Adjusting squish band without head gasket

[Vintageman]

plug at 20 degrees means I still don't have dial gauge that screws into plug threads.

The plug hole in head is at a 20 degree angle with piston stroke. So I need to take Suz numbers which are in line with plug hole and convert to direct with piston movement for how I measure today. cosine 20 is 94% of Suz indirect numbers

Really these T350/T305 are late 60s design same porting scheme, getting about same (+/-10%) HP per cc as the Yams of the smae era.
That is real field data for old school 2 stroke a rare find

In fig 4 you can see how just a intake mod can boost upper mid and even top end peak shifts a bit and it hurts bottom end but not much ... Depends how far you go three examples shown. fig 8. The Ex mod you can see it shifts the whole thing overto right and yes more peak power and rpm. If too much it actually bows down midrange loss even more.

Both mods are a trade off of bottom/mid for top. I am no pro, but sure been my experience on the old streat/dirt bikes and late 70/80s piston ported sleds engines if I start muddling.

[tz375]

I think we are wondering off topic a little. H1 heads have vertical plugs IIRC, so that comment does not apply here.

Stock timing is something like 24mm BTDC or 2.88mm BTDC. I'd start at 2.0mm and work up from there.

Raising the exhaust port doesn't necessarily change jetting up or down. In theory, a change in pipes and ports will raise gas velocity through the intake which will require a slight leaning out of main jets. If the intakes are much larger and the pipe is not generating strong pulses, it is possible that the motor will need richer jetting - especially at low to mid revs/load.

[Vintageman]

TZ your correct about H1 plugs straight

Dyr can take cosine 20 degrees of Suz BTDC timing to convert from indirect to direct as I do as an option

I do think I am getting "higher gas velocity" and will try one step down on main. It sure feel to rich when I crack WOT..

[tz375]

Let's clarify terms. The term indirect or direct usually applies , in this case, to measuring piston position when the spark plug is at an angle. With vertical plugs, direct and indirect are the same. Direct means taking the head off and measuring piston position with a Dial test Indicator. Indirect means measuring down an angled spark plug where the reading is just one side of a triangle and not the actual piston position.

[jeff kushner]

If the intakes are much larger and the pipe is not generating strong pulses, it is possible that the motor will need richer jetting - especially at low to mid revs/load.

Looking at his pipes. if the other matches the one we can see, it appears to have a fairly short mid-section but all things being equal, the strength of the pulse is generated by the angle of the converging cone at the rear of the center section. His appears to be a little faster than many so I would guess a "above average" pulse strength...FWIW

BTW--VERY sharp looking bike!! I love the bikini fairing. It looks like it was made to be there!

jeff

[tz375]

I could tell you just how fast the pulses are moving and their pressure characteristics, but then I'd have to kill you - as they say....

They are RD Yamaha pipes from DG and are remarkably good value. Not the "best" in terms of outright power perhaps but in terms of bang for the buck they are excellent. The integral mufflers have been removed and replaced with weld on mufflers for a more modern look.

It should be a pretty good package with the flat slides he already has and those H1 squish heads.

[Vintageman]

Dyr,

Those 28mm flat slides seam farther away from engine than stock or is that just an illusion?

I think 28mm may be a better fit than 32mm OEMs (quite a bit of carb for 155cc).

With 32mm you really nead to think about how much you snap throttle wide open when the engine RPMs are not up for it yet.

Cheers

[Suzukidave]

It looked to me that the carbs are not even attached to the cylinder .

[tz375]

Looks that way Dave. 32mm on a 350 twin is pretty huge in any language too.

RD350VPVS a.k.a. RZ350 makes up to 70hp on stock 26mm rounds slide carbs, so I can't see a T350 needing much more. 28mm flats should be fine.

[Vintageman]

Grabbed my glasses this time.

