I need some guidance with my bike.

TLDR: Been fighting with the bike for a year to try and get it running right while throwing spare money at it when I get the chance. Rebuilt the carbs, reset the pilot jet fuel mixture. Got it started using starter fluid a few nights ago and ran it long enough to get it up to full operating temperature though was still getting sputtering at low rpm in any gear with severe loss of power when sputtering. Continued messing with the pilot jet fuel mixture screws till they were about 3 1/2 - 4 full rotations out from soft bottom and the bike was running absolutely flawlessly, sputtering gone, had good power all throughout the band. Put high octane fuel in it while out on the same ride to see if that would help further (not sure if it did or not), rode it quite awhile to actually ENJOY the bike for the first damn time since owning it, it was GREAT! I get home and park it, next morning it absolutely REFUSES to start, sputters slightly here and there but mostly has no power while turning over, starter fluid wouldn't even get it to turn over. I reset the pilot jet fuel mixtures screws to 2 1/2 and drained the gas to put regular octane fuel in it (read online that higher octane fuel requires higher compression on cold engines to start), and replaced the spark plugs while grounding them first on the engine to ensure sparking. It acts like it is trying to start a little better now, especially with the choke on, got it back to the point now that a small spritz of starter fluid gets it to actually turn over again.

I have extra Jets, from left to right -> 112, 80, 43, and 120



Should I try throwing in a size 43 pilot fuel jet and see if the bike is any better? I had high octane gas in the motorcycle the night it was running really, really good. But then once it got cold and the next morning I tried starting it - till now it just refuses to start and sputters on one or two cylinders.

I just rebuilt the carbs from the ground up by taking them to church, cleaned them out really good, broke them apart for fuel rail cleaning and used carb cleaner inside all the jet passageways, replaced any O-Rings while putting brand new 40 pilot and 122 main fuel jets in it.



This is what the old sparkplugs looked like after I took them out, top row is freshly removed, bottom two is after attempting to clean using Alcohol and a soft toothbrush.



After fresh charge this is the standing voltage of the battery I am using, it says negative because I had one of my prongs in the wrong slot on the multi-meter but it's the same reading either way.



Using a paper airfilter in the stock airbox, I repaired damage to the stock airbox using epoxy to seal the leaks.



I have (since troubleshooting) removed the paper fuel filter and am running a straight line to the carbs, all vacuum ports are sealed.

Any assistance or suggestions would be appreciated greatly, if anyone suggests that upping the pilot jet might help then I'll throw in the four 43 size jets I have and see if it helps.

 

Try push starting it. Roll it down an incline and drop it into 2nd gear. If it starts then your battery or wiring is weak and its dropping the voltage too low to fire with the starter engaged. I had a similar problem and a new battery and fuse box solved it.

 

If you had this:
"and the bike was running absolutely flawlessly, sputtering gone, had good power all throughout the band"
And now have this :
"I get home and park it, next morning it absolutely REFUSES to start, sputters slightly here and there but mostly has no power while turning over, starter fluid wouldn't even get it to turn over."

I would look for an electrical issue. Make sure the spark plug wire caps have good connection with the wires, check for loose or corroded connections. Perhaps a "cold solder joint" in the TCI.
I'm thinking electrical first.
If it ran that good once, the carbs SHOULD be fine.

 

First off thanks for the great detail for what you have done with your trouble shooting. Also the pics are great and really help those of use trying to help, keep it up.

When you did the rebuild on the carbs did you wet set the carbs? If you put the bike on the center stand and look at the oil window if it full? If you pull the oil filler cap do you smell fuel? If the petcock has not been rebuilt and if the wet set of float jet is not stopping fuel is could be flooding the engine and or going into the crank case. Could be...

I would go back to basics, with the plugs out check to see if it will turn over, if so check the spark on each plug to make sure you have a nice blue spark. I don't know what tools you have at hand but using compressed air to blow out each cylinder to make sure they are not flooded might help too. Then put the cleaned plugs back in and see if it will start for you.

