XJ750 Running fine but general issues.

Hello, first off I just purchased a 1982 Yamaha Maxim 750, I've just did alot of general maintenance on it such as: Fresh oil and filter, brand new air filter, brand new spark plugs, tore apart the carbs and cleaned them best I could with carb cleaner and compressed air, fresh gear oil in the final drive (don't know how to access the front side of the drive-shaft to change the gear oil if there is any there), and washed the bike.

My general issues I've been having and hoping to seek assistance on are as following: Bike MPG is 27 and when at idle I can faintly smell gasoline while sitting on the bike which makes me think it it overly rich, when starting from a dead stop the bike bogs immensely and acts like it's having serious fuel issues and loses nearly all power unless the bike has been properly warmed up and ridden for Abit already. If not you need to hold the bike at 3k rpm while starting to be able to go without issues, the bike doesn't want to start when cold unless you use starter fluid to get it warmed up first, and finally the starter grinds really loudly and doesn't turn the bike over when attempting to start it but I think the starter just needs to be replaced.

 

Welcome to the site! I think you need to take a look at those carbs...If the bike has been sitting for a long time not being run, the carbs are need need of some TLC.
https://www.xjbikes.com/forums/threads/in-the-church-of-clean.14692/
That is the link of how to do the carbs the correct way. There are no short cuts go getting these carbs to work okay and think that will work. They need proper care and respect when you have them off the bike.

As for the starer, I hope you are right. I think some of the 750's has started issues but I have been lucky so far. I would guess another informed member will be along in a bit to help you with that.

Congrads on the bike, looking forward to more of you posts on getting her running the way you want her.

 

Well the thing is too @Timbox , The person I bought it from gave me an extra set of carbs with it, but they look different. So I don't know if their the carbs that were supposed to originally come with the bike or if the ones on it now are the originals. Even if they are different shouldn't adjusting the duel-air mixture allow me to run them anyways if their not the original carbs?

 

1. I agree that the carbs need to be pulled and properly cleaned.

2. The starter motor should be rebuilt, not replaced. Parts (for darned-near everything) are available from @chacal
Replacing your starter motor brushes w/ pics
The battery must be in top-shape, and the switches and relays in the starter system must also be in good condition so the starter can spin as fast as intended, or the starter clutch will slip.
The charging system should be checked as well, just to make sure the battery stays charged properly.

3. Having said that, the most common cause for the starter clutch to slip is having the wrong oil in the bike. Choosing Oil for a Wet Clutch Motorcycle
What oil did you use?

4. The engine is of unit construction, so the transmission and engine share oil. There is no seperate gear oil, aside from the final drive.

5. Read This First

 

You need the correct carbs for the engine. There are ways around that, but simply adjusting the idle mixture will not make the bike run correctly unless the carbs have the correct airflow rate (which is a function of the size of the inlet) and jetting.

Carb identification can be a bit tricky because Hitachi didn't mark them very well, and some of the parts used to identify them can be swapped.
The best way is to look for the Hitachi logo on the carb bodies, and note which main, and pilot jets are installed.
Hitachi logo:


You might also look on the bottoms of the float bowls. They were ink-stamped at the factory, and sometimes the ink is still legible.

At your 6th post you can link pics. Post a few more times and then put up pics of both carb racks so we can help you identify them.

 

Alright I'm at work right now, I work night shift 13 hour shifts, I'll post pics and such tomorrow. Thanks for the information so far everyone!

 

I don't have a 750, I'm sure someone will come along with more machine specific knowledge, this is a great place for that.

I'll second the church of clean write up. I've not suffered the worst of it, but there are all kinds of posts here of mystery issues that resolved when somebody finally gave in and took their carbs to church, properly. If you haven't come across it yet, the Information Overload post is a fantastic bit of reading. It'll help get you up to speed on just how to care for your new, vintage bike.

Also someone will mention, at some point, don't forget to check your shims, as well as your brake line and tire date codes.

