XJ750 Intermittant running (solved). Now mid range bog.

Hi Guys,

Newbie to the XJ community and to bikes in general but I am having some problems with my XJ. Heres the situation. I bought the bike with 11,000 miles on it. I have ridden it about 300 miles and I have been installing various components such as handlebars, a new seat and small things here and there. My clutch is poorly adjusted, I know that much myself, however my bike was still running fine. I even rode the bike 120 miles in one day a week ago. I fired up the bike yesterday and let her warm up and started riding. All of a sudden the bike died out at a red light. I tried firing it back up but heard a rattling noise coming when I hit the starter. After I finessed the starter it fired back up. I started riding and the engine was running perfect. I got 1/2 a mile and I was on the throttle pretty hard for most of that time. All of a sudden the bike cut out and left me stranded on the side of the highway. The bike died about 2 miles from my house. I got a ride home but I got a ride out with a buddy to try and bring the bike back and we were able to get it to start and run for 1/2 a mile at a time. The chain rattling noise was intermittent every time we tried to fire the bike back up. I am getting weak spark, however I tested the ohms on the pickup coil as well as the IG Coils and they all checked out. I fired the bike up yesterday and tried to test it out. It ran well for a little bit, maybe a 1/4 mile then the bike started bogging and nothing happened when I turned the throttle. It seems that this issue happens when the bike finally warms up. The bike is a 1982 XJ750 Maxim BTW. These issues all started presenting themselves after I changed the seat out, until then the bike was running like a top. Sorry !! I know its a bit of a read but any help would be appreciated. I don't want to give up on this bike, when it runs it goes like the clappers.

Also, when she dies sometimes I have to give her choke just to get the engine to fire up again.

Thanks for your help once again !!!

 

Welcome to the camp!

A weak battery will give you the rocks in a coffee can sound. Or weak electrical connections that maybe loosened even more when you bumped them changing your seat.
But here is what you really need to do. . . .
Pour yourself a nice glass of bourbon, get yourself a basket of bacon and start reading all of this (including links within it):
http://www.xjbikes.com/forums/threads/the-information-overload-hour.27544/

There are several basic things that need to be done with an old XJ that you recently acquired. These things are very important to insure reliability and safety. Valve clearance, brakes, tire date codes, electrical connections/ fuse box, Church, starter refurb, petcock rebuild, vacuum leaks, synching, wet setting, etc.

All very doable with assistance from the fine folks here at XJBikes.com. All very necessary to get that safe, reliable and FUN bike in tip top shape.

 

Is it possible the seat you installed is blocking intake to air cleaner( hopefully you still have the stock airbox) if it blocks off it can cause stalling.

 

+1 on a possible air intake restriction.

Have you checked the valve clearances? Tight exhaust valves will cause exactly what you describe.

Ignition coils can test good when cold, but fail when hot. Are there any signs of cracking on the coil bodies, or the plug wires?

Also; do all of these things if you want a reliable motorcycle: The Information Overload Hour

 

Hey guys so I got a new battery going to test that this afternoon, old battery was low on fluid. It was running good enough that I took her for a test drive and she died 1/2 a mile in. I had to wait 5 minutes before I could fire her up because I kept getting the chain rattle noise. Even when I limped her back It died a 1/4 mile in and I had to wait again before starting it. Today I fired her up and she ran beautifully then started to die as she warmed up. I am going to check the running voltage when I get back from work. Starting to think this is a stator issue. Like I said bike was running great, then I started having all these issues. Read through the information overload last night and got quite a few good tips.

 

It's worth checking the stator output, but that's not likely to be the whole problem (even if it is a problem). If you find that the output voltage is low, it probably needs cleaning and new brushes.

 

Well, charging system is up to spec, fired up again today fires right up. It seems like it dies with the heat, the rpms just start dropping a little and it dies. Let the XJ sit for 5 seconds it will idle all day. It mainly starts dying after putting her in gear. I am really at a loss guys, like I said it was running beautifully and all of a sudden its having these problems

 

My exhaust valves seem to be in spec, I am sitting at 0.006, 0.007, 0.007 and 0.006. I am super stumped here. It was running fine before, also unfortunately I bought it pods but it ran for 330 miles on pods. I am using go no go gauges and it seems to be in okay spec. Also intake valves are checking out too. Charging system works, coils check out, guys i'm really stumped.

 

Did you re-jet back to stock after ditching the pods, or is it still on pods?

 

its still on pods and was jetted for pods as well. Basically after I threw on the valve cover it idled fine and revved up in neutral good as well. I put it in gear and tried to rev it with the clutch pulled in it just hesitated and would die. I have checked the inside of the carbs they are nice and clean. Like I said the bike was just sitting for a period of 5 days and started having all these problems afterwards.

