correct or suggested oil mixture for 76 yamaha it400

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dks9269

Member
Aug 20, 2009
2
0
i tried a search on this subject to no avail. i just bought a 76 yamaha it400. my first 2 stroke and dirt bike. the guy i bought it from used some kind of natural oil (bean oil?), using a higher mix ratio. he suggested for practicality i start using a synthetic oil and mixing it a little leaner. are there any suggestion on what ratio i should use? (i'd like to know the factory suggested mix too if someone has the same bike/owners manual). The bike seems to be in great shape (though sometimes it will stall at idle), but other than that...
any help keeping it running good would be greatly appreciated.
thanks!
 

BadgerMan

Mi. Trail Riders
Jan 1, 2001
2,479
10
40:1 full synthetic and 93 octane in everything. All bikes new and old, chainsaw, blower, weedeater, etc.
 
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Enduro_Nut

~SPONSOR~
Feb 7, 2002
1,155
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TRexRacing said:
In what?
Click to expand...

Everything from my '76 DT400(bought new), '77 Husqvarna... the list goes on all the way up to a modern bike(don't have one right now).

I ran 40:1 Golden Spectro through the 70's - 80's and went with Silkoline pro2sx in early 2001~. I mix 93 with 108 or 110(For fuel stability only!). My '77 250 Husky went 1 1/2 yrs('06/'07) and one vintage national cross country championship(13, one hour races), 8-10 local mx's and the ring only showed 7 thousanths wear which was still under recomended replacement!! I am anal retentive when it comes to my vintage iron... if I had failures or premature wear I would change accordingly.

I think running under 50:1 full synthetic is throwing money out.
 
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whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
Older 2 strokes run stronger on their recommended oil ratio, than diluting it with some modern miracle oil, and thereby dumping WAY MORE GAS into the engine. If you are going to run leaner oil ratios, you can rest assured that you will need to lean all the carb circuits to compensate for the excess gas. 77 RM370, 20:1 with Maxima 927 and shell or BP premium. Didn't the IT have an oil pump originally?
 
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dirt bike dave

Sponsoring Member
May 3, 2000
5,348
3
whenfoxforks-ruled said:
Didn't the IT have an oil pump originally?
Click to expand...

Nope. Premix offroad bikes.

IMO, 32:1 would be a nice safe ratio for an air cooled big bore that its hard to find parts for.

I'm sure it would be fine at 40:1 or 50:1 with a good oil and casual riding, but oil is cheap and 30+ year old crankshafts are expensive.

If it was a 125 race bike, i could see running 20:1, but not for a big bore trail bike.
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
I wouldn't even think of running my old pig 77 or 78 on 32, never! Too loose, translates to even more vibration, and a hotter running engine, IMO. 20 seals up nice, really good throttle response, nice bark. Rods are unavailable for the rm 76,77 370 and 78 400. I used to burn up 125 engines running 20:1(75 cr125), wished I would have tried 18:1. How are parts for the IT?
 
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wfoyz250

Member
Dec 20, 2008
14
0
I've been using a 32:1 in the old '79yz250. 50/50 mix of 110 LEADED race gas and 93 pump. The jetting is spot-on and the plug burns clean.
Maybe a lower ratio might be an option for prolonging bearing life.
 
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mas2de

Member
May 3, 2009
45
0
12 or 16:1 for break ins
20:1 is recommended for all ITs '76-'80 mixed with 91

For all the '81 ITs 16:1
'82 and '83 is 24:1

This is what Clymer ("and competition experts") say and I'm sure is what Yamaha recommended. Anything else we can help with?

