GT750 fuel consumption

[tz375]

Anyone know what the average round town consumption is likely to be on a 750?

Mine has spent more time on a dyno than on the street, but yesterday I poured about a gallon of gas in the tank and took it for a nice gentle spring run. It was really just around the block and the local forest preserve and it felt like it was running out of gas when I pulled into the drive - after about 6 miles......

Sure I would it out a couple of times but nothing crazy. The tank sounds like it's basically empty, so that works out to about 8-10 per gallon. And yes it's a little rich at the bottom end and not so much wider open, but puhh leaze!

[Craig380]

Was the tank bone dry before you put the gallon in? I wonder if the tank is trapping some juice that even the reserve pick-up can't get at?

[Alan H]

Brim the tank - then do 50 miles and brim the tank again. Divide one by t'other and Robert is your Ma's Bro.
6 miles with a spit of go juice will end up with pain. Oh and try it on UK prices!!!

[GT750Battleship]

Should return 17km to the litre,ridden at sane speeds & revs?
Regards,
GT750Battleship.

[pjmcburney]

I know mine's not terribly economical, but it never gets worse than 8l/100km.


I have a mate in Sydney with an L that regularly gets 5l/100km or slightly better.

Anywhere between five and eight per hundred is eminently achievable I'd say.

[tz375]

So I drained what little splash was left in the tank and of course there was more hiding in there than it seemed. In fact there was more or less half a gallon.

I drained it with the filler cap closed and sure as God made little green apples, the flow soon slowed to a trickle. crack the cap and flow resumes. We all know what that means. Clogged, blocked or non functional vent. Right?

The filler cap is a new, anodized billet, aircraft type cap with check valves to allow the tank to breathe. That all fine if the system has a fuel pump to pull gas out and create sufficient negative pressure to crack the valves, but a little gas in a gravity feed doesn't create sufficient pressure drop, so the valves stay closed.

A little micro surgery and we have air flow and probably fuel flow. Second test today if it doesn't rain.

Then maybe we can start to log some relevant data. I'll have to move the CHT probe because it cools off as soon as road speed increases. The RPM pick up has been rewired to try to get a more consistent signal, but the A:F numbers are looking marginally rich up to 1/4 throttle and progressively leaner as it goes to WOT. Time for larger needle jets to go with the 120 mains. I might have to add a set of EGT channels to confirm what the lambda numbers.

It's educational.

[Madbuffalo]

Sounds like you got it figured out then. Hope the second test launch turns out better than the first. At 8mph you might as well be driving a mack truck.

Josh

[tz375]

Sounds like you got it figured out then. Hope the second test launch turns out better than the first. At 8mpg you might as well be driving a mack truck.
Josh

The first post was a bit tongue in cheek, but 8 MPG would be a little worse than expected.

One thing I forgot to mention was that it is so perky. I have ridden my RZ and the GT back to back, and the GT is just so much quicker off the line under moderate riding. It's not as smooth and refined as the RZ, but it's miles quicker and the brakes are amazing. I was convinced that the RZ was the most fun bike ever created, but that faith is being severely shaken.

And at the moment the GT still has stock CV carbs and a 3 into 1 pipe. Of course the compression is still a little high and that really helps its perkiness. And losing a hundred pounds probably didn't hurt either.

[Madbuffalo]

Richard, If you need a second opinion on that RZ I'd be willing to stop by and take a spin on it, purely for scientific testing of course. I got the chance to ride one about 10 years ago and the clutch mechanism failed within about 1 mile, but man was it a trip for those few minutes! The RZ comes up on American Chopper of all places once in a while and they still refer to it as "one of the most fun bikes we've ever had". One of my favorite bikes I've never owned.

[tz375]

Josh, RZ350s are fun bikes for sure.

Just after I bought this one - way back in the early 90s I stumbled across a low mileage Red white & blue 86VFR750 which was far more glamorous. The VFR was sexier looking, and more refined in every way. It was arguably one of the best looking bikes Honda every designed, but when push came to shove I sold the VFR and kept the RZ. The RZ was just more fun - and at a saner speed.

The RZ is just light and snappy in a way that other bikes can't be. And yet I'm being seduced by this hot rod GT that is pure hooligan. I should take them both to a Test n Tune day at the strip to see how they compare there, but on the street at lowish speeds the GT just has so much more low end punch where the RZ needs more revs to get out of its own shadow.

The problem with all that is that it's making me think about my other GT project where the objective was more at the top end and to heck with bottom end. On the street that punch out of corners is exactly what I was aiming for.

If you are ever on the north side of Chi town, be sure to drop in and take the RZ for a spin. I'll try to replace the 20 year old Metzler Comp K's with something softer. That pair are as hard as the concrete in the drive.

[Craig380]

@TZ - have you done some porting / internal work on the GT? And where did it lose 100 pounds (apart from 30-odd pounds in the exhausts, of course )

[tz375]

Porting? Check
Compression? Check
Lighter wheels? Check
Carbon fiber side covers? Check
Light exhaust? Check
No air box? Check
Small battery? Check
Alloy fat bars? Check
and so on.

The motor has a light port job and very high compression. Uni filters, different jets, small oil tank, flattrack seat etc

http://s1106.photobucket.com/user/tz375 ... ort=6&o=13" onclick="window.open(this.href);return false;

[Craig380]

Wow. Just ... wow. She looks wicked. Excellent job!

Is that a modified Strader 3-1 pipe?

[tz375]

Thanks,

The pictures show the original Strader pipe that the one owner bought when he rode the bike back in the day. Strader used a complex baffle design to restrain noise and it went through several design iterations. The pipe is really thin wall and very light. Looking at discoloration around the collector area, I'd speculate that's the next restriction to be addressed. Strader made the collector outlet the same size as each of the individual headers, presumably to allow for a each cylinder to "see" the pipe as if it were the only cylinder using the pipe.

That makes a lot of sense, but trying to stuff three times the volume of gas through the same hole is likely to be an issue. It's that balance of gas flow versus wave dynamics that is always to the front in a multi pipe design.

That pipe has now been chopped and welded with an absorbtion style perforated tube, but I need to try a perf. tube with larger percentage open area to see if that helps to reduce decibels.