LO206 - Surging at idle and lack of revs 3-4 laps into race

The key here is that it is the RIGHT type of Tygon. I forget the term but there is a lined and an un-lined fuel line they sell.

DO NOT GET THE LINED TYGON. The lining reacts with gasoline and turns to mush and will collapse in the line, rendering it useless. I think this type of line is intended for food or drug use instead of automotive.

Don’t ask me how I know, but I know.

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I took a look and it looks totally fine. I put a fresh gasket between the new head and the plenum (thanks for the new word haha). I have not had any impacts to the right side of the kart.

The hard thing I am faced with is that I can’t start up the engine while at home because I live in an apartment complex. I have a single car garage which is my workshop but I don’t want to push my luck by making a ton of noise. I think I am just going to take it in to the local shop at this point. I like fixing things myself but I have ran out of ideas for what it could be.

Never mind, looks like that little gap along the rim of the pump, left of the pulse line was there the whole time.

I did notice that I had to have the idle mix screw backed out ~3 turns in order for it to idle. Otherwise it would drop revs and die on the stand. That combined with moving the needle clip to p2 seemed to get it to idle okay around 1800-2000rpm on the stand.

That tells me it was too rich at idle even with the needle clip on the second leanest position. So either not getting enough air or getting too much fuel. Right? Not enough air seems unlikely given nothing is visually wrong with the intake, air filters or carb. Too much fuel then? Float at .870 should not be an issue though. Drop looks okay too and the needle does not bind going in and out. Hmmm

Any chance this is a bad batch of fuel?

How is the spark plug wire?

Fuel - If this was the issue, would it cause intermittent issues like I was having? The fuel I was using was ethanol free pump gas. However, it wasnt totally fresh though (about two weeks old). Personally, I don’t think the fuel would degrade so significantly in such a short time considering it was ethanol free. Also, I feel like if it was a gas issue, I wouldnt have had two practice sessions without any issues and then a problem in Qualifying, no issues in Heat 1 or Heat 2 and then a problem in the Final. I used the same batch of fuel the whole day (and weekend).

Spark plug wire - I thought of this on race day and checked it out. No cuts or any issues that I can see. It snaps onto the plug well. I even used a zip tie to pull it away from the head a bit before the final because I thought that the high temps of the head might be causing the issue if the wire was touching it. Spark plug itself was brand new before the Final too.

Doing more thinking on the surging symptom at idle:

At first, I thought that this was due to an issue with the fuel delivery to the engine causing a lean condition. However, when thinking about this issue considering how far I had to unscrew the idle air mix screw, I am now wondering if it was due to letting in so much air at idle.

I couldnt get it to want to idle when the needle clip was at P3 (middle). The engine dropped revs and died while trying to idle even with the idle air mix unscrewed ~3 turns. So I dropped the needle to P2 (leaner) and then it started idling okay with air mix unscrewed 3 turns. That is a very lean idle mix considering temps were only in the low 80s and RAD was 95-96. So while the engine would then idle, it was also surging which could just be a product of the extremely lean idle mix and not indicative of some “issue” persay.

So then that has me thinking, “why wouldnt the engine idle with a more normal (and richer) mix?” That could be due to the engine not getting enough air (probably unlikely given air intake issues are more likely to cause too much air via leaks) or it was getting too much fuel. The only thing I can think of which could cause that would be the inlet needle getting stuck open. I’ve checked that and it does not seem to be the case. Perhaps the inlet needle isnt closing correctly?

Sorry for the stream of consciousness post. Just trying to write down my thought process diagnosing this issue so that if I am making any incorrect assumptions or conclusions, you all can correct me. At this point, I think it might make the most sense to just buy a new carb and see what happens.

On my car, I had a situation where the car was running well. Filled it up, it ran fine for a little bit and then poorly. Put in fresh fuel and it ran fine.

Was wondering if it was a similar situation.

I hope you figure it out.

Could a faulty kill switch be causing these issues? I took my switch out to inspect it and noticed that the prongs are incredibly loose and wiggly. They tighten up when the button is depressed. But when I was checking with my multimeter, there was only a connection between the ground prong and the button thread intermittently. I wonder if the internals are getting tossed around and and they vibrate they make random split second connections as I drive? Could explain when it had issues when I got hit due to the forces going off the track and coming back on. Could have partially made a connection?

Are they supposed to be super loose?

They are pretty loose after a period of time.

At this point with all you’ve tried just about anything left is possible! It wouldn’t be the first time that kill switch is causing an issue but it is rare.

It’s a circuit interrupter lever rather than a true button, so it could be partially shifting. Was it loose at all in the actual mounting plate?

Another possibility although I’m skeptical is the flywheel key is sheared and the flywheel is shifting on timing from time to time, again super rare but have seen it…usually though with they the engine just won’t run at all.

While I think I of it. It’s worth checking the ground wire to make sure it’s not grounding against the engine anywhere along its path. Sometimes it gets pinched.

Yeah I thought of that and as far as I can tell, the ground is properly attached to the block and the lead going to the coil is not pinched. It is routed under the top plate through the “hole” (don’t know the name for that little hole thing).

