Topic: Thoughts about points

[PeWe]

Adjust the air screws so idle smells correct from too rich can be one way.  When I used my std CB750 K6 carbs it was easy to adjust them.
Everything std: mains 105, std pilots (probably 40), needles in middle. Air screws so it did not bang and bubble during decelarations.
4-4 off, 4-1 in: I changed main jet only, 115. I might have tried 120 too. (still std airbox)

836, ported head, cam, small conical pods, loud 4-1. Still std pilot jets, needles 1 notch richer (lower step), mains until it stopped run better when releasing throttle a little at full speed (Speedo at 210 kmp) Or no obvious too rich and sooty plugs. I have seen my old carbs, there are 147.5 jets in them!! This was with the fuel from the 80's.
Air screws still so it will not bubble at throttle deceleration. I guess I started with the recommended in users manual.

Ignition was stock Honda

Exhaust can make the carb tuning tricky too
I noticed this year that it is almost impossible to find a proper tune on low speed with a wide open exhaust.

Work better with diffusers in (not too restrictive though) exhaust back pressure. Maybe in combination with a hot cam that has relatively long overlap. Exhaust Lotus Root 4-4.
I think this is the difference between street and race use. A race bike has no need of smooth and even slow riding, but need the extra power it can get. Not too unrestricted, I got more max power with No numbers 4-4 (HM 300 replicas) than the wide open Lotus Root, both without diffusers proven on dyno runs. This surprised me so I change ignition, advanced and retarded which did not change the outcome on the dyno with wide open Lotus Root 4-4 which had better power between 4200-6800 rpm only.

I have been in contact with Ripple Rock Racers about their 4-2-1. The longer muffler (16") gives more power than the shorter (12") and is not that loud either.

[rotortiller]

I have a difference of opinion regarding the idle screws on the earlier, non PD carbs.

So do I. The pilot air screw theory pretty basic, like taking a straw and drilling a calibrated hole in the side while sucking eggs LOL. I find reading/following the manual and understanding a specific system much better than spraying paint. Glad you cleared up some BS sir, that is always a good thing.

rt

[Deltarider]

I have a difference of opinion regarding the idle screws on the earlier, non PD carbs.

So do I. The pilot air screw theory pretty basic, like taking a straw and drilling a calibrated hole in the side while sucking eggs LOL. I find reading/following the manual and understanding a specific system much better than spraying paint. Glad you cleared up some BS sir, that is always a good thing.

rt

The link I posted previously, seemes to give some problems here and there. Honda4Fun used to have it on their site, but I can't find it anymore there. So here's another one: http://cincinnaticaferacer.com/wp-content/Manuals/HondaCarbManual1975.pdf Download takes some time (31 MB). Although there's more interesting stuff in the 34 pages, the chapters AIR-BLEEDS and IDLE AND LOW SPEED SYSTEM matter most in this respect. Unless you have a particular interest, you can leave the pages that deal with CV carbs for what they are.

[Geeto67]

These engines can run at 20:1 A/F mixture with today's fuels, as they are knock-resistant in order to cope with auto EFI systems, which can be slow to respond to sudden driver's foot requests. This was not the case when they were first designed, so the carbs were set conservatively rich to prevent warranty claims: sparkplug replacements were cheap as compared to pistons. And yes, you can get more torque with richer mixtures, a racer's favorite carb tweak - but racers go to the track with boxes of sparkplugs handy!

This is pretty fascinating. I had not considered the consistency of fuel because there were only a couple of years I had for the lead fuels before they disappeared. In the 90's I had the valve seats hardened and the compression lowered from 10.5:1 to 9.5:1 in the GTO just so I wouldn't have to deal with pump gas issues so it never was a concern for me. On my cb750s I detonated in manhattan summer traffic and started running premium to stave off it during the hot season, but otherwise never had a fuel related problem.