What did you do to your Yamaha today?

The knowledge on this forum can't be measured by the weight of gold, some really sharp cookies in this jar. Personally I've been on 2-wheels since I was a little kid and always had a knack for small engines. Now I'm in my mid-50 and still learning, always someone here with a good pointer, suggestion or reminder that comes from their own experiences and I learned to trust them very early on.

I put another 250-some miles on my 750 SECA this afternoon without a problem, I credit the others here for keeping me in line. I picked my 1981 SECA 750 up in a number of boxes and milkjug crates and spent over a week straight working 10 hrs/night putting it together, both the factory manual and xjbikes forum were within arms reach. The technicals are right on the money.


So today was a ride up to the north shore seeking some cooler weather and a hard running return trip down the interstate sometimes running 80+ for extended periods. Didn't find any relief from the heat & humidity but had a good ride. Seems my endurance in the seat is slightly shorter than the fuel tank but I managed and got a headlight full of bugs. A good day on the SECA.

 

So, took the 83 XJ650 for an hour long ride. First full ride with the new standard bars. Really makes the bike feel like a whole new bike.
The relaxed feel of the stock buckhorn bars are comfortable but the smooth higher reving sound of the 4 cyclinder 650 just does not match for the Japanese cruiser look of the bike.
Before I got going I had a run away idle event. It was at 8K and tried stopping and starting several times, raising and lowering throttle while bike was off.
Looked at the carbs and the butterfly plates were moving with the throttle. Shut off the choke and still was reving high.
Then I realized I had tucked the throttle cable some today and then looked at it and it was a bit kinked. So pulled it out and yup, that was it.
2 things. I should really re route that cable long term as well as lube it.
next I marked the idle position of the butterfly axle on the right carb. vertical is the current idle position and fully twist is just shy of 90 degrees.
What might have clue'd me in would have been to push down on the throttle couplings where the carbs connect together to verify the butterflys where closing.

It was a good ride and currently happy w/ the new bars. More UJM than before.

 

Thanks for the info
I will be degreasing the engine next weekend
And looking into it.
Paul

 

I had resurected an 82 xj650 this winter. When I purchased it I told him he had an oil leak as I saw oil all on the lower and side of the bike.
I guess he got sloppy w/ the oil change cause after running it for a few times, the smoke stopped and after wiping up the engine, it did not come back.
Like Hogfiddles says, the pipes also smoked some for a while after getting it running and then stopped.

 

I got my Yamaha a bit dirtier today.



Nice 100 mile ride followed by a not so nice 30 mile ride. I stopped for gas about a half mile after going on reserve. Filled the tank. Started the bike, it was balky (which it usually is not). Sounded... off, like it wasn't running on all cylinders. I started home and it was missing, sputtering, but running. It would go 65mph but still sounded like it wasn't running on all four. It seemed to sputter, then up around 7000 rpm it would suddenly smooth out and yank my arms out of my shoulders. Got it home and took a look at the plugs. 1, 2, and 3 were the normal light tan, but 4 was sooty black. So I figure it's not an ignition problem (since 1 and 4 are on the same coil), but cylinder 4 running way too rich. Trouble is... what brought this on? The bike's been running just fine for the last thousand miles, and just like that, after buying gas, I've got a carbon-fouled plug and it's running like crap. Just coincidence? Ingested something into carb #4? Hmm...

No time to mess with it now (it's too hot anyway). FWIW, I left the gas on for a few minutes and the carb didn't overflow, so it's probably not a stuck float valve. Any thoughts...? Wanna place bets on whether I'll be pulling the carb rack... again...?

EDIT: before I pull the rack I'm going to pull the hat off carb #4. I am not an expert on CV carbs but understand enough theory to think that if the piston/needle gets stuck in the up (or even partially up) position, the carb would behave like a butterfly carb with a huge jet dumping fuel into it... which would kinda replicate the symptoms I experienced. Tomorrow. Time for Italian dinner...

