Some diagnostic help please!

[Rick G]

The TCI stops functioning below 10 to 10.5 volts. Most electronic systems do this. When the starter is cranking the engine, voltage will drop below the thresh hold of function , the starter will still crank the engine however.

[Tiger]

Rechecked the battery voltages this evening. 9.8v cranking

This is not enough for the coils to fire up a Vision!!!

                  8) ....... TIGER ....... 8)

[Rikugun]

Wow! What are the symptoms of vapor lock when you are cranking?

I've always understood it to mean the engine cranks over fine but won't start and acts as if it's not getting gas.  It seems that in your case the starter may not be turning over the engine properly when hot. I'd investigate battery/charging and starter health first. If hot starting problems persists move on possible vapor lock causes.

[Jimustanguitar]

I've always understood vapor lock to be when fuel gets hot enough that bubbles form and cause blockages in the tiny carburetor circuits. Is this the same understanding of vapor lock that you guys are referring to?

If so, I don't think that vapor lock is to blame either. I still think that you have a cranking speed, or voltage problem. Could also be idle mixture or carb sync.

[Rikugun]

I've always understood vapor lock to be when fuel gets hot enough that bubbles form and cause blockages in the tiny carburetor circuits. Is this the same understanding of vapor lock that you guys are referring to?

Yup, more or less. Liguid turns to gas due to high temps. Sometimes it's associated with mechanical fuel pumps bolted to the block of older cars when there is too much under hood heat. They are designed to pump liquid not bubbly liquid on it's way to a gaseous state.  :( I'd think the V's pulse pump is located in a prime position to suffer the same problems when the conditions are just right.

[Rick G]

Iain, I am most offended by your avtar! It has no place here. Take it down before its is taken down for you!

[iain]

Sorry Rick G didn't mean to offend more of the riders of vision, of course I will remove my avatar.
As we all know soft porn is a no no and now lets add religion to the list, so my new picture is of a cute wee baby ,
Iain
NZ

[The Prophet of Doom]

That's better Iain.  Who wouldn't like a picture of a cute wee baby.  I particularly like the fact that it has a moustache - not unlike Magnum PI

[pinholenz]

You guys crack me up. All this down under Kiwi humour really must look distinctly below the belt to all the upright folk on the other side of the planet - but I am glad you changed your avatar Iain. I was sad to see Roro's bottom go though, - it was truly a mesmerising work of art.

Back to the topic at hand. Has anyone had a go at soda blasting their carbs? Results OK?

[Rikugun]

That's better Iain.  Who wouldn't like a picture of a cute wee baby.  I particularly like the fact that it has a moustache - not unlike Magnum PI

What!?  :o That's just crazy talk...Magnum PI's mustache laughs at that baby's mustache.   ;D   ;D It does look somewhat familiar though. Charlie Chaplan perhaps?  No, that's not it. Oh well, it'll come to me....

[Rick G]

It seems to me that I have seen  a picture of a fellow  , who looks a lot like that baby , only a lot older . I seem to have seen it in a history book or maybe on the history channel. It will come to me , I'm sure.

[iain]

Rick ,I know who your thinking about , when he got older he was one of the village people .Not sure which one though, my money goes on the Cowboy or the Contruction worker or the biker, and at long odds the black guys at the back

[pinholenz]

Thanks for the advice and tips on dealing with my problems when I started this thread. Here's an update:

1. After going for a run, she doesn't want to restart when she's hot - especially if I stall. The starter really struggles to turn the engine over. It comes up to compression and then stops. If I was starting a Ford Model A I'd say the timing was too advanced. If I leave it for 5 minutes, she cranks over and starts fine. Any ideas what the problem is?

After rebuilding the starter, I installed a digital voltage meter on the horn circuit. The readout was 14.2 at idle but the charge dropped when the engine got warm. I was running on battery only. When the engine was hot, the additional compression/weaker battery meant that she wouldn't turn over under compression. Leaving it five minutes, the battery recovered and the engine turned over OK.

Solution: Replaced the stator with a used Suzuki XS600 G7 stator, and the Regulator/Rectifier from a Suzuki as well. We now have a good charge and battery. Starts easily under all conditions.

