Author Topic: Help, 750 is coughing and then dying. (Read 3740 times)

jollyradar · « **on:** June 25, 2013, 05:20:14 PM »

Hey guys, Any help is appreciated.

So i've had the 750 out a few times this year and the last time I was out I just rode across town. On the way back it started coughing and would completely shutoff if I didn't feather the clutch to keep it going. Made back home (2 miles round trip) and it shut off 100 ft from my driveway and wouldnt start again no matter what I did. I pushed it home and let it sit a few minutes and it fired right up.

Since then, I've checked the floats. I checked the plugs, I checked for spark. I double checked all of my electrical connections.

Now it idles fine as long as it is resting on the side stand but as soon as I set it up right, it coughs and dies.

Anybody experience anything like this in the past?

Some key items to note: CycleX power arc ignition. CycleX 80k volt coils. CycleX regulator.

Thanks for the help.

Vinhead1957 · « **Reply #1 on:** June 25, 2013, 06:24:54 PM »

Plugs will tell the tale! Are they wet or dry? Wet look at electrical dry look at fuel supply

kghost · « **Reply #2 on:** June 25, 2013, 06:36:07 PM »

Simple first.

Is there sufficient fuel in the tank?

The tank has a normal and reserve position.

When it gets low the standpipe in the tank will not pick up fuel. Putting it on the side stand sloshes more fuel over the standpipe if its on the left side.

Also there is a mesh over the standpipe. Any chance it's plugged?

jollyradar · « **Reply #3 on:** June 25, 2013, 06:54:08 PM »

Should have included info about the plugs. Plugs were wet.

Petcock is on the right side of the tank. No screen over standpipe, screen in bottom of petcock is clear. plenty of fuel.

Thanks

kghost · « **Reply #4 on:** June 25, 2013, 06:56:20 PM »

Could have one or more floats/float needles sticking.

Too much gas in the bowls.

Anything out the overflow tubes?

jollyradar · « **Reply #5 on:** June 25, 2013, 07:05:08 PM »

I've checked the floats and needles, nothing coming from the overflows.

I wish that there were, I'd have a place to start

I will say that I can get it moving and with in 30 feet in seems the engine just dies and then most of the time it comes right back. Kind of like a long misfire.

Does anyone know of a way to test the cycle x ignition?

I just had the though of hooking up an inductive timing light to each plug to monitor spark, that should tell me if the ignition is cutting out, correct?

again thanks for the help I'm losing my mind on this one.

jollyradar · « **Reply #6 on:** June 25, 2013, 08:28:35 PM »

Ok I just hooked up the timing light and I have good spark all the way through the power band on each cylinder even with it sitting up right.

Still coughs and dies if I dont feather the throttle.

kghost · « **Reply #7 on:** June 25, 2013, 08:30:30 PM »

Plugged up idle jets?

Some trash or water get into the carbies?

jollyradar · « **Reply #8 on:** June 25, 2013, 08:54:56 PM »

Pulling the carbs now.

jollyradar · « **Reply #9 on:** June 25, 2013, 09:55:36 PM »

Ok so one of the idle jets was crushed. Replaced with 4 new ones. Problem remains. Idles better though

kghost · « **Reply #10 on:** June 25, 2013, 09:59:03 PM »

Sorry it sucks pulling them........

With your ignition set up....it should work or not.........

There's an outside chance of a coil packing up......but usually not two at once.....

I suggested carbs because it runs and idles on the side stand.

Soon as you tip it up......cough cough....,,yes?

Makes me think its fuel related. Especially if it will sort of run if you feather the throttle.

kghost · « **Reply #11 on:** June 25, 2013, 09:59:29 PM »

Did you check the emulsion tubes on the idle and main jets?

jollyradar · « **Reply #12 on:** June 25, 2013, 11:38:56 PM »

I also think it is fuel related.

Checked the Emulsion tubes and they look good on all 4 carbs.

I'm wondering if a bad float bowl seal could cause fuel starvation? Has anyone ever heard of that? I think 2 of mine maybe bad. I'll replace them either way, but not being able to sort this out is killing me.

kghost · « **Reply #13 on:** June 26, 2013, 01:57:44 AM »

Both sets of emulsion tubes in each carb?

