Moby 50v Knocking/Pinging and losing low end

Have a 50v w/ sha 15.15 (65 jet), 32:1 oil/gas, ported/case-matched, stock exhaust, b9hs, stock timing, 2-ball variator, decked head/smoothed cylinder top. Had to tune the bike after porting, thus the 2-ball and decked head.

Two issues here, sorta related maybe?

1. After a good warm-up, the bike loses it's low end umphh, b9hs is all they had down at kragen or 1977. My brand new b9 was a bit dark after only a quick ride, b10 I'd have to down-jet quite a bit.

2. At full throttle it makes a knocking/pinging noise. I just decked the head. Not too drastic, I got it so the lip around the squish zone was just about blending into the concave part of the head. Smoothed down cylinder and head and bolted it back on without a head gasket. No air leaks, carb-cleaner-tested.

I tried 91 octane as per Elliot's recommendation, but it makes no difference. Elliot said timing might also cause it to knock. The timing on this is "stock," as in the magneto had never been removed before I got the bike, so I assume it's stock. Should I adjust the timing? I've got a lot of experience timing my 103, but never delved into the moby so I'm not sure what to adjust away from stock given the porting and decked head.

Hoping to figure these two things out, they're the only problems holding me back from saying "i'm done" (for now). Thanks.

Re: Moby 50v Knocking/Pinging and losing low end

correction, i'm running 89 octane.... the dude before me pumped 89 into his car, so I may not have actually gotten one whole gallon of 91.

Re: Moby 50v Knocking/Pinging and losing low end

whats the compression after it warms up?

Re: Moby 50v Knocking/Pinging and losing low end

Only about 125-130 I think.... but my gauge totally sucks, it doesn't hold compression, so it's probably a big higher.

Seems like you'd need nearly 200psi to have pinging problems.

Re: Moby 50v Knocking/Pinging and losing low end

definitely check your timing dude, it can go out of adjustment real easy. i used to go by the "its never been touched so its fine" persuasion until i realized in many cases that just aint true.

Re: Moby 50v Knocking/Pinging and losing low end

The Manual says stock timing is 2mm BTDC. I'll have to check, and if it's still 2mm BTDC, maybe bring it back a bit?

How do you tell when the points begin to open on a moby when you can't see inside the flywheel?

Re: Moby 50v Knocking/Pinging and losing low end

You have to take off the magneto. Kind of a bummer.

Re: Moby 50v Knocking/Pinging and losing low end

oh, you have to remove the whole thing? greeeat.

Re: Moby 50v Knocking/Pinging and losing low end

this is _exactly_ what I was looking for. Thanks to creature Bret back in 04'.

"The timing system is actually very simple and easy to set, once you understand it. There are two holes on your timing cam. They are designed both to hold the rotor in sync with the cam, and to indicate timing. Do this, take a small allen tool and stick the long end in your spark plug hole(allen tool is preferable because it cannot fall into your engine). Then put a tape measure up to it. Rotate the piston to TDC. Note the relation of allen tool and metric tape measure demarcations. Rotate the rotor counter clockwise until the allen tool has dropped 2mm. The two holes on the cam should be exactly up and down, and the points chould not be open, but they should be about to. This is the break point. now rotate the cam clockwise until the two holes are pointing through the axis of the engine(through the spark plug hole). Your points should at maximum gap, .12mm to .15mm. Keep rotating clockwise and when the smaller third hole is throught the axis of the engine, your points should be closed or nearly closed."

Re: Moby 50v Knocking/Pinging and losing low end

The timing cam can still move out of alignment even if the flywheel is still timed correctly. Take the damn thing off and time it for real. You might have crappy points in there, you will not know till you take it apart. Think of it as a learning experience!

Re: Moby 50v Knocking/Pinging and losing low end

oh, of course finny. It was going to happen eventually. Either i'd need to change it for performance or to replace the condenser/coil when they finally go out. There's always a little learning curve.

Surprisingly, the points look fucking great, considering the condition of this thing when I got it.

Having a little trouble getting the cam off, afraid of torquing it super hard.. it's probably never been removed.

Re: Moby 50v Knocking/Pinging and losing low end

OK.... so it's still making those crazy clicking (pining/knocking?) noises at higher throttle--- faster rate when I'm going faster. So I finally pulled my cam and started messing with the timing with the idea that knocking is usually a result of too far advanced timing, right?

First, I figured I'd re-set it to stock. So I followed the advice here and here to set my timing to stock (2mm BTDC, with the holes lining up just as they say).

