Lost top end of powerband...

[feedmelies]

Here's another one for you guys.

 

Okay, I have had my quad for a couple years and it has run beautifully. So this summer my family went on vacation at a new place and I re-jetted it as best I could before heading up to a higher elevation. I did pretty well guessing on the jetting, but it ran a little sluggish wide open. I figured then it was just because of minor jetting issues. I guess it still could have been.

 

After the trip, I put the right jets back in, cleaned the carbs and all. Then I started it up and ran it down the street. Low end was fine. Mid range was fine. But when I hit the top end of the power band, the part where it is supposed to try to rip my arms off, I had nothing. So I fiddled with the air fuel adjustment, setting it back to two turns out from closed and went from there. I couldn't fix the problem, so I figured some dirt must have gotten into the jets. I re-cleaned the jets, assembled, and bam. Worse than before! Terrible throttle response, wouldn't rev that high and sounded terrible. Plus it didn't want to start very easily.

 

I have made sure the jets are correct. I checked compression, a perfect 150 in each cylinder. I changed my spark plugs. Each cylinder is firing. I have gas. I have oil in the case. I was doing all the aforementioned adjustments without an air filter on, so I know the engine had air. I replaced the fuel lines going to the carbs and I know it is getting fuel.

 

So I started looking around my engine hoping for something to stare me in the face. Now, I have a boost bottle. Yes, I know they blow, but it came with my quad and I never bothered to take it off. I remembered what others had said. Boost bottles = cracked intake boots = lean out engine. My intake boots have some cracks on them around the bottle, but they were always small. Maybe the cracks have finally penetrated? Is there a way to tell?

 

My question is this: what do you think is causing my performance problems? Is there anyone out there that has experienced cracked boots from a boost bottle, and do you remember the symptoms?

 

This is bugging the hell out of me, and I have plans to go out to Glamis on the 26th!

 

Thanks for the help guys.

Edited October 15, 2007 by feedmelies

[shee rips]

if your compression is actually at 50 psi im surprised that it runs at all.

if you were running it without an air filter while testing it then you may have sucked in some dirt and pooched your cylinders. that would explain why it steadily got worse.

if i had to guess i would also say you were lean when you rejetted or the higher altitude. how high did you go from where you normally ride and how much smaller jets did you use.

edit: the boost bottle could also be to blame because they are known to crack the intakes or have a wire wear through it and cause the motor to run lean

Edited October 15, 2007 by shee rips

[feedmelies]

if your compression is actually at 50 psi im surprised that it runs at all.

if you were running it without an air filter while testing it then you may have sucked in some dirt and pooched your cylinders. that would explain why it steadily got worse.

if i had to guess i would also say you were lean when you rejetted or the higher altitude. how high did you go from where you normally ride and how much smaller jets did you use.

edit: the boost bottle could also be to blame because they are known to crack the intakes or have a wire wear through it and cause the motor to run lean

 

Sorry 50 was a mistake. I forgot the 1. I have 150 exactly in each cylinder.

 

I was running my quad on the street, so I don't think dirt could have gotten in the carbs that easily. At least I hope not.

 

This place was about 7,500 feet, and I usually run at Glamis. But I put the original jets back in the quad, which (in the past) my quad screamed with.

 

So is the type of behavior I described typical of being too lean?

Edited October 15, 2007 by feedmelies

[Coupelx]

if your doing your test runs with no air filter, there could be your problem. mine falls on its face with no air filter when it its the powerband.

[feedmelies]

if your doing your test runs with no air filter, there could be your problem. mine falls on its face with no air filter when it its the powerband.

 

But in the two years or so that I have had it, small test runs on the street without filters never did any damage. I mean, I only run it one minute tops. Plus, I know my carbs are clean and my compression is fine.

Edited October 15, 2007 by feedmelies

[BANSHEEMANIAC]

put the filters back on and try it. if it aint better, try the choke to see if its leaning or to rich.

[BANSHEEMANIAC]

oh... did you sync your carbs, just asking.

[feedmelies]

put the filters back on and try it. if it aint better, try the choke to see if its leaning or to rich.

 

The thing is that I have always tested it with the filters off and it ran perfectly. I have never noticed a difference between having them on or off. But it cannot hurt to try. I'll also look more closely at how it runs with the choke on. Good advice there.

 

oh... did you sync your carbs, just asking.

 

The slides move up and down in unison. I have never messed with that, fortunately.

 

I am going to the stealership tomorrow to order new intake boots and a crossover tube. Even if it isn't the problem, I need to get rid of the boost bottle and the harm it has already done.

[Coupelx]

the air filter is a restriction, however small, and affects jetting.

[xXBlessedWithDeathXx]

i had that problem today. i have a 2 in 1 carb and after all was said and done it was sucking air after the carb and before the cylinders. i pushed the carb in to much and what i thought was a tight fit with the hose clamp wasn`t. on the carb where it meets the boot is a notch that fits into the boot thats notched. it was pushed in to far causing it to suck air. maybe this happened to you or you didnt tighten them clamps.

[shee rips]

if your airbox is dirty at all on the inside i wouldnt run it at all without a filter, assuming that you run an airbox. i would test with it on because thats how you ride it and it will run slightly richer with the filter on it.

also in my experience a lean motor will rev but wont perform too well under full load.

first thing i would do is get new intakes and crossover tube and see what that does for you. Hopefully that will solve the problem :thumbsup:

[feedmelies]

if your airbox is dirty at all on the inside i wouldnt run it at all without a filter, assuming that you run an airbox. i would test with it on because thats how you ride it and it will run slightly richer with the filter on it.

also in my experience a lean motor will rev but wont perform too well under full load.

first thing i would do is get new intakes and crossover tube and see what that does for you. Hopefully that will solve the problem :thumbsup:

 

Nope, no airbox!

 

Next big step is seeing what new intake boots and a real crossover tube does.

[feedmelies]

I have an update.

 

I took off the intake boots and inspected them. It didn

[feedmelies]

This will be my last update. A poster on this forum that lives near me was kind enough to take a look at my quad. He noticed that oil was starting to leak out of the right cylinder (the one that is emitting the most exhaust) right where the pipe and the cylinder meet. Also, he found that the transmission oil was abnormally low, despite my checking it a week earlier and seeing that it was fine. He came to the conclusion that my engine broke a crank seal and that the transmission oil was being sucked into the right cylinder. This explains perfectly why I lost top end performance