Idle and main?

Dunno that 2 bad bowl gaskets would do the thing you describe.....

jollyradar · « **Reply #14 on:** June 26, 2013, 12:57:16 PM »

Yea. I replaced all of the idle jets and check all of the main emulsion tubes.

So I tried something new, the further I lean the bike to the right the worse it gets/faster it stalls.

I've been reading on some other forums about breathers tubes being clogged so I'm off to blow those out next.

iron_worker · « **Reply #15 on:** June 26, 2013, 03:17:05 PM »

My guess is float related since it seems to be related to the angle of the bike. Perhaps the float is hanging up on something...binding on the bowl itself, bowl gasket is pinched, bur on the float needle tang, etc.

Check that all floats move freely. Check for rub marks inside the bowl.

Ensure that the bowl gaskets are being seated properly and not somehow getting pinched.

Check the "tang" of the float where the needle rides. If it has an indent or bur then polish it until it is smoothe and shiny. The needle couldn't getting hung up on that roughness and causing it to bind.

IW

jollyradar · « **Reply #16 on:** July 09, 2013, 09:38:02 PM »

Ok so after a busy week and waiting on some new bowl seals I got around to working on the bike some tonight.

I checked the float heights and made sure that the needles were completely stopping the flow of fuel, all good there.

Then I filled the bowls to half and shut off the fuel.

I cleaned and recleaned the breather barbs.

I double checked the kill switch wiring and spark on all 4 cylinders.

Everything is the same. Bike runs fine on the side stand and backfires and dies upright. The further right I lean the bike the faster it dies.

I'm at a total loss here.

grumpy · « **Reply #17 on:** July 09, 2013, 09:48:27 PM »

Rather than too much fuel, maybe it's not enough air? Filter clean?

Vapor lock from clogged gas cap breather?

dead mice or other foreign matter in the pipes?

what about the breather lines coming off the fuel rail?

old gas?

obviously grasping at straws here....

Duke McDukiedook · « **Reply #18 on:** July 09, 2013, 10:10:50 PM »

Do you have inline fuel filters? Petcock screen clean and rust free tank?

jollyradar · « **Reply #19 on:** July 15, 2013, 05:03:13 PM »

Video of how the bike is operating.
Not a valid vimeo URL
Just before I took this video I had the carbs off again and verified the float heights and cleaned the breathers.

Just to recap, because this is the part that really bothers me, this problem started while I was riding the bike.

lucky · « **Reply #20 on:** July 15, 2013, 05:21:31 PM »

CB750 ...What year???

Intake type?
Exhaust type?

Make sure the floats are all set correctly BY THE BOOK. Measure them .
Not some other method.

lucky · « **Reply #21 on:** July 15, 2013, 05:24:52 PM »

Quote from: jollyradar on June 25, 2013, 09:55:36 PM

Ok so one of the idle jets was crushed. Replaced with 4 new ones. Problem remains. Idles better though

Idle jet was CRUSHED!!! Wow can you explain how that is possible?
Tell us what year this bike is.

Vinhead1957 · « **Reply #22 on:** July 15, 2013, 05:24:55 PM »

Did you use new gas also?

lucky · « **Reply #23 on:** July 15, 2013, 05:27:44 PM »

Quote from: jollyradar on June 25, 2013, 11:38:56 PM

I also think it is fuel related.

Checked the Emulsion tubes and they look good on all 4 carbs.

I'm wondering if a bad float bowl seal could cause fuel starvation? Has anyone ever heard of that? I think 2 of mine maybe bad. I'll replace them either way, but not being able to sort this out is killing me.

It is not the cause of a float bowl seal.
Do not replace those unless they are broken or leaking.
Slow down and think. Do one thing at a time.
Be methodical, not like a chicken running all around pulling stuff off and buying stuff.

jollyradar · « **Reply #24 on:** July 15, 2013, 05:29:11 PM »

Bike is a 71.

The idle jet was crushed, though not flat. It looked like it had been stood on end and hit with a hammer (which I assure you never actually happened) effectively closing all of the emulsion holes.

I have swapped out the gas 3 times since this started.

I was slow and methodical the first two weeks, Now I want to ride.

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Author Topic: Help, 750 is coughing and then dying. (Read 3740 times)