Topic: 1975 CB750 Hard start

[John G]

Any suggestions where I should start to get my motor started? I have to almost kill the battery to get it to go. Full choke, no choke ar half choke. If I give it twist of throttle while turning it over nothing happens. If I give it just a hair on the throttle it fires on maybe one cyclinder. Eventually after It does start it has to warm up a little and then it runs like a top. Any ideas and I'll be on it. Thanks

[M 750K6]

Are your choke slides adjusted properly, so they all fully close? Battery on the way out? Tired wiring /connectors, are you getting a full 12+ volts to the ignition.

[John G]

Thanks Hot Shot,
The chokes we set after assembly of the rebuilt motor but I'll check that first. The battery is basically new and the twelve volts to the ignition will also be checked. Tired wiring  / connectors....if you mean spark plug wires and cap assemblies, they are new and were ohm checked. I'll getback to you after I do some of your suggested research. Thanks again.....John

[scottly]

Is the ignition timing set properly?

[newday777]

How long has it been since the carbs were cleaned?
I'm wondering if the idle circuits and or the slow jets and ports are plugged up from setting with MBTE gas setting in the carbs.

[John G]

My carburetors are set with this needle 1/3 out. Does that sound to mall?

[seanbarney41]

1/3 of a complete rotation from bottomed out?  Yeah, that's too small.  No air to emulsify idle fuel.  Try 1 full turn out + or - 1/4 turn.

[jonda500]

Before trying to start mine if it's the first start of the day, I always give it a couple of kicks with the choke closed, the throttle held wide open and the ignition switch off (in winter 5 or 6 kicks!). Then I release the throttle, turn on the key and it fires and starts immediately!
John

[M 750K6]

How did you set your float levels. The shop manual shows you how.

[BenelliSEI]

Check the base setting for you year. From memory 1.25 turns from closed (all the way turned in, gentle bottoming).

[John G]

Carbs were all set up during the motor rebuild. No leaks and they were adjusted by a local pro shop. I'm going to adjust that needle jet once I check the book and see if that helps. Great suggestions from you guys. I'll keep you posted.

[rotortiller]

Try it with the kick starter in case the ignition has too much of a voltage drop. Likely not your problem but something I'd rule out first.

[John G]

It is starting much better now. So much better. Tomorrow after sitting all night will also tell better. As for kick starting it; I dislike the way there's to much in the way. Could be my feet are too big but I find it a pain to kick over.

[John G]

Man what a different ride with so much more power and response now that the air screw has been opened. I'm at 3/4 of turn out and I'm looking forward to trying the starting proceedure tomorrow. Fingers crossed.

[Stev-o]

It is starting much better now.

My bikes do not like throttle until it fires so I use this procedure:

- Turn on fuel and ignition
- Set full choke
- Hit starter for 10 seconds max. If no fire, repeat as necessary.
- Once fired, give throttle as necessary and reduce choke to about half for a few min, then remove.
- Ride!

[M 750K6]

It is starting much better now.

My bikes do not like throttle until it fires so I use this procedure:

- Turn on fuel and ignition
- Set full choke
- Hit starter for 10 seconds max. If no fire, repeat as necessary.
- Once fired, give throttle as necessary and reduce choke to about half for a few min, then remove.
- Ride!

My '76 is the same as this, except it likes 2/3 choke after it has started (full choke to start). I then ride off on 2/3 choke and drop it to no choke after 100yds. At the first junction, 400yds, it idles without throttle. Average bike: standard airbox, exhausts. carb internals and 1 turn out on idle screw, tickover is set at 1400rpm hot, compression is nothing special 140 to 150psi hot.