 

Okay, now that I'm on a computer instead of my phone I can reply to afew things. I already cleaned the carbs best I could with carb cleaner and compressed air, I've worked on carbs before in the sense of cleaning and adjusting them but I have never actually known when I needed to change jet sizes and such, I just took the starter off and am planning on either just taking it apart and trying to clean it up best I can and lubricate it, or buying the rebuild kit to do it properly with. The battery I know is good because it's the same battery that came off my sports bike, he didn't sell it to me with a battery. Also something else I guess I should just throw in here till I hit the "6 posts to be able to post images" is that the dash has all the warning lights on, like every single one. It's warning me about anything from the headlight all the way to the oil pressure which cannot possible be correct so I think the master warning fuse or something in the dash is blown, the gas indicator works though, that's a plus. One of my neighbors who is an elderly mechanic says he can hear it not firing properly on one of the cylinders, and I should take a laser thermometer and see which piston is running cold by checking the exhaust. The bike sounds like it is running fine to me, if not it does have a small short hiccup every now and again where it feels like a single cylinder isn't outputting the right power so I believe him. Once I get to 6 posts I'll send pics of both carbs onto this thread.

 

The warning lights won't come on at all if the fuse for them is blown.

More likely the systems monitor isn't hooked up properly, or the things that the system monitor looks at aren't hooked up. The oil level float (there is no check for oil pressure) can be sitcky from sludge and cause a low oil fault to be shown. the remedy for that is to run a dose of Seafoam in the sump until the next oil change.

It does a self-check when you start the bike, and the only thing that should remain on is the LCD for the sidestand being down and the fuel gauge.
SInce you're not using the orignal-type battery the systems monitor will throw a battery fault (because the battery acid level sensor is not hooked up). There is a simple workaround for that which will let you use a SLA battery and still be able to monitor the battery health.
Pay attention toe Rooster's first post in the thread, as the resistor value is what allows the systems monitor to throw a warning if the battery voltage gets low.
http://xjbikes.com/forums/threads/battery-sensor-we-dont-need-no-stinkin-battery-sensor.820/


If you press the warning control button the big flashing red light will shut off for around 15 minutes.

 

Well about the gauge assembly, it dosn't blink it's just a solid red and light, and the two buttons on it don't do anything. I have another gauge assembly for it but it's in like 80 bajillion pieces because the guy before me was trying to put brighter lights in it, but ruined it in the process. Does anyone have a wiring diagram for the Yamaha Maxim 750? I figured I was just gonna buy another universal head unit for it (one compatible with analogue Tachometer) and wire it in if I could find a diagram.

 

This is her by the way, really clean looking for a 30+ year old bike.

 

Here's the wiring mods to remove the rectangular instruments

 

I'm curious about this bike and am hoping K-Moe can shed some light

I have an '82 Maxim 750 same as Maxwell's but our gauges are very different.
Was this a Canadian vs American thing?

here is my cluster

 

Raskel My XJ750j Maxim has the same cluster as yours. lights on the bottom.
I suspect that Maxwell may have a seca set up for a cluster

 

Maxwell has Seca gauges on his bike in the picure from his last post.

Which I didn't even think about, or notice before.

@Maxwell Partridge
The Seca gauges are not wired the same as the maxim gauges, and that's why yours don't work.

This thread will be of more use than the one I provided earlier, unless you go ahead with fiting non-OEM gauges.
Maxim gauges instead of Seca's? I have the answer for you!
The swap is the reverse of what you need, but you should be able to work that out unless you have a set of Maxim gauges to install.

 

Is his bike actually a Seca and not a Maxim? I don't know what the defining characteristics are

looking at other pics, the tank on the Seca has indents whereas the Maxim is smooth

 

this is photo from owners manual light, s on the bottom and my service manual shows the same thing. the 82 and 83 maxims are a very unique bike as it does not share a few parts with the seca 750. no headlight relay, controls are just for the maxim 750 but are the same as the xj1100

 

his is a maxim just wrong cluster.
maxim has a fat style tank and sidecovers are a triangle style made from aluminium and plastic trim

 

That indicates that the CMS (Computer Monitoring System) is stuck in the standby state. The CMS does not become active until the bike is started and one leg of the AC generator supplies power to the CMS to enable the system. Odds are either the charging system is not working or the white wire from the AC Generator to the CMS is open. The check and warning reset switches will do nothing until the CMS becomes active.

This is a good indication that the CMS is properly powered and should function.

I believe you should be able to install the Seca gauges on the Maxim and have full function. Conversely, the Maxim gauges on the Seca will not work unless a ground is added to the 9 pin connector as the Maxim uses a separate ground connection for the CMS at the 9 pin connector.

