Archived Posts

[Admin]

Dave, with my 750 basically in stock trim (battery, oil tank etc) I would only have room for a stock airbox, and I'd guess they're about 2 quarts! Zooke has been trying to talk me into putting it back on, and if I'm hearing right, you would tend to agree?

The boots to the carbs would be the biggest pain since they're not even close to stock size.

Dave, did you hear what my current RWHP is on Blueboy, after my latest porting and carb install?

Lane

[Admin]

I believe a properly designed airbox will yield better all around performance than open carbs or pod filters. I found this article by Kevin Cameron on airbox design, see link and scroll down to airbox section.

http://www.snowtechmagazine.com/article ... petemp.php

[Admin]

DTKid wrote...

Your bike averages 3-4K rev. not actually high enough to worry about the inlet speed, air filter tuning. ( thats for the new R6 that rev at ave 12K)

My experience is that it's actually at lower revs that an airbox does the most good. Airbox resonance permits better flow at lower intake velocities, whereas at higer revs/intake speeds the mass flow of the higher speed moving air "rams" the intake charge.

[Admin]

Next step for my race bike thing I'll try some screened velocity stacks I've had around for years, I'll see how they work at next race at Sandia. Of course at Sandia I'm sure jetting and gearing selection will be way different from sea level tracks.

Sandia is pretty dirty, and our dust devils make it worse. I would save the stacks for a cleaner avenue. I'll be there, as usual. We need to meet!

[Admin]

H2Tuner, what would be the advantages (if any) of a variable-volume airbox? The reason I ask is that I designed and built something like that for a physics experiment that I did in cooperation with one of my professors.

And Tuner, I ask you because through long experience growing up on the farm and in the Army, the best results come from the guy with the dirtiest hands.

[Admin]

How do you determine the proper length of the inlets, and volume of the box? Lane

With a few thousand dollar puter program, or some flow dynamic phd level college classes......

Maybe we should get somebody with a flowbench to figure it out for us. There's this guy in Texas...............


Lane

Hmmm wonder that would be? Would it be a Certain person that has a Hatered of Just about anything.

[Admin]

OK guys, I admit I know nothing about flow rates and airbox volumes. Like most shade tree mechanics, I dick with it till it works good and call it good. I do not race so I'm not trying to squeeze every last nano HP out of every cc.
But the velocity stack issue prompted me to post these pics. This is a radically modified GT750 currently for sale in Norway for $5500 usd. The pics were sent to me just yesterday by fastbike. IMHO the bike is super slick - tricked out everywhere you look. Note the intake. Looks like velocity stacks to me.

[Admin]

Velocity stacks have worked on two strokes for years and years, they are usually called air cleaner ducts. Some are srtaight ended, some have a flare, some are short, some long, but all are there, in place and work. So do the individuals in the pics above, just not as good as when a nice, correct volume STILL AIR BOX is used in conjunction with them.

Oddly enough a still air box can be non pressurized, or low pressure, like some two stroke roadracers.

As far as active airboxes are concerned, Kevin Cameron and I always thought along the same lines, as the engine is actually a living, constantly changing entity, with an ever changing DCR, it also would need an ever changing exhaust pipe and air inlet system, including active change venturii. Power valves and reed valves have helped bring this about, but there are other methods thqt need to be visited and developed.

Honda, on one of their V4 500's, changed the exhaust volume in the pipes by water injecting them. By inserting moisture into the primary pipe, and causing it to become steam when it mixed with the hot exhaust gasses, the resultant steam effectively changed the pipe volume and velocity, making the engine think it had differing pipes for certain load conditions, giving better power within a wider powerband.

[Admin]

CRY!

So, I've been spending the last week working in a rush to get my 380 up and running before the season's over. This week has been beautiful and to make sure I'd have some riding time, I took a few shortcuts on the bike.

I'm planning on doing a complete restore, but not this week. I still need to paint the tank, get new sprockets, my clutch cover needs to be replaced probably (it doesn't seal properly). And the one thing that I thought could probably wait until some time this winter - is the nylon gear that turns the points lobe. I was sadly mistaken! I noticed it had a crack in it when I took the cover off to polish it - I knew better.

I had just finished up putting everything together on the bike, and it wouldn't start. I decided that it must be either my timing, or the gas. So, after a long hour or so, some bad gas , some bad gasonline , and fiddling with the dwell and timing on the points, IT RAN!!! I was so excited. She kept tryin, and tryin to fire, until she ran for about 30 seconds. It was a thing of beauty. - I even have a video I'll load later. Mind you, she only ran on two cylinders. The sad thing is when she stopped running, she didn't start again. After kicking it just a few more times, I noticed that the lobe wasn't rotating.

So, I'll have to order a gear, hope it comes within the next day (might as well replace the clutch cover while I'm at it), and then get her on the road.

Wish me luck fellas. I'm still hopin to ride her before the weather goes bad.

I'll be posting pics, and maybe videos as soon as I can find my USB card reader.

[Admin]

That gear was a poor choice on Suzuki's part, I'm afraid. Glad it started, though.


Lane

[Admin]

Don't ever try to turn the motor over with the nut on the points cam, the plastic gear will break.

[Admin]

That's the kicker. I read about that before hand, so I didn't touch the nut on points cam. But, after I took off the cover, I found that the gear already had one long split from the center to the outer edge. I thought to myself "It's been like that up until now, I shouldn't have too much trouble with it"



I knew better, I was just trying to fool myself. The bike let me know I shouldn't/can't do that.

[Admin]

How important is having the correct jetting on a two stroke? After reviewing the specifications that forum members sent, I looks like my bike has a combination of GT250 parts.

The carb venturi is a 28mm so its a "A" type carb.

Jet In Bike Spec (from suzi2carb.jpg)
Main 113 92.5
Needle 0-0 0-2
Pilot 25 30

It looks like the bike has a "L" set of jets in a "A" carb.

The bike was hard to start on the first start-up. Seemed to run OK after warm up but I haven't tried to set the carbs (too cold). Is it worth the effort to get the jets right???

[Admin]

Its vital to get the jets right. The big risk on a 2 cycle engine is that you are likely to hole a piston or seize the motor if you are running weak (main jet too small generally.)

Jetting depends on the level of modifications to the engine/exhaust & carbs. If you have a stock set up and just want to home in on the best settings, go up one jet size and compare the performance with the stock jetting. Keep an eye on the plugs (plug chop test) to gauge the mixture setting.

Lots of advice on the board so keep everyomne informed so they can help

Good luck

[Admin]

Had something strange happen today. Went outside after Cincinnati got blown out by the Tampa Bay Bucs to see if I could get the old girl to run. Got it started and warmed up.

The bike didn't return to idle quickly after rev'ing it up. Then the RPM's started to climb. I couldn't get it to come down and turned off the key. It kept running (don't know what RPM since the tach cable vibrated out at this point). Tried the kill switch, still running at full RPM. Thinking that I might have a short, I tried pulling the plug wires off the plugs. THE BIKE STILL RAN!!! It stopped atfer I snapped the throttle a couple of times and it stumble to a stop.

I check the slides and they seem to be free, connected the tach cable and tried the bike again. It started up but still doesn't return to idle very well.

Any thoughts about why the bike continued to run after pulling the plug wires?? Could I have lots of carbon and its dieseling off of hot spots?? I'm planning to pull the carbs out and look if anything got loose. Any other thoughts??

Thanks again for the help.