 

I think you have the wrong carbs for your bike if you need to put in a 43 you should check the Jets in your carbs to confirm that they are actually for your bike. I believe 43 is a stock jet for your bike. What Jets do you have in it now?

 

Plugs 2 and 3 which share a coil don’t look very good. If you unscrew the cap and run your ohm meter thru the cap I’m curious how it compares to caps 1 and 4. I am not sure if your bike should be 5k or 10k resistance. When I resurrected my 550 two caps had corroded so bad they were open. The spark jumped thru the connection but it made the spark at the plug that much weaker. Other than that maybe coil is cracked or otherwise compromised.

 

This seems like a solid start. I remember when my 82XJ650J would have a hard time starting in not only wet weather but damp, humid weather, I changed the coils and all was good again. I couldn't understand how my bike can run soo good once warmed up and dry but act like an idiot when damp. These bikes need all the voltage/amperage possible when starting. I think we can all agree the available electrical power from these bikes is minimum from the get go.

 

It's funny you say that because my house actually is located right on a hill. but if I try to drop it down the hill here and got forbid it will not start I am kinda screwed since I have no way of getting it back up to my house..

I meant as in it will not turn over under ITS OWN power, it will turn over perfectly fine with the battery, sometimes when pressing the starter button it will sit with all the lights off/dimmed for about 2-3 seconds THEN engage the solenoid to enact the starter, but other than that electrical seems fine but not saying I'm an expert and know exactly what I'm doing, were you able to see the video I posted at the beginning of the thread? Also, the spark plug wire caps have all been cleaned out with electrical parts cleaner, used a small brass wire brush to clean them internally, then put "dielectric grease" in each plug to keep out moisture and corrosion since I just got bare metal with the brass brush.

What is wet-setting a carb? I set the fuel levels by bending the tangs gently using needle nose pliers to 3mm below the carb bowl line on each carb using a PVC pipe and some clear tubing attached to the drain nipple on the carbs, each have been set to the appropriate level. I more or less HAD to do this step because the bike kept flooding out when I put it on the side stand but kept running when on center, with XJ550H guiding me I set the fuel levels that way. Oil level is full using the properly rated oil for the bike (It has the specification for wet-clutch motorcycles, and my bandix clutch is slipping bad but it's just shot I think, it does not really bother me too much though honestly). I have not checked the oil cap for any odor and can check once I start messing with it today and give an update in 3-5 hours. I checked the spark on each NEW plug when installing them, each one was clearly visible and blue, plug three seemed ever so slightly less in terms of strength but they all seemed well enough, I used to ride motocross back in the day and have worked on bikes before so based on my experience the spark SEEMED fine. I used canned air on each cylinder before putting the new plugs in each one. It still would not start even with new plugs and blown out cylinders.

Well when I was trying to get the bike started before I pretty much fouled out the plugs because I drowned the bike in starter fluid, it was a mixture of me getting very annoyed and confused why the bike ran so good the day prior and now just wouldn't start at all. I have now gotten it back to the stage of being able to start the bike on starter fluid, it will sputter over on its own power for afew seconds before dieing, I'm making sure not to foul the new plugs again so I was VERY SPARINGLY using the starter fluid at this point.

Should I check standing voltage while under load from the starter/turning over the bike and see how far it drops? The battery in it is not actually meant for this specific motorcycle, it's much bigger than what the battery tray can hold but as 13.14 - 13.20 standing voltage when not under load and 20 CCA.

 

check the voltage at idle and at about 2500 rpm. Idle should be about 12.8 volts and at 2500 maybe 13.8+. If it is low, as mine was (11.5 at idle and 12.6 at 2500 rpm), check your alternator brushes.

 

I don't know if you guys can see the video at the beginning of the thread that I posted, I have it set as unlisted but the link is there so you should be able to see it. I cannot check the voltage at idle and 2500 rpm because I cannot get the bike started. I did check the bushes as stated in that video and used electrical parts cleaner + a pencil eraser to clean the contact points and bushes. The bushes still have a ton of life left in them, their by no means ready to be replaced with how much material is left.

