DOHC Starts sometimes, not others...

[Jeremy Corbin]

Hey guys!

My '82 Seca has been giving me a LOT of trouble the past few months. I'll ride to work (about 25 miles) and then when it gets there it wouldn't start again and would force me to tow her home. When I'd get home, she'd start again, leaving me scratching my head.

I thought it might be related to temperature (since I knew the jets that were installed by the PO were mismatched and wrong) so I bought a matching pair of 45's for the idle jet and installed them AFTER I had boiled the carbs for good measure. The bike fired right up at 1/3 choke at 70F at 2 turns out. I let it warm up and then dialed in the idle jets so she purred nicely around 2-1/4 turns out. I checked the spark plugs for color and they looked good, then quit for the night.

The next day, it was closer to 55F and she wouldn't start at any choke setting. I hooked the battery charger up (cause I nearly killed the batt) and thought that maybe it was a bit too lean, so I added another 1/2 turn and she fired up again. I dialed in the jets to 2-1/2 after she warmed up and then quit for the day.

Another day goes by: She fired right up at 70F again with Full choke (but quickly backed it off) so I moved it out of the back yard and into my parking spot out front, expecting to ride it to work....

Alas, tonight when I tried to start her up (80F and varying choke settings) she wouldn't start at all.

Something is up that is totally screwing with my enjoyment of the bike. I was thinking that it had something to do with the jets, but this amount of inconsistency is driving me crazy. Overall, from *before* changing the jets to now it has shown the same type of ill behavior by starting up fine some times and not even pretending to start at other times.

Just to be clear, she has 14K on it and all I've ever adjusted was the carbs. Stock air box is present (with filter), but the old intake boots from the box to the carbs fell apart in my hands a while ago, so I replaced them with other rubber hoses, but the plumbing goes where it should. The exhaust is the stock H Pipes. She ran okay for a long time, but became increasingly unreliable since last fall.

I'm lost... and losing my mind.... so any thoughts about be appreciated.

 

[willem]

could be a few things. Your petcock could be clogged, or your inline fuel filter (if you have one, which you should), your valve clearance could be way out of spec, you could still have a passage in your carbs that is gunked up, you could have air leaks in the carb boots or in the exhausts, it could be an electrical issue..

go through the steps here and see how far you get with it. I can tell you, my seca was a real pain at the start, leaving me stranded by the side of the road on multiple occasions, but since I covered all the maintenance issues it has been running like a champ and is very reliable, in all weather conditions.

 

[User9053]

If you have the stock airbox your jets should be miss matched, reason being the battery takes up a lot of the airbox space making the airflow to each carb different. My PO changed them to matched jets and it ran like crap. Changed it back and finally had midrange. I'm running a MAC 2 into 1 exhaust so I went up 1 on each.

 

[Jeremy Corbin]

Quick update:
I started running through the check list and stopped when I hit the part about spark quality. It turns out that part (if not all, hopefully) is that the spark on each plug is weak, thin, and yellow. Primary resistance at the coil is around 3ohms (within tolerance) while the secondary resistance was over 80Kohms (tolerance is 7.9K within 20%). Both caps were also inconsistent with each other. New plugs, caps, and wires are on their way.

Months ago, I had found the exact "factory" settings for my carbs and noted that the pilots and needles were matched, but the Mains were offset for the exact reason you described (weird airbox shape). The factory pilot jets are 42.5 and I found that the bike needed to be 3-1/4 turns out to run correctly, hence my decision to go up to 45's. I'm now at 2-1/2 turns out and when she DOES start she purrs like a kitten. After I get the spark strength up, I'll know more.

On a side note, I noticed in a Mikuni BS34 rebuild guide that there are two rubber plugs over the pilot jets. My carbs have no such plugs, but still ran correctly for over a year. These plugs are to block the pilots since they get their fuel from the mains, allegedly. Has anyone else run into any detrimental effects by not having them?

Checking the valve clearances is on the upcoming agenda since I recently acquired the little thickness measurement thingies. (I'm totally spacing the name now.)

I'll be sure to update again.

 

[willem]

feeler gauges

about the rubber plugs on the jets, if your bike didn't have them and it ran well without them, they probably don't belong in there. These carbs come in a wide variety of flavors, so it is likely that your rebuild guide doesn't 100% match your bike's carbs.

I'd expect the bike to run much better with new plugs, caps and wires.

