carb upgrades ? 1980 xj 650

needle valves dont seem to have an adjustment. I've just got the bike running great at idle (valves set , synced, air fuel set) but i have popping at higher rpms. Wide open is good so main jet is sized proper, everything tells me the needle jet needs to come up ? Any recomendations ?

 

welcome to the forum, I would do a plug chop to see where the mixture is when it is popping.

FU

 

RICH, LEAN, or possibly even ritually UNCLEAN or OBSCENE: THE CARB REBUILDING FAQ:

Let us begin by warning you, though: an engine that is out of synch may perform AS IF it has a lean, or a rich, or a hanging idle, or a no-idle, or a run-away idle, or any variety of different conditions------if your engine (carbs) have not been synched, then that at is the #1 issue that you should attend to first, before you even READ any of the guidelines below and go and try to adjust and fiddle with things and change settings THAT AREN'T THE CAUSE OF THE REAL PROBLEM!!


Question #1: Why Isn't It Running Right?:

Below is a semi-useful "general rules-of-thumb" list to help you recognize and diagnose fuel-mixture problems.

All of these descriptions assume that the carburetors are cleaned and operating properly, are stock (no jet kit), the valves are adjusted properly, and the engine has been synched.

If any of the above procedures, tasks, actions, or activities have NOT been checked or performed, then do them first, or otherwise all your other efforts will barely even give you "casino odds" at striking it rich and determining what the real cause(s) of your symptoms are......



Typical Symptoms and Causes of a Lean Fuel-Mixture Condition:

- Poor acceleration; the engine feels flat.

- The engine won't respond when the throttle is snapped open, but it picks up speed as the throttle is closed. (A too-large main jet also mimics this symptom.)

- Idle speed falls after you blip the throttle, then creeps back up.

- The engine runs hot, knocks, pings and overheats.

- A lean pilot circuit condition can be responsible for a creeping or hanging high idle, where the rpms stay high then slowly drop down to the set point.

- The engine surges or hunts when cruising at part-throttle.

- Popping or spitting through the carb occurs when the throttle is opened. Or popping and spitting occurs through the pipe on deceleration with a closed throttle.

- The engine runs better in warm weather, worse in cool.

- Performance gets worse when the air filter is removed.

- Fuel levels that are too low will cause a lean condition.

- Pilot fuel circuit that are partially or completely clogged.

- Fuel jets that are too small for your application.

- Pilot mixture screws being set too far “in”.

- In cases where an overly lean fuel condition is suspected, the application of a small amount of "choke" may decrease or eliminate the symptoms. If the use of the choke “fixes” the problem, suspect a partially or fully plugged pilot mixture circuit.



Typical Symptoms and Causes of a Rich Fuel-Mixture Condition:

- Engine acceleration is flat and uneven and loses that "crisp" feel.

- The engine "eight-strokes" as it loads up and skips combustion cycles.

- The engine's idle is rough or lumpy, and the engine won't return to idle without "blipping" the throttle.

- An overly rich pilot mixture is usually the culprit when the idle drops low then slowly recovers.

- The throttle needs to be open continuously to maintain acceleration.

- Black, sooty plugs, a sooty exhaust pipe and black smoke from the tailpipe that stinks of unburned fuel.

- Poor fuel economy.

- The engine works better when cold. Performance falls off as it warms up or the ambient temperature rises.

- Engine performance improves when the air cleaner is removed.

- Fuel levels that are too high will cause a rich condition.

- A choke system that is slightly hung open or has leaky plunger valves. Leaky valves can be determined via a measurement of vacuum using your synch sticks (or vac gauge) --- while watching the gauge, apply a small amount of downward force on the top of the plunger valve. If it vac draw changes, the plunger isn't sealing very well. Over time a small ridge may build up on the tapered brass plunger valve surface (Hitachi carbs) that may be possible to polish out, or a deformity forms on the rubber seals (Mikuni carbs) that may be possible to reform back into shape.

- Fuel jets that are too large for your application.

- Pilot and main FUEL jets being reversed.

- Pilot and main AIR jets being reversed.

- Pilot mixture screws being set too far “out”.

- Main jet needle set at too “high” a position (on some Mikuni models), or that has “risen up” within its head cap (on Hitachi models).

- A simple test for an overly-rich condition is to remove the air filter element, and see if performance improves. A very dirty air filter will cause an overly rich condition, AND, even if the filter was in good condition, the great increase in airflow accomplished by removing the air filter will tend to dilute an overly rich fuel mixture, and thus allow you to focus on determining the cause of that situation.



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.



Why your engine seems to be schizoid:

A hanging idle---one that stays high and slowly comes down when decelerating---is a sign of lean mixture. The opposite case, where the idle drops dangerously low then rises, is a sign of rich mixture.

