Three system failures

[NorazDad]

Hey Guys
This for us "old pensioners" you know who we are...
Just to review: 81H, HHB PMA, pamco, E adv, leds all around, vdo perm volt meter, ko, no relays or switches other than ignition and run. Rebuilt top end with Mikes jug kit 500mi ago.
Story: Went for a hundred mile run. Some through towns and neighborhoods some on country roads at 60 mph @ 3800rpm. Running great. Stoped for a cigar and a view of a river. Then breakfast
After breakfast we took off with intention whereby my bike died on the way out of the parking lot. I noticed that I had failed to switch the petcock on. Tried to kick it, no go. I looked at the glass fuel filter and it was dry.
Failure one. I had to bleed the carbs to get gas to flow. Must have been airlocked.
Got gas...hooray.
Failure two. I noticed that the right side carb was partially dislodged from the manifold. Yes there was a backfire when I started it after breakfast, but I thought nothing of it...dumb. So I loosened the manifold clamp and worked the carb back in place and tightened it.
Then I kicked for twenty minutes. Eventually I thought that I was flooded. Didn't have a full road kit, so I couldn't pull the plugs to check their wetness. Never again.
Finally I called AAA. I have RV + 100 mi free tow. Great deal.
While waiting I thought, "when it doesn't start first kick it has to be ignition" then I decided to check the ignition fuse and there we have it
Failure 3. Blown ignition fuse.
My friend ran and got me a pack of 7.5s
Each one blew as I checked as many connections as I had fuses
Then the wrecker came
So now I am fixing to figure it all out
I'm thinking it is in the headlight jug where I wired my volt meter. Must have left something exposed. If you saw my post on initial installation you may have noticed it was sketchy install at best. I will build a proper mount this time. And I am going to clean up all connections in the headlight jug.
What about the backfire dislocating the carb? It has happened before. I will re check timing once I get it started again. But the last time it happened, I rechecked timing and it was spot on.
The bike runs great. Idles at 1200 all day and it is strong through the whole power band with only a little jitter around 3200rpm. Never been much above five k though.
Well there you go.
Questions?
Admonitions?
Head shaking?
Ran great before
Will run great again...but could use a little discussion
Thanks guys
I know only the retirees will have the time to read all of this so have a go. I hold you in the highest regard.
Thanks
Rob

 

[TwoManyXS1Bs]

Oh, man. Today just wasn't your day.

- Do you have one of them demon-defying bell things?
- Did breakfast weigh-in at over 40 lbs?
- Did you forget to take "old service station" pics?

Karma stuff.

Sounds like you need to isolate the "blowing fuse" down to one item. Maybe the coil, maybe the ignition?

Edit: Bleed the carbs to get gas to flow? That ain't rite...

 

[mrtwowheel]

Do this when fuel line goes empty, open the gas cap and blow into the tank. It shouldn't take much pressure to get the fuel to flow again. Don't inhale the fumes, that will make you stupid.

Scott

 

[retiredgentleman]

Are you using a capacitor, in lieu of a battery? That might explain the back fire.
Using LEDs with a PMA is a bad idea. The regulator will have a very hard time to prevent high voltage. If you plan to keep the PMA, then install a 55 watt incandescent headlight and an incandescent tail light as well. Going down the highway at 60 mph, your PMA is producing 200 watts, but your bike was only consuming 100 to 120 watts. The regulator is heating up and may burn out.

High voltage may have damaged the ignition.

If you want to use all LEDs, then the stock alternator/stock type regulator/battery is the way to go. With the stock charging system, it has the ability to reduce the alternator output to match what the bike is consuming. A PMA can't do that.

Never heard of an airlock in carbs.

 

[5twins]

I think an occasional backfire out the carbs is kinda normal for these. It happens mainly when the motor is in the "gray" area between hot and cold, at least on mine anyway. I've learned to look down and check both carb mounts when it happens. I've popped my carbs out a couple times already.

 

[mrtwowheel]

Yeah, like I've said before, you haven't joined the XS650 club until you've backfired and blown a carb off.

