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irregular RPM when idle

  • Thread starter Thread starter Anonymous
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Anonymous

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When I start the engine of my GS 750 '77 it runs very irregular.

What can I do to make it run smoother.

Other question:
Why are not all exhaust pipes evenly hot?

Thanks

Rob
 
Re: irregular RPM when idle

rob_panis said:
When I start the engine of my GS 750 '77 it runs very irregular.

What can I do to make it run smoother.
Click to expand...

There are many possibilities. Do you have all the standard air intake system mounted and screwed down? That is all very sensitive stuff, and it must be situated exactly as the manufacturer intended or it will be trouble.

Other question:
Why are not all exhaust pipes evenly hot?
Click to expand...

If one of the exhaist headers is cold, that cylinder is not firing. You need things for a cylinder to fire: air, fuel, compression and spark.

Air is easy. Make sure that your air filter is attached and clean as said above.

For fuel, make sure your carbs are clean as demonstrated in the Carb Cleanup Series.

Compression is easy to check if you have the tool. Find a compression tester and follow the instructions. Be sure to get a 12mm on that will fit your spark plug. They seem to be smaller than typical automotive plugs.

Last is spark, also easy. Pull the spark plug out, note its condition. Refer to this page for descriptions: http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html If your plug is oil fouled or make sure that you start with a clean plug of the correct gap as per your GS manual. Do not assume that the plug manufacturer set them correctly. Every engine is different. Once you have a good plug, have the plug out of the cylinder but still connected to its ignition wire. Touch the plug to the engine case to complete the circuit, then turn over the engine so that you can see the spark. It should be blue and fat, easily seen during the day. Yellow sparks are no good.

So you see that the most difficult component is fuel, and that's why there are so many carb questions floating around the forum.

Check it out and tell us what you come up with.
 
Re: irregular RPM when idle

A 77 750 is points ignition. If you still have the points system in it, the reason for irregular running is usually due to a difference in ignition timing between the 1,4 pointse and the 2,3 pointset. also, old points with pits will cause uneven and rough running. The first thing I would do is replace the points, gap them and set the ignition timing. After that, if you still have a pipe or two that at idle rpm is a different temp or cold, then you need to reset or clean your pilot jets. set the fuel pilots to 1 1/4 turns out, set the airscrews to 1 3/4 turns out and then do a vacuum synch on the carbs setting them to about 10 in hg at 1200 rpm.
also, check your air filter to be sure it is clean.

Earl


rob_panis said:
When I start the engine of my GS 750 '77 it runs very irregular.

What can I do to make it run smoother.

Other question:
Why are not all exhaust pipes evenly hot?

Thanks

Rob
Click to expand...
 
I have allready cleaned out the air intake, cleaned the (very dirty) filter. Cleaned the carbs. And all plugs are giving nice sparks.

So now I'll do the ignition point thing.
If that doens't help i'll go for the pilot jets.

Hope it works
 
I usually recommend setting the max points gap to 14 thou, but I've recently been doing some tuning on my 750 and it sppears to run a little better with the gaps set to 12 thou. When you set the static timing, pay close scrutiny to getting both sets of points to open at precisely the same instant. They both must open exactly on the timing mark, a little this way or that is no good. It will not run worth a crap if your off more than 1/2 degree.

Earl


rob_panis said:
I have allready cleaned out the air intake, cleaned the (very dirty) filter. Cleaned the carbs. And all plugs are giving nice sparks.

So now I'll do the ignition point thing.
If that doens't help i'll go for the pilot jets.

Hope it works
Click to expand...
 
Thanks all.
I got some new ignition points, installed them properly.
Also got one new sparkplug (That was the one cilinder running cold).

It now works excellent.
Runs smouth even goes 120 km/h in third gear again.

I still have to do some tuning on the gaps for on even smoother running bike.

Thanks all for the help.

Rob
 
my manual says a point gap between 0,3 and 0,4 mm?

Is this the same as your 12 and 14??
 
Divide the metric by 25.4 to get inches.

.3mm = .3/25.4=.0118" or .012"
.4mm= .4/25.4=.0157" or .016"

That's all the help I can give here. :lol: :lol:
 
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