'82 Seca 750 Refresh Project: Now Scooby's Bike

Hello my friends.

I thought I’d start a thread for the Seca 750RJ that followed me home from the 2019 CNYCC that is hosted by our gracious host Hogfiddles. I had mentioned this new addition in the clinic thread, but as I continue to clean, sort and organize things I figure I’d share some details and progress (who doesn’t love before and after pictures?) and ask questions as they arise. One in particular at this point… but I’ll get to that down the thread.

Day 1… On the trailer. Really good bones in need of a cleaning.

 

One of the first things I did was deal with the fuse box. There were some funky things in there with a previous upgrade.

Additionally, I found that the old girl had some furry dinner guests.


Here is the clean up I did. Wire colors are not exact, but I made sure the gauge matched. Donor wires came from my old Volkswagen wire stash.


For the clearances, I had to remove the valve cover of course and found the source of my oil leak. A home made gasket! Only 1 shim out of spec, so that got swapped out with a new one… Clearances in spec now… Thank You Len! The cover gasket and bolt “doughnuts” were dealt with accordingly as well.

 

Then on to more cleaning up and polishing of things as I waited to place the order, then receive the carb rebuild kit from Len.





Carb rebuild kit came lightning fast from Len (of course) and on to the teardown, clean and rebuild of the carbs… The first stage of breakdown...

 

Hey, Give a girl some privacy while she’s taking a dip!


Clean #3… Dirty #4!



Here’s #1 all dressed up and waiting for for the family reunion…



Almost there… Orange Juice caps make nice carb caddies!


All back together… Benched Synced, Leveled in my home made carb rack holder, Wet Set and ready to go!

 

After reinstall, of carbs, she fired right up… It was awesome. She screamed up to +6k quick, but when I backed off the idle adjustment screw, the idle came back down.

More Info...
- I set the air mixture screws to 2.25 turns from soft seat position.
- Brand new plugs
- Did a vacuum sync and got everybody playing nice together
- Using the Colortune, I was getting a nice blue on all cylinders (or so I thought... feel the question coming here?)… Did not touch the mixture screws at this point.

Here’s the problem/question(s)…

I can’t keep her running... seemed ok at first, but I believe as the plugs quickly began to get dirty, it got worse quick... plugs are deep black sooty now… not wet.



Seems like things are getting worse… probably as the carbs continue to build carbon…

Here is the color tune working in #4… at this point it was seemingly running a bit better in this video.


I guess I’m having trouble “reading” the color tune. Seems like a good blue in the window, but it’s a bit misleading as there is the actual spark from the metal prong which can be seen only momentarily in the video unfortunately… Hard to differentiate between the spark jumping to the collar of the color tune and the overall explosion of blue… I’m not sure I’m being clear here… I apologize.

Here’s another video of #2 color tune. In this one it is a better view of the actual spark… not just the explosion… Am I seeing purple? I’m so confused….


Where I’m at now is that I have a low popping sound that can be heard in this video…


What are your thoughts on next moves here?
Quarter turn clockwise on the mixture screws?

It’s tough to keep her running at this point to even try to get the vacuum sync up and running. With the increasing popping at throttle, I’m scared to break something!

I’d love to hear all thoughts.

Thanks…

 

2.25 is lean, it don't cost nuthin, try 2.5 or more. that plug never got hot, it might look rich because it only fired every third or forth time and then just went poof

 

Nice work! Think of changing to a different type of plug? Are the coils as hot as they should be? You seem to have taken care of all that needs to be done to make her fun like she should. Coil wires are okay? Have you looked down the cylinders to see how much if any, carbon is on the pistons? If there is a lot in there, cleaning them up might help?

 

Hmmm. I was thinking it was rich because of the black color. Opening it up a bit is a good idea.
Still, the colortune (which should be the answer to getting the mixture correct) baffles me...

I put NGK BP7ES in there.

Resistance? That's a good question. I have a "cheapy" Harbor Freight meter... though perhaps I put it on the wrong setting...

