SOHC.co.uk Forums > CB750
Flat spot 65-70mph
JonnyB:
uk_kev wrote:
--- Quote ---If it is all set correctly then I would think it is the jetting due to the filter change more than the exhaust? I wonder do the sport version with the single pipe use the same jetting as the four pipe models? if not then that may be a starting point.
--- End quote ---
That's a good point, I remember before my re build I didn't have this problem, but I did have to change the carbs, from an unknown model, and now I too have a flat spot. Any one know the 750 F1 jet sizes?
Spitfire:
Hi Ray,
Does it drive through the flat spot ? It does sound like carbs to me but I am no expert, check the simple things first:
Make sure that the choke is operating correctly, the K7 has a choke cable rather than the simpler mechanical choke of the earlier carbs.
Give it a quick run with the air filter element removed, just leave the airbox empty.
Check your float bowls for dirt, check the main jets are clean, K7 main jet should be 115, slow 35.
The K7 series was similar to the CB750F2 and had the same later carbs with the accelerator pump.
Buy a good manual, David Silver spares sold me a good one for the CB750F2/K7.
Jonny the jetting for the F1 is 105 main and 40 slow.
Cheers
Den
uk_kev:
Spitfire wrote:
--- Quote ---
jetting for the F1 is 105 main and 40 slow.
Den
--- End quote ---
There you go, this could be all you need to sort out the flat spots, just change the jetting.
uk_kev:
Someone has mailed me saying that if you change from the 4/4 pipes to the 4/2 pipes then you need 120 jets?
uk_kev:
After reading the \"satanic\" CB750 site they recomend, For carbs with velocity stacks or individual pod filters, 125 mains seem to be a good starting point.
So it seems you pays your money, and takes your choice.
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