air pulses OUT of my air filter By curmudgeon (Read 703 times)

[curmudgeon]

A lady at work asked me to check the brakes on her scooter.

Trailered it to my house and find out it hasn't been started or run for 3 years.

Replaced all hoses, replaced cracked air intake, cleaned the carb, removed the PAIR system, set the valve clearance.  The exhaust valve had 0.150 clearance (!!!) and the intake had no clearance cold.  Both now set to .005 cold.  I'm an old farm boy and have done all my own maintenance on small engines including many motorcycles over the years, so I've rechecked everything twice, and pretty sure I've done it right.  Everything but the PAIR looks familiar.

Motor starts and idles well now, but won't rev over 6500 RPM when on the center stand. I get mild popping above 5000 RPM.  I also seem to be getting a lot of reverse flow back through the carb and air filter. Strong pulses out the air filter above 5000 RPM.  A compression check shows 90 PSI, which seems low.

Is there something special I need to know about these engines, or does this scream "bad intake valve"?

I'd rather not dive any deeper than I have to...

[Alleyoop]

well 90 psi is low I am surprised it runs as good as you say it does. Normally anything below 120 psi one would have a hard time starting it and keeping it running. When you checked the compression did you hold the throttle wide open to allow as much air in as possible if not it will register low.

Popping at high rpms indicates to much fuel, try leaning it out using the Fuel Ratio Mixture screw(turn it clockwise to lean it out).

Also you do not say what it is a 50cc or 150cc etc..
Alleyoop

[curmudgeon]

Ya caught me out, thanks. Too many diesels, lately. Checking compression with the throttle open gets 150 PSI, which is a lot better. Again, many thanks.

Will the idle mixture screw actually affect the high RPM mixture that much? I currently have it set 2 turns out. I'll try changing it. Pilot jet is 35, main is 105. It's a Keihin (sp?) carb. I don't know how better to identify it. Owners paperwork says 150CC, Kaitong, marked Velocity. I am at 6500 ft, owner lives at 6000 ft, so running rich is not hard to believe. Any jetting help appreciated.

[Alleyoop]

Great!! that carb is the normal carbs that come with the 150s and the Jetting is right on. One other thing you may want to check is the ENRICHER make sure it is working if it is not shutting off the extra fuel after 4-5 minutes from starting it will run very rich which may be the problem the other thing to check is the AIR FILTER make sure it is not clogged with dirt and or oil that will also cause it to run very rich.

NOW to check the ENRICHER take it off and lay it on its side then PUT YOUR THUMB OVER the hole and start the motor and keep the thumb over the hole and then watch the ENRICHER it should start to EXTEND OUT about 1/4 of an inch withing 3-5 minutes.
If it doesn't extend out that is probably your rich problem it is not shutting off the fuel after it is warmed up.
Alleyoop

HERE IS THE ENRICHER RECTRACTED WHEN YOU FIRST TAKE IT OFF COLD:


HERE IS THE ENRICHER EXTENDED AFTER 3-5 MINUTES OF THE MOTOR RUNNING:

[rapidjim]

You also need to be careful when adjusting these carbs. They do not respond quickly when adjusting them. With the scooter on the center stand, start the scooter and let it warm up and set idle so the back wheel barely starts to turn. On the left side of the carb, adjust the air mixture screw ccw 1/4 of a turn and wait 20 seconds, if the RPM increases, then continue turning the screw ccw, 1/4 of a turn at a time waiting 20 seconds between turns until the idle decreases, then back the screw cw 1/8 of a turn. Then reset your idle screw so the back wheel barley starts to spin. If in the initial adjustment ccw, the idle dropped, then turn the screw cw 1/4 of a turn, waiting for 20 seconds between turns, repeating the above procedure turns until the idle drops, then turn ccw 1/8 of a turn, reset idle adjustment.

[curmudgeon]

Thanks again for your help.

The enricher appears to work properly, and measures 15 Ohms. Air filter is clean. Runs the same when air filter is removed.

More info on behavior: If I get the engine up to 6000 RPM and it is in a steady-state sputtering mode and cover 3/4 of the air intake area, then it speeds up and runs to red line. If this was an old tractor or simple carb that would tell me the mixture is too lean. On this carb the vacuum operated main needle I'm not sure.

I don't have any other main jets, so moving the needle up and down is my only tuning option. I think it is close to maximum rich right now. (Clip lowest on the needle.)

[Alleyoop]

Yes your correct if it is sputtering and not POPPING and runs up after cutting off some air then it needs more fuel on the top end. So get a 108 and a 110 main jet and stick it in there.

This trick of the trade works at any throttle position and very accurate to what the motor needs:

1. Run it up to where it starts to act up AND THEN back off the throttle 1/8-1/4 of an INCH and HOLD IT THERE:
A. If the motor speeds up it is LEAN
B. If it sputters and settles down it is RICH.
Alleyoop

[curmudgeon]

Thanks again for your help.

The clip had been at the center setting. Moving the clip up on the needle made it run worse. So I moved it to the lowest position on the needle (richest.) That helped a bit.

Then I noticed that it appeared somebody had drilled the airbox. I stopped up all but what I think is the original hole and it will now run above redline on the center stand. It would only pull 4000 with my 220# butt in the seat. I'd ordered some 12 gram rollers for the variator - originals were 17.3 gram. I put the 12g rollers in and it now pulls 5000 RPM. Speedo is broken, feels like maybe 50 MPH? This will be a city commuter, so 50 MPH top speed is probably fine, but it's still anemic off the line with a flat spot at ~3500 RPM.

I'm thinking I need to get a bigger main jet - even though it's hard for me to believe the stock jet (105) is lean at 6500 ft. How big should I start with if I open up the other four 1" holes?

Any other suggestions?

Thanks again.

[Edit to add:  You posted while I was typing. Thanks, I'll get a 108 and 110 jet.

[Alleyoop]

The 12 gram rollers will help a lot with your rpms it should rev up to 7K+ with 12 gram rollers and will be stronger at the low end due to the higher rpms. The flat spot is because it is to rich at mid range because you dropped the clip. When you get the bigger main jets move the clip back to the center to help out the mid range.
Alleyoop

[curmudgeon]

Thanks again, I'll follow your advice when I get the new jets.

[curmudgeon]

Got the new jets and installed the 110. Worked a treat!

Now does an estimated 55-60MPH, no bogging, no flat spots. Very responsive.  The intake bucket has 4 extra 3/4" holes in it, all opened up.  It was cold tonight, so summer at 6500 ft may drop me to the 108 jet, but this was a great help.

Needle on center c-clip slot.

12 gram rollers gets 5500 RPM  CVT operation.  I'll try the 8 and 10 gram rollers when I get them, but I think the 110 jet and 12 gram rollers is a great place to be at 6500 ft.

6500 ft robs about 23% power from a sea level engine, so I'm really happy with this performance.

Thanks!

[Alleyoop]

FANTASTIC!! Good job BRO
Alleyoop