Nickjtc,
I think our bikes, (1979 US CB650) have a hotter cam than the other 650's; not sure about Canadian bikes. What kind of top speed have you achieved? I've had mine up to 85mph and she seemed to still have some pull left in her. I'm just wondering what an average top speed is for a 650?
Well, as to top speed I can get my '79cb650 to 120-125.(mind you thats at a little under 11,000 RPM)
And thats taking into account my speedo is 5-10 mph off.(was reading 130ish)
Thats with the mods/new parts I have now, but I could do just a hair under 120(by the speedo) with stock everything last year as well.
The bike is a 1981 cb650.
Runs great, pulls hard, WILL NOT GO OVER 100km/h! it pulls hard in the low gears, less as you shift. Runs out of steam @100km/h (60mph) @approx 5000rpm.
I open the throttle all the way and it just stays there.
If I pull out the choke even slightly, it slows down immediatly. pops on deceleration. stumbles slightly when accelerating off idle. I have tried swapping parts with my wrecked 650, which was running at 99.9% same year etc. etc. etc. any used parts listed below are off this bike.
I have done the following: new in tank fuel filter, used petcock, new fuel line, removed automatic petcock, rebuild and the carbs (3x) and tried the carb's off my wreck (both are cv carbs with 120 main jets and pilots set at 1 1/2 turns), new plugs, new caps and wires, used coils, replaced connectors at coils, set cam chain tension, checked valve adjustment, new air filter (honda), set ignition timing, new carb-to-head rubbers, used battery, air box cover on / off.
Stock air box, may have aftermarket exhaust - four into two, quiet megaphones,
I set the ignition to "s" and lined up the rotor to the pickups.
Caps and plugs are correct type (can't remeber the part #) I tried removing the air filter but this just made it hard to accelerate off idle, would just stall, and no effect on top end.
I think it is running a touch lean on idle (popping on deceleratio and stumble off idle, worse with air filter out) way to rich in the top end, especially over 5000rpm under load (top gear). There is only pilot jet adjustment on these carbs and I think this is my idle - off idle problem and will work this out in time, the low top end is my main concern! There is no smoke at idle, does not smell rich at idle and at full throttle it slows down immediatly with slightest amount of choke. very little if any smoke if I snap the throttle wide open 1000-9000rpm in neutral.
I am thinking exhaust as I know I am getting air and fuel in and it is fine through the mid range. Is it even possible for the exhaust to cause this? Could the mufflers be two restrictive in the top end and the leaking header pipe causing low backpressure at idle? The exhaust on my wreck is a 4 into 1 with a 2 1/2 inch megaphone on it - LOUD, very free flowing. I have tried everything except the exhaust, cdi system, and engine. I have put MEGA hours into this and would like an oppinion before I waste anymore time or money. I would hate to swap more parts, such as the exhaust, and make it worse!
PLEASE, any help would be appreciated. I strained my brain and run out of patience. -Dave
Ok, you have tried running with and without the airfilter.
set the timing.
it tuns worse with the choke on....
Because you starve a motor of fuel with the choke on, and increase the amount of fuel, I'm assuming it's rich, not too lean.
You mentioned that when you go WOT(i'm assuming not from a closed throttle) it has a "flat" acceleration, little if any.
Again i'm thinking to rich?? You have a set of 110's or 100's of jets to try?
Have you checked you are getting spark on all 4 cylinders?
What spark plug gap are you using?
What is the resistance of the spark plug boots you are using?
If you don't have an ohm meter(or multimeter) you might think of getting one, I have found them to be an invaluable investment.
Have the carbs been synchronized?(another invaluable investment BTW)
Do you have a manual?
And did you do a static, or while running?
Have you checked the timing advance mechanism??
I had a NIGHTMARE with my timing advance mechanis.
Mine would either not advance and stumble BAD above 5000rpm, or get stuck in the full advance position making it a nightmare to get it started.
Removing/cleaning and re-instillation did WONDERS.
You mentioned the bike was a rusty bucket when you got it, you may need to either remove and clean/lube it, or possibly replace it with the one off your wreck.
OH, and one other thing, have you checked for kinks in the gas line?
good luck, lets keep the 750 owners jealous, and get all the 650's running!
l8r