Starts up first kick, accelerates great, idels fine, but still makes that incessant clicking noise at higher speeds (the sound I'm assuming is pre-detonation/knocking/pinging).

When I set it so the holes line up through the axis of the cylinder at TDC the point gap is at its widest and looks like the right gap by eyeball-- I don't think it's _ever_ been changed. But when I rotate the clutch so the piston is 2mm BTDC the points aren't even close to opening, they start opening when the piston is like .5 BTDC. Is that right?

It's stock, I don't think the flywheel has ever been removed, it never slipped, and the points are immaculate, the adjustment screw is tight, and has probably never been loosened. So it's all stock.

what do I do about this clicking noise?

Re: Moby 50v Knocking/Pinging and losing low end

I mean... if I adjust the points so they start to open at 2mm btdc, by the time the piston finally reaches TDC, the point gap will be HUGE. That can't be right either.

Re: Moby 50v Knocking/Pinging and losing low end

you can just adjust the gap, though. thats what that second screw on the points in for.

Re: Moby 50v Knocking/Pinging and losing low end

add a gasket or two. this lowers the compression a tad. Radio control car trick.

Re: Moby 50v Knocking/Pinging and losing low end

Jerry Franek /

Jaym--what second screw are you talking about? Seems to me you can set the gap correctly and then rotate the loose cam to get timing set at 1.5-2.0mm--the only way to get both correct.

Re: Moby 50v Knocking/Pinging and losing low end

No gasket if possible, I want the compression so I get more low end out of my ported cylinder.

Jerry, the confusing part is the gap is only supposed to be .12mm, and it's supposed to be at maximum gap when the piston is at TDC. If I adjust the point screw so the points begin to open at 2mm BTDC, by the time the piston reaches TDC, the point gap will be well over .12-.15mm

Re: Moby 50v Knocking/Pinging and losing low end

Your cam follower on the points is too worn, thats why your gap is so huge

Re: Moby 50v Knocking/Pinging and losing low end

well, actually the gap is supposed to be .35mm-.40mm, not .12mm, so I'll have to try again.

I doubt it's worn, that thing is solid, there's only like 3k miles at the most on this thing.

Re: Moby 50v Knocking/Pinging and losing low end

yeah, i was wondering if there was suddenly a new theory about points gap or something. i always set mine to about .38mm.

Re: Moby 50v Knocking/Pinging and losing low end

when you set the timing, are you _just_ lining up the holes with the axis of the cylinder? thats a nice rule of thumb but youre basically eyeballing the whole process.

get an analog meter and you can test for continuity between the points and the ht coil (or something like that). you set it up so that as you rotate the cam, just as the points open you will see it on your meter. if you have a meter with a buzzer its even better... less to keep your eyes on and you can _really_ hear when they break. this allows you to determine the _exact_ moment at which your points break. much more accurate then lining the dots up or whatever.

also, you might want to consider dropping the engine, removing the head, and physically measuring TDC and mm BTDC. this is how i do it every time i set my timing, which is rarely because i do it meticulously. this, as opposed to the allen wrench in the spark plug hole method.

the only reason i mention these techniques is that every sloppy method you use to set the timing adds error to the final product... so its worth it to make sure every step along the way is as accurate as possible. some will argue whether or not the allen wrench technique, line up the dots technique, etc are "sloppy", and i do know they are widely used, but it just doesnt sit right with me. if you wanna eliminate variables, you gotta eliminate variables.

on an entirely seperate note, one thing you may want to consider is your wiring and grounds. i wish i could hear this knocking/pinging youre talking about to really say for sure, but i suffered from symptoms like this when i first got my moby. at high rpms, everything would vibrate so much that my spark would cut out and make a pop/knocking sound. imagine the sound made when you run over a dime-sized-diameter rock head on. i use that analogy because thats what i thought it was at first, when it happened about once a week.

i tried to fix this by swapping out novi coils. every time id swap out a novi coil, itd make it better for a while and then itd happen again. turns out it wasnt the changing of the novi coil that made a difference at all, it was the fact that every time i put on new coil, i made sure all the connections were good and the problem went away until they vibrated loose.

i eventually took care of the problem by simpling taking apart the wiring harness, making sure all the connections were squeaky clean, all the grounds were solid, etc. Double ground shit if you have to. sand down areas where rust or dirt or grime has accumulated. whatever you can do to make sure your wiring is tip top.

might not have anything to do with the problems your having at all, just throwin ideas out there.