 

put the colortune away for now and tune for peak rpm. turn a mixture screw in or out 1/4 turn, if the idle goes up leave it there if not put it back and go to the next one.
first pass don't try to make it perfect, just better. second pass go by 1/8 turns, higher rpms is better. now do a running sync again.
make another pass over the mixture screws again. the process is easier if you start on the rich side and lean it as you go.
take it for a ride get it good and hot and make one more pass over the mix, if it was stumbling on take off open the screws 1/8 turn

 

you can add some heat shrink to the exterior of the color tune if that is where the spark jumps from

 

Soot is an indication of an incomplete burn, either rich or lean. Follow Polock's advice.[/QUOTE]

 

Update:

I pulled the plugs, gave them a quick brushing and reinstalled. I also turned the screws out to 2.75 turns as a starting point. I then followed Polock's instructions and did a pass across all 4 screws. Then I did another vacuum sync. Not perfect, but much better... Here's what I have now.



No test ride tonight, and tomorrow is booked, but I plan to get it done on Tuesday. I'll update again.

Thank you so much my friends.

 

go over the screws again after a ride while it's good and hot. getting it up to full temp makes a difference

 

+1

 

Curious about the indications on the sync as well... Am I looking for a specific number when at idle? Or is it just more important that all four are doing the same thing at the same time?

 

same thing same time

 

Update:

I'm glad I not only recorded video of a decent idle, I posted it as proof... Why? Because when I went out there today to start it up and giver her a run... I was back to the popping, stalling, can't keep her running issue.

Rats!

I literally did not do anything to it after that running video. I shut everything down, and left everything as is... sync gauge and all.

After fiddling with it for a while, I decided to check again if the bowls were getting fuel... Source on PRI, loosened the drain screws, it seemed like it didn't refill as fast as it could have... #4 actually drained completely and it took a wrap of the screwdriver handle to apparently get the refill going. Perhaps this was just coincidental...

I decided to shorten the fuel line to the tank that I had sitting on the toolbox maybe there was too much slack I thought. This resulted in the fuel filter breaking!

Rats Again!

With no other way to connect fuel source to carbs, I used a clear-ish bic pen body so I could see the fuel supply. My set up...



When all connected, (again, at PRI position) it doesn't seem to allow fuel AT ALL into the carbs without a massaging (pinch, squeeze, etc) of the line. When it finally starts to trickle down, It never exceeds the level that you see in the close up. After start up, the level disappears and never returns...

Enter stage left, the popping and general unhappy-ness (both me and the bike!).

Cap on the tank is OPEN by the way.. so now I'm thinking that if indeed my issue is a lean condition, the fuel level in the bowls is getting too low and not able to recover... When I we set the floats, I left the carbs for a few days with fuel on prime connected... no leaks, no change in level.

Perhaps I have a petcock problem. I don't have one of those nifty (Expensive) auxiliary tanks used for tuning so that I can rule out fuel delivery as a possible problem.

Given my makeshift set up, shouldn't the fuel "fill" the pen body? I'd think so, but if not, at least keep a consistent level after startup? Interesting...

My next move is to get a new fuel filter and alternate source for the fuel. This may take a bit as I'll need to cobble something together... Unless I can borrow one from a certain semi-local fellow XJer (cough, @saftie , cough, cough).

Until the next update... and again, thanks for all of your problems solving considerations, and of course willingness to share your years of XJ experience.

Update to the Update:

Skip the petcock issue for now... With my limited knowledge, I feel like it is a lean issue. Just tried again, She will start and run (all be it miserably) with the choke on. Once I back it off, she starts to pop and things get worse. All screws are at 3 turns counter clockwise from seated.

Maybe my float levels somehow changed. They were "dead on" when level on the bench. Now they read slightly lower on the bike, but I think that is to be expected as once carbs are installed, they are not level anymore.

