Re-re-reviving my '81 Seca 750

From the It's Always Something files, she is suddenly idling rough this morning. Dry, garage kept, has a half tank of gas. Was running fine* on last ride on Sunday. Started up fine, but it died out at the first light (after warm up, 5 suburban blocks, removing enrichment along the way, my SOP). Usual idle is a hair above 1k, now sitting about 2 hairs below. Seems fine off-idle - maybe a LITTLE hesitation. Last time I had this, one of the spark plug boots was loose, but messing with them didn't seem to help. I got to work OK and hope to get home without incident and work on it over the weekend.

Only change was a few ounces of Seafoam in the crankcase this morning ahead of a planned oil change over the weekend. Can't imagine that having an impact, but . . . .
Last valve check was Fall 2022, about 2.5k miles ago. At the same time, the carbs had been freshly Churched by Hogfiddles. There's an inline filter on the fuel line and it looks clean.

Only other recent oddness is near the end of my last ride, my right turn signal stopped flashing. Was hoping it was a sign of a bad bulb, but front, back, and Atari all light up (solid). So, something else to track down, but again, just mentioning it. Does NOT seem to be an under-voltage situation - was reading 13.something when running, 12.8v when sitting. AGM battery was also new in 2022.

 

Try new spark plugs

 

Those were renewed in the Great Rebuild of 2022 as well, but I'll take a good look at them for sure.

 

Can seafoam foul the plugs l wonder, never used it.

 

From the crankcase side? I'd think the rings would have to be REALLY bad for there to be a connection there, and it's not like I'm burning through oil. I've never had a problem with it before - neither in the gas tank nor the oil.

 

I have NEVER had seafoam kill plugs. (Crap that the seafoam dislodges might..... )

plugs— a fellow at the Carb Clinic had a bike that had a dead battery..... we got a new battery, and the bike fired up, but minus #4..... then after it ran for a bit #2 started cutting out. Then when trying to run around the lawn a bit #3 went out.
He went home and put new plugs in, it fired right up, and went for a ride.

Try new plugs anyway

 

Gas cap vent blocked?

 

@chacal, was behaving the same on an aux tank. But of course Dave was on to something.

I may or may not have solved it. First, my memory was faulty about the new plugs, which I discovered when I looked back at my notes. I did NOT replace them at the time, I think because I was confused by the whole resistor plug thing or something. Also discovered I'd bought new boots from Len, since #4 had been flaky, but never did install them. So today I replaced all boots, trimming back the leads a bit since #2 and #4 looked SKETCHY. Still have stock coils, so leads JUST BARELY had enough extra without being taut. Afterwards, she smoothed out nicely. Put it all back together, could only go around the block b/c Mom is out for the evening and I've got kids to watch.

Ran great until I got back in the driveway, but then is started acting up again. Had to walk away at that point. I will say THAT 'acting up' felt different and I almost wonder if the engine was overheating at that point (was a hot one today and I'd been idling quite a bit in the garage). We'll see what she does in the morning.

I also discovered the turn signal issue is more than likely due to a bad bulb after all. Went to swap left and right and not only did the left bulb work OK in the right, but the filament fully broke on the flaky one when swapped - so it had been MOSTLY dead.

Pics of the pulled plugs 'for fun.' Qute a difference. 1-4 L to R

 

#4 is looking a bit sooty.......

 

1. What’s the condition of your oil?
2. May want to try a different TCI

 

So, when you're working on a bike you've had for nearly 30 years, it's good to trust your gut. When I said it was good, then then halfway around the block it acted up, maybe overheating? What it really felt like was fuel starvation. BUT I had plenty of gas in the tank and had even tried the Prime setting.

Was still rough this morning. Went to take the tank off to dig back into it only to discover the fuel line was pinched when I'd replaced the tank yesterday. I put the fuel line in the right place, and it fired right up and idled smoothly. Just went for a 50 mile Father's Day ride. Back in business.

And yeah, a fresh bulb fixed the turn signal situation as well.

