jetting for straight avgas (tz250 4dp)

[mattyam]

since owning my tz250 ive yet to ride it. a former owner tells me it was ran on avgas and giving the engine a once over indicates its completely stock. ive yet to do check timing,  head volumes and check squish the porting is untouched and the pipes are stabndard yamaha (92 4dp) i checked the jetting and both carbs are identical and as follows. 420mj  22.5 pilot neddle clip in the middle (6fi80-61).  i need to check the size of the power jet but does this seem ballpark?

Edited November 20 by mattyam

[dab33]

No idea tbh, but as I said to you before go see Andy Ball at 2T engineering. He will check all the above before he even runs it on his Dyno. I really cannot recommend him enough.

If you want someone that's methodical he's definitely your man. Two strokes are his business.

[Mellorp]

TZ manuals will help 

https://drive.google.com/drive/folders/11DKo53I_E8NGRnYefAq1Co076fVjZQAW

[Ray Von]

Full avgas wasn't the best way to run these, I ran RGV kitted race bike with volumes and squishes based on TZ250s and it was always 50%avgas 50% superunleaded.

Avgas is relatively slow burning compared to standard petrol.

The forum pervert, who also runs tz250s @bogman will guide better on these no doubt.

[Johnno]

My experiences with AVGAS has shown me the performance advantages lie in timing increases.  As in cars and 4T bikes.

In 2 strokes I've used it and it's just cleaner and somewhat crisper, you can't really fiddle with the timing, but  I didn't touch jetting.

I just use our quite good 98 ULP ( whatever that is elsewhere ) and Toluene at 10% in my Beta 300, it runs cleeeean.

There is a ( in my onion ) wives tale  telling folk to run their KTM 300 EXC's on 95 octane as the higher octane stuff is harmful.

My 300 has a compression ratio of 11.6 to 1.   If you had a 350 small block at that ratio, can you imagine running regular unleaded in it??

Furthermore, wouldn't having 2 stroke oil in there increase the compresion?? 

I would think the jetting would remain the same.  It's just run better and safer.

Edited November 22 by Johnno

[bogman]

Tz manuals specify avgas from years 91-96

ul after that

 

[bogman]

Nowt wrong with avgas,also nowt wrong with a 50/50 mix

just need timing and vols to suit

[Johnno]

Is it blue AVGAS?

There is unleaded AVGAS.

The Blue stuff is still Awesome but it doesn't have the lead and aromatics that Shell A and BP100 did.

[bogman]

The blue stuff is approx 102 Mon.

[Rick448]

The stuff we have is 110LL. 

[Ray Von]

Any advance at 112LL?

[mattyam]

yes blue avgas. im not chasing the last horsepower, more along the lines of avgas been kinder  and more convinient really. the manual says 1.5 btdc for timing. ill give everything a check

[bogman]

Correct

i I think 91-95 are 1.5

96 is 1.9

97-99 is 1.7

2000 onwards something like 2.1

blue avgas is 100ll,they rate it differently to regular petrol but it’s roughly equivalent to 102 mon/???? Ron

[bogman]

Each cyl will require its own timing,check the burn back on the side electrode?needs to be around 3/4 back for optimum 

[bogman]

Also dependant on vols/compression ratio too.

does my head in

[mattyam]

bit of a minefield to say the least. i think once i establish the setup is safe ill leave it be, making allowances for obvious changes in weather. ill er on the side of caution

[bogman]

I run mj sizes 420 spring autumn down to 390 in summer

[mattyam]

do both cylinders run the same respective jetting?

[2639]

Just to add; we ran our race mopeds on 50 50 Avgas /super unleaded. 

But Im sure a small amount of acetone was added as a binding agent between the two. 

[Johnno]

I'd see a TZ250  in the pits when I was racing,  in Marlboro colours,  it looked stunning and sounded amazing. I obviously considered getting one.

But I thought about how all we monitored and adjusted on my 600 was tyre pressure I decided we had the equipment specific to us.

[2639]

On 11/22/2024 at 10:11 AM, Johnno said:

My experiences with AVGAS has shown me the performance advantages lie in timing increases.  As in cars and 4T bikes.

In 2 strokes I've used it and it's just cleaner and somewhat crisper, you can't really fiddle with the timing, but  I didn't touch jetting.

I just use our quite good 98 ULP ( whatever that is elsewhere ) and Toluene at 10% in my Beta 300, it runs cleeeean.

There is a ( in my onion ) wives tale  telling folk to run their KTM 300 EXC's on 95 octane as the higher octane stuff is harmful.

My 300 has a compression ratio of 11.6 to 1.   If you had a 350 small block at that ratio, can you imagine running regular unleaded in it??

Furthermore, wouldn't having 2 stroke oil in there increase the compresion?? 

I would think the jetting would remain the same.  It's just run better and safer.

Second to last bit.

Theres some wires crossed here.

The amount of oil does affect things. But it doesnt increase compression. Adding the necessary oil decreases the octane rating as it is distributed throughout the fuel and this dilution causes a reduction in detonation resistance.

So if things are borderline for detonation or pinking then too much oil, perhaps in conjunction with poorer quality or condition fuel, then maybe a temperature increase and detonation could occur. 

