Windshield effect on MPG?

I have an older, '83 Kawasaki KZ1100 LTD - low 27K mileage, runs great, has aftermarket Dyna coils, valves adjusted perfectly - new matched Dunlop tires at 32 PSI, new OEM air filter - everything would seem to indicate I should be getting maximum MPG from the bike - whatever "maximum" IS for this bike...

Only significant mods to the bike are larger main jets - 135's instead of the OEM 120's, to better work with the Kerker 4/1 exhaust setup - and then, there's a pretty large added windshield - pics below.

Now to the issue - out for a ride yesterday - first decent longer ride since I bought the bike last fall and winter weather set in. Been going thoroughly thru the bike since then, both routine stuff, as well as a few upgrades mentioned above.

I rode 70 miles, average speed about 60 MPH, temp at 65 degrees, altitude 3500 feet - level road. I topped off the tank before and after the ride, and it took 2 gallons for the 70 miles - 35 MPG.

That seems low for this bike - it starts easily, idles great - and runs great thru all gear ranges and RPM, and has good power - so shouldn't MPG be better? I wouldn't think the Kerker header and accompanying larger main jet would make a serious drain - but what about the relatively larger full windshield - will one of those drop MPG significantly? Has anyone here added a windshield similar to mine, and seen MPG in the same range as I'm getting?

Here's pics of the bike - taken before I switched back to the new OEM intake setup:

Wellll..My '75 Z1B 900 stock carbs ,airbox 4n2 Mac Exhaust , stock jetting and gearing...gets around 33MPG!! I do have a question though, is that a PlexifairingIII Windshield? If not what brand?
I am thinking about getting one for cold weather riding, did it make a difference?
By the way....Beautifull Bike!!!!
Thanks

TZ ED

YES, it is a Plexifairing - very nice mounting setup and hardware, will remove relatively quickly and easily if desired - and makes a BIG difference in riding, especially in cold weather - no buffeting - even if it DOES cost me a few MPG, it WILL stay on the bike!

Thanks for your post - it helps to get enough responders to form some sort of average.

Plexifairing III? AKA "Barn Door"?

I have one on my 750 twin but I'm thinking about getting something smaller.

It's big enough, for sure - but sure keeps the wind and other nasties off nicely - payback may well be MPG - but I need more data...

You can pick up some MPG by re-gearing. I went up a countershaft tooth on my 82 K2 1000 LTD. I run a Vetter and side bags, and have done 1400mi trips with the average up around 45.

hi and it is a nice bike sorry cant help you but would like to know more about header and pipe :huh: thank you

My '78 KZ1000 gets about 37-38 mpg @ 60-65 mph. Stock carbs and pipes. I changed sprockets to the lowest numerical gearing available for hi-way riding. I think my mileage went up a mile or 2 when I added the Windjammer fairing. I cut 3" off the 'Jammer windshield so I could see over it.

The Windjammer is more aerodynamic than I am. I think your mileage is in the acceptable range.

I believe the 135 jets are too large. I read some guidelines that recommended 2 sizes for a 4:1 exhaust; and 2 more sizes for pods. Then they recommended subtracting one size. This would mean 3 jet sizes over stock, which would be 120 + 2.5 + 2.5 + 2.5, or 127.5. And at 3,500 feet of elevation, even that may be too rich. I am guessing that you have BS34 carbs. Mine are BS32, and stock jetting is 107.5. My bike ran best by going up only one jet size, but I have almost stock exhaust, and standard air box and filter.

Regarding the windshield: I did a comparison on my KZ650, running with a windshield that was about half the size of yours. (Of course I have half the displacement also). I did 3,000 highway miles at about 75 MPH; then removed the windshield and did another 1,500 miles at the same average speeds. MPG averaged about 2% BETTER without the windshield. I would have thought that the smooth plexiglass shape would be better, but apparently the wind can find its way around our bodies, arms, helmet, etc. easier than the windshield. My windshield has a lot of turbulance taking place right behind the outer edges.

The speed you run makes a tremendous difference in fuel economy. At 60 MPH, I would have expected better than you got. My guess is - that the carb jets are hurting you more than the windshield. If you run faster, then the windshield will take its toll. Hope this helps.

