Starting a direct drive 2 stroke on the trolley

2 Stroke Kart Engine Forums
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Hi everybody (in the voice of Dr. Nick)

Having seen a couple of YT vids (Power Republic was one) of starting a DD 2 stroker on the trolley it looked really easy. Power Republic wrapped a strap around a back tyre and yanked, and the other was a chap just twisting it with his hands.

After priming the fuel line to the carb I initially attempted the strap way with no success. Then tried with my hands, again, no dice.

There just feels like there is too much compression to really get the speed up.

I did try with the throttle closed (although it is setup to have a tiny opening around the edge) and with it held partially open by setting the throttle pedal in a couple of different positions.

New to karts BTW. This is my first kart that I seem to have been rebuilding it FOREVER!

Any advice would be most welcome.

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It’s tricky at first. You have to use small amount of consistent force until you’re past compression then suddenly ramp up speed with a much harder but constant pull.

You can make it a little easier on yourself by using a taller ratio. ie one that would reduce your RPM on track. That will reduce the compression effect you feel and make it easier to turn over.

You can also experiment with the number of wheel turns per pull if you’re using a strap. 2 or 3.

You may have to choke it for the first pull. Hand over the mouth of the carb. Remove the air box if there’s on one there. It should at least kick a couple of times. One thing worth noting is that the PVL ignitions usually don’t spark until 450 RPM, so the engine needs to be turning fast enough to generate a spark. If it’s an older Motoplat ignition, they tend to spark at 150rpm.

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3

one more trick: after you prime the carb, remove spark plug and rotate tires with a bit of open throttle. This will completely prime the engine. Then put spark plug back in and follow the above. I usually have no issues on the stand, then 10 seconds later I put it down, push it, and it will take a marathon to get it going, go figure. Also keeping the low screw in by 1/4 to 1/2 turn (leaner) just for the first few seconds helps (as soon as it starts, you bring it back out). High compression is normal, way higher than modern engines

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Thanks for you replies.

It is a Motoplat system, and it does spark when removed and I’m turning the engine over.

One point I didn’t mention: after priming the fuel line a small air bubble persists in the line just before the carb. It’s quite small and only takes up about half the width of the pipe. When turning over the engine without the spark plug fitted the bubble is pulled into the carb suggesting fuel flow. But when I stop turning the engine the bubble pops back out of the carb and sits in the fuel pipe.

It’s a good point about setting the jets. It’s a used carb so I don’t know what setting it is on. Should I just wind them all the way in and back them off a 1/4 turn to get a baseline setting? I’m sure the proper setting is out there somewhere on the information super highway.

The carb is a Walbro WB19 for reference.

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On my old direct drive 100cc kart I’d just prime it. Spark off, turn wheels whilst covering the carb until fuel flows out.

I always put the spark back on the cap and lay it on the engine while I spin the wheels

A small flat head screwdriver between the stop and throttle arm gives it just enough throttle to fire.

Then just a strap around the tire and find the compression point and pull. Mission complete :smile:

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Just tried again. At first I got some fuel out of the carb after priming and turning the wheel by hand. Took it just past the compression point and pulled the strap. Nothing.

Tried the whole process several more times and could not get fuel to come out of the carb.

I’m still getting a small air bubble in the fuel line just before the carb. Is that normal or a sign that the seals in the carb are gone?

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Begin with pressure test the carb. And rebuild if it has been a long time ago.

Check if the cover is tight

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The air bubble is normal. I’m surprised you didn’t even get a pop out of it.

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Take the airbox off and see if fuel is flowing. If the airbox is full of fuel, your carburetor needle and seat is leaking and you’re flooding it.

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I had already taken the air box off. I had primed the line, then turned the engine over with the spark plug out and my hand over the carb air intake.

First time, I got fuel on my hand (not excessive), but on successive times it stayed completely dry.

Next port of call will be to rebuild and pressure test the carb.

I thought karts were supposed to be simple!?! This bloody thing has been fighting me every step of the way. I will not be beaten by a lump of bent Italian steel tubes and a flipping 100cc 2 stroke motor!

