82 XJ750 Seca - Performance degrading

I picked up this bike beginning of the winter... ran like a champ, 9900 miles on it. Rode it a couple times a month over the winter... no problems, crisp clean running.

Getting ready for the season I have so far:

• Changed air filter
• changed gear oil
• new plugs, gapped

Changing main oil / filter and fuel filter next. When the shop has time I DO plan on eventually getting the carbs cleaned and synched but she was running so good initially I thought I might make it into the season when the rush dies down...

Over the last month and a half I've noticed:

• When the engine gets nice and hot and as the outside air temp has gotten above 60, above 4K rpm a slight knock or popping... tightened all exhaust and it seemed to help a little for a while
• This last week or two with outside air temps above 70, just crappy performance... sluggish and what feels / sounds like missed combustion strokes below 2500 rpm. When up at 55 mph and 4200 rpm, pegging the throttle does accelerate, but with hesitations and skips along the way...
• It does not look like I have any stuck choke mechanical / plungers, etc.
• It seems to continue getting worse each time I ride and am afraid to go further in case something mechanical is going on.

One big thing: At the onset of these issues and with advice from a long time older bike owner, I started putting in high octane fuel... I'm hoping it may all be just that and will drain it this weekend. I did also treat one tank ago with Seafoam to get the carb cleaning started...

Any advice MOST appreciated, thanks

Tim

 

check the valve clearances
clean those carbs
check out ignition system ohm it out
trim plug wires back 3/8 inch wire could be corroded

I only use Hi test non ethanol fuel at the end of the season. Run tank low fill with HT last 2 to 3 tanks and store bike with it.
High test does nothing for your bike as it is a low compression motor big waste of money

 

I never use high octane in the tank. It doesn't do anything for a bike or car that doesn't call for it. I would use fuel that doesn't have ethanol if there was a station near me that carried it.

 

Carbs. Higher octane can't mask vacuum leaks or compensate for plugged fuel passages. It also offers no benefit for an engine that was designed to operate on low test fuel.

 

Air filter? Small rodents can mess up an filter in days

 

Do NOT let a shop clean your carbs unless it is Hogfiddle's shop.

 

Like others have said, there are basic things to check first. Carb cleaning/tuning is all for naught if the valves aren't in spec. Start there.

It does sound vacuum leak-ish to me, but switching to higher octane gas is just masking a problem to make yourself feel better... it's like Seinfeld changing the 34 on his jeans to a 33 - makes him feel better, but doesn't actually solve anything.

Most common areas on the carbs are the intake boots themselves (that rubber breaks down and cracks over time), and the butterfly valve seals (which also breakdown over time, and our bikes have seen much, much time). IF the carbs are gunna be cleaned and haven't been to church (full teardown, clean, rebuild), that is probably a smart move, since they will be down for maintenance anyway. Saves you from pulling the rack twice. Expensiver, yes. betterer than wasting your time with flacid solutions.

 

when the valves get hot the clearance gets smaller, so if your valves are tight to start with they get tighter.

 

I'm betting that 9900 miles =zero maintenance from new.
Consensus is tight valves and dirty carbs.

 

Everyone wants a quick fix, but those are like all the diet secrets on the internet - Invented by quacks who tried something and got lucky once.

 

a quick fix is air in the tires, valves and the church of clean is not.

 

Well my update is fuel in the oil so hope I didn't drive it a little too long

Tearing it apart now...

 

I'm hoping that you're just breaking the carbs for a refresh, and not breaking down the whole bike.

 

I'm with k-moe. Probably just needs a petcock rebuild and perhaps new needles and seats to solve the gas in oil issue. Of course all the other stuff mentioned probably needs attention also.

 

Your valves won't be able to get that tight yet. That's not the issue.

My bet is you're overheating due to thinned oil. Smell your crank case to see if there's a gassy smell in there.

 

Today: drained all oil, replaced filter, removed all exhaust ( have another one to put on minus the mufflers)

Tomorrow: new exhaust, drain gas, inspect petcock, new inline fuel filter, inspect and clean floats-needles, then replace oil if pretty good.

I left it on prime not running once by accident when I got the bike... Hoping it was just that and a stuck float.

Valve cover is leaking just a little anyway so figure why not check the valves and fix that next.

 

If you're leaking at the valve cover, you'll need a new valve cover gasket and donuts for the valve cover bolts.

 

I checked my local Yamaha shop this morning and surprisingly they have one

 

The dougnut rubbers are as important as the gasket is. They are what puts pressure on the gasket so that it seals. Once hey harden, even a new gasket will leak.

 

Out with the old

In with the new(er)

 

Yup..... That'll make it perform a whole lot better

 

Nice. Did you rechrome them or just polish them?

 

Lol... I know it won't but the other ones look so crappy

 

Scored on eBay...

 

Why does everything take longer than you think?

between running around with kids all I got done was the oil, pipes, and tap on the bowls....

Had to drill a few exhaust clamps...

 

I'm so happy!!!!

If you can't tell, this is my first bike

So I was in an overheat condition due to fuel in the oil. With the new charge of 20-50, warmed her up and went out on the same stretch she was hesitating on before... Smooth and snappy now, new exhaust is nice and tight and it purrs.

Thought it was crazy that my carbs or valves could go whacky that quick.

I had tapped around the bowls preride and warm up... Now that I know of the issue I'll watch it like a hawk.

Wish I could get to the carb clinic but it's a bit far for me.

