Stumped. Won't start

Hi all,

Thank you in advance for your knowledge and advice about these bikes.

I've bought myself a bit of a Frankenbike. It's a 1983 XJ650 Maxim engine in an XJ750 Maxim frame.

Can't get it to start but the starter turns over.

Here's the facts:

-My compression cold is 125, 108, 115, 125. Thats the throttle wide open but the engine hasn't run so it's not a very true picture. Or is it too low and that's my issue right there?
- I just did the valve adjustment and everything is in spec.
- I've tried two sets of carbs that I know work on other bikes.
- I just did an oil change and there is no fuel dripping into the oil.
- Fuel and vacuum lines are new.
- The fuel tank is full.
- I'm running an inline fuel shut-off valve in addition to the petcock. Fuel is definitely flowing through that.
- I'm running an aftermarket and transparent in line fuel filter. There's a tiny bubble in it that pulses when I turn the engine over.
- It has strong spark on all four cylinders.
- I've tried spraying carb cleaner into the carbs when turning it over.
- I'm running K@N pod filters and I've tried starting it with them on and off.
- It has a larger battery, normally assigned to the XJ750 but this is an XJ650.
- I've tried several different CDI's and there doesn't seem to be an issue with intermittent spark.

I believe I had it running once a year ago but I can't recall.

Any advice is much appreciated. I'm totally stumped.

Cheers,

Aaron.

 

It would be difficult, because the leads are different lengths, but is there any chance you have the plug caps connected incorrectly? I.e. swapped 1 with 2 and 3 with 4? Or has there been any rewiring that could have resulted in the connections to the coils having been swapped?

The 108 is concerning, but shouldn't prevent it from starting.

The pods are definitely going to make things more difficult.

Are the plugs getting wet?

Not sure about using carb cleaner as starting fluid. Maybe that works... I've never tried it. Normally I would use propane, but you can't do that with pods. Maybe try some proper starting fluid instead.

 

I disagree with the stuff about pods - it should start with or without, leave them off for now. When you say you have spark, I assume that's with four plugs removed spinning her over? The trouble is if the battery voltage drops due to starter load, you lose that spark. Try the spark test with a spare plug, with all four plugs installed.
If no spark get a set of jump leads and a car or car battery.
If you're happy with spark, give it full "choke" and see what happens - if it still doesn't start pull the plugs to see if they're wet - if somake sure it's fuel!
If your plugs are dry on full enrichment it will never start, and you have a ca rb problem. I would go with the propane test or use instant start - ether.
One other thing - make sure the plug gaps are good and they're clean!

 

I've done that in a pinch when I was out of starting fluid. Used it to see if an engine would fire, not as a starting aid though.

Are the cams timed back in correctly after the valve shim check/change?

 

Just thowing this out it is possible the wiring harness for the 650 could be different than the 750 ,the TCI could be different , you may have to compare wiring diagrams .

 

The 750 wiring harness does have differences, but nothing that would prevent the engine from starting and running.
The TCI is the same.

 

If the plug wires are all in the correct position, then I'd suggest swapping in new plugs (or plugs from a running bike). It is highly unlikely that all four would have this problem, but it is entirely possible for a plug to be fine resting on the head, but not fire when under compression.

I would also crack the float bowl drains and make sure that fuel is reaching all four bowls. It's not all that uncommon to have an air buble in the fuel transfer tubes on the initial fill. Cracking the drains allows that bubble to move so fuel can flow.

 

You guys are bloody amazing. I see some great advice up there.

I'll let you know what I come up with when I get back to my bike this week.

 

I am here to lift your stump...

Maybe.

All the above.
I would also add a focus on the battery and it’s voltage when cranking. Measure the voltage at rest and then when cranking - report back. Also consider going through all electrical connections and clean, die-electric grease and retighten them. That made an amazing difference for me.