83 Maxim Suddenly Won't Start

Hasty

1982 Maxim XS400
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After some great advice on here, I had solved my problem with leaking "gas" and got my bike idling the best it ever has. BUT then I tried to take it around the block, it died halfway and now it won't start. Looking for ideas on what I can check to try and track down my new issue. Relevant info:

- When I hit the starter, it cranks and sounds like I'm getting combustion, but won't catch and start.
- Compression is in spec (142 psi on the left, 148 on the right)
- Valve clearances are all in spec
- Carbs have been disassembled and cleaned several times while tracking down my last issue and once after this new issue started. They've got brand new diaphragms and float needles. Idle circuit appears clean when I blast cleaner/air through it
- Battery and spark plugs are both brand new and I have spark on both sides (attached a spare plug to the boot, touched that to the plug in the engine, saw spark across the gap)
- Idle mix screws are 3-1/2 turns out from seated

Before now, I had never had any problem at all getting it to fire up (all my problems came once it was running). What's the next thing I should be checking to get it to start again?
 
I agree with what Jared said. First check for a fuel delivery issue to the carb. Verify you have flow from your petcock to the carbs then that you have the correct fuel level in the carb float bowls (use some clear 1/4" (6mm) tubing attached to the bowl drain and visually verify the level in the bowls.)
 
lol @Buddha definitely a good one to double check! I did confirm that there's plenty of gas in the tank. Chrome and Jared, it's good you brought up the fuel levels because I'm actually not 100% sure I've been measuring them from the right place. The manual says 3 +-1 mm from the "mixing chamber body edge" so is that the split between the float bowl and the rest of the carb body (red line in the photo), or the bottom of the ridge where they fit together (blue line in the photo)?
 

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Oh also I rebuilt the petcock a couple weeks ago so I can confirm it flows with vacuum on RES and ON and freely on PRI. I put an inline fuel filter on it too so I can see the gas moving through that
 
lol @Buddha definitely a good one to double check! I did confirm that there's plenty of gas in the tank. Chrome and Jared, it's good you brought up the fuel levels because I'm actually not 100% sure I've been measuring them from the right place. The manual says 3 +-1 mm from the "mixing chamber body edge" so is that the split between the float bowl and the rest of the carb body (red line in the photo), or the bottom of the ridge where they fit together (blue line in the photo)?

That's a question for captainchrome, he seems to know a lot more about it than I do
 
I think it is the red line on your carb as it is the joint you see from the outside. I think your fuel level is too low (much better than being too high, so good on ya!).

If it were me, I would set it 3mm below the red line and try it, but I would also monitor carefully to see if I get any of the symptoms of too high a level (fuel coming out of the air filter joint, rising oil level in the crankcase, smell of gas from the breather). You are on the right path, just be careful and try it. If this isn't it, you will know pretty quickly.
 
Awesome thanks, I was away over the weekend, but should have a chance tonight to try and raise that level a bit and see if it helps
 
Life got in the way for a bit there and I didn't have time for wrenching, but just got back to it this week. I ended up getting a carb rebuild kit from MikesXS so I have the float needles AND seats now and my fuel level is up to where it should be on both sides. Still no luck starting though. Possible it's the starter motor?
 
@Kitchi, yep battery is fully charged. When I turn the key, the green neutral light and the red light on the cluster come on along with the headlights. Then when I hold the ignition button, the bike cranks for as long as I hold the button, but never catches and starts
 
when you say the starter never catches do you mean that it dose not turn the engine over or the engine just turns over and never starts
 
As far as I can tell the engine is turning over, but not starting. Gas is getting pulled through the petcock and exhaust is coming out the tailpipe so I assume that means the engine is turning, right?
 
The engine is turning over.
Seems you had an over fueling issue with your carbs I would suggest you change all your spark plugs even if they are new as they are probably fouled.
you might be able to take them out and clean them to solve your issue .
FYI after you change them or clean them don't be surprised if you get some back firing out of your exhaust and your bike might smoke for a bit until all the fuel us burned up. You probably have a build up of raw fuel in them.

Funny thing I am working on a Maxim 650 for a friend of mine and he also had a over fueling problem. this is exactly what i had to do to get his bike running.
 
Well I'll be damned. Put in some new plugs (after drilling out a bolt that I stripped while checking the starter motor. Can't ever fix a problem without creating a new one...) and the bike started right up! It idles now and I even took it out for a 5-10 minute ride with no issues. Needs some tuning, but it's running the smoothest it has since I got it. Thanks so much @Kitchi for the suggestion! I never would have thought to change the spark plugs since they're so new, so you saved me hours of headache checking other stuff
 
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