79 ATC90 no spark - timing chain off?

[MastaFlyMason]

I just rebuilt the topend on my 79 ATC90 and now I have no spark. Set the valve timing, and points gap. When I was assembling the topend at one point the cam chain dropped into the engine and I had to fish it out, would this mess something up? Like now my flywheel T and F don't line up the way they should and that's why I don't have spark?

[Devilsclaw]

What do you mean they don't line up like they should?

The cam lobes should be pointed towards the crankcase, valves should bothe be loose, mark on cam sprocket lined up with notch on opening, piston at TDC and T mark on rotor line up with notch on stator. If that is all correct then it is timed in relation to valves and piston. Bet you are 180 off.

[MastaFlyMason]

piston at TDC and T mark on rotor line up with notch on stator

What do you mean by this? Can you go into further depth

[MastaFlyMason]

Nevermind I know what you are talking about to line up the T yes it is lined up. Ignition timing is set, valve timing is set, points gap looks good. Wiring all checked out. What else could I check?

[hoosierlogger]

The timing chain has nothing to do with you not having spark. If your timing chain was off and everything else was correct, you would still have spark, just not at the right time.

[MastaFlyMason]

It doesn't seem as if any voltage is coming through the stator. I can hold the black wire and pullstart it and I don't get zapped. What would cause that?

[coolpool]

Now I'm a little worried that your troubleshooting the electrical by "feel". Do you have a manual and basic tools like a analog volt meter? I say analog because the digital ones don't seem to react fast enough to sense the quick pulse.

[MastaFlyMason]

I have a digital voltmeter no analog

[hoosierlogger]

I should rephrase my previous post, the only way a timing chain can have any effect on you not having a spark, is if you forgot to put it in. You have something else wrong in your system. There is something you forgot to hook up, or hooked up incorrectly. The timing chain will only dictate when you get your spark. Hence the name.

[MastaFlyMason]

I should rephrase my previous post, the only way a timing chain can have any effect on you not having a spark, is if you forgot to put it in. You have something else wrong in your system. There is something you forgot to hook up, or hooked up incorrectly. The timing chain will only dictate when you get your spark. Hence the name.


OK i've checked my points gap and ignition timing and they look to be perfect. Is there anything else I should check? I might just put the damn thing on craigslist I feel like i've checked everything

[MastaFlyMason]

OK I poked around with a multimeter and found a shorted wire and finally got it fired up and running. Almost there, but now I have one last problem. When I start it up it doesn't want to run without the choke on. I'm assuming that would be a lean condition. I checked to make sure there weren't any air leaks and I'm sure there aren't, is there anything else I could check? I might just buy an eBay carb and call it a day, I'm sick of messin with the damn thing

[MastaFlyMason]

Can I use a 110 carb if I get a new intake manifold?

[coolpool]

Does it run better or the same as before the teardown? Stick with your stock carb. Clean it thoroughly and check the float height. Set your air/idle screw to factory setting too. BTW there's no guarantee the eBay carbs work any better; and it will need to be cleaned too before use.

[86125m]

I just have one thing to say there is no such thing as a 79 atc 90. in 79 they switched to the 110. so you either have a 77-78 atc 90 or a 79 atc 110

[MastaFlyMason]

My mistake it is a 77. I just putted around on it today and it was running ok at first but then it started bogging out and backfiring out of the carb and exhaust. I do not have the stock intake, I am using an aftermarket eBay cone air filter. I thought I was running lean but I pulled the spark plug and it looked totally black so I'm not sure. Would backfiring be from a rich or lean condition?

[86125m]

Those cone filter do not work right out of the box with these three wheelers you have to jet your carb accordingly. To run correctly with stock jetting you have to have a filter like an uni or the original filter with the stock box to run correctly. This is most likely why your bike is not running right.

[hoosierlogger]

Cool you got it running!!! What was the problem that it didn't have spark?

[MastaFlyMason]

It ended up being a wire grounding out on the engine because the shielding was chewed up. Poked around with the multimeter and got it all sorted out. Does anyone know what size the stock jet sizing is? I don't see it marked anywhere. Are Keihin jets universal? Like any Keihin jet will fit? I'm planning on buying the next two jet sizes and trying those. Thanks!!