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compression?
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Posted by: Trx4Life

Hey if I have a bad ring or a bad spott in my head gasket is it still possible for the bike to run ok? After rebuilding it I had it jettted and it ran like a bat out of hell. Then the next day it never would run the same. I thought it was beacuse the weather was kinda nasty when I jetted it, so i rejetted it a few times brought it to pros to have it jetted. It just never has run the same, I noticed a little smoke the other day and was just wandering if the head gasket or rings might be worth looking into. The bike runs real good just not makeing the power I know it should. Please help.

Posted by: Prey

they will run alright if they are down on compression, i would definately do a compression check, a compression checker is like $25 and well worth the money, you can buy them at basically any auto store.

a question though, you posted in the predator forum with a TRX4Life screen name, which machine do you own? if you own a 450R you have to bypass the decompressor on the cam to get an accurate reading from the compression check

i could be wrong, as i have personally never had the valve cover off of my predator but i dont think there is a decompressor on the cams

Posted by: 1fstpred

There is a decompression device on the exhaust cam, on the predator. The manual takes that into consideration during the check. I would have to look up the acutal numbers but the number 90 comes to mind.

Posted by: Trx4Life

I have a pred and the wife has a yfz. The name is before i came to my sense. Now that 90 is that for a 12.5 to one piston? To check it i just put a wranch on the gear on the side and roll it slow to top dead center????

Posted by: Prey

quote:
Originally posted by Trx4Life
I have a pred and the wife has a yfz. The name is before i came to my sense. Now that 90 is that for a 12.5 to one piston? To check it i just put a wranch on the gear on the side and roll it slow to top dead center????

maybe i am out there on this one, but why are you bringing the piston to TDC for a compression check??

Posted by: Trx4Life

No im the one out there never done it before. Thats why I was asking

Posted by: 1fstpred

I still need to check on the 12.5:1 compression numbers but that 90 was stock. when you do go to check the compression just use the starter and bump it over a couple of times.

Posted by: Trx4Life

yea i bought one last night and kinda read the papers and figured it out. Its around 108 well inbetween 105 and 110 that sound close?

Posted by: Prey

quote:
Originally posted by Trx4Life
yea i bought one last night and kinda read the papers and figured it out. Its around 108 well inbetween 105 and 110 that sound close?

how is it idling? smooth, or a little ruff?

your running the same reccomended fuel for a 12.5:1, and the airfilter is clean?

guess i am a little stumped

Posted by: Trx4Life

idles good has a little hesitation if you punch it from an idle other than that it runs good.
im running stright c12 in it.

no box so i clean the filter every time i ride it.

Posted by: 1fstpred

Sounds rich to me. What does your plug look like?

Posted by: Trx4Life

its kinda white ish some one told me it looked lean

Posted by: 1fstpred

kind of whiteish? Look at the white center all the way down into the hole. It should look clean to a grayish color. NOT BRIGHT WHITE. Then look at the arm, it should not be black nor should there be a white tint to it. Should be a light brown. Look real close at the center electrode. Verify that there are NO specks of metal attached to it. That would mean you are way lean and parts of the piston are burning off and attaching to the plug.

Let us know

Don

Posted by: Trx4Life

well we went ride yesterday and I check it in the middle of the day it looked kinda whitish. i was always told as long as it wasent poping it was alright. I know it has a 140 main in it right now not sure on the needle but i know it is a perty thin one. i know when i was trying to jet it my self with a 160 main it wouldent even rev up about half way into the throtle it would start sounding like it was hitting the rev limiter.

Posted by: Prey

quote:
Originally posted by Trx4Life
well we went ride yesterday and I check it in the middle of the day it looked kinda whitish. i was always told as long as it wasent poping it was alright. I know it has a 140 main in it right now not sure on the needle but i know it is a perty thin one. i know when i was trying to jet it my self with a 160 main it wouldent even rev up about half way into the throtle it would start sounding like it was hitting the rev limiter.

i guess i am beggining to think you are way too lean,

i know they are not the same but, with my air box open (provided yours is) i was running a 175 in the BSR carb, without cams and head work

in my 06 450R with hrc kit and sparks BC pipe and filter, i am running a 172 in the FCR

also are you running kehein jets or another brand, just because a jet says 160 for example does not mean it is the same size as a 160 from another maker. the dynojets run smaller (meaning you have to use a larger jet to get the same amount of fuel) than everyone else for example

Posted by: Trx4Life

I thought with the smaller needle you dident need as big a jet. What clip on the needle were you running????? I think if the top one is 1 im on 5 or 6

Posted by: Prey

3rd clip on both the 450r and the predator

Posted by: 1fstpred

I agree it sounds like a lean condition to me. With your mods in Tucson, AZ. I was running a 185 mikuni.

Posted by: Trx4Life

yea but you think the fcr would make a difference in the jetting ????

Posted by: Prey

quote:
Originally posted by Trx4Life
yea but you think the fcr would make a difference in the jetting ????

if not 185, you need to at least be in the 170's on that main IMO, i thought the preds came stock with a 150 mikuni jet?

Posted by: Trx4Life

alright i think 170 is the biggest i got ill try that and drop the needle all the way down.

Posted by: 1fstpred

Only do one adjustment at a time. change the jet try it then the needle if it needs it. IMO

Posted by: Prey

quote:
Originally posted by 1fstpred
Only do one adjustment at a time. change the jet try it then the needle if it needs it. IMO

yep good advice