Its ALIVE!

Hey Everybody,

Hope you are all having a happy and safe Easter. I finally got my 1981 XJ750 started yesterday...popped the carbs on and it started right up, but ran a little rough, plus it seems like I had a bit of a hanging idle. I checked all of the manifold boots with carb cleaner and it looks like I may have had a slight leak at #2, so I just went and ordered a new one.

Quick question...I left off my airbox to carb boots to see if bike would start, figured I would put (wrestle) them on when I was sure the carbs were cool. I know that not having them on will probably make the bike run a little lean, but that would not have anything to do with a hanging idle, would it?

 

Possibly ...but your sych screws need adjusted ...i just finished doing mine..i have stock airbox...hooked up my carb sync gauges...and if you adjusted 1 and 2 then 3 and 4 then 2 and 3 if you are correct all gauges should read about the same..i ended up having to adjust the valves 3 were way to thight ...put your airbox back in. If your snych is off could cause it to race...Or you have a vaccuum leak...just a few random thoughts..

 

You'll run very lean without the airbox connected. Yes that can cause a hanging idle, but since you found a vacuum peal take care of that first (and stop running the engine without an air filter).

When you deal with the intake boot, be very careful or you will snap a bolt off. Start soaking them with Kroil or PB Blaster now.

If you can narrow down the leak to a crack then you can scrub it clean, fill it with RTV and leave well enough alone until you need to replace all of the boots.
Replace the vacuum port caps while you're at it.

 

Thanks for the replies... Jetfixer (A&P Tech?) yes, I bench synced it.. I have an airbox on it, but this is the first time this motor has run in 2+ years, so I only ran it a minute, with a fan on it, to see if it would run, without the carb-airbox boots on the carbs (I have them). So, yeah, I'm going to take them off again, bench sync again, replace the #2 intake boot, then re-mount with all correct rubber pieces deployed
k-moe... I have already had the boots off and did my take on boot repair. Most people would have thrown them out, JB-Weld on several rough areas, then this flexible black rubber spray, pretty cool and easy to use and seems durable so far... made my own gaskets... I'm glad only one is leaking And yeah, parts store tomorrow for new vacuum caps. I have replaced the vacuum p-cock with a manual one, from a Yamaha Raptor.

 

Oh, I forgot to ask; according to my wiring diagram the oil switch is listed as an"Oil Level Switch"... so it is a measure of level, not pressure/temp change?

 

Yes. Oil level, not pressure, not temp.

 

I hooked up both oil level and neutral indicator lights today, and neutral works exactly as it should...oil level, not so much. I have them both hooked up the same way, i.e. power to one side of light, wire from switch to the other side. My oil level light comes on and stays on all the time... bad switch?

 

Bad or stuck, or you don't have enough oil in the sump.
Run soem Seafoam in the oil (according to directions on the can) and see if it comes sunstuck after a few hundered miles. As long as you have oil in the glass at rest then you can ignore the oil warning.


I want to be sure of something. You say oil warning light, but on the 750 there is a big red warning light, and the warning that it is for is shown on the systems monitor. You ar seeing both the big red light and the oil warning on the LCD?

 

Did you by chance CHANGE the oil level sensor (from another model)? The "computer" bikes use a different sensor from all the others, although they look identical and fit the same way......

 

k-moe... I have enough oil in the sump, I always check the sight glass before I even turn it over. I did away with the Atari, so all I have is a light I wired to the sensor, same way I wired the neutral switch.

Chacal...No, I did not change out the sensor, it is the one that was in the bike when I got it.

I will probably try the Seafoam, as this bike sat for 2+ years until last week when I fired it up. If that does not fix it, I may just do without it. Oil temp or pressure might be useful information, but when I can just lean over and check the sight glass for level, well, this might be one instance where being Fred Flintstone would be acceptable

 

Doing without the oil light will work, but having it is far from useless. A drop in oil level while riding ends up to be just as damaging to the engine as a loss in pressure. Having the oil pump sucking air is a bad thing, and you can't check the oil level until after you stop, and if you don't know the oil level has dropped.......

 

I believe that on the computer bikes, the sensors "works" in a different way.....the position of the float inside the can creates a variable amount of resistance, and the computer in the dash triggers the warning light when a certain resistance threshold is met.

On the non-computer bikes, I think it becomes a go/no-go type of switch, i.e. when the oil level falls enuf, contact is made, current is passed (or grounded), and the light comes on.

I think you need an oil level sensor for a non-computer bike............

 

test the connector for resistance would be the first place to start

 

Len, the depth of your knowledge about these bikes never ceases to amaze me.

