What did you do to your Yamaha today?

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.

 

Found myself going head-to-head with a Charger R/T this afternoon. Both going south on hwy 65 at the stoplight and I took off rather hard wanting to keep the traffic way behind but then I noticed a Mopar keeping up with me so I went for the redline, he was right there. Went for 4th and the redline again at full twist, think he was waving at me. Went for 5th and he never left my front fender. I was going for 9000 but had to cut back heading into the next wave of traffic, so far he's the only one to keep up with me and while the SECA 750 isn't the fastest bike on the road it's not exactly lazy with the rich jets and rider who isn't afraid of a full twist redline. According to my GPS we max'd at 102 and I have the feeling there was more to go.

 

Been picking away at the exhaust and carbs and related gadgetry in the evenings this week. Tonight I fired it up for the first time. This was a motor I was originally rebuilding for my other project 750, but the starter clutch in this bike finally forced me to change plans. Not a full rebuild by any means...starter clutch, primary chain guide, a couple main bearings, etc.

Fired right up and sounded great though. Pegs, levers and rear brackets and it'll be back on the road.

 

Changed the bars AGAIN. These are a tad wider and flatter. Debating bending them a little backwards.
I also put on an adapter that raises and brings back the bars 1" up/back.

I really disliked the buckhorn bars that Yamaha put on this bike and really liking the feeling and ride with the new bars. Wish I did this last year.
The idea that a 4 cyl bike in a relaxed cruiser format would work is besides me. Maybe people liked it back then especially when the Honda Rebel came out. (My friend had one in the 2nd year it came out and I borrowed it from time to time).
I just like the feel of the UJM format better. I may have mentioned this before but I do like to make things historically stock (maybe adding to it) but I just can't ride this bike with the stock bars and enjoy the rides. Maybe if I were taking 3-5hr rides I'd appreciate the buckhorns but that is not how I ride this one. I have 2 other bikes for longer rides.

 

Looks great this those bars. Master cylinder is at an angle though.

 

Those bars do look really nice. I kind of enjoy the feel of the buckhorns on the 650, but I tend not to ride very aggressively.

 

I dig the bars as well.

 

On the road again. Feels smoother and quieter than before, but I guess I did fix a couple nagging exhaust leaks while it was apart. Wasn't sure if the black motor paint would be a good thing or not, but it's growing on me. I probably owe this thing a seat cover and a paint job now. Red tank? Stick with all black?

 

WOW Absolutely impressive

 

Yeah, I'm with you on the buckhorn bars. PO had put flat bars on mine, I flame heated and adjusted them up slightly (they were bent anyway), but I found being too straight (across ways) gave my wrist joints a hard time. So I fitted some seca copy bars, only to find these were bent on one side, and STILL giving my wrists a hard time. So I will be adjusting these, with the help of a long piece of pipe, preferably on the bike, to correct the LH droop, and sweep them back slightly, fingers crossed.
Actually, I have a set of 900S bars, and they look about right, maybe I should just try them first?

 

Hey everyone, I’m new here, been reading quite a bit off of this site for a while however..

I have an 84’ Yamaha XJ750 maxim.. I love old bikes and fell in love with this one as soon as I seen it. And took it for a ride. So I bought it about 3 weeks ago now..

Everything is working great as far as I can tell.. I had a couple issues the past couple days with electrical and figured out it was a loose clip in the fuse box giving me troubles, not that I’m surprised given it’s the glass fuses and 40 years old lol

I’ve read about upgrading the fuse box to a bladed set up and want to do this. Can someone lead me in the right direction to which fuse box would be ideal/fit on this bike. It’s a fairly tight space between the seat and the air box.

Appreciate any advice or tips for this bike aswell. Thanks guys!

-Steve

 

Think I’ll be going with some inline fuses for now until I find something I’m sure will fit properly.

The inline fuses don’t seem like a bad way to go. As long as they’re rated higher than the fuse I’ll be using, which is only a 20 for the main fuse. I just don’t want to be driving it the way it currently is; with the clip/glass fuse being loose.

 

Fit a blade one like this and stick to the recommended fuse ratings for your machine. The old Yamaha factory clips break they are old now.

https://www.12voltplanet.co.uk/low-profile-standard-blade-fuse-box-side-terminals-6-way.html

 

I spent most of Thursday cussing at the bike because I could not get the damn thing to idle.

Backstory: I thought I had everything going well until I went for a ride last week and one cylinder stopped firing. When I got it home, I found plug #4 was filthy with soot. I figured this was most likely caused by my having not believed the idle mixture screw really only needed to be 9/16 of a turn out, when the other three were 1-1/2 and 2-3/4 turns out (what I found when I pulled the EPA plugs and removed the screws). Well... apparently the range of correct adjustment on these carbs really is that wide. So... new plug, set carb #4 to 9/16 of a turn out, go for a ride... bike ran really well, even lost the flat spot and burble around 6-7000 rpm. But, when I stopped at a friend's house, the bike wouldn't idle. Starting at 1050 rpm, it gradually slowed until it stopped. OK... turn up the idle speed screw, idle comes up to 1200... 1500... 2000... Back down, it again stalls. Take it for a ride, pull in the clutch and the idle doesn't drop. Come to a stop, it sits at 2000 for the better part of a minute before very slowly dropping to 1500... 1000... stall.

Sigh.

Last time I had this behavior, it was caused by bad throttle sync; #1's throttle was effectively fully closed at idle. Fixed that and the bike idled at a nice steady 1050 for as long as I might want it to. So I got out the vacuum gauges and checked sync... and they were all dead on. Well, that's not it. By now I had burned my fingers enough getting those vacuum gauge hoses on and off the intakes to call it a day. Since the bike did idle OK when #4's mix was too rich (about 2 turns out), I kinda suspect it's now a little too lean, so I will probably try nudging it up slowly until I find a place where it will idle properly and not foul the plug.

