Author Topic: 1978 CB 750f Fires but only a few times then quits (Read 7485 times)

apetersonboy · « **Reply #50 on:** February 17, 2014, 03:49:18 pm »

Giving it a little gas when it fired caused less action. It'd then quit firing on the next revolution, or have one or two louder fires and then nothing.

seanbarney41 · « **Reply #51 on:** February 17, 2014, 04:07:37 pm »

From your video, it doesn't sound and look like there is anything significant preventing your bike from starting. I think you just need to fiddle around with different combo's of choke, throttle, etc. Once you get it started and get it rough tuned so it behaves relatively predictably, you will quickly learn many subtly different techniques to start it under all weather and conditions. This comes naturally to people who grew up before the advent of fuel injection. Try turning up the idle speed knob in half turn increments...I wouldn't go more than 1 and a half turns?

apetersonboy · « **Reply #52 on:** February 17, 2014, 04:23:32 pm »

You're right Sean! I was just piddling with it a bit ago and it ran for about a full second!!

Thank you a lot for your advice!

Stev-o · « **Reply #53 on:** February 17, 2014, 04:27:20 pm »

Have you gapped the points?

seanbarney41 · « **Reply #54 on:** February 17, 2014, 05:46:59 pm »

Once it starts, keep your hand in the throttle until it warms enough to idle, once it's fully warmed set the idle speed screw so that it idles about 1100 rpm...

apetersonboy · « **Reply #55 on:** February 17, 2014, 06:33:57 pm »

Quote from: Stev-o on February 17, 2014, 04:27:20 pm

Have you gapped the points?

I haven't, but I will tonight if it says how in my manual. How long does it take? Is it hard?

apetersonboy · « **Reply #56 on:** February 17, 2014, 07:02:22 pm »

IT LIVES!! I played with the idle screw and it runs! Rough, but by god it runs. Thanks everyone!

apetersonboy · « **Reply #57 on:** February 17, 2014, 07:45:08 pm »

I took off the tappet covers to see if the valves were getting oil. They looked oily, but not wet with oil. I also heard at a swap meet that oil is supposed to squirt out of there if you pull off a tappet cover, is this true? If so, I don't think my head is getting oil.

LesterPiglet · « **Reply #58 on:** February 18, 2014, 04:55:34 am »

It will only squirt out with the engine running.
It doesn't actually squirt, it gets flung off the moving parts.

apetersonboy · « **Reply #59 on:** February 18, 2014, 05:16:46 am »

Quote from: LesterPiglet on February 18, 2014, 04:55:34 am

It will only squirt out with the engine running.
It doesn't actually squirt, it gets flung off the moving parts.

It definitely wasn't getting flung off. Do I have a problem?

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apetersonboy · « **Reply #60 on:** February 18, 2014, 10:41:27 am »

A little progress

https://www.youtube.com/watch?v=c1x_iMNw4go

LesterPiglet · « **Reply #61 on:** February 18, 2014, 11:02:40 am »

When the engine catches rev it with the throttle to help it along Don't go mad with the revs.

apetersonboy · « **Reply #62 on:** February 18, 2014, 11:48:28 am »

Quote from: LesterPiglet on February 18, 2014, 11:02:40 am

When the engine catches rev it with the throttle to help it along Don't go mad with the revs.

At the slightest turn of the throttle it dies with a louder thump. Also I still don't know if the head is getting oil so I'm kind of wary of trying to start it anymore

LesterPiglet · « **Reply #63 on:** February 18, 2014, 12:08:22 pm »

Are those carbs clean? Undo the carb bowl drains and see if any crap comes out.

KayOne · « **Reply #64 on:** February 18, 2014, 12:30:07 pm »

This may be a long shot, but hook up a voltmeter to one of the coils and see if the voltage is present while cranking and when it is running. Expect the voltage to drop while cranking and increase when running. If the voltage disappears you may have a bad ignition switch or kill switch (or connector etc.).

apetersonboy · « **Reply #65 on:** February 18, 2014, 03:14:24 pm »

Quote from: LesterPiglet on February 18, 2014, 12:08:22 pm

Are those carbs clean? Undo the carb bowl drains and see if any crap comes out.

The carbs are rebuilt and have been stored in my room in a box. They should be spotless inside. I will check though. Should I do that while they're on the bike?

Jerry Rxman Griffin aka MuthaF'er · « **Reply #66 on:** February 18, 2014, 03:36:54 pm »

You should have already done that to at least determine if there is gas in the float bowls.

Are you confident that the float heights are set correctly?

apetersonboy · « **Reply #67 on:** February 18, 2014, 03:38:32 pm »

Quote from: Jerry Rxman Griffin aka MuthaF'er on February 18, 2014, 03:36:54 pm

You should have already done that to at least determine if there is gas in the float bowls.

Are you confident that the float heights are set correctly?

I used the drain screws to check if there is gas in the bowls.

I am unsure about the float heights. When I had them rebuilt I told the guy what I am running for intake and exhaust and he said he set it up accordingly.

apetersonboy · « **Reply #68 on:** February 18, 2014, 06:55:00 pm »

IT LIVES. Tinkering with choke and air idle screw resulted in the engine running rough for a few minutes, after clearing out it runs GREAT!

Aside from cutting out when at idle and throttle is openned way up, it has no issues. Beyond stoked right now guys.

Thank you for your time and patience with my questions!

Stev-o · « **Reply #69 on:** February 18, 2014, 07:30:06 pm »

Good news. Once you find the best starting procedure, you'll find it easy to fire up.

On my '78 K, I would give it full choke, two twists of the throttle then hit starter button.

News:

Author Topic: 1978 CB 750f Fires but only a few times then quits (Read 7485 times)