There is an add or period test somewhere (T305) Suz was bragging about "Volumetrics" or something like that and why they justified using 32mm on intake.
Yes I think 28mm are a good/better fit too. I don't dislike the 32s either

Since he tested the 28 flats before his mods it will be interesting to see what he finds out for jetting

I want to be clear about timing. I chose to advance mine to help midrange... will back of some versus OEM but not much.

When you have one setting you needs to pick what you want.

As most know through experience and simple research you run higher rpms better to retard some.

The ideal thing would be to have it profile for you automatically like more modern 2 strokes.

[dyrberg123]

I think we are wondering off topic a little. H1 heads have vertical plugs IIRC, so that comment does not apply here.

Stock timing is something like 24mm BTDC or 2.88mm BTDC. I'd start at 2.0mm and work up from there.

Raising the exhaust port doesn't necessarily change jetting up or down. In theory, a change in pipes and ports will raise gas velocity through the intake which will require a slight leaning out of main jets. If the intakes are much larger and the pipe is not generating strong pulses, it is possible that the motor will need richer jetting - especially at low to mid revs/load.

THX, so TZ that Means i will start from 2mm, right angled on the piston - or through the plug hole now that i have H1 heads right?

BTW, i have had a job change, so now i am working offshore in the oil industri, thats why i have been off line a few days.

And thanks for your comments, great to get som feedback from some passioned, all others think i am way off...

Carbs are now on, wasn't in Picture, had to make some off center pin bolts to get the rubber boots to fit.. But thats just part of the fun:-)

I will be running in the weekend - cant bloody wait!

[Vintageman]

Dyr

I finally found the chart again that covers down to 20 degrees and up (just about linear up here too as stated). It is T305 service manual but same timing as T350 course. Here it is->

http://www.oldjapanesebikes.com/mraxl_G ... index.html" onclick="window.open(this.href);return false;

Since this is given adjusted for stock Suz head with angled plug and you now have straight plug (inline with piston stroke) via H1 heads. you need to multiple the distance shown by cosine 20 degrees or (0.93969...)

I think people are advising 20 degrees to start (Many RD boys say even 18). I agree start here.

I settled more to stock timing. I like it for how I ride. I have revved it up quite a ways for quite a while (many seconds) just fine. Like I said about my mod Ex port that's where it like to run now and I aim to please it. I am waiting for my T350 heads to return with .020" (1/2mm) off them and will back off timing a degree in case I now have too much heat,

I just have to remember, the bike is air cooled only! never designed to have peak power at these higher limits.

[tz375]

We set a TZ to 1.85mm with straight heads/plugs and that's 19 degrees with 15:1 CR and huge ports.

Your bike is stock at 24 degrees BTDC, back off to say 20 degrees to play really safe which is close enough to 2mm on your set up through the H1 plug or onto the piston crown with the head off.

22 degrees is around 2.43mm
24 calculates out as 2.88mm Strange - that's the same as the manual.

Are we sure that the stock heads have angled plugs at 20 degrees to the vertical? If so, the manual is wrong. That manual says the plug angle on a T20 is 20 degrees and the 305 is 10 degrees. I have no idea what it is on a T350 though.

[Vintageman]

Tz375 and dry

I had check both the t305 and t350 late back when and was the same angle.
ill'check again when head comes back today or tomorow. I have both sets and will correct if wrong.


I thought i read 20 degrees for T305 but if you just saw 10 use that. I'll check this too, but have been know to make errors. sorry if i did

[tz375]

I'm not saying you are wrong That's what I thought I saw in the file that you sent us to for the 305. I don't have either motor, so I can't check and in this case it doesn't matter because he has H1 heads with vertical plugs. ]

It's interesting that the conversion from degrees to mm for a direct reading are the numbers that Suzuki quote for reading at an angle through the plug hole. One was or another the Suzuki data is wrong in the book and would result in retarded timing. Unless, of course, the mm data is correct and someone in the technical writing dept screwed up with the conversion from mm at an angle to degrees.