 

Thanks, but note I started off by saying "I believe" rather than as it being a factual statement!

 

But as usual a good call by Len. I just verified the Seca 750 oil level sensor has closed contacts (zero ohms to ground) when the crankcase is filled with oil.

 

As usual, thank you one and all for your sharing of knowledge. Rooster 53, that would explain why a light comes on and stays on. The possibility of a computer connection for operation on my bike did occur to me, and thanks Len for that bit on information. k-moe, I was not trying to besmirch the value of the Yamaha oil monitoring system, just thinking out loud if I had to consider something else. I would agree that *any* kind of oil monitoring system is better than none, but I think Ill talk to Len as a non-computer sensor may be the shortest route from a - b

 

I didn't think you were maligning anything; I was just pointing out that the light has a useful function.

You can keep it as a simple warning light. The computer monitor is fancy, but it's not the only way to keep track of things.
Swapping the oil level sensor is the easiest method. There is an electronic route, but swapping sensors is so easy that it's not worth the bother.

 

I didn't think you were maligning anything; I was just pointing out that the light has a useful function.

Cool, because I *heart* that big Japanese girl I keep locked in my garage... err, that didn't sound right...

 

your oil switch connects to the bulb through a resistor and diode the switch is to ground .
the oil light also connects to the starter solenoid that's why it comes on when you hit the starter.
same oil switch is in the 82 maxim
what is your bulb wired to the switch on 1 side and ? red white wire for power?
no diode and resistor?
if the switch operates as roster said closed when full. then with out resistor and diode is why it is on


this is what I think you discribed so when light goes out your low on oil

this is shown in the haynes manual for 83 maxim the resistor and diode ON YOUR BIKE is likely in the box

 

the oil switch for a 550 is open when full and closed when low.
550 switch dimentions
diameter at base under o ring is 29.9 mm. 44.9 mm from top of unit to top of mounting flange (where it mates to motor)
2 mounting screw holes 42.32 mm on center. 54,14 mm wide ear to ear , 33.9 wide at 90 degrees to center line of screws.
might fit check chacals catalog for the o ring part number of yours and a 550 would be the place to start. body sizes may be the same.

possible fits
HCP1536 Aftermarket oil sender unit-to-oil sump pan O-RING, fits all XJ550, 1984-85 FJ600, 1992-98 XJ600 Seca II, XJ650, XJ700, XJ750, all XJ900RK, RL, N/FN, F, and S/SH models, and all XJ1100 models.

IF you have bypassed the starter function of the oil light which tests the oil light I would leave the light as always on that way if it is off you need to check oil.
if you switch oil switch you will want to add a button to confirm light works before starting bike so you know the safety system is working .

 

XJ550H, yes, I have it hooked up as in the first diagram. The second diagram is similar, but on mine the wire (originally) went from the switch into the Atari, and I guess there had some of that computational voodoo worked on it

Len seems to think it is a difference in the sensor, and If I use one from a non-Atari model, I should be ok. For now I am just using that LED for a brake light.

I have a question: I got it all back together and substantially done today, but the idle I am not satisfied with. My question is this... I don't have pics (will get one tomorrow) but I think you all know what I am talking about... on all four of the diaphragms on my carbs, on the plastic retaining ring at the top, it is not a continuous circle, like others I have seen. There is a split in the ring, and a good 1/2" gap or so. Is that a problem?

Thanks!

theDog

 

I think the rings could be a problem if not full could be a vac leak page 122 shows full ring

there is a diagram in the haynes manual for a 650 showing what you would need to do to fix the oil light if you went to the non computer oil switch.
i will get the page # 243

you can see how there is a diode and resistor hooked to the oil switch and connected to the solenoid
thats what makes the light light when you hit the starter
resistor and diode are part of the diode block
650 diagram

 

I forgot that I have that same manual in a .pdf, and yup, that is what it shows on page 122. That is so weird...all four have virtually the same width gap in them, as if it were a manufacturing thing. The diaphragms were in kind of sad shape when I rebuilt the carbs, ended up patching one or more pin holes in all four of them...maybe Ill have to go with some JBM replacements...

 

The top ring for the slide diaphram may, or may not be a full circle. It dosen't matter one way or the other so long as the diaphram is secure.

 

Thank you, k-moe... I did not know that. Here is a pic of one I pulled, the diaphragm seems secure, but there are a couple of pinholes again, so I will fix those and check the rest.

 

Liquid electrical tape will close those pinholes up and last almost forever.

 

Good idea... I will pick some up tomorrow and see if I can dodge the new diaphragms bullet