SOHC.co.uk Forums > CB500/550

Questions re Yoshi mods

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Seamus:
Thank you all for your comments.
Will get to play with it soon, I can take it to work next week and put the mot emissions probe in each exhaust and see what I get, (good idea K2-K6).
Will also do some digging and see if I can find out which Yoshi grind was used. I have a receipt somewhere.
Will post any useful info that I find

Seamus:
Had a dig round and found the original advert for the bike. My friend bought it and spent a lot of money to get it looking right. Unortunately, he could not ride it due to a serious illness and has given it to me.
Specification :
1972 CB500/4 K1
605 Yoshimura big bore using cb 550 barrels, decked to compression ratio of 10:1
1/2 race camshaft, street special. YH500-121-00
gas flowed and polished head
Dyna ignition
Dyna coils
twin disc conversion
Oil cooler.
It came with the original forks and hub (500/4), originla 500 barrels and pistons and a spare set of big bore liners.
The chap who did this work restored classic racing cars for a living, so assemed he knew what he was doing. I may be able to get his contact details from my friend.

K2-K6:
It'll be interesting to see roughly where it is to give you a guide.

I know it's not run under load for those about to point that out,  but it does give something to understand and work on.

Seamus:
Will report back next week. To be honest, I dont know if it goes well for what it is as I have nothing to compare it with. Last bike was a 600 bandit and a fireblade before that. Kind of throws the seat of the pants thing

Seamus:
Well, I popped into work today for something else and checked the bike while I was there. At idle, I got the following.

                      Cyl 1       Cyl2       Cyl3        Cyl4
CO                    2.0        1.8          2.0         3.3
CO2                  2.6         2.3         2.3         3.2
Lambda            2.7         3.3         3.0          2.1
HC                  840          293       600         335
O2                  15.2         15.5      15.5        13.1

At approx 4000 rpm

CO                    3             3            2.2           4
CO2                  2             2            2.2           3
Lambda           2.5           2.7         3              2
HC                  900          310        110        250
O2                  14             15.6       15          13

Going by the HC values, it is running rich, a lot, especially No 1. Will try float levels first and a general tune up, valve clearances (assume to be standard). Running dyna coils and dyna ignition and non ressistant caps and plugs. Perhaps a new set of resister plugs, but will do a search to see if these are required with this set up

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