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How does a bike run when it has not been jetted properly?

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

Guest
1977 GS750 with pods and header.

I bought this bike with the mods on it. The bike had done some racing (wired bolts etc), it has original electronics on it (points). It allegedly has a bore kit in it, but I can not confirm

It runs good and runs strong. It likes to idle at 1500 RPM rather than 1100. I have not toyed witht the timing or points at all and I assume that could be the culprit. How would the bike run if it had these mods and had not had proper jetting?

Thanks
rgierer
 
like mine....

haw haw haw

:lol:

Nah, mine runs pretty good. Just stay upwind of it at stoplights. The fumes will make your eyes tear up. :wink:
 
The jetting may or may not be right, but first replace the point's and do the timing.
Then come on back.
 
Oh! and check your valve clearance's,then if you can do a comp test, then we look at the carb's.
Need any help just ask
 
If you're sure the motor and electrics are functioning properly, here is a little insight to carb jetting:

1st, there are three curcuits that the carb uses. The pilot circuit is used for idleing and up to about 1/4 throttle. From about 1/4 to 3/4 throttle, you are on the needle curcuit. 3/4 to wide open is all the main jet circuit. Each circuit It's been said that the proper way to tune is to work backwards, that is to get the bike to pull hard on the main jet at wide open throttle first. But to ride the bike in any way, you must get it to idle decently. If the bike doesn't pull hard at WOT, you need to change your main jet. Too small of a main and you will have a lean condition, most likely the bike will surge and probably pop some. Too rich and you will be flooding the cylinders and the bike will feel weak. From there, it's said you should do the same with the needle circuit, shimming the needles or adjusting the "E" clip if you are lucky enough to have one. Symptoms will be the same as the main for the needles. The pilot circuit is the most complex, as it's harder to tune properly when you are dealing with a bike that can pull hard even with a poor mix at 1/4 throttle and less, but to change the characteristics of this circuit, you need to adjust idle screws (does the 77 have a mixture screw as well?) and jet sizes.

In a simpler answer to your question, all the following are clear indicators that your bike is not jetted correctly:

1. Flat spots (poor pulling/power) at any range of the throttle
2. Exhaust popping
3. Inability to get a good idle
4. Poor fuel mileage
5. Running "hot"
6. Surging

The quick way to determine any of these problems is to put new plugs in, run the bike for a few minutes on one of the circuits (at 1/4 throttle for example), kill the ignition immediatley, and then pull the plugs. If the fireing tip and insulator is white, you are running to lean. If it's dark and sooty, you are running to rich. This can be done on any of the circuits, but you should use new plugs for each test.

Note that there are 1000's of things that can seem like a jetting problem when they aren't. Do a compression test, if that isn't ok fix the problem. Exhaust leaks, intake leaks, bad ignition, poor timing, poor float heights, bad fuel delivery- all these can seem like a jetting problem, as well as many more things.

Take all the above at your own risk, I've been trying to get the jetting right on my bike for months. I know the rules but apparently can't seem to follow them.
 
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