Petcock affects start-ability

[VFan]

Last week I could smell some gasoline, days later I could see a leak originating from the petcock down the vacuum hose to the manifold intake. Two days ago the leak increased slightly and since then the RJ has been very difficult to start, like 15 minutes to finally get going. By chance, I happened to have an extra petcock so I swapped them out and now presto, I'm back to instant start first touch of the button.

What's going on? I wouldn't have ever guessed that a slight leak would affect start-ability of the RJ. I have a clear fuel line so I can verify that there is free flow of fuel to the carburetor with no air bubbles. Other then coinciding the two changes of bike behavior I never would have guessed the petcock as the source of my starting woes.

Does this make sense to anybody?

[fiat-doctor]

Just a guess, but perhaps fuel is getting into the intake from the small vacuum line to the petcock?

[davexz]

Or if there is vacuum leak in the petcock then that cylinder would have a vacuum leak.

[kwells]

replace the diaphram and you'll be good again.

[Oz Vision]

I think the petcock may be the cause of my hot starting problem. After discounting several other possibilities, I swapped it for the grungy one off the grungy Vision I bought last month and it seems to have worked, although still to road test. I dismantled the original petcock - the diaphram and o rings were not obviously shot, but the fuel hose elbow was loose in it's housing and came out with little effort. How is it supposed to be held in place?

[Lucky]

its a press fit

[Oz Vision]

I think the petcock may be the cause of my hot starting problem. After discounting several other possibilities, I swapped it for the grungy one off the grungy Vision I bought last month and it seems to have worked, although still to road test.

Nope, it failed the road test, so it's not the petcock.
Starts fine when cold, runs fine, idles at 1100 but will not restart when turned off at running temp. Leave it for 30 minutes and away it goes like nothing is wrong. I have cleaned carbs twice, checked float height and levels, can't find any vacuum leaks. Stator and reg/rec test ok but perhaps I need to look at them again.
What components are likely to fail when hot, but work when cold??

[Lucky]

when you say it won't restart, what do you mean? will it crank at all? if so, does it crank fast or slow? are you cracking the throttle when you try to restart hot?(you shouldn't, no choke either)  more details, plz, describe what happens...

[Oz Vision]

It cranks and cranks but is slow. I do twist the throttle but have never used the choke - warm climate. There is the occasional pop which sounds like fuel igniting (guess that suggests it's flooding - maybe the whole issue is that simple?. I had convinced myself that it was getting too much air). Volt meter drops to 9 and 8v momentarily when cranking. Battery is good, 12.6v at rest. I also have a brand new one that I have tried but still cranks at the same rate.  There are frequent kick backs from the starter. Starter was dismantled, mitre undercut and new oil seal installed 2,000 klm ago. I installed a set of Tiger's cables at the same time. When bike is running the voltmeter sits around 14.2v.
If left for 20 minutes or so, it will start!

[Lucky]

Volt meter drops to 9 and 8v momentarily when cranking. Battery is good,

doesn't sound like it, the TCI needs about 10v to fire (on a 12v system 9v is a 25% loss)
I would start by checking the battery. basics first.  check the water level. if you can, do a load test on the battery. but your basicly doing a load test on it when you start it...
Sounds like you have a weak cell or 'open hot' in the battery...

[VFan]

I would start by checking the battery. basics first.  check the water level. if you can, do a load test on the battery...

As an aside question. Anyone have any opinions on the accuracy of conductance battery testers?

Kent

[Oz Vision]

Thanks Lucky, but still no go.
Changed over to the brand new battery last night. Started then and started fine this morning - dropped to 11v-10v and fired within 2 seconds.
Rode to work -15 minutes, switched off,
try again, crank is still slow, voltmeter down to 8v and no start!
Wait 15 minutes, try again - dropped to 10v and fired.
Turn off, try again immediately - failure! Down to 8v again.
Waited a further 30 minutes and it started.
As suggested, I am no longer twisting the throttle.

[Lucky]

I'm going to preface this post by saying that often times a problem isn't just one thing, but may be a cumulative problem of 2 or more things, especially on a 30 year old bike.  don't discount the 'minor' test results you encounter.

the fact that your dropping voltage way down on a hot restart suggests a couple of things.
first, double check your charging system. run the FULL electrex fault finding chart (sorry, Electrosport. i still refer to them by their old name)  don't skip steps.

second. don't discount the things you've already repaired/replaced. cables/wires, etc. You have a problem, it has to be somewhere.

third, do a voltage drop test & post the results.

one other thing just struck me:  do you know that if you put the key in the bar lock position, & go just a little further, you turn ON the parking lights?  could you be doing this & draining the battery?

[kwells]

how bout vapor lock?

[Rikugun]

Anyone have any opinions on the accuracy of conductance battery testers?

For a lead/acid cycle battery I think a hydrometer is a more cost effective tool. A battery "on the way out" can have seemingly good voltage - especially right off the charger. A quick test of the battery solution's specific gravity will tell you if the battery is viable or not. Even a low cost, bike specific sized tool like this can be a powerfull diagnostic aid.

http://www.batterymart.com/p-ez-red-super-compact-battery-hydrometer.html?utm_source=Google&utm_medium=Base&utm_campaign=ComparisonShopping

[JohnAMcG]

I dunno, I have never used the specific gravity tester, it hangs on the wall.  Pops has every tool ever known.  The load tester is just faster, easier, and gives a real idea of how it will perform under load conditions.  I used it to check tigers cables vs my old ones with the starter on the bench.  No load on the starter and had a clamp type amp meter on the wires.  Old one drew 21 amps, tiger cables pulled 18.  I am getting my two tests mixed.  I didn't check voltage drop over tigers cable with the load tester, but got no noticeable voltage drop on my old wire connecting the load tester to a good car battery.  Even while really putting a heavy load on it 200+ amps.  Anyhow, just my two cents worth.

[Rikugun]

I have never used the specific gravity tester, it hangs on the wall

Zero experience with it yet quick to dismiss it's value.  ???  I do understand everyone uses what they are comfortable with though.

I've used both and find load testers can be ambiguous - especially ones with a fixed load and a pass/fail gage. They will give false readings when used in applications outside their intended amp load range.  For the casual enthusiast, the purchase of an adequately sized, clamp style amp meter and a decent load tester may be daunting compared to a $5 hydrometer. Then there is the use of the tools and interpretation of the data. You admit yourself to getting your two tests mixed up.

There is a place for all the great tools out there but not everyone has a pops with every tool known to man. And I understand load testers, clamp amp gages etc can be used to diagnose things other than battery health. But, assuming you allready own a VOM - if you have a bike you should - I stand by my recommendation to add a hydrometer as an effective and lower cost alternative for testing a battery's health. Just my 2 cents! ;)

[JohnAMcG]

You are right, data interpretation is the key.  Once you find out that your acid is within spec, or not, there is not much data to interpret.  You just hang it on the wall and upgrade to a sealed agm battery.  I know I am spoiled as for tools at my disposal, but that doesn't make me a bad person. 
The clamp meter was actually very reasonable at harbor freight, about 50 bucks if I remember, and also has test leads, volts and ohm reading etc making it a very versatile diagnostic tool.  I still have one of those fixed resistance load testers, and it has been very reliable for decades.  The new one has variable load, volt and amps guages.  If just looking at batteries you can set it to the cca of the batter and check voltage, or set it to what your bike actually draws while cranking and see what the voltage does.  Or if you have a static one, you can do the math,  either way, there is a wealth of data to interpret. 
The question was asked about the testers, you already posted about the gravity meters.  My experience is with the other, and that's why I put the disclaimer of having never used the gravity meter.  I didn't mean to slight your method and believe me if I dismissed its value, it wouldn't be on the wall.  That space is at a premium. 
Perhaps my migraine put a bad tone on my original post and caused me to mis interpret yours.  Although to me, recommending a specific gravity tester to someone asking about load testers is  like if someone wanted to know what a good toothpaste is and you tell them floss.  -JM

[Rikugun]

I agree 100%! Cavity free teeth are useless if they fall out due to gum disease. Floss after every meal!  :laugh:  :laugh:

And in the interest of accuracy, you brought up DC load testers. VFan asked about conductance testers.   Either way, I'm guilty of offering floss where he asked for toothpaste. ;)

[JohnAMcG]

Yeah  :) :)  I don't know much of anything about those.  I think they put an ac current into the battery, and measure what comes out.  Plus side is they will test a dead battery or fully charged all the same.  When I take my battery back to aitozone they put it on there, last two times the battery was toast but their test said it was good.  They said they will swap it regardless, but have to do the test.  That is the extent of my experience with them, so for a couple hundred dollars, I  am skeptical, and would sooner pull the hydrometer off the wall.   ;)
On an unrelated note if you think you got it bad look up coital cephalgia, and you'll know why I am so cranky.