Topic: F2... Starts one second, won't the next... What gives?

[billdramp]

I have this 1977 CB750F supersport I've been working on getting on the road, the problem is I can't seem to get it to start consistently. If I can even get it started, It is a VERY hard start the first time, and then if you run it hard for at least 20 minutes it will start easier for awhile. BUT, if let sit for a half hour or so... I cannot get the damned thing started again.

1. I am getting decent spark to all 4, at least when I check them
2. Timing is spot on
3. gas to all 4 float bowls
4. Stock carbs and airbox
 
When I kick it over it sounds like it fires... but it just gives up on me.

Could it be flooded?

Any insight would be very helpful.

[Short Round]

Carbs clean?  Plugs new? How old is the battery?

[billdramp]

1.The carbs were gone through by me... They appeared to be in good enough shape, but I soaked them etc anyway. I did not replace any parts though.
2. Plugs are brand new D8EA's
3. Battery is brand new

[jdigga]

Did you pull and clean your slow jets?  Soaking or cleaning them in situ isn't enough if they're plugged up.

Have you done a valve adjustment?

[billdramp]

I cannot remember if I pulled and cleaned the slow jets... I assume I did. I have cleaned what seems to be a million carbs, I always pull any jets that I can, clean them with tiny wires and carb cleaner and blow compressed air through everything.

Now... I have NOT done a valve adjustment.

Guess I should? But would that keep me from starting?

Cheers,

Billy

[scondon]

is your choke and accel pump working properly? pilot jet fuel mixture screws set?  

  The pilot jets in these carbs are pretty small. Just enough to keep a warm bike running, but often make cold starting impossible without using the choke and blipping the throttle to get gas squirting to prime the carbs.

  The F2 has well documented problems with the valve guides and this can lead to compression loss which can also lead to difficulty in cold starting.

[billdramp]

is your choke and accel pump working properly? pilot jet fuel mixture screws set? 

  The pilot jets in these carbs are pretty small. Just enough to keep a warm bike running, but often make cold starting impossible without using the choke and blipping the throttle to get gas squirting to prime the carbs.

  The F2 has well documented problems with the valve guides and this can lead to compression loss which can also lead to difficulty in cold starting.

I believe the choke to be functioning properly, The accelerator pump is another story. I really don't know. I took it apart and everything looked to be functioning with no signs of noticeable wear.

Damn, I was really hoping to not have to pull these carbs again.

Valve guides... I should do a compression test I suppose and see what I come up with.

[scondon]

If you pull the airbox you can verify if the accel pump is working, gas will squirt out of the standpipes(located in each carb air intake) when the throttle is twisted. You can also check if the choke butterfly's are closing fully when choke cable is pulled.

   I hate pulling these carbs too. Maybe try adjusting the idle fuel mixture screws when the bike is warmed up, possible that a too lean or too rich condition is making cold starts difficult. I'd guess too lean, but each bike is different. A special carb adjustment tool is required to reach the mixture screws when carbs are on, Motion Pro sells a fairly inexpensive on that is adequate for the job.

[bryanj]

The pilot jets dont come out easy but block up easy. They dont screw in but are a push fit and have to be gripped tight, twisted and pulled to get em out

[750goes]

Also the carb mixture screws are located on the engine side of the carbs and they are screwed in for lean and out for rich...

do you have clean fuel running into the carbs

[billdramp]

Ok... Just a quick update,

I changed the gas out with fresh gas... checked valve clearance and timing again with the same results.

I pulled the airbox back off and sprayed a bit of starter fluid into the carbs and the bike fired right up. So I pulled the carbs again, and tore them apart. Pulled all jets and such and soaked in carb cleaner, the pilots seemed to be clogged before blowing compressed air through them... I ran out of time before being able to put them back on before work this morning, but will throw them back on this evening and post results.

I am still unclear about the Accel. Pump diaphram... mine has only one hole in one of the two ears, But after reading some old posts on here, some posters have actually made a hole in the other ear of the diaphram with good results. I just find it hard to believe that Honda would have made this problem on this many of the accelerator pump diaphrams? But what the hell... I will give it a shot before throwing them back on the bike.

Hopefully I don't get so mad at the airbox this time and throw it across the garage again.

Thanks for all the help,

Billy/Portland

[billdramp]

Just back from the shop. I put the cleaned carbs back on the bike and the bike started up instantly! Must have been those damned pilot jets... It is starting every single time now.

I dreaded dealing with the stupid airbox so much I went and bought some pods and threw them on.

Rode it around tonight... seems to be running great!

Thanks to all the help from you guys another one is back on the road where it belongs!

...Now I just have to find it a new owner. The garage is overflowing from my Honda addiction.

Cheers, Billy / Portland

[billdramp]

Put the bike on Craigs List before bed last night. Woke up to three or four voicemails from potential buyers.
Sold it to the first guy who came to look at it with the cash. The guy has never ridden a bike before and has no idea how to... and I sorta half assed tried to talk him out of it. He had no idea how to shift, where the clutch or brake was etc...
But he still wanted to ride it home with no helmet, liscence, tags etc. in the rain.
I didnt have the heart to let him die, so I threw on my leather and took it across town in the pouring down rain with no tags or turn signals.
Hope he doesn't crash and ruin that perfect tank.
It's always hard to let go of a bike you nursed back to health.
Especially under those circumstances!!!

Anyhow... that was my F2 story. So long pal.