popping at the end of the straight

DAMON HIGHT

I have developed a problem of my motor popping at the end of the longest straight . It sounds like a lean pop but I ran jets fatter and fatter until I couldnt drive the kart off the turns beacause it was so rich ( using a 175 jet where I would usually use a 162). It seems to happen more on the first lap or two and then will go away but sometimes it randomly shows up every four or five laps or so. It will occasionally blow the power valve off. I tried my backup carb with the same results. I bought a new fuel pump and gas line from the tank to the carb and still had the same results. Someone said it could be the battery and I plan to replace it. I tested all day tuesday and never found the problem in a dozen sessions.The pipe has just been recently repacked and there is only about 4 hours on the motor since its last rebuild. I tested the pulse line for leaks and found none, it was replaced with the rebuild and looks fresh. I probably wont be able to test again before my next race and I am hoping to eliminate the problem. I am of course concerned about damage to my motor but I cant seem to nail the problem. Any suggestions would be much apreciated, Damon

Bob Wilson · Posted: Thu Nov 25, 2004 8:14 pm Post subject:

Definately try a new batterey. It does sound electrical. Do you use an Iridium plug? That will help in a low voltage scenario. Also check your float level. It seems like every time you re-build a Rotax, a new personality emerges from the engine. Good Luck!
_________________
Bob Wilson
SPS Racing

DAMON HIGHT · Posted: Thu Nov 25, 2004 8:34 pm Post subject: Thanks for the reply

Thanks for the reply. Yes, I do use the Iridi$$m plugs and tried a brand new one to cross that off the list. I will check my float level that seems like it could possibly cause the problem if the bowl ran dry. I have a dellorto primer from green flag motorsports and after reading your post I checked what it said. It says to adjust the floats so they are parralell to the flange and that normally they should not need to be adjusted. I dont doubt that they may need to be adjusted i just dont have any experience setting them any other way than this. I guess I would try adjusting them to hold more fuel and if so should there be any method to my madness when I do. I took a good look at the reeds and they look fine. I think the only thing left is the ignition. Any one know the typical symtoms of Rotax ignition failure or are they allways different? Thanks again, Damon

Mark Owen · Posted: Fri Nov 26, 2004 10:53 am Post subject: popping top end

This may sound simple, but check the intake inlet to make sure you didn't install it backwards in the air intake box. Larger holes go to the outside. This seems simple but I experienced the same symptoms you described and chased many high dollar solutions before a 14 year old young man discovered the problem.

Cody Tracy · Posted: Fri Nov 26, 2004 5:22 pm Post subject:

ours did this same thing. it was crankshaft seals. we replaced them and it ran great.

alex vendler · Joined: 14 May 2002 Posts: 49 Location: Venice, Ca.

I had a an issue like that and discovered that I was running too rich. You stated that you blew your power valve off and that means a popping on the exhaust side, no? I thought that too lean caused popping on the intake and would blow the carb off instead. Try running a smaller jet and see if it helps.

Alex

Ron Arsenault · Joined: 06 Oct 2002 Posts: 32 Location: Canada, Quebec,

Damon, as you can see, the symptoms you are having can be caused by just about anything. A good maintenance of your motor will definitly contribute to a better running one:

1) Always clean out your carb after a meeting (end of the day, every day)
2) Make sure the fuel intake valve seals properly (See your dealer for explanations)
3) Make sure the floats are well adjusted (See your dealer explanations)
4) Make sure the Carb is well secured to the intake manifold. You should NEVER be able to turn it by hand once screwed in.
5) Make sure the water temp is proper Operate 50-60C
6) Make sure the powervalve is clean and operates smoothly
7) Make sure your exhaust pipe is on straight and seals well on the manifold
Cool

Make sure the motor seals seal well. You can check by doing a leak test on the motor.
9) Make sure you are jetted for the moment. You can use MaxJet (http://maxjet.ca) with a reliable weather station. If you need to go more that + or - 1 jet from this, there is a problem somewhere.

Hope this helps.

Regards, Ron.

DAMON HIGHT · Posted: Sun Nov 28, 2004 9:22 pm Post subject: popping

Thanks again for the replies. I was using the Maxjet with the race jet weather pod and I had the symptoms with jetting as suggested and almost every jetting combo i could think of on two carbs with the floats adjusted as suggested im my Dellorto primer. One carb had one race and the other was just completely gone through. I honestly dont believe the problem is the carb. I could see it being the seals but I would not know how to leak test the motor. Is there an easy way to do this or does it have to go to the shop? Thanks again, Damon

david khan · Posted: Mon Feb 07, 2005 9:14 am Post subject:

i have this same problem and i was wondering what the ultimate solution was. i was at moran this weekend and ran a 172 jet and still had occasional pops at the end of the straightaway. rpms were never over 12,700
the pin was set at position 1
i was running motul 800 40:1

tia
dk

DAMON HIGHT · Posted: Tue Feb 08, 2005 4:46 pm Post subject: No mo popping

It was the battery. Ran like a champ with a new one, Damon Wink

Mark Spikes · Posted: Tue Feb 08, 2005 8:51 pm Post subject:

Ron,

When you say, "clean out the carb", what does that entail? Disassembly?

mark