Seca 750 Died on Highway - Rough Engine Noise

Hey, guys! First technical post on here, looking for some advice, please. Forgive me if this has been covered in another thread; I couldn't really think of what to search for.

I bought an XJ750 Seca about two months ago. I was mainly taking short trips (~5-8 miles) around town, no highways, and she was running great. Last week, I finally decided I was comfortable taking her on the highway, so I took a couple of trips to and from work. Only took until ride #3 until this problem happened.

I was cruising along, doing about 70, and I noticed that the engine didn't sound quite normal. I kept riding and listening, and decided it definitely sounded weird and was getting louder. I also thought I could feel more heat around my ankles than usual, but I might be imagining that.

I took the next exit, pulled in the clutch, and she almost sputtered out and died. I quickly revved her up to keep the engine running, and that's when I noticed the sound clearly. It was a rough sound, almost a sputtering, but it was still smooth/symmetrical/not-random (don't know how to describe it better than that). Almost like one or two cylinders weren't firing. So I just let the engine die and coasted into a parking lot. No smoke, no leaks.

I couldn't get her started back up, and still can't. She makes a low, burbling noise like there's firing in one or two cylinders, but just not enough to turn it over. Trying the easiest thing first, I went ahead and replaced the spark plugs with NGK BP7ES's, taking out the cheap Champions that were in there. Still no dice, even with a push start.

Now, I am willing to learn to work on this thing myself, but I haven't really done any mechanical work.. haha I have few tools and almost no free time. But does anyone want to field a guess or two at what might be going on here?

Thank you in advance! Any help much appreciated.

 

Could be several things, the plugs you pulled were they black, white , grey, brown ? If bike is to lean you could have burn't a valve , To rule this out you will need to do a compression test ( you can buy a gauge or rent from Autozone) take all 4 plugs out ,hold throttle wide open and crank over until gauge needle stops moving you should get between 100-150+ PSI (100 is way low but cylinder could go higher with a little oil put in cylinder ) If it is 100 or less you have a problem. Another thing your carbs could need rebuilding , OR is your fuel line kinked? try to open float bowl screws , see if fuel flows out or not. If you have stock vacuum petcock is it in PRI or ON/
PRI will flow all the time..ON flows only with engine running. IE if fuel line is restricted it can cause a lean condition and will result in a "hot " running engine. Another possible problem could be coils are cracked and engine heat broke them down. ( I replaced mine with 82 Honda CB750 coils ) or have you changed out the fuse block for blade fuses? Battery weak could cause misfire . Just my thoughts cheers

 

Thanks for the reply, Jetfixer!

I'm no expert, obviously, but the plugs that came out seem to be in good shape to me. The white part is still mostly white, no obvious pitting/corrosion/deposits. They were gapped correctly, too:



I know there are carb problems, as with all these old bikes, it seems. The guy I got it from said he cleaned it three times, but I'm sure he didn't take it all the way apart or do a real rebuild of any kind. That's the first thing I plan on doing when I get some more cash. Hoping that will help the hard-to-start problem, too.
Haven't checked the fuel line, but nothing has been tinkered with since it was running. Petcock has always been "ON". Battery is newish and I think it's good.
Everything else you said, I'll have to research.. haha

Thank you!

 

Verify whether the plugs are sparking, and then a compression test is the next step..........

 

valves, tight valves don't usually act up until the engine gets good and hot. Then they stop sealing and the compression goes away. sometimes it starts again when it cools down but with other problems it might not. How many miles on it?

 

Thanks, you guys!
Polock, about 300k

 

Is it 30 thousand or 300 thousand? I. Should have also included adjusting valve thanks Polock ...check the fuse block ignition fuse.

 

I'll pipe in and suspect valves too. At 30,000 miles it should be on the 7th valve clearance check, but probably hasn't had but one or two.

 

Haha yes, 30k, excuse me.
Alright, cool, thanks!
Carb rebuild and valve adjustment are top on the list.
The Church of Clean also mentioned engine syncing. Anyone care to link me to a read in what that is?

