Low end bog

[wvspeedfreak]

I need some help figuring out a bog.It happens right off the line and bogs for about 10 feet or so and then takes off great.I had this problem when I first put this engine together and it ended up being a weak torsion spring.I replaced the torsion spring again today and it didn't help at all.
I am leaning towards it possibly being a jetting issue and was thinking about changing the needle position to see what happens.I am open to suggestions though as we are hitting the dirt drags this weekend and I would like to put the launch back in this thing :D

[dericsdad]

our bike started doing that on the starts last race, and i found a melted/flat roller weight. Make sure the variator slides aren't sticking/hanging up also. The air speed screw adjustment is critical on starts as well. Dan.

[hotquads1]

if you got rollers that are .5 lighter give em try just for starters.
marc

[wvspeedfreak]

Thanks.I will try some stuff today.

[wvspeedfreak]

Ok,here is what I did.I went from 5 gram rollers to 4.5 gram ones and made a slight air screw adjustment.The bog is gone and it comes out of the hole like a rocket.However,I am not getting a full shift on the variator.I did the magic marker thing and it is only going about 2/3 of the way up now.It has a brand new 1500rpm Koso spring in it right now.With the 5 gram rollers it was getting a full shift.What should I try now?

[THARNESS]

I would try alternating the 4.5 and 5 gram rollers and see if that helps. I would also try "breaking in" that new torsion spring for about 20 mins and then doing the magic marker test again before I did too many adjustments.
Good luck.

[hotquads1]

Hi Jason,
splitting the roller weight may put in right on, also condsider warm weather may be making your jetting richer , that would inhibit the max rpm which is needed to push the belt further , If you like the holeshot your gettiing then ( check plug reading at full throttle chop) try leaning the main jet to compensate for the hotter weather , this should increase rpm and make belt travel higher even with same rollers. As Tom mentioned once that new t-spring is broken-in it will shift sooner and further , that should happen in only about 30 minutes run time which has probably been reached. Keep in mind the power you make on a 60 degree spring Day will not be matched on a 90 degree muggy summer day , the oxygen content in the air is lower due to lack of density, jetting helps regain proper mixture but will not help carry more oxygen into the cyl. good luck
marc

[wvspeedfreak]

Thanks again guys.I split the roller weights and the take off was still good and the variator shifted farther out.It still isn't what I call a "full" shift but it is close.I am leaving it as is now because like you guys stated,if the torsion spring gets a tad softer it will be shifting all the way out.It is about 92 degrees and muggy here today too.

[dericsdad]

Sounds exactly like the problems we just had last night trying to tune for todays race! Brand new 1500 koso torsion spring (only 2 motos) and we were cutting out badly last night on top end. Finally went down a size on the main, and it was much better, but was only reving to just above 10k. Today it was hotter than it has been, but a little less muggy, and it ran great! Still need to tune a little more on the clutches though, cause he usually holeshots but today we could only manage 2nd or third on the starts. Finished 2nd and 3rd overall in both classes though.

Marc do you have experience with the DR Pulley Variator? I think it is time for us to replace our 2 year old stock one that has been turned//modified and resanded several times.

Thanks, Dan.

[bulldogfallon]

The Dr. Pulley Variators are nice....Seems like the guys that pick them up are really happy with them.

Have you guys tried working with the ZTR springs?

[hotquads1]

Originally posted by dericsdad
Sounds exactly like the problems we just had last night trying to tune for todays race! Brand new 1500 koso torsion spring (only 2 motos) and we were cutting out badly last night on top end. Finally went down a size on the pilot, and it was much better, but was only reving to just above 10k. Today it was hotter than it has been, but a little less muggy, and it ran great! Still need to tune a little more on the clutches though, cause he usually holeshots but today we could only manage 2nd or third on the starts. Finished 2nd and 3rd overall in both classes though.

Marc do you have experience with the DR Pulley Variator? I think it is time for us to replace our 2 year old stock one that has been turned//modified and resanded several times.

Thanks, Dan.
,
Hi Dan,
The symptoms your having are a little different than speedfreak, cutting out on top end would be a lean main jet or ignition related, the fact that it ran better when it was hot and muggy points again to , too lean of main on the day before corrected by warmer weather which requires smaller main. Pilot jet should only effect the idle to 1/4 throttle performance. I like the Dr pulley Variator and clutch , I have seen a couple of the variators with center bushing working loose , but cant explain why , the ones on my bikes are working great and have had no issues. I assume you are running a tach since you gave us RPM reading , try a couple of main jets while taking tach readings to choose best one, but watch plug readings to keep a safe tan color , if it is almost white , that is too lean for me.
marc

[dericsdad]

Thanks Marc, I had to re read what i typed last night, and now i know why you were talking about our pilot jet... Sorry, i was a little tired last night when I typed it. I edited it. We dropped the "main" jet down one size to help the top end. Haven't touched the pilot or needle yet. May move the needle around a little to see if we can clean up how it runs from 1/4 to mid throttle. It sounds a little fat there to me. It is affecting his starts a little. Thanks, Dan.

