Yikes, awful fuel economy.

[Detman101]

Hello all, Just checking in.

I took the GS750 for it's maiden voyage this weekend with my cousin riding along with me on his Harley just in case it died on me. The bike performed good. We filled it up at the gas station and the indicator sat at the "F" mark. By the time we got to the bike shop 14 miles away it was sitting on the halfway mark!! 8O 8O

Now, I know that the stage-3 kit will increase intake and fuel consumption but impossibly by that much. From what I see so far the bike is now running a little lean in the 3-5k RPM zone requiring further adjustments.
Getting light popping and slight hesitation. After 4th gear everything is fine and no issues so I know I need to readjust my jet needles again. I'm going to do this after trying the "radiator-hose-as-carb-manifolds" trick and see if I can get it to steadily idle that way. As it stands now the bike will idle at 2000 rpm or whatever I set it at but surge when I get it going.

That could be due to the lean condition at 3-4krpm or it could be leaky boots. Either way I'm trying the hose trick then inspecting the boots. These things are way thick! I don't see how they could crack or leak!






Dm of mD
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[lhanscom]

Are you sure that you actually used all that fuel, or is your gas guage just reading 1/2 tank? The fuel guages aren't real accurate. If you're having mixture problems, which you are if things are popping, then you're not going to get great mileage anyway, as you'll be giving it more gas to compensate for the power loss. While you're looking for air leaks, check out the o-rings between the head and the rubber boots, these tend to go bad. Good luck, and fix the lean problem quick so you don't burn a piston. I like to get it a little rich, and work back from there, I find it safer.

[Detman101]

O-rings?? There seem to be o-rings built into the boots.
Do you mean the little gap on the carb where it goes
into the boot to the engine? There seems to be a ridge
inside the boot that slips onto/into that gap on the carb
hole to the engine.
*See picture please*


Guess I have to buy some extra ones then...

I, too, like it richer but the smell of gas was so heavy
that it burned my eyes just riding the bike. Perhaps I'll
richen it half a clip by taking out the adjusting washers.
Yeah...that should do it. Then I can tackle this unsteady
idle problem...



Dm of mD

[Anonymous]

fuel milage

I'm pretty sure that its your fuel gauge and not the bike. Unless your dripping it out on tne ground....................My 78 Gs 1000 gets about 39 to 42 which I consider to be poor(carbs) my old 750 Honda supersport got from 40 to 50 mpg..............................my fuel gauge rarely shows full but it sits at half a tank okay sometimes

[Detman101]

I'm praying that it is my fuel gauge. The gas would have
to be flooding for it to run down like it seemed to. I will
see just how many miles I get out of this tank and get
my figures from there.

Thank you,
Dm of mD

[Hoomgar]

My last carb rejet/rebuild left me with a kick butt running bike but the worst gas mileage I have ever seen on a street bike. I got an average of 20 MPH. If you were getting what you really said then your 750 was eating about the rate of 5 mpg. I don't believe that is possible. If you were leaking that much you surely would have noticed it. I would bet large dollars on a faulty gas gauge.

[Detman101]

Awesome, Thanks hoomgar. I'm really having second thoughts about this stage-3 jet kit now. I still have my stock parts and if the gas mileage doesn't get into at least the 30MPG range then I'm going back to stock.
Good thing I didn't sell the parts on ebay hehe.


Dm of mD

[frosty5011]

Detman,

The o-rings Luke was talking about do not go where you indicated. You have to take off the rubber manifolds (2 screws holding them to the cylinder head). Then you can see the o-rings he's talking about.....there is a groove on the mating surface.

[Anonymous]

I think Detmans boots go from the carbs onto aluminum spigots on the head like my 1100. I don't believe they bolt on like my 400.

Steve

[Detman101]

Yes, I have the bs32ss carbs like the ones in the carb cleaning
guide. There are no o-rings. The manifold boots have an o-ring
looking ridge built into them that go into the gap on the
carb body and the manifold inlet.
See picture in my second post up above please for references.

Dm of mD

[KEITH KRAUSE]

My manifolds have both the raised ring inside that mates with the carb body groove and an o-ring that fits in a groove on the front of the manifold. I think you should have the same manifolds. Can you show a pic' of the front of them?
Replacing these with radiator hose is a poor choice, they'll leak. You'll never get the jetting correct with intake leaks. If the manifolds are cracking, (can you show some side pic's of all 4?) replace the manifolds and o-rings, coat the o-rings with hi-temp' brg grease and torque to 6 ft/lb. Manually sinc' the carbs at least. THEN see how the bike runs and work on the jetting.
The gas gauges are not real accurate.
You sound frustrated, but you can't cut corners to save money and expect the carbs to work right. You have to use the correct parts and be patient with the jetting.

[Detman101]

My thanks again Keith. I will take off all 4 of the manifold boots
tomorrow after work and take pictures and look for cracks.
Can you recommend a clamp that will clamp tighter than the stock
ones that come on the manifold boots? I want something that will
completely tightly seal and hold that boot on the engine.
Also, what is BRG Grease? Is that just high temp grease?

thanks,
Dm of mD


EDIT: IT'S HERE!!!

[KEITH KRAUSE]

Brg is just short for bearing. The stock clamps, if yours are the correct ones, work fine. If you look, they are designed to fit on the manifolds. The carb body's groove mates with the manifolds raised ring and the clamp tightens down beside this. If you try to use a regular hose clamp, I would be concerned about how wide it is. It might exert pressure differently than the slim, stock clamps. It could tend to crush the groove/raised ring section of the manifold.

[Hoomgar]

I was thinking that same thing Keith and should have voiced it.
You can get a lot of torque on things with those hose clamps and
it would be real easy to even crush a 20+ year old aluminum based
thin walled part if you were to get crazy with the tightening of it.
If you do use hose clamps Detman be sure to watch how tight
you make them.

[Detman101]

Thanks for the advice guys.
After checking my carb boots I can't find
any cracks. I believe that the surging was
due to the lean condition the bike was running in.
I noticed that the tach didn't bob up and down when
I was idling. Only when I was riding in traffic in the
3-5k rpm range. I will reinstall my boots and adjust the
carbs now. Thanks guys.
Time's gettin close hoomgar...soon I'll be riding with you in another month or so.

Sincerely,
Dm of mD