dying at stop; LOW idle By OMN (Read 3,831 times)

[OMN]

ok, running into a problem. roketa 250b is hard to start after sitting a couple days. always has been.

also it used to die when slowing down. turns out the exhaust valve was tight, so we loosened it to .005 and it worked great for a couple months.

now we have the same "dying at a stop" problem. checked the exhaust valve tonite, and it's still good: .006"

took off fuel line from LH side of carb. it pulses out gas when cranking.

A/F mixture screw was at 2 turns; re-set to 2.5 turns out.

still dies when slowing down. still hard to start.

i replaced the enrichener when we originally had issues. i don't think it's working but i'll check that this week. but that shouldn't mess with operation once the engine is warm, right?

what else should i check, since it doesn't seem to be the exhaust valve. would a too-tight intake valve cause the same symptoms?

thanks, all
ron

[cruiser]

Hi, ron. Both valves have to be set properly especially for low speeds and idling.

Default for the enricher is the cold setting (needle retracted) which means it will already be set for a cold start. If the needle does not extend it will really show up as a rich condition once the engine is warmed up. This will mess up the idle. If the enricher is sticking in the warmed up condition (needle extended), then you will have trouble starting because the enricher circuit will not work but it will not affect the idle once the engine is warmed up.

[terrilee]

valves

[richardthescooter3]

I have the mc-54-250b, had issue with starting, here is something to check, plus if those intake clamps are loose you will have trouble Also check those vacuum lines.

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[richardthescooter3]

How does it idle, mine had a rough idle and stalling at stop signs, Turned out to be a my main spring in my clutch was weak, (it had my clutch still egauged in low speeds and stops) replaced it, problem solved.

[OMN]

Oct 1, 2012 10:21:01 GMT -6 richardthescooter3 said:

How does it idle, mine had a rough idle and stalling at stop signs, Turned out to be a my main spring in my clutch was weak, (it had my clutch still egauged in low speeds and stops) replaced it, problem solved.

for the past several weeks, it's been running like a champ. last week when i drove it, it seemed like maybe it wasn't getting enough fuel when i came to a stop, but it didn't stumble or die. now it's acting fuel-starved when i slow down. it's worse when i stop suddenly, especially up an incline.

at first i sure thought it was the exhaust valve, but it's at .006". after the motor cools, we'll check the intake as well just to be sure.

would the exhaust valve being slightly too loose cause this same problem?

ps, i also checked the a/f mixture last nite and put it at 2.5 turns out. no change.

thanks, all! we're about to take it apart again and see what we can find.

;-P

[terrilee]

im NOT sure about 250's
i have a 150
and the settings are .004 and .005
so................

[OMN]

ok, just checked. the intake valve is at .005" and the exhaust is .006"

is it a problem that those are both about .001" too loose? i've always heard it's best to err on the loose side.

also i believe the enrichener must be working - it starts right up cold, and holds a strong idle. the enrichener itself also gets very warm.

BUT, here's the wierd deal. on the center stand, it idled strong at about 1800-2000rpm for several minutes after starting. revved it, hit the brakes, etc - all was well. then suddenly after revving and hitting the brakes, it would start lugging and eventually die. it's acting like it's not getting enough fuel to recover from the very low idle that happens when i hit the brakes. once restarted, i had to give it just a little throttle for a couple minutes until it would finally hold itself back at a good 1800-ish idle.

i thought i'd try richening the mixture, so i pulled the carb needle and lowered the clip a notch. it seemed to accelerate a little stronger, but didn't change the low-rpm problems.

i checked for vacuum leaks. pulled and wiggled hoses, visually inspected intake boots, and sprayed WD-40 around all the inlets i could find. during this vacuum test, the engine was idling smoothly at about 2000 rpm. it never changed.

i found a vacuum hose that runs from the RH middle of the carb up to a vaccum thing on the top of the carb (looks like an air cut-off valve). this hose is only about 3 inches long. i found that pulling the hose didn't change anything, but if i covered the hole on the side of the carb body, the engine would immediately bog and die.

there is also a short hose coming off the LH side of the carb, near the top, with a 90-degree bend in it. if i understand correctly, this is a fuel overflow??? i found that when i covered that hole, the rpms went up about 50-100 rpm.

so, what do you think i should look at next? to reiterate, everything has been really great for the last month, or about 850 miles. then suddenly within a week/50 miles, it's back to its old tricks. no changes since about 6 weeks ago when we did a full PDI with new enrichener, valve adjustment, etc.

any more ideas?

thanks for your help, in advance!
ron

[richardthescooter3]

I have the mc-54-250b roketa, I have mine set intake .004 and exhaust .006 I would check your needle jet to see if its in correct, discovered mine wasn't, the spring was not on the needle, maybe the clip on the needle came off. (fix mine and what a difference in performance) make sure that diaphragm seal properly, that will make a big difference

[richardthescooter3]

Here is pic of needle jet.

