Tech Babble: So, I was reading the 1981 Yamaha EGA manual...

and although it pertains mostly to the operation of their primitive, largely disfunctional EGA itself, the sections on how to troubleshoot the dreaded "excessive levels" of HC (hydrocarbon) and CO (Carbon Monoxide) are very interesting.

Aside from the things we've discussed ad infinitum, like clogged or restricted pilot jets/circuits, they brought up a couple of things we rarely think about, and EMPHASIZE some as being more important than might be realized for certain symptoms.

For instance, if the bike "hesitates off idle" the remedy given for CV carbs is to adjust the float levels.

As expected VALVE ADJUSTMENT is at the top of the list for a "proper state of tune." They of course emphasize the condition of the air filter, and spark plug condition and gap.

One unexpected mention, because it doesn't seem to be all that common, is leaking enrichment plungers. (Not shutting off completely.) Is it an overlooked possibility for some of the interesting results some folks have seen when trying to ColorTune?

Another thing we all know about, but is apparently easier to do than we ever thought, is "contaminated" (with gas) oil. According to Yamaha, all it takes to contaminate the oil is overly rich running, or again, incorrect float levels.

The thing that stuck with me is how they keep coming back to float levels for various idle mixture adjustment problems.

That, and confirmation that use of the YICS blocking tool is required for making mixture adjustments on YICS-equipped bikes. (ColorTuning crudely replaces the use of the EGA.)

Just thought I'd toss some of this out there; have at it. It was an interesting but dry "read."

 

Well I can vouch for the over rich running contaminating the oil. 3 times I had to drop the oil due to too rich a run. I had to learn the hard way about float levels affecting the mix, at first I wouldn't have it becuase I coudn't see how the bowl level had anything to do with the atomized mix.... well being the worry wort I am I always smelled the case after every ride (still do) and I noticed that over a few days the case oi woud begin to take on a slight gas smell. after several bouts I began to re learn what I thought I had a handle on. In doing this I learned that 2 mm of bowl level can change the mix noticeably. Once I took the time to get the bowl levels really right (tube) my problem stopped.
One of the things that threw me was the static measurment. At 17.5mm my wet level was too high, to get the correct wet level I ended up with a static measurement of 20 mm (there about).
It took many micro tweaks, put the bowls back on and repeat, repeat, repeat.
I was "hung up" on that static number. I cleand the floats....you name it. In the end I chalked it up to the bouancy value (for lack of a better term) had changed for whatever reasons over the last 29 years. Guess I could have got new floats but...
Anyway the point of this drug out post is to point out how tricky and critical those wet numbers are and hopefully anybody in that stage for the first time will read this and save on some oil changes like I didn't

 

RUNNING too RICH isn't going to be the cause of finding FUEL contaminating the Crankcase.
There will come a point that an EXCESSIVELY RICH Mixture will FOUL and cause the Engine to stall.

FUEL finding its way into the Crankcase is generally caused by a combination of PETC0CK and FLOAT VALVE problems.
The Float Valves definitely contributing to the problem by either:
Leaking when shut
-or-
Float Height issue / Float not closing.

If you are getting FUEL in the Crankcase; its getting in the Crankcase because;
Its leaking by the Petc0ck
The Float Valves aren't stopping it
Its rising out the lowest orifice and trickling down into the Sump.

An Engine would have to be in a dreadful state to run so rich the crankcase fills-up with gas.

There would be a host of warning signs.
Not being able to go very far without changing the Plugs ... one of them.

 

Rick, I wasn't talking about the "filling the crankcase up with gas" syndrome.

I was pointing out that according to Yamaha overly-rich running and/or incorrect float levels can "contaminate" the oil to the point that it becomes detectable as higher CO readings with the breather connected than it does with it disconnected.

If the condition that causes this is left unattended, eventually the oil will be contaminated enough to begin to suffer decreased effectiveness.

This is much more subtle and covert than gas puking into the crankcase in large volumes. That one's generally obvious.

 

The Yamaha manual could have instructed the Yamaha Tech to simply dis-connect the crankcase breather while the engine was running on the EGA machine to confirm excessive gas fumes in the oil - -

so modern day XJ-ers using a ColorTune could do the same.

but selling an oil/filter change at dealer rates is always good !!

 

The manual DOES instruct the tech to disconnect the breather for making the adjustments; then to re-connect it and see if the CO level climbs.

I don't know if the ColorTune is "sensitive" enough to show a change that subtle.

 

Re: Tech Babble: So, I was reading the 1981 Yamaha EGA manua

Good tech babble, Bigfitz. Stuff like that catches my attention, too, especially when the non-Yamaha manuals (Haynes, etc.) don't mention such things.

Another one that caught my attention while reading the Yamaha service data information on the XJ CD, was Yamaha's observation that "engine RPM will drop 50-100 RPM with the YICS tool installed, and CO and HC specifications should be monitored at this lower RPM, 1100-1150 RPM."

I guess I bring that up only to question whether that would have any impact on our RPM setting for the Colortune method. I (and many others on the forum) have mentioned that after YICS installation, the idle drops so much that the RPM screw has to be turned in a tad to get the idle up so she stays running. Things that make you go "hmm".

 

The factory service manual calls for sync to be done at 1100-1150 RPM as well; and it also says that you may need to turn the idle up a tad to get it back to 1100~1150 after the YICS tool is deployed.

Since ColorTuning is a "visual substitute" for the EGA; I would have to say that the same thing applies; Colortune with YICS blocked and the idle raised as needed to attain the specified range.

 

I guess I never thought about how much of a difference a millimeter or two fuel level in a carb bowl can make.. I will CERTAINLY be bench-syncing the fuel levels with the highest level precision I can manage before I put them back on the bike. Thanks for the insight!

PS: I STILL need to purchase myself a factory service manual for my bike.. the Haynes manual is OK, but little gems like this would make it a very worthwhile purchase.

 

The whole adjustment "range" is a total of only 3mm. That's why using fuel and clear tubing to verify is so important.

Having a factory book helps a lot; having both plus this site is the best way to go. NEITHER book is 100% accurate; but the factory books do cover some of the outright omissions in the aftermarket manuals.

 

Does anyone care to speculate on the effect of centrifugal force acting on bowl levels? I know that it has an effect on BMW carbs.