1978 XS650 won't stay running

[livetoride21]

Hi Everyone, I have a 1978 XS650 SE.
Bike is stock and has been semi-restored. Motor is fresh, ignition system is fresh, valves adjusted and cam chain adjusted.
I can't seem to get the bike to run off choke.
It will run choked, and run if I give it a little bit of throttle without choke (while cold), but as soon as I give it a small twist it will cough out the carbs and die.
If the bike is warm, it will not run at all without the choke on.
I just epoxy sealed the gas tank as I had an issue with rust getting into the carbs, and did a very thorough cleaning of them. However, I have a feeling there may still be a small bit of rust blocking part of the pilot circuit, and spots to pay special attention to? the small holes by the butterfly were clear last I checked.

thanks!

 

[Guss80special]

I’d say you are on the right track. Clean the carbs really well. Then clean them 3 more times . That’s what I had to do. I have a 80 Special. Different carb, but same issue. I ended up replacing all carb component save for the diaphragms which are in fine shape. Have fun. Might want to get a new tank if it has holes. Imo lots of carb cleaning threads already in this forum. Good luck.

 

[livetoride21]

thanks for the reply! the tank is actually in very good shape. The bike just sat in the back of my father in laws garage for 30 years without being run until last year.
The tank was cleaned out very well, but there was still very fine rust that would break free from time to time and create havoc. Hence why I finally epoxy coated the inside of it with Caswells 2 part epoxy coating.

As far as I'm concerned, if it will run well on choke and modulating the choke, it is not an ignition or valve adjustment issue, it is merely a fuel issue correct?
I'm going to check all the small passages once again and find my trust high E guitar string to clear them out.
I'm assuming it's either one of the small holes in the carb bell of the hole in the float bowl that passes to the pilot that must be blocked.

 

[5twins]

Yes, even though you cleaned the pilot circuit, it can plug back up in an instant. For testing if it's clear, you can start with something mild like WD40. I don't resort to the carb cleaner unless it's really needed. Compressed air is also almost a requirement for blowing the passageways clear. I rarely poke any. Another possibility is really bad butterfly shaft seals. If they're shot, not sealing, and sucking lots of air, that would create a very lean condition. The fact that you must have the choke on seems to be indicating that.

As an indication whether the carbs did get crap in them again, I would drop a float bowl, gas still in it, with the carbs still in place. You can do so using a stubby screwdriver. Look at the gas in the bowl and see if there's any dirt sitting in the bottom.

 

[livetoride21]

alright so I cleaned the carbs once again, and now I can get it to idle, however it will pop at idle as if it wants to die. If i spray WD40 in the carb bell while it's running it will drop to a normal idle without popping. it's really strange. I'm beginning to wonder if my float heights are off as all passage-ways seem to be clear, I'm going to pull the carbs off one more time, double check the float heights and double check the pilot jet air supply is clear. any thoughts?

 

[angus67]

What are you setting the floats to? Should be 25mm

 

[5twins]

Actually, for the '78-'79 carbs, the float spec is 24mm (±1mm). I tried that full range on my '78 (23, 24, and 25mm). It seemed to like 24mm best.

 

[livetoride21]

I have brass floats, so I had set at 27mm. But I'm going to check again, last year when I rebuild the carbs, I had rigged a clear tube to verify level, but I'll have-to recheck.

 

[5twins]

The clear tube check is the best way to verify fuel level. With your floats set correctly, this is what you should find, fuel level about at the seam of the bowl and carb body .....

Your 27mm setting would produce a level that was too low, something like this .....

Let me ask you this - is the bike hard to start? That was the problem with the bike from the above pic. Both carbs had the floats set wrong and the fuel levels were too low. Here's the other carb, not as bad but still off .....

 

[livetoride21]

Thank you for the very detailed reply 5 twins!
I guess I should give the full story now to clear things up.
Last year I rebuilt the engine, carbs, changed all the timing chain guides, and gave it a good tune up after the bike had sat since 1983 in my father in laws garage.
I did about 200 km on it, fighting with rust getting into the carbs from the gas tank. I changed the floats to new brass floats as the old ones were very corroded and changed all jets and float needle/seats. I had originally adjusted the float levels with the clear tube method, but I have taken the carbs apart since to clean rust debris so they could be out of wack now. (I had only checked with a ruler.)
I've since cleaned the gas time a second time with the drywall screw method, vinegar, then acetone and coated with Caswell epoxy coating. No more rust is present.
all passages in the float bowl are clear for the main, pilot and startup circuits.
The bike starts easily on choke with the electric start, however once the choke is turned off, it will idle high for a bit but spit and pop. If i spray wd40 in the carb bell while it's running, the idle will drop to a normal level and the bike can be revved without stalling, otherwise it will stall.

Ignition Timing when last checked was spot on and has not changed since the bike was running well.
Valve adjustment and timing have not been modified since the bike was running well also.

I've also done an ignition tune-up (new coils, wires, caps, plugs and condensor) so I'm sure ignition is good.
Could the timing advance be causing this problem?

With all of the above said what do you think?

 

[livetoride21]

Well managed to get her idling and running well. For anyone that this may help in the future, the issue was the float levels. For whatever reason, at some point I had set them at 27mm. At first when I reset to 24mm the carbs immediately began to overfill and flood our the carb bell, the reason for this was the way I had adjusted the float level. The tang should not be at an extreme angle to the float needle, if it is, it will push the needle at an angle and cause it to not seat proper. Instead, I bent the tang as close to perpendicular to the float needle as I could, then readjusted the actually brass floats to be at 24mm. I then tested the carbs separately by sealing off the fuel crossover and using a clear tube. At 24mm in both carbs, one was perfect (gas up to seam in carb) and the other was overfilling and flooding. Not all float needles are created equal and I had to set one carb to 25mm and it was perfect. Hope this thread helps someone in the future.

 

[gggGary]

Should look about like this.

The bent tangs never end up more than a little away from flat with the bracket.
Float needle springs do get weak and or clogged with varnish.