Noob Mechanic

[Dregles]

Hi guys,

I got my first motorcycle in August, a '78 XS400, so I've been lurking in here a bit but just signed up. The bike I got had 5500 miles on it and more or less ran fine when I got it. However there are a few small issues I'm trying to get to the bottom of. It dies when idling sometimes. This issue seemed to be getting worse gradually and it happened more after riding for a while.
The other thing is the choke stopped functioning properly a few weeks after I got the bike. Now when I pull it out it pretty much just kills the engine and it definitely won't start with the choke pulled out anymore.
I took the carb apart and everything looked really clean inside. The floats seemed way off so I bent the little thing and got them to around 26mm. I also figured I should check my valve clearances and they seemed to be too tight so I adjusted those. Now it won't start
I don't know what I'm doing and so many things I read assume certain baseline knowledge that I don't have. If anyone can help get me going in the right direction I would be very grateful.
Thanks in advance

 

[JPaganel]

The history is nice, but right now you have one problem - no start. Presumably, it turns over.

So, do the usual no-start checks - air, fuel, spark.

See if your air filter is clean (although, to be fair, to gunk it up into a no-start takes work)
Do you have fuel in the bowls? Do you have enough fuel in the bowls? Check with a clear tube in the drain.
Do you have spark? Are your plugs clean?

 

[amc49]

If the starting issue began with valve adjustment you are likely holding a valve open to leak.

 

[Dregles]

Thanks. There is definitely fuel in the bowls. The plugs look dry and fairly clean. I haven't checked for spark, but I think I understand how to do that now.
AMC 49 what do you mean about holding a valve open to leak?

Unfortunately I don't think I can try starting it again because I broke one of the valve cover bolts So I'm waiting on a replacement part.

 

[amc49]

The valve clearances when set right are very close to zero. Anything closer has the ability to hold a valve open leading to zero compression which will not run at all. Or start.

 

[Dregles]

I'm pretty confident I didn't set the valves too tight. If anything might be in the loose side.

I might just have to go through the carbs for a third time, even though they looked clean from the get go.

 

[JPaganel]

The valve clearances when set right are very close to zero. Anything closer has the ability to hold a valve open leading to zero compression which will not run at all. Or start.

Intake is 0.08-0.12mm and exhaust is 0.16-0.20mm. That's enough for you to feel them wiggle at TDC.

 

[Dregles]

Yeah that's about where I set them. I'm guessing probably need to get back into the carb. I should've done valves first but I didn't want to start the bike after the carb because I was about to do the valves

 

[Dregles]

Also charged up the battery to 100%, .maybe that'll help. Question is should I try starting it with one of the valve covers missing or is that a bad idea?

 

[amc49]

You'll throw oil all over the place.

If talking about the missing bolt only then you are likely OK, but the whole cover off will make a mess.

 

[JPaganel]

Also charged up the battery to 100%, .maybe that'll help. Question is should I try starting it with one of the valve covers missing or is that a bad idea?

Yes, it will spew oil out the adjustment hole. Not bad enough to run the engine dry, but bad enough to make a mess.