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[OMN]

i believe the diaphragm is sealing well and in great shape. the needle feels like the spring is correctly in place. my needle has only 3 clip options. it was in the middle. i moved it to the lowest (richest) setting last nite with not a lot of noticeable difference.

any other thoughts, anyone? this thing is kicking my butt! especially since it worked GREAT just a few days ago and i haven't changed ANYTHING.

i was thinking maybe fuel delivery so i hooked up an external tank and clamped off the line from the scooter's tank. all that did was flood it.

thanks for the input - please keep it coming! :
ron

[terrilee]

get a sray bottle with slightly soapy water
get your scoot to run, and then spray all lines,
fuel. air . intakes, etc
and see if anything bubbles.
if it does , you have a small leak that is screwing up

[alleyoop]

First thing to do is Start it up and let it warm up idleing until you see the RPMS drop after the ENRICHER cuts off the extra fuel. Then Adjust your FUEL RATIO screw to get the HIGHEST IDLE from the fuel ratio mixture screw. Mind you 2- 2 1/2 turns out IS JUST A GOOD STARTING POINT but may not be the CORRECT mixture.


Also the ACV VALVE that you said if you block it off it makes it die is correct. That valve is for your deceleration, BY DEFAULT it is ALLOWING AIR to pass through, When Enough Suction is applied like when decelerating it CLOSES the AIR PASSAGE and allows some fuel to be sucked in so the motor does not run LEAN and backfire(that is how that part works).

So from where the Fuel ratio screw is currently set FOLLOW this procedure:
Alleyoop

First Start up the Scoot and let it warm up At Least 5 minutes so the ENRICHER cuts off the Extra Fuel.

YOU WANT TO GET THE HIGHEST IDLE OUT OF THE FUEL RATIO MIXTURE:


So from where it is currently set FIRST TRY richening it up more:

1. Turn it 1/4 turn Counter Clockwise and wait about 10 seconds to allow the motor to catch up with the new setting. LISTEN or look at your tach:
a. If the IDLE GOES UP REPEAT #1, UNTIL the IDLE does not change or drops a little THEN TURN THE SCREW CLOCKWISE 1/8 and that should be the highest IDLE from the Fuel Ratio Mixture and go to #3.

**** IF ON THE FIRST 1/4 TURN COUNTER CLOCKWISE THE IDLE GOES DOWN OR DOES NOTHING, TURN IT CLOCKWISE 1/4 TURN TO GET IT BACK TO WHERE IT WAS AND GO TO #2****

2. Turn it 1/4 turn Clockwise and wait about 10 seconds to allow the motor to catch up with the new setting. LISTEN or look at your tach:
a. If the IDLE GOES UP REPEAT #2, UNTIL the IDLE does not change or drops a little THEN TURN THE SCREW COUNTER CLOCKWISE 1/8 and that should be the highest IDLE from the Fuel Ratio Mixture and go to #3.

3. If the idle is TO HIGH NOW LOWER the IDLE USING the IDLE SPEED SCREW so that your REAR WHEEL JUST WANTS TO TURN... Go to #4.

4. Now give the Throttle a quick twist and let go, the Motor should Rev up nice with no sputtering or hesitation and come back down to where you set the idle.

*** IF TURNING THE FUEL RATIO SCREW Clockwise or Counter Clockwise DOES NOTHING Then the Pilot Jet AND OR ITS PASSAGE ARE Clogged and you will have to clean the Jet and CLEAR OUT THE PASSAGE. And go through the Procedure again***

[OMN]

sweet - thanks for the suggestions. i'll try these tonite if i can, then post up results. thanks, all!

hey alleyoop - what do you use to adjust the a/f mixture screw? mine is on the bottom of the carb and hard as heck to reach, especially with a hot exhaust... plus my shortest screwdriver is an inch too long to clear. if i can get in there with a screwdriver impact bit, that may do it... is there another trick i'm missing?
;-P

[alleyoop]

Well if your hand is to close and you burn yourself, Get a nice piece of Thick Wire or a metal rod about 1/8 thick and Smash the end of it Flat to make it like a screwdriver tip bend it about 1/2 inch from the edge and you will have a long piece to grab and turn the screw away from the hot manifold. Some what they do is loosen the clamps and turn the carb enough to get at the screw turn it 1/4 straighten it tighten and try(problem is the motor is not running and that is not a good way to set it properly). You have to be able to adjust it while the motor is running so you can tell IF and when you turn the screw a little the IDLE goes up or down.
Alleyoop

Get a little mini set like this:


Or make your own: