'82 Seca 650 runs perfect when cold and lean when warm

...or is that just the general pattern of lean running, period? Let's back up and start at the beginning.

I have a 1982 XJ650RJ Seca. I did a round of cleaning on my carbs a few months ago and have been struggling ever since to get it running just right. I did a valve adjustment, replaced the throttle shaft seals and rebuilt the petcock. Pipes and airbox are stock. The bike starts instantly and idles fine when cold; I don't know the RPM but I would guess 1500 RPM.

The carbs were bench synced using a .0015" feeler gauge. The mixture screws are 5 turns out and the idle adjustment screw is fully closed. I sprayed starting fluid around the manifold and mixture screws this evening and got no reaction; I did the same with propane last week and also got no reaction. I checked the filler cap vent tonight and it seems OK; the gasket needs replacing so it's actually letting too much air in if anything. I had a filter inline, but I removed that because it was causing a much more serious lean condition. I checked the #1 pilot jets tonight and they appear to be positioned correctly (the fuel jet is towards the engine side). Informal plug chops show #1 lean and 2/3/4 slightly less so. I've attached a pic of 1 & 4.

It runs perfectly until it warms up fully, at which point it starts to run lean. The main symptom is that when I close the throttle while in gear, the RPMs don't drop until I either brake or pull the clutch. So if I'm going 45mph in 3rd gear and I close the throttle, I'll keep going 45mph. If I pull the clutch, the revs will drop slowly.

I've ridden to work (16mi) a few times this week and it's pretty consistent: it runs perfect for the first few miles, then it goes lean and stays that way until I park it. It's ridable- I can cruise at 75mph no problem, and it keeps pulling from there, but it just doesn't feel quite right.

The big things I haven't done are the float levels and a full sync. The drain screws are trashed and the floats looked OK when they were on the bench. I just haven't felt like drilling out the screws yet, although it's probably inevitable. I have a carbtune to do the sync but I've always had terrible luck using it in the past; in fact the last time I did it they got so far out of whack that I had to pull the rack and do a bench sync to get back to baseline.

One unknown is if the PO ripped the insides out of the muffler. It's definitely on the noisy side for having OEM pipes. This could contribute to lean running, right?

So I'm far from done tuning, but the fact that it's so good when cold tells me I'm not totally off base. (Sorry for the wall of text!)

 

Hi,

You could probably bennfit from syncing your carbs. I used the method described here http://xj650.blogspot.com/2009/04/how-t ... carbs.html because my drain screws are trashed also. I had to sync them a few times to get it right, mostly because I was using 2 different diameter paperclips. Once I fixed that I got it spot on. It idled at 2500rpm when it was hot which I eventually fixed by turning the air screw. Now it idles and runs great. I would also recommend cleaning your carbs again as long as they are off and check for leaks around the carb holders and vacume line.

Hope this helps.

 

Not sure what this is "I checked the filler cap vent " but if its sucking in air that could keep rpms from dropping right? Have no clue if an/or how it is related to fuel mixture.

When I was doing my float levels I had to do the "clear tube method" b/c not all of them needed exactly the same level. I am definitely not an experienced mechanic, but I wanna say floats are more directly linked to lean/rich mixture problems then anything else...

 

I'm talking about the fuel filler cap on the tank. There's a vent in it so the tank doesn't develop a vacuum as fuel is drained.

Regarding the bench sync: I did the same procedure described in the article, but using an actual feeler gauge instead of a paper clip. They're pretty much perfectly bench synced. What I have not done yet is the final sync with the manometer (AKA Carbtune).

 

Five turns out on the mixtures should put you rich. Something's not right.

The "behavior" (symptoms?) you described is more what I would expect from a RICH condition.

How did you set your float levels? Dry is only a start, they need to be checked using gas and the "clear tube" method.

I would also re-bench sync, using 3/16" wide strips cut lengthwise from a plastic pop bottle; and leave yourself some adjustment on the idle stop screw (run it in a few turns and THEN set the carbs up.)

The bench sync, like dry measuring the float heights, is only a starting point. See where you are after a running vac sync.

 

Well, I did a sync with the Carbtune but haven't been able to take a test ride yet. My fingers are crossed...