 

One observation is looks like your throttle linkage at the throttle does not look like it is hooked up it is hanging , try turning in the idle a couple of turns, make sure your petcock is set to fuel ON or PRI , have you opened the drain screws and made sure fuel flows out of bowl?

 

The throttle linkage is connected and functions properly with fresh coating of WD-40 for lubrication, it has a SMALL amount of tension on it from the idle screw so I don't know what you mean by "does not look like it is hooked up it is hanging". The petcock is in the ON position, it does not have PRI option. I've drained each bowl to ensure fuel flow and had to do that last night when I was swapping the fuel over to regular from high octane as a trouble shooting measure. I drained the tank fully and then drained each carb body, put in about a half a gallon of gas, then added a small amount of Marvel Mystery Oil to help oil and lubricate anything the gasoline might come into contact with.

 

You can remove the spark plug wire from the cap. There is a "pin" in the cap that goes into the wire thus contacting the inner conductor. Mine were rusted a bit preventing TOTAL power to the plug.
I really think you should start with the starting circuit top to bottom, don't assume anything. Special K and Timbox are right on the money.
Let's get this bike STARTED and then find out what's causing the non-starting issues. Perhaps it IS flooding after sitting or it's just not getting ALL the voltage to the plugs.
Did you do a compression test?
Were looking for air/fuel, spark and compression in the proper amounts.

 

Alright I'll take your guys consideration to heart and start there, Though something else too for my XJ750J, XJ550H was telling me that the pilot jet for gas should be a 43 size, I currently have a 40 in there as was recommended beforehand by himself and K-Moe, assumption is that Chacal might of updated it since then? Would throwing in the 43 size jets real quick make any REAL NOTICEABLE improvement? I guess my question really is as follows: "Would a 03.00 size difference drastically effect how easily the bike would be able to start?" and secondly "I have two Carbs for the bike, their both Hitachi carbs, I also have a random Makuni carb in the parts box that came with the bike too, besides the actual jet sizes is there anything specifically different with the carbs? Non-removable jet sizes, or even different designs? I am positive that I put the correct air main/pilot in, and the fuel are (as stated before) 122 and 40, so I'm just trying to figure out if I need to go all out into ripping into the electrical system or if I should try the other carb first, I really hope the carb I have is the correct one because the other one is really nasty.. I CAN clean it out, but I really don't WANT to."

XJ550H was telling me that I MIGHT have a set of carbs meant for an XJ650 currently on the bike, besides jet sizes is there really a big difference between the 750 and 650 carbs? When rebuilding the carb that is currently on it I used aftermarket jets, fuel rail seals, and emulsion tubes, could there be something else going on with the carb still?

 

So with the assistance of XJ550H once again, we have determined that the carb is indeed from a 650 bike..

"Yep, it would appear that the carb was originally for a 650 then. I'm holding the salvageable jets in my hand right now and I have 2 50 and 4 195 jets. The rest got mangled too roughly when taking them out of the carbs and ended up having to be extracted using an extractor that ruined them.

So now that we have IDed (atleast what we can only now ASSUME because we don't know if one of the POs swapped jets around on their own into the carbs too) that I am trying to run 750 jets on a 650 carb. The question is, "Besides """SERVICEABLE""" jets, are there ANY OTHER MAJOR differences in the carbs that would effect the ability to start and/or run the motorcycle?"

So now the question is above as to if running the 650 carbs could be causing this MAJOR upset with the bike, the other carb set I have (actually the carbs in the picture for my profile) appear to be the correct 750 Carbs since the jets I robbed from it for the air jets were correct for my 750 (put into the 650 carbs currently on the bike) and the fuel jets I took from the carbs currently on the bike were 195 for main and 50 for pilot.

 

"I CAN clean it out, but I really don't WANT to."

LOL...I'm printing this out and hanging it in my garage!!!!!