A bike that runs better when hot is probably lean, and a bike that runs better when cold is probably rich.

But sometimes a bike that can be adjusted "just right" when cool, but actually starts exhibiting signs of running lean (hanging idle) as it warms up. And if the idle speed is then re-adjusted while the engine is warm, but eventually falls and the bike dies (especially when sitting at a stop light). Or if the pilot screws are adjusted, then it's too rich when cold---all in direct contradiction of the above observations.

Experience shows that this is a sign of worn throttle shaft seals.....the aluminum carb bodies expand with the heat, but the steel throttle shafts---resting comfortably in a nice cool airflow---don't heat up and therefore don't expand. Once the shaft seals get old and hard, they no longer are able to flex and fill the gap.....so the carb starts drawing air around the shafts, leaning it out.



Why does my engine sometimes backfire when I first turn on the key (without attempting to start the engine)?:

- When you kill the engine, the intakes will still have some remaining (un-burned) air-fuel mixture remaining in them. Upon powering up the bike (turning the key on), the ignition system will apply 12 volts to the coils, thus charging them. Of course, that constant current is not good for the coils, so few seconds later (if the engine is not started) the TCI shuts down the coils by grounding them (to protect the coils from overheating) which cuts the current to the coils and thus triggers a spark to the plugs. If there is enough un-burned fuel in the intake manifolds or the combustion chambers, and if the valves are held open by the camshafts, a backfire thru the exhaust header and/or thru the intake manifolds/carbs/airbox can result.

 

great info i re synced my carbs and got them to dial right in and the popping went away runs mint now
thanks

 

1980 xj 650 just got the bike back together after a long winter of rebuilding
bike runs great took it out today went 100km down the highway and stopped for a coffee everything perfect up to that point. bike sat for 30min. started back and it wont go into second gear no matter what i do. clutch cable was just adjusted and hasn't moved goes into first easy then neutral and stops there. had to leave the bike at a friends. going back in the morning any suggestions where to start. could this be an easy fix? or am i looking at a tranny tear down ?

 

INTERNAL SHIFTER MECHANISM PARTS:

Inside your shifter case side cover are a variety of levers and linkages that translate the motion of the your shifter foot pedal into movements that operate the SHIFTER DRUM, which in turn operates the SHIFTER FORKS which then engage or disengage the various TRANSMISSION DRIVE GEARS. Worn or damaged RETURN SPRINGS can prevent the shifter from operating properly, and are the first thing to check if your bike will not go into gear, is "stuck" in a particular gear, or if you cannot "find neutral".

Of course, there may other issues which could cause the same problems, particularly the dreaded "disintegrating primary chain guide" issue, but it's always best to determine whether a simple problem exists first..........

Pictures of the inside of the shifter assembly can be seen at:

http://xjbikes.com/forums/index.php?threads/20246

and

http://xjbikes.com/forums/index.php?threads/28233



A good write-up on the typical problems and issues involved with these parts can be accessed at:

http://xjbikes.com/forums/index.php?threads/19227

http://xjbikes.com/forums/index.php?threads/48591

However, please note that the exploded diagram attachment on the 19227 page is "typical" for most XJ-series bikes, the actual mechanisms will differ slightly between different models (the diagram shown in the 3rd post is correct for the XJ650 - XJ900 models; most other models use a variation on the same theme).

NOTE: if this describes your situation:

Couldn't get her out of (whichever gear you were in when the problem occurred).

This situation can be caused wither by a broken TENSION SPRING (the small linear-acting spring) or by the TORSION SPRING (the one with one straight arm and one "hooked" arm). Both of these springs are designed to keep the pawl arm properly engaged with the shifter drum "star wheel" segment. Note there is also a long SCREW which retains this star wheel to the shifter drum; if that screw is loose, it will allow the star wheel to rock back and forth or not even engage with the drum, also resulting in the same type of issue.

On early XJ650 engines and XJ750 Seca engines, the original torsion spring used was somewhat weak, and was replaced by an upgraded spring on later model engines, which also required a slightly different spring collar (sleeve) to be fitted.


NOTE: if this describes your situation:

"Today, after a downshift, the shift pedal would not pop back up automatically."

This problem tends to be caused by a broken TORSION SPRING (the one with straight arms on both ends of the spring) which is supposed to center the selector shaft segment. The earlier 1980-81 XJ650 and XJ750 Seca models were especially susceptible to this problem, and an upgraded, thicker spring (which required a thinner spacer collar underneath) was introduced to the 1982-later models.