2.  Under load, the engine hesitates when I open up the throttle. The accelerator pump is working OK but I suspect that it isn't activating quickly enough? If that is the cause, what's the fix for that?

Over the months I have had the carbs off 4 or 5 times to clean them, replace "o"rings etc. Last time was to clean the idle jet to the rear carb because that cylinder got lazy and  cut out at idle. I was distressed to find that the same thing happened after my last clean. Went away for 10 days on holiday and magically, problem was gone when I came back. Yay. I had read that this sometimes happens with the XZ carbs. I am now a believer.

I thought that my throttle-on hesitation problem was because the accelerator pump wasn't reacting quickly enough when I opened up and it needed adjusting/stronger springs. Then I read in an old post that one member had solved his problem by putting in a WEAKER spring, (from a Biro) on the accelerator pump rod. I.e, the opposite of what I had done. So I have reduced the amount of spring on the pump rod and that has indeed reduced the hesitation. Still not good enough though. Next time the carbs are out I will replace the spring with a weaker one. 

It seems that  the hesitaion is caused by an overly rich "shot" down the carbs and that the weaker spring helps to regulate the rate at which the accelerator pump delivers its petrol.

There's been some great weather here this summer and at last I am beginning to get to know my XZ a bit better.

[Rikugun]

John, thanks for the update. It's really nice when an open thread is revisited and some closure given.  :D Glad to hear some problems have bee resloved and hey, what a surprise - a weak charging system was part of the problem!>  :laugh:  :P Sounds like you experienced some Vision carb magic too which is nice. All bonding moments for sure and how enjoyable the Vision can be when reliability/driveability issues are resolved.  8)

Your theory of overabundant accell pump output is a new one on me.  ??? Almost seems counterintuitive but can't argue with results! ;)  When you change the spring out again do let us know your results. Thanks.  :)

[QBS]

Excellent!  +1

[The Prophet of Doom]

The accelerator fuel stream is barely atomised, and there's a lot of it.  The Yamaha Intake and Carburetor mod kit manual specified backing off the accelerator pump by 5mm.  I think 50mm-60mm from the bend to the nut is the recommended setting.

There are lots of combined causes for stumble:
Check your accelerator stream is a spray, not a jet and that it doesn't hit sides of carb or butterfly
Check float level, and emulsion tubes / jets for blockages
Check round grey air filter and tube for blockages
Check for air leaks in YICS and manifolds
Check carb sync
Check you have a good strong spark
Check your mixtures

If you are getting a cut-out, suspect electrical. 
Is your rev-limiter playing up (can be disconnected), or could be as simple as a loose connector on the crank pickup.

[pinholenz]

Thanks Roro, that's a pretty comprehensive checklist and I think I have most of them covered thanks to advice and previous posts to the forum. I am not getting cutout at any point, she is just gagging when I am aggressive on the throttle, but comfortably redlines in those gears that take me up around the legal open road speed limit.

The two niggles not yet fully ticked off are my accelerator pump settings (strength of spring and length of the accelerator link rod) and  a small butterfly shaft seal leak on my rear carb. This will affect the mixture on that carb, but I am noticing that the more mileage the bike does, the smoother the idle becomes. (Probably improved compression from rings and valves getting comfortable after sitting for years.)

I will work through these two issues then tweak the mixtures and  re-sync.  In the meantime I will try not to beat the traffic at the lights or accelerate to overtake anything faster than tractor on a straight road. I sure feel stupid when it gags for a second like its going to die and then streaks away like a scared cat.

Update: Tonight I adjusted the accelerator rod length. It was easier to do on the bike than I expected. Is the standard measurement from the bend in the rod to the far end, or from the bend in the rod to  the point where the spring begins?

I shortened the rod as far as it would go. Still some hesitation when I open the throttle under power, but it is now more of a gasp rather than a gag. I will keep tweaking it and try a weaker spring than the replacement for the rusty one.

[Rikugun]

For me, installing a new accell pump diaphragm and shortening the rod adjustment made the biggest difference in curing the lag you describe. I'd hasten to add this was after installing new throttle shaft seals which finally allowed for a proper idle mixture adjustment.  :)