 

I use a lawn mower gas tank as a fuel supply. How much fuel do you have in your tank( happens a lot being to low)?

if your floats drop so low that the needles bind or does not drop enough to drop needle there is a second tang that hits the float pin post it was set at factory for factory needles, after market are about a mm longer. could be po messed with them. look at the droped float level see if they are all even.

the carbs on bike are slightly angled. which would account for slight lower level if measured at rear of bowl. bike on center stand also affects level some bikes the manual says to raise the front tire

 

XJ650G manual base manual for all 650 and 750 bikes

 

Just came in from garage again. I actually found a fuel filter replacement locally at advance auto parts. Filter fills and stays full. So I think that is sorted out.

Still, the problem exists and it is the same across all cylinders. I pulled, cleaned and reinstalled again. At 3 turns out. Same condition... only seems to run on choke, and not well at that. Plugs look very black and sooty.

The thought had occurred to me that perhaps I still missed some grime in the cleaning/rebuild... but on all four? And apparently the same way?

Air box is clean. It does however have one of those stupid UNI filters. I guess a stock paper one should help bring back the airflow to what it should be.

She’s kicking my butt!

 

if you set to prime air may go back into petcock leaving line full and no air

 

Yes, fuel supply issue sorted out. Other issue... not so much.

Seems like a simple problem with my mixture. At three turns out on the screw and STILL needs choke to keep running? Hmmm.

I'm going to spin it out even farther and try again. If that doesn't work, maybe the problem is opposite. Maybe it's too rich...

 

Anytime I have had that bad of popping I have had a fouled plug, and that has occurred before when I was doing some testing and started the bike several times with the choke on and never rode it. Plugs could also foul from a weak spark, so it would be a good idea to do the ignition circuit ohm checks just to be sure, particularly on the secondary side to verify the caps and ignition coils are OK. Plugs can be difficult to clean once fouled, so I would go for new ones if in doubt.

 

can you keep it running with the throttle/idle knob long enough to glance at the sync?

 

Yes... If I use the idle knob, I can keep her running, but that's with choke on.

Each time I give it a new try, I've pulled the plugs and wire brushed them and replaced them. She will start with choke ON immediately. She will run... (No throttle) As she continues to run, and warm, I try to ease the choke off... I get about half way off choke and she starts to stall... I can give her throttle, and she will rev, but as soon as I let off, she starts to stall. If I try to remove all choke and stay on throttle, the popping starts and it sounds terrible... I'm afraid to break something so I give up and shut her down. Wash, rinse, repeat. I know, I know, doing the same thing and expecting different results is the true mark of insanity!

Today was booked up so I didn't have a chance to pay any attention to her. I can go either way with the mixture screw to see if things change. I plan to make another attempt tomorrow. If I turn the screw IN, I'm going to turn to 2 times from seated as apparently 2.25 was not working.

Of course I went to the manual. My plugs (All of them) are textbook for a rich condition. I believe the choke is in good order and if anything I have too much air based on the UNI filter.


Though as @k-moe said, sooty could mean either lean OR rich...

@Rooster53 makes a good point with the weak spark potential and I attempted a ohm check as per directions in the manual...


Primary coil coil check was giving me numbers that fluctuated between 3.9 and 4.1. I used two different Harbor Freight gauges with similar results. Those numbers seem high against the 2.5 +/- spec.
When I attempted the secondary coil check, I got absolutely nothing on either coil... but I then did the check on my Maxim 700 (who is extremely happy and healthy I might add) and got nothing either (1 & 4 or 2 & 3) and got the same NOTHING so I'm sure I'm not using this thing correctly.

Today wasn't a total loss though, The Seca made a fine server this evening...

It was tough getting the rib eyes in sync... I heard bacon will help to move away from a "lean condition."

 

The meter is likely set to the lower scale, it should be set to the 200k scale when doing the secondaries.

 

Did a check on secondaries... this time with the dial to the correct position... (thank you @Rooster53 ). It’s reading 22.5 ohms. Seems high, no? Both meters displaying the same.

What position should the meter be set at for the primary check?

