No Power in Left-handers

Jared Langenfeld · Posted: Mon Apr 02, 2012 6:40 am Post subject: No Power in Left-handers

I had my first regional event this past weekend and was very happy with the new-to-me chassis and the engine felt strong through 95% of the course. Over the winter I went from a flat-top piston to a 2005 piston and a mod head.

I bought the chassis at the end of the season last year and did two events in the old chassis with the current motor and at the last event, the motor would fall flat in a high-load left corner. Fast forward to this past weekend, and the same thing happened to me at the test & tune on Saturday and the event on Sunday. Each day had a high-load left corner and the motor would fall flat when I got back onto the throttle at mid-corner and the motor would be flat through the whole straight following the corner. The left-hander was a 5th gear sweeper and my data logger showed a sustained 1.2-1.5 g's through the corner for 5-6 seconds. On my second run, I tried going down to 4th and it fell even flatter than when in 5th!

Anybody have any ideas? I am thinking it is most likely a carb issue. I have a PWM pump-around system, so it *shouldn't* have any fuel issues in high-load corners. It doesn't have a problem with high-load right corners, just when turning left. Sounds like I can't do any circle-track racing!! Laughing

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2008 Mike Wilson with Honda CR125 shifter

Danny Kao · Joined: 17 Nov 2008 Posts: 192

I have three guesses:

1. Vent/return fuel line back to tank pinching to the seat and seat strut.
2. Loose grounding wire.
3. Loose spark plug wire.

If I guess any of this right, you own me a ice mocha at Lincoln. Smile

Ken Schilling · Joined: 01 Dec 2005 Posts: 1347

In addition to the above, check the following:

- clean your pumps of any oil
- make sure your pulse line isn't pinched

Don't' ask me how I know... Laughing

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Ken Schilling
#21x / S4 / ProKart Challenge (PKC)
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Good luck is where preparation and opportunity meet!!!

The opinions I express are mine alone and do not reflect those of any organization of which I am a member.

Larry Andrews · Posted: Mon Apr 02, 2012 6:01 pm Post subject:

Maybe the fuel tank pickup tube has gotten rigid and cannot move to the right side of the tank. Pretty easy to check by unscrewing the cap and pulling the tube - it should be at least a little bit floppy.

Jared Langenfeld · Posted: Mon Apr 02, 2012 8:13 pm Post subject:

Thanks for the suggestion guys. I will check all the fuel lines. I also ordered a couple fuel pump rebuild kits just in case there is something wrong with the fuel pumps.
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2008 Mike Wilson with Honda CR125 shifter

Joe Ricard · Posted: Tue Apr 03, 2012 4:49 am Post subject:

It definately is a lack of gas in carb bowl.

Not knowing how them fancy schmancy pump around things work the suggestions above all seem reasonable.
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Arrow AX-8/ Rotax Sr.

al nunley · Joined: 13 Nov 2006 Posts: 3038

It could be something as simple as the brake disk not sliding side to side and dragging on the pads. Or a tire rubbing on something. I’ve done that. You might check the axle and make sure it’s not moving in any of the bearings.
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If the data does not support the theory, get a new theory. (Al Nunley)
All else being equal; Compression is the Holy Grail.
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Tom Reynolds · Posted: Tue Apr 03, 2012 7:33 am Post subject:

How much gas were you running? If you were running a minimum amount, the fuel pickup is sounding like a good cause.

Jared Langenfeld · Posted: Tue Apr 03, 2012 7:50 am Post subject:

Thanks everyone for the suggestions. I'll add axle play to the list to check.

After watching and listening to videos of my runs, the motor running flat was happening a few more times than I thought, but just momentarily and almost unnoticeable. It really only happened for a noticeable amount of time in the high-load sweeper.

Tom, that was my first thought but I had plenty of gas in the tank.
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2008 Mike Wilson with Honda CR125 shifter

Scott Boito · Posted: Wed Apr 04, 2012 7:43 am Post subject:

The problem with my motor on corners turned out to be the bizarre coil I had - the coil wires themselves were compromised and on high-G corners the torque on the coil housing caused the wires to separate and give only intermittent ignition. I have, thankfully, fixed that by replacing the whole ignition with another stock 98/99 system and my problem is gone.

Your situation, assuming the ignition system is sound, sounds like a fuel line pinch or pick-up problem.
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Steve Lower · Posted: Fri Apr 06, 2012 4:54 pm Post subject:

Check that your fuel line isn't being pinched by the seat. You would be amazed at how much a seat will flex under a high load corner. Even if you have extra seat struts.

If you have the fuel line between the primary seat strut and the seat, move it outside the strut, give it a little slack and loosely zip tie it in a poistion where you're sure it won't get pinched AND won't be able to get near any moving parts of the engine.

We expreienced this years ago. Chased it almost an entire season. Engine would fall flat on it's face getting back to the throttle coming out of a high load left hander. Never had a problem on right handers. We actually corded a set of tires at a banked asphalt oval trying to replicate the problem.

To give you an idea how much a seat can flex. I had our ignition box mounted to the side of the seat with over 3/4" of clearance between it and the flywheel. When taking the engine off a couple weeks ago for a rebuild, I noticed the ignition box had been gouged almost 1/4" deep by the flywheel. And we have an extra seat strut near the top. The seat is flexing right at the hip joint area where I would have never expected.

Try rerouting your fuel line like I said above. I'm betting that's your problem.
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In Racing,
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meticulous attention to detail,
and the latest engine technology,
things sometimes inexplicably just go....

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F125 #31

Jared Langenfeld · Posted: Wed Apr 11, 2012 6:27 am Post subject:

I got my fuel pump rebuild kits yesterday. So I took off the fuel pump and tried to blow the opposite direction of the fuel flow to see if the check valves were bad and I was able to blow air backwards on the supply side pump but not the return side pump. I wonder if a bad check valve in the supply side pump could cause the motor to go flat in high-load corners? I will rebuild the pumps before the even this Sunday and see if that fixes the issue.

I have rechecked all my fuel line routing and there shouldn't be any pinch points. The only minor place of concern is the pulse line makes a u-turn to go to the pump and it possibly could be too abrupt and pinch. If I'm still having issues after rebuilding the pump, I will use a longer hose for the pulse line to make the u-turn not so abrupt.
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2008 Mike Wilson with Honda CR125 shifter

Joe Ricard · Posted: Wed Apr 11, 2012 10:28 am Post subject:

My money is on the bad check valve on supply side of pump.
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Arrow AX-8/ Rotax Sr.

Steve Lower · Posted: Wed Apr 11, 2012 12:07 pm Post subject:

Jared Langenfeld · Posted: Wed Apr 11, 2012 5:40 pm Post subject:

I believe I may have found the issue.

In the picture is a 2mm allen wrench. Yes, I found three pebbles and a piece of hair in the supply pump. The previous owner didn't have a fuel filter when I bought the kart.

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2008 Mike Wilson with Honda CR125 shifter