Suzuki 2 Strokes

Greetings all,
Has beeen a while since I was here. What with Covid, family problems etc.
But I did find time for a Covid lockdown project, I purchased a Reed valve kit from John Aylor.
After much work with the Dremel I got them fitted.
Only thing I haven’t done as yet is to grind in the boost ports above the inlet.
The positions suggested in the instructions for the kit would have them exposing the ring gaps, which all my research says is a big no no.
I have come up with 2 possible solutions.
1) Remove the port bridge and machine one boost port that would go between the gaps, ( ring gaps are approx 25mm apart )
Without the bridge, the port is 49 mm wide, so should not present any problems with piston being trapped and rings don’t go down that low anyway.
2) Move the ring gaps further apart and put the ports where John suggests. Has anyone had any experience doing this?
Has anyone else fitted this or a similar kit? Any thoughts or tips are appreciated.

Even without the boost ports, midrange is much improved with the kit. But I would like to get the most out of it.
Using wasn’t a problem, went bigger with needle jet from P0 to P2 , 45 idle up from 35 and main jet from 260 to 280.

Regards
Andrew

hi andrew, i've done a similar thing, but with a gt250 and made my own reed block etc and fitted rd350 reeds. i found mr graham bell's book [2 stroke tuning] an immense help. especially the section about porting and cylinder scavenging. it's a bit heavy going, but there are plenty of illustrations to help you through it. there's plenty in there about boost ports and whether to use them or not. well worth a read
cheers, dd.

Thanks for the reply DD,
The design of the boost port is not my problem.
I am purely worried about the position of the piston ring gaps in relation to the boost port.
Would not be an issue if the ring pegs were more than 25 mm apart and right where you would want to put the port.
Is it possible to move the pegs further away from the inlet port.
Does anyone have experience of doing this.

Regards
Andrew

Why not ask John Aylor? He’s a smart cookie.

i had the pegs moved on the pistons for the gt285 i built
s.e.p at kegworth did them for me, so yes, it can be done
cheers, dd.

You mentioned you went from 260 mains to 280 - what carbs are you using? Are these aftermarket VM34 or stock carbs? I am asking since I currently install aftermarket VM34‘s on my GT750 and even 220 mains are still way too rich. I guess I will end up below 200 mains once weather conditions will allow for test rides.

Time for an update, not been here much due to family issues and others calamities.
Bike is running well with the reed valves.
Have had to richen jetting up considerably, am now running 300 main jets on the VM 34 carbs.
Wolfgang mentioned that he was running 200s, makes me wonder what type of main jets, hex like me or the old round type?

Andrew

Hi Andrew and welcome back.

Not surprising that you ended up with larger main jets than before the reed conversion. On a piston port motor, the inlet reversion means that pressure pulses pick up fuel each time they pass the needle jet outlet. Reed motors have a lot less reversion so they pick up less fuel on the way through, and hence the need for larger main jets.

What did you end up doing with the boost ports? The worst situation would be with a ring peg close to the side of the port, allowing the end of the ring to spring into the port and snag. Ideally the ends would be well away from the port window to reduce snagging. Another alternative with small (narrow) ports is to have the ring peg right in the middle of the port. That way the ring is unlikely to spring into the open port as it passes it because the unsupported length is relatively short.

Twisted ports on a T/GT500 and GT750s add all sorts of complications not just to rings and pegs but also to flow patterns. Boost ports really need to be balance left to right i.e. not skewed to one side or the other but centrally located. If not the gas columns will not meet in the center and may harm flow and power.

Hi TZ,
Yep, I agree with your assessment of the fuelling, just wish I had access to a dyno here in Dubbo Australia. Would make setting jetting a lot more accurate. I could travel 7 hrs to Sydney but don’t have time to currently.
Haven’t added boost ports yet, though I do have recently acquired a spare set of barrels to experiment with. I figure with some very careful measurements , I can add a pair of narrow channels (12 mm) up the back of the cylinder wall , avoiding the ring gaps.
Have toyed with removing the inlet port divider to make it easier. I dont think the port is too wide that it would cause any problems. Could then put one boost port centrally and miss the ring gaps.
Any one have any thoughts or have tried removing the divider?

Andrew

Check out an RZ350 or Banshee cylinder to see how they put a boost port above a divided inlet. That's probably the simplest solution.

On the later model TR500 (water cooled, piston ports) they had boost port set into the top of the port divider