 

the chances of both coils going bad at the same time are about the same as winning the lottery.
"only runs with the choke on" has been on here thousands of times.
you don't want to hear it, i don't want to say it, but
your pulling those carbs again

 

Those are some dirty words... heh...

but I guess a man's gotta do what a man's gotta do.

 

Ok, please don't laugh.

I think that sometimes we need to go through these trials as the necessary part of learning. I'm chalking this up to a rookie mistake... After all, with only about 5 years of XJ ownership, I am still a rookie. With the carbs still on the bike, here's a picture of what I found after removing #4's top assembly.

My mixture problem is consistent across all 4. That being said, what was bothering me was that it was unlikely that the problem was a un-zestfully clean passageway somewhere within a single or even multiple carbs... but all 4?


Upon disassembly, I drew this diagram... I must have swapped the numbers at that point and then used the wrong info to re assemble all carbs. Here is what I scribbled on the work surface...


I haven't opened the other tops yet, but I'm sure I'll find the same situation.

I might just fire my XJ mechanic!

Will update again.

 

But aren't those installed correctly, the larger jet (pilot) to the front of carb?

That is a good reading with the caps on - approx. 11K coils plus two 5K caps for 21K

 

You have the air jets in the right places. The service manuals have the photo miscaptioned. Below is the correct info (matching what you have).

 

I want to cry.

 

this worked for me twice, only tried it twice. carbs still on the bike>get a glass jar, perfectly clean, wipe the bottom of the float bowls, drain a bowl into the jar, go to prime and give it a rinse, take it out in the sun and look for anything that wasn't there before. now take the slide out of the carb, take the pilot screw washer o-ring out, lay a paper towel under the carb, get your new can of carb cleaner with red tube, put it in the pilot air jet, eye protection, blast away, look on the paper towel for anything, put it in the pilot screw hole , blast
away, do that three more times.
can you tell i don't like to pull carbs? if you see chunks when you drain it maybe just pull them, if not a chunk that could plug a jet could have gone anywhere

 

I can't tell you how much I appreciate your willingness to work with me here on this. I have resigned myself to the fact that I am going to pull the carbs again.

It's ok.

I'm going to do it as soon as I hit the "post reply" button. This forum is truly why I love these machines so much. They are just a bunch of really cool (and often shiny) parts that are bolted together in the correct order without this community... At least for me.

I think I might have a fuel delivery problem. I rolled the bike out to the apron of the garage due to the uneven drop of the drive way. That said, I was able to get the front wheel high enough while the bike was on the center stand to completely level the carbs as if they were on my home made stand.

I put the fuel tank on PRI, and opened #4 drain screw. Guess what... Not a whole lot came out... And it didn't recover either. Correct me if I'm wrong... but shouldn't the bowl begin to replenish as the fuel level drops? I tried #3. That bowl was only half full and again, as I drained it, it never fully came back to spec.



I'm sure the floats are dropping... When I was wet setting, I made sure the "full" state of the fuel was at the spec measurement, but I obviously didn't do enough "drain-refill-drain-refill" testing.

Again, a properly working float/needle/seat should begin to replenish as soon as the fuel drops, correct?

In any case, I'll pull the pilot screws again and give the passages a blast while the carbs are out.

 

Popping usually indicates synch being off, when I did my carbs I set the floats at 17.5 mm measured with a 6 inch scale measured from the flange without the bowl gasket in place. Never bothered to wet set , I have both the 4 vacuum gauge manifold and the Morgan 4 motion , I had my carbs close with vacuum gauge . I used the Morgan synch and wow what difference I was off on number 2 carb , no popping at idle, no popping on deceleration, no stumbling and plugs are set with colortune plug all 4 uniform in color.

 

Well... I thought I had figured out the problem. Indeed I did have a fuel delivery issue. I pulled the carbs again and dropped the bowls. I hooked up the fuel source and let it flow... Only it didn't go anywhere! No bowls, floats hanging... and no fuel was dropping out of the carbs.