I have been watching and listening to my videos from these sessions and I am starting to wonder if it was my clutch all along. I didnt notice it overheating or smoking or anything day of, but:

  1. Getting worse after a few laps in a session checks out with a clutch heating up.
  2. Having the engine not be able to reach peak revs seems possible if the clutch is slipping.
  3. Once issues start occurring, it being super hesitant especially out of the corners where I lift, brake, then come back onto the gas - seems to check out with a clutch issue IMO.
  4. In the final, after I was hit (and driven over…), we went off the track into the grass. I somehow managed to keep it straight and got it back to the track. However, that involved a few solid seconds of keeping the gas floored to get through the grass. Listening to the video, the engine holds an RPM during that time which sounds like I should be going faster than I was going through the grass. Like, how you might spin your tires trying to drive in wet grass and the revs are high because your wheels are spinning. I wonder if it was the clutch slipping instead of the tires spinning (because it is a LO206 after all haha). As soon as I reached the track again, the “engine” started having the same issues. Lack of revs and super hesitant out of the slower speed corners.
  5. In Qualifying, after the issue was getting worse, I drove into the pits and sat at the pit entry for a second idling while I looked at the carb and tried to see if anything obvious was wrong. The video shows that my memory was correct: the engine was idling there just fine. No issue I can hear at all. But, when I eventually called it and tried to throttle over to the scale, I didnt go anywhere…That seems in line with the clutch slipping for some reason (heat or other issue?)
  6. Also, not being able to recreate or diagnose the issue in the pits / on the stand makes sense if it was the clutch.

Does this new theory make sense to you? I’ll post links to the videos when they finish.

It makes some sense. Although i would think if you were slipping the clutch, youd see higher revs. What clutch do you use and how often do you service it?

Oh that is a good point it wouldn’t be low on revs but higher if it’s slipping. Shoot.

It’s a Hilliard flame and has just 5 races on it. I clean out the groves and dust every race and give the drum a light wipe with WD-40. I run two white and two black springs with one heavy weight in each shoe.

Here is what it looks like post race before I cleaned it.

Looking at the mychron data, I am seeing that in the slowest corner the minimum RPMs are from 3200-3500. I was running a 16x55 gearing which is standard for this layout. But I definitely barely hit the limiter towards the end of the straights. However the Saturday practice and the first morning practice on Sunday, I was running 17x59 playing around with a slightly lower gear ratio to see if it would be a better qualifying gearing.

But 3200-3500 is pretty close to the engagement speed of my clutch and definitely touching the lockup speed. The chart puts engagement at 3200 rpm with 2 black + 2 white + 1 weight per shoe…. However, in two of the corners that really hesitated, the RPMs look to be remaining around 3700-4000rpms.

So I dunno now. On one hand, i think there might be some slippage out of at least one corner per lap. However, if it was overheating and slipping, it should be over revving not under. What does excessive chain lube getting into the clutch drum look like behavior wise?

Here is a screenshot of RS3 of three laps from my qualifying session where my engine had a major issue. The pink lap is the reference lap which is the best time I did this day. It was in Heat 1 with the same gearing as qualifying. Pink is after I lowered the float height due to my theory the engine was running too lean.

Qualifying session lap key:

  1. Blue is lap two of the session and the best lap of the session.
  2. Green is lap three of the session and 0.700 sec slower than Blue
  3. Black is lap four of the session and is multiple seconds slower than blue. I knew I had a major issue at this point.

On the blue lap, I was running with another kart and keeping pace. However, I can see on video that he was pulling away from me on out of the back esses. By the beginning on the green lap, I visually see him pull away from me enough to think, “huh…that is odd”. By the exit of the esses (sectors 7,8 and 9), he pulls away so fast that I know for certain something is up with my engine. You can see my revs and acceleration are down compared to the pink reference lap and the blue lap just prior to this one… On the exit of the final corner going into the black lap, my engine feels dead and the RPM trace shows it. It is down 300 rpms compared to the same spot on the track two laps prior. You can see on the exit of turn three (sector 5 going into 6), the RPMs just are not there. The trace is nearly flat.

So yeah, that is a good data visual of what I was feeling in qualifying. After the black lap, I knew I had to come in as it was getting worse. That is when I idled for a bit in the pit lane with no issue and then couldnt even accelerate to the scales.

Hope this helps!

How’s your chain alignment and tension? I’ve lost very noticeable power in 206 from my rear sprocket walking after a few laps. It doesn’t fit all your symptoms, just that one.

It is well aligned, carrier and sprocket are tight and it has not moved on the axle. I’ve had issues related to this in the past so that was one of the things I looked into at the track. Axle and everything spins freely.

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Since we’re chasing ghosts at this point, I’ll add to Caleb’s comment about chain alignment. Is there any chance your entire axle is sliding left to right under load? I had that with my son’s kart a few years ago in cadet. Moved just enough to drag on the brakes slightly and cause him to be slow compared to other kids on track.

You know…I did have a new axle this weekend…Interesting theory! I will check after work today! If so, I don’t think it is substantially out of wack though because one of the things I thought was happening while at the track was my brakes rubbing. I confirmed that the gap on either side of the rotor were the same and looked normal. Also, I am not sure why it would cause intermittent problems.