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Old school meets new school

25 Jun 2020 19:00
formulaz1
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Old school meets new school #1
hey folks, so thankful for this resource. In 1979 my brother in law bought a new IT 175. I was 12 and fell in love. I'm in my 50's now and my son bought a new chinese 4 stroke bike and suggested I do the same. He's not a liberal but couldn't afford anything else so I didn't rain on his parade. So, I remembered my love for the IT and found a 78 250. To my dismay it had a recently installed once over weisco piston in it. Historically not a fan of weisco. The guy planned on it being his baby and said he went through the whole bike but then came across a IT 490 and changed gears. I went with 20:1 with maxim 927 and b8es ngk. Smokes like hell and blubbery as hell. Tried 36:1 and it ran better but didn't want to get up on pipe. Changed plug each time I made a change and always looked shiny black. I took the exhaust apart to make sure it wasnt saturated with oil but wasnt bad. The only time it seemed to run like it should was when I took the uni-filter out on 36:1. Smoke is better on 36:1 but the only way it seems snappy like it should is no filter and 2.5 turns out on air screw. Jetting is stock, idles all day without a problem. Leak down test is perfect. Compression is perfect. Reeds are fine, no light shining through. Hoping someone has a setup that will get her running like she should. Sorry so long but figured I'd cover all the bases to avoid 100 questions. Thanks for the opportunity to be involved in your community and look forward to your input.

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25 Jun 2020 20:00
YZBill
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Old school meets new school #2
I run all my MX bikes on 32:1 with 927. If you’re just doing trail riding you might want to run a 40:1 ratio. I run 50:1 in my trials bike. Proper jetting of the bike makes a world of difference. Also 36:1 is a richer air-fuel ratio than 20:1 (less oil = more fuel) which is why your plug was black.

I’ve been running Wiseco pistons for 30+ years. Never had one fail, but I’ve had plenty of OEM pistons fail.
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25 Jun 2020 20:32
MarkT
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Old school meets new school #3
Probably the filter. Or more exactly, the filter oil. Either over-oiled or using the new "sticky" filter oil by chance?

I had an issue with my "time capsule" Husqvarna... Original TwinAir filter was degraded. Still can buy them new. Used modern filter oil. Ran pig rich. Jetting was stock and bike was in "like new" condition. Very annoying!

After trying a bunch of stuff and finding out how much Bing charges for jets these days :EEEK :EEEK :EEEK on a whim I bought the TwinAir filter oil kit from Rocky Mountain ATV. (Had some bonus bucks I needed to use or lose.)

TwinAir oil is very thin and must dry for a few hours. When dry, filter is not "sticky" at all. Catches dirt great though. Richness cured. Bike ran like new again. I used the "Liquid Power" original formula.

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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26 Jun 2020 00:38
Dirtboy
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Old school meets new school #4
+1 on the TwinAir filter oil MarkT!

I use that on our modern dirtbikes, (18' crf450r and 19' ktm sxf 450) and filters are cleaned every other ride. Easy to wash out, easy to re oil and never had a dust passing through issue B)


I am looking to buy good condition 1969 DT1 gas and oil tanks

1968 DT1 x 2
1969 DT1B
1969 DT1-S
1971 DT1E
1974 DT250A
1998 Kawasaki KX60
2018 CRF450R
??

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26 Jun 2020 04:39
formulaz1
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Old school meets new school #5
thanks for the input, while too much oil makes sense, in my case there was VERY little oil on filter.

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26 Jun 2020 05:25
RT325
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Old school meets new school #6
I think its still blocked in either the tail pipe or in the spark arrestor in the tail muffler. Arrestor is way down in the tail muffler if still there. also will grow in the pipe to the chamber from the muffler & can grow where the pipe ends at the main chamber even if it looks ok just eyeballing in the end. Slide the garden hose in till ya sure its way in.

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26 Jun 2020 06:22
MarkT
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Old school meets new school #7
There have also been many complaints about Unifilters being restrictive on some DT models. Uni's design for those DT models uses foam that's at least twice as thick and appears to have smaller pores than the original Yamaha filter.

I don't know about the design of your model Unifilter or how it compares to stock. I will say Yamaha wasn't stupid... their foam filters... even the strange looking "fuzzy foam" air filters of that era... flowed air very well.

Foam filters can also look brand new, clean, and properly oiled and not flow air properly. The foam itself can go bad... I've experienced this problem with foam filters... one filter was less than two years old!

Last thing I can think of is fuel. Are you running standard pump gas? Or race fuel? I have a friend that decided to run VP C12 because he heard it's a great fuel for racing two strokes... it is... His bike blubbered like hell on it. Went back to pump gas and ran great again.

P.S. Changing the amount of oil mixed in the fuel to "jet" the bike or cure excessive smoke/spooge is not a good idea in my experience. It doesn't work. As was said, reducing the premixed oil increases the available fuel and makes the fuel ever so slightly less viscous so it flows through the jets easier which also increases the available fuel. Less oil in the gas = richer air/fuel mixture. Richer air/fuel mixture = more smoke and unburned oil coming out the pipe.

Using less oil will give the appearance the problem is better... it will smoke less... heck, oil smoke and spooge will stop completely if you go to straight gas... but it will probably seize on straight gas before the residual oil burns out of the pipe.

You can run a lot of oil in the gas without excessive oil coming out the pipe if the bike is jetted properly. I've run 927 at 20:1 with little to no smoke and no spooge dripping out the pipe or sprayed the back of the bike. Bike was jetted well. I've run race engines on 16:1 (not 927 that I remember) with no excessive smoke or oily pipe issues. These bikes like oil... I would not run less oil than 32:1 on 927.

Perfect jetting is for racing... for casual riding I don't like to jet that lean. A little smoke and spooge is fine and as long as bike runs clean... even if it "just" runs clean... I prefer to stay towards the rich side.

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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26 Jun 2020 06:53
formulaz1
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Old school meets new school #8
Took the pipe and silencer off and silencer apart, wet but no standing oil. Silencer had no packing either.

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26 Jun 2020 10:41
formulaz1
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Old school meets new school #9
Mark T. Thanks, 90+ pump gas. I will go back to 32:1 per your recommendation, inspect the filter better and try some jetting changes. Ya know, one thing I forgot to mention is no matter how long its been sitting, it starts on the second kick with no choke. Needle and seat is fine cuz I can leave the fuel on and days later nothing comes out the overflow. Could float level cause it to be blubbery from quarter throttle through full throttle?

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26 Jun 2020 13:31
YZBill
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Old school meets new school #10

formulaz1 wrote: Mark T. Thanks, 90+ pump gas. I will go back to 32:1 per your recommendation, inspect the filter better and try some jetting changes. Ya know, one thing I forgot to mention is no matter how long its been sitting, it starts on the second kick with no choke. Needle and seat is fine cuz I can leave the fuel on and days later nothing comes out the overflow. Could float level cause it to be blubbery from quarter throttle through full throttle?


That tells me it is jetted way too rich. First thing you should do is remove the carb, open it up and get the numbers off the following parts:
1. Main Jet
2. Pilot Jet
3. Needle and clip position
4. Jet Needle
5. Slide
6. Air Jet (if it has one)

Being able to start without the choke is a sign your pilot jet circuit is too rich (big).

Blubbery from 1/4 to WOT is a sign the needle, needle jet and main jet circuits are too rich. Start by raising the clip on the needle one groove at a time and see if it improves. If the clip is in the top groove you need to drop the main jet by one size and return the clip to the middle groove.
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