 

Well if it has stuck up it will be weak, not rich...

 

Really? I would have thought that with the needle pulled all the way out of the jet the carb would be dumping fuel into the throat like mad. But, as I said, I am not a CV carb expert. We'll see when I start taking things apart, I guess.

 

What pulls the fuel out of the jet? Vacuum. No vacuum no fuel. The point of the slide is to regulate the vacuum seen by the main jet/needle assembly. In a correctly working carb, as the volume of air increases the vacuum below the "closed" slide would increase (non - linearly), by connecting this vacuum to the top of the slide (via the hole in the bottom) the slide lifts against the spring until it reaches equillibrium (hence CV or constant vacuum). All this means the design and operation of the needle is simplified, and the carb cannot "fall flat", or overfuel.
By changing the size of the hole in the bottom of the slide you can change the rate it rises, and how it responds to pulses. By changing the rate of the spring you can change the vacuum at the needle, and also when it reaches fully open.
Simple eh?

 

Simple, maybe. I'm not an expert on the specific carbs used in the XJ series, or on multi-carb systems (I have years and years with the big single Kehin CV carbs used on Harleys and Buells and KLRs).

Of course, the dirty plug could be a red herring. It definitely is running too rich on that cylinder, but it was dry (no fuel or oil on it), not bridged (as my old two-strokes were prone to do), not covered in fluffy ash... just black with carbon on 3/4 of the insulator. So out of adjustment on that cylinder, but maybe that is an independent problem.

The obvious direction to look is something related to having gone on reserve and filled the tank just before the bike started running badly. When a bike is running perfectly, then I do something, then it runs horribly, there's reason to suspect the something I did was related. So what did I do? Flipped it to reserve for maybe half a mile (I was coming into town with the intent of buying gas, about 110 miles on the tank, and the engine sputtered a bit as I pulled up to a stoplight). Filled it up, switched back to main on the petcock. Went inside to answer the call of nature. Came out, popped the seat and got a wrench out of the tool kit to tighten a loose bolt I had noticed on the front fork. Put tools back, closed seat, went to start bike. It was reluctant to start and sounded wrong, more like a twin than a four. Seemed slow and rough, sputtered and surged, seemed to smooth out and run properly when I had it up over 7000 rpm. Stopped at one point to see if maybe the fuel tank was vacuum locked (I had recently replaced the cap with an aftermarket one and thought maybe the vent was bad, though it had gone a couple hundred miles without incident on the new cap). This involved shutting off the motor, and it almost didn't restart. Continued running horribly till I got home, about 30 miles in all.

So I suppose the flip to reserve might have allowed it to ingest something that clogged the fuel supply, though I had cleaned the tank as part of reviving the bike. The petcock is converted to manual operation, and the only mode in which it could fail (the spring-loaded vacuum plunger opening) would cause it to not fully shut off, not restrict flow. There is a screen on the petcock, but not an inline filter.

I guess I will start by removing the fuel line and making sure fuel flows. Next step might be to clean or replace the plug and see if it runs any better (on the hypothesis that prolonged rich running on #4 fouled that plug to the point where it coincidentally started running badly. And then (sigh) start looking into the carbs themselves...

But first... today is dedicated to brewing beer. The bike will have to wait until tomorrow, unless the brew goes unusually quickly.

 

Continued, during a short break while the enzymes do their thing...

I quickly dismissed the easiest possibilities. The petcock flows plenty of fuel, and the slide in #4 was in its proper position. So much for that. Now I am making hypotheses and testing them. Let's look at the plugs. I mentioned #4 looked badly carbon fouled. Here's a picture of #1 and #4:



Even #1 looks a bit dirtier than I would like after only ~2500 miles, but there was a lot of screwing around and adjusting in that period. #4 is covered with soot, and smells of unburned gasoline. If I understand the secondary circuit correctly, either both #1 and #4 fire, or neither fires, because they are in series. Izzat so?