As for sooty #4, it really was. Again, that was the old one. Interestingly, when I'd first pulled it after getting home from work on Friday, it was a nice tan. That soot was from troubleshooting - or troubleSOOTing, har - at idle. Once things cool off I'll pull the new plugs and see how those look now.

And just to wrap up (for now), the oil looks good as it's only got about 2k miles on it, but time-wise it's overdue and coming out in the next few days - thus the recent Seafoam dosing.

Oh, and I got into some cicadas on today's ride. Dodged all but two, i think - one on the windshield and one on my pant leg. Eech.

 

Glad to hear it was a simple fix

 

Got the oil change in today as well. A good Father's Day.

 

The new plugs after a 50 mile blast yesterday. So clean!

 

Bike still needs a little tweak. May e due to the plugs being at full bang potential, the RPMs were floating a bit on shifting and coming to lights on the commute today. Hadn't noticed it on yesterday's ride, but that was pretty continuous blasting. Did think throttle was not as snappy. A carb sync should solve it, I'd think. Always something.

 

Plugs may be a bit lean yet, too. Double-check for vacuum leaks at the intake boots.

 

Never circled back to this, but some VERY minor tweaking of the carb sync brought everything back in line and purring nicely.

 

Ok, just in the last 2 days, my oil light is REALLY annoying the hell out of me, so pulling the sensor for manual cleaning will likely happen sooner than I'd wanted (planned to do it this winter). Oil level is confirmed good, have tried 2 Seafoam treatments, and it still acts a fool with little rhyme or reason. It comes on with some hard accelerations, but not all. Sometimes a gentle rise in the road, or a seam in the pavement can turn it on OR off. Occasionally it's on for a flash or two, but lately it's more likely to stay on for a minute or more. Just long enough for me to get annoyed, cancel the warning, have it clear and then re-activate. Yesterday morning, it didn't come on once in 26 miles. Today, at least a half dozen times.

Aside from needing to replace the seal (which seems to be leaking anyway), my big concern is going to be dropping the exhaust, which, to my knowledge, has never been done. Do I need to mess with the header bolts, or can I just (try) to separate the header pipes from the collector (and how much damage will I do to the already-rattling collector when I do?)? I did have the megaphones off in late 2022, so hopefully those come back off fairly easily, but any tips appreciated.

 

Exhaust bolts suck, no matter the vehicle. Start spraying everything on it with penetrating fluid days or weeks ahead of time. Spray it, ride it to get some heat in it, spray again, rinse and repeat.

 

Many times, the collector rattle is actually due to the heatshield on one side or the other.... they’re welded on across the top and bottom, by there is a welded-on ring clamp at the front and back. Often one of THOSE rust through and then make an awful rattle. I just wedged a thick piece of leather in there, and I’ve also just carefully bent the heat shield out just a bit so the vibration does cause metal contact anymore.

Sometimes, the rattle is inside the collect itself, as it gets a loose rusty part, and I’ve also had rattled that are actually inside the muffler as the baffles get loose.

 

I cleared all the crap out of the mufflers and checked the heat shields when I messed with it all 2 years ago.

 

Of course, on yesterday's ride home from work, even with two HARD pulls up to 50 and 70 MPH, no oil light at all.

Make it make sense . . . .

 

They joy of an old bike. Oil level indicator is wonky, and you’re waking it back up..... or, you may have a loose wire somewhere——

 

The saying is with the Vmax - if you're not making the oil light come on you aint riding it right...

 

I have wondered about a loose or grounding wire, but ran out of time to run that down this weekend.

 

A new gremlin has appeared - not sure yet if mechanical or electrical.

When I de-mothballed the bike late 2022, I'd noticed the turn signal switch felt a bit . . . gummy. Turning it on was fin, but cancelling in the middle took more effort than I remembered. When I got back on the road this spring, I finally decided to try to degunk the switch. I didn't want to go too aggressive with contact cleaner, so I just spritzed some IPA (not the beer) in the switch and it was immediately better.