 

[Jeremy Corbin]

Well, the plugs, caps, and wires came from Mike's XS. Despite using the references for the plugs, the ones that came, B8ES, do NOT fit my bike. The plug is too wide to fit into the head. Back to the drawing board on that, but for now I cleaned the plugs up and installed the caps and wires. Bike didn't want to start, but with full choke she came to life, warmed up a bit, then died at idle again. I even turned the idle speed screw quite a bit. There's this spot where it'll idle too high...like 2200... and then a 1/4 turn back it barely holds 1000. If I crack the throttle it never stumbles or hesitates like a vac leak would do.

Going back to the list, I decided to use the feeler gauges on the valve clearances. Everything is within spec, mostly on the tighter side.

Timing is next, but I can't get the little cover off the big cover to read the timing. The cover for the generator gear (to turn the engine for the valve clearance check) came off just fine, but the timing cover won't budge.

Here's a question: How can I tell if the carb boots are worn out and are seeping extra air into the cylinders? They aren't cracked or obviously leaking. They're stiff, but not enough that I can't get the carbs back on or anything. $45 for a new pair just puts the project out 2 more weeks and "shotgunning" parts onto the bike isn't my idea of troubleshooting.

 

[willem]

spray some brake cleaner, starter fluid, or even deodorant around the carb boots while the bike is running. If there is a change in rpm, it's cause it's sucking the flammable spray into the engine and burning it (hence, you have a leak)

 

[Jeremy Corbin]

Update:

After using the Starter Fluid spray test, this is what I have found: The carb-side of each boot is leaking even though the clamps are tight. I'm guessing this is where the leak is and ultimately the cause of the inconsistent startup/idle.

I am surprised that the bike was trying to die with the spray instead of idle-up as I anticipated. I figured with a air leak it would idle up as the ratio became more in-tune with what the engine wanted.

Ambient temp is 80F, choke is off, bike is warm, idle set to 2000RPM(-ish). It did NOT want to start and required full choke and lots of patience. I nearly had to get the battery charger out.

So, new boots (and clamps cause these are kinda sucky) are in my future. Anything else I should watch out for?

 

[xschris]

Could also be the butterfly seal leaking. Where you are spaying also hits the outer ones.

 

[Jeremy Corbin]

Update:

Fired up the bike (same as above) and specifically sprayed the butterfly seals and they seem to be fine. I had a small reaction on the LH carb, but with the position of the in-line fuel filter it is difficult to hit the seal specifically without some overspray onto the carb boot.

So, carb boots will be ordered and installed. Hopefully I'll have it all squared away soon... The summers'a wastin'!

 

[willem]

It's not a bad investment anyways, those carb boots. Makes for a much easier job taking the carbs off and putting them back.

 

[Jeremy Corbin]

As it turns out, the carb boots from MikesXS do NOT fit my Seca. After a quick email chat, I'll be returning them for credit. It's too bad that they don't fit since it kinda forced me to re-use the existing ones. I managed to start the bike and get it warm, then after I made sure the boots were warm, I tightened them down really good so they wouldn't leak. After another Starter Fluid test, I'm satisfied that they'll hold until I can get a hold of some better ones.

Here's what the bike is doing at the moment: She's starting and running. Whether that holds for all temperature conditions, I'm not sure yet. Chances are good I won't be taking her on the ~50 Mile Round Trip to work until I've had a good shakedown run.

 

[Jeremy Corbin]

Shakedown complete:

The bike is running fairly well. I will fill the tank and track MPG to ensure it is running okay but it feels a little weak in the pants. 2 turns may be too lean since she feels really strong when I have the choke on "just barely."

Since the shakedown run went well, I went ahead and rode her to work (50mileRT) and everything went well.

So, the synopsis:
-I bottomed out the pilot jets and decided that two turns out was the most reliable on the 45 jets.
-I tightened the carb boots as far as I could since they were leaking and MikesXS does not have the correct replacements.
-I must work on the boots from the carbs to the airbox, or elect to replace the airbox and run with pods. I'm not excited about trying to remove this airbox after evaluating the things that need to be relocated or removed just to remove it.

Things are good, Mileage pending.

 

[Jeremy Corbin]

Nope. Nope. Nope.

It's been months since I've updated this and I'm still having issues. I gave up and sent the bike off to the local shop (who had it for 8 weeks!!!!) and they cleaned the carbs out, replaced some o-rings, and they couldn't get it to not start. However, when leaving for work tonight it did the same crap it always did.... turns over and doesn't start.

The shop couldn't get it figured out.
I couldn't get it figured out.

Is there something so subtle that I'm just totally missing? I'm leaning towards electrical just because it's so intermittent but it has to be so.... random.....
Like: Is there any way a the neutral switch would allow the starter to turn but not send the right signals where they need to go? That sort of thing.

