bike no workie

Soooo... I recently picked up my 82 xj750 n upon getting it immediately tore down the carbs n slapped them back on. Drained the tank n threw in new fuel n it fired up. I picked up some 4 into 1 pipes n installed them, checked my valves, which are in tolerance according to my trusty feeler gauge, and then bench syncged. Long story short bike started now bike doesn't. Checked for spark n has good spark in the number 4 plug haven't checked the others, cranks over like it wants to but fails to. My question is am I supposed to go up on my mains with the 4 into 1 pipes? That n the fact that I don't have the stock air box on the bike and the pipes make me think that it may not be getting enough fuel but I thought it woulds still start. Any input would be greatly appreciated

Sid

 

4 into one wont prevent it from starting. Is the battery 100% ? Float levels probably need checking.

 

Try turning the Petc0ck to PRI for 45-seconds.
Return to FUEL.
See if she runs.

TEST by trying to Start with Starting Fluid.
If she pops with Starting Fluid but quits, ... you have a Fuel Delivery issue.

No pop, ... Ignition related.

 

What did you do with the carbs? Odds are its fuel delivery.... But swapping out the air box + pipes seriously complicated matters.


Oh... Lets get the easy forehead slapper out of the way.... How's the battery?

 

You're between a rock and a hard place.
There's really no established formula or recipe for tuning CV Carbs to perform well without the airbox and requisite back-pressure from exhaust.

For as many who have tried and claimed success; there are dozens and dozens who have failed to get it right.

What should you do?

You should attempt to baffle the exhaust ::: some way ::: to raise back-pressure to help alleviate inertial flow exacerbating the Lean Condition prevalent when the airbox is removed.

Then, re-install the Airbox ... and get the Bike running very well.
Tuned.
Once you have the Plant able to Idle and Accelerate as it should, ...
THEN, ... experiment.

KNOW the Plant will run well without performance issues BEFORE you attempt to discover some modified tuning process with multiple obstacles to overcome.

Begin your experimental tuning with a default baseline to be able to return too.
Especially, if you are unable to find satisfaction re-jetting, stage-kitting, re-jetting, un-stage-kitting, re-jetting; wishing there was actually a known sure-fire remedy or a bona fide solution to solving a decades-old riddle.

You'll hear this mantra used most frequently:

"You ... need ... to ... re-jet!"

 

As far as I know the battery is good... I had it on a trickle charger prior to attempting to start it because it was dead the day prior. I still have the stock exhaust which I will put back on and see if this helps with the starting issue. The airbox is in tact just set aside in my pile of parts because I was planning on running pods even though they are the devil. I know it may be a pain tuning it but I will fight that battle later down the road. For now I guess I will put back everything to stock and see if she will fire up... As for carbs I did not mess with the internals other then soak them in carb fluid and replace the pilots mains and some of the float filters. After getting it to start I synched them... I will try the pri for 45 seconds prior to starting however I know the float bowls are holding fuel because I drained the carbs and a good amount of fuel came out the bowl I don't know I they are properly leveled other than eye balling the tabs when I replace the bowl filters.

Thanks guys for the input that has moving on to see if I can get this bike figured out

Sid

 

You're going to need to go back and wet-set the float levels, accurately.

You also need to pull the carbs down further; replace the o-rings on the pilot screws and flush those passages; pull and clean the emulsion tubes inside and out, etc. Soaking the carbs may have done more harm than good; there are throttle shaft seals trapped in them that can be damaged (it they weren't toast already.)

Do a compression test.

How did you "sync" the carbs? A running vacuum sync with YICS blocked? The bike needs to be fully warmed up for that, like 20-mile ride warmed up.

 

I bench synched the carbs using 2 paper clips.

Sid

 

Use 5mm ~ 8mm wide strips of business card or cut from a 2-liter soda bottle next time.

Meanwhile, you've got things to be done first; see above.

 

Here's a question-- being I've done THIS before.............

Double-check to make sure that you re-attached the vacuum line from the intake boot to the petcock.

Dave F