But not today. With a three-week, two-up trip to Maine a week away, I have more important things to work on than this antique bike.

 

I started her up today and listened to the sweet sound of a machine that wants to get back on the road soon. Unfortunately, that will have to wait a couple of weeks for my left wrist to heal up. A recent stupid household accident left me with a fractured radius that had to be realigned with a plate.

 

Made one more attempt on the bent frame XJ1100 today. I figured it would either be fixed or scrap, and I think it's time to call it....scrap. I put quite a bit of heat on it and did get it to move a bit, but by my measurements the valve cover will still hang up on the frame.

Time to stop the bleeding I suppose. I would be more enthused about it if I didn't already have an 1100, and just how many of those things does a guy need?

Plus I really needed my shop table back.

Probably be listing it for part out soon.

 

Took a 2hr ride on the 83xj650 this weekend. I think this may have been the longest ride so far.
I had been running the replacement vacuum petcock on PRI for the past year and FINALLY hooked up the vacuum line to it.
Started out running 10 miles @ 70mph on a local highway to verify flow would keep up, then ran about 80 miles total in those 2 hours down mostly country back roads.

 

Over the weekend I max 2 k over the rattle can paint job last weekend. Thanks to the help from
the members I am making progress on my xj650 barn find. This weekend will be replacing gear shift cover gasket and shift shaft seal.
Now that I am running the engine have discovered smoke on pipe underneath that cover. Hope everyone has a great week

 

Never thought I'd see myself in triplicate...

 

Sorry if I did something wrong.

 

I had this same issue and assumed my shaft seal was bad. After digging in I found that the neutral switch assembly was cracked and causing a weeping oil leak.

Just an fyi. Good luck!

 

Nah nothing wrong, things happen... even on this forum.

 

Thanks will keep that in mind

 

Just bought an unnecessary tool that I’ve been wanting for a while. Its a Motion Pro 8mm Mini Bleeder tool.

It’s got a check valve built in. It should make future bleeds a breeze

 

Nice

 

So what did I do to my Yamaha today... went for a nice ride and scrubbed the chicken strips off the rear tire.

 

Under the heading of "Stupid, but it works"...turning the crank during valve adjustments with that damned shallow, square, stamped steel crank trigger has always frustrated me. So I took my cheapest pair of China-grips and custom ground them to clamp at an angle so they clear the shifter and foot peg. Clamp once for the whole procedure.

This was my first valve adjustment on this motor since lapping the valves, setting lash, then putting about 150 miles on it. The 4 intake valves were all on the slightly tight end, about .10 mm. I'm guessing they probably seated in a bit after lapping and initial adjustment?

 

(Yesterday) Got a nice ride in with some of my best buds up into the lower Kettle (Whitewater up towards Waukesha, then back to Lake Geneva and home) . Light on pics, but long on scenery. Also discovered what I thought was a fuel line weeping is actually the petcock gasket. Is it that time again/already (thought I replaced 2 years ago, but looking at records, I'm still on the one from the prior rebuild - circa 2010?).
https://www.relive.cc/view/v7O92DM1zL6

 

Petcock gasket against the tank or the vacuum diaphragm back cover? Last time I had mine apart I sanded the aluminum mating surfaces with 400 grit on a surface plate. Unbelievable how not flat and rough the original surfaces were.

 

Would love a report after you use it.

 

Looks to be the mating surface w/ the tank, but I haven't pulled the tank for a close look yet - dummy me filled up at the end of the last ride to make it harder on myself. Will burn some off first.

 

My SECA turned 42,000 today... at an average speed of 100 MPH up the interstate.

 

Nice, you're rackin' 'em up faster than me. We hit 40k around the same time and my last fill-up (Sinday) was at 41,3k.

 

I can't get enough of the bike! Was out again today and caught a 650 SECA Turbo in the wild going around lake Harriet in south Mpls. Don't know who it is or if your a member here but dude that's one sweet bike! Seriously looked like he just drove it off the showroom floor of W.I.W. Motorsports.

 

The wrist and clutch lever grip are healed up enough so I was able to get a short ride in just before the Saturday afternoon downpour. Felt so good.

 

Cool! You were down in my neighborhood!

 

An odd troubleshooting bit, but it might help somebody else someday...

For the past week or so, the 750 has been sputtering under load, WOT or close to it. I suspected fuel flow or plugged filter, so pulled the line, switched to prime, everything flowed fine. So I was scratching my head and on to more mysterious causes, but on a hunch hooked the hand vacuum pump up to petcock and found a slow leak in the diaphragm. Probably getting fuel at low demand and high vacuum, but closing up at low vacuum. Changed diaphragm and all is well.

 

Mounted the windshield on the 750 today. I had previously planned to use the threaded holes where the grips attach, but ended up just drilling new holes lower down. I had to bend the mounting rods to make them work at this angle.

I tried to get a line-of-sight photo, but it didn't capture my view very well. I'm normally looking over the windshield, with the top of it probably 50' down the road in front.

Nice evening for a ride, but the deer were just nuts and I had several uncomfortably close calls and was glad to get home in one piece.

 

I used to live behind the old Currans on 42nd years ago so I know the 'hood really well.

 

Took the '83 XJ650 with me on my week vacation out in Ocean City Maryland.
Ocean City in the background across the bay.
On last tank fill, I calculated 50mpg. However, The speedo seems read about 3mph faster at about 45-50mph so I think I"m closer to 45-47mpg