 

[doodsaibot]

I may have read over what you have done already but have you checked in or cleaned out the gas tank? I have some purple power rust remover on order that will show up in 2 days time. On that same token, if there is rust it may be dancing around in the gas tank and plugging up the petcock or possibly the fuel filter? I also noticed that my gas was dark yellow in the tank so that meant there was rust in it. I know that sounds way out there but give it a shot if you haven't yet. I will be doing that on Thursday to my bike as well.

 

[Jeremy Corbin]

Tank is clean: I had cleaned my tank out last year when I saw "white" residue on my gas. It turns out the little sock filter for the petcock was slowly eroding. I cleaned the tank out and everything looked fine after that. The bike has an inline filter on it as well, but even with the weird gas it never acted like this.

Interesting factoid: I nearly killed the battery while trying to start it Sunday night, so I threw it on the charger. I put it back on today and bike fired right up; No hesitation.

So here's my question: Is it possible for the battery voltage to be high enough to turn the starter but low enough that some electronic function to not do what it needs to? The ignitor box doesn't quite have enough voltage? I'd kick myself if all I needed was a new battery (this one is maintenance-free).

 

[XS400NJ]

Somewhere earlier you said that you have new spark plugs on order, did you put new ones in? In my experience for bike to start you need air, fuel, and spark. With consistent problems you are getting I would make sure I have fresh gas, new spark plugs, and air filter I can easily blow trough to start with. After that comes presence of spark and fuel mixture out of carbs. Old dirty spark plugs may cause problems you are getting.

 

[willem]

Yes it's possible for the battery to crank the engine, but not produce a good spark.

Check the voltage on the battery when full, should be about 12.6 - 12.8 volts. While cranking it shouldn't drop below 12. If you get it running you should have a little higher voltage, in the 13.5- 14.5 V range depending on rpms. If the battery drops below 12, it's dead. If it doesn't have 12.6 volts when charged, it's also dead.
If your bike doesn't produce about 14 volts while running, your charging system is dead.

Unscrew the plugs after trying to start the bike. Are they wet from fuel? If they're dry, you need to look at those carbs again. Also try the starter fluid trick (spray combustible fumes like starter fluid, brake fluid or even deodorant into the air intake of the carbs). If it doesnt fire with that, look at the carbs. If there's no reaction to starter fluid, and the plugs are wet, it's a spark issue.

Twist the plug caps off and cut a half inch off the spark plug wires. Twist on some new plug caps, put new plugs in and try again. You can also test the spark plugs by putting the loose plug into the spark plug cap and sparking it against the engine case (so you crank the bike with unscrewed plugs). You should have a nice, strong, blue spark.


oh and stop going to that shop: if it's a bad battery they should have been able to spot that!!

 

[Jeremy Corbin]

Belated Updated:

As it turns out, it was definitely an electrical issue.

I had the bike at the local shop TWICE and they couldn't make the bike produce the issue but one time, so I picked the bike up and just felt defeated. However, when I got the bike home I started to think about how I park the bike (ie center stand vs side stand). I usually park the bike on the center stand at home and at work since it's more stable, but I had noticed that the bike would often not start on the center stand.

When I got the bike home from the shop the second time, I went ahead and just crouched down on the LH side of the bike and pitied myself for a moment about how I couldn't figure this out. Then I noticed a single black wire with a eyelet on it just dangling in space. Based on how the wire was shaped (bent into place over time) I couldn't see anywhere that it was supposed to mount to. It looks like something bracket-like WAS there, but fell off at some point. There is almost no way to see this wire unless you're in precisely the right spot. It's kinda hidden behind the regulator but doesn't belong to it.

I tried an experiment:
-I grounded the wire (since it was black) to a piece of frame and started the bike... which it started immediately.
-I left the wire ungrounded and the bike failed to start.
-I left the wire ungrounded, let the bike fail to start, and while cranking I grounded the wire and it started immediately.

I have no idea where the wire goes, or what it was supposed to be doing, but I found a bolt nearby to assign it to. The bike has started every time since I grounded it securely.

Looking back on this thread, I'm shocked at all of the different places that I was looking for the issue. I thought it was fuel. I thought it was ignition. I thought it was air. Discovering that it was a random ground that had lost it's home and that I missed most of the summer-riding I could have had was super frustrating.

 

[Unkle Crusty]

I made a note to look for that wyre sometime, and be aware in case my 83 Seca quits.

Unkle Crusty*