Yet another newbie with running problems

I've been on a lot of forums and the amount of good info here is simply staggering. So much in fact, that I'm not sure where to begin so I'll lay it all out here and see where the arrows lead.

The patient: 1982 XJ750 Seca. Sat for years. Bone-stock as far as I know except for maybe one thing: Exhaust is 4 into 1, with a SuperCrap muffler. Did 750 Seca's go 4 into 2 originally?

The symptoms:

Originally, (after reassembly) bike started, would not idle. Rode well, good power to the redline, just no idle. I turned up the main idle screw in the center. (Is this bad? Does it richen the mixture or just adjust a throttle armature?)

Now, all plugs foul with black soot quickly, the bike loses power near the redline and generally runs not so well. A bit herky and jerky.

All electricals work fine except that the signals don't cancel anymore. New battery, new plugs. I have a complete, spare set of carbs. Can anyone recommend a reputable rebuilder? I have the skill to learn, but lack the working space, and time.

Thanks!

UPDATE:
In the last few minutes, the info I've found tells me I'm in for a world of pain. 4-1 Supertraps require rejetting. Pod filters (I have them) require rejetting. I"m 99% sure that the carb is stock and hasn't been rejetted. You have to drill for that, and they haven't been drilled.

I'd rather put the bike back to stock configuration and just clean the carbs. 2 new questions: What is the stock exhaust config and where can I get a normal airbox for this thing?

 

Did you clean the enrichment circuits per Gamuru's description in the FAQ?

Are all of the Idle jet passages clean?

 

I'll say "no". I also found Rick 'O Matic's post on slider "sticktion" and I'll tell you that my sliders don't move as freely as he says they should.

My spare carb set's sliders move better than these things. I'll put them on and see what happens, but used is used, and used is usually dirty. I want a professionally cleaned set of carbs on this bike to see what happens next.

You're right up the road from me. Want to help me clean 'em?

 

Your airbox awaits you on eBay, I saw one today as a matter of fact.

Exhaust system (4-into-collector box-into 2) will take some doing, contact these folks first: http://motolane.com/ Clint is good people. Then sign up with a scrapyard parts locator service such as http://www.uneedapart.com/ and start trolling eBay while you wait for your exhaust system to come to you. You may have to buy it in bits and pieces (experience speaking) but they are out there.

Hopefully you won't have to pull the motor to install the stock airbox like we are forced to do on the 550s.

CARB SLIDES GOTTA CLUNK. Half, go help the man with his carbs huh?

 

GEEZ, I almost forgot... check with chacal on the exhaust system parts you never know what he might have...

 

Roger that.

Also, the bike starts ok when cold if you use the enrichment toggle. Even starts when it's bitterly cold.

 

Yes, unfortunately, you do. :-(

 

Pod filters usually require re-jetting. SuperTrapp exhaust, not neccasarily. You can remove disks to increase backpressure. Are you sure that the carbs have not been re-jetted already? Too much fuel can be as bad as too little, for performance.

My 1100 had pods and a SuperTrapp on it when I got it. It would not start when cold, and turned the plugs sooty black once it did start. Was popping out of the carbs until warm. The mixed symptoms had me scratching my head for a while. Found 3 of the 4 enrichment jets plugged in the float bowls. That solved the cold starting problem. Added 6 plates to the exhaust to eliminate the plug fouling. ! or 2 plates don't make too much of a differance. Mine had 7 on it to start.

Pull off one of the float bowls (can do that while it is still on the bike), and see what size your main jet is. Then go from there. How many plates are on the muffler now?

 

Having the carbs gone through by a pro, off the bike, will run you $250 plus parts easy, could be more.
You say it ran great until you turned up the idle, that will foul plugs.
Even if you put clean carbs on, which I suspect is a chunk of your problems.
You will still have to synch them and fine tune the enrichment circuit on each one ie colortune.
If it ran great the jets have probably been changed or there was no need.
Supertrapp plate compensation?

After I had adjusted valves, synched carbs, colortuned as best I could.
I thought I was golden, wrong.
I would foul plugs after about 2 miles, have to swap out the spare set.
It turned out to be the enrichment circuits were corroded to hell.
The slides were sticky too but I feel the enrichment circiut was the fouling culprit.

So as some one said putting back to stock reqiures pulling the motor.
As Mikey said you can pull a bowl off and see what size jets are in there.
If it has been jetted I would say have the carbs that are on the bike rebuilt.

 

Hmmmmmmmmm........lots of good info guys. Thanks.

From what you're saying, someone must've pulled the engine to swap over to air pods. I ain't doing that. I guess I'll have to make a carb work somehow, even if I have to mod it.

I don't mind paying $250 or so to have the carbs gone over by a pro the first time. After that, I'll maintain it myself.

I have 5 or 6 plates on the Supertrapp. And to think, I was going to remove some to quiet it down! So, I'll add some plates and install my spare set of carbs to see what happens. I'll pull the jets on the original set of carbs to see what size they are. Where does one get Supertrapp plates?

Uh...on the jetting issue- There are jets that are underneath blanking plugs that are meant to be unadjustable, and then there are the two removable jets..the idle jet and the main jet. Are you referring to these?