 

Oh also update, she stopped firing once warm so I tried to get her to fire with some starter fluid sprayed in the airbox, guess what fired right up. All my jets are clear and clean and the bike was running like a champ. Very confused, however, this does seem to definitely be carb/fuel related.

 

In your original post you mentioned that you have been installing new components here and there. Did these symptoms arise shortly after a specific new component was added?

 

It came about after I installed my new seat which I have since taken off. I also fiddled with my fuse box as well, but I am fairly certain that is not the issue since it started on starter fluid.

 

With the seat off there is zero chance of a wire being moved or pinched. Physically inspect the wiring under the seat and look for breaks or chafed insulation.
The seat may have caused something to short out.

 

Guys, here is what I am thinking. I bought this bike from a buddy who actually rebuilt the carbs. He did not however rebuild them according to the church of clean or do any sort of syncing. I did pull of the carbs on Friday and gave it a quick whirl. It is running the old fuse box which is in dire need of upgrading. I have accepted an internship offer in San Jose this summer.. From my observations today the bike will fire up on choke, warm up and then die. I am thinking that the bike is starving for fuel after the choke is shut off. I am actually kind of glad that the bike stopped working because this gives me a chance to get the bike ready for a intense trip through the heat of the southwest. Here is what I am thinking take the carbs off, clean according to the church of clean article, ensure no vacuum leaks, throw the carbs back on, and replace the fuse box with a modern box. I know this is a bit to read but I have seen you guys on the forum posts quite a bit and you seem like an expert. Do you have any suggestions for me besides these things to prepare the bike for this trip. I did knock out the valve clearances today which is good. This trip is going to be quite brutal on the XJ.

Thanks if you made it this far.

 

Your trip will not be brutal on the bike. It will be more brutal on you. Get yourself a hydration bladder.
Your plan is sound.

 

Let me preface with saying that I have a 82 Yamaha XJ750. I got it back up and running and cleaned the carbs out and it was running great. I put around 500 - 600 miles on it, however, last night it developed a problem. It now bogs at 2800 - 4300 rpm. I am preparing for a cross country trip in 3 weeks so this is a bit of a problem. I just finished up sorting the electrical system, switched to the glorious blade fuse box and all that jazz. Like I said it was running great and i've been riding it a lot as endurance to see if I can break anything. Better to break something at home then half way across the country. The bike will pull at WOT, however, where as it would just accelerate up hills even in 5th at 35mph. Really need help here guys. Finals are rolling around the corner for me so I don't have time to be diagnosing constantly. Really coming here to ask for help finding the problem.

 

check to make sure your rubber inlets between airbox and carbs are all tight and secure, your symptoms sound like the throttle slides are not behaving, sounds like a pod filter installation to be honest.

 

from
TALKIN' TECH: Various thoughts on various issues

The pilot fuel circuit is active from idle up to about 2500-3500 rpms, and at about 3000 rpms the main fuel circuit starts becoming involved, and by 4000+ rpms the main fuel circuit is responsible for about 80%+ of the engine's fuel supply conditions.

could be the jet fell off.

 

Cleaned the carbs how?

This way?
IN THE CHURCH OF CLEAN

If not, then they didn't get clean.

Are you using an inline fuel filter?


BTW. I'm meging your threads so we can keep track of what has, and has not, been done. That helps with diagnosis.

 

Hey guys, thanks for such fast responses. Yes the carbs were cleaned church of clean style I pulled my carbs and checked all my jets they look pretty good. I am running a inline fuel filter. I really freaking wish that the guy I bought it from hadn't added the pods but alas he did. The thing is it was running great, I just gunned it from 3rd last night and then it hesitated and started presenting these problems. The bike fires right up and the loss of power is surprisingly linear. I just want to have the bike back to 100% before this trip though.

 

Also it seems to rev in neutral pretty well. Ugh just want to fix this it was running like a top. Just fixed up the wiring, all the electrical is finally up to snuff. The previous owner was using a paperclip for the headlight fuse because the clips broke !!!!!. Put that fuse box in real quick. Just need to sort this out and I think she'll be ready for this trip

 

hearing about the PO's paperclip fuses leads me to believe nothing was done to compensate for the installation of pod filters. There is lots to read on this very subject, some of the best information right here on this site.
Many believe it is just a matter of jetting but that is actually the easy part. The airbox does restrict the intake flow but that serves a purpose with your CV carbs. Think of this suction as a power assist for opening your throttle slides. Without the correct amount of vacuum you loose control of the slides, which is why it is stumbling. Typically with the pods the slides will not properly open as your right wrist rotates, your wrist cranks more because its not accelerating then the slides slam wide open, terrible to ride. This can be compensated for by softer diaphragm springs and larger hole to the diaphragm chamber. Getting this right is even more difficult when at the same time the jetting is thrown off balance.
You will be best served to find an airbox, you may need to remove the motor but you will be rewarded with a bike which responds to your wrist as intended.

 

take a look at your spark plugs , clean the podfilters

is your fuel filter in correctly ?

 

So the interesting thing is that its not really presenting itself as bog. More like power loss. I also discovered that one of my mufflers has basically just broken off thanks to rust could this be the problem ? I assume especially with a carb one side being open pipe and one side having a muffler might cause backpressure issues. I noticed that it actually revs "smoothly" although it seems to sound different. It almost sounds like a harley below 4000 rpm and then it comes to full song above 4K. Just thought I might post that to help update on the situation. It actually still runs reliably been using it to get around campus just fine. Getting close to my starting date though. I am supposed to leave for California on May 13th.

 

Also, I am definitely going to probably drop the motor in California and refit the stock airbox most likely. I could pay for a shop to rejet the carbs but it seems like to get all of the HP running the stock airbox is best.

 

Also just stating that it was running pretty well before it just started doing this. I have pulled the carbs off, double checked float levels and I went through and checked the vac pistons and such. Everything is good, only thing I noticed is that the muffler finally snapped on the right side :/. Also I am including some pics of the bike cause I think its pretty neat. I changed the handlebars and seat. When I got it it had a chopped skateboard as a seat haha.

 

Go Boilers!

 

looks like they chopped the tail off.
how much of the frame still exists behind the shocks. and did they weld in somthing to connect both sides together?
that little bracket that is supposed to go across from each side is not just a fender mount it keeps the frame from bending resulting in one shock having a different height than the other.
I will post a photo to show what I am talking about both full frame and a hacked frame.

 

photo of hacked rear frame and what should be there

 

Yup. I am going to be welding in a u hoop to the end here soon which should fix that up. I just want to get this fudging low end problem solved. Like I said it was running fine even with the pods on but now it almost feels like choppy at low rpm. Its not that it won't run its just the engine sounds choppy. Once I get above 5 it sings like it should. I checked my pilots again, removed my inline fuel filter just to check. Idk, I am at the end of the rope. Is there anyway its my coils ? I mean I checked them like 2 months ago but I have put like 1600 miles on her in the last 2 weeks in preparation for this trip. Like I said she runs but she sounds off in the low end below 4.

 

If you have pods what size are your jets? For starting point you go up 2 sizes try it if you still have a flat spot go up 1 more check . This is problem with pods . Are your carbs synched? I use a 4 vacuum gauge set up if done correctly this could be part of your problem. What do your plug color look like brown to tan good , white lean, black sooty rich . One other thing to check is compression if you have a cylinder down on compression this could be an idication of potential problems.

 

look at spark plugs,what do they look like? possibly replace the spark plug caps, as far as the coils(ignition and pickup) go in spec works

 

well guys now the problem has gotten even worse (not boding well for the trip). I rode her in the rain two days ago and she was sputtering in the rain no thanks to the pods. Came back the next day and it wouldn't rev over 2k I figured okay water in the float bowls. Drained bowls and tried again still nothing. plugs are 1/2 brown, 1/2 white. I obviously am running lean, I have the jets, ordering some new main jet holders so that I can put in the jets cause my friend way over tightened the mains. Honestly I wish I could just get 4 x emulsion tubes. The carbs were just rebuilt. Also since I have the carbs off I am going to double check the bench sync. I just need to get it to run so I can at least get it 20 miles to my friends place so I can vac sync them. New problem is that it won't rev past 2k, if I open the throttle a hair and my stars line up it gets past the 2k mark and then it will pull all the way to redline. My guess is pilot circuit ? I fiddled with the pilot settings moved from 2 1/2 to 3 turns out. I reset it but still no dice. Cutting it super close here haha, still determined. Its a good bike and I really dig it. New seat hoop has been welded in as well so that should cure the uneven shock problem potentially. Thanks for all the help guys !!

 

Okay guys fixed it, it was clogged emulsion tubes. Now I have to ask. How hard is it to put the stock airbox in ? I am cutting it close but I think putting the stock airbox in for the trip would be awesome because everyone seems to say that if you want all dat power you need to run the stock airbox. Do you think I could do it in an evening. I am just your average level wrencher. I haven't undertaken any big task except for maybe the carb rebuild. I saw a video where a guy got away with just removing a few of the lower mount bolts and the engine dropped to where he could finagle it in. Granted that was a XJ550.

 

A hair dryer helps get it warm it is more pliable.