Thanks so much everyone for the great advice.

 

That wans't a sign of overheating. It as the sump being too full and not allowing the pistons to fall without resistance.
Make sure to check the oil level every time you go to ride, even after you get the carbs refreshed/ rebuilt.

 

Level was perfect though? Never left the sightglass.
After smelling I could tell as soon as I dumped it. It flowed pretty thin...

 

Are you using oil?
Did you note he level on the center stand with the engine off for at least 5 minutes?
If you saw oil in the sight glass with the bike on the sidestand then it was way overfull with the gas/oil mix.

 

Well I don't know what the PO had in there... I had only ridden it 10 times or so before this issue

But yes, I had topped it off only and with the correct oil and measured before every ride on the center stand

Whatever it was it was black and thin when I dumped it... Might explain why the engine didn't mind as much when the outside air temp was more like 50.

 

OK,

So I changed my oil after some bad float needle things going on... checked all my bowl levels again... perfect.
Had thought my fuel line had a kink in it because I installed a good sized clear fuel filter so I could see what was going on so I installed a 90 deg. elbow to make sure no flow problems.

The reason I thought I had flow problems was after bowl settings the bike would either rev really high after hitting throttle and stay there for a bit. Or just start randomly dying after warm up and only keep going by adding some choke (enrich). So this all happened again on my test ride and I limped it home. I also noticed the whole engine, crank case included, getting really hot and overheating which I think can happen from running lean???

Knowing that the carb bowls at least were good I removed the petcock because even on prime I could see through the filter the fuel was just spitting through at a low rate and not filling the filter. With petcock removed I tried to suck on it (After cleaning) and no flow...even on prime. Took it apart and could not find any obstruction whatsoever.

So the question is... anyone ever had the gasket in a petcock rotate and block the passages?(only thing I can think of) and would this lack of fuel condition really cause my engine to get that hot?

Thanks a bunch.

 

Moving this into your exising thread so we can keep track of what's been done, and what's been suggested.

 

Except when it IS a sign of overheating due to gas-thinned oil....seen it enough tines, and worries me when I find bikes like that---how close did someone come to blowing themselves up. We've even seen bikes here that caught fire

 

But does it seem reasonable to get very hot with FRESH oil? Just from being partially starved for fuel?

 

Like is it normal to burn my hand trying to get at the idle screw after a 5 min ride?

 

Yes.

 

Well that makes me feel a little better... I've been studying all morning 'cause I'm freaking out something REALLY bad is going on, but now I think:

• When I said my bowl levels were perfect, they were right where I set them, I actually ball parked it a little too much and I'm going back to actually mark the bowls and check. I think they may be a little low still.
• Also, I've had my carbs on and off so many times I'm wondering if I'm starting to make vacuum leaks as I can't be sure cause it's been windy but I'm thinking I might be hearing something.
• Putting in a new petcock... I think the low flow condition I found could also make the bike run crappy but by the time you park it, hook up tubing, and check levels again it looks normal as they had time to re-fill.

It was running so well for a few weeks and I was really enjoying it and wanted to get through the summer... but if the above doesn't work I'm going to square one... valves, carb church, sync, colortune....

By the way... thanks again all for the newbie support.

 

OK, so I've learned my lesson and am repenting . A week ago the resetting and new petcock above made no change.

I went to look at my carbs again last night and after a week ago spending a few hours setting bowl levels, meticulously, in a level stand, I check them again and they are all low. So I said the heck with this crap and am starting from the beginning.

1. I pulled the valve cover and am going to take shim clearances after work tonight... then check the list here again for where I can get shims if needed. Mechanically the top end LOOKS fine... no crazy wear, chain OK, guide, etc.
2. I have new boots because everything since going down hill ACTS like a vacuum leak, and even though I don't see any through-cracks, the boots are cracked a fair amount on the outside. Will be new intake gaskets and tube covers as well.
3. Carbs being mailed to church for proper cleaning and bench setting.
4. Then I'll see about getting help for running adjustments...

I took some pictures and was wondering if anyone could comment... below are intake valves 1-4 in order. Is the burnt oil buildup typical or valve stems leaking too much?

Also, the picture of the plug is typical of the four... weird brown coloring on only one side?

Any comments appreciated...

 

that is a nice looking plug brown on tang is good

 

It appears you might be burning oil valve seals come to mind , agree with XJ550H that plug looks good.

 

or years of build up try using seafoam in your gas when you get running it will help remove the deposits

 

Okay this is scary the smallest feeler I have is .008 and these are my clearances

 

Oops I just realized the clearances on the site are in millimeters I'll get the right feelers and get back

 

NAPA or Autozone should have a metric feeler gauge to do the job.....

 

Or burnt valve causing this to happen

 

GearWrench - Metric Feeler Gauge Part # 2274

KD tools part #2274 any auto parts store can order it for you using the KD tools part number

 

OK, checked shims and looks like I'll only be changing one. #1 Exhaust.

• Currently .254mm
• Installed shim is Y270 (2.7mm)
• Need to add .094mm to get to .160mm clearance
• So need Y279? (280 actually)

Anyone want to check my math?

 

it would be easier if you measured in metric. add 275 shim

.010 = 0.254mm -.05= 0.204mm max clearence


you may also want to consider exhaust #3 needs a change. this is due to the overlap of the spec in inches .006=.01524mm

 

I bet gas & oil mix real easy with a piston like that .....lol