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1986 GSX750esd carb issue?

  • Thread starter Thread starter oldboyonrgv
  • Start date Start date
O

oldboyonrgv

Guest
Hi
Wondering if anyone has an answer to this one.

Bike as above - has a 4 into1 system and K&N airfilter in standard airbox.

Bike has been dynoed and produces 84BHP so engine is sound and jetting is optimised.

BUT at 4-5K revs on a constant throttle the bike seems to 'pull back' and then struggle to pick revs up once more throttle is applied. Carbs have been stripped and cleaned four times so they are cleaner than new!! after each strip and clean the bike has been set up on the dyno. The only thing I can think of is one of the CV membrane's has hardened off, although they have also been checked on each occasion the carbs have been off. I am a bit stumped now.....
 
Are you sure your bike is a 86? because the model that you posted is a 83. And unless you are from somewhere other that the state's we didn't get a GS750es in 86, we got a GS700es. the last letter in your model tells the year and I believe 86 is a G.
As far as your power lag , you could try shimming your needle up. Or you could buy and install a Dyno Jet kit because in order to really optimise you fuel system to your pipe and filter. that will have to be done.
 
Sorry yup I am in the U.K - the bike is a European import (Belgium) and is a 1986 vintage, you are correct it came into the U.S as a 700..

As I said before the bike has been set up on the dyno so its not a jetting issue...
 
OK But I didn't say it was a jetting issue , I said you needle height may need changing. And to really optimize, the dyno jet kit would be a plus because it has the better needles. I'm not familiar with the bikes over seas but would dare guess they have the standard needle that are not that great for tuning
 
Surely putting a spacer under the needle will richen the mixture?
 
No, putting a spacer under the clip will only increase spring pressure. What is needed is to remove the thick nylon spacer above the clip and replace it with a few washers with less total height than the spacer.

Yes, it will richen the mixture, but that will relieve the symptoms that you describe in your first post.

.
 
Considering that it is a European bike to begin with and probably came stock with adjustable jet needless, if they need adjustments, I would just change the E-clip position or add a 3mm flat washer to adjust half clip positions.
 
Thanks for the replies folks.

Hmmm I dont think you understand the issue... I already explained that the bike has been set up on the dyno, so the mixture is correct through the rev range - no point in mucking about with the needles because the mixture is correct.
I think you are getting mixed up with the flat spot which usually worsens when you fit a 4 into pip and a filter, this is not that issue.

So thinking caps on, the problem manifests itself on the cruise at 4-5k rev's, I have semi convinced myself that one or more of the cv slides are closing down but was hoping some one would confirm that.....

By the way despite being new to this forum - I have been building and racing bikes for many years so have come across most situations before, its just that this one has me beat at the mo....
 
If the engine is "hunting" between 4-5K, the main jets need to be richer more than likely would be my guess.
 
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