Honda Twins banner
1 - 4 of 4 Posts

·
Registered
Joined
·
32 Posts
Discussion Starter · #1 · (Edited)
Hi gang, any thoughts on a couple of things would be appreciated! I've been taking the 1981 CM400c restoration project out for longer and longer runs as the weather warms up and I've noticed a couple of anomalies. Fyi, I'm on my 3rd tank w/ Seafoam and it's really seemed to smooth out the full delivery, particularly under acceleration. Engine pulls really strong. (Upon posting I realize this should be moved to the SOHC section of the forum)

1. I forgot to turn the petcock from 'off' to 'on' yesterday after stopping for lunch. Bike fired right up, and it rode normally for 2+ miles, accelerated fine merging onto the highway, then began to sputter. I assumed it was running low on gas so went to switch it from 'on' to 'reserve' and noticed it was in the off position. Almost 3 miles with the fuel off seems weird. I shut the fuel off on the last half mile of my ride home and the bike ran normally.

2. When starting up cold, I need to use full choke for a couple minutes, choke off I let it keep warming up for a few more minutes. Throttle response upon revving is smooth and without hesitation. As I start to ride for the first few hundred yards there's always some hesitation and stuttering through first geared into second until I get it up to 6K rpm, then fueling smooths out. Seems like it's running lean on lower rpm?

3. Hadn't really noticed around the twisty back roads with constantly varying speeds, but riding the highway yesterday at constant cruising speed there's a light stutter If I keep it at anything around 4.5 to 5.5 rpm. When I open the throttle it springs to life and zips along smoothly. Again, seems like it's not getting enough fuel.

4. The previous owner added an external fuel filter, but I don't know if there's still a filter inside the tank. Guys at the local shop said having 2 filters could cause fueling issues and that I should pull out the one inside the tank if it's in there. What do you think about that advice? (how does one go about removing the internal filter?) Tank isn't bad inside but it's not perfect. I'd like to clean and reseal soon.

5. If having two filters is restricting gas slow, why can the bike run for 2-3 miles with the fuel shut off? If fuel is getting past the petcock isn't there a risk of it flooding the bike when not in use?

Many thanks for any insight and remote diagnostics.
 

·
Registered
Joined
·
32 Posts
Discussion Starter · #2 ·
One other note to mention. Idle when warmed up sits around 1.2K to 1.4K when I bring it back from spirited riding it idles at just a hair under 2K rpm. not sure it's connected but just thought I'd mention just in case. Bikes got less than 16k total miles.
 

·
Registered
Joined
·
2,475 Posts
#1 and #2, this is normal. You can go quite a ways on the gas in the float bowles, fuel lines, and fuel filter. It does take some time to warm a bike engine up to operating temperature.
#3, Goes along with your second post. You have dirty carbs, and maybe a vacuum leak.
#4 and #5 Two filters does not make any difference unless one it totally plugged.
TOOLS
 

·
Registered
Joined
·
32 Posts
Discussion Starter · #4 ·
#1 and #2, this is normal. You can go quite a ways on the gas in the float bowles, fuel lines, and fuel filter. It does take some time to warm a bike engine up to operating temperature.
#3, Goes along with your second post. You have dirty carbs, and maybe a vacuum leak.
#4 and #5 Two filters does not make any difference unless one it totally plugged.
TOOLS
Thanks T, as it seems to run better each time out I'll continue with the Seafoam treatment for a while longer. In the meantime I'll research vacuum leaks on the forum.
 
1 - 4 of 4 Posts
Top