Engine dies as I soon as accelerate in 1st gear

[Spargett]

So I started my bike up yesterday (1962 CB77) and had some interesting problems. As the title says, the bike would choke and die as soon as started to accelerate in 1st gear. It was a little cold out 45°, not sure how much of a influence this would have had. I'm about to tear alot down later this week and double check a few things, but I'd love to hear some ideas before I do so. Anyway, here's what happened to help get some theories on what might be causing this.

1. 40°-45° outside
2. Closed choke completely and fired her up.
3. Started right away, at which point I moved the choke to about 80% closed where she idled beautifully at 1,000rpm. (There was some very subtle backfiring for about 30 seconds that went away)
4. Let it warm up for a minute, then opened the choke all the way and let warm up for 5-8 more minutes.
5. Touched the engine and confirmed that it was nice and toasty.
6. Shifted into first and eased her away, as soon it gained enough momentum to take off, dead. Died right there.
7. Had a bit of a hard time starting it again, but got her going. Idle wasn't nearly as smooth from here on out. Warmed it up a bit more, thinking maybe I had jumped the gun.
8. Sure enough, I shift back into first again and as soon as I started to take off, RPM's started dying. I gunned the throttle enough this time to get going down the street a bit, but it was choking the whole 20 yards until it finally sputtered out.
9. Repeated this 5-6 times until I finally gave up and wheeled it home.

It was running just fine the other day. It was about 60° out, but again, not sure how much this affects these bikes. I had plenty of gas, the carbs are as clean as can be and synced pretty well. I could prob tweak them slightly better, but like I said, it ran great just the other day. I checked for a gas vacuum, no problems there. Petcock was just professionally replaced, as well as professional tune-up (timing, etc.) from Charlie's Place. New ignition as well. Battery was fully charged via tender for the past few days. Again, I'm all ears as to any potential causes. Talk to you soon.

P.S. On an unrelated note, my tach/speedometer started making a whining noise. Then a few minutes later the whining became more consistent and the tach needle started jumping all over the place (1,000 - 8,000 then back down and up), even though the idle remained consistent in reality. From what I hear this might have something to do with lubrication/cable? I can prob get a video of this if anyone needs to see it. Always something right?

[LOUD MOUSE]

I think the cap on the tank is defective. Do the run again with the cap loose and ya may be OK. The cap has/is a for sure problem because even when new would not allow the tank to vent air. Check it out. ...................lm

So I started my bike up yesterday (1962 CB77) and had some interesting problems. As the title says, the bike would choke and die as soon as started to accelerate in 1st gear. It was a little cold out 45°, not sure how much of a influence this would have had. I'm about to tear alot down later this week and double check a few things, but I'd love to hear some ideas before I do so. Anyway, here's what happened to help get some theories on what might be causing this.

1. 40°-45° outside
2. Closed choke completely and fired her up.
3. Started right away, at which point I moved the choke to about 80% closed where she idled beautifully at 1,000rpm. (There was some very subtle backfiring for about 30 seconds that went away)
4. Let it warm up for a minute, then opened the choke all the way and let warm up for 5-8 more minutes.
5. Touched the engine and confirmed that it was nice and toasty.
6. Shifted into first and eased her away, as soon it gained enough momentum to take off, dead. Died right there.
7. Had a bit of a hard time starting it again, but got her going. Idle wasn't nearly as smooth from here on out. Warmed it up a bit more, thinking maybe I had jumped the gun.
8. Sure enough, I shift back into first again and as soon as I started to take off, RPM's started dying. I gunned the throttle enough this time to get going down the street a bit, but it was choking the whole 20 yards until it finally sputtered out.
9. Repeated this 5-6 times until I finally gave up and wheeled it home.

It was running just fine the other day. It was about 60° out, but again, not sure how much this affects these bikes. I had plenty of gas, the carbs are as clean as can be and synced pretty well. I could prob tweak them slightly better, but like I said, it ran great just the other day. I checked for a gas vacuum, no problems there. Petcock was just professionally replaced, as well as professional tune-up (timing, etc.) from Charlie's Place. New ignition as well. Battery was fully charged via tender for the past few days. Again, I'm all ears as to any potential causes. Talk to you soon.

P.S. On an unrelated note, my tach/speedometer started making a whining noise. Then a few minutes later the whining became more consistent and the tach needle started jumping all over the place (1,000 - 8,000 then back down and up), even though the idle remained consistent in reality. From what I hear this might have something to do with lubrication/cable? I can prob get a video of this if anyone needs to see it. Always something right?

[Spargett]

I'll most certainly check out the cap. I think I remember seeing some people who drilled an extra hole in their cap to alleviate pressure.

Out of curiosity, how would the cap only come into play as slowly accelerate instead of idling? I can rev the RPM's just fine in neutral. Wouldn't that be drawing just as much gas/pressure? Just trying to understand the theory.

I think the cap on the tank is defective. Do the run again with the cap loose and ya may be OK. The cap has/is a for sure problem because even when new would not allow the tank to vent air. Check it out. ...................lm

[LOUD MOUSE]

VOLUME OF AIR.
Loosen the cap and see. ...............lm

I'll most certainly check out the cap. I think I remember seeing some people who drilled an extra hole in their cap to alleviate pressure.

Out of curiosity, how would the cap only come into play as slowly accelerate instead of idling? I can rev the RPM's just fine in neutral. Wouldn't that be drawing just as much gas/pressure? Just trying to understand the theory.

I think the cap on the tank is defective. Do the run again with the cap loose and ya may be OK. The cap has/is a for sure problem because even when new would not allow the tank to vent air. Check it out. ...................lm

[e3steve]

Every time, Ed. Every time! Your oblique view of a symptom never fails to astound me..... All down to experience!

Scott, see here about your instrument prob: http://www.honda305.com/forums/viewtopic.php?t=2526 and http://www.honda305.com/forums/viewtopic.php?t=3561 .

Just to elaborate on Ed's diagnosis: when you rode the bike with an ambient air temp of 60ºF, the 'warmer' head of air in the fuel tank would have presented a degree of pressure to the fuel flow to the float bowls. Now the air is (at least) 15ºF colder, the fuel flow will create a vacuum much sooner in the tank above the fuel level; this will manifest itself as fuel starvation. Honda offered an interim solution for the affected fuel caps:

[e3steve]

Just to elaborate further, Scott: if you've ever part-filled a polypropylene fuel container at summer temperatures and left it in the garage, notice how much it starts to implode after the drop to Autumnal or Winter temps. If your fuel cap vent is blocked (or non-existent) then it would be no surprise to suffer fuel starvation.

[Spargett]

So just to update. I took off my petcock bowl to discover what looked like gooey rust depositing in the base. I then pulled the float bowls off my carbs and discover the same thing, which leads me to believe that my tank is rusted, though its hard to get a good look (see post).

I cleaned the petcock out completely, which needed it anyway as well as pulling off the carbs to do the same.

I also ordered the heavy duty fuel tank repair kit from Classic Honda Restoration since there appears to be some grey epoxy looking substance inside of the tank. Maybe the Kreem I hear people talking about?

With that I decided it'd be a good time to drain the oil and replace my clutch cable since the bike was half apart already. That lead me to my current issue of not being able to remove the kick start shaft to take the right crankcase cover off.

I pulled the plugs (see attached photo) and it looks like they're carbon sooted to me for sure. I had a feeling I had been running the carbs a little rich, this seems to have confirmed it. I didn't set the float height perfectly the first time around. I think with the combo of possible improper choke control could be the culprit.



I'm also going to drill an additional hole in the gas cap tonight to avoid any pressure issues as soon as I get her put all back together.