WABBMW wrote: I believe the 135 jets are too large. I read some guidelines that recommended 2 sizes for a 4:1 exhaust; and 2 more sizes for pods. Then they recommended subtracting one size. This would mean 3 jet sizes over stock, which would be 120 + 2.5 + 2.5 + 2.5, or 127.5. And at 3,500 feet of elevation, even that may be too rich. I am guessing that you have BS34 carbs. Mine are BS32, and stock jetting is 107.5. My bike ran best by going up only one jet size, but I have almost stock exhaust, and standard air box and filter.

Regarding the windshield: I did a comparison on my KZ650, running with a windshield that was about half the size of yours. (Of course I have half the displacement also). I did 3,000 highway miles at about 75 MPH; then removed the windshield and did another 1,500 miles at the same average speeds. MPG averaged about 2% BETTER without the windshield. I would have thought that the smooth plexiglass shape would be better, but apparently the wind can find its way around our bodies, arms, helmet, etc. easier than the windshield. My windshield has a lot of turbulance taking place right behind the outer edges.

The speed you run makes a tremendous difference in fuel economy. At 60 MPH, I would have expected better than you got. My guess is - that the carb jets are hurting you more than the windshield. If you run faster, then the windshield will take its toll. Hope this helps.

I got this bike late last Summer - thru the winter months, I've been working my way thru some badly set up BS34 carbs - bike came with PODs and the Kerker header and a VERY restrictive un-matched muffler - and the bike was running extremely poorly - especially at low speeds and at idle - way too rich! Some PO had apparently up-jetted strictly by "recommendations", rather than by testing experience - the main jets were 130's, and the pilot jet was a 40. Plugs were running extremely blackened with soot.

I opened up the exhaust, dropped to 120 mains, and 37.5 pilot - did a valve adjust and installed 6-slot needle to replace the single slot OEM - and reinstalled the OEM airbox with a new filter - bike ran great at all speeds and gears/load - but was noticeably down on power, and plugs running white as snow - needles were down in the 4th slot from top at that point.

I then went to the 3rd slot from top on the needles, and the 130+ main jets, and power returned, and plugs run a good tan color under the riding conditions stated in the lead post. If anything, I might drop the needles 1 more slot, but need to get more riding time before any more carb adjustments, as it is, plugs may well run a bit lighter at higher speeds, 2-up, and/or up in the steep mountain grades we have here - heavier engine load - and then too, there may well be rides down in lower elevations, where the jetting would benefit from being a bit on the rich side...

I'd far rather have the engine running SLIGHTLY rich, than lean, for obvious reasons - and since the plugs are reading well in the ball park, sorta hate to drop back down to the 120 main jet levels where power fell off and plugs looked too lean - besides, as close as I am now to what appears best running, I sorta doubt a main jet change would provide more gains than losses - if anything, I'd be tempted to next drop the needles one more slot, then see how the plugs read - but doubt MPG would be significantly improved.

One of my main purposes in this thread, is to see what other owners of similar bikes - those in the same KZ1100 displacement as mine - do on MPG, either with, or without windshields, to see how mine compares. So far, it sort of a mixed bag - with my bike set up as it is, not being all that far off from other similar bikes.

Thanks for your well detailed and thoughtful post - more input always appreciated!

With those CV carbs your Mains and Needle position do nothing for mileage when cruising.
Its all about the pilots and mixture screw adjsutments.

The pilots should be the stock 37.5 you say is in there, as the 40's would be to herky-jerky performance wise.

If you tune your mixture screws for highest idle, then they ARE too rich in comparison to the stock positions.

For example:



The bike should be running reletively lean at and off idle - as there is very little load nor power demand, and generally tuons of air cooling the motor. Closer to stoichometric or leaner is perfectly fine.
When you demand power - the engine demands fuel and swings back towards the richer side of things as it transitions to the Needles, Mains even more.

Dont be afraid to have fairly lean plugs for cruising. They should have just a whisp of black ring down at the bottom of the porcelin where it meets the metal inside, and a nice toasty marshmallow brown ring around the tip and thensome. The rest being reletively clean and white is fine - so long as there is no black/silver specs and the heat strap reads around the middle. Then timing and combustion is good.



You want excellent fuel economy - tune your mixture screws about a full 1/2 turn leaner than the highest idle point on those carbs.

"They should have just a whisp of black ring down at the bottom of the porcelin where it meets the metal inside, and a nice toasty marshmallow brown ring around the tip and then some"


That, describes my plugs EXACTLY!