1982 Seca XJ750, ZRX1200 has company now.

[bikerphil]

Does the bike still have the OEM 40 year old coils on it? That could cause an intermittent firing issue. They can become weak and not be able to fire both plugs simultaneously. I'm assuming it's a wasted spark system.

[Bonz]

The carburetors are not the issue. I've done enough of them to know when they've been cleaned thoroughly, with all candor. They have been taken apart and ultrasonically cleaned and put back together basically new. It's not them.

[cajun31]

I just did a search on Ebay for a set of carbs for your bike and there are several listings available. Saw one set for $99.00.

[Bonz]

Getting back to the Seca 750 as the summer progresses. Three and a half weeks to go on summer break before the ankle biters start showing up again.

Valves... one intake and one exhaust are way tight, IMO. As in .004" #2 exhaust (.006-.008 spec) and .002" #4 intake (.004-.006 spec).

As JeffH said to me recently, hopefully some adjustments start making logical outcomes. Nothing has produced the solution. Specifically #2 not firing at idle, and then fire intermittently as RPM increases. Something I haven't mentioned, #4 runs hot at idle via the IR thermometer reading. Maybe there's something in the tight intake valve on that cylinder, as again, logical adjustments/solutions have not given logical outcomes so far.

Motorcycle shops are closed on Mondays, as they probably are everywhere else. Will make the rounds to a couple local shops tomorrow and swap a few shims with them.

Hopefully tomorrow I'll be able to check this off as a solution or just another step in the process.

Fwiw, used the "zip tie" method (but used a bent piece of 12 ga coated wire) to hold the valves open to pull the shims on all buckets (whether needing adjustment or not) to note sizes after taking measurements. Felt better using the wire as I was neurotic a zip tie could break and be a pain to get out.

For pulling the shims, used a small flat blade screwdriver in the bucket cut out, pried the shim up just a little bit, keeping the screwdriver in the small gap. Put a small squirt of brake cleaner into the gap, pushed the shim back down then repeated once or twice, and the shim popped right out with the screwdriver. I had ordered a dental cleaning kit with a pick and plaque scraper from Amazon for 6 bucks but after using it on the first shim, the method evolved to just using the screwdriver and it was easy peasy.

[Bonz]

Most of you guys here won't know CaptainZap. He was a guru, lived north of me in denver. He got me to my first XS11 rally in 2011 out in Durango. He ran the tool in his 80G full-time as well. Going to that rally was the Genesis of the Colorado rally I started in 2014. Unfortunately there's only so much room on the ride and the command central location, however looks like 16 bikes this year. It's the old guard, guys that have been doing this since the beginning with me in 2014.

[bikerphil]

I have tried to get a hold of Yahman about a year ago with no luck. My friend bought a Yahman YICS tool back in '18 for one of his XJ's and he leaves the tool installed all the time. He wanted another for his second XJ. I think they would be pretty easy to copy, not much to it.

[Bonz]

Well darn it. Fired up the bike today and number two is still cold at idle. Around 2,000 RPM is when it starts getting warm. I was overconfident the pilot circuit was clean. Going to block off the yics with a t-shirt tied in multiple knots and get a sync as the last ditch effort, before pulling carbs to give #2 pilot a thorough additional cleaning.

[Bonz]

Brass cleaning brush is going to be fine in aluminum. I use brass brushes in a Dremel tool to clean out master cylinders, brake caliper piston holes, etc. No harm.

[DiverRay]

Brass on the aluminum head? I'd use a fiber brush on the ports with Berryman's B-12 Chemtool as the cleaning agent. If the carbs are off, you should be able to see the brush as it goes between the intakes.

[Bonz]

Good info on all counts. Haven't opened the YICS passage,don't have an idea on how dirty is. However Hoppe's No. 9 and a brass brush is my plan.

[Schming]

I have an '83 XJ750MK and have used the YICS tool, made by Yahman ? The tool works fine but I have found that a Color-tune after, without the tool, then another sync with the tool while keeping the idle at a constant 1100 rpms, gave me the best results. Also the YICS passage needs to be clean to work properly.

[Bonz]

Thanks for posting those links, I've read all three of those more than once during this process. But good to have them here for others to see if they read the thread.

Many riders say tuning without the tool makes a pretty good running bike. After my experience, the gauges absolutely were not telling the truth.

[DEEBS11]

https://xjbikes.com/forums/threads/carb-sync-yics-tool.12104/

https://xjbikes.com/forums/threads/carb-synchronizing-on-a-yics-xj650.14472/

https://xjbikes.com/forums/threads/yics-tool-versus-non-yics-tool-carb-sync.25520/

https://www.ebay.com/itm/12710885301...Bk9SR_zd0anFZw

[DEEBS11]

Bonz, my understanding (I had a 650 Turbo YICS) is that a YICS engine can't be synced without the tool. You will receive false readings (much like what you are seeing).


Main jetting differences from inner and outer cylinders have zero impact on the pilot circuit. Only the pilot jets and air flow, The mains do not come on line until the needles raise out of the emulsion tubes.

[Bonz]

School year is finishing for teaching middle school kids math. Hallelujah. I had a chance to fire up the Seca and play with the sync screws. Cylinder number two was not firing so to speak at idle, the pipe stayed cold.

If you recall I used the Morgan carbtune and got them "balanced". Also I did it without a YICS type tool. Pilot circuit is clear. The only other issue I could see was the butterfly plate was closing off the idle hole the pilot system feeds #2 at zero throttle.

That could happen if sync screw is adjusted with all four carburetors providing vacuum to the system. Got the bike warmed up, adjusted the 1/2 sync screw to a smoother idle not using vacuum readings. Number two header started coming up in temperature at idle. Before it would only come online if I held engine RPM 1500 RPM or higher with the throttle. Which says the butterfly plate may have been blocking off the pilot circuit hole at idle.

Next time I fire it up will tell the story if it behaves like it did today, lol.

Then it's get the new tires mounted and get the bike on the road.

With that said, number one and four header temperature idling for a bit is around 200° F. Two and three are sitting around 170° or so. There are situations where outer cylinders and inner cylinders with the same jetting will run different temperatures. Any thoughts on dealing with that at idle? First thought is leaning out the pilot system on two and three with screw adjustment. I realize mains can contribute a bit, however to my mind not that much at idle.