XJ650 Sputtering and lack of acceleration after 5k RPM

Bike is an '83 xj650, bought recently as a project bike. Was not running properly from purchase, with some PO hack work. Checked valves and compression, all good. Ripped apart carbs, took them to church, fixed jetting, floats, and needle to proper specs. New plugs (had to buy BPR7ES due to BP's being discontinued here), and already had new coils installed.

So the problem. Revs up to redline in neutral with no problem. Under load, will Rev up to redline in 1st with minimal sputtering, but 2nd through 5th after around 5k RPM will sputter and not accelerate. Thought it was a fuel problem, so tried running on prime, shortened needles, and adjusted fuel mixture. All to little to worse effect. Opened up airbox, and seemed to help little, but still only started to pull before sputtering out.

So I'm out of ideas, any help appreciated.

 

Are you running those plugs with non-resistor plug caps? You should be.

In the part where you took teh carbs to church; what do you mean by "fixed jetting"?

 

Unfortunately there are existing resistor plug caps on the bike. I know that technically it should be either one or the other, but the local bike shop advised that it shouldn't be too big of an issue.

As for the jetting, I fixed the locations, as some jets were switched main/pilot. I checked all the sizing in the manual and confirmed the correct size.

 

Haynes manual has the pilot air jet and main jet labelled incorrectly...

 

Did you put the air jets in the locations cited by the manual, or did they get put into the correct locations?

 

Is there another model of spark plug that is equivalent to the bp7es that is still in production?

 

BP7ES is still being made. All of my local parts stores have them in stock.

 

I can't seem to find them anywhere up here in Ontario, and even trying to ship from the states I don't see anymore than 1 available.

Do you think this will be the solution to my acceleration problem, or just something that will help finetune the bike in the future?

 

Canadian supplier - https://fortnine.ca/en/

US supplier - XJ4ever of course

 

It's not the cause of your current problem, but in a TCI system the total resistance on the secondary side ajusts the spark duration and does affect performance. If you can't get the plugs locally, then just get non-resistor caps (you can replace the resistors in the factory caps with brass slugs if cost is an issue).

 

Lots of variables and unknowns...If it were me, I would start with fuel/air first.

Thinking in terms of throttle position...

Is it only sputtering past 5000rpm under full throttle?

Does it accelerate past 5000rpm under 1/2 throttle without sputtering?

When sputtering does the use of the enrichment circuit smooth it out?

Tried running with gas cap open?

Is there an aftermarket inline fuel filter?

Assuming a factory airbox...

What kind of air filter is used? K&N? Standard pleated paper filter?

Exhaust type? 4 into 1 etc.

 

5K under load sounds like the main jets to me.

this is important

 

i tryied to purchase ngk plugs on line at the auto parts store by make and model of bike did not show the ngk plugs and when i searched for the plug number it came up as in stock but did nor fit my bike the site said. they had them i bought them

 

NipponDenso second plug type

 

I run Autolite AP63 or just plain 63 these cross reference to the NGK . My local autozone does not stock the NGK 7ES nor BP7ES of course dude told me they didn't carry motorcycle plugs ...he was totally shocked when the girl showed him on his computer how to find them. The Autolite plug was the "HOT" ticket when I had my Virago 750 on the forum and they worked great.

 

Throttle position is irrelevant, will accelerate to approx 5k and then no longer accelerate, and sputters. Shifting to lower rpms will give instant acceleration again.

I tried the enrichment circuit, makes no difference. Almost seems like lack of air, not fuel. Tried running with gas cap open, the seal seems to be mostly gone anyways, gas leaks out if filled to the brim. No aftermarket filter.

Standard airbox, with a brand new hiflofiltro air filter. Exhaust is a newish 4 to 1 exhaust.


Fortnine has been out of stock on those plugs for weeks. I may try those AP plugs, as after several hours of calling around ngk bp7es seem to be completely unavailable for the time being.


Thanks so much for all the helps everyone, really appreciate it.

 

A few other things to check , if your running a fuel filter try removing it ,could be a restriction and see if any change . Your synch maybe off my Johnny Cash bike idled perfect , the Morgan Pro motion columns were perfect , with them hooked up took off at wide open throttle number two and four were at top one and three were lower . Had to adjust them this has helped, but still playing with it got bike to 70 but it is no where like my yellow seca .