Also, on the syncing issue- How do you get a blanking tool for bikes with YICS?

I think what' I've done here is trick the bike into idleing by playing with that star screw. Now it idles but it runs like crap because I richened it up too much. So I need to lean it out. It'll stop idling but it'll stop fouling it.

Then I'll figure out why it doesn't idle. Well...at least it seems like this can all be traced back to the carbs.

 

re: Point #1: Not necessarily, a PO may have simply hacked the airbox to bits to remove it. INSTALLING it in one piece requires removing the motor.

re: Point #5: Chacal (see the XJ4Ever parts thread) has the GOOD YICS tool at a reasonable price.

re: Point #6: The "starwheel" idle screw adjusts the "master" throttle stop when you adjust it you are moving the "stopped" position of the throttle (butterfly) shaft(s.)

You're going at this backwards. You need FLAWLESSLY clean carburetors that go "clunk." And can squirt carb cleaner three feet out of their enrichment wells. And have had their float levels all properly tested and adjusted.
Then you "BENCH" sync those flawlessly clean carbs.
Then you check your valve clearances and adjust them if needed.
Then and only then, vacuum sync
Then colortune and plug readings which is where you will begin to figure out if you need to rejet or not.

SKIPPING ANY of the above will only lead to frustration and alot of "tail chasing." You cannot begin fine tuning less than perfectly clean carbs on a motor with a couple of tight valves, it just won't happen.

 

Points taken. Well, I'm back to my original search to find someone to get them clean from me, and then I'll take it from there.

 

You are looking at the main and pilot jet sizes. They are the removable ones. The screws under the blanking plugs are for idle mixture. You will need to access them to make adjustments.

Follow Fitz's suggestions to a tee. Pull the carbs, clean them spotlessly clean, making note of jet sizes, check and adjust valve clearances as needed. Colorltune and sync. carbs. Then see how things go. Chacal has a nice YICS tool. Mine came from him. He also has everything needed for the valve clearance check and adjust, including shims and valve cover gaskets.

You can get plates from Dennis Kirk for the muffler. I believe they come in packs of 6 and 12. I would do the above first, before adding any plates, though. As I noted in my 1st post, I pulled and cleaned the carbs 1st, before messing with the muffler. See where you stand on the jet size issue.

5 or 6 plates does sound like too few, though. You can e-mail their support dept. on their web-site, and they will answer you. But again, pull and clean the carbs 1st. On these, and many other older bikes I guess, it's always the carbs. Mike

 

I just looked back at your original post. The carbs are not that bad to pull or clean, especially with pod filters. Why not do them yourself? It is not that difficult, and doesn't require that much space. You can get new jets from Chacal as well, if needed, rather than drilling the ones you presently have. You will probably do a better job than someone else will on your carbs, because they are your carbs. Maybe find a member from here that lives nearby you that is willing to help. Will probably save alot of time as well as money. If you just can't swing it, there are a few members here that clean carbs for cash, and will do the job right. Just a thought. Mike

 

I removed and reinstalled the airbox on my 650 several times without pulling the motor. I am pretty sure that the 550 is the only one that the motor must come out.

 

No. The engine definitely has to be removed to pull or install the airbox on a SECA 750... unless you want to cut it into pieces, as I did when removing mine.

 

Thats weird. I didnt figure there would be much difference between the 650 and 750. I know for a fact it will come out and go in on a 650.

 

Don't you have Mikuni carbs on the 650? The 750's came with Hitachis.

EDIT--------------------------------------------------------------
Hmm... nope, the Haynes manual says they're all Hitachis.

I can tell you that the Haynes manual shows two airboxes... one for XJ750(UK) and the other for everything else. Thing is, the XJ750(UK) one has the internal duct and stepped front face that mine has, and the "all others" does not. Mine is not a UK model, but Haynes isn't perfect either.

When I tried to remove my airbox without pulling the engine, the bottom hit on the crankcase bulge where the alternator mounts and wouldn't clear between there and the frame. I had removed the starter, but that only allowed me to move the airbox further forward, without giving enough room to remove it entirely.

 

Sushi; did you see my posts earlier today about the absolutely pristine Seca 750 exhaust system that went up on eBay in two "sections" (headers/collector in one auction, mufflers a different auction.) These are like-new take-offs that the guy stored properly. http://cgi.ebay.com/ebaymotors/YAMAHA-X ... ccessories and http://cgi.ebay.com/ebaymotors/YAMAHA-S ... ccessories

 

Sure did, it's on my ebay watch list.

I'm not pulling the engine just to install the stock airbox though. I'll run pods and rejet if necessary.

I would prefer to revert back to stock exhaust though because I imagine it's quieter and I perfer the look over the single Supertrapp. Especially because mine's got a dent in it.

 

MUCH quieter but you'll still have a nice howl at speed, at least the 550s do. Good luck on the exhaust, the 'Bay has been pretty quiet lately, buyer-wise and I've grabbed a couple of real good strikes recently. (NOS flasher cancelling unit for less than $20 for instance.)