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finally got it running... well at least at some RPMs????

  • Thread starter Thread starter Anonymous
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Anonymous

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I bought a 79 gs750 about two months ago. I finally got it running and registered. I have been driving it for a couple of days now and have a porblem.

The thing is that the bike runs pretty good up to about 4000 RPMs and then looses power from there till about 6500 RPMs. After 6500 RPMs it takes off like a champ again. WTF? I have pulled the carbs cleaned and put them together. I also set them to the factory settings I found on this sight. I didn't however sync. them basically because I don't know how. Could this be the problem? Else, maybe the fact that I am waiting on a factory style air filter so I made one to fit it could be the problem? I think the one a made isn't dense enough so it could be getting too much air. Other than that maybe I should time it again or something. Is this a common problem at all? I have been searching this sight and haven't found my problem yet.

P.S. Thanks to all of those who post information on this sight. I dont' have a manual for my bike yet and because of this sight I was able to get it running.
 
Out of sync carnbs are most noticable down low. Once the carbs start opening up the difference isn't that great unless they are way out. The filter could be the problem. Get the proper filter before you start playing with jetting too much. You may need to raise the slide needle a notch.
 
Most def the filter

Most def the filter

I'm pretty sure it is the filter. I've owned a GS650, GS750 and a GS850 and any change in air resistance from the airbox makes a huge difference. Try putting in the stock filter that you are waiting for and that should remedy most of your problems.

Best of luck!
JV
 
Re: finally got it running... well at least at some RPMs????

As Billy said, out of synch carbs are most noticable low in the rpm range, however (I have a 79 750) and I know from experience that the correct air cleaner/airbox restriction is essential. Its also a fact, (on my 750 anyway) that a carb synch if set to the wrong vacuum levels will result in a HUGE flat spot between 4000 and 6500. I would expect that your plugs are burning very light. I dont believe the problem is your carbs themselves, it is the vacuum range they are working in that is incorrect.
The carb vacuums cannot be set correctly by sight or ear, it must be done with vacuum stix/guages. Set the carbs to draw 10 in (25 cm) Hg @ 1200 rpm. You can get a vacuum carb stick from cycle recycle for about $30
(if I remember correctly).

(I know the books and it appears most people agree the carb synch is done at a higher rpm than I use, but I have done it both ways and found setting at a low rpm (for a stock 750 anyway) gives the best results and smoothest running engine.)

If you buy the carb stiks, just yell when they arrive and I or someone else will be glad to post on how to use them and set up the carbs.

Earl

MLJL said:
I bought a 79 gs750 about two months ago. I finally got it running and registered. I have been driving it for a couple of days now and have a porblem.

The thing is that the bike runs pretty good up to about 4000 RPMs and then looses power from there till about 6500 RPMs. After 6500 RPMs it takes off like a champ again. WTF? I have pulled the carbs cleaned and put them together. I also set them to the factory settings I found on this sight. I didn't however sync. them basically because I don't know how. Could this be the problem? Else, maybe the fact that I am waiting on a factory style air filter so I made one to fit it could be the problem? I think the one a made isn't dense enough so it could be getting too much air. Other than that maybe I should time it again or something. Is this a common problem at all? I have been searching this sight and haven't found my problem yet.

P.S. Thanks to all of those who post information on this sight. I dont' have a manual for my bike yet and because of this sight I was able to get it running.
Click to expand...
 
Thank you for the replies. I know a guy that works for beer. He is kind of a motorcycle buff. I bet he would sync the carbs for me. How long does it take? I don't want to ask someone to do a pain in the ass thing for me if I can buy this tool and figure it out. Thank you all again fo rthe replies.
 
I know a guy that works for beer. He is kind of a motorcycle buff.
Click to expand...

In a way, don't we ALL work for beer ? (that is my major philosophical observation of the day). Just don't give him the beer till he's done, of course. :D
 
If you decide you want to buy a set of carb sticks I have a set I don't need. I've got RS flatslides on my bike and the carb sticks are pretty much useless for me. With the flatslides you just bench synch and forget it.
 
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