 

I found resistor caps and resistor plugs an issue .

 

OK, the sputter is at 5K regardless of throttle position...only backing off the throttle makes it better.
A couple things come to mind here.
What needles are you using?...Y-10?...all the same?
Floats wetset?...3mm?
Clunk test OK? With the hats on, do they all return at the same rate?...diaphragm tabs in the correct place.

Did you re-jet for the pipe? What main fuel jet are you using? Main air jet?

The only other things I can think of that could block fuel flow are the screens in the carbs and the screen for the petcock, assuming that the fuel line is not kinked.
BTW the enrichener circuit adds fuel AND air.

That's all I can think of for fuel and air, other than a blockage in the airbox...something silly like a rag or mouse turds etc.

Perhaps the PO had the same problem and replaced the coils?

What kind of new coils are they? oem? aftermarket?

Have you ohmed the new coils? pick-up coils?

I don't know how to check a TCI box for functionality...other than swapping with a known good one. The correct TCI box (YICS 650 should be red 5G2...I think) shouldn't make a difference at 5000rpm...timing curves are the same above 4100rpm.

 

All Canadian model Yamaha’s after 1977 came with resistor plugs and 5k ohm plug caps as per Transport Canada regulations

 

That is interesting. I didn't know that, I'm going to look into it.

 

what your describing is a bike with stock carbs and a 4/1 pipe with a high flow air cleaner.
now look up some posts where guys went to pod filters, notice the rpm where they have trouble. yep 5K
does that tell ya something?

 

Sorry for the late reply. It snowed 3inch here today, and I haven't been able to take the bike out for testing, but I'll answer what I can.

Needles are all y-10. I dry set, I can grab some fuel line tomorrow and test wet levels. Passes clunk test, and diaphragms seem good.

As for the jetting, the PO used the dynojet kit. So the air jets are all stock, fuel jets pilot is stock, main was changed to 112.

Cleaned all the screens, vacuumed airbox, and checked for any blockages/pinches.

They are new oem coils, I ohmed them out, and they show proper readings. I was also curious about a malfunctioning tci, but I've never heard of one just not working in the topend. Maybe someone more experienced could chime in on that one?

Thanks to everyone again, hopefully we can get this figured out soon.

Oh, and I ordered some of those AP63 plugs, maybe I'll have some better luck with those.

 

When I dry set mine to 17.5mm, I found the wet set at 5mm...should be 3.

112 mains are stock YICS...both 5N9 and 15U from the service manuals.

 

Another thought , warm bike up run close to 5k and open choke see if it picks up any ,this will show as fuel problem .

 

dyno jet kit did po drill the hole in the slides per the kit and maybe cut the springs down?

 

112 main is not enough for 4/1 exhaust probably needs 116 and even a 45 pilot.

 

Soo, tore the carbs apart again. You were right, floats were low. But that doesn't seem to be the problem here. Still the same problem. I tried the choke thing that was suggested before, still no difference. I was going to increase the jet size, but afte reading the stickied thread it says to add 4 for 4in1, but -2 for stock filter, and -2 for all Calculations. If someone else has more experience, or a thread where someone else has this issue, I'd love the input. It does appear that the slides were drilled, however the springs appear to be uncut and original.

Is there anything else I can try?

 

Good that you sorted the float levels.

Do a plug chop at 5000rpm...what do the plugs look like?

Using the stickied thread calculations, you should be using 114...as a starting point.
112 +2=114

Good piece of advice here...

 

Just re-read your post...

The jet is a DJ112 not a Hitachi jet 112. I misunderstood that part...hence the suggestion to go to the 116 main (Hitachi).
Dynojets don't translate to the Hitachi jets.

If you are using a Y10 needle and a Dynojet main...I don't know how well that would work together, if at all.

 

Interesting, I'm going to have

Alright, getting real frustrated with the bike now. Synced carbs perfectly with a manometer, confirmed idle mixture, and double checked float levels. Brand new plugs. Took it out for a spin, same damn problem. Now this time I pulled the plugs right away, and noticed something interesting. #1,2 and 3 are black and sooty, while plug #4 is a perfect shade of golden brown. Not sure what to make of this new information.

 

You're running rich...plugs are fouling because there is too much fuel and not enough air.

 

Confirm you did a plug chop at 5000rpm and inspected the plugs without idling the engine.

