S65 carb woes

lukelaw1

Active Member
I have only seen a s65 motor once maybe twice, and I thought that model had a flywheel with timing advance. If not please let me know for future reference and disregard below.

I need to know the problem, this is driving me crazy. This is really really really out way out in left field but hear me out. I think you said bike will start easy and idle fine, but as you increase rpm, bike stumbles, floods out and etc. What if at idle the timing is correct and as rpm increases a weak or broken advance spring is advancing timing to much??? Once unburnt fuel keeps loading up the plug motor get further and further behind.

Can you check the timing with the light as rpm increase to confirm it is still on the f mark?

Oh and also check the woodruff key for a partial shear or worn keyway on the flywheel that could cause misalignment. You can also confirm top dead center with head off. top dead center should be t on the flywheel to case notch.
 

Gary

Well-Known Member
You are correct on the flywheel,very similar to an H or SL/XL engine or even a CL. In the same vein I wonder how it would run if at all, if the points cam is 180 off. Your idea of putting a light on it might be well worth the effort.
 

allenp42

Well-Known Member
You are correct on the flywheel,very similar to an H or SL/XL engine or even a CL. In the same vein I wonder how it would run if at all, if the points cam is 180 off. Your idea of putting a light on it might be well worth the effort.

I agree. Don't see how it could run at all. I have a ND (Nippon Denso) advancing flywheel, Mitsubishi advancing flywheel, and a Hitachi advancing flywheel. The one thing they all have in common is the fat side of the lobe faces toward the keyway. As the flywheel turns CCW, you can see the points open and close as it passes the timing marks on top top. The only way I can time one with the timing advancing 180 off is to use opposite "window" (timing marks not in sight), which is 180 degrees off.

I took a pic to show the fat part of the lobe (Hitachi). If you look closely, you will see a slight bevel edge on the cam lobe. From what I have seen, the amount of bevel may vary a bit but the grind for the lobe is always the same. For what's worth, the one Mitsu flywheel I have the bevel is a little more CCW than a Hitachi, but it's still pointing more toward the keyway than the other possibility.

I used a green sharpie to make the bevel edge. This should make it easier to determine if the timing mechanism is correct.

However if I were in your shoes, I would still probably hook up a timing light just to be sure that nothing crazy is going on with the timing.
 

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Sams65

New Member
Thanks for the continued input everyone - some clarification below;
I think you said bike will start easy and idle fine, but as you increase rpm, bike stumbles, floods out and etc.
Unfortunately the over-rich condition appears as soon as the bike is fired up. It accelerates up to a certain point and then just falls flat on its face, refusing to pick up any more speed. I'm guessing due to getting loaded up with fuel like you said. But yeah, the bike starts up easily (a little too easily, without choke) and idles super rich.

I did check the dynamic timing a couple of times when I was switching out points/condensers etc and the F mark appears at idle. There are 2 additional notches on the flywheel after F that appear when revs are increased, for timing advance. (Why there are 2 notches, I have no idea) This makes me think the timing advance mechanism and springs are ok. I did force them open with my fingers, when I had the flywheel off and they snapped back as they should.

I currently have the head off the bike and was hoping to lap the valves before I put it back together. (My compression numbers are still bugging me) Once everything is back together I'll do another test with the timing light and REALLY pay attention to the markings this time.

Just to throw another variable in there - What do you guys think about issues within the exhaust system? That's one of the only component on the bike that has stayed untouched through this whole ordeal, other than getting a cleaning. I don't have enough know-how when it comes to the intricacies of exhaust science/back pressure etc but I know there used to be a mouse (or some other animals) nest that I cleared out when it was put back together. it's a fairly simple, single piece unit so it's hard to 'get inside' it. I have run it with and without the baffle which is removable, but it made no difference. Just another thought.
 

allenp42

Well-Known Member
I did not expect this to be an issue. If the timing advance was shot, maybe pre-ignition from advancing the timing too much?? The most timing advance I've see is in the range of 12-15 degrees and one version of the Hitachi and every version of the Mitsu flywheel I've seen have a stop to prevent it from to far north of that. But since you had checked everything else, why not check the timing advance.

(Why there are 2 notches, I have no idea)
That is a good question. I assume timing advance. The distance from the F to the notches is real close to what I have seen first hand when using a timing light. However, I have not seen a reference to these marks in current docs or in an old manual I have for a C65/S65.

Exhaust? You could just remove it for test to rule out an obstruction. Since you chasing ghosts, quick test to rule it out.
 

Gary

Well-Known Member
Exhaust? You could just remove it for test to rule out an obstruction. Since you chasing ghosts, quick test to rule it out.

If you do that don't run it too long and when your done plug the exhaust when your done with a rag or something. You don't want to leave it open the valve may cool too fast and warp. I may have an old s65 head pipe,I'd have to look if you want - it's yours for the shipping. You could put it on and extend it with a piece of electrical conduit if needed. It would make it way faster too ;):LOL:
 

OLD CT

Well-Known Member
I never owned a S65 but a CT70 needs a minimum of 10 minutes idle time plus at least 10 minutes of part throttle ride time to run ''normal'' or fully warmed up. Then I can gun it and have a responsive machine.
 

Sams65

New Member
If you do that don't run it too long and when your done plug the exhaust when your done with a rag or something. You don't want to leave it open the valve may cool too fast and warp. I may have an old s65 head pipe,I'd have to look if you want - it's yours for the shipping. You could put it on and extend it with a piece of electrical conduit if needed. It would make it way faster too ;):LOL:

This is good info thanks! I futzed around with the exhaust the other day and after spraying, poking and prodding, aside from all the chunks of carbon and unburnt gasoline/goo that emerged there's a loose piece of something rattling around. From what I can see, it looks to be one of the donut shaped inserts (diagram attached) It's impossible to get out but was able to sort of wedge it to the side.

muffler.png

Not sure if this would have been enough to case issues or block air flow, but will try it out as soon as I get things back together. Your offer is very much appreciated and I might take you up on that - at this point willing to accumulate as many spares as possible just to get to the root of this...

