1982 xj650rj seca tuning

Okay, So after my rebuild, i've gotten the bike to run and occasionally can get it to hold an idle. However, intermittently it will rev straight up to 5-6k on startup. Hinting at a vacuum. leak. This video below was taken 20 minutes before my high idle started.



Plug 1


Plug 2


plug 3


plug 4


I've recently taken the carbs to church. Full teardown. breaking the rack, soaking each carb in carb dip for 2 hours, rinsing off with hot water, replacing all seals, and new jets. Replaced the carb boots with OEM items purchased from Chacal (not the cheap ones that tear instantly). From this post i've got a few questions to help get her back and running perfectly:

1. Feedback on the plugs? they've got maybe 5 minutes of run time on them.
2. From the video, shouldn't the carbtune be reading a higher vacuum amount? (i thought on my xj650 maxim, I was getting higher amounts)
3. Potentially thoughts on the sudden 5-6k idle? My potential thoughts are:

3a. Vacuum caps on carb boots. I have new rubbers on them, but currently do not have the clamps installed. Proved to be too big of a pain to get those on.
3b. Airbox lid seal. I've noticed that 1 corner of the airbox has a slight "lip" on it that doesn't appear to be a complete seal. Would you believe this would explain the potential airleak to cause a rev that high?
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Any other thoughts are appreciated. Looking forward to getting her back on the road after 5 months.

 

Have you performed a running (vacuum) synch yet? If not, start there!

 

Like with the carbtune? Yes I've done that.

 

Did you wet-set the float heights?

 

Yes I did. Even retested on the bike to make sure that none were too high and they are all good.
On that thought though, with the new front end, the front sits lightly lower than stock. Based on this, should I adjust the wet set level of the carbs? Instead of being 3mm from the bowl top?

 

1. Are you sure you have the air jets in the correct places? Bigger number toward the front of the bike, smaller number toward the seat of the bike.

2. Check to see if your pilot jets have been drilled bigger

3. Make sure your cables aren't kinked

 

Air jets are in correct places.

Pilot jets have not been drilled bigger. Unless Chacal is secretly drilling them

Cables should be good. But i'll double check. I know that the throttle cable snaps back, but i'll double check the choke cable and the throttle.

 

Is it fully seated in the carb bracket?

 

Yes I even get a little slack on the carb side of the cable just to make sure that it wasn't an issue. Once she's dialed in I'll adjust the cable slack to a better spot.

 

I would say yes the readings should be higher, and what you have is almost useless to do a proper sync when you consider the bouncing. I don't have a Carbtune Pro, but I am guessing that first of all the dampers / restrictors are not present, which may attribute to the low reading as well as the unsteady readings.

1, 2, and 4 look sooty, but only 5 minutes the engine was likely still on choke so I don't think it means much and you need to wait until you get it sorted to do a proper plug color evaluation.

I would go through the pain to be sure they are sealing particularly since the high revs may be a result of a vacuum leak. Seems I remember you can put the clamp on the cap and then just push the cap on. Not so easy getting off though on a hot motor.

 

Your Bike looks great... See your running CB750 Coils ..Two thumbs up, got them on my Seca 750.

 

As Rooster said,

Make sure you have restrictors in your Carbtune vac lines, or you will get low readings as have....

Make sure those vacuum caps have clamps on them....it is not that hard to get them on.....put the clamp on the cap, & you should be able to push them on.

 

Carbtune levels should not matter as long as they are even... with that said - I agree with Rooster (and your own initial observation) - something ain't right there. Any chance of another bike (you still have your Maxim?) in the neighborhood that you could hook the Morgan up to?

 

I have seen people hang ( and I have hung ) the Morgan Carbtune upside down as well for sync'ing.......might give you a better shot at sync'ing.....( the rods will drop into the gauge further )...give it a try....

But make sure you have restrictors in your vac lines.....

Just sayin....

 

Thanks guys! I thought something was strange since the last time I did the carbtube. I even remember holding the bag of resistors and thinking, do I need these? Haha it was right under my nose.
Okay, I'll hopefully try to Resync carbs on Tuesday and install the clamps on the caps too. Thanks again!

 

I believe there is a couple of sets of restrictors in there, so use the smallest ones...it will work better for the readings......if you don't have the restrictors, you can borrow my Carbtune.....

 

Thanks! I'll let you know if I run into issues. Glad there's another xj rider in San Diego

 

So i had some extra time today after work and took the carbs off to check a few things. I noticed that the fuel levels after doing another wet set test were a tad low. I'm currently re-adjusting these now. Hoping that by going over the carbs yet again, i can get everything dialed in perfectly. Hoping to not have to take the carbs off the bike again

 

One thing about float level , I flip carbs over measure from flange with no gasket set from tip of float set it at 17mm ... then check wet set this gets you in the ball park. On mine this was spot on.

 

I tried that approach and got some very inconsistent fuel levels. So I've gone with the longer method, check each float level and adjust. And repeat until it's in spec.

 

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 !