Quick question, last week on in the pre finals my sons karts was really sluggish and on the start was bogging down so much so that 4 guys passed him and he was left behind, couldn’t make enough power. One of the tuners said the carb was running lean so he adjusted the needle. Come finals he had the exact same problem, out of the pits on the warm up lap not so bad but when they lined up for the rolling start and he got on the throttle the kart just bogged down and everyone passed him. He retired the kart 5 laps later as he could not make enough power to catch up. Any suggestions? Motor was rebuilt 2 races ago, put the carb on the leak down tester and it goes to 9 and holds there……
Thanks
With my similar KA when this happens to me, its usually too rich and possibly the plug is fouled. With that said it could be lean too as that is a symptom of lean. If this problem happened after a rebuild I would look at what is different from when it was running fine. Was the carb redone as well? If it was, I would give it a once over. If it wasn’t it probably should be. Set your needles to your baseline settings and go from there.
After the rebuild it ran fine (last race) in the morning we couldn’t get it started, missed practice. Brought it to the tuner and he changed the plug and got it running. Carb was rebuilt at the beginning of the season. I’m going to rebuilt it tomorrow since I have a spare kit lying around. Just so frustrating for my son as we just can’t get a handle on this VLR. One weekend it runs, next weekend totally different.
Carb setting issue. Either too lean or too rich. The KA will ‘lean bog’ so if it’s too lean it won’t accelerate, not sure if the VLR has the same thing.
How old is your son? Is he able to tune the carb on the track? This is the exact situation where that skill can be helpful.
I am surprised this is happening. It was a problem I always had with the Yamaha KA100 but the KA is almost set it and forget it. I believe they even use the same carb too. It sounds like you have easy access to your engine guy, I would consult with them for advice. Make sure you have have fresh fuel and a consistent oil mixture.
He’s 15. I had a driver go out there 2 weeks ago and set the carb, ran fine, but now it dosen’t. My younger son (13) we have zero problems with his VLR. This one is a total mystery to me
Have you tried swapping the carbs? It’s very possible to have a carb that is just “off” or isn’t particularly matched well to the engine. I have had KA carbs that ran like trash with one engine but ran great on another.
Also the carb is something you’re going to have to tweak on a little bit everyday. Ambient temp, humidity, etc. all will require a little tweak to keep it running well. That being said, it SHOULD run reasonably in most conditions, so this is a bit unusual.
We had a karter with a new KA that complained about having no power and he couldn’t get over 13k rpm. It turned out that carb was defective. You might want to try swapping carbs just to see if that fixes the problem.
1 Like
Thanks guys. I bringing 2 carbs with me this weekend. Fingers crossed
1 Like
I think I may have found a problem. I purchased 2 motors, one I had shipped and both needles broke so I ordered 2 new needles. The place I ordered them from may have given me a high and low for a different carburetor. The VLR needles do not have a an H and L on them I think those belong to another model tillison, also the high needle has a finer thread. Now that was on my spare carb, the one my son raced with, it looks like he’s running 2 of the same neddles!
1 Like
Those are definitely different. The threads on the needle with the H don’t look good, I hope they didn’t screw up your carb body.
So I thought the KA and VLR carbs were the same but they are not the same but similar or at least they are different part numbers. On the KA the H and L needles are not labeled either and they are each different. I used an engraver on mine when new so I don’t mess them up.
I have mixed them up before, easy mistake and would definitely cause it to run poorly. Good find. Hopefully that fixes it.
Yeah the tuner didn’t see the difference and put the one with the H in my carburetor, might be junk now, but I was able to pull it out and put the correct needle in there and seems to be ok. I’m just going to buy 2 new needles and start from there