Was the crankshaft rebuilt?
The bearings were replaced and the crankshaft was balanced & checked by a shop, when I had cases apart.

I never owned a S65 but a CT70 needs a minimum of 10 minutes idle time plus at least 10 minutes of part throttle ride time to run ''normal'' or fully warmed up. Then I can gun it and have a responsive machine.
I had read something similar elsewhere on the forum which is why I decided to ride the bike in its current condition to see if things improved. Must have rode around for 10 mins without improvement. The only difference was all the gasoline just started to carbon up, with the plug/heads ending up sooty as opposed to wet.
 

Sams65

New Member
Read post: cdi kit or stick with points. This this the same scenario you have?
Are you referring to this: https://lilhonda.com/index.php?threads/cdi-kit-or-stick-with-points.17129/

If so, there are definitely similarities, but where as theirs seems to idle fine when its cold, but not when hot - mine will hold idle regardless of temperature, but does so only without choke. If throttle is blipped at idle, it wants to die out when the revs fall back down to idle. Plug comes out completely saturated with gas. These rich symptoms continue while riding and after engine is warmed up.

The bogging while riding is also similar but they mentioned WOT getting up to redline. I didn't get anywhere near redline, the bike would bog out somewhere after half throttle. Plus, mine would never pick back up if I closed the throttle (classic symptom of lean condition)
 

69ST

Well-Known Member
If you're talking about new, OEM, parts in perfect condition, there should be no need to lap valves. The "brakleen test", i.e. holding the valve closed with fingertip pressure only, filling the port with enough solvent to pool around the valve, is very effective. No seepage into the combustion chamber (remains completely dry) means the valve is sealing well.
 

OLD CT

Well-Known Member
A picture of the spark plug may help. If it is black and sooty, rich. Or white, too lean, you need to adjust the needle clip accordingly.
 

Sams65

New Member
Apologies for the lack of activity as of late - finally getting back at it.

While the head head was off, I did a fluid leak test by pouring gasoline into the combustion chamber. The valve seats started seeping almost immediately. (this was with the springs installed) Here's the weird part though: With the engine assembled, using an actual leak-down tester, it only registered about 1-2% leakage. (this was on a cold engine) These are with brand new parts (head and both valves) The head was NOS and had some surface rust on the seats which I cleaned up with WD40 and a scotchbrite pad. So not sure if some micro-pitting could have contributed to the leaking?

Not sure what to make of this - I have a local shop that can cut the valves/seats for a reasonable price so will likely take that route.

In the meantime, I'm looping back around to the carb... After test running the engine and removing the intake tract (from carb to head), multiple drops of raw fuel came dripping out. Contextually speaking, if compression was poor, or spark was weak/mistimed, I would assume the engine wouldn't be able to light such a fat mixture. We're talking a lot of raw gas making its way into the combustion chamber. (unless I also have an air leak :cautious:)

And with liquid gas sitting in the intake, the logical place would be to look is up the path to the carburetor. No?

Speaking of carbs, another part I just realized that was never replaced was the slide. I've tried a couple of them, but both used. I would assume worn out slides usually lead more towards a lean condition, but I might order a new one just to rule it out.

To recap:
  • Compression tested around 135psi (cold) / leakdown numbers OK
  • **With head removed / solvent test: valve seats do leak**
  • Spark timed correctly to F mark, advances at two lines (II) mark on flywheel
  • Points gap in spec
  • Carburetor: All parts *except* for throttle slide replaced
This is starting to get stupid. Thanks everyone for the continued suggestions & help. (and patience)
 

Gary

Well-Known Member
Frustrating I'll bet is an understatement.... Before I'd cut the valves I would try laping them,you can do that yourself easily. I have included a old picture of my S65. It had parts of 2 engines to make 1 useable, I hesitate to use good because it was very low budget, sometimes even old gaskets were reused. One carburator had a slide so worn it's chrome was worn down to the underlying brass. It still ran pretty good though. In the end the engine was pulled and the rest was set out for garbage pickup

S 65 10-73.jpg
 

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69ST

Well-Known Member
135psi might be a decent number. Compression gauges can be notoriously inaccurate with displacement this small. If this is an NOS head w/new valves (or NOS), I'd try lapping the valves, before cutting the seats. As long as you can reach uniformly solid metal with the contact band close to being centered (vertically along the valve face) and no more than 1.5mm wide (.8-1.25 would be better), you should be good-to-go. I leak-test using Brakleen, it'll find gaps too small for gasoline. IMO, valves are sealing properly when no Brakleen gets past the valves...using thumb pressure to hold the valve tight against the seat. It's a high standard...and...with new parts, sometimes valve sealing will improve with runtime.

As for the liquid fuel you found, are you 100% certain that wasn't a result of fuel slosh + spillage from removing the carb?

Don't be fooled by an engine that will fire a rich mixture when cold. You know how pig-rich the mixture gets with the choke closed? Well...it's just as rich when it's needed to cold-start. The explanation is basic...only gasoline vapor burns. When the engine & fuel are cold, only a small fraction of gasoline goes from liquid to vapor state. Once up-to-temp, far more of the fuel vaporizes and the mixture goes truly pig-rich. The same volume of liquid gasoline inhaled can "act" very different due to temperature variations.
 
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