When I pulled the seats, the screens were all blocked up.


I guess the "touch" of anti seize that I put on the threads was too much. I know, I know, (At least now I know... heh) I shouldn't have put any anti seize in there.... When I initially pulled the carbs apart, they were really stuck in there and I didn't want that happening again...

I pulled the seats & jets and gave them another blast of carb cleaner. I put everything back together, put the carbs back on the bike and...

Same Result.
Popping as described previously... The smell of fuel is pretty intense.

I didn't think to bench sync again when I had the carbs off, so perhaps I should pull them again and start from square 1?

Also, what are your thoughts on the potential condition of my plugs at this point. I've been giving them a brush off here at there, but it is it possible that I've "ruined" them?

On the bright side, I'm really good (and fast) at pulling and reinstalling the carbs.

I might need a @hogfiddles intervention.

 

Unless you sand-blasted them, or broke the porcelan, or cleaned them enough to require regapping, they will work as intended.

 

only place you would use anti sieze would be a little on mixture screw, drain screw and any external screws not on jets or valve body

 

cut loose for some plugs, you could work on this for a week and then find out it was the plugs all along.
that would piss of the pope

 

Yeah, I guess. These WERE new plugs. Couldn't hurt I guess...

Though... Like you said with the likelihood of two coils failing at the same time... I'm having the exact same problem across all four.

 

if all you did was get into the float bowl your sync should be good, check it, give it a tweek.

 

I agree with you. In the moments where the intake is pulling vacuum, looks like all silver indicators in the sync gauge look even... but just during those moments... those fleeting little moments...

I'm going to pull the carbs again... I'm going in without a plan... cover me...

 

You should be seeing vacuum all the time that the engine is running. Even if you're just turining it over with the starter there should be enough vacuum to show on the gauges.

Mind satisfying some curiosity with a video of what you're seeing?

 

When I do a bench synch ,I cut two business cards in half put one each , under the butterfly plate ,turn the synch screw while pulling on card till I get slight resistance on the card , once I get this on all four carbs hold carbs up to a strong light source you should see a slight gap at bottom of the plate. If and this is a big if your plate is not fully seated you might find one plate is slightly off( I know it happened on my carbs , one plate was off ever so slight ) just my bid to help cheers

 

Of course. Glad I didn’t pull carbs yet. Will go through the attempted start up scenario tomorrow and record it.

As for the fleeting moment thing... that was my attempt at drama. What I was getting as was that it isn’t running long before I allow it to stall or decide to shut it down. Just to scared to beak something.

 

do a compression check on one cylinder. when mine is running real slow before a stall the cam chain starts slapping around. could yours have jumped a tooth? is it that bad?

 

I have to look into this.

Went out and attempted it again for the purposes of recording video. It was a bit of a juggle with trying to keep her running, recording and of course keeping the inexpensive (CHEAP) tuning fuel bottle filled (it's only 300ml). It drains fast... another symptom of the larger problem... perhaps.

You'll see around 2 min, I began backing off the choke so you can see and hear what happens. At the audible pop, there is a push of air that comes from the airbox intake. Seems like there is a delay in the response from the carb tune. It also does not display very high at all, unless on throttle.

 

1. Do a compression check. There should be more vacuum than that at idle.

2. At 2 min of runtime from cold the engine is not usually going to be warm enough to start backing the enrichment off.

3. That pop is a backfire (a true backfire through the carbs) which is a sign of being rich (likely from all that messing you did with the throttle during warmup).

4. Can you start it and keep it idling without turning the throttle?

 

Will do... Engine cold? Hot? Or does it matter? Also... All plugs come out, throttle open on start button and completely disconnect the coils (thin wires) from their connectors, correct?

Yes. I just got it going and stayed on for at least 5 min till I shut it down. Choke was in the ON position. Forgot my phone in the house so I had to scramble back in to get it to record the following... Here is 2+ min of that run.

I am not touching throttle at all... It is rising and falling on it's own.