 

and the plot thickens air jets indicate euro 650.
what about the main jets?
Years & Models: 1980-1 XJ650 4K0 and 4K1 models (UK/Europe)
Carb Manufacturer: Hitachi
Carb Series: HSC32
Carb Model ID: 4K000
Main FUEL Jet Size: #110
Pilot FUEL Jet Size: #40
Main AIR Jet Size: #50
Pilot AIR Jet Size: #195
AIR COMPENSATOR Jet Size: unknown
Starter FUEL Jet Size: #40 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #Y-11

 

Well I'm pretty much at a standstill, I just got home with some carb cleaner and other cleaning stuff but I don't want to bite the bullet and clean the "750J" carb unless I absolutely have to since it's just painstaking and annoying to do. Anyone have any idea as to if the 650 carbs (with 750 replaceable jetting) would be the issue here? I don't know if they are pretty much the same exact carb just with different pilot and main jets for gas and air, or if there is something deeper that is mechanically different about them that can be causing my problem.

 

the only thing would be slide needles from 750J carbs put into mystry carbs to complete the transformation you can just swap the whole assembly diaphrams slides and needles.

you seam to have a set of carbs that belong in europe this could be but more likely the po (previous owner) went to far trying to go to pods. I have been seeing some fb posts where podders are changing fuel jets and air jets. not a good idea IMHO there is a ratio for air jets to fuel jets and increasing them both would minimilize the effect of larger fuel jets. just my personal thinking .

 

So quick update, seems the other carb has pilot jets 40, and main jet 110 in it. But the main jets are weird looking, their small and VERY rounded on the edges, they look completely wrong compared to the jets from my main carb currently in the bike.

 

It says 110 AB on it, these were in the "spare" carb in the main gas jets.

 

ANOTHER update... The needles in this carb I am tearing apart are Y-13 which is the corrent needle size for my 750, so assuming that I have 4 y-13 needles here and there are 4 jets for gas/air pilot/main of each carb.. How much you want to bed that the carb I have on the bike has the incorrect Y-11 size needles meant for the 650? I'll have to tear into that tomorrow, I'm too frazzled atm, Thanks everyone for all the information and help thus far, I guess in realist I should of just "KISS"ed... "Keep it simple stupid", my problem was I thought the PO before me had even the slightest competence, hahaha!

 

Welp, I put the carb back on and I'm back to the initial problem, I can get the bike started with a small spray of starter fluid and once warmed up it stays running but it will idle low ever now and again, almost like a single cylinder misfired and the engine is struggling for half a second to catch itself then it goes back to a normal idle. like the bike runs at 1200-1300 rpm idling, then will suddenly dip to 800, then go back up to 1200-1300.

so I just ran it for about an hour and a half to get the spark plugs bakes with enough fuel to see which cylinder is not firing properly. I'm gonna let it cool down first before pulling plugs though.

 

Max, I see your avatar is that PCV pipe thing you were working on. Are you currently using that with your carbs?

 

No, I posted earlier that I actually fixed my airbox that was falling apart, I chunked out all the back plastic and took a hard-thick plastic binder and epoxied the plastic in place to seal it, it's working fine now. I know that running that PVC contraption I was attempting to use would of caused multiple other issues, but I ended up converting it into a carb stand that I used to set the level in the fuel bowels to 3mm exactly below the carb bowl while level on the X Y Z axis.

 

So I got quite the juice update for you guys, take a look and tell me what you think my issue MIGHT of been this whole time hahaha! I'm gonna run to advanced auto and see about getting replacements, thankyou so far for all your guidance, I'll update you again after I've replaced the boots and cleaned up the wiring abit!

 

Hey guys real quick, sorry for my language but is this wire even f***ing removable? I've been jerking it off for like 10 minutes, pulling, twisting, twisting the other way, tried pushing in first, it spins in the socket but will not come out. I don't want to just HULK it and accidentally break something. Do I need to break open the ignition pack there??

 

No. It is not. The caps can be removed. They screw on/off. The wires are molded into the coil body. Search "coil surgery" for photos of the Dremel-based process for replacing wires.

