Xj650 driving me nuts

Hi there!Think this is my first post here so far I was just voyeur.A year ago I started converting my xj650 into cafe racer and everything was great during the building and upgrading until I came to the point of running the bike.What a nightmare was the first start, the bike started after 1 hour and was working on 3 cylinders, wasn’t running smooth and the conclusion was that the carbs were not clean.Removed the carbs, disassembled them and cleaned them completely, made setup as the workshop manual suggests and bench synced them and the bike started right away after 4-5 attempts.Again the bike wasn't running smooth, throttle was choking after 2-3000rpm and the conclusion of the friends and everyone I contacted was I need stage 3 jets since i upgraded the bike with pod filters and converted the exhaust 4-1.Sent the carbs to the shop and cleaned and upgraded the jets to stage 3 by a professional carb rebuilder and also he bench synced them and its even worse.The bike is starting after 2-3 attempts but it throws black smoke from the exhaust and its choking right aways after I try to add throttle and when I try to rev it.PLEASE HELP since I’m seconds away from selling it dirt cheap since I’m sick of watching the bike everyday and not be able to ride it.

 

Your main mistake was converting to pods.

 

Have you checked the fuel level in the carbs, did you wet set them?

https://www.xj4ever.com/setting fuel levels.pdf

Did you make sure the float bowl enrichment jets were clear?

And guessing you never had it as a runner before doing the pods?

 

Yes!The damage is done now what?

 

The carbs were at mechanic who does carburetor stuff for 30yrs.He disassembled the carbs, cleaned them in ultrasonic tub, polished the needles, installed stage 3 jets and polished them and bench synced them.

The bike was running fine with the previous owner which is very good friend of mine but it was stock xj650 4K0

 

Removing the air box and fitting pods will affect progression and full throttle running, but my experience is it will not affect idle, once the mixture is set using the mixture screws.
It should start and run, idle normally on pod filters.
So if it doesn’t, put everything back to original, set mixture screws 3 turns out from soft bottom, fuel level to spec, bench set the balance according to the butterflies passing the idle jet holes.
If you do all this I guarantee it will start and idle normally. It might not run very well on the road (but mine did), I would expect it will be weak in mid range and full throttle, and then you will need different needles and maybe springs and jets.
Sadly I still haven’t got around to doing and documenting this, so good luck. You have other issues besides pod filters.

 

Thank you? What are my other issues?

 

I already have stage 3 jets installed this is after the jets

 

Hi mate, I have pods as well as other engine mods and it runs fine. Did take some tuning though. Pods alone wont need stage 3 jets, sounds like your running very rich. Check the jet size you had before, my guess is pods will need jets around+2. Eg if your jet size was 120, then increase just a bit to 122.
You might even be good with standard pilot jets and a big bigger on the mains.

I had a similar issue as my engine build. Another thing that helped me was changing the plugs to iridiums.

 

Thank you buddy.Now I have stage3 jets and its worse that with the standard jets.Also couldn’t find BP7ES at the moment so I bought BPR7ES ones with resistance and the spark plug caps are NGK with resistance.Finally found BPR7ES and W22ep which are recommended in the service manual.Will try one of these and will see what will happen.Also I have option to try another carb from 750(not sure if it will fit in the boots) and another xj650 carb.We’ll see

 

What size jets do you recommend?

 

Hi mate, check this link to find your model, http://xjbikes.wikidot.com/carb-specs

should be 40 pilot and 110 main. XJ750 carbs will fit but have bigger jets and different needles.
What size are your jets now? If your pilot is now 40, I’d try something like a 42 to start with.
Also what pods do you have? I have K&N and found the cheaper brands can sometimes block the air inlet when they are pushed onto the carby, that could be your issue so check the inside profile of the pod isn’t blocking the air slot on the front of the carby when it’s in position.
Check my You tube channel as there’s probably some videos there that might help you.

 

Mannn i watched your videos on repeat for months!!!

Now the bike has stage 3 jets(as the mechanic who cleaned, re jetted and bench synced the carbs said)

By air inlets you mean about these?
https://postimg.cc/gw0N8bFm

What buggs me from the very start is that the spark plug pipes and spark plugs are with resistance I’ve read that the spark plug pipes should be with resistance(service manual says the same) but not the spark plugs

 

I would strip and check this mechanics work. I would also not recommend r series plugs as well as the resistance caps - you want one or the other, not both. Thing is the main jets only kick in under throttle open, when the slides start lifting, so the standard idle jets should be fine - unless of course your pod filters are indeed blocking off the air jet at the mouth of the carbs.
Strip, check everything, rebuild.

 

Also some of the friends said that the bike is running very rich so I closed the mixture screws about 1.5 turns from fully closed and I think the mechanic who rebuilt the carbs turned them 2.5 turns from fully closed and someone here suggested the mixture screws should be turned 3 times from fully closed

 

Yep, there are the air inlets. I personally like Iridium plugs, these have resistors built in so you shouldn't use them with stock plug leads that have a resistor in the plug end.
If you have stock plug leads as well as resistor spark plugs then there is too much resistance and you wont get an optimal spark.