 

Carb synching. Making sure that the throttle plates in each carb are matched to the vacuum that each cylinder develops so the cylinders are "in tune" with each-other instead of working against each other.
Links on how to bench synch, and perform the final running synch are in the Church of Clean; last section, near the bottom of the page.

 

One other possible problem could be a blown head gasket..doubtful but possible another reason for compression check

 

Thanks for all your input, guys. The saga continues!

Finally got the bike to the shop last week. They did a compression test and a leak-down test, and all looks good. Cylinder 1 is a hair light on compression, but still totally fine.

They started troubleshooting the issue, and found out almost immediately that it needed the petcock replaced. They said, with an alternate gas tank and petcock hooked up, it started and ran beautifully. Great news, I'm thinking! They stuck an aftermarket petcock on there and called it good. They also said the battery was on its last legs (which I suspected, since I accidentally killed it a few weeks ago...), so I had that replaced as well.

Well, I get the bike back and she seems to be running perfectly. I get on the highway, going 65-70, make it about 14 miles... Same exact problem happens again. Felt the heat at my ankles. She starts sputtering and clearly losing power. Extra gas just makes her sputter more and sound worse. I pull in the clutch and the engine dies.

So, I was thinking this was something heat related -- possibly the valves, like Polock said -- but I'm confused.. I let it sit overnight to try it totally cold the next day. I got it started, but it took more work than usual. Once it was running, I took it for a ride, and it took less half a mile for the problem to start right back up again. The engine definitely wouldn't have been up to highway-level heat that quickly, right? It's weird that, once it dies once, the problem persists.

Anyway, I didn't get the valve adjustment or carb rebuild done. I guess those are still next on the list. Don't know if that will fix this issue or not.

 

Fuel tank vent gets my vote. Vents fine at low RPM, but when the motor is really sucking fuel, the vent is restricted enough to starve it for gas. Go make it happen (die on the highway etc) again, and then open the gas cap when it happens. Count to 15 and try to start it. OR, take it for a good long ride with the gas cap unlatched (not a great idea, but would work for troubleshooting).

 

Or just clean out the cap vent since it's such a simple job.

How to (this covers a full cap rebuild, but will show you the wheres and hows of the cap vent):
Gas cap repair

 

if it is the valve adjustment, you don't want to let it happen too often

 

Agreed. Valve clearance checks and adjustments are a basic maintenance item, and should not be let-go.

 

Valves for sure need to be checked. Petcock? Rebuild it, but to me I would think you would pass into a lean condition as the carbs starve for fuel and things should rev up before it dies. . . ?

 

Here's a dumb question...how much gas is in the tank?

Gary H.

 

If it happens again... Put the petcock on PRI, give it a minute to fill carbs back up, and try starting it. If so, great. If not, open the gas cap to remove internal vacuum if cap vent is plugged.

If that doesn't do it, I'd be looking more toward a TCI issue, or related issue ( coil breakdown, pickup breakdown..... ) due to heat.

Finally for now--- open your oil filler cap and take a whiff--- if it smells like gas, your oil is thinned out and you're simply overheating. THAT would require some immediate steps:
Drain/replace oil
Rebuild carbs/petcock

Among other things----

All before starting it up again

I'm not convinced it's a valve clearance issue yet

Dave F

 

What do your plugs look like? black , white, brown ? This will give you some indication on your carb/ engine condition. If your carbs are dirty (internally) or jets are wrong size ( mine were miss matched by P.O. ) or mixture screws are not set right , synch is off ( yes may run at idle is you have a puttering at idle out exhaust or kinda of a popping when reved and back to idle synch is off) Agree valves at least need checked , and could be a fuel problem, are you running a fuel filter? ( recommended)
just a few thoughts on your problem.

 

Thing is, with multiple 5-10 mi trips and a couple long trips with no issue then all of a sudden things happening, I DOUBT it's a "wrong/misplaced jet" issue.

