2006 Linhai GMI 407 carb issues By wcraig (Read 1,893 times)

[wcraig]

Looking for some help to tune this carb so the engine will idle. Engine starts fine hot or cold.

What I've done:
- Flushed fuel sytem, cleaned tank, pulled carb and cleaned thoroughly, replaced fuel filter, spark plug. Engine starts and drives well. But, will not idle. If you crack the throttle, it'll keep running but, it is way too rich with black smoke at low rpm.

I've read through carb tutorial on air/fuel adjust and nothing seems to take adjustment, either idle speed or mixture. The pilot and main circuit were blasted with carb cleaner and compressed air and appeared to be clear.

I've been nable to locate any diagrams on this particluar carb, any help is greatly appreciated.

[richardthescooter2]

After warm up, what is your RPM'S? Have you check to make sure there is no vacuum leaks? Have you tried turning the idle screw clock-wise 1/8 turn at a time to see if your idle goes up?

[wcraig]

Not sure about rpms, i won't idle cold or hot.

No vacuum leaks to be found and turning the idle adj doesnt do anything. You can the set screw rotating cam but, even bottomed out, still no idle.

Engine sounds like it's choking with lots of black smoke. Almost souns as if choke is fully engaged and will not release as engine temp goes up.

Any possibility of a faulty temp sensorsomewhere?

[Alleyoop]

If it is blowing out black smoke, check your VACUUM line going to the Fuel Pump or Petcock whichever one is on there it may be sucking in gas through the VACUUM line in which case it is bad. You are getting to much fuel from somewhere. Also check your Air Filter it may be Clogged and not letting enough air in.

You can also try turning the Fuel Ratio Mixture counter clockwise until it stops and turn it back out 2 1/2 turns and see if that helps.
Alleyoop

The 250s usually come with a 30mm Carb Most come with one like this:

[Bashan]

If it was mine I'd also pull the auto-choke and make sure it's seal is OK and the mechanism is OK. I realize you said it starts hot or cold but weird things happen on scooter engines.

[wcraig]

I'll recheck the vacuum lines, I did find a too tight intake valve but, it didn't make a difference when I put it back together after adjustment

My carb doesn look like the one you posted, where the fuel mixture screw is on bottom this one has a brass plug with wires connected. Looks like some type of temp sensor. It says Keihin on the side, has a 128 main and 38S pilot.

This thing is dumpin so much fuel at lower rpm it's fuel fouling plugs on short order but runs fine at anything over half throttle. I think it it had an adjustment where these 2 wires plug in , I might just get it to idle.

All the choke circuit appears OK, I'm tryin to hook up 12v to it and see if it expands the 3/16 or so over 5 min.

I'm not against dumpin this carb for something thats readily interchangeable and has all the adjustments and less wiring.

[Alleyoop]

How about on the LEFT side of the CARB Do you see any screws near the intake side of the carb OR on the AIR FILTER side of the Carb?
Can you take a picture of your carb the Left Side mostly that is where they would have some adustment screws.
I will try and find a carb picture like yours. But they all should have a PILOT JET adjustment Fuel Ratio Mixture or an AIR RATIO MIXTURE.
Alleyoop

P.S. Is your throttle cable on the RIGHT SIDE ON A BRACKET or is the THROTTLE CABLE going into the top center of the CARB.

[Alleyoop]

You can also try lower the needle maybe someone messed with it and raised it. So take the top of the carb off only two screws and pull the diaphgram with the needle and take the needle out and HOPE it has slots on the needle with a clip to adjust. If so move the clip one notch up to lower the needle.
Alleyoop

[wcraig]

The pilot jet adjustment is on the left front side, cables attach to bracket on the right side with cables coming in from the bottom.

I have carb body soaking in carb cleaner overnight

[Alleyoop]

GREAT!! Take pictures of the CARB on all sides and post them I can then copy them and label all the stuff on it for when others have that same kind of carb and have trouble.


Oh so it does have a FUel ratio mixture screw COOL, that makes it easy. Turn that screw clockwise until it stops and AS YOUR TURNING IT COUNT the number of turns it took to stop.
If it took more than 2 turns to close then turn it out only 2 1/2 and try that.
Actually to correctly adjust it you want the HIGHEST IDLE out of that screw AFTER THE MOTOR IS NICE AND WARM at least 5 minutes idling.
WHEN ADJUSTING only turn it 1/4 at a time and listen for the IDLE(RPMS) you want them to go up. ALways start after it starts and the motor is hot TURNING it COUNTER CLOCKWISE(RICHER) 1/4 turn. If the IDLE(RPMS) go up you repeat the 1/4 turn until it does noting or the IDLE Starts to come down.

If going COUNTER CLOCKWISE on the FIRST TURN lowers the IDLE then go CLOCKWISE with the 1/4 turns.

ONce you have the highest IDLE out of the FUEL RATIO SCREW if the idle is to high the you lower the IDLE using the IDLE SPEED SCREW so that your REAR WHEEL just wants to turn or is turing very slowly.
Alleyoop

[wcraig]

update.........the fuel pump was damaged internally and engine was sucking fuel through the vacuum line into the manifold, no wonder it wouldn't idle. Previous owner or someone had made a mess of carb internals so I rolled it into the parts bin and scored a new one complete off fleabay for 99.00 shipped.

Engine runs great now. On to a cooling system, final drive flush and new tires.............