Fwiw. I think one of the biggest things that you have to adapt to is the speed difference between the two aproaching a corner. You are always more likely to roll off too early after stepping from a 583 to a 620. There isn't a fantastic amount of difference in the top speed, but even that extra 5-10 mph will have you braking a long time before you did on a 583.

My 620 was too much of a dog to just get on and ride it at first. In hindsight i wish i'd never touched it; the exhaust bellowing smoke, the wooden seat. It would have all been better than the embarressing few horses towing it along now. I think i'll trade it in for three beans

Just my two peneth,

I had a ride on a 620 that whilst was very well put together, was not super trick at the end of oct last year at mallory in the cold and got down into the 1:01's in three sessions, i'd done 1:02.97 on my 583 when we raced there at the first round. Really didn't feel any different in the places you could open the throttle on it, and it turned and stopped far better than my 583 did.

I do think that its in the mind as the difference in power is pretty much negligable, its not like the difference between a 600 and a 1000 jap four.

Jimbers really has got on well with the 583 though so far, couldn't believe it was the same person after watching him at anglesey!

In fairness your 583 was fresh at the start of the season & the 620 was tired with 4 or 5 bhp down after a hard season & in need of a refresh.

Mmmm
 

How would removing FIM's and Power Commanders affect the 620's and could the weight difference be made greater to find some of the difference?

The trouble is the one I bought was broke and did not run any improvement on that isn’t really messing it up.

Going with the 750Ssie ECU has its problems, the rev limiter kicks in at 9200rpm meaning you have no over rev, also it is normally connected to injectors that are designed to flow 22% less fuel than those of a 620. Then there are the slotted/adjustable cam sprockets which means the cam timing can be all over the place. On one of my cylinders the inlet was opening at 4 degrees AFTER TDC when measured at 1mm of lift, the Standard Factory figure is 12 degrees BEFORE TDC, so having cams retarded by different amounts and by up to 16 degrees doesn’t help.

With Only 55bhp on tap compared to my 583s 51.5bhp I doubt if its anything to do with the throttle opening after all it’s a pussycat compared to the TL1000S and 916 I raced in SoT and the Blades I ran in the Open and Powerbike. Paul P probably thinks the same of his 620 when compared to the 888 based bike he use to race in SoT

The Frustrating thing is I bought a crashed but complete M620Sie to turn into a race bike, it came complete with two black keys, the red master key and the code card yet did not want to run. I spent hours and hours going over everything to try and get it sorted, but there was nothing I could do with the standard parts, either the clocks or the ECU were prohibiting me from getting it to run. I tried the breakers for second-hand set-ups but there were none available, a FIM was outside the budget so I opted for the 750Ssie ECU route

My advice to others is to start with a running 620 that is either using a standard ECU or something like the FIM unit on Trouty’s bike or a bike with a proven record

Which is still a lot better than most 583s... ;)

Eh?? You've lost me there Kev after the word problems... ;)

For what its worth I've done reasonably well in both classes. I found, as did many others, (Fil, Chris Wood, etc) the bikes to behave totally differently. Cobby has also rode both bikes and enjoyed the handling of the 583. The 583 engine has different weight and turning characteristics to the 620 so we found the bikes needed to be ridden differently. I've had to learn alot of racecraft with the 620 as it takes more care to ride faster than the 583 but once mastered you can cane it just as much as the 583 and pull 3-4 secs a lap (on average over the tracks) faster, but the 620 will bite back! As its going faster than the 583, its also more on the limit of the tyres.

Dont forget I have a very capable 620 for sale if someone fancies the transition.

This is just my opinion.

Andy

I have to agree with Jon, Andy and Tim's views.

620s' are much quicker, in the right hands, ex racers - Geoff, Cobby, Dom, Hawk etc (look at the records)... or those who have spent a few years learning how to ride them - Rattler, Andy. Very FEW amatuer racers, have transitioned from 583 to 620 quickly and easily.

Personally on my 583 I could be very direct and (clumsy?) when riding it and hussle it about. The 620 required more finnese? as it was going much faster, as Jon said, at the critical points of braking and in sweepers ie Assen or Cadwell! 5th gear flat out up Charlies on the 583, no problem? on the 620, clench sphincter!!

620's are more on the limit of tyres I agree completely.

I have ridden a number of 583's and 620's. IMO for a newbie, the 583's are easier to ride well, by virtue of their setups. The 620's are more difficult to ride quickly as you need much more confidence and learnt ability.

For me class A is just having a rest.

Leave it well alone and go race.

You, lucky, lucky, b4rstards.

haven't ridden a Class B bike so cannot comment, but I do know that the Class A bikes are not always that easy to ride. It takes some serious adaptation of riding style to get along with them as they are moderately quick but still bite back.

I am clearly having some tyre issues at the moment as I have had the back let go on me twice now on fastish corners, not something i have had previously and maybe due to me swapping to the bigger bikes with slicks in between?

Not sure what the answer is tbh, i think we need more people to try Class A and see how they enjoy it as it's hard work at times but rewarding if it goes well.

I am sure we will be back at some point, just cant say when that will be just yet!!