Big starting problems

1981 Yamaha XJ650 Maxim

Hi everybody. I would really loved to have made my first post just an enthusiastic introduction of some sort, but unfortunately I'm having some troubles with my bike.

I've been working on my valve clearances for the past two weeks, and after two weeks of ordering shims and swapping them out I finally finished and got the clearances either in spec or as close to spec as I can get them. While I was working on this, I made the mistake of taking the cams out. It was on impulse and I regret doing it now.

I put everything back together, and now it starts very rough and backfires out of the exhaust and the carb. The clearances are better than they were before, and i could swear that i put the cams back in properly. when i go to inspect them in a Few days, how dead on do those timing points on the cams have to be? That's one problem.

The second problem, which could be related to the first problem is that a shop that worked on my bike did not replace the coils with OEM coils, they didn't label the cables to their plugs, and I didn't think to label them when I pulled them all off. How do I figure this out?

The third problem is that gas is now leaking out of one or two of the carbs air ports when it feels like leaking out. I think I fixed it by cleaning them and making sure that there were no blockages, but for safety's sale I would like any extra tips possible.

I'm intermediate level when it comes to mechanics. I've been making mistakes as i've been going along and I've sorted them out easily enough without asking for help, but I don't want to new up my engine, so I'd appreciate any help I could get.

 

With valve clearances, they are either in spec or out of spec, there is no "close". Unless you're using standard gauges instead of metric....you should really use metric.

The timing marks on the cams have to be dead on. If the mark isn't lined up with the hole, they're off.

The left coil fires 1-4, the right fires 2-3. It doesn't matter which wire from left coil you put on 1&4 because of the wasted spark system. The coil fires both wires at the same time. Same with the right coil for 2&3.

The air jets overflowing with fuel is usually a symptom of a faulty float valve or incorrect float height settings.

 

Welcome to the forum....suggest you wet set your floats and repair that petcock otherwise you will end up,with a sump full of gas.

 

One coil fires 1/4; the other fires 2/3. Coming from the coil, it matters not which wire goes to which cylinder, just as long as they go to the right ones.

If you take a brief look at the file Installing Dyna Coils, on page 7 you'll see what I'm saying. (No, we're not going to actually change out coils here.)

You might have to go through them again. At the very least, double- or triple-check the fuel levels. Offhand, either a float needle is sticking in the seat, it's binding because the floats are hanging too low in the bowl when it's empty, or the fuel levels are set too high.

Setting Fuel Levels

I knew less than you when I started. Don't worry; you've got this.

"The fool doth think himself wise, but the wise man knows himself to be a fool." -- As You Like It, Act V, Scene I

Thou art wise, methinks.

 

@adrian1
Thanks for the welcome. The carb problem sorted itself out. I think it was because the floats were hanging too low in the bowls (schmuckaholic), and the petcock is in great condition.

Now, I put the cables on their proper plugs and gave her a whirl. She started, and there were no more backfires, but either I need to hold open the accelerator a bit, or the choke needs to be fully open for it to run. Then I had trouble getting it started after I let it die, but this doesn't surprise me, because I needed starter fluid to turn her over beforehand. I didn't push the issue for very long because I don't want to proceed just yet without checking my next theories out with all of you first.

It sounds great, and the engine revs just fine, but like I said before, it needs a little bit of help. I won't have time to open the valve cover back up for a triple check on the timing marks until Sunday, but I'm wondering if maybe the idle needs to be adjusted on the carb accelerator lever. The reason that I say this, and the one of the reasons that I decided to put the valves back into spec in the first place (other than the fact that the bike has 23000+ miles on it), was because the bike would want to stall out at a standstill. I had thought that maybe it was also that there was too much pressure on the clutch from me not hooking the cable back up properly when I replaced the friction pads, but now I'm wondering if it's the idle.

What do all of you think?

 

Have you properly, individually and accurately wet-set the float levels yet?

Is this a YICS motor?

Did you do a running vacuum sync? With YICS blocked if applicable?

 

I'm assuming the shop took care of that when they rebuilt the carbs. Does this need to be done every time that they're taken off, and is that why one of the two floats that I looked at seemed to drop lower than the other?

I have a 1981 xj650 Maxim. Sooo...I dont't know. Do I have a YICS motor?

