Jetting needed with change of engine oil? (2 stroke)

Michael Forrest /

I recently looked up the viscosity of gasoline (15.6 @ 60*F) and then figured out the viscosity of different engine oils at the same temperature. Then I averaged the viscosity for two fuel/oil ratios, 30:1 and 50:1 and found significant differences. Castor 927 with gas had a 33% viscosity increase going from 50:1 to 30:1 and Motorex had a 12% increase. I had no idea there was such variation.

Have any of you noticed a need for different jetting when you switched brands of engine oil but kept the same fuel/oil ratio?

Re: Jetting needed with change of engine oil? (2 stroke)

Charles Cole (OFMC) /

I have been using 927 for a number of years Great stuff. I also mix using info I gleaned from this article from peeps VERY serious about what the do, and is their livelihood. Insides are clean as can be and no other issues. I mix at 85-90:1

Here's the best write up on oils I've found. I've been doing 2Ts since before the triples were around. Pre 70s. Scroll down to oils/mixes or enjoy the wholew read. Very informative.

http://www.klemmvintage.com/kaw500h1.htm (edited)

Re: Jetting needed with change of engine oil? (2 stroke)

Alan Jackson /

A 1970's uk bike mag put a two stoke middlewight on the dyno and tested oil mix ratios and power. increasing the jet sizes with the more oil rich ratios so as not to run weak.

and surprisingly they found the bike produced the most power at 20-1

the opposite of what they had first thought.

ever since then instead of trying to use as little oil as possible - like most two stroke owners I assume

I try to use 30-1 or even 25-1.

Re: Jetting needed with change of engine oil? (2 stroke)

Alan Jackson /

that's a good read but ive always wondered why Kawasaki recommend such large piston to bore clearances.

also their "break in" treatment flies in the face of bedding in the rings and there is no wonder the pictures of the pistons show blow back.

every one thinks differently but to bed rings in I get the engine warm and then give it as much loads it will take but for 1 mile journeys so the engine cannot get too warm and seize. I was also told letting the engine overrun is brilliant for bedding the rings in ie rev it in first to high revs then shut throttle and let engine braking work on the rings

microscopically a new bore has lots of tiny peaks and troughs.

force the rings to lop off or truncate these peaks by forcing them outwards ie only way to do that is under lots of load, also use a crap oil.

if you use synth or a good oil the rings will just glide over these peaks and not bed in.

and what you get is the rings basically moving over lots of thin peaks. instead of larger surface area truncated peaks. less compression, worse sealing more blowback etc.

I used to baby my bikes during run in,. no load etc and then I wondered why I had tea stained bores after a hundred miles.

I now do it the 50 mile lots of load but only for very very short spells and have no blow back whatsoever and lots of performance.

I bore my 64mm bore ish Yamaha to 0.03mm.

that article says new tight rings can snap if overheated. I thought that's what ensuring enough ring gap prevented?

I always check my ring gaps on new motors.

all good fun

Re: Jetting needed with change of engine oil? (2 stroke)

nope, the viscosity of oil mixed into gas has nothing to do with anything. in the engine the gasoline readily evaporates and the oil condenses onto the working surfaces.

that klemm article is pretty good but i expect my pistons to look like that after 1000's of miles not hundreds. they are tuned on a razor edge. you can see that oil beginning to varnish on the skirt, once that builds up you're hosed. get enough varnish to stop heat transfer and you will have a four corner sieze in seconds.

these guys are running much hotter piston temps than you see on even a pretty highly tuned moped. plus you gotta remember piston velocity on a 60 mm stroke vs a 40 mm stroke is way way higher so 7000 rpm on an H1 is probably like 10 or 11k+ on a moped... too lazy to do that math, but that is some true ragged-edge shit. not to mention not a lot of fin capacity relative to the power output, always a limiting factor in vintage racing.

Re: Jetting needed with change of engine oil? (2 stroke)

To me anyway it seemed like he was asking if the different viscosity of the mix would affect flow rate through the orifice of the jet and cause changes in air fuel ratio due to a thicker oil lowering the volume of mix delivered over a set time.

If this was actually the question then I could see the possibility of there being a difference, but I also see the possibility of that difference being so negligible that it means nothing.

Re: Jetting needed with change of engine oil? (2 stroke)

Re: Jetting needed with change of engine oil? (2 stroke)

kevin Smellaflange /

loss of horse power = wearing out the soul.

..but seriously the new syn oils are able too brake in motorcycles now...

20 second bursts of speed in november is different than august & humid.

Re: Jetting needed with change of engine oil? (2 stroke)

Alan Jackson /

so what do people think about needing reduced quality lubrication during bedding in the rings? Ie the first 50 miles in which load must be placed on the rings to truncate those peaks properly?

Re: Jetting needed with change of engine oil? (2 stroke)

> Alan Jackson Wrote:

> -------------------------------------------------------

> so what do people think about needing reduced quality lubrication

> during bedding in the rings? Ie the first 50 miles in which load must be

> placed on the rings to truncate those peaks properly?

First tank ( usually good for 50 to 100 miles) : mixed @ about 32 to 1 cheap dino oil .

After that^ , regular everyday 'activity' .

Re: Jetting needed with change of engine oil? (2 stroke)

Overpriced Parts /

If a kit manual calls for 2% synthetic oil that’s what I run,

I don’t run junk oil at double the amount to carbon seize rings and everything up

Re: Jetting needed with change of engine oil? (2 stroke)

> Ken Roff Wrote:

> -------------------------------------------------------

> I don’t run junk oil at double the amount to carbon seize rings and

> everything up

I've never had that happen , Ken .

Re: Jetting needed with change of engine oil? (2 stroke)

Alan Jackson /

> P D Wrote:

> -------------------------------------------------------

> > Ken Roff Wrote:

>

> > -------------------------------------------------------

>

> > I don’t run junk oil at double the amount to carbon seize rings and

>

> > everything up

>

> I've never had that happen , Ken .

me neither and its only for 50 miles or so.

I even tried dry top end assembly once, no oil on rings pistons or bores.

but I realised within an instant everything gets bathed in oil from the fuel mix.

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