BOGS/RUNS BAD/DIES help?

this is my second thread. I thought if i made on in the technical discussion area it would get more traffic. Any ways here we go. Bike : 82 XJ750J pods and open exhuast. ran good a few months ago before tear down. I even tried to start it up every couple days to keep the gas flowing somehwhat. Carbs are CLEAN and jetted correctly. It ran fine before for the most part.. Now to start it i have to hold the start button down for 10-15 seconds and it will finally start, but it runs like crap and sounds like crap. If i hit the throttle it bogs down. If i feather the throttle carefully i can get it to rev up nicely. After i have it revving nicely (doesnt last long) i try to put it in 1st gear and give it ago. as i let the clutch out it just bogs and dies everytime. Its like im trying to take off from a stop in 4th gear or something. Is this a clutch, fuel, bad gas, valve adjustment, or roll it down a hill kind of problem.
Someone please help THANKS

 

Bad gas is an easy check
Running on all cylinders when it "runs like crap?"
Coil check is pretty cheap assurance too

 

When it ran good a few months ago did the bike have stock exhaust and air box? Can we assume the purpose of the tear down was to modify the exhaust and intake.
Have you done the basics? Wet set floats , carb sync and valve adjustment.

 

First clue is starting poorly. With a fully charged battery, except in the dead of cold winter, an XJ even only in decent tune with good fuel will ALWAYS start better with a quick blip of the starter motor, more than 4 revolutions and you've already begun to suck out the battery's ability to properly fire the coils. This is just how they work. In fact there should be a sticky or tech article entitled "Your XJ likes to start right away, if you keep cranking it's going to keep croaking!"

Our instinct (mostly derived from Honda's, Mopeds, Mowers, etc.) is to keep the starter switch mashed until you hear fire. NO NO, just hold it for a moment, and when you let go 'varoom,' the XJ fires out of nowhere!....<--if v in spec, and c's are CLEAN, and gas is good.

Second clue is 'jetted correctly.' This is a bold statement which most NASA engineers would be lying to claim it on their XJ. When it is running, is there any smoke flowing out the exhaust? What color? Running both PODS and open pipes makes it VERY hard to tune properly. The good news is this happened after your tear down, that means it's reversible and can be fixed. I suspect something in your carbs is just wrong. I'd go back into your carbs and make SURE they are first clean, assembled correctly, and then carefully bench synched. See where that gets you.

 

thank you everybody for the quick replies.
gonna check all the easy checks first (what i should have done before i posted)
Orignially the bike had pods and custom open exhaust. The guy i bought it from is a guy that knows carbs really well that being said "jetted correctly" is a bold statement. Also before i let it sit it ran well . I need to go over the basis really . I guess i just needed to see it all in posts from you guys.

a couple more things im curious about. The emulsion tubes: i know they should move and slam down with ease. But should they do this while assmebled and carbs on the bike? I try to move them but they wont budge while the carbs are on the bike and fully assembled.

I just pulled the plugs and all plugs are black and sooty. they may have been wet but dried by the time i pulled them (severeal hours after starting the bike)

 

Okay just to be clear im not sure if its called the emulsion tube but im talked about the brass cylinder that slides up and down vertically where air comes into the carb.

 

We call those the carb slides, and YES they should move easily. They will have slight spring pressure holding them down but should easily lift with one finger. If they don't then problem found. The emulsion tube is the tube the carb slide needle goes into, it helps the fuel atomize as it enters the air stream.

Looks like you will need to pull the carbs and give them a through cleaning and inspection.

 

Yes sir. Carb # 3 and 4 Carb slide is stiff and wont go up and down. Sorry abuot the confusion with the name of the part. Im used to carbs that have the needle and slide connected lol. I appreciate your help and another thorough carb cleaning is in order. Hopefully this will fix the problem. Originally when it would start it sounded to me like it was starving for air, maybe this is why i thought that. Thanks again

 

Good to know that you may have found the problem. It is taking me two rounds to learn what the true concept of "clean" means for this carbs. There are so many little parts, springs and passages that must be cleared, it is really easy to over see them.

After that the next task is to wet-set the floats and bench sync them before going back on the bike for the final tuning.

 

You asked about valve adjustment. Having your valve clearances in spec is critical enough with a stock bike; if yours aren't in spec then trying to tune the carbs on a modified bike will just be that much more impossible.

If you haven't checked your valve clearances yet, do so. And get them in spec before proceeding.

You'll have much better luck with a modified bike if everything that's NOT modified is 100% before you try to compensate for the mods.

 

No i have not checked the valve clearances thats next on the list. About 6 months ago the previous owner had bigger cams put in it . Hot cams i think. Im not sure on the size or the clearances or anything. I dont have the paperwork around here somewheres with receipt and possibly specs on it . Im not sure if the "stock" clearance is the same if its aftermarket cams. that would be my question for when i check the valve clearance.

 

o jeeze. At first i just thought maybe the oxidization stuck them but the other day when i had the bike running i didn't notice the slides moving while on the throttle. would this be dut to a vacuum leak or something? I should add that previous owner put a harley petcock on it. which flows well, I just didnt know if it needed to be a vacuum operated petcock

 

A vacuum operated petcock isn't a requirement, just a convenience.

Valve clearance specs will be the same regardless of the different cams.

Valve clearance how-to: http://xjbikes.com/Forums/viewtopic/t=14827.html

Part Deux: http://xjbikes.com/Forums/viewtopic/t=29209.html

Wet-setting floats: http://www.xj4ever.com/setting%20fuel%20levels.pdf

Your carburetors are vacuum-operated. When you twist the throttle, you open the butterflies. The carbs then respond to the difference in manifold vacuum in relation to atmospheric pressure and the slides are lifted via the rubber diaphragms due to the vacuum produced "above" them. They were designed to live in a controlled-air volume environment; putting pod filters on them upsets this and makes it that much more necessary that everything else be 110% right if you want to have any hope of them working.

If your carbs aren't truly, religiously clean and the slides free to move, the diaphragms intact, float levels properly set, etc., they won't work right. Read this: http://xjbikes.com/Forums/viewtopic/t=14692.html and this: http://xjbikes.com/Forums/viewtopic/t=2908.html and have at it.

Valve clearances greatly affect manifold vacuum hence the need for those to be correct before any serious carb tuning can commence.

You have a highly-modified bike. If you hope to have ANY chance of getting it running anywhere near close to right, you need to get serious about this and do it thoroughly, correctly and in order. Halfway measures or quick fixes are not going to work. Stop trying to ride the bike and FIX IT.

If you want to make some actual progress here, then get a manual, get serious and do it right. Otherwise you'll be at this for a while.

 

What Fitz said is right. Found out when I worked on my bike. It is sorta like building a building in a way. If you skip getting the foundation set square and correct, nothing else will come out right. It is a step by step process with these bikes. They like to be romanced just in a certain way and order...

 

Pods ... --> ALONE <-- across the 4-Pack upset the delicate balance needed to have the Diaphragm Pistons RISE as needed.

The 1/4 -- 2/3 Firing Order causes a rapidly alternating infusion of the Intake Airflow.
TURBULENCE ... where Turbulence is NOT intended to be present.

The Intake Air is GULPED into the Air Horn ... when it should be SHAPED and ACCELERATED.
The SHAPED and ACCELERATED Intake Air passes over the Top of the Main Nozzle ... causing Decreased Pressure within the Tube thereby SIPHONING Main Jet Supplied Fuel up into the Air Stream.

The Turbulent, non-shaped, poorly accelerated Intake Flow fails to Decrease the Pressure above the Nozzle ... initiating a LEAN Condition.

Additionally, the Turbulent, un-shaped, non-accelerated Intake Air Flow is GULPED below the Diaphragm Piston ... is of insufficient Shape and Speed to adequately Decrease Pressure below the Orifice at the Piston's Bottom ... resulting in a Less Efficient Pressure Reduction at that Orifice leading to the Piston(s) prolonged Rise ... the Needle(s) are extracted slower further contributing to the Lean Condition.

Velocity Stacks help SHAPE and ACCELERATE the Flow.

Some measure to reduce the Turbulence between the 1/2 & 3/4 Carbs might prove helpful.

Covering the Inboard sides of the 1/4 Pod and the Outboard sided of the 2/3 Pod would --> "likely" <-- reduce the Turbulence which intensifies as Rpm's increase.

::: You might experiment by fabricating a set of Shields fashioned by cutting two Clear Plastic Cup lengthwise to be affixed to the appropriate Inboard/Outboard of the Pods to see is a reduction in the Turbulence between Carbs results, :::

 

Thanks everybody. im not trying to ride the bike and fix it. I do have a manual. i refer to it many times a day and study it when im not working on the bike. . Im not trying to fix bare the bare minimum and get away with it. The cams were replaced about 6 months ago. i was under them impression that they would not just go out of spec that quick if they were done correctly when the cams were changed. Since that is not the case i will start from the top. Thanks everybody for your help i appreciate the help and feedback. Now i gotta go get to work

 

Okay gentlemen, once again thanks to everybody who has been helping me out.
I got a little ahead of myself the other day. i finally got a break from work at 2am so i wanted to work on the bike. I wanted to check the valve clearances first but i did not have feeler gauges, and all the stores are closed being 2am.Planning on going to harbor freight when they open becuase reguardless i need to check the valve clearances. So went ahead and broke that carb rack down and cleaned the carbs, wet set the floats, and changed the oil. I was gonna give the bike the chance just to see if there was any improvemant... It ran great for about 10 minutes then went back to bogging down if i hit the throttle. So as i read in a few other threads that once warm the valves tighten up. so needless to say as planned i went and got a set of feeler guages as soon as the store opened. gonna check the valves tonight, and find some to shims to buy. That being said heres a pic of my plugs. they were brand new now here they are after 10-15 minutes of idle/soft riding.. ok they pics are too big to upload. but anyway CYL1-white CYL2-brown paper bag CYL3-white CYL4-brown paper. bag

not black and sooty now so im thinking valves in clearance then a bench sync will make a good runner. What say you

 

I like the logic of the shield idea, might give it a try

 

Yeah I've edited this same post about 13 times lol. So i guess i was just a little nervous because i know i need to get this exactly right. The hardest thing was trying to determine what "clearance" is as far as pushing the gauge between the cam and shim. But i read a post (sorry i forgot who wrote it ) that said its feels like shaving with a safety razor. That helped me out alot. enough of the blah blah. here's the specs.


Cyl 1- I .06mm, E .10mm
Cyl 2- I .10mm, E .20mm
Cyl 3- I .08mm, E .15mm
Cyl 4- I .08mm, E .14mm


so correct me if im wrong please, all are out of spec with the exception of Cyl 2 E (.20mm) should i go ahead and replace that since its so close to out of spec?

Last question would everybody agree that since most of these are out of spec that this would be my problem with bogging down with throttle after it warms up?thanks to everybody for your help. tomorrow I will be removing each shim to see what shims I need to order.

 

In spec is in spec. Leave #2 exhaust alone, clearances tighten with mileage.

Those are all tight (except exhaust 2) and yes the motor will run like crap (and you won't get a decent vacuum sync.)

The rest all need one size smaller shim except exhaust #1, that one will need to come down 2 sizes to get in spec.