BETA Rev 4T

[Ferretflasher]

Just had a good ride on my mates Rev 4T and offer the following observations.
First, its very much quiter than a Monty 4RT, it does not have that bark to the exhaust the Monty does. The engines appears to run quiter too.
Second, it pulls off the bottom-end a bit stronger than the Monty and is just as smooth but it lacks the Montys top-end power though. We have noticed that in hot weather the engine is a bit 'woolly' or hesitant off idle, this we believe is due to the pumper-carburetter being too rich. On a cold day or in the rain, its not noticeable but today in the UK with temperatures about 22 C it is noticeable. It clearly shows the difference between EFI and a conventional carb. We shall strip the carb down one day and look at reducing the ammount it pumps when the throttle is opened.
Third, still is a heavy bike unlike a Rev 3, but its offset by a smooth engine with loads of bottom end grunt.
Fourth, it wont stall as easily as a Monty does and is easy to kick-up while in gear. The clutch action however is a poor as that of an 05 Monty, its on or off, with no easy medium to get you out of trouble when wobbling about as I sometimes do.

These examples we have in Blighty are the pre-production examples and have now all been sold. We all now have to wait for BETA to start proper production sometime in August or September. It is very well built and should do well in proper hands, just so long as BETA dont try to cut corners or make some production cost saving with the real thing!!
FF

[richardr]

Very interesting observations about the differences in the 4-bangers. . I was considering going to a 4-stroke the next bike I buy so that is helpful for me to make my decision. . .

Only one thing puzzled me. . you talk about operating the bike on a hot day and then you say it was 22 degrees. . . Which one was it - 22 degrees or hot? ("HOT" around here is anything over 35 degrees, below that is 'Mild')

[Ferretflasher]

Well anything into double figures is hot for us in Blighty, but I acknowledge that for you folk down-under its still considered cold. Anything around 35 degC would be a state of emergency for us but i dont believe that even you hardy bunch would ride and perform trials in those temperatures!

Anyway, my original point is that the action of a pumper carburetter on a 'mild' day with temperatures above 22 degC appear to make the bike a tad rich off the bottom-end. I can speak from experience that a Monty with EFI does not suffer this problem ( well mine dont!!) .

It would be interesting to hear from any other 4T riders from Aus who could comment on how their machines perform in the mid-day heat. Incidentally, we hear that GasGas are thinking along the lines of side-valve large capacity low-reving engine for their future machines. This concept is very appealling if you think about it...the engine would be very short....this would allow for an unusally long-stroke crank to give a very torquey engine. Anyway thats a few years away given their shakey financial position...if ever!!
FF

[Neo]

Incidentally, we hear that GasGas are thinking along the lines of side-valve large capacity low-reving engine for their future machines. This concept is very appealling if you think about it...the engine would be very short....this would allow for an unusally long-stroke crank to give a very torquey engine. Anyway thats a few years away given their shakey financial position...if ever!!
FF

Please tell us more!!!!


Best of balance.

Neo

[Tee-Why]

Well anything into double figures is hot for us in Blighty, but I acknowledge that for you folk down-under its still considered cold. Anything around 35 degC would be a state of emergency for us but i dont believe that even you hardy bunch would ride and perform trials in those temperatures!FF

We actually started our summer events in 35 degC days unfortunately (in WA anyway). Yes it was way too hot, and not really that enjoyable, but try and stop riders from getting a taste of action for the start of the season with new bikes to try out!

Watch hot starts with pumper carbs, easily flooded if from stalled, my KTM enduro use to be a bitch to get going.

Also this is the Technical Help section, not sure why you posted in this topic?

[Ferretflasher]

The Rev4T has a small hot start lever that sits on the clutch lever to assist warm starts, my understanding is that it admits more secondary air into the fuel/air mixture and thereby weakens the mixture to assist starting. Is this the case or have I got it wrong?
The YAMAHA WR F's also have hot start levers to assist starting but to my knowledge they admit extra air also, so my second question is how did the KTM flood so easily?
FF

[Tee-Why]

Not sure about current pumper carbs, but I had a 40mm Delorto pumper on a 600cc on the KTM. Easily flooded if throttle moved (ie pumped) when starting and particularly if it didnt fire the first kick or if stalled engine.
Trick was to use the valve lifter and prod a few kicks slowly to clear, then give a good kick.

[splint]

I've seen some of those FCR pumper carbs on KTMs and Yamahas squirt fuel for up to 7 seconds from the factory! The earlier mods were quite easy to fix by simply limiting the operation of the pump mechanically. Ideally it should be around .3 to 1 sec of squirt time, this is all the motor needs to help get it off idle any more would result in a large flat-spot. Its a lot harder on the current enduro models as the FCRs have evolved and are now using a diaphragm type as opposed to the eariler lever type set up.
It would be interesting to see what setup the carby 4t bikes are using?

[Ferretflasher]

The pumper carb on the BETA Rev4 is a MIKUNI type with a diaphram type slide/needle. Given Mikuni's reputation of carbs fitted to the Rev3, we are to hope that the Rev4 would be better equiped but time will tell. I dont yet know what sort of Mikuni it is, Ill have a look later this week.
Same start method is needed whatever 4 banger we have, absolutly NO throttle when kicking it up! However once its running, it runs cleanly and no flat spots. Anyway its good....but not as good as EFI!

FF