Jerrod's 82 Yamaha XJ-750 Maxim

What's up guys, just bought my 2nd project bike. A 82 Yamaha XJ-750 Maxim. I started by removing the stock handlebar mounts, and took a set of stander mounts from a 87 Virago and installed them. Worked well, but now I'm to my broken Speedometer. It has this instrument cluster that looks kinda like a car dashboard, it's not in very good shape, and as I said the speedo is toast. But my Head and Brake lights run to a chip in the center of the cluster, and won't work without it. Is there anyway to delete the entire cluster, and install traditional gauge's?

 

Use an 83 750 maxim or 82-83 xj650 maxim wire harness and gauges is the quickest way.

 

I agree 100% with the suggested solution. As long as the recommended models also have electronic tachometers, it should be largely plug-n-play. There may be a different sub-harness required in the headlight bucket, check with XJ4Ever. Speedo is mechanical, so no issues there.

 

My neighbor has a 87 Virago that he is scrapping,

Copy that, thanks.

 

there is a thread on atari delete with wiring diagram.
or you could keep computer part and just tuck it away.

if you pickup a 83 750 maxim forks you could easily remove head light and replace with a round one

 

Hey what's up guys? So the instrument cluster on my 82 XJ-750 Maxim was toast, so I took the speedometer from a 87 Virago that I have sacrificed, and installed it. But no cigar, my assumption is that the XJ's Speedometer drive spins in the wrong direction to operate the Virago's Speedometer. So does anyone know of a good speedometer I can get that will work? I don't wanna spend money, and run into the same issue.

 

Try a 650 maxim speedo or 83 750 maxim will work

 

Ok, thanks.

 

have you checked the cable and drive unit in the wheel.
virago speedo drive is on left side of wheel it should be spinning the same direction.
Virago uses same drive hub on wheel as 650 and 750,

 

The Virago and all Yamahas of the period use the same speedometer drive. The problem lies elsewhere.

Make sure that the tabs on the drive coupling aren't bent and that they engage the slots in the wheel.

As mentioned: make sure that the cable is intact and lubricated.

Make sure that both ends of the cable engage their respective hubs.

 

What's up guys? I picked up an 82 XJ-750 Maxim last week, and the exhaust is toast, completely unsalvageable. So after searching online, I wasent able to find a stock replacement, so I settled on a 4 into 1 header, with a trumpet style slip on baffle. My question is, are there any signs I can look for, that would indicate that the bike is running too lean, or too rich, So I can then Jet my carbs appropriately?

 

Indication of running too lean and hot would be a blueing of the header pipes and the colour of the spark plug electrodes would be white-ish. Also the revs could hang up before settling down at tickover.
Too rich and the colour of the plug electrodes would be very dark and sooty in appearance.
Possibly other indications could be present.

 

-first point: most aftermarket exhaust systems are single-walled, so blueing of the pipes will be normal even if not running lean. (Get the tuning just right and they may "stop" at golden-brown and never make it all the way to blue.)

-next point: by removing the original exhaust collector box, you change the dynamics of the exhaust system enough that re-jetting may be be required. The "magic" of the XJ's exhaust system is in the collector box; the mufflers make very little difference tuning-wise. (There is a lot more magic in the intake.)

-as long as you retain the stock intake; that is airbox, stock air filter, etc., you may not need to re-jet, just adjust.

-you cannot hope to begin valid carb evaluation and tuning unless -your valve clearances are in spec; -and your carbs are 100% clean, float levels wet-set, etc.

-spark plugs are "read" by looking at the coloration of the "flame ring" and the ground electrode below the bend. Today's gas can produce some very interesting coloration (what does bright yellow signify?) on the insulator, the flame ring is the key. (The "flame ring" is that portion of the plug just beyond the threads that the ground strap attaches to.) You will probably be able to tell based on how the bike runs whether it needs to be re-jetted, as long as everything mentioned above is dealt with.

How many miles on the bike? Any history, has it been sitting or has somebody else been fighting with it?

 

I have to agree; compatibility is not the issue here, something else is amiss which means there is a good possibility your original instrument may be OK.

Flattened out tabs on the drive unit are very very common...

Simple diagnosis: disconnect instrument, spin front wheel in forward direction, observe exposed end of cable to ensure it is rotating.