 

Bad assumption.

The "downstop" position of the floats is important; but what is more important is the precise level at which they shut off fuel flow. Once properly adjusted after being rebuilt, they should hold adjustment for a good long time, with only an occasional check needed. But they do need to be accurately wet-set to begin with.

Don't assume the shop did a correct sync either. If they aren't familiar with these bikes, chances are they "winged" it. Did you take them the carbs, or the whole bike? If you just took them the carbs, then you still need to vac-sync the carbs to the motor.

You can tell if you have a YICS motor by looking at it. It will have "YICS" cast into the valve cover. If it is, the YICS passage needs to be blocked to do a proper running vacuum sync.

 

Yes, I agree with Fitz. You can't bring your 32 year old bike to a bike shop and expect them to do it right. They are not familure with this type of bike. I learned this myself. They probably didn't clean the carbs properly and the floats probably wern't set or sync'd. Even if you don't know a lot about mechanics you soon will. If you took off the carbs you will need to sync them to the bike and you will also have to do a color tune. You also must have your valves in spec before doing anything. I would start there. Close isn't good enough.... They need to be right. Then you need to make sure your floats are correct then you need to sync the carbs then you need to color tune then you need to sync again and color tune again. These things must be dead on for the bike to run correctly.

 

Yep. Agree with all of the above advice especially setting the floats correctly. I rebuilt my carbs, set the floats, and still had a cold start problem. Turned out to be the tiny enrichment circuit pickup in the carb bowl that was plugged on all 4 carbs. Once I had that sorted and it started easily, I tackled the valves since it was half apart anyway. Then I made my own YICS tool and vacuum set the carbs (borrowed an old, dusty unit from the bike shop in town that they forgot they even had on the shelf). I must have had the carb bank off 10 times before I had everything running correctly.

The process of properly setting the carbs on my XJ has been the most time consuming part of making it a reliable daily ride. I'm so glad I kept my head, maintained my patience, and methodically performed all of the recommended steps. Stick to it and search for all of the needed information offered here. Just follow their sage advice and all will be well.

 

everybody keeps saying that they have to be perfect, but if the clearance is near .156 at the moment, the spec is .16-.20, and the shims are only available in .05 intervals, how am i supposes to get it perfect?

 

Oh, and can somebody direct me to the posts that I need to wet-set and color-tune?(vacuum) This is a very active forum and I'm sure that there have been more than one post that lays this out.

Also, are you guys sure that adjusting the idle isn't something that I should give a go on? I'm only asking, because I'd like to be thorough on everything before I wet-set, do a color tune, and vacuum sync, only to find that the damn thing still won't run. lol

 

There is no such thing as perfect, just a matter of how accurate.

Your problem is you are using SAE feeler gauges. If you had a metric set the 0.15 would go but the 0.16 would not. You'd call it 0.15 and go down one shim size.

My Venture service manual lists the same valve specs as your XJ, BUT it also lists them in SAE as intake 0.004" - 0.006" and exhaust 0.006" - 0.008".

If it were mine and the 0.006 gauge didn't feel very loose I'd go down one shim size.

 

I was going back and forth between two feeler gauges. Between the two I could inspect .10, .12, .127, .13, .15, .156, .172, .18, .20, .202, et cetera. I was able to get most of them around .172 and .18 (where .156 was completely free to move around, and .20 wouldn't fit) so I accepted those as in spec, but on one intake and one exhaust the .172 wouldn't fit and .156 was perfect. If I drop one size, it could go above .20. If in-spec is in-spec and anything else out-of-spec, then dropping a size will produce the same result: out-of-spec.

 

Nope. Use metric feeler gauges. The chart and shim sizes put the valve clearances in spec with accuracy to two decimal places. You are trying to cut things too fine.

In your case 0.15 fits, but 0.16 would not, so go down one shim.

 

So your 0.006" (0.152mm) would be loose. By the rule of thumb I use I probably wouldn't switch it either.

What needs to be understood is the book presumes you are using metric gauges with a precision of 0.01mm. So when they tell you 0.16 - 0.20 mm what they are really saying is the lash is in spec when 0.16mm gauge will go but the 0.21mm gauge won't. In other words: 0.16000...mm to 0.20999...mm. Assuming the shims are perfect there will be exactly one that works.

