Fine tuning a new build

[simon998]

Hey folks,

I'm just finishing up a new build. It's running well but the powerband is at 7000rpm and the bike is very wooly up until then, I think it would be genuinely dangerous on the road pulling out of junctions etc.

The bike is a bit of a Frankenstein build with a range of mk1 frame & engine, mk3 loom/cdi box, mk2 front end etc

Engine wise, it currently has:

10W bottom end
Ported 10W barrel
Skimmed 10W head
1.00mm oversize piston
'Banshee' coil
10W carb
K&N filter (Tried it with the standard airbox and it was worse :/)
Micron exhaust

Any ideas on how I could fiddle with this set-up to get it a bit more usable lower down in the rev range? My dad has the same set up on his bike, minus the ported barrel and he's on a standard bore and his is just as quick but the power ramps up a lot more gradually and comes in sooner. Mine comes on at 7k like a 2t scrambler.

Cheers.

[stusco]

What about the carb/airscrew?

[simon998]

I haven't had it apart in a while. Can't even remember what jet is in it. I'll chuck the oneoff dads bike on tomorrow and see if it makes a difference.

I put a 28mm keihin PWK powerjet on it, purely because it was sitting beside me on the shelf, but once it hit 6k it just let out a loud backfire and wouldn't rev any more. I'm guessing the jetting is way off on it.

Carbs are a dark art. I wish I knew someone with the knowledge to show me how to work with them

[simon998]

www.vintagebikebuilder.com/mikuni-tuning-and-jetting-guide.html#

Actually found that site vvery helpful for anyone wondering the workings on a mikuni carb.

According to what I've read, it seems like I need to change my needle jet, the main jet seems fine as the top 25% of the rev range is great.

[guiri]

Nov 25, 2019 13:07:50 GMT 1 simon998 said:

Hey folks,



Any ideas on how I could fiddle with this set-up to get it a bit more usable lower down in the rev range? My dad has the same set up on his bike, minus the ported barrel and he's on a standard bore and his is just as quick but the power ramps up a lot more gradually and comes in sooner. Mine comes on at 7k like a 2t scrambler.

Cheers.

Well.. porting it will give you just those characteristics you dont seem to want.. so why did you do it..