Suddenly I have running issues

Flooding on prime could be a stuck float too...

I'd drain the float bowls as well - into a clear/clean container - let it sit so the water has time to seperate... be interesting to see if you just got unlucky and had a bit of crap go through.

 

When I 1st got my bike, I had to build the carbs (also replaced the needle and seatsand foat bowl gaskets)
I couldn't get gas to the carbs and found out about the PRIME position on the petcock. (that got me plenty of gas thru the filter) 8O
Well that bike ran pretty good but I left it in prime, and 2 days later when I got home from work there was a big puddle of gas under my bike (couple of gals. = about $6.00-$7.00 worth of gas just going to waste in the oil and on the ground.) :evil:
I spoke to a friend who knows Yamahas and he told me that the needle and seats on these bikes were never meant to hold the head pressure of the gas in the tank and that PRIME as we now know was only for filling the float bowls.
I would suspect that you have areally flooded engine, probably the oil too, did it ruin the needle valve rubbers? You'll have to pull it apart to find that out.
After going thru my carbs for about the 3rd time I ended up with #3 cylinder really rich I could pull the plug and see gas mist coming out the plug hole.
The way I knew which cylinders were giving me trouble was 1) start the engine and while it was idiling quickly touching the exhaust pipes at the heads to see that they were all evenly heating.... when the other 3 were so hot that I didn't dare touch them I noticed that #3 was only a little warm.
2) I then did the color tune test and found that #3 only had spark and that the plug was soaked when I pulled it. :cry:
I found that I had at least 1 malfunctioning needle and seat assy. possibly 2
what a pain in the.....
That petcock is really necessary, it's the only sure way to shut off the gas to your carbs. If you need a kit I'll send you the website for one but you probably know where to get it already.

Good luck

 

I should have mentioned that if you tap on your float bowls sometimes you can free up a float that is stuck open!??
I also suggest that you check your oil for gas contamination as it seems that that is the 1st place the gas will go when a float is stuck open.
(usually a float that is stuck is because of a particle between the needle and seat but it can be because of mechanical problems too)

 

The float bowl gasket is a brown medium paper (you should be able to make the gasket but I bought mine with the new needle and seats)
Soaked plugs or black soot on plugs are fairly reliable indicators.
The fuel will go into the engine and to check you can simply pull the filler cap off and smell in the hole to see if you smell gas in the oil, if you get gas in the oil it will simply look like you have plenty of oil in the sight glass but really it will be overfilled and the gas breaks down the oil.
I tap with the handle of a 3/8" drive ratchet or extension (for #2 & #3) but be careful not to break anything because it is soft metal.
Cylinders are 1 thru 4 left side (sitting on bike) to right

http://cgi.ebay.com/ebaymotors/ws/eBayI ... 4649437543

link to petcock kit $23.50



http://cgi.ebay.com/ebaymotors/YAMAHA-X ... dZViewItem

link to needle & seat valves under $40 he can also sell you the gaskets, even though he's in New Zeland he got it to me in 3 days!!!!


Hope that helps. Good Luck.

 

Your compression is fine, your oil is shot, replace it. As for the petcock, yes, your in prime, turn it! Your sooty sparklers are a good question. I'm going to suggest they may be due, in part, to the prime setting issue. Check the new ones at the end of the week and see how things shape up.

 

Its my opinion but i wouldnt run the bike with the oil as it is. The engine may get more hot than normal and that oil/fuel misture may ruin some rubber seals.
I think

 

The petcock was definatly set to prime. As everyone else said you need to set it to run.
I am not sure what effect that might have had on the needle valves over a period of time?
Your sparkplugs say that your running rich.. see the black sooty electrodes. It looks like they are all the same so this isnt just one carb...
I'd definatly check the petcock youll need a couple of foot of fuel line and a small open top container.
Tank on or off the bike, connect the fuel line to the petcock (in place of the regular fuel line)
with the petcock in run there should be no leakage of fuel into the container,
With the petcock in prime there should be free flow,
if this is the condition then you should look to your vacuum line to check its integrity, was it connected correctly on both ends is the hose broken?
If everything looks OK so far you need to try putting some vacuum on the vacuum line to see if the petcock opens in the run postion, if it does then it's ok, but does the fuel stop running when the vacuum is released?
anyway you have probably figured out the rest...

I suspect that your oil is so fuel contaminated that it is causing a rich condition when the engine gets hot as the gas vapors are cooking off of the oil in the crankcase and being vented into the airfilter and into the carbs in addition to the gas you are normally using thru the carbs.
BE SURE to CHANGE THAT OIL, and the filter.
Yes that oil will harm your engine, maybe not immediatly but your oil is not lubricating properly and an engine that revs like these do needs it's oil to be in good shape to protect your engine.

So..,. change the oil and filter,
change out those old plugs,
and fix that petcock and dont run it in PRIME.

If it still runs rich then the carb repairs begin....

GOOD LUCK

 

You know Sno I didn't look to see but I'm not sure if you bike has a vacuum actuated petcock so if it doesn't then forget the trouble shooting like I described. You'll just have to operate it by hand to test!?

 

Petcocks often fail... especially on Decades old Motos
Your Carb Float valves should be Neoprene tipped.. If not.. replace them with such.. The rubbery ones are a whole different quality than metal tipped things. IF your petcock is Vacuum type (it dosen't look like one) then A rebuild kit is available If ..manual You really must turn it on and off manually... every single time. a Nuisance but fool proof. prevention, besides that was the designed intent.
Hopefully you haven't been running Premix in your crankcase for too long or your bearings would/could be wiped (seriously damaged).. Leading the pore old Moto directly to the Scrap yard.
Just like people: when Aged, maintenance requirements double or triple.
G'luck..

 

Hey Snow
You will let us know what it was wont you?
Hoping you do.

 

I wouldn't worry too much about fuel in the vacuum line. It will just go into the inlet and get burned up. However if it is flowing down the line then the diaphragm may be split.

The diaphragm can let a little fuel thru under vacuum thru a very tiny vent hole in the diaphragm that allows it to go back and forth.

 

No that isn't quite right ... fuel into vacuum line will shut out that 1 cyl, unless you get the rpm's up ... where it will burn well and suddenly you have a 4 cyl ... or in the recent case where this happened ... a 2 cyl ... it was a GS500.
Cool.
Srinath.

 

Sno if your still leaking gas thru the vacuum line... I'd say you still have a petcock issue!? srinath seems to have something there. that could also run into your cylinders and thru the rings and into your oil.... here we go again.