Hi everyone!
So I'm back home from the US for a couple weeks and have been frantically working on bits and pieces of the bike.
I installed a Lucas L488 tail light, it's fantastic. I'll take some photos and update her tomorrow. Same with the plate holder I made up.
I think I've finally sorted out my battery charging issue. I've ordered a SLA battery as per Allan's suggestion. Although Grafton City Batteries sent me the wrong battery (it didn't fit) so I'm still waiting for that to be sorted out.
But my real problem now is I've got what I suspect is a carb related issue and I thought some of you might be able to help.
When I start the bike from cold, it hardly needs any choke. Maybe 2-3 seconds of full choke then it settles into an idle with a few blips of the throttle. If I leave the choke on, the plugs get fouled quick smart and I have to pull them to get her going again.
So it idles with no choke at 1200 rpm no problems. It pulls great. Granted, I have little experience for comparison. It certainly doesn't do wheelies up the street, but it's quick with no lag.
However after the bike has warmed up, the idle starts creeping up. It settles at about 2300 rpm and 'hunts' every now and then. When taking off from a stop or low speed (like in traffic), the throttle hesitates and stumbles. In fact, in all low RPM's it lags and has flat spots. It's quite unnerving. It only does this when warm, say after 5 minutes of running.
Now keep in mind everything about this bike is new or replaced or rebuilt. So I doubt it's bad o-rings or worn jets/needles as I've read can be the cause for symptoms like this.
I've followed fellow member Timbo's manual to the letter (note: I used the stock float heights). I used new stock Honda needles and emulsion tubes, and the rest from the Keyster kits. I 'benched synced' them by eye as I don't have access to a carb tuner.
I have had some battery over-charging issues so I am concerned it could be an over-powered electronic ignition (if that's even possible). However as I haven't the tools to balance the carbs or externally test float heights, I'm leaning towards it being a carb issue.
I've had a number of suggestions from members of the Yahoo CB400F group, ranging from balancing the carbs (tried again to get the right 6mm-to-5mm adapters for a borrowed carb tuner today, received a very unhelpful and just a general lack of care given by Kawasaki Mornington) to checking the grease behind my advance mechanism. I will work my way through them.
Before tearing into the carbs chasing ghosts, on my mechanics advice, I had a dyno run performed this morning. Here is the graph:
So as you can see, it peaked at 30.9 HP at about 8000RPM. This engine is completely rebuilt. New pistons, rings, rebore, reface, new valves, NOS cam shaft, new cam chain. Is a decrease from the stock 37HP to 30.9HP acceptable?
The guy at the Dyno place (
Dyno Bike) turned the idle screws out a further 3/4 turns, so now it's at 3 1/4 turns. Quite far apparently. So much so he was worried they might vibrate out. He said that might help with the stumbling at low RPM. He also suggested changing the pilot jets as it was running quite rich at idle.
However, overall he did say that I should be happy with the above graph, and that I shouldn't bother chasing perfection on a bike made in 1975 because they weren't perfect new.
Now not having anything to compare to, I'm just not sure if this result is acceptable or not. Personally, I don't think a noticeable flat spot at ~3500 RPM and a stumbling take off is the best I can do. I just don't know where to start to fix the problem. A carbie balance probably. Then advance mechanism/timing, then jet sizes.
Anyway, the sleepless nights continue!
Rick.
