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Discussion Starter #1
today i came back from glamis and it was a blast!!! it was calm for two days then yesterday it rained and was winding but fune to carve the dunes. we went to china wall the day it rained and i took my 87 and it did well for being a stock bike with a slight compression increase. the bike just went up it. then today we went to the same hill again with my 89 250r. now this bike is all stock(except fmf fatty pipe silencer and KNN filter) and has a virgin motor. i rejetted to 162 main jet and left everything else alone. it pulls really good but it seems that when i hit full throttle that it just wont rev higher even though the throttle is pinned! also my 87 made it up the steepest part of china wall in 3rd gear pinned and it didnt even hiccup once. but my 89 goes up and im pinned into 3rd gear nad all of a sudden about halfway up the hill it just starts to bog really bad and even down shifting in first wont get it to pick up the rpm. i also checked the plugs on both bikes before we left and my plug was really messed up. it was all black and i had changed it the season before. so i am thinking that it might be rich. because i remeber that when i had my 157 jet in there it went up most hills in 4th gear!!!but here are my stats so if so one can help me out it would be greatly appreciated!
carb stock 89 carb
main jet is 162 everything else is stock
stock bore and compression
knn airfilter
fmf fatty pipe and silencer
13/39 gearing
and i run 91 octane gas and i mix 12 ounces of golden spectro mix with 5 exact gallons of gas
87 is all stock except knn and ct rebuild but it is stock everything else
i also ride in glamis most of the year so i would like a jetting that is optimal for that climate.
 

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it sounds like you are WAY rich to me.....since you say its a virgin motor, maybe its just tired too.....losts of possiblities here. do your self a favor and use redline oil and ditch GS. i have had nothing but problems with it. doesnt seem to burn clean to me.
 

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did you try changing the jetting? from your description its pretty vague but it does sound like it could be jetting. could need a top end too, whats your compression?
 

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Discussion Starter #4
did you try changing the jetting? from your description its pretty vague but it does sound like it could be jetting. could need a top end too, whats your compression?

well i have the 157 that it had in there before because they recomended to go up atleast 2 sizes in the main jet so i bought that 157 but to me it was lean because of the bogging because it was fine when it had the stock pipe too. and it was running good when it had the 157 just i thought it might be lean do to the bogging(wasnt use to the changed power band with the adition of the pipe) but im going to check the plug after i wash it and also change the jet to the one i had in there (157) i dont think it could be Time for a rebuild it seems to have more resistance than the 87 which has a full motor rebuild and seems to have more pinch at TDC but you never know. i also bought some diffrent oil as well it is smokeless formula so not sure what brand. but where can i get that redline oil? and i will change the jets and see how it does. also hoe can i check compression with out buying that expensive guage?thanks again though.
 

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how expensive is expensive? the simple analogue compression testers can be had for around $30 if i remember correctly.
 

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First of all, you probably have a 158 main as Keihin numbers go 150, 152, 155, 158, 160, etc. Secondly, one jet size up may be all you need, if anything at all. Not every engine is going to be the same. Double check that your spark and compression are ok (and your air filter is clean). Start with a new, properly gapped spark plug of the proper heat range and take it for a rip. If it bogs and breaks up on the top end and won't rev out with the 162, then drop ONE jet size at a time until the top end clears up. You'll get it dialed in.
 

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Discussion Starter #7
First of all, you probably have a 158 main as Keihin numbers go 150, 152, 155, 158, 160, etc. Secondly, one jet size up may be all you need, if anything at all. Not every engine is going to be the same. Double check that your spark and compression are ok (and your air filter is clean). Start with a new, properly gapped spark plug of the proper heat range and take it for a rip. If it bogs and breaks up on the top end and won't rev out with the 162, then drop ONE jet size at a time until the top end clears up. You'll get it dialed in.
okay now that your talking about spark plugs i wanted to know if it is fine to use the BR8ES plug and where should i gap it too?.020 ect. and any where you guys recomend on getting the compression gauge and what would be an ideal psi for a stock motor? ill find that jet because if i remeber it is a 157 unless they gave me the wrong one...... i also have the stock one but i guess i will go buy the other jets they have so i can tune it up really nice. and i will do a full check after i wash her she is pretty dirty and working on her like that might lead to something falling into the engine or carb. but is there any way i can tell just by revving the engine also? because i cannot ride right now do to the place i used to ride at is closed and i can only go to glamis and thats 2 weeks away... well thanks for your help it is really appreciated especially for getting my baby running right.
 

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Proper jetting must be done riding the bike. Everything changes when the engine is under load. As for which plug, I'll have to check my Clymer manual when I get home but I would run whatever came stock in the bike. Same for the gap. I'll have to double check that. Definitely wash it up nice before you do any wrenching on the engine, carb, etc.
 

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Discussion Starter #9
alright thanks alot show and go. your a big help.
 

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Whats the altitude where your at? Here its 2200ft. I usually ran between a 148-152 when I had about about the same set-up you have now. The stock ignition is weak on a 250r so gap it down to .018...
 

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Discussion Starter #11
alright ill gap the plugs to that. i ride typically in glamis so i really dont know what that is. maybe sea level or a hair above or below not sure. im going to try that and then see how much the performance jump is with the gapped plug and new jetting.
 

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Discussion Starter #12
well just finnished getting the r's ready for glamis this week and i was dumbfounded by ehat i found in my 89. i thaought the jet i had was a 162 or 163 but it was a175!!!! i also looked at the previous jet that was in there and it was a 168!! man was i of. those guys at chaparral dont really know how to give you good info. ewll no im going to go see how she does with a 158 and 0.018 plug. hopefully good. and anything i should look for if it runs lean?? what are the signs of running lean? thanks again.
 

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I bet you're about right where you're at. Maybe a 160. I had the same setup when I got my bike...stock carb, stock motor, FMF fatty pipe, filter. I was rich still at Glamis running a 162. If you're too lean it'll run hot and have a "pingy" sound to it. In the dunes, I always prefer a tad rich rather than a tad lean. Out there, you're just on the pipe so much. And I'd rather scrub a bit of power than seize a piston in the middle of the sandbox. Been there. Getting towed out of the dunes behind a sandrail SUCKS!
 

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pick up a couple jets from a local dealer, then you'll have them along. it doesnt hurt to have a nice basic jet kit. take 15 min to dial it in at the dunes.
 

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Discussion Starter #16
yeah you are right. with the 168 it was running great but it still drank too much fuel(this was the initial jet i got when i purchased the pipe.) but i had some bogging effect and i thought dam still too lean but nope i think it was rich. so you guys think 158 is good? i think i will put another new plug as the one in there was still new but had some use still had all the colors from when i put it in. so i will put a new plug in and then ride it and hopefully can check and see if it is running lean. and by whit to you mean the electrode and little arched thing or the ceramic part? or as in a pasty white?
 

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The important thing when you're jetting a bike is not to make drastic changes. You should only drop one main jet size at a time. If a 168 was a little too rich and it was bogging and the plug was dark and wet then drop to a 165 with a fresh plug (don't forget to gap it!) and try that. Make sure your air filter is clean then grip it and rip it!
 

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Discussion Starter #18
alright thats good info right there but waht happens if you do change it to a significant ly smaller number?
 

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I agree. One jet at a time. Better to be rich than to seize it up.
 

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alright thats good info right there but waht happens if you do change it to a significant ly smaller number?
I'm telling you the proper way to jet a bike. No questions asked. This process takes some guesswork out of it and prevents you from jumping around with jet sizes. It's just the right way to do it.
 
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