SOHC.co.uk Forums > CB750
Clutch plates
Trigger:
The Main jets on a 750K started out at 125 and then Honda dropped them to 120 on the early 750K0's. I have lost count on how many different carb numbers that were fitted to the 750's over the 10 year period.
The early 750's had 300 exhausts which have less back pressure than the 341's so, the jet range was 125 down to 120 but, some had 110 in the K1. Then the 341's were fitted to the K2 onwards that had 110 as standard in the UK. And the K2 was sold in the UK from August 1972 to 1975. Don't know about the K3, K4, K5 as these were USA bikes.
And then the K6 came out in the UK with 110 or 105 jets.
I have also lost count on how many different needle numbers across the 750 range and can be a struggle to find the sweet spot sometimes. My own K6 runs sweet with 110 with a little discolour on the plugs, pulls well and gets a little scary over 110 mph.
I always set the RPM at 1150 rpm as this puts less strain on the engine. Never had a 750 that was happy at under 900 rpm.
Martin6:
Thanks for explaining Trigger.
I recently replaced 2 of my K6's carbs with better condition ones, bought as a bank off ebay, complete with gantry. I replaced the brassware, so all 4 were consistent with 105 mains. Relived the jetting is the only difference on the later bikes.
Trigger:
--- Quote from: Martin6 on July 27, 2023, 08:09:47 AM ---Thanks for explaining Trigger.
I recently replaced 2 of my K6's carbs with better condition ones, bought as a bank off ebay, complete with gantry. I replaced the brassware, so all 4 were consistent with 105 mains. Relived the jetting is the only difference on the later bikes.
--- End quote ---
Are the carbs all the same number stamps ? No need to replace the brass, just used the original brassware once cleaned .
K2-K6:
--- Quote from: Trigger on July 27, 2023, 01:03:34 AM ---
--- Quote from: Athame57 on July 26, 2023, 11:46:13 PM ---
--- Quote from: Trigger on July 26, 2023, 11:37:24 PM ---No good in a 400 engine. You need to use 10w/40 or 15w/40 mineral oil ;)
--- End quote ---
Thanks for this Graham. Next time I'll get that instead, surely nothing will go bang using it in one change though? :-\
--- End quote ---
Too thick for a 400 gear box pump ;)
--- End quote ---
Ultimately detrimental to hi-vo type drive chain primary too.
Natural development state of 5 viscosity oil, survive in these engines at outer limits with thicker oils with functioning and compromised lifing because of this.
Related to flushing of internal bearing surfaces via oil throughput to replenish oil film, take away heat and not fail the shear properties of the oil. Used in much higher torque installation with ATF oil in plsce, will easily reach 200,000 miles or more, but lucky to see 50,000 in these engine for practical service life.
No suggestion to use ATF ;D but you can see the balance being struck with the specified engine oil they ask for.
Johnwebley:
Interesting comments about multi grade oil
I always thought the lowest number was for cold viscosity,
And as such would get pumped around a cold engine easier to get oil to bearing during initial start,
The larger number is the hot running thickness,
But, am I correct??
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