Re: Moby 50v Knocking/Pinging and losing low end


thanks a lot for the lengthy response, it's very much appreciated.

I think I _may_ have discovered the problem. My plug wire is short, so it was always bent drastically at the novi coil end, well it cracked on the inside of the bend, but I just couldn't tell. I think that sound may be the spark snapping against the metal on the coil. If I touch the coil when it's running I get a WICKED shock.

It's funny, because I used to get that clicking sound when I first got the bike and it eventually went away--- maybe it was the plug wire positioning itself differently and stopping the wire from grounding to the coil.

Anyways... I have to get a new wire going from that to eliminate that variable.

in the mean time, now that I've ruined my timing, I'm also teaching myself how to do that, haha. I think I got it set right... but it might be a bit too advanced cause it's running kinda hot and backfires now and then.

Re: Moby 50v Knocking/Pinging and losing low end

well i cant keep myself from being wordy no matter how hard i try, so you get words whether you like them or not.

there you go, back to basics... plug wires can be an issue on mobies cause the variation of the engine. although, you will probably get shocked if you put your finger too close to any ht coil.

ill give you a little more in depth timing setting help (or at least how i do it, whether its helpful or not) once i get done playing super smash 64

Re: Moby 50v Knocking/Pinging and losing low end

wooh ok. smashed the shit out of mine foes.

anyways how i usually set the timing is, like i said, drop the engine, take off the head. bring the piston to 2mm BTDC (measured and marked accurately!) and keep it there. now set up the meter so that when the points are closed, you get a resistance reading on your meter. preferably you have an audible meter so that when the points are closed it will put out a beeeeeeep. now put the timing cam loosely over the crankshaft and rotate it slowly until that beeping _just_ stops, or the needle drops and you dont get a reading anymore. wiggle back and forth until you find the perfect money spot. then, making sure everything stays as you want it, drive that sucker home with a 14mm or so socket and a mallet. after i get the timing where i want it, i generally cut a hatch mark across the top of the cam and into the crank. when you line the line on the cam up with the line on the crank, thats were you want your timing at. this way you dont have to reset your timing every time you take off/replace your cam or stator.

some say 1.5mm btdc is a bit better for mobies, so err on that side.

Re: Moby 50v Knocking/Pinging and losing low end

try setting your timing and points and then check the timing again after everything's all together.

unplug the two light leads from the stator and hook up a multimeter to the grey ignition wire and the other multimeter wire to the ground (the motor or plate, whatever). That way you can make sure shit's right after it's all together.

your'e running a b9hs plug?

damn girl...

Re: Moby 50v Knocking/Pinging and losing low end

gotta run a b9hs.... the engine heats up and the low-end goes away. that's what elliot and others have recommended.

Re: Moby 50v Knocking/Pinging and losing low end

Jerry Franek /

I think Steve is just right on setting the timing..except for pulling the head.

I think a worn cam follower (maybe it's the original one!) makes it impossible to set both gap and timing to spec simultaneously. I played with this for a long time with two sets of points I got from BJ 3 years ago--he warned me that these Indian points had followers which were too long and needed shaved down.

I think I've spent more time messing with timing than anything else on my gurls.

I think I've never seen any difference between 1.5mm and 2mm settings.

I think I'll get another beer.

Re: Moby 50v Knocking/Pinging and losing low end

Make mine a double and maybe try some 100LL AvGas when you are done.

Higher compression needs a higher AKI 'anti-knock index'

One gallon from the local airport couldn't hurt.

As a test.

Re: Moby 50v Knocking/Pinging and losing low end

i dunno how much you decked your head, but i really doubt you decked it enough necessitate the running of higher octane gas. worth a shot, i suppose, but i really dont think this is the issue.

yea pulling the head is kind of laborious on a moby cause you have the drop the engine, but it is the most accurate way to measure mm btdc, as far as im concerned. well, unless you have a thread-in depth gauge, which is quite possible, but i do not. ive seen quite a few clever diy tools but i havent got around to making one.

sticking an allen wrench in the spark plug hole and measuring it with a ruler just doesnt cut it. too many variables, too many ways to be inaccurate. especially when the precision of your ruler is probably +/- .5 mm anyways.

Re: Moby 50v Knocking/Pinging and losing low end

Yeah, and if I can set it and forget it, it would be worth the trouble.

how bout' something clever to gauge the point gap?

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