I also replaced the rubber caps on the sync inlet nipples. The old ones were rock hard so hopefully this will help.

 

I'm cheating a bit with my posting- the above post was actually written at ~8pm.

So I just got back from my test ride. Perfection. Well, I'm sure a colortune session could improve it but the major problems I described before are gone. I suspect the rubber covers on the sync ports were the culprits. I didn't make any attempt to check the float levels.

I'm doing a victory dance right now

 

rich condition would make it idle higher. i don't think lean would. but one just never knows.

gas tank vent cap has absolutely nothing to do with performace. it's just to let air in so that the tank doesn't create a vacuum. they always go bad. letting fumes into the atmosphere. but i've never seen one or heard of one plugged up stopping the fuel from flowing out and down into the carbs.

i think the float height is irrelevant to performace. unless it's to the point of flat out flooding so the engine don't run.

right now i'm running at 18mm. float height. ive had 16 and 14. and absolutely ZERO effect on performance. other then readjust the mixture screws and resyncing the carbs.

bike ran the same no matter what height. idle speed all the way up to highway speeds.

course. my motor isn't in perfect shape.

 

Next time you take the carbs off hold them up to the light, look threough the bottom of the butterflies at the amount of light coming through. I bet they're all not the same. I THINK that's because the compression is different in each cylinder which would pull different vacumes if they Were all identical. So a true sync is to compensate for the cylinder imperfections. Whadayathink?

 

Update!

So I decided to check the intake manifolds for leaks. You can guess where this is going...

[...wailing and gnashing of teeth...]

So the shop fixed my damage for $100: 3 of 4 intakes ended up snapping their bolts. I let the shop break the 2nd and 3rd after I mangled the 1st. Then they did the helicoil thing and hot tanked the head.

I now have installed a new headgasket, intake gaskets, cam tunnel seal, valve cover gasket and blind sync port caps. I also found that the #1 carb had the diaphragm seated wrong. I checked sync, tweaked the mixture (by guesswork, no colortune here) and took a few test rides. We're pretty close to perfect now.

I just pulled the plugs and they are all light tan, confirming what my butt was telling me.

So that's pretty much that.

Details:
- I used Chacal's upper engine gasket kit, but only a few pieces of it (headgasket, cam seal, intakes, block to head o rings). Still a fine value.
- I used permatex copper spray on the headgasket
- I used permatex aviation sealant on the head nut washers and antiseize on the threads
- lots of antiseize on the intake bolts (duh) and a little on the valve cover and exhaust bolts
- the cam tensioner bolts are seized so I just left it and smeared some RTV around the edges

Also I ran the headers through an electrolytic process to remove rust, then hit it with a wire wheel, wiped it down with PJ1 cleaner and painted the mes with VHT flame proof paint. It looks good so far.

 

Good job man. I have the exact opposite problem. Bike don't run well untill its hot and been ridden for 5 mins. I put the slightly larger 42 puilot fuel jets in, like the canada models, but I don't think that's the issue...

 

It ain't pretty but it's mine:



Actually the cosmetics are finally coming to the top of the list. I didn't want to put any funds towards that until I got the running issues ironed out. No sense prettying up a basket case.

 

hey cool- notice your working on an 82 Wing. I am just finishing up my 81 Wing and may have a buyer lined up. I went minimal dumping the Bates bags, basic black Hondaline fairing etc.... The wing has been a learning expericene. Its a much better enginerred bike that the Concours i just got done with. I like reading about your adventures. Just got 82 Seca and will be starting to tinker with it this weekend.
Jeff
82 Seca Rebuild

 

Thanks, jeffhestand. I decided to work on the Seca before the Goldwing because the worst possible case with the Seca was that I couldn't find the air problem. The Goldwing may have chewed up its bearings so it might be utter toast. I figured better to get the one with the good odds on the road first.

So my Seca celebration was cut a bit short by the starter petering out. I was having to tap it with a mallet while holding the button, and eventually even that trick didn't work. It had always sounded a bit anemic when cranking so this wasn't unexpected. I tore it down a few days ago (a comically easy task), cleaned the commutator with scotchbrite and replaced the old grease. Upon re-installation it spun up like it had just left the factory.

Next up: new tires, new seat cover, new headlamp.