[rider1234]

Can someone reply how the air acrew effects take off and how to determine which way to go with it. Does the needle clip position effect it as well? Thanks alot

[hotquads1]

The air screw directly controls the idle mixture curcuit and off idle , it also slightly effects the other curciut mixtures. On a 2-stroke the Airscrew is turned in to richen the mixture and turned out to lean the mixture , goal is to obtain clean idle with sharp response . In the case of a full throttle take-off, the air screw would merely benefit in the effort to reach highest rpm with quickest response , it would only be a factor for a moment then needle clip for a moment and ultimately the main jet is in play once Throttle is wide open and rpm have climbed.
marc

[rider1234]

So if im having a problem with the bike taking a few seconds to gain its RPM's it may need a needle clip adjustment?
When the bike is on the stand and I punch it, it takes a few seconds to rev out. seems slow and gradually revs out. Do you think i am on the right track by adjusting the needle and pilot?

Thanks

[hotquads1]

my first guess is your roller weight is a little to heavy for your current t-spring Pressure. If you havent allready , replace t-spring and check rollers , before tuning carb , it can be very frustrating if you dont. What carb do you have ? what is current jetting ? what size engine? I dont think a needle clip adjustment will correct your issue if it is as you stated "takes a few seconds to rev-out" this is more commonly a problem with shift occuring to soon .
marc

[dericsdad]

Marc,

If you haven't read my post in the polaris mini section, we found the real problem with our 90. The needle jet (the thimble looking piece the needle attached to the slide goes down into) was worn big from the needle vibrating around in it, and was flooding out the engine! that is why it was rich on the pilot. We replaced it last weekend, lowered the clip on the needle, and it is a rocket ship again! Just thought I'd post it here for anyone chasing jetting/bog issues. Thanks, Dan.

[wvspeedfreak]

Ok guys,it has been a little while since I made the original post but I seem to be back to square one.....

This bog (read my original post for the details) started when I installed a B-52 top end.Like I stated previously,I managed to pretty much eliminate it with a roller change.This week I took the top end apart to freshen it up,just honed it and replaced the rings.Now the bog is back as bad or worse than it was before :confused: From a dead stand still,if he takes off like you would when the gate drops,the quad takes off slowly for about 15-20 feet then it is like you flipped a switch and it goes.It pulls hard through the midrange and top end.It is driving me crazy :scary:

Right now here is my set up:

90cc air cooled
B-52 top end
Keihin 24mm carb
Koso intake
Trinity pipe
Koso compete rear clutch
1500 Koso t-spring
2000 Koso clutch springs
Alternated 4.5 and 5 gram rollers
Stock variator
Malossi belt
19 tooth front sprocket
30 tooth rear sprocket

Any help is greatly appreciated!

[neveready]

could be a few things. Which stock variator do you have? What is the tranny ratio? high or atandard? Sounds like it could be a jetting issue. How does it react if you hold the brake and give it about 1/4 throttle? does it launch better if you load it up with the brake and gas or if you just stab it from idle? sounds like it could be lean on the pilot. we have seen many with this similar problem and it can be extremely frustrating but if you make adjustments one at a time and work at it you will get it, and right about then the weather will change and we get to start all over again:D

[wvspeedfreak]

It is the variator that came in it from the factory is all I know.I have only changed the rollers in it.It does not have the high ratio transmission,it is standard.It takes off better if you just stab the throttle from idle instead of loading it up on the brake.
I did move the needle one step richer but that didn't help so I put it back where it was.

[bvmracing]

You should check the carb intake flange.
Take it right off machine and squeeze all around looking for cracks.
My buddy had exact same problem.

Good luck!

[wvspeedfreak]

Well,after talking with neveready I may have found some of my problem.I totally forgot about installing the Malossi belt at the same time I put the B-52 on.Evidently the Malossi belt is wider than the stock belt and it isn't going all the way down in the variator.Once I get that squared away I will see what happens.I need to find a shim for the variator now or put the stock belt back on :p