 

So the only thing that I can do it replace the spark boot caps? Could I of damaged something inside the coil pack by trying to twist out that wire? or did it just spin in its connector?

 

There's no connector. If it was spinning, that's probably bad. Measure the end-to-resistance. Should be 12 to 15 KOhm, without caps, IIRC.

 

How do i measure end to end resistance if I cannot get a prong in there? XD You mean try measuring from the end of the coil to the connector coming out of the other end of the coil pack?

 

Yes. The plug wires are the two ends of the secondary winding. With the caps removed, you can measure from the end of one plug wire to the end of the other plug wire.

 

Coil wire 1 to 4 measures this.

 

I read on the forum that some owners have fitted Honda CB750 SOHC coils to their Yamahas, just another option if you need to replace them.

 

Can you link me to that page? I'd like to read more into that because the coil wire for cylinder 2 is pretty bad internally, I don't think I can even find a brass brush small enough to get in there, let along not rip up and destroy the rubber housing in the process.

 

https://xjbikes.com/forums/threads/cb-750-coils.88468/

 

Jetfixer fitted them on his machine.

 

Thanks!

 

One thing I noticed from your picture is that you inserted your test probes deep into the wires. This may affect the way the caps make contact with the internal wires and may mean you would have to trim the wires back. I also note that your #2 and #3 caps are at 5K ohms while the outside caps ate at 10K. This is the scenario I had also and used regular spark plugs at the outside cylinders and 5K resistor plugs at the inner. This brings the resistance at all cylinders to the specified 10K. See this thread:
https://xjbikes.com/forums/threads/86-xj700-coil-to-cylinder-total-resistance.126529/

 

I just ran to the store and bought some brand new plug boots, all reading over 10k so I'm happy with that now, I feel there is not a connection issue there anymore due to resistance. But once I tried starting the bike I had the same exact problem, the bike turns over, sounds like 1-2 cylinders are firing, and the others are not. I'm still HIGHLY DUE for a shim adjustment I'm just waiting on parts from Amazon, won't get here till the 26th Rip.

I really don't know what else to check, I'm going to go for a ride here in alittlebit just to see if the low rpm stuttering under load (at around 1500 - 2500) is gone, once I get back I'll let it idly while checking the standing voltage while idling, and the voltage at 2500 to see if there is any major difference and I'll post my findings here.

When I had it warming up just earlier I had to use a small spray of starter fluid to get it to actually fire up and once I did it took right off, started up beautifully, stalled on me once but I let the idle drop too low because I was adjusting the idle rpm screw that I assume it was my fault, but once even fully warmed up it continues to have the issue where it will idle, then drop to 800-900 rpm, then catch itself and go back to a normal idle before doing it again every 4-7 seconds or so. Also when I held the throttle open abit (at around 4k rpm) there is a very audible hollow popping sound coming from the exhaust, it sounds almost like a faulty fire or even a complete misfire, I'll upload the videos to youtube and post them here in this thread.

Can you do me a favor and reply saying whether or not you can see the video AT THE VERY START of this thread, it should literally be the first thing you see called something like 750 cold startup issue part 2 or whatever, I have it unlisted but posted the link here so I just want to make sure you guys are able to see it.

 

The 5K/10K story is what the manuals say, but OE coils don't read that way. They are 5K (or 5.5K) for all caps.

https://xjbikes.com/forums/threads/resistor-spark-plugs.119522/

 

Yes, I can see the video.

 

I got the bike back together once again and fiddled with it, now it idles perfectly, no bog. The low end rpm sputtering is gone and it feels good throughout the powerband, my solution was to change out the sparkplug boots, clean out the sparkplug wires best I could with electrical parts cleaner spray, and adjust the pilot air/fuel mixture screws out more, their about 3 1/4 out from soft bottom and the bike is running like a dream again. I'm waiting for it to cool down and get cold so I can take out the plugs and see how the fuel is burning on each cylinder. I just rode it for 38 miles and plan to take it back out again tonight but I'll have to wait and see if it's going to rain.