 

Ok, so camshafts are back in, and set perfectly. Some of the clearances are off still by the slightest bit, but I'm gonna put that aside until next week when I get more shims (I ran out of 2.65s, 2.70s, and 2.75s), and until I order a strictly metric feeler gauge. I wet-set the carbs today, and after about two hours of ad nauseum adjustments, they're perfect. After making some much needed minor adjustments to the idle screw, I gave her a whirl. She sounds great and idles better than she did before. However comma a vacuum sync is now desperately needed. I can't pull back on the accelerator without it sticking at around 4,000 rpms. So that's my next task I suppose. A synchronizer gauge set costs about $70, but I'm going to call a few shops in my area tomorrow to see if they'll just do it for cheaper than that. I don't want to buy a gadget that I'm only going to use once.

 

You can build a differential manometer for less than a thousand pennies. http://web.ncf.ca/ag136/carbsynch.htm

 

On the subject of aligning your cams. I had trouble getting the intake can aligned. The wrench would not clear the head casing. Took a grinding wheel to an old 7/8s wrench. That gave me enough clearance to align the can perfectly, about 1/8 of an inch.

 

So I couldn't borrow a sync tool, and it's too expensive to buy, so I made my own using the bottle method. I started the bike and ran it for a bit, but my battery died in the process (I'm scratching my head on that one too). Anyway, I figured since I need to wait until tomorrow morning to plug the charger in while I'm in class, I can post my finding so far and ask for advice.

The no. 1 carb bottle completely drained out while no.s 3 and 4 went up to 3/4 of the bottles and number two went to about 1/4. I know where the screws are, but does clockwise increase the vacuum or decrease it? Also, what would you guys do?

In an unrelated question, what do I have to do to get this thing to cold start. Seriously, I'm tired to going through cans of starter fluid.

Have a good night everybody. I'll talk to you tomorrow afternoon.

 

It won't cold-start (even with enrichment - the "choke?") because it's still horribly out of sync plus your valves aren't where they should be.

-Get the valves IN spec. Not close, in spec. There is only one shim that will put any particular valve IN spec, if it's out, it's out. A few tight valves are going to make it hard to get the vac sync right.

-Revisit your bench sync.

-The bike needs to be fully warmed up before you can do an accurate vacuum sync (or any carb adjustments for that matter.) Not "ran it in the garage for a while" warm; 10-mile ride warm. Use a house fan to blow air over the motor when tuning; if it begins to "act up" and refuses to behave, surging, idle bouncing all over, etc., it's getting too hot. Shut it down and let it cool for a bit, then continue.

-The charging system doesn't start to truly do anything until about 2000rpm and doesn't come to full output until about 2200rpm. Extended idling on an already soft battery can easily run it flat.

-When doing the vac sync, closing the butterflies increases vacuum; opening them decreases it. You want to make very small adjustments, blip the throttle in between and allow it to settle down again before adjusting again.

-Keep in mind that #3 has no adjustment other than the main knob so you are bringing the others to it; and that when adjusting #2 it also adjusts #1 with it. You sync #1 to #2; then using #2's adjuster, bring the pair to match #3. Number 4 is independent, you just match it to #3.

ALL OF THE ABOVE ADVICE IS COMPLETELY WORTHLESS if your valve clearances aren't right first. Quit trying to sync the poor thing until they are.

 

You cannot always get them perfect. It would be better in this case to go slightly wider than spec, because these clearances nearly always become smaller in use. Then the clearance would soon drift into the correct range. If you made it smaller then the clearance would drift away from the correct range.

A company which had a showroom and did servicing round here (long gone now) would charge you for a shim job every time, but would only do the job if there were rattles; the clearances were loose. If there were no rattles the clearances might be tight and could eventually tighten more and burn out your valves, but they didn't care.

 

They don't have to be "perfect."

They DO have to be in spec. Near .156mm is too tight; one size smaller shim would put it at "near" .206 which is better than being tight.

I'll do you one better: DROP the bloody .006mm (.00024") it makes it much easier (which is why we recommend using metric feelers, rather than imperial feelers with metric equivalents.)

Drop it. If your valve is at .15mm; it's out of spec. One size smaller shim makes it .20mm, in spec. DONE.