Yesterday, a new behavior was observed after months of reliability. The turn signal would only stay on if I held the switch left or right. As soon as I released it, it went off. After about half an hour, it was back to working properly for the rest of that ride. Then, on the way home, it was fine again, until about 15 minutes in when it stopped working correctly for about 5 minutes and then was fine.



Have not had a chance to take the switch apart yet, and I also wondered if it might be a fault with the auto-cancel unit. It was pretty hot when it first acted up and I wondered if that heat would prematurely cancel the signal. But when I rode home, it had cooled off considerably - upper 60s, so not putting a lot in that theory now.

Anyone seen this? It will probably be a couple weekends before I can get into the control body.

 

What happens if you disconnect the auto cancelling unit?

 

I would have used kroil, rather than an IPA.... you may have intoxicated the switch.

 

The turn signal thing, like the oil light, is VERY intermittent and very frustrating. LOL

 

Heh, I forgot the actual point of my post - what are y'all using for fuel line? I feel like I'm always wrestling with it - have tried various things from the auto parts store and I'm not sure what's on there now, but the OD seems too big for the standard clamps and the ID seems a TOUCH too tight to be able to get fully on the barb of the petcock.

 

Warm it up just a tad with a heatgun and it’ll slide right on—- unless you heat it too much, then it’ll just mush into a pile.
Put the ring clamp on anyway.

 

A different OD will require a different clamp.

 

Ring clamps are adjustable

 

Long time no write. The bike was laid up a little bit over the winter getting the petcock sorted, new fuel/vacuum lines, and a couple other small things. Had drained the cab bowls, so it fired up readily this spring/early summer. I ran about 2 tanks of gas through it and then on one commute home, it started missing. By the time I got home, it was really wanting to die at idle and I had to feather it at lights and restart it a few times. Once out of about 3k RPM, it was fine.

My initial thought was to suspect the spark plug wires, as they were still original, and when I trimmed them back last summer after some other missing, they ended up a bit short. In fact, when checking the plugs, the #3 cap came right off in my hand. So I bought new wire, did the coil surgery, and . . . it was still running rough. Checking header temps, the #3 sits about 30 degrees (F.) cooler than the other 3 (220F versus 190F). I tried swapping wires, plugs, and coils, but it was always #3 acting up. It got to there it wouldn't idle at all.

With new confidence in the ignition, but not a ton of time, I let it set a couple weeks, tinkering here and there. I semi-resolved to pull the carbs and blow the snot out of them with carb cleaner, but first decided to try the ol' Seafoam treatment - which I've had mixed results with in the past. I went with the 2+oz/gallon mix for the couple gallons left in the tank (about half). I ran it until I could smell it was in the carbs, and then let it sit. Over the next couple days, I would run it a little, and it seemed it was getting a little better. Somewhere along the way, I bumped the idle screw up a little and it would stay running without being on top of the throttle. Yesterday, I took it around a few blocks and it seemed a bit better, but still nowhere near 100%. I decided to ride in to work today, and it's considerably better than it had been. I even stopped for gas (and added more Seafoam) and was able to lower the idle screw again (idle had crept up to 1,500RPM). There's still some occasional missing - mostly in the 2-3K RPM range. Can definitely feel the power coming in and out.

I may end up having to get back into the carbs, but maybe, JUST MAYBE, I'll get away with an Italian Tune-up this time.

When my (Italian) buddy made that comment to me, I was also reminded of the acronym for Fiat - Fit It Again, Tony! (Or Ford - Found On Road Dead). So I came up with one for my Seca, "Something Else Croaked Again." So it goes with a 44 year old beastie/bestie.

 

Actually, looking through my post history here, seems #3 has been a problem child. Compression was good last time I checked, but I should check again. My other thought, though, is that the #3 is where the vacuum line runs from the petcock. "For fun," perhaps I should try capping it off and running the vacuum off #2 and see if that makes any difference? Can't hurt, right?