Sounds to me like a " I finally got hot enough to cause an electrical breakdown" issue. Fuel starvation usually happens sooner, valve clearance issues don't usually show up like that either..... Usually much slower and subtle decrease in power over a long time.

 

He states bike is running "HOT" my opinion , it is running lean so it is possible float level or wrong jets or both "Could" be part of the problem , and yes I agree with Hogfiddles fuel starvation , could be at fault, as well as coils breaking down ( both not likely BUT it is possible) when engine gets hot. This is one issue that will require some true trouble shooting IE try what is suggested one item at a time , check fuel cap vent if ok , pull the tank off check coils for cracks with engine hot and in the dark see if you can see sparks with engine running (use an alternate fuel source) . This is just a few thoughts of how I would start approach...and this does not cost you anything to check this.

 

I agree fuel starvation after many miles is a long shot, and coils not likely unless you're riding in rain and didn't' tell us.

BUT.....I said TCI breakdown due to heat--- then possibly other electrical like coils, pickups.....
At THIS point I am still leaning toward the TCI

 

+1.

Gary H.

 

Agree could be TCI breaking down it does get hot, but unless he has a spare TCI to swap out , as quick way to find out. I recall a test in the manual. Have not had any problem so I don't recall what it involves besides a volt meter. I know my original coils had cracks in housing ,but bike ran ok, but much better after I swapped to the CB 750 coils ( everyone says things like this , but it was true struggled to get past 5500 rpm now no problems ) This was just my experience your results may vary ... sounds like a drug commercial exept for the swelling lasting more than 4 hrs..

 

Looks like you're getting plenty of help but I wanted to point out that this is exactly what mine did when I had ignition problems and was only firing on two cylinders. Mine ended up being a pinched cable from engine re-installation so I doubt you have the same issue. Figured it would be worth mentioning, ideally you will be in a position to test the pickup and ignition coil immediately after it happens to see if one or the other is failing after warming up.

 

Or he could mail his TCI to a fairly nearby member (cough, cough) and have it tested in a reliable machine.

 

Damn, you guys are a wealth of information! haha thank you for all the replies. I haven't had time to read and think about all of this yet, but will check back in soon.

 

That's why we're here

 

I'll jump in here and address the one issue that hasn't been touched yet.
Happens every summer when it really starts getting hot.

Heat Related Thermal Break Down of the oil!!

DFW area with temps in the high 90's to low 100's
High speed highway running. 75-80 mph. For the slow vehicles.
Crankcase/Trans getting hot.

Under these conditions you absolutely need to be running 20w50 oil. And an oil cooler!
Oil is both a lubricant, and coolant.
It is a coolant in the fact that it transfers the heat from the moving parts to the alloy castings.
Oil can only absorb so much heat before it reaches heat saturation. Once this happens the excess heat from the moving parts can not be removed.
Clearances get smaller, Fuel boils/vaporizes, and eventually engine seizure. Everything else mentioned is just a further aggravated symptom.

Start with an oil change using a good quality (wet clutch compatible) 20W50 oil.
Install a good aftermarket oil cooler.
Then progress onto the other issues that will still need to be looked at. Carbs, Valves, Etc...

~Ghost

 

A lot of the 20W-50 motorcycle oils I see (from googling) are synthetic. I also read on this forum synthetics are bad for a wet clutch motorcycle.

Are 20w-50 motorcycle synthetics such as the Mobil version JASO certified and safe for wet clutch applications?

 

Look at this on eBay http://www.ebay.com/itm/151951540675

Gary H.

 

Any JASO MA certified (or compliant) oil will do.
I run long distances in high temps and have had no problems with Rotella Triple-T 15W-40, even before I added the oil cooler. You could try that if you can't find a 20W-50 that's suitable.

 

Rotella Triple T 15w-40 is what I use

 

I use yamalube 10w-40 in everything all the time

 

I use one of these two depending on ambient temps.

Gary H.

 

~ Pulling up the hip waders~
No Oil Thread Here Guys!

~Ghost