What I cant give you is a guide on what ratio would do to octane... but it will always be down.

(Noting; I understand the fraction of lead in 100 LL Avgas is way higher than leaded fuels used to be. So whilst lungfuls of spent 747 may invigorate the soul... its probably a good idea to keep pregnant children away from yer TZ. Or summink)

[Johnno]

23 minutes ago, 2639 said:

Adding the necessary oil decreases the octane rating

I always assumed this and indeed this was a part of my arguement to the folk who believed running a lower octane fuel in their 300 2T was better.

The old Belray 2T oil I beleive contained octane booster, if the oil has that, great.

Blue AVGAS has a LOT less lead now than it used to.  I'm thinking it'd be the lead that a TZ would want less so than the octane.  I use Toluene in my 300 2T bike because it runs way cleaner and is much more crisp without being wispy farty lean.  I spent a lot of time getting it like that, took me 4 different needles in the carb and various clip positions to get it as near to perfect ( for my climate and bloody,  altittude etc )  as I could and it is. 

Years ago I ran a tank of AVGAS from the last of my supply and it loved it.  I figured it was the lead but then I could get Toluene free at my then work place and tried it.  I was impressed with the results.  I can get tolly delivered to my door easy peasy. If I didn't have any,  I'd just go with ULP98 from the servo.  

10% Toluene is said to raise the octane by 2 points.  It's in petrol anyway.  Do I try to convince folk to do as I do?

NO!  Some if not most would disagree strongly with a lot of the things I do.  That's fine.

 

[bogman]

11 hours ago, mattyam said:

do both cylinders run the same respective jetting?

Some bikes do ,a lot have staggered jetting and timing too.

for example 

stock timing on mine is 1.9

but the bike is set up at 1.92/1.87

likewise jetting is one size richer on the LH cyl.

[John21]

54 minutes ago, bogman said:

Some bikes do ,a lot have staggered jetting and timing too.

for example 

stock timing on mine is 1.9

but the bike is set up at 1.92/1.87

likewise jetting is one size richer on the LH cyl.

 I think a V2 2 stroke is bound to have different jetting for each cylinder. Different inlet tracts, different cooling,etc

[Johnno]

I just glaze over imagining the TZ I'd have smoking like a second hand stove or nipping up at the end of the straight 

[mattyam]

57 minutes ago, Johnno said:

I just glaze over imagining the TZ I'd have smoking like a second hand stove or nipping up at the end of the straight 

theres a lot  of people that would say dont bother with a tz or honda rs, you will never reap the benefits unless your a seasoned racer. they require deep pockets and running one at its peak performance each time out requires a weather  station and a box of jets ect. there probably right aswell but  owning and riding a proper race bike around a track has been a dream since i was a kid. normal kids my age lusted after gsxr1100's ect. i was always fascinated with the  thoroughbred stuff.  truth be told im more of a racer at heart although my racing experience is limited. im not what you call a typical motorcyclist. ive done everything back to front hence why im 41 and only just got a big bike on the road (legally this time). 

[John21]

6 minutes ago, mattyam said:

theres a lot  of people that would say dont bother with a tz or honda rs, you will never reap the benefits unless your a seasoned racer. they require deep pockets and running one at its peak performance each time out requires a weather  station and a box of jets ect. there probably right aswell but  owning and riding a proper race bike around a track has been a dream since i was a kid. normal kids my age lusted after gsxr1100's ect. i was always fascinated with the  thoroughbred stuff.  truth be told im more of a racer at heart although my racing experience is limited. im not what you call a typical motorcyclist. ive done everything back to front hence why im 41 and only just got a big bike on the road (legally this time). 

Have you ridden it yet?

[mattyam]

9 minutes ago, John21 said:

Have you ridden it yet?

not yet, it will probably be in spring now for me. 

unfortunatley i didnt have time this year before the weather turned. i dont fancy  tip toeing around cadwell in the frost 😀 to be honest im just working my way through, checking it over, making sure its setup safely. maybe a blessing in disguise that ive not got out on it yet, i did change the rings. everything was hunky dorey there. 

Edited November 24 by mattyam

[bogman]

2 hours ago, Johnno said:

I just glaze over imagining the TZ I'd have smoking like a second hand stove or nipping up at the end of the straight 

They all do that sir

[bogman]

1 hour ago, mattyam said:

theres a lot  of people that would say dont bother with a tz or honda rs, you will never reap the benefits unless your a seasoned racer. they require deep pockets and running one at its peak performance each time out requires a weather  station and a box of jets ect. there probably right aswell but  owning and riding a proper race bike around a track has been a dream since i was a kid. normal kids my age lusted after gsxr1100's ect. i was always fascinated with the  thoroughbred stuff.  truth be told im more of a racer at heart although my racing experience is limited. im not what you call a typical motorcyclist. ive done everything back to front hence why im 41 and only just got a big bike on the road (legally this time). 

It doesn’t matter what other people think regarding ownership of the tz/rs.

yes they’re not for everyone and as you say they’re a money pit.

i feel privileged to own and ride one even if I can’t ride it like a gp god.