 

It’s worth a try. Maybe a leaky vacuum line

 

So, first let me start off by saying I really wish that at 51 years old, I'd have learned to overcome my squirrel-brain and be more methodical.
Secondly, an image:



When I went to leave work, I fired up the bike and was pleased it started right up. As I squared away my phone, lunch bag, etc., and before I pulled my helmet on, I smelled a strong scent of gasoline. I looked to the petcock (a petcock I've rebuilt twice now in the last 6 months or so - with quality Len parts) and gas was spurting out of the little pressure regulating hole in the grey plastic block of the body (right next to the vacuum nipple). It was pulsing out in time with the engine. I immediately shut it down. I tried the prime and reserve positions of the switch, but it leaked even worse then. When I pulled the vacuum line off the petcock, it was full of fuel as well.

SO, I"m pretty sure the misfire mystery solved - and if I'd been more methodical and not written off past evidence, it would have revealed itself sooner. What was the last thing I changed? The petcock. When it started acting up and I pulled the spark plug from #3 (again the cylinder which feeds the vacuum for the petcock) the plug was NOT overly lean - it was dark/rich, maybe even wet. I'm now certain THIS WHOLE TIME, it's been pulling fuel trough the petcock somehow and drowning out the cylinder, NOT starving it.

I got a ride home (26 miles), borrowed a trailer, and rescued the bike last night with a buddy. Had I not just filled the tank, I might have tried some way to take the petcock out, get it home, fix it, and return with it, but trailering seemed the better choice.

I have not had a chance yet to tear back into the petcock to see what the hell I've done wrong - I've rebuilt it in the past with no issue. The first time I reassembled it, it was not shutting off w/out vacuum, and I needed to clean up the valve seat better. I'm assuming I've either torn the diaphragm, or maybe it just wasn't sandwiched properly between the layers of the body.

I'm tempted to just replace it with a standard on/off/reserve valve. Open to suggestions for a source if others have done this.

So glad I didn't blow'd up.

 

Last time mine leaked I smoothed the mating surfaces with 800 grit paper on a surface plate. Not sure if it did much everything is ok for now.

 

I polished the surfaces when I did the valve seat, but I'll take another look, perhaps this evening.

 

Sadly, it looks like the pics are MIA in the rebuild thread. This is a note to self for later: https://www.xs650.com/threads/rebuilding-yamaha-vacuum-operated-fuel-valves-petcocks.20662/

 

Could any fuel get into the crankcase?

 

I'm not sure how it would. The petcock is operating properly in that no fuel flows while there is no vacuum. It's just that it's coming out of the wrong place when there IS vacuum as well. And the carbs were rebuilt by Hogfiddles 2 years back so I have pretty good faith in the floats at this point.

 

I found the problem - a small tear in the diaphragm on the valve side allowing gas through along the shaft and through that relief hole (and into the vacuum line). TEENY TINY tear - big problems. Planning my course of action.

 

1. If fuel leaks through the petcock, the only thing keeping if getting to the crankcase through one or more leaky float valves in the rack. That’s is a COMMON cause for polluted crankcases. Most people attack the carbs but don’t address the petcock—-/ or vice versa, instead of addressing BOTH. The carbs, as long as they are in good condition, will stop the gas if the petcock is left on PRI ( and the bike isn’t left out in the sun to create excessive pressure……which SHOULDN’T happen as long as the ball-valve in the tank is working properly ….. lol)

2. I would not expect gas to get to the crankcase in this particular case, though.

dfox

 

First, Len continues to be a class act and a replacement diaphragm is already wending its way through the Atlanta USPS Distribution System - lord help it.

Second, in the interim, I managed to 'buy it now' with 45 seconds to spare to get overnight delivery on a Chineesium petcock from the 'zon. Had some points saved up, so it was essentially free. Got it yesterday evening, installed it, and she purrs like a freakin' kitten again. So now I'll have a spare when the replacement diaphragm gets in.

Looking back at my post history, it's so frustrating that this was likely a problem all along and I kept missing the signs - the biggest one being it running REALLY WELL on the aux tank (no vacuum to get fouled). REALLY kicking myself on not thinking it all through better.

Anyway, back in business (well, when the heat index gets back down from 'zon territory). Again. For now. And hey, new spark plug wires (replacing the 44 year old originals) is seldom a bad idea.

 

That's the truth..........