Scott

 

[retiredgentleman]

I've never had a back fire or a carb pop out of its boot........................seems abnormal to me.
Nothing surprises me anymore, when I hear these PMA tales of woe.

 

[mrtwowheel]

I remember an article in Cycle magazine. The guys were intentionally causing backfires on different bikes. They really liked doing this while riding through the city, and especially when riding between tall buildings, like it was much more fun when there were other people to hear it. Some bikes were easier, by just flicking the kill switch. I think the 2 strokes were louder. Those guys were so influential in sales that they got as many test bikes as they wanted, they even disassembled any test bike that they wanted to.

Scott

 

[Bob Kelly III]

LOL I remember My Dad being Hopping mad at me one time when I was playing with our D2- gas powered crawler...it was hand crank and magneto powered ignition and I was adjusting the magneto back and forth and would get the loudest ear shattering back fire if i went too far on one direction, he came all the way up to the barn to yell at me saying what the hell are you doing ? are you trying to destroy that thing ? every time it backfires it's like taking a sledge hammer to the top of the piston ! I told him I didn't know that and I was sorry that I wouldn't do that any more.... and that seamed to satisfy him and he wondered off... ( I think it woke him up !) but I've always remembered that
and when I hear a back fire I cringe not because of the noise but because the possible damage it just caused !
about 10 years later a VW and I had a go around... I was driving it back to the ranch when all of a sudden it started backfiring and lurching
at the same time.... I killed it and popped the distributor cap and the points screw was gone..... so I left it there and walked home and when Dad asked why the VW was down the road I told him it was backfiring so I killed it and walked home... he nodded and said are you going to leave it there ? I said no , I am heading down there with some tools and I'll bring it back if I can.... about 4 hours later I had it home... the points screw was underneath the points plate and below the vacuum advance stuff.... I had to pull the distributor turn it upside down and shake the shit out of it to get it to fall out...... then put it all back together , timed it with a trouble light and it fired right up and ran like a top.....
Upon my arrival at home Dad said with a silly grin on his face What did you forget ? I said nothing ...for once ! LOL and I explained what went on, then he said... Oh so you did forget something ? I gave him a puzzled look, he said last time you adjusted the points in that thing you forgot to tighten the screw that holds them points down ! ..... he had me there ....and he was right too ! LOL
.....
Bob.......

 

[gggGary]

I've had carb removing backfires on points bikes, but nary a one so far on the 79 survivor, none I can remember on pamco bikes either. Darned royal star venture has yamaha's convoluted "anti pollution" anti misfire system that produces constant decel backfires. WTF! The forum norm is to remove the whole mess, that cures it. prolly will one of these days.
Just got a wood splitter that needs a blow on the gas cap to start, then runs fine. Figure a few tanks in, it will be cured.

 

[mrtwowheel]

I have 2- '81 CB750C s that have the vacuum petcock units removed, this makes for a very short fuel line with not much down hill to the fuel lines. When the main runs out and is switched to reserve there is almost always an air lock, half a breath blown into the tank gets the fuel running again. At the first set up I had the reserve so that it worked great at 70mph, I would tell the wife that we just ran out of gas, she couldn't even notice, not sure what the difference is now. I think a smaller filter with 90* would fix this, but I can't find one that is 5/16" only 1/4". Yeah, I should fit the small 1/4" filter to these two bikes.

Scott

 

[NorazDad]

Ok, I agree with RG. There was no failure in the gas line. As I was assuming it was not starting due to flooding or lack of gas to begin with is absurd. Once the bike kicked over, the natural vacuum process would have begun. The bike was not starting due to an electrical issue and therefore there was no draw on the tank.
I'm glad to be baptized into "the backfire blew the carb off it's boot club". Now to prevent it and make sure I always check. I did notice that the vacuum hose on the side that blew off had separated from the nipple, however. Whether that was what caused the backfire, I don't know or if it came off when the backfire occurred. Don't know, but I will secure that hose a bit more robustly.
On to the isolation of the short...