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I like to say karting simple but not easy. You’re dealing with something that’s purpose designed to race so there’s a definite amount of annoyance at the beginning.

Didn’t plug get wet at least? Sounds like this is a piston port, maybe a KT with a warlbo carb?

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No the plug didn’t get wet. On the first turn over with the plug out I got what appeared to be a light mist of fuel spurting from the spark plug hole. After that nothing.

The engine is a piston port. Tal-Ko BT82.

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13

So…if you’ve done all that then it could only be 4 things (assuming the engine isn’t shot)

  1. Advance
  2. Opening/closing pressure of the carb
  3. Initial carb setup (high/low screws)
  4. Electrical: spark plug, coil, cap etc…
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I’m going to order a rebuild kit for the carb. Rebuild, pop-off test it, check the ignition advance and try again.

The spark was good, so I’m happy with that side of things.

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Ah, you have a TKM. Has the engine been recently checked over? Ideally you want to at least check for air leaks if not. Carb gasket, crank seals, crankcase halfs, base gasket.

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It was a used engine and I’ve no idea on when the last rebuild was.

I really wanted to get it running and give the kart a shake down before sending it off to be serviced and rebored into a senior engine.

I’ve had the barrel and head off to inspect myself and the top end seems fine, at least good enough for it to run if not perform at peak output. And at that time I replaced the piston rings, base gasket and the carb gasket. As I mentioned in an earlier post, it has really good compression.

Would the crankcase halves gasket and crank seal make that big of a difference? They would only pull in a minimum of extra air if they were past their best surely, only slightly weakening the mixture.

Due to the cost of the engine service and rebuild, I really wanted to get the thing driving and see if I will really enjoy karting as much as I expect. Then I can go all in and book my license test and enter a race.

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The crankcase half leak is pretty rare I probably should have left that out.

Crank seals go hard and a very common issue. If they leak, it will make it hard to start and/or keep running. It will lean the engine out and as a bonus, if the leak in’s bad enough it will prevent the pulse to the fuel pump in the carb. In which case even if it does fire up…. It will shut down pretty quickly.

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Time for an update:

I started the wretched thing!

After life getting in the way. And a small families worth of outdoors equipment (bikes, tents, etc.) accumulating in the garage and quite literally getting in the way, I mostly didn’t touch the kart over the winter. I’m very much a fair weather kart tinkerer.

Two days ago I drained the fuel tank and got myself some fresh super unleaded.

I adjusted the ignition timing thinking that was the stumbling block. Span the rear wheel. Nothing. Nothing except compression.

So, adjusted the timing back the other way to pretty much where it was before. I wound the carb jets all the way in then reset them inline with manufacture recommendation: low jet 2hrs + 30 mins, high jet 17 to 19 mins.

Point of difference here is that previously when setting up the jets, I took the view that the clock face has 12 hours. This time I took it that the clock face has 60 minutes!

Time to do this again. I stick a cable tie in between the throttle arm and the stop. Let’s do this! Grip the back wheel and give it everything I’ve got. Here we go!….. Nothing.

Arrrggggghhhhhhh!

Right, you have been living under my roof for more than three years now. I’m not going to live in an abusive, one sided relationship with you any longer if you aren’t going to give anything back.

I bend the cable tie over to give a bigger throttle opening. And add couple of drops of petrol down the spark plug hole just to help things along. Grip the wheel again. Slowly turn the wheel to just past TDC. I mutter under my breathe: “Start ya bstrd”. I give it everything I have left.

Holy ****! It takes off. The wide throttle opening has it revving its nuts off.

I can’t believe it. That was easy. Why wasn’t it before!?

I pull the cable tie out and give it a quick rev up and down. Seems good.

I look at my palms, the left one is black, covered in rubber. The right one is half black. And half red. The wide open throttle caused the engine to rev so quickly that the rear wheel took half the skin of the palm of my hand.

At least it works.

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19

That’s awesome! Good job not letting that abusive engine wreck your life! :wink:

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I broke my finger once hand starting an engine. Turns out the ignition was way advanced (something like 3.0mm) and no, it wasn’t be that set it :joy: