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GS400 tuning issues

  • Thread starter Thread starter TrikerJoe
  • Start date Start date
Mekanix said:
Hard to tell anything while its on the stand. But it should rev to the mood easily.

I've been finding allot of info on the 500's upping to 140-150 mains and 40 pilot and then shimming the needle up 4mm. That alone is what they claimed worked best without using a kit.

The carbs are a little different than yours Pete. Its just in the bowls and how they designed in there.
Click to expand...

Thanks very much for the numbers. I've ordered every second size main up to 150 so that I can tune it up. Hopefully I'll be able to get the tune a bit closer on the main stand until I can get it out on the road for proper tuning.

Until then, should I start a new thread on drilling the vacuum slides to find out what size hole I need? I'm still getting used to the etiquette side of the forums...:confused:

Thanks!!!
 
Etiquette here is pretty forgiving. And its still in the realm of performance/tuning anyways.

First thing is to get the main right for the best top end pull at wot and not running lean. Then you can play with the rest of the ranges.
 
I've been able to get out on the road for some test runs!
Here is where I am at now.

140 main jet
Jet needle at position 5
Stock pilot jet
1.5 turns out on the AF screw
Vacuum slide hole drilled to 3.14mm from 2.82mm
Vacuum slide springs swapped from 111/112mm to 107/108mm springs from a spare set of gs400TX carbs.

After drilling the vacuum slide hole and putting in the shorter springs, I am able to get through my midrange to WOT to do some drag style plug chops and those chops are coming up with white plugs, so I am guessing I need to go to a larger main jet?

That is what I will do next and report back.
Thanks for your interest!
 
White plugs is definitely lean, so keep going :)

When you say needle at position 5, is that the position furthest or closest to the tip?

If that's the furthest position, then you likely have it far too lean as it will lower the needle.
 
pete said:
White plugs is definitely lean, so keep going :)

When you say needle at position 5, is that the position furthest or closest to the tip?

If that's the furthest position, then you likely have it far too lean as it will lower the needle.
Click to expand...

Position 5 in this case is the one closest to the tip, furthest from the end and closest to the middle if that makes it more clear!:) The setting that pulls the jet needle the furthest out of the needle jet.
 
Ok cool, that's the richest setting... just thought I'd best make sure :)

Oh, and one thing GregT mentioned earlier in the other thread about a flat spot in throttle response after drilling...

I'm starting to see what he's saying now, and yes I guess that's probably what I have now.

I can just crack the throttle up to say 1/4 and get off the line like I used to pretty much.

However, if I crack the throttle a bit more than that, probably 1/2 or more... it's a world of difference and she hauls in comparison.

So yes, I think the drilled vacuum holes does give a bit of a flat spot in the throttle range... but it's not a bad thing at all :)
 
Ok, here we go again!

So I opened up my carbs once more to swap out to my 150 mains and decided, just for kicks that I would double check my float height.
Prepare to laugh at me... the float heights were around 25.5 mm (spec is 22.4).
I must have measured from the wrong spot last time as I hadn't done as much reading on the subject as I have now, and this has been corrected to 22.3mm on each float, measured from the gasket mating surface rather than the lip around that mating surface.
The difference is, as I'm sure you will all already know, quite astounding. I can now run around at different throttle settings and everything feels much much better.
It's a little cold out today (-6C this morning), already went for one test ride this evening. Seems to be some color in the plugs but I will have to do some more plug chops to be sure. WOT is feeling pretty darn good!!!:D
I'll let you all know when I find out more!
 
pete said:
Ok cool, that's the richest setting... just thought I'd best make sure :)

Oh, and one thing GregT mentioned earlier in the other thread about a flat spot in throttle response after drilling...

I'm starting to see what he's saying now, and yes I guess that's probably what I have now.

I can just crack the throttle up to say 1/4 and get off the line like I used to pretty much.

However, if I crack the throttle a bit more than that, probably 1/2 or more... it's a world of difference and she hauls in comparison.

So yes, I think the drilled vacuum holes does give a bit of a flat spot in the throttle range... but it's not a bad thing at all :)
Click to expand...

Wrong way round - a flat spot is a LACK of response - without drilling you had a flat spot where the vacuum wasn't enough to lift the slides and airflow stalled. Drilled, the system works as intended and slide lift matches the engines needs.
 
GregT said:
Wrong way round - a flat spot is a LACK of response - without drilling you had a flat spot where the vacuum wasn't enough to lift the slides and airflow stalled. Drilled, the system works as intended and slide lift matches the engines needs.
Click to expand...

Actually Greg, I'd meant to come back to this and say I think I'm mistaking response at low rev's with a flat spot :o

After doing the drilling I just kept opening the throttle because it was so fun... but of course anything below about 5K is just not the same as above say 5.5K... therefore my misinterpreted flat spot...
 
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