- Joined
- Apr 24, 2012
- Messages
- 1
I've had a friendly dispute with a well known UK enginemaker who is a great bloke but a bit stuck in about 1972. This isn't a moan about him - he is a national treasure.
He's built a lovely new top end for my 850 with larger inlet valves, and what with other engine mods including large dia. straight through pipes he thinks its capable of 80hp. It isn't. When I took it on the dyno, set up for an AFM of 13.25%, it was so rich it was off the scale on 320 main jets. I got about 59hp, but leaning out to 270s brought me 72hp and was bang on the AFM. Torque was about 20% higher and smoothed out a number of holes which I'd noticed on the track.
When I told him the news rather than being pleased with the outcome he went ape. 320s is what they ran in the 1970s, they didn't need dynos to tell them when a bike was right etc, etc. He took the bike for a run on the 320s and announced it "crisp and sharp." It doesn't feel like that to me, instead of pulling cleanly it seems to drown. He's convinced that on 270s the bike will blow, but the graphs don't lie, or do they? Is 13.25% too lean? I read in a recent old bike mag that 14.5% is ideal... I'm worried. I'd love the extra 13hp, but I'm not going to enjoy the blast unless I think the motor will hold together.
Dave Jackson
He's built a lovely new top end for my 850 with larger inlet valves, and what with other engine mods including large dia. straight through pipes he thinks its capable of 80hp. It isn't. When I took it on the dyno, set up for an AFM of 13.25%, it was so rich it was off the scale on 320 main jets. I got about 59hp, but leaning out to 270s brought me 72hp and was bang on the AFM. Torque was about 20% higher and smoothed out a number of holes which I'd noticed on the track.
When I told him the news rather than being pleased with the outcome he went ape. 320s is what they ran in the 1970s, they didn't need dynos to tell them when a bike was right etc, etc. He took the bike for a run on the 320s and announced it "crisp and sharp." It doesn't feel like that to me, instead of pulling cleanly it seems to drown. He's convinced that on 270s the bike will blow, but the graphs don't lie, or do they? Is 13.25% too lean? I read in a recent old bike mag that 14.5% is ideal... I'm worried. I'd love the extra 13hp, but I'm not going to enjoy the blast unless I think the motor will hold together.
Dave Jackson