Thanks again everyone for so much help you and the rest of the forum has given me, I'll update you guys again tomorrow after trying another ice-cold start to see if I'm still at square one. Keep in mind to just get it started earlier I had to use a small amount of engine starter fluid, that was before I adjusted the idle screws out more to 3 1/4. When the idle screws were at 2 1/2 the engine would sputter and bog at low rpm when under load and sounded like it was lean popping.

 

I gotta say, even for it's age it still looks beautiful, especially from alittle bit of a distance, like 10+ feet.

 

Yes it does just like my XJ

 

The only problem I'm having now is the engine will not start again when it's ice cold, if it is already warm and has been pre-ran the engine takes right off but on cold startup it refuses to. I have the pilot mixture screws out about 3 1/4 turns from soft bottom, if their in any further the bike sputters and leanpops at low RPM load. Any ideas?

When I tried starting it this morning it started right up almost instantly, then after about two seconds it sputtered like it ran out of fuel and died fast. Then it refuses to start back up again and it doing what it did in the video at the very beginning of this post, turns over but acts like it's sputtering on only two cylinders or something. I'm positive that a small spray of starter fluid would get it started but I don't want to have to rely on that every time I want to ride it from cold start.

 

These are the brand new plugs I put in about 3-5 days ago, they've been ridden over 80 miles and this is how they look. Same issue as before the bike will refuse to start when it's cold to the touch, but if it is warm/hot it nearly instantly starts every time.(granted that is if the bandix clutch does not slip)


I actually just went to the store earlier and had to ride the bike down my hill in neutral then dump it into first to get it to start up because it wouldn't start, it would just turn over and sputter till eventually the starter clutch slips and stops spinning it over. I have to run the bike with the pilot jets 3 1/4ish the way out from soft bottom or else the bike has HORRENDOUS "low"-rpm-under-load power loss and sputters like it wants to die (once warmed up). It still does that if the bike is cold or in the process of warming up, but once the bike is nice and toasty it runs flawlessly, no sputtering, great power.

Does this starting issue seem like it is more ignition based or carb based? I've torn this carb apart well over 5 times already, cleaned it out so that it's perfect inside (no joke, the carb bowls themselves I cleaned with a soft paint brush and carb cleaner with a little de-greaser to get them spotless), everything is WITHIN spec jet/needle wise for the carb (y-13 size needle, 43 size pilot fuel, 122 main fuel, 225 size pilot air, 80 size main air), Float level set to 3mm EXACTLY from bottom of carb body (down the side of the bowl).

I'm just getting so at my wits end with this bike, I have so much time into it and genuinely like the bike so I do not want to have to sell it, but this starting problem is just absolutely pissing me off to no end... Should I start back tracking from the coils up through the ignition system to ensure there is no corrosion or serious rust in any of the electrical systems? Should I rip back into the carb AGAIN and double check everything for a 10th time, should I just start replacing shit randomly in the electrical system and see what happens? I'm just so damn lost with this f***ing bike. I'm also getting more and more annoyed because some of the shit I need to further work on the bike still has not been shipped due to COVID19, I ordered it the third of this month and STILL won't get it till the 22cd, but yet I can order a dildo and it says it will arrive guaranteed within 4 days.

1982 Yamaha XJ750J

 

Did you clean the small jet at the bottom of each float bowl? It feeds fuel into the brass tube in each float bowl for cold starting. I missed them on my XJ 900 f and after l cleaned them bike started from cold all the time. Beware wear goggles if using carb cleaner. I used a tiny pin to clear the jet. Just be careful you don't want to damage it as it is soft metal. To check if it's clear l sprayed carb cleaner into the jet and it exited from the tube. If the float bowl jets are blocked the mixture will be too lean to start the engine from cold.

 

Short answer is that almost every situation with these bikes that relates to running but not running well is carb based. In a few cases they're engine based (bent valve and such). Ignition pretty much works, or it doesn't.