1982 xj650rj seca tuning

Okay so I got around to trying to correctly use the carbtune, however I'm running into an issue that's preventing me from actually tuning the engine. When the bike first starts it idle perfectly. However once it warms up the idle will continue to climb. So this points to a vacuum leak.
My question is, while the bike is idleing with the vacuum leak are there tests which can be done to confirm where? Or can/should I wait for it to cool down and use some butane gas or starter fluid to test certain areas?

I'm rebuilt the carbs and replaced everything possible:
- all jets back to stock size. Jets in the correct location (opposite of manual)
- all rubber seals replaced. Throttle shaft and pilot mixture screw rings and fuel rings.
- carbs are wet set to spec now
- carbs are bench synced to the closest toilets can measure with a fine needle.
- also replaced the carb manifolds with OEM ones. Not the cheap ones which fall apart. With seals and clamps onto of 3 ports.

Thoughts?

 

Can you back the idle screw out to lower the idle once warm? Final idle speed should be set with a warm engine. How high is it revving?

You should have the sync gauge hooked up at this time. Is it indicating a badly out of sync condition?

Are the pilot mixture screws set at 2.5 turns from soft seat? If so, try backing them out another turn to start the tuning process.

 

I can back out the idle screw. I did that and got the rpms to change from 4K back down to 2k but then noticed that they continued to climb again. From a cold start (90 degree outside) I had to do small blips on the throttle for a minute to get her to idle consistently at 1k and then after a few minutes it went up to 4K.

1 thing that was strange is after hooking up the carbtune with the restrictors I wasn't getting any reading. However I remember hearing someone say they had to turn there's upside down and then I got a decent reading across all 4 cylinders. Nothing that was very out of sync.

My pilot mixture screws are set to 2.5 turns. I can try to back them out to 3.0 and see how that effects everything.

 

Some common causes of a high idle:

- A lean air-fuel mixture condition, which can be caused by a variety of problems......vacuum leaks, plugged or too-small fuel jets, etc. Old or "stale" gas may also cause a lean fuel-air mixture to occur temporarily (until the fuel is used up!).

- A vacuum leak somewhere in the intake system.....intake boots, internal o-ring seals, etc.

- Mixture screws not properly set or adjusted.

- Vacuum piston sticking or stuck in a partially raised position.

- Idle speed screw set too high, or set to create a "proper" idle speed when the engine was cold (and thus results in a "high idle" once the engine reaches operating temps). The idle speed when the engine is cold should be modulated via the use of the choke (enrichment) control system.

- Butterfly valves opened too far; synch screws out of adjustment.

- Throttle cable wear, adjustment, or throttle lever brackets installed incorrectly or interfering with other nearby objects (cylinder head fins, etc.).

- Choke (enrichment) circuit is stuck "open"....this can occur even if the choke lever is rotated to the fully closed position, if for some reasons the choke plungers are not fully closing (cable wear, cable adjustment, bent finger brackets, or installation problems). In addition, even if the choke plungers are "closing" fully, if the choke plunger valve face or its seat are worn or scarred, this will allow fuel to leak part the plunger and richen the mixture even if the plungers are closed.

 

Thanks chacal!! Question for those reading, when starting your bike on full choke (when it's not freezing outside) what rpms do you see on idle?

I'm suspecting that a good portion of my problem is that my idle screw is set incorrectly. When starting up the bike from cold (80-90 outside) I can only barely use the choke. I haven't dared to try full choke. This hints that I could have the idle screw set way too high. As well as some potentially smaller issues. Hmmm

 

This is probably okay. Typically, unless the outside of temps are below 40F, choke should not be necessary at all (or only a slight opening for just a few seconds).

 

Hmm. Then I'm thinking that my idle screw setting isn't the main problem. I got the bike to idle at a good range for a few minutes before the rpms went up to 4K. So I guess it's back to airleak testing.

In your experience how big of an issue could a faulty airbox be? If my lid did not properly seal would that explain the airleak and rpm increase?

 

Okay so I found a video of my work from yesterday. Turns out the bike idled high on first start, ran for a few seconds and then idled in the sweet spot.

 

I might setup the go pro on a tripod so I have reference to everything and can better describe exactly what is occurring

 

So I made some progress today. After getting the bike to idle and preforming a vacuum leak test with propane, I did not see any changes in the idle. After letting the bike run for a few minutes I slowly adjusted the idle set screw to get the bike to idle just over 1K and it will now usually idle without issue. I have to slightly use the choke on first start up or ride the throttle for a minute to too.

After getting a steady idle, I took the bike around the block a few times. Now i'm faced with a slow return to idle. The main issue is shifting between 1st and 2nd. (a few times the bike stopped in neutral because the rap's were too high to smoothly shift). After this I hooked up the color tune for a quick reading. Since I wasn't in the optimal of places (in an uncovered parking spot at 5pm in the afternoon) I couldn't really get a clear reading. But the good news is that all 4 cylinders had at least some shade of blue.

If I can get rid of the slow return to idle, I should be set to then tackle the last few items on the bike.
1. Adjusting steering bearing. Could do with a 1/4 turn tightening I believe.
2. Replace my oil drain plug crush washer. I'm getting the smallest leak which causes a little bit of smoke after a ride
3. Build a mount for the speedo sensor and calibrate.

 

hanging idle can most times be cured by tweaking the mixture screws richer.
Now that you're getting near to riding this thing, you need to be aware that there are warnings associated with mixing radials and bias-ply tires.
Since you put a GSXR front end on it which I assume has a 3.5" rim with a 120/70 radial, mixed with the 2.15" OEM rim and bias rear tire you might want to take it easy.
As I read long ago, radial rear with bias front can work but never to go radial front, bias rear.

 

I'm sure mine will be different however I get no reading of rpm on my gage with the white wire from the original tach connected. Where did you pull your rom signal from in the end ?

 

Kind of a shot out of left field here since everyone is chasing vacuum leaks and syncing issues, but asking because 5-6k seems wicked high for a vacuum leak. You mentioned you changed the front end. I can't blame you there, I dropped new handlebars on my 650 Maxim to improve handling and looks. I know when I did that, I didn't replace throttle cabling at first, and it took me quite a few iterations to find a cable routing that took up my slack, and consistently didn't bind anywhere. I would see unpredictable revs until I got that sorted out. If you know you've squared that all away, you can disregard this, but I figured it was worth mentioning.

 

^^^ certainly a shot worth mentioning.
Seen out of synch at 6k also.

 

I spliced the tach signal into the orange wire of the coils. The same should work with splicing into the grey wore as well. There's a wiring diagram in my build thread.

 

Thank you sir !