
DR5HS NGK? Gapped to 0.024" to O.028".
Points 0.012" to 0.016"

Look at the plugs closely and make sure no one has been at them with a stiff wire brush trying to clean them. If you have doubts about them, try new ones.

Good luck!
 
I got her to start! Alas not run unfortunately.

The valves were an issue. All of them were way over tight. After loosening them up, compression was up to 135 in the top cylinder and 145 in the lower cylinder. The engine turned over but would not stay running after opening the choke.

I’m thinking it’s probably a fuel issue. (At least I’m hoping so. Much easier to fix than a spark issue!) Messing with the carburetor helped some but I didn’t have much time today. Do you have any tips on where to start adjustment wise? I was kinda flying blind putting it back together after cleaning.

Good notes on checking the water intake. I checked the mouth on the lower unit and it looks clear. I haven’t opened up the intake manifold yet but it might be worth it to check it’s clear.

You know, you never know until you know :)
 
Valves and valve seats likely need attention if there was no clearance.----Does spark jump a gap of 1/4" or more?
 
Hopefully no damage from tight valves. I'm thinking not or otherwise the compression probably wouldn't have gone up. If one had "kissed a piston", you would probably already know. But, since you have a way to inspect inside the cylinders, you could check for witness marks of any past valve to piston contact.

It was probably the reason you say it was "sooty" in the cylinders. As the valves get tighter from wear, the engine runs less and less efficiently.

I don't know how you "cleaned" the carb, so I'll just touch on some basics

Those carbs are beautifully simple but can get plugged by deposits.
Carburetors need to "breathe". I don't recall specifically how many float chamber air vents the old ones have but most have 2 vents. 1 right side and 1 left. They aren't always easy to locate but, if you pull the bowl off, you can see the tiny holes at the inside top of the body. If you use the carb cleaner spray straw and shoot cleaner in those holes, it should exit at the outside top of the carb body. Step 1 in carb cleaning.

The carb NEEDS atmospheric pressure (14.7 psi) pushing down on the fuel in the float bowl to help the fuel overcome gravity and move UP and through the jets, passages and delivery orifices. That, along with "pressure drop" (often called vacuum) in the carb throat (Venturi) pulling on the fuel is the basis of how they work.

That carb will have a series of tiny delivery "orifices" at the top of the rear of thr carb throat near the throttle plate. Only one of those little holes can be seen when the plate is closed. That is the idle circuit delivery orifice. If you open the throttle plate all the way you can see the rest.

If you remove idle mixture (or pilot) screw and spray cleaner in that opening, cleaner should exit the idle orifice. If not, place the cleaner straw directly over the idle orifice and spray in there. Fluid should exit the screw opening.

At the other end of the carb throat, where the "air guide" bolts on, there will be a hole in the flange just above the carb throat. That is the air jet opening. You can spray into that opening and, hopefully, fluid will come out in several places including the idle set screw opening. If so, the air jet is clear.

I need to stop for now but I'll try to pick this up later today. If you're interested that is.
 
If valves have no clearance the hot gasses may damage ( burns ) the exhaust valve and seat.----A bit of valve grinding compound will restore the fit.
 
Back
Top