 

Ok, this is interesting. Because my 74 CB-750/4 will hang RPMs like you described, until it gets warm, and then will run fine

20,000. And no it runs and rides, low on power though. My CB-750/4 will put it to shame as is. The collector box is roached, the tip had completely rusted away and was non-existent. It was basically running on the factory downpipe's. Very low on power, gets up to speed, but virtually no pick up to speak of. The header and baffle are due to arrive tomorrow, so I removed the rotten factory exhaust today. That's how I discovered the collector was completely rotted out.

 

The top* of the collector had completely rusted away. Not tip.

 

Oh, and the Header I bought is black. So discoloration is probably not gonna be a very clear indication.

 

I recently bought a 82 850 Maxim, and discovered today, that the Speedometer drive cable will only rotate when the Bike is rolling backwards. When the Bike is rolling fowards, the cable does not react, obviously resulting in my speedometer not working. Does anyone know what could be causing this? The only thing I can think is that the previous owner disassembled the speedo drive, and possibly reinstalled the gear backwards, if that's even possible. I'm Completely stumped, and any theroy's are welcome.

 

If your XJ is outrun by a 60s design Honda you may wish to undertake a compression test.

 

Please stop

Yes, I've learned that, what's happening is my cable is not rotating when the bike is rolling fowards. It rotate's counter clockwise when the bike rolls backwards, but does not respond when rolling fowards at all. The only think I can think is, the speedo drive was previously taken apart, and then reassembled backwards, if that can even be done. I'm confused lol. I have access to the Virago speedometer drive. Gonna try and see if it fits.

 

You may be right, didn't pay anything for the XJ, so I have no problem fixing it. And the CB isent stock, has a cam, and a few other things goin on. Not saying it's some Superbike lol, but it outran a 104c.i Harley heads up, which I believe is 1700cc. It does ok. But yes the XJ is ment to be a bit of a step up in power.

 

It has no trouble starting or idleing, no smoke of anything that would indicate the rings are gone, besides acceleration being kinda low. Was gonna see how it respond's to a functioning exhaust and go from there.

 

As suggested above, a compression test is the best place to start with any old bike you aren't familiar with. Personally, for me it's a pre-purchase prerequisite due to the high unavailability of things like pistons and rings for a lot of old bikes. I don't want to buy into a mechanical dead-end.

 

You sure the inner cable isn't broken in the middle somewhere, and only "catching" itself enough to spin backwards? The other possibility is that the tabs on the drive are mashed and not catching except when you rotate the wheel backwards. There's really no way to put the speedo drive together backwards, as long as it's on the left side of the wheel its innards should be turning the proper direction. The Virago unit should fit fine, it has the same part number.

 

Compression test will help diagnose low power. If the results are poor you then need to see if it's bores (worn or stuck rings) or valves (burnt, bent or poor clearance adjustment). Have you checked air filter?

 

Yeah, I didn't think reverse assembly was even possible, just didn't make sense. It is on the left side, and the cable is intact. The drive on the Virago seems to be the exact same part, unless the axels are different sizes it should line up. Gonna give it a shot I guess.

 

At the end of the day, I have a speedometer app on my phone that works well. I would just like to have a fully functioning Bike.

 

Yeah, someone has been screwing around with this speedo drive for sure. The screw holding the cable in place is completely stripped. Looks like I'm gonna have to take an easyout to it.

 

Soak it really well in PB blaster first. It's exposed to a lot of wet and grime.

 

Will do.

 

Just bought an 82 750 Maxim, it runs decent but is down on top end power. Doesn't have much trouble getting up to speed, or maintaining it. But feels very restricted in the top of the RPM range. Feels normal at around a quarter throttle and under, But just feels restricted above that, like it's not getting enough of something. Original thought was high speed jets were dirty. But now something else has started. After around 20 minutes of riding, the Bike starts backfireing hard, and then stalls. Was able to choke it, and get a little further up the road. But I made the mistake of stopping, and it would not start again for a half hour. But then started and ran fine, like nothing had happened. I cleaned the floats and jets, and the 2nd carb from the left was much worse then the others, it was black in the intake side where the air filter clamps. Im assuming this is the cylinder that is backfireing. Has anyone ever had something like this happening?

 

Sounds to me like you have to go through the fuel system. If is was not running well at first and then as you were riding got worse, sounds to me like junk in fuel. Top right of every page is a icon, click it and start to read up about these bikes.

https://www.xjbikes.com/forums/threads/tech-topic-the-real-costs-of-maintenance.14581/

Always making sure the gas tank is clean, you don't want to clean the carbs all up and then have them get full of crud again from the gas tank. Good luck and keep us posted.