 

One easy telltale: The Maxim has the alimunim 'square' handlebars. The Seca has plastic covered round bars, and the brake master cylinder is not located on the bars.

Another is the shape of the gas tank, and the lack of a rear cowling behind the seat on the Maxim. The Maxim also has chromed fenders, where the Seca has a body-paint colored front and a semi-hidden plastic rear.

There's at least a dozen other small differences that are easy to spot once you know what they are.

 

Hey guys, sorry I've been silent, work has been kicking my ass, I'll grab those pictures today!

 

Tore down the carb again and actually replaced some of the parts in it from a spare carb I had, Apparently I had 3 carbs total, one is a Mikuni and the other two have the hitatchi logo on the side so I'm assuming those two are the correct carbs for the bike. I had to replace 2 of the main jets in 2 separate portions of the carbs since the ones originally in them were chewed all to hell, you couldn't take them off without locking pliers, and one of the carbs is missing a brass plate that goes under the rubber seal on the top portion of the carb, I have no clue what these are called so I will give a description now so you may know what it is: ""On the top after taking off the chrome-plated part there is the spring that comes out, the rubber flexible seal that goes around rim, and then the needle attachment to it. You pull that whole assembly out and then there is a brass plate screwed in with a single flat head screw also made of brass that covers two jet-looking screws."" So one of the carbs is missing that plate, and before rebuilding it using parts from the spare carb one of them was missing the actual jet located in there, I pulled it from the spare and put it in. So to my knowledge so far it has everything it needs now, except one single carb is missing that plate, I'm going to put it back on the bike tomorrow and see how it runs.

How far out should I back the air-fuel mixture screws to start getting a baseline for how to adjust it? I currently have them backed out 2 1/2 (half rotation) turns from bottomed out. Thanks so much for the information so far!

 

plate not needed it was removed from the assembly process by yamaha

2-1/2 turns from soft bottom is base line . open them all up to 2-3/4 turns

you now have 4 hatachi carbs correct?

 

@XJ550H I don't have 4 Carbs as in 4 Carb Assemblies, I have a single carb Assembly that is 4 Carbs linked together that all run from the same throttle/choke cables and gas line.

 

That's what he's asking.
There are 4 carbs to a rack. WHat yoy wrote mesde it seem like you had a rack consisting of 3 Hitachi carbs and one Mikuni carb, which is physically possible.

 

Nah, Their all Hitachi and always have all been, but it was missing some parts as in that brass plate that he said isn't even needed, and one of the holes under that plate was missing the brass screw where (I am assuming) gas goes through.

 

Other than that, all I did was clean it out extra good again, and replaced some of the brass jets since the previous owner apparently destroyed them using locking pliers and completely crushed it. So I swapped some that still had the flat-head ends into the good carb from the parts carb. Now I'm waiting till tomorrow to put the carb back on the bike and try and start it up to see if it is running any better, I'll update you guys again then.

 

The screw for that plate goes into a blind hole, so you don't need them in there either. Gas will never get into the upper part of the carbs. It'll go into the crankcase long before then.

 

There are three brass screws in there though?

 

There is one screw to hold the unnecessary plate (both missing in the pic), and two air jets.

 

Oh alright, thanks for clearing that up for me! Like I said I'll post an update tomorrow when I get it running again!!

 

When you guys say to back out the fuel mixture screws x amount of turns, do you mean full 360 degree rotations, or half that per "turn"?

 

full turns from soft bottom.

the jets under the diaphrams are air jets . shown in photo above

 

Alright, before I put it back on I'll bottom out the air mixture screws again and back them out 2 2/3 turns using full rotations per turn. I know what the fuel mixture screws are I just didn't know what those jets under the rubber diaphrams were. Is it alright that when bottoming out the mixture screws they don't all end in the same position, I.E. not all flatheads look the same at dead bottom?

 

Yes. There is some variation as not all of the screws were cut exactly the same (e.g. the slots are not clocked to the threads).
They are registered from the needle contacting the seat, so don't bother trying to match the slot orientation from screw to screw. Just count turns for each individual screw.

 

Alright, Thanks!