Which causes me to wonder... has the #4 plug been getting dirtier and dirtier, and just happened to reach the point yesterday where it wouldn't pass a spark except at high rpm? And in that circumstance, would #1 also get no spark at all, or a weak spark? Questions, questions... and these BP7ES plugs are getting hard to find... I really oughta convert over to non-resistor caps and resistor plugs...

Back to the brewery. Enzymes are done for now...

 

Your theory is only correct if there is a break in the HT circuit, if this happens both will be out. But, if one of the plugs fouls, and the Ht runs down the carbon deposits, you'll get spark in the good plug, but not enough in the dirty one. Hence people will tell you that once a plug misfires it's scrap, if it went on long enough.

 

Hmm... interesting. Hadn't thought about carbon tracking down the plug, but I guess that if there's enough on the insulator it'll happen. My old Kaw triple two-stroke used to form carbon whiskers between the electrodes when its plugs were first installed. After about a hundred miles the bike would start missing, I'd pull the plugs and remove the whiskers (I called it "flossing" the plugs), and for whatever reason the whiskers would not re-form. I cleaned up the #4 plug; the carbon came off pretty easily with a brass toothbrush. I hope it's still usable, as these non-resistor plugs are damned hard to find anymore.

Anyway. I went back through my records and found something interesting about the carb adjustments. When I drilled out the EPA plugs from the mixture adjustment screws, I found the factory had set them as the following: 1-3/8, 1-2/2, 2-3/4, 0-9/16 (#1 to #4, turns out from lightly bottomed). This is a 1980 with the coarse thread screws. The settings on #3 and #4 struck me as odd, and I wondered if I had somehow moved them when extracting the plugs.

When I reassembled the bike, I set them all to an initial value of 2 turns out. When I checked the screws today, and looked at the plugs, I saw this:
#1: 1-7/8 out, plug looked a bit dirty but OK
#2: 2 out, plug looked good
#3: 2-1/3 out, plug looked a bit lean
#4: 2 out, plug carbon fouled

So apparently the 2-3/4 and 0-9/16 on #3 and #4 from the factory were correct. I have no idea why #4's screw should be so far in, but I suppose there is variation and you just have to live with it. I have set them to: 1-1/2, 2, 2-1/2 and 3/4 turns out, which are all just a little bit richer than the factory set them. I will try to start the bike and see how it runs tomorrow. With a great deal of luck (which seems in short supply at the moment) this will solve the problem.

 

Just remember that carbon-fouling (= incomplete combustion) can be due to either an overly rich or an overly lean condition:

Why are my plugs carbon-fouled (dry, sooty black deposits)?:

- Carbon fouling is the result of incomplete combustion----for any reason. It is most often associated with an overly rich fuel mixture (whatever the cause), but can also be caused by an overly lean fuel mixture (or poor spark, etc.) In a lean-mixture condition, most of the un-burnt mixture gets pumped out the tailpipe, but some fuel droplets remain in the cylinder and add themselves to the next intake charge. That's not a very precise way of metering the mixture, so when it's finally rich enough for a spark to ignite, that particular charge may be too rich, resulting in incomplete combustion and plug fouling. So carbon-fouled plugs can be due to rich or lean conditions.......your Colortune spark plug will tell you for sure. If you have a light blue or white-ish flame, intermittent flame, and/or intermittent flashes of yellow within an otherwise white-ish flame, then your fuel mixture is too lean.

And by the way.........if the spark that happens to ignite this overly-rich mixture is the "wasted spark" (which occurs in each cylinder at the top of the exhaust stroke, it will occur JUST AS THE INTAKE VALVE IS OPENING ---- so the backfire pressure wave may be directed back up the intake tract!



If it is overly rich, then the checks would be:

- fuel height in that bowl
- partially stuck (open) choke plunger valve and/or scored/injured choke plunger valve face or seat
- something else


Also, the easiest fix may be to just replace the plug and see if the problem goes away.

 

I'm also going to say check to see if the enrichment needle is fully seated when it's in the off position, chased my tail on that one myself until I accidentally tapped the needle on the top and the engine smoothed out. Turned out I had slightly tweaked the lifter fork when I disassembled the enrichment bar during the rack teardown and never gave it a thought.
Over the last four tanks of fuel my 750 has been giving me a solid 40-45 MPG running around 65-70 MPH on the rural roads and will pass the century mark with ease. Idle is dead even and very little enrichment is needed cold. Around town it's very easy to ride, no power dead bands or jerkiness going through the gears. Running #124 mains and #42 pilots on the stock float settings and they're right on the money for a 4-into-1 exhaust.

Recent Craigslist ad for a brilliant red 1982 SECA 750 with just over 10,667 miles on the clock. Seat is rough, tank has a big drop dent in the RH side but it's priced at $500 w/clear title. Been going through my I-O-U book to see who I could collect from but... I'm totally square. Bike is located in Bacus Minnesota which is about 2 hours NW of Duluth. Posting ID: 7764919211
Every time I look at this post I have to wipe the drool from my keyboard. It's clean... the bike is anyway.

 

Good info on the 4 into 1 jetting for the 750. Hope you find a few shekels to get the Seca.

 

Working on it but being in between the jobs is slowing my progress.

Neighbor kid Connor on the other hand come scootin' home this afternoon on a first generation Hayabusa that he picked up for $7500. The old saying holds very true for this kid about a fool and his money. Apparently he got some lump-sum settlement last week and was itchin' to buy the meanest & fastest bike he could get his lanky legs over, shortly after noon I see this flat black & gray streak fly down our private road... shoulda hit him up for some bucks and save him from himself! At 19 Connor isn't big on wise decisions or thinking for himself so it's no surprise to me really but I went over and looked at the bike and gave it a shakedown ride... bike like this should really come with a roll of toilet paper and a life insurance policy for the surviving family. I'm not a pro rider by any means but I have plenty of experience, nothing prepares one for this sort of power be it mentally or physically, for a beginner this is a death sentence. I gently rolled on 1st and 2nd going further on the grip thru the remaining gears before saying Uncle. Two words come to mind... at the start its Stupid Fast, at the end its Organ Donor. The front of the faring looks like the pinched end of a turd but at the moment my mind was on just how fast it went to the 11,000 redline with ease almost like it wasn't unloaded. It sounded really cool but I was doing my best to keep my 220 pound fat@ss from sliding over that rear hump. I don't know the bike well enough to really wring it out but with all that go it has plenty of stop and turning on a dime gets me a nickel and five pennies. Just hope he makes it long enough to start basic in August, I assume he's headed to Jackson or Benning. He isn't big on listening to responsibility either so maybe the ARMY will change that, if nothing else he just might become the fastest PFC of his company.

So I put some gas in my tank and rolled some miles on my SECA, honestly it doesn't need much right now and I'm thankful for that.

 

Got the motor back in. I must have told myself about two dozen times, "Hey dummy, remember to put the airbox back in first." so naturally I didn't do that and got to pull the motor back out again...

 

That's.....fast!!

 

I had a small oil leak coming from my drive sprocket area. Once I removed the sprocket cover I found the area was a mess so it was tough to figure out the source.

I the oil was leaking from the shifter shaft seal, but I was wrong.

It ended up being a crack in the neutral switch assembly. The OEM O ring was fine but I have a new one on the way for good measure.

Below is the offending crack (I think.). It’s hard to say for sure as there were hairline cracks everywhere. The neutral switch part number has been replaced since my bike was built and I bet they changed the plastic formulation a bit.



I cleaned the entire area. Now I’m just waiting for parts.

 

Went for a quick test ride after working on the brakes forever. Ready to install the right carbs (34 m.m.) to the 750 engine soon. Day was nice and it was a much deserved put. Next time, I will add more petrol to cruise longer.