 

As best as I could, yes. I know that means they are running rich, its just a question of why only on 3 cylinders. Or is it really the opposite issue, where 1 cylinder isn't getting the same amount of fuel as the others.

As for DJ vs Hitachi jets, I couldn't find any info on sizing. 112 dyno are the smallest available. I actually managed to find a set of 112 hitachi jets a couple weeks back. I can try to switch them out, but that is the jet sizing that dynojet reccomends. I also tried pulling the air filter to give it the most amount of air. It helped a little bit, but nothing extreme.

 

Hitachi jets are sized by the opening in mm. Dynojets are sized by flow rates. But a Dynojet kit comes with needles that should be used with their jets.

I don't know about mismatching Dynojets with Hitachi needles...should be investigated.

If it was me I would put in the Hitachi 112's with the Y10 needle and do another chop....

Maybe someone else @Toomanybikes @XJ550H @k-moe @Jetfixer @hogfiddles will chime in with some different advise.

 

I was having the same issues with my bike after identical similar mods. I know all bikes are different but we solved our issue after swapping needles to the 750 needles (Y-13s). The Y-10s were dumping way too much fuel after half throttle causing it to sputter due to flooding it out under heavy acceleration. Also did it at light throttle as well but was hit or miss. The needle swap cleared it up and is completely gone. We went with 112 mains and 40 pilot (stock). Runs like a top now. Hope you can figure this out.

 

Interesting. Just wanted to confirm, you had an xj650, stock airbox, dynojet 112 with y-13 needle?

 

I actually have tried with both the dynojet needle at the lowest setting, and the y10 needle and it didn't seem to make a difference either way. I may try to put the original hitachi jet back in tonight.

 

Not entirely, I have an 82 xj650 maxim. I installed a 4-1 mac header, high flow filter, 112s from jets R us, and Y-13 needles. After the header install the same problems arose. Did the valve clearances and problems were still there not as bad but similar to yours. Getting 750 needles fixed it.

 

if the po installed a jet kit maybe he also shimed the needles or if they are dyna needles the needle is set up to change height.

DJ marks the jets with there own code so you ccant buy a kit and tell your friends what size they are.
you could measure them with metric drill bits or get the jets you think that they should be by the mods you have and dump the dj needles

 

I was so desperate to fix this issue I almost bought a jet kit and my buddy who was helping me work on my bike told me to get the 750 needles. It was driving us both mad for sure.

 

Well holy shit. I managed to fix it, and damn does it ever fly now. So after some very careful investigation of the jets, I compared the Hitachi 112, to the DJ 112, and a dj116 that I had here. I noticed that the DJ112 was even bigger than the 116. The PO must have drilled it out, or a mistake from the factory. So I said screw it, put in the Hitachi, and took it for a spin. Insane pickup, great throttle response, and all that carb work definitely paid off in a smooth running bike. Ended up putting about 150k on it this evening. One thing I did note is that the top speed was about 130km/hr. In the book/online it lists the topend as around 180. Is that one of those "top speed with a tailwind down a 45° slope" or a number I should be expecting to see somewhat close to?

Thanks to everyone who helped me out, I definitely still have alot of work to do to the bike, but it all makes it worth it when I can at least take it for a spin.

 

Nice!
I had a look at the Dynojet site. There is no mistake from the factory and I doubt the PO drilled it. Looking At Stage 1 the DJ116 is smaller than the DJ112...Stage 3 the DJ122 is smaller than the DJ118. It's all in the wording...

Regardless I'm glad you worked it out.

 

Thats a number that you should reach even with a good headwind, and be able to hold until you run out of road.
When stock anyway.
Now? Maybe. Maybe not.

 

Glad all the ideas could come together to help you reach your end result! Thanks for sharing, I hate unfinished and un-updated threads! Be safe out there, ride out!!

 

Should I be looking to increase my main jetting in the future then? I'm fairly confident that is most likely the cause. I now have all original jetting with my 4in1 exhaust. Or will that be the restriction that prevents me from getting there?

 

Where did you manage to find the sizing? Also, do you know where up here I could find some larger hitachi main jets? Would still like to properly adjust the jetting.

 

The factory exhaust is not restrictive, and your 4-1 is likely less restrictive than that.
Start with a compression test.

 

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