Clone popping issues? Read here....

slonomo

Hey everyone. Thought I'd post my experience with popping sounds from the exhaust.....

This condition is usually caused by the following: (on new good condition engine)

1. Too much valve timing (exhaust valve open during combustion) This would actually result in exhaust popping sounds during acceleration or cruising. This fix for this is to simply back off the timing.

2. Lean condition. Some think the sound is coming from the exhaust but it's actually coming from the carb. So it's a backfire. More fuel will cure this problem.

3. Too rich. Running with too much fuel will allow some of the leftover fuel/fumes to ignite in the exhaust pipe after combustion, or during deceleration. This is very common. To cure the popping sounds, lean out the fuel mix or back off one jet size.

In my case in the last two days it has been #3. So here's what I know. I have the cam, rod, 1.3 rockers, pushrods, .010" milled, port and polished head. So I worked my main jet up to 1.25 mm (drilled) and it ran fantastic. Had lots of power up top. However, the exhaust was popping every time I lifted off the accelerator. Sometimes it was obnoxious. I think a better exhaust would tame this down, but right now I'm stuck with the Vegas Carts loud performance spark arrestor.

So, after much research on the net, I have discovered that racing engines when properly tuned usually pop from the exhaust on deceleration. Wow, never would have thought this. Ok, so when you watch a motorcycle racing event, look at the exhaust when they slow down for a turn. Yep, flames. Ok, so my engine was running great but popping....guess it was properly tuned.

I did some plug readings. Black and sooty, not real thick, but def on the rich side. So I backed off one jet. Still black. Still popping. Backed off another jet size. Bang! This was it. Almost no popping, and very little soot, and still easy to start. I feel like I just won a war. This was killing me.

What's the down side? Well, after backing the jet down, I can tell the power up top in the rpm range is not as strong. So I obviously leaned out the power up high, around 4500 rpm. So my cam that loves to make power in the 4500-6000 rpm range is now limited by the fuel. For now this is ok.

My question is, if I'm running on the leaner side at 4500, am I going to damage something? Obviously if I'm racing the engine at that rpm for extended periods the answer would likely be yes. But I'm not, prob cruising at 4500 rpm max once in a while.

With the stock cam, the cart never popped. With the cam and the stock rod, the cart never popped. With the billet rod....popping. So I'm guessing that the billet rod is so much more rigid at rpm that the compression is more accurate and causes the popping?

Any input appreciated. If you have any similar experience please share....

BGW

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Tinken

At which rpm is it popping and which jet did you lean?

slonomo

All rpm above 3000 rpm as far as I can tell, I think it even pops at lower rpm but not as noticable. I had the main jet to 1.25mm I believe. Backed it down to 1.0 mm. Not sure what a stock 440 jet is since I drilled it out lol.

slonomo

Here's a pic of race bike with the back fire flames. This is from leftover fuel in the exhaust igniting, which is what was happening to mine.

Here's a video of a bike with popping....

Attached Images

bike flames.jpg (37.8 KB, 0 views)

LarryDrivesU

My similar popping issues whether low rpms or max 4500 rpms and backfiring when decelerating were eliminated when I added a 1.5" pipe to the 1.25" header pipe going under the axle to a 1.5" inlet and outlet small car muffler plus reducing connector to connect 1.25 Vegas cart silencer as the tail pipe. I braced the header pipe to the axle which reduced vibration. The tail pipe points to the driver side behind the left rear tire. The muffler is supported also. It's as quiet as stock.

04 ezgo txt 8person, VC 460cc stock, 10"with 21," comet, 28deg driven

slonomo

Nice job Larry! I spent 4 hours last night (til 2:30am) adding an atv muffler to mine. I have to say it's WAY quieter. And yes, it completely erased any left over popping sounds also. I think we are on to something here. I think I will rejet the carb and see what happens.

army

No problem with exhaust restriction choking the engine back at mid to high RPM for either of you?

LarryDrivesU

The top speed stayed the same at 32mpg . Stock VC 460cc with 6:1 gears. I don't have a tach however, the acceleration feels the same as it did when I had only the header pipe with Vegas cart silencer. I purchased the 460cc for more acceleration than the robin 350cc I had with the 6:1gears. I'm happy with about 33 1/3% more acceleration from a start with the 6:1gears. I can now accelerate my 8person taxi as fast as the 6person stock taxi carts and I didn't lose my top end. I didn't want to put on taller than 21" tires because, then I would need v-twin horsepower. I didn't want to spend that much for a little more acceleration. I would have been happy with 25% more acceleration.

aladd6

Anybody got pics of the idle adjustment screw. Think I am adjusting the wrong screw. I get back fire through exhaust no matter which way I adjust the screw that I thought was the idle.

army

that's the spirit old chap!