 

Alright, so I got another update. I got the carb back on the bike, it was struggling to start so I tore it back apart and adjusted afew screws along the bottom of the bowls and put it back together. It starts and idles fine especially once you get it warmed up but once you try to start going it bogs, like as if though it is getting too much fuel or something. Anything under 2-2.5k rpm makes the bike bog, you have to hold the idle at around 3-4k rpm to go from a dead stop and keep it above that when switching between gears, any ideas? I've tried adjusting the idle screws abit but cannot seem to find the sweet spot, I'm gonna mess with it more today once I get up later, I work night shift so I'm only now just going to sleep (6:20 AM EST).

 

There are no screws along the bottom of the float bowls to adjust.
The only screw-based adustments are the idle mixture screws (along the top of the carbs next to the enrichment plungers), and the throttle plate synchronizations screws (along the throttle shaft between carbs. The synch screw for #3 is the idle speed adjustment knob).

What screws did you turn?

 

What I mean by I adjusted some internals along the bottom of the bowl was that I took out the jet s and put them back in to ensure nothing was clogging them after blowing air through them. I adjusted the air fuel mixture screws along the topsides of the carbs near the inlets to the head of the engine.

 

How many turns out do you have them at now?

 

When I put them out to about 3 1/4 the bike was struggling to run and was bogging alot, when I put it to about half that it runs but bogs at low RPM (2k and under) but once you get higher in rpm it runs fine. Just for clarification I am talking about the screws above the butterflies on the carbs, not the screws attached to the throttle bracket.

 

the jets you swapped in were they from a set of hatachi carbs? mikuni jets are not marked in mm size but flow rate.

did you confirm the jet sizes you swapped in from the other spare carbs?

when you took jets out and blew air though them did you do the passages they cover as well?

and are jets in the correct location? main jets larger with washer under the aspirator tubes with smaller

 

1. Yes from same carb
2. I do not have a way of making sure they are the same size but by eyeballing they looked exactly the same.
3. The passages were already fully cleaned and had air blown through them last time I cleaned it, I've done a complete teardown and cleaning twice already.
4. I put them back together the exact same way they came apart, I've worked on carbs before and am good with intricate details (Thanks US Navy) and under the bowls of both carb sets look exactly the same, so I'm assuming they are correct. The smaller jet has the brass washer under them.

 

Hatachi carbs correct

bright light magnifiying glass jets have numbers on them

ok good

pilot jet smallest on left. main jet largest on right with washer
if reversed this is you issue

Rule #1 is never trust the P O if he had his hands in it all details need to be checked in your case jet location

 

After alittle more diagnosing me and my neighbor were able to figure out that Cylinder 1 is not firing fully, there is very weak power coming from it (too dark and engine was hot at the time of testing so couldn't take out plug and see if it is just weak spark).
I'm pretty positive that my carbs internals look exactly the same as the picture above.

 

TCI systems have visibaly weaker sparks thanother systems (the spark is not actually weak though).
If #4 is firing than #1 shoudl be too, unless something is wrong with that carb, compression is low, those valves are out of spec, or the sparkplug is bad.
Swap the #1 and #4 sparkplugs and see if the problem follows the plug (they fire from the same coil).

 

Alright, I'll do that tomorrow, Thanks K-Moe!

 

Alright so update! I know it takes me time between posts and I apologize. I swapped plugs from 1 to 4 and the low power from cylinder 1 completely disappear and didn't show up in cylinder 4 (confused). I'm rolling with it, I vacced the carbs and adjusted the throttle screws between carbs like this: ""Adjusted main throttle idle screw on underside of carb to get RIGHT BEFORE you get hanging idle when blipping the throttle, then adjusted each carb afterwards to match the vac reading from the main carb (carb 4) and now the bike is purring like a kitten (unless cold with choke)."" Now for the mixture screws I pulled them back about 3 3/4th turns and the bike would still sound like it was bogging and sputtering at low RPM, giving me a signal that it is running rich still, continued backing them out slowly between test rides till their all about 4 3/4ths full turns backed out and the bike seems like it is running perfectly now. Only question I have now is I have read other people saying that their 750s get up to 145MPH, mine struggles to go anything faster than 75 (not to mention it wobbles like a bitch when it gets past 70) so new tires and a balance are in it's future.

Thanks for everyones help so far!

EDIT: Figured I should also mention when I checked the spark plugs they were black and wet, so I know it was running rich.

 

the 750 does not go 145 mph top speed is around 125 mph. wobble could also be steering neck bearings, wheel bearings (front and rear) swing arm bushings.

 

Any particular reason my 750 might be getting on 27 mpg, is this normal?