Topic: Still Kicking

[Vintageguy]

Have a 1978 CB750F in fairly good state of tune with stock exhaust, airbox and factory jet carbs. The bike starts immediately with the starter, but is tough to start cold with kickstarter. The best I have ever done is 4 kicks to start, with more usually needed. I use full choke, gas on of course, with what I believe is a good battery fully charged. What am I doing wrong (if anything), or are these bikes just hard to cold start with the kicker? Thanks to all in advance.

[bryanj]

The 78 was designed to run so lean for the US market that it could be your problem. There is an accelerater pump on the carbs so you could try twisting the throttle to squirt a bit extra fuel in, it may or may not work

[Stev-o]

When the engine is warm, will it kick start in one try?  [it should]

I have a couple Kawasaki's, kick start only, I would be very happy if they kicked over cold with four kicks.

[ekpent]

4 kicks or so on a cold engine doesn't sound too unreasonable. Can't offer too much feedback though because I just use the magic button.

[TwoTired]

Note: The electric start turns off the headlight while the button is pressed.

The headlight remains on while kick starting.

Could be the electrical draw is lowering your spark voltage enough to delay start.  Also, a cold battery has less voltage potential.

As a test, take out the headlight fuse when trying to kick start.  Does it get easier?

Cheers,

[Vintageguy]

The bike will warm/hot start on first kick. Will try the headlight fuse removal approach the next time I'm out there. Thanks for all replies. That is why I like this particular forum. Honest, helpful input with no judgement/BS. Thanks, again.

[Alan F.]

Since you mentioned that you're using choke, have you made sure your choke is closing completely when you pull the cable?

[HondaMan]

Yep, like ByranJ says above, the F2/3 and K7/8 bikes suffer harder-to-start issues from their lean carb settings.
If your choke is closing correctly, you might try setting all 4 of the carb's idle air mix screws out another 1/4 turn from where they are now. Usually this will not be so much as to cause fouled sparkplugs.

Many of them have dried-up O-rings above the tiny flat washers on the tips of their air screw (it's like a needle), and when they are stiff and dry from not running (and being 50 years old!) they can cause extra-lean starting troubles because they develop a cup-shape and seal poorly from being hard now. After the engine is running for about 2 hours they get wetted enough to become softer, but get hard again when things dry back up for a few days. Changing them is possible right on the bike, if you're flexible and patient: you will have to make up a tiny hook of mechanic's wire to pull them out, along with their washers, if you do. They are TINY, and the washers hard to find, so don't lose 'em! If you go that far, PM me: I might have some of the O-rings separate from whole carb kits, gotta go look. It is also possible to get just the rubber parts in rebuild kits for these PD carbs: check at PartsNmore or CB750Supply for those kits. DO NOT get the kits with the brass needles and jets, or if you do, DON'T use those: they are not calibrated right (much too lean) and if you think it's hard to start now, you'll think this is Nirvana compared to how it will start (and run) with those miserable parts aboard. I've re-rebuilt too many of the PD41/42 carbs (especially the PD42b series) that were rebuilt using those kits, only to find the bike won't even run afterward.

[scottly]

Note: The electric start turns off the headlight while the button is pressed.

The headlight remains on while kick starting.

Could be the electrical draw is lowering your spark voltage enough to delay start.  Also, a cold battery has less voltage potential.

As a test, take out the headlight fuse when trying to kick start.  Does it get easier?

Cheers,

If the battery is capable of supplying the 100 or so amps the starter draws and still have enough voltage for the ignition system, it should have no problem with the headlight drawing 5 amps while kick-starting.

[TwoTired]

If the battery is capable of supplying the 100 or so amps the starter draws and still have enough voltage for the ignition system, it should have no problem with the headlight drawing 5 amps while kick-starting.

Key words- If and should.  Gotta love your precision terms.  Want to guess how many times these words show up in proof of theory?  But, it must be Nice you know how strong his battery is with your super human intuition.  And that his starter is actually drawing 100amps, With clairvoyant measurement techniques.  Do you do that by pressing your forehead onto the computer screen?

Someone piss in your cornflakes this morning?  Or is it just the grinch warming up before Christmas?

Let’s go Brandon!

[Alan F.]

Wow, somebody help me move this couch.

[Jimcg]

Note: The electric start turns off the headlight while the button is pressed.

The headlight remains on while kick starting.

Could be the electrical draw is lowering your spark voltage enough to delay start.  Also, a cold battery has less voltage potential.

As a test, take out the headlight fuse when trying to kick start.  Does it get easier?

Cheers,

TT, I'm not the initial thread starter but think in the same direction as your answer to him.

On my 650 I always turn the lights off before starting, thinking that the easier it starts the shorter the time for starter and battery to work and the longer they will last. Would pulling the fuse remove even more load at starting moment than just switching the light off?

I especially think small improvements are important when the bike hasn't been used for a while and starting process takes a little more time.

/Jim

[TwoTired]

I don’t have access to the 650 wire diagram right now.  But, I understood that there was no separate switch for headlight or lighting from factory.  The headlight came on with the key on.  The starter button interrupted the current flow to headlight when pressed.  Still, there is some drain going on between the time key is turned and starter button pressed, which of course takes some battery energy.  With good wire and switch connections and a strong vigorous battery, this is not usually an issue with everything in good nick.

If you have a headlight switch, can you tell if that is a mod from stock?  Is your switch for all lighting or just headlight?  My 74 cb550 has a general lighting switch that includes the head and all other running lights.  It starts about the same with switch on or off when the battery is newish.  But after some use and battery wear, it definitely starts easier with all lighting turned off.  On this bike the headlight fuse removal would only drop part of the load, and the switch even more.  However, on the newer models that came standard with no ability to turn off general lighting and headlight, the starter button only interrupted headlight current as would a fuse full.

So, if your lighting switch turns off all lights, instrument bulbs, tail, running lights and headlight, that switch would be more effective at reducing battery drain than simply pulling the headlight fuse.

Cheers,

[Jimcg]

...

So, if your lighting switch turns off all lights, instrument bulbs, tail, running lights and headlight, that switch would be more effective at reducing battery drain than simply pulling the headlight fuse.

Cheers,

Thanks! 👍 I'll have a look how the switch operates when I can spend some time with the bike during x-mas holidays. Figured it would be useful to know before it's time to wake it up in a few months, when snow and salt have disappeared from our roads.

/Jim

[Vintageguy]

Thanks to the help in this forum, I got it to run in three cold kicks. Don't think I had the choke closed all the way, but also gave it a couple of twists on the throttle first. Thanks again to all who responded. Have a great Christmas!