Put the XJ650RJ on a dyno today..

The Honda dealer down the road from me has a deal where it's $30 for three dyno pulls. So I decided to do a few since they have a sniffer for the exhaust and I have no idea how my bike is running in regard to lean/rich. Here's the numbers. Hopefully the quality is good enough, if not let me know and I can post a PDF.

According to the dyno tech it's running pretty rich, but not terribly. I might try and switch to a high flow air filter to try and lean it up without having to mess with the mix screws. Those make me a bit nervous since the service manual says never to move them. But all in all 52 horsepower at the rear wheel isn't too bad for 30+ years old and 56,000 miles on the clock.

 

Get yourself a Gunson Colortune and set the mixture screws. The manual says to not touch them because the EPA told them to say so. An aftermarket filter can lean the mix out, but you'll never have any control of how much.

 

why does the horizontal scale read time? where is the rpm scale, if the time scale is really the rpm scale then you ran it up to 13K ?

 

No idea, I forgot to ask. It's in time, not RPM. He did run it to redline though. (Not over)

Might be they don't have a way to measure RPM on bikes without a diag port.

 

They normally just have a lead which clips to a spark plug lead

When they did my RD350LC, it put out some kind of electrical interference which was screwing up their computer and they had to reboot it so they ended up having to do it without a rpm reading

 

is it possible they cannot measure rpm due to the wasted spark ( I think that is what it is called)? it is my understanding xj's fire on the exhaust stroke as well as on power stroke.

 

That would just require halving the resulting signal. Most $20 tachometers can do that. There could have been a preferential reason for the tech not measuring engine RPM. Was he under the impression that the bike would be raced and set the dyno to record time to peak HP for that reason?

 

I wouldn't expect the mixture screws to have much impact at WOT. And even less of an impact as the RPM's increase.

Has it always run rich? How do the plugs look?

 

I do not think he has never adjusted them.
" I might try and switch to a high flow air filter to try and lean it up without having to mess with the mix screws. Those make me a bit nervous since the service manual says never to move them."

 

I understand. My point is that I don't think changing the mixture screws is going to do much anyway.

In other words, I would concentrate elsewhere for a solution.

 

How are you supposed to adjust the mix, if not with the mixture adjustment screw?

 

They are idle mixture screws. To adjust WOT, you have to mess with the jets or other stuff like air filters and/or exhaust.

That's why I was asking if it always ran rich. Trying to figure out if your specific bike has a problem or if that's just the way they were tuned originally.

 

Ah. I couldn't tell you. I've only had the bike for a couple months now and havent been able to tell from the plugs. I did find tonight my bike currently has a K&N filter on it, but it looks pretty old. I'll probably try and replace it here with the same K&N or an OEM filter.

 

there are other things that can cause richness. the place to start is with the pilot circuit by adjusting the pilot screw(mixture screw). a colortune is the tool you need to adjust the rich/lean.
have you ever tried to adjust the pilot screw?
the enrichment circuit "Choke" could be passing fuel even when off.
you could ask at the shop for a price but likly would cost as much as a color tune tool.

go with the oem filter sometimes the k&n filters can cause problems, is the rest of the bike stock?

 

The average shop will charge more than the cost of a color tune...and likely not actually do anything. I'd guess that the choke might be at fault too. From the factory the XJ series was set on the lean side, so being rich at all points to either someone changing things, or worn parts, or sticky slides, or.......

What maintenance have you done to the bike, if any?

 

Bike is bone stock except it has one of the aftermarket 4into1 exhausts on it, came to me that way. It's in rough shape so I'd like to replace it at some point. Already been looking at the colortune, the 14mm one is the right size, correct?

 

read The Information Overload Hour it is in the signiture line of K-moe's post
Why are my plugs carbon-fouled (dry, sooty black deposits)?:
you need a starting point with the many things that could be happening

4 into 1 K&N filter
read about rejetting in The Information Overload Hour

"This is why re-jetting is usually needed even if you keep the stock airbox and the stock exhaust, but use a K&N low-restriction filter, or even if you drill holes in the stock airbox, or leave the filter lid off."
and you have a 4 to 1

 

Oh...fuel levels. If the fuel level is too high it will run rich all the time.

14mm yes.

 

If I'm reading it correctly the jetting is a bit lean at about 4500-5500 so if you can shim the needle it will rich up slightly main jet may need up 1 size and color tune is for idle mix and transition to needle. Dyno run is for full throttle power so if you give her full pull at 3000 in top gear she'll bog until 4500 then get going. Vac slide carbs will be on the needle until about 6k then main jet from there to infinity and beyond

 

Just a note on the rpm scale. For a point of reference, due to the mathematical equation used to calculate hp from torque numbers, hp and torque are ALWAYS equal at 5252 rpm. Therefore, the spot on the graph where they cross is 5252 rpm.

 

No worries. You'll get the experience as you mess with it.

As for your running rich issue, I'm no expert on getting the most power out of an engine, but I do remember that max power does come from a mixture below stoich. I'm not sure how rich you need to get before you start giving away power from being TOO rich, but I do think max power occurs on the rich side of "perfect".

Maybe what you're seeing on the charts is actually what you want. When you're at WOT, you're trying to get max power and running rich under that circumstance is probably a good thing. Just don't know HOW rich.

In other words, I wouldn't want to be running that rich under all conditions, but running like that at WOT may actually be a good thing.

Not sure I'm saying that right... Does any of that make sense?

 

According to my research the pilot system is the main fuel supply up to about 25% throttle when the needle begins to have greater influence and at wot the main is the primary fuel source. That being said, the pilot system is feeding fuel at all settings, certainly not just idle, and if they are set rich then the bike will be running rich at all settings but more pronounced at lower throttle settings. Changing the exhaust system changed the effect of the factory settings and probably requires re-jetting and pilot setting to get back to optimal setting. Like K-Moe said, I would start with the colortune plug, set all pilots to a lean setting (white flame) then open to get blue flame, then install new plugs, take a 20 mile ride and read the plugs. The adjust the pilots (about the width of a dime at most) and repeat the ride and plug read until you have perfect looking plugs. Starting from a somewhat lean setting with new plugs allows you to read the plugs easier since once they are sooty or black it's hard to see the change.