What I did was replace the OEM coils with aftermarket and with plug leads that don't have resistors. I then use NGK BPR7EIX and it has run fine once I got to tuned.

There should be a number stamped on the jets so you can see how much bigger they are from stock. I'm guessing they are too big. Pilots should be 40.

Another problem might be that the choke is not closing properly which will have the engine run very rich all the time and cause problems like you have. When the engine runs try pushing the choke levers down to ensure they are fully closed. If the idle speed drops when you manually push on the choke lever (on the carby end) then you need to adjust the choke lever or cable.

 

Why do you think the mixture screws should be somewhere specially set? They should be where the idle mixture is correct, personally I would just start from known setting, say two turns out, then add say half a turn open to each. If the rpms climb I would presume it was weak previously, so I would repeat the process, until the rpms drop. Then back the other way half as much, repeat until the fastest idle is achieved. You have to adjust down the idle speed screw as required between adjusting the mixture screws. So once you get fastest idle with all, screws the same, start tweeking each one for fastest smoothest idle. Too much in will give you an erratic misfire, too much out will give you a rhythmic misfire, and emissions and smoke.
Once you have nailed the mixture you need to do a running synch, then check the mixtures again.
Of course this only sets the idle mixture, the idle jet sizes affect where the idle screws set for best idle, but also massively adjust transition from idle to main jet/needle. And the main jet size sets the maximum fuel output, as important as this is the emulsion tube (with its outlet jet on top) and the needle hanging into it from the slides. And while we’re on about the slides, where they are at any one time is down to how much vacuum is below (constant vacuum remember) Vs the spring above. How quickly the slides move is set by the holes in the bottom.
So all in all a lot to get right. Forgot to mention the air jets, which add air to emulsify the fuel coming out of both idle and main jets, bigger fuel jets in theory need bigger air jets, if you go a long way bigger.
Complicated? Difficult to set right? Yes, absolutely. Taking out the air box can have a huge effect, don’t underestimate it.

 

Understood sir.Thank you to all of you for helping me with such a delicate topic

 

Finally weekend so I can work on my bike.Got another set of xj650 carb to test them out.This set has 43-112 jets so its identical to the sizes Mezzmo suggested to use.Also removed the filter rubber seals to check for clearance and looks good to me, here are the pics:





Also managed to modify the original air box rubbers.Will try this combination too:

 

Updates: Modified original airbox rubber joints don't fit the frame

 

Good luck, as long as those Carbs are clean inside it should run.

 

Thank you so much for the help!!!Bought new sparks DENSO W22EP-U so first ill try the carbs with stage 3 jets with new sparks and if the results are same like last time ill mount the new carbs with 43-112 jets

 

New carbs new results.Replaced the sparks with brand new denso w22ep-u(without resistance) and in the process of changing the old NGK sparks ive found one faulty NGK spark.One thing I noticed checking the spark of the new denso plugs is that the spark is not red and that big like on the NGK bpr7es.The bike dont throw black smoke as previously and the first start was almost perfect but after couple of starts the bike again started to raise rpm as you add throttle.If i gave throttle 2-3 times one after another the bike starts to raise rpm over 5-6000 so I had to shut it down on the run button.Here are some videos:

First start


second-third start

 

If you attach some logic to this, you will see that the engine cannot rev up to 5000 rpm without air (and fuel). So if you don't have massive air leaks then I suggest your carbs are either not closing off or not ballanced. If the rise changes as the engine heats up it's because the mixture is off.

 

I just watched your vids, in the first one it looks like youre having to close the throttle to bring the rpms down - pointing to stiff butterflies or cable. Doesn't sound like 5000 rpms tho?

 

The symptom I tried to explain is not shot on these videos and its not when the bike is idling.It was like the throttle stuck and the bike was climbing in rpms so I had to shut off the engine on the engine stop switch and that happened after I tried to rev the bike more aggressively and opened the throttle 3-4 time one after another very quick.Sorry for my bad English since English is not my native language so I don't know the right terms to explain my self

 

Looks like you are making progress. So that was new carbs with the stage 3 jets? If so, I would try those carbs with the stock jets to see what happens.

 

Thank you!Looked and also sounded like a progress to me too.These are the new carbs I got to test them out with 43-112 jets.

 

You know, sometimes its just good to be able to see the carbs opening and closing, which means putting them on the frame, attach the cable and open close throttle...

 

Yep, test them with the 43 and 112. I think it will be better. Once you fit them check the choke is adjusted so its fully closed and that the butterflies work properly before starting the engine.

Before you put them on the bike you could also shine a torch behind each butterfly to see if they are closed all the same amount...

 

Both videos are with 43-112 carbs

 

One more question, does RPMs not dropping after revving sound like a timing problem or air leak problem?

 

See above ^

Apply logic, fix one issue at a time, you will get there. Balancing carbs is more important than you think, however, a good bench set should give you a rideable bike.