Topic: Yet another jetting advice thread. 74 550 but there's engine mods.

[Dimitri13]

61mm pistons (592cc 10.5cr)
Webcam 358b camshaft (.330 lift 288° dur).
MReick stage 3 port with port-matched intake runners.
Stock intake plenum with the "velocity stack" boots but a large single air filter attached to that.
Stock coils and points but with HondaMan's transistorized ignition.
Carpy's Yoshimura-style exhaust with the baffle (I use that word lightly) installed.
NGK D8EA plugs (instead of the stock D7EA ones. That's what my parts store had in stock and also I thought it would be a good idea going for a colder plug given the performance modifications)

I can't remember exactly which jets I have in there now but I think I I went up to 105 mains and 42 slows with the needle in the stock position? Or I could just have the stock 100/40 jets in there, Idle air screw is the stock 1.5 turns out.

Anyway, this is the first fire after being totally rebuilt with the aforementioned mods. I didn't have a change to check timing or pull plugs but it was running very lean (about 16.5:1 or leaner) at idle and part throttle but fattened up a bit at more open throttle down to 12.5:1ish. This is assuming my afr gauge is correct but it's brand new and I don't see a reason it wouldn't be. I can also hear pinging/detonation (noticeably different sound than valvetrain noise) which is why I'm convinced it's running lean assuming timing and spark are within reason.

I'll be checking everything I can tomorrow but I'd like to get some input in the meantime, hopefully help me come up with a plan before I get started.

[Dimitri13]

Checked the plugs. They were clean (as in looked like they were never used) and smelled like fuel. I don't know if the fuel bowls filled up overnight and spilled or evaporated into the engine.

Checked valve adjustment, points, and static timing. All were spot on.

After checking my stock I believe I have 115 mains and either 38 or 40 slows (likely 40 because I don't think I'd put 38s in there).

I'm thinking going straight to 45 slows might be my best bet? Leaving the 115 mains in there for now.

[seanbarney41]

hey man...you the man with the wideband.  You tell us.  I can't imagine hearing pinging without being under load unless timing is wayyy advanced.  Perhaps a clear tube check of fuel level in the bowl is in order.  I have not found pilot jet size to make as much difference to idle mixture as a low fuel level would.

Seriously, I am just following along to learn.  Not many have posted successful results of wideband use.

[Dimitri13]

Just opened the carbs, apparently I did have 38s in there. Undersized from stock to begin with.

I didn't think to adjust the idle mixture screws when I had it running the first time so I'll see what those do.

About to get it running as long as the float bowl valve thingies don't get stuck again.

[Dimitri13]

Just got it fired up again. The more i listen to it the more it sounds like an exhaust leak than pinging.

Idles at about 12.5:1 and breaks up a little, varying between 11-13.5:1. When I say idle I mean with no throttle input but it doesn't hold a steady idle yet. I keep having to adjust the idle speed screw because it either starts running away or dying out.

Plugs 1-3 looked normal tan, but plug 4 was noticeably carbon fouled.

I don't know if this helps but exhaust pipe temps are about 550 on 2 and 3 and about 450 on 1 and 4. I can only assume 1 and 4 are colder because they're on the outside.

[Dimitri13]

Okay so static timing was fine.

Hooked up my strobe light. 2-3 is at the F mark at idle, but doesn't really advance at all. 1-4 is at the advance mark (second set of | | marks) and also doesn't advance from there.

So it seems my advance plate is shot? I think I might be reusing the one I had so it's an additional 7 years older.

[Edit] Messed with the points and screwed it up because I misread the instructions since it's been so many years. Basically I put it at the F mark then adjusted the points gap. Good way to scare the neighborhood pets. Fixed it after that.

[scottly]

Sounds like the points cam is stuck. Clean it up, lube it, and re-check dynamic advance.

[Dimitri13]

So after all that fiddling around trying to get the points gapped and timing statically set still couldn't get it right.

Shoved everything out of my head and just followed the gap and timing steps without bias. Got it pretty spot on except that 1-4 showed 2-3 on the plate. Drove me crazy. I did it three more times and still had the same result. Quick Google revealed that I probably put the advance's eccentric cam on 180 out when I cleaned it. I did. Got timing set one last time.

Fired up the bike and I was still reading advanced. Retarding the timing killed the bike. Then I remembered my electronic tach and that it reads twice the RPMs it's supposed to because of our wasted spark ignition system. I forgot about that and was basing the 1200RPM on the gauge as 1200 actual RPM.

Dialed back the idle a bit and it ran alright.

I think I'm still having some ignition issues with the ignition maybe missing? I'm only basing that on the fact that my strobe light wasn't flashing consistently and that the bike is still running a bit rough. Jetting seems to at least be in the ballpark. Once I get the ignition spot on I'll come back to it.