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Hey guys, I thought I would run this senario by you and see if it sounds familiar to anyone.
I've been searching and reading back posts for a couple of days now without any luck so I thought I would go ahead....let me know if this has already been asked and I missed it.
...O.K.
Long back story...
I've bought a 1980 GS750 ET with 20K on it and a full Kerker header on it awhile ago and it ran great when I got it. No flat spots, no hesitations, all with the stock airbox on it. The guy I got it from had just go it in trade and didn't know if any carb work had been done.
I took it home, did some burn outs with it and then, pulled the air box out to get at the battery to check for charging system problems, changed plugs, (same heat range), plug caps, and eliminated the vacum petcock and just have an in-line shutoff now. (Yes,I plugged the vacum fitting on the carbs that the petcock pulled vacum from.)
Put it all together and I have a big, BIG dead spot at 3 grand. Now, it idles PERFECT, revs up to 3 like and animal...and then almost dies as soon as I get to 3.
So I pull the carbs and clean them. (They were clean anyway.) No cracks or holes in the diaphrams on the CV slides. And no visible modifications inside. Put them back on and still no change. So I pull them and clean the hell out of them again. (By the way the mains were 117.5 when i opened the bowls.)
No change.
So I pull the airbox, run pod filters, (K&N) and jet up a size on my main jets. AND I clean the carbs again.
Flat spot moves up 500 rpm at MOST, but is still the same.
Every time I check the plugs they are grey\white. And its a odd "paint like" white if that makes any sense....not a burned or ashen quality about them....but a almost perfect smooth paint like color to them.
So I change plugs.
3 times. Every time a brand new set of NGK's and they all come out the same.
So I kept going up in jets. Two more steps. Not a whole lot of change in the flat spot. And the plugs never changed color.
A freind suggest's that the intakes are leaking. I pulled them and took a closer look, and they do have some small cracks, but nothing that makes it through to the outside of the intakes. But I went ahead and siliconed them up and then wrapped them in good 3M super 33 electrical tape nice and tight. (just to see if I might get a result...I plan on changing them with new ones in the future.)
But, no change at all.
I keep coming back to the fact that it ran fine with the airbox and old crappy plugs and caps....but not after I put good ones in and re-installed the airbox.
The elimination of the vacum operated petcock couldn't have caused this.....so what am I left with?
I mean this thing ran fantastic and now I can't possibly get it past 3 grand no matter what.
I guess that's what I get for fixing what wasn't broken.
Any ideas?
Thanks . Sorry if this is repetative.
I've been searching and reading back posts for a couple of days now without any luck so I thought I would go ahead....let me know if this has already been asked and I missed it.
...O.K.
Long back story...
I've bought a 1980 GS750 ET with 20K on it and a full Kerker header on it awhile ago and it ran great when I got it. No flat spots, no hesitations, all with the stock airbox on it. The guy I got it from had just go it in trade and didn't know if any carb work had been done.
I took it home, did some burn outs with it and then, pulled the air box out to get at the battery to check for charging system problems, changed plugs, (same heat range), plug caps, and eliminated the vacum petcock and just have an in-line shutoff now. (Yes,I plugged the vacum fitting on the carbs that the petcock pulled vacum from.)
Put it all together and I have a big, BIG dead spot at 3 grand. Now, it idles PERFECT, revs up to 3 like and animal...and then almost dies as soon as I get to 3.
So I pull the carbs and clean them. (They were clean anyway.) No cracks or holes in the diaphrams on the CV slides. And no visible modifications inside. Put them back on and still no change. So I pull them and clean the hell out of them again. (By the way the mains were 117.5 when i opened the bowls.)
No change.
So I pull the airbox, run pod filters, (K&N) and jet up a size on my main jets. AND I clean the carbs again.
Flat spot moves up 500 rpm at MOST, but is still the same.
Every time I check the plugs they are grey\white. And its a odd "paint like" white if that makes any sense....not a burned or ashen quality about them....but a almost perfect smooth paint like color to them.
So I change plugs.
3 times. Every time a brand new set of NGK's and they all come out the same.
So I kept going up in jets. Two more steps. Not a whole lot of change in the flat spot. And the plugs never changed color.
A freind suggest's that the intakes are leaking. I pulled them and took a closer look, and they do have some small cracks, but nothing that makes it through to the outside of the intakes. But I went ahead and siliconed them up and then wrapped them in good 3M super 33 electrical tape nice and tight. (just to see if I might get a result...I plan on changing them with new ones in the future.)
But, no change at all.
I keep coming back to the fact that it ran fine with the airbox and old crappy plugs and caps....but not after I put good ones in and re-installed the airbox.
The elimination of the vacum operated petcock couldn't have caused this.....so what am I left with?
I mean this thing ran fantastic and now I can't possibly get it past 3 grand no matter what.
I guess that's what I get for fixing what wasn't broken.
Any ideas?
Thanks . Sorry if this is repetative.
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