40dt suzuki idle inconsistent

[bitsy4643]

Still baffling problem

Solarman, thanks so much for your patience, but following problem continues. Could reed valves cause this problem or malfunctioning fuel pump? Can squeeze bulb when starting to die, with no effect. Float setting per manual is .35 to .51, Presently set at .45. Could adjusting float either higher or lower from .45 have this effect?


1996 suzuki dt40 is slow to start, will idle for 3 or more minutes at 800 rpms, then idle will slowly regress until engine stops. If you turn idle adjustment screw before it dies completely back up to 800 rpms, will run at this rpm speed for a few minutes and then begin picking up rpms to around 1200 + . Readjust idle down to 800 rpms, will idle fine for few minutes until slowly regressing or stopping as before. Carb is immaculate, float set correctly, new fuel needle valve and seat , and all new gaskets. Gas is fresh and has sea foam. Any help greatly appreciated
Idle mixture crew at 1 3/4.

[Solarman]

No, reed valves are like check valves, allowing vacuum in from carbs, but not allowing pressure to blow back out of carbs. This is how 2 strokes keep running. If you have alot of popping back through carb throats, really noticeably, then maybe reed problems.

Have you checked your fuel pump to see if diaphragm & check valves are in good shape? If weak pressure because of either of those problems, this could affect running.

You could have a bad CDI/ECU? If everything else checks good.

Good luck. Post back how its going when able.

[bitsy4643]

no solution to idling

New float, needle valve and fitting, new gas, have switched fuel lines and tanks, no fuel leaks, no flooding indication at carb throat, float setting .35 to .55 recommended , set at .45, no change when fuel bulb squeezed when dying {still firm}. Once engine dies , hard to restart, If shut off while idling correctly will immediately restart but rpms will be much higher than when engine shut off and then go into same idling pattern as stated previously. Can reed valve produce these results? Thanks for your patience and help

[Solarman]

Again, Bitsy, reed valves will not cause this. The reed valves are like check valves, allowing fuel and air into cylinders (during vacuum stroke of piston) from carbs, but not allowing pressure to blow back out of carbs during compression stroke of piston. With bad reed valves your motor will not run. This is how 2 strokes keep running. If you have alot of popping back through carb throats, really noticeably, then, yes probably/ maybe reed problems.

Check all electrical connections to and from CDI/ECU on your motor. Your ignition sensor? It sends a signal to cdi to fire plugs, and for timing? Check those electrical connections.

You could have a bad CDI/ECU? If everything else checks good.

Good luck. Post back how its going when able.

[bitsy4643]

Runs good, no miss at any rpms, will not idle

Solarman, thanks again for your help. Purchased another carb, soaked both in Gallon gunk carb cleaner. Blew out all passages, did notice main jet had a different array of holes. However, replaced carbs one at a time and no noticeable difference in engine performance. Still same as before. Also, checked reed valves, and as u say, they were in excellent condition. On idle speed adjustment, at a certain point when idling about 600 to 700 rpms and starting to lose rpms, 1/16 to 1/8 clockwise, minute amount, turn on idle screw will keep engine running but will slowly, 3 to 5 seconds, increase rpms to 1500. Could timing or ecu cause this. I am not familiar with crankcase pressure or if that could cause this problem. This motor does not miss at any rpms. 120 compression both cylinders and this at one time was an oil injected engine. Could that be a factor? Thanks

[Solarman]

Bitsy, on your motor you have a mechanical timing advance system. Your timing advance is controlled by your throttle, through linkages attached to the stator base. As you increase or decrease the throttle, the stator/timing base moves because of the linkages connected.

Now, if that linkage system has any real worn out bushings, sloppy loose connectors, loose mountings, or is able to move slightly on it's own from vibrations at idle, you could get these symptoms?

It is very difficult this side of computer to analyze your situation.

Good luck. Post back how its going when able to let us know.

[Rolin_forrest]

bogging

my dt40 seems to be fine at quater but as soon as i give more gas it sounds like its smothering...

anyone know what the float hight should be? im on the point of giving up

[Solarman]

Bitsy, if you hold carb as it is on motor, and raise float up, it should shut fuel off just before float is level. If set lower, then float bowl will run out of gas at higher rpms. If set higher than level, then float won't shut fuel off completely, and excess fuel will overflow and drip out of mouth/ throat of carb when running.

Bitsy, have you looked at linkages to see what activates, or changes exactly where your motor has this problem? Are linkages connected improperly somehow, mixed up?

Good luck, post back when able to let us know how it's going.

[bitsy4643]

Checked linkages

Solarman, thanks again for your patience.
checked and isolated linkage for solutions. No appreciable difference in operation. Back to carbs. There are 3 very small holes at top inside of carb, between rear throttle plate and engine. Do these provide fuel at idle, as engine only seems to die if throttle plate is almost completely closed. Holes should be clear as carbs soaked overnight in gunk solution, but maybe not. Do these holes provide fuel at idle condition? Any sure way to check if holes are completely clear? Thanks

[Solarman]

Yes, after soaking, blow each of those little holes clear. Those holes provide fuel and air mixture for idle, for each cylinder.
Air compressor with small nozzle (does not have to fit inside holes, just against, to push good air pressure through after soaking.

Post back when able to let us know how it's going.

[bitsy4643]

Solarman, thanks again, ready to take to shop, but reluctant as part replacement could be very expensive. I believe you know more than any shop. Many parts already replaced. Symptoms still persist and very confusing. This morning started engine, reduced throttle to idle, engine ran @ 300-400 rpms for several minutes without fail or fluctuation. Shut engine off, came back in several 5 minute increments. Engine started immediately and idled perfectly. Shut engine off, restarted in 45 minutes, would immediately die unless you adjusted idle screw to remain running. Will idle at that rpm for several seconds, then suddenly up to 1500-2000 rpms. Completely baffling and frustrating. Thanks again.

[Sealfie]

Have you tried to change your spark plugs? Two strokes dont like idle for too long. Sounds like obvious fouling to me. And also, when u have changed them, test the engine in normal operation, not in consistent idling.

Post back with the happy news later

[Solarman]

Ok, bitsy, next time you start it up, use a can of carb cleaner with the tiny straw, and give small/slight little shots around base of each carb, very slowly, waiting a moment between shots, for any abnormal running. We're looking for possible air leaks around intake manifold to carb gasket area.

Good luck, post back when able to let us know how it's going.

[bitsy4643]

idle

Solarman, Getting more consistency at idle, but still not 100 per cent dependable, As, Before, Motor starts with full throttle and choked. Can adjust idle after warm up, to 400-600 rpms. Will now idle at that rpm indefinitely, but when you throttle up and then bring throttle back to idle as before, engine runs at 1200-1500 rpms for several minutes, but eventually and not changing any settings, will settle back to correct idle speed, 400-600 rpms. What action reduces rpms back to idle and would you have any idea why it takes so long?
Thanks

[Solarman]

Eventually? What does this indicate? An amount of time?

"but when you throttle up and then bring throttle back to idle as before, engine runs at 1200-1500 rpms for several minutes, but eventually and not changing any settings, will settle back to correct idle speed, 400-600 rpms."

Well at least it's going down to idle, rather than up? Seems you must have done something right??

Did you clean carb(s) again? Did you do anything different this time?? Have you been adding a fuel cleaner/ stabilizer to tanks of fuel? Could be a smart move, in every tank, especially if only ethanol is available.

On my motors, that action is dictated by the ECU, and is automatic, i can't adjust that throttle action. Your motor?? Maybe controlled by ECU, CDI, possibly even the tach control?

Post back when able to let us know how it's going.