Modena kk1 issues

We have a modena Kk1 with some weird issues. We just cant seem to locate the problem.

Kart was running awesome for a bit then one day take it to the track and it wouldnt want to rev past 7-9000rpm. Not matter what we did, it would just bog down like it was choking or hitting the limiter.

Things we checked: spark plug(first thing) , silencer, coilpack, fuel, carb.

We then assumed well lets get the top end and bottom end done as it was time for one anways. The shop then said hey give me ur motor and ill give you a newer modena with the updated piston with a fresh rebuild on top and bottom end. Swapped out the motor and took it out…same exact issue. We are going crazy here. Taking it to the shop on monday Nov 4. Just wanted to see if someone has any ideas before we do that.

Wow that’s a good one.

What exactly was swapped in the swap? Just the engine? Ignition as well? Carb?

I guess it could be a poor ground but that would show up on the rev counter.

Water in the fuel?
Tired or gunked up fuel pump?
Cracked reeds?
When you say the carb was checked… what was checked exactly?

Ted,

James is all over this one with most of the same questions I would ask. Weird to have the same issue across two different motors. A few questions I have, more or less in order:

Does the motor exhibit this behavior on the stand (no load), as well as under load on track?

Is the choke on? (black lever flipped up)

Is anything obstructing the airbox/intake?

Was the fuel system swapped over from the previous motor? If yes, have you tried replacing the fuel pump, and/or verifying that all of your fuel lines are properly plumbed?

Were any electrical parts swapped over from the previous motor, including coil, stator, coil wire/plug boot? If so, have you confirmed that all are affixed properly?

Are the floats working properly, and is the needle seating properly?

Is the slide opening properly when the throttle pedal is at 100%?

Have you inspected the reeds?

Have you inspected the piston or cylinder for unusual wear/damage?

I would start with these, and see where that gets you. I’m curious to hear if the shop you take it to finds the issue, and what the cause was! Best of luck!

A bad coil would stall it after running for a little while. But an engine swap would fix that.

A bad fuel pump or clogged filter would make it go extremely lean. I’d think you’d see that on the sparkplug first, and it would also rev like crazy on the stand.

I take it you checked your throttle cable and pedal attachments such that you’re getting full throttle, right? If you aren’t, now’s the time to fix it.

The other thing that could be restricting you, and where my money would be based on the symptoms, is a plugged exhaust. Exhaust throttling will restrict power the whole way up and can stop it from revving at all.

Kart would not rev on the stand or on the track. Would not rev past 8-9000.

But we still havent tried. We took it back to the shop and he will figure it out. Too busy with work. But the mechanic said its gotta be something stupid. Cus the only thing that was not changed was the silencer and throttle cable. So we are thinking its one of those.

Between the time when the engine ran OK and the time that it didn’t, was the air box or silencer removed and was the open port in the engine plugged with a rag or paper towel? Perhaps there is still a rag in the air box or silencer. Try removing the chain to see if the axle spins freely.
Also verify the slide in the carb is completely opening. Best of luck.

A busted silencer would do it for sure… it would make it flatline.

So originally how this all started was, my buddy changed out the spark plug and didnt realize the cap was meant for shorty style spark plug. He took out and started doing what its doing now. He then put old plug back in but it kinda only temporarily fixed and started acting up again. He changed the reeds as they were cracked then so new reeds, same issue. Rejetted, same issue. NEW MOTOR. SAME ISSUE lol

I was joking with my buddy when we went karting and told him that it would be funny if it did the same thing with the new motor lol.

Would it work if we disconnected the silencer and ran an open pipe? Cus we did and no success but im not sure if the silenener would help or not

I’m not sure how much your engine depends on having the silencer in place. The pipe on its own should produce a back pressure wave but might need the assistance of the silencer. The modena Kk1 site lists a contact phone number. If you haven’t tried them, I’d give them a call. 301-667-1320.

It should still rev up on the stand better than it has. Track, different story.

When you figure it out let us know. I’m super curious.

Yeh its at the shop my buddy got the kart/motor from. Hes just been busy with other karts.

I will post once i get an update. Im really curious as well.

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