XJ650, XJ700, XJ750, and XJ900RK engines:

HCP5140 OEM shifter shaft TENSION RETURN SPRING, for use on all XJ550, FJ600, XJ650, XJ700, XJ750, and all XJ900RK, RL, N/FN, and F models. If this spring is broken, your shifter pedal will not engage the shifter drum and you will get "stuck" in gear and not be able to shift. This is the small, short, linear-acting spring.
$


HCP5150 OEM shifter lever shaft TORSION SPRING, for use on all 1982-3 XJ650 models, all XJ700 models, all 1982-83 XJ750 Maxim models, 1983 XJ750 Seca model, and all XJ900RK, RL, N/FN, and F models that use the collar underneath the spring. If this spring is broken, your shifter pedal will not "return" to center after each shift operation. This is the torsion (coil) spring with the two straight arms.
$

HCP5134 OEM shifter lever shaft torsion spring COLLAR, for use on all FJ600, 1983 XJ550 models that use the collar underneath the spring , all 1982-3 XJ650 models, all XJ700 models, all 1982 -83 XJ750 Maxim models, 1983 XJ750 Seca model, and all XJ900RK, RL, N/FN, and F models.
$

HCP5143 OEM shifter lever shaft TORSION SPRING WITH COLLAR, for use on all 1980-81 XJ650 and XJ750 Seca models that use the collar underneath the spring. This is the set that is needed to update the weaker spring (without a collar) originally used on the 1980-81 XJ650, 1982 XJ650RJ Seca, and 1981-82 XJ750 Seca engines. This is the torsion (coil) spring with the two straight arms.
$


HCP5142 OEM shifter shaft PAWL ARM, this is what operates the shifter drum star segment. For use on all XJ650, XJ700, XJ750, and all XJ900RK, RL, N/FN, and F models.
$

HCP5133 OEM shifter shaft pawl arm TORSION SPRING. For use on all XJ650, XJ700, and XJ750, and all XJ900RK, RL, N/FN, and F models. If this spring is broken, your shifter pedal will not engage the shifter drum and you will get "stuck" in gear and not be able to shift. This is the torsion (coil) spring with one straight arm and one "hooked" arm. You should carefully inspect the pawl lever where the "hooked" end of this spring contacts, and make sure there are no sharp edges on the pawl that will "saw away" on the spring where contact is made with the "hook".......if so, gently and minimally remove some material from the pawl arm to "round" the contact area with the spring.
$

HCP22156 Aftermarket shifter shaft pawl arm TORSION SPRING. For use on all XJ650, XJ700, and XJ750, and all XJ900RK, RL, N/FN, and F models. If this spring is broken, your shifter pedal will not engage the shifter drum and you will get "stuck" in gear and not be able to shift. This is the torsion (coil) spring with one straight arm and one "hooked" arm. You should carefully inspect the pawl lever where the "hooked" end of this spring contacts, and make sure there are no sharp edges on the pawl that will "saw away" on the spring where contact is made with the "hook".......if so, gently and minimally remove some material from the pawl arm to "round" the contact area with the spring.
$

 

well looks like i have chucks of tensioner in there so motor is coming out
ill get back later when its done

 

anyone know what year motors will fit in the 80 frame with out having to do much modification, just in case this doesn't work out lol

 

Welcome to the Forum neighbor, I live down the road in New Liskeard. What model is your XJ?

 

All years of XJ650 engines will fit. All years of XJ750 (air-cooled) engines will fit. There are differences between the Maxim and Seca engines; engine mounts (solid v. rubber), foot controls, and a few other things, all of which can be changed out to suit.

Stick with your engine though. Any used engine will need the primary chain guide replaced. Just go slow, follow the service manuals, and if you snap off a bolt have a machine shop take care of extracting it.

 

this engine looks good all the gears are in good working order, pulled the belly pan and it is full of plastic, all unbolted just waiting for help tomorrow to lift it, read the manual a few times now everything seems pretty straight forward and nothing broke yet so we'll see how it goes with the motor on the bench. I'm going to take the time and paint the frame while im at it and do piston rings, and anything else wore while i have the engine out ( i wont get another chance till it's too late)

 

hey JaiFer nice to see there's xj's in the area mines a maxim H i've had it for 5 years now, but this is the first year for taking it serious, hopefully i can get it back on the road this summer and i'll look you up

 

You probably won't need rings or any other internals. Honestly you have a very modern engine with a very long service life. The chain guide broke down from age, not from use.

 

Sounds good. Good luck with the build.

 

you wouldn't happen to have a supplier for parts around here? can't seem to find the chain guide i need

 

We do. His username is Chacal, and he has posted in this thread twice.

 

i read in his catalog that he doesn't ship to canada

 

We ship to Canada (worldwide, actually) every day of the week (except Sunday, but only because the post office is closed......)!