 

No, the tanks clean, Not that simple. It's more Systematic then that. Starts after the same amount of run time, everytime. And it always takes the same amount of time to start running again. I would say the Coils, but the previous owner installed a brand new set a week before I bought it. I don't believe the lack of power, and the stalling are connected. My lack of top end power, is either the fuel line I ran is too small, or my air intake is clogged up. And since the plugs claim it's running rich. I'm gonna go with the intake being clogged.

 

I also considered the fuel could be boiling, becuse the petcock is very close to the head. But I have a clear fuel line, and it is not. Also the prong for the prime tube on the petcock has been broken. I'm not sure what kind of issues that could cause?

 

Yeah, I'm on a non running period right now. And all it does is crank and backfire, so I know it's getting spark. And after the correct amount of time pass's it will fire up like there was never a problem, and run fine for another 20 minutes, then do it all over again.

 

And thank you for the link, I am new to the XJ. But not new to classic bikes. My first ike when I was 15 was a 78 Yamaha 650 Special. Owned a CBR-600 for a few years, and became a Dad so I decided to slow down a bit. This past summer I did a frame off restore on a 74 CB-750/4 that involved completely rebuilding the top end. It's my daily now. But I've wanted an XJ since I had my XS, and that leads me here. I did get the Bike for dirt cheap, but I have good cash on deck to get it going again. Rebuilding old motorcycle's has become a big part of my life I suppose. I enjoy it. This bike is a runner, it is Machanically sound, something weird and unpresadented is going on with it though, the last guy couldn't get it figured out. But Im going to.

 

And if someone has experience that I do not, I am very interested in that knowledge.

 

I had a pick up coil fail only when hot. When it first failed it had a big backfire just as I pulled in to the drive way. I was lucky that it failed then. After it cooled down it would start then after a bit of time it would stall. At that time the pickup coil would not show continuity.

 

Sounds like it is starving for fuel after a few minutes. Are you sure the gas tank cap is venting properly? I assume the valves have been adjusted. I had a situation where my bike would sometime shut off when I hit the brakes and wouldn't start for 10 minutes or so. Turned out to be bad alternator brushes. That reduced the voltage so much that at idle, or very low rpm, there wasn't enough voltage to fire the plugs and lights at the same time. You might check your voltage. Should be at least 12.5 at idle and close to 14 at 2500-3000 rpm.

 

See and that was my original thought as well. But previous owner said he just replaced the coil, showed me the Receipt and the coils look brand new. I suppose he could have bought a bad set, I think it's unlikely. But possible I suppose.

 

I'm talking about the pickup coils that are on the left side of the engine under the cover. I hope we are on the same page.

 

Let's stop guessing and start diagnosing.

First things first.
Are the valve clearances in spec?

 

Hmm, interesting. It is a replacement engine that previous owner installed. And if he decided to set the lash, and just snugged them up instead of using a feeler gauge, that would definitely hang the valve's and cause over heating until the swell subsided. And I have seriously considered that it is overheating.. Seems like a logical place to start. Where should they be set in thou?

 

Ah, this is shim's. Hopefully he didn't feel the slight play, and thought that ment they were worn.

 

By all means check the valves if you have not done so, however I would agree with lostboy that you are describing a pick-up coil failure.

The logic behind that is if one pick-up coil goes out, the TCI will fire incorrectly (opposite cylinders of working pick-up) causing the backfire and no running. You can simply ohm out the pick-up coils at the TCI six pin connector when the bike fails. Gray to Black and Orange to Black should be 650 ohms +/- 10%. The resistance will increase a bit with temperature, but slightly out of spec is not a problem, you are looking for one to completely open or short to ground.

 

Both me and the previous owner thought Coils too, I had a car do the same in highschool. But he did replace them. I guess I just wanna cover all base's before I spend 60 bucks on a new set of coils.. I wanna be Positive that it's not overheating or something..

 

Becuse the coils that are on it are less then a month old. And they were purchased brand new. Yes it is possible he bought a bad set, that does happen. But not very often.

 

You're not on the same page. There are pick-up coils and output coils.

 

Got it!! It was the air filter, it was nasty and was causing a super rich mixture which was over heating it. I also installed a larger fuel line, and it cut my dead spot on the top end in half. I think what's left is my aftermarket seat restricting the intake..

 

You're just gonna pretend the valves are fine right up until the motor won't run anymore, right? Because I see that happening... Just check 'em, then you'll know how close you are to disaster... You need to learn this, because they need to be checked every 5000 miles or so.