Is it bad at all to run synthetic mix in old bikes? I know it isn't good to run synthetic engine oil in your old vehicle or if you used regular oil in the motor w/o cleaning it. (not sure why. I believe it makes pockets of oil or something and things start to deteriorate faster or it burns up the distributor bearing or something. Ecspecially in old Chevys)
 
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dks9269

Member
Aug 20, 2009
2
0
parts are certainly harder to find for a 76 IT400. i actually just paid 120 for a new (remanufactured) intake manifold. i'm sure i could of found an older used one for less at a salvage yard.... though i did see someone actually selling one on ebay for 235!! Whatever, the newness was important to me for that particular part.
in '77 they made many changes to the IT models which make it hard to swap parts with the different years. i've had more luck looking at parts from the '76 YZ400. right now i'm in search of a aftermarket silencer to replace the old stock one, but i've only been able to locate stuff made for the 77 year models. crap.
I'd love get in contact with any other '76 IT400 owners to swap information with...
by the way thanks for all the oil gas ratio advice. i decided to run a full synthetic at 32:1.
... and if you know any other '76 IT400 owners send them in this direction.
Thanks!
 
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jason33

Member
Oct 21, 2006
655
0
20:1 if you want to eat plugs
i ran 32:1- 40 in the 400 a friend had, i think 32 mostly cause it was 2 mil over bore, (that bike was stupid fast!!! power out the !@ss)-- 6 speed as well im almost certain (used special cylinder bolts) 76-78 i cant remember what year, it was the one with the really bad (steering rake) was more like a chopper hahaha
great motor though prolly one of the best motors for a cart,or 3 wheeler conversion
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
jason33 said:
20:1 if you want to eat plugs
,or 3 wheeler conversion
Click to expand...
That about sums it up. You either did not know how to ride it, and or maintain it. 20:1 does NOT guarantee eating plugs. Ignorance eats plugs.
 
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helio lucas

~SPONSOR~
Jun 20, 2007
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whenfoxforks-ruled said:
Ignorance eats plugs.
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that was hard. i am ignorant and i am pretty sure i do not eat plugs...
 

whenfoxforks-ruled

Old MX Racer
~SPONSOR~
Oct 19, 2006
8,129
2
Merrillville,Indiana
helio lucas said:
that was hard. i am ignorant and i am pretty sure i do not eat plugs...
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I never thought of you that way at all Helio. I thought you are like the young Eric Gorr of Portugal. I would believe eating a spark plug would damage your teeth, and all points till it comes out.
 
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helio lucas

~SPONSOR~
Jun 20, 2007
1,020
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whenfoxforks-ruled said:
I never thought of you that way at all Helio. I thought you are like the young Eric Gorr of Portugal.
Click to expand...
while that is not the true, not even close, i do THANK you for the praise. i do respect eric´s work.
quoting WFFR: " It almost made 1 eye sweat"
whenfoxforks-ruled said:
I would believe eating a spark plug would damage your teeth, and all points till it comes out.
Click to expand...
a picture explains it better than a thousand words... :uh:
 
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jholtman

Member
Aug 23, 2009
2
0
Back in the day (1970's) the 2 stroke oils were either petrol or castor based oils and required 20:1 ratios. Today, the oils are synthetic and are way better than the old oils. Many people have problems understanding what I am about to explain. If you take a 2 stroke that is jetted for 32:1 and decide to be "safe" and run the ratio at 20:1, you have just LEANED out the fuel mixture and you are headed for a HEAT SEIZURE. Conversly, if you take a vintage bike that is jetted for 20:1 and change to 32:1 you are now running RICH on fuel. Both 20:1 and 32:1 are acceptable ratios but I think that 20:1 is not needed with todays oils. Unless you fail to use any oil at all, most engine failures are caused by lean fuel mixtures, not lack of oil. A side note to this is that the old oils actually burned in the cyl (oil burns hotter than gas) whereas synthetics pass though for the most part unburned. The bottom line is: what ever ratio you run, you must jet (both main and idle jets) for the proper mixture or you may lose an engine or foul plugs. I have been running motocross engines since 1971 up to the new rage of the 4 strokes and once I learned this concept, I never lost an engine and always made good clean power.
 
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