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Jetting and pre mix question.

  • 69DT-1250
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Jetting and pre mix question. was created by 69DT-1250

I don’t want to open the old best oil can of worms, but I am wondering what pre mix ratio and jetting are being successfully used in a 1978 IT 175? I read an old magazine article on a 77 that said the stock jetting and 24:1 with the yamalube worked good at all elevations the bike was tested, so I was thinking of going with that, but I wanted some other opinions and experiences. Really haven’t seen much about the jetting in these bikes. 

Thank you,
Ryan 
27 Feb 2021 16:55 #1

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Replied by Biknflyfisher on topic Jetting and pre mix question.

My 1983 IT490K seems to be pretty happy with 28 to 32:1 using Yamalube 2R.
 
1983 IT490K; 2007 Yamaha FJR 1300,
2003 KTM 450exc
Too many fly rods,,,
27 Feb 2021 17:16 #2

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Replied by darinm on topic Jetting and pre mix question.

My guess is stock jetting and 32:1 with any modern oil would work just fine, but I'm not an IT owner. Did that for two years in my '72 CT2 175 with no issues. I love the trail tech temp gauge to a visual for what is happening as adjustments are made to jetting and mixing, good peace of mind for $50.

www.trailtech.net/en-us/shop/accessories...2-DZj0QaAsHBEALw_wcB
1972 Yamaha CT2 175
1972 Suzuki TS 185 Sierra
2016 Yamaha WR250R
27 Feb 2021 18:04 #3

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Replied by MarkT on topic Jetting and pre mix question.

I would run a lot of oil in an IT175.  It's a 10,000+ RPM engine and they are hard on big end rod bearings.  Keeping the bottom end happy works best with lots of oil.  In the smaller, higher revving engines, using a super oil at a lean ratio was a recipe for short rod bearing life.  A couple of my friends (brothers) got new IT175's in 1977.  One ran 20:1 CastrolR...  other ran BelRay at 50:1.  They always rode together...  we rode a lot back then.  The brother running 50:1 blew the bottom end bearing in less than 3 months.  I don't think it was under warranty but the dealer fixed it...  It happened a second time a few months later.  His brother never had a problem with an identical bike the whole time.  After that he went to 20:1 like his brother and was fine after that. 
Was BelRay the problem? Maybe.  But it's a good oil.  I can't prove it but my feeling is the rod just didn't get enough oil.  Bottom end was pretty dry when we took it apart.  By the way, the DT175 of that era used an identical crank and they live forever but don't rev as high or make as much power.

Stock ratio was 20:1 which is what I'd use with Yamalube2R. 
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
The following user(s) Liked this Post: JayB, asco, 69DT-1250, darinm
27 Feb 2021 19:39 #4

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Replied by darinm on topic Jetting and pre mix question.

We should really just answer "Wait for MarkT to respond" on all 175cc related threads :)
1972 Yamaha CT2 175
1972 Suzuki TS 185 Sierra
2016 Yamaha WR250R
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01 Mar 2021 11:17 #5

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Replied by Mothersbaugh on topic Jetting and pre mix question.

darinm wrote: We should really just answer "Wait for MarkT to respond" on all 175cc related threads :)
 

It can be rather humbling to get in a word before he speaks, can't it?
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01 Mar 2021 16:55 #6

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Replied by MarkT on topic Jetting and pre mix question.

Please don't wait for me or be in any way reluctant to post...  I just do my best to help and share my experiences and knowledge...  a lot of which I learn from you guys!!! 
Rare to see a bad big end bearing in a DT unless it got rusty.  But kind of rare to see a good big end bearing in the same basic crank used in the YZ/IT.  Dirt/rust is probably the biggest reason for a big end failure...  starved of oil is #2.
The main reason I think it was the lean oil mix with 50:1 is the lack of oil in the bottom end upon disassembly.  I've had a lot of engines apart and that thing was bone dry in comparision to what I'd call "normal". 
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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01 Mar 2021 17:27 #7

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Replied by Schu on topic Jetting and pre mix question.

He's like The Great and Powerful Oz.
  • Pay no attention to that man behind the curtain! ...
  • You, my friend, are a victim of disorganized thinking.
Schu

CT175B, CT175C, JT1' JT2' DT360A, GT80B, DT100B, DT125B,
DT175B, DT175C, DT250B, DT400B, Z50, SCR950

Someday, you'll own some Yamahas
01 Mar 2021 17:37 #8

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Replied by Mothersbaugh on topic Jetting and pre mix question.

MarkT, we ain't afraid of you. We're just in awe.

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Often I'll stick my neck out and hope for some feedback, and when I get some feedback/correction from you, it is always carefully said. All part of learning what I need to know here.

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01 Mar 2021 19:32 #9

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