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Author Topic: 1975 CB550 won't start ** now rev's too high  (Read 2355 times)

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Offline cnd_guy

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1975 CB550 won't start ** now rev's too high
« on: September 13, 2014, 03:54:31 PM »
Hey guy,

Finally got the bike back together and now it won't start.  The starter will turn the motor over but it seems like there is no spark.  Here is what i have done to the bike:

Gas Tank - repaired and sealed
Petcock - cleaned (checked and fuel does flow thru)
Carbs - cleaned, new jets, gaskets, bench synced.  There is fuel in the bowls
New plugs, oil and battery.

The bike ran before i left it for 10 years, not sure why it wont turn over.

I'm pretty green when it comes to bikes but if you talk slowly like I'm a 5 year old i could probably figure out what to do.

Thanks
« Last Edit: June 19, 2015, 09:02:30 AM by cnd_guy »
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1974 CB550 Four

Offline cnd_guy

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Re: 1975 CB550 won't start
« Reply #1 on: June 19, 2015, 09:01:54 AM »
New issue with the bike.  I was able to get it running.  It would start great and idle nicely (1100 rpm).  I took it to the mechanic to finish the safety and it passed.  While talking to him he said that the idle is broken and that the engine rev's too high.  I was confused bc when i left the bike she was purring like a kitten.  I went to start the bike to drive home and sure enough she reved up to 3000 rpm's without even touching the throttle. 

I'm super confused, the carbs have been rebuilt and sync'd, new throttle cables, it was running great, what's happened to my bike? lol
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1974 CB550 Four

Offline Tews19

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Re: 1975 CB550 won't start ** now rev's too high
« Reply #2 on: June 19, 2015, 10:12:19 AM »
What did the mechanic do to the bike? Idled fine and now the idle is broke? Does he mean the idle screw is broke?
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Offline evanphi

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Re: 1975 CB550 won't start ** now rev's too high
« Reply #3 on: June 19, 2015, 10:51:42 AM »
He broke it... he should fix it!
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--Evan

1975 CB750K "Rhonda"
Delkevic Stainless 4-1 Header, Cone Engineering 18" Quiet Core Reverse Cone, K&N Filter in Drilled Airbox
K5 Crankcase/Frame, K4 Head and Cylinders, K1 Carbs (42;120;1 Turn)

She's a mix-matched (former) basket case, but she's mine.

CB750 Shop Manual (all years), searchable text PDF
Calculating the correct input circumference for digital speedometers connected to the original speedometer drive

Offline harisuluv

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Re: 1975 CB550 won't start ** now rev's too high
« Reply #4 on: June 19, 2015, 10:53:53 AM »
sometimes the high idle symptoms start after the bike is warmed up/hot.  if you just got it running for a bit yourself, then you might not have even known about it.
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Offline evanphi

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Re: 1975 CB550 won't start ** now rev's too high
« Reply #5 on: June 19, 2015, 10:58:03 AM »
Ride around for awhile to warm up bike, then lower the idle speed.
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--Evan

1975 CB750K "Rhonda"
Delkevic Stainless 4-1 Header, Cone Engineering 18" Quiet Core Reverse Cone, K&N Filter in Drilled Airbox
K5 Crankcase/Frame, K4 Head and Cylinders, K1 Carbs (42;120;1 Turn)

She's a mix-matched (former) basket case, but she's mine.

CB750 Shop Manual (all years), searchable text PDF
Calculating the correct input circumference for digital speedometers connected to the original speedometer drive

Offline cnd_guy

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Re: 1975 CB550 won't start ** now rev's too high
« Reply #6 on: June 19, 2015, 11:00:05 AM »
@evanphil

That's exactly what i've done, it's better but not totally fixed.

As always, thanks for the responses guys!
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1974 CB550 Four

Offline DaveBarbier

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Re: 1975 CB550 won't start ** now rev's too high
« Reply #7 on: June 19, 2015, 07:33:58 PM »
He said, "the idle is broken?" What the hell does that even mean? Does it fluctuate or once warm does it stay at 3k steadily? Check for air leaks?


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1978 Honda CB550K
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Offline cnd_guy

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Re: 1975 CB550 won't start ** now rev's too high
« Reply #8 on: June 22, 2015, 02:13:47 PM »
It does fluctuate, how do i check for air leaks?
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1974 CB550 Four

Offline flybox1

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Re: 1975 CB550 won't start ** now rev's too high
« Reply #9 on: June 22, 2015, 02:21:54 PM »
i agree the bike should be returned to the owner in the same condition.

sounds like a vacuum imbalance....when was the last vacuum sync performed?
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'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
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Offline harisuluv

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Re: 1975 CB550 won't start ** now rev's too high
« Reply #10 on: June 22, 2015, 04:36:13 PM »
Just search for vacuum leaks, there are many ways to do it.

So what the heck does the idle is "broken" mean.  Can you please elaborate on this?  Or at least elaborate on what your mechanic told you?  This word is so vague, it really tells us nothing save for you have some kind of issue with your idle?
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Offline cnd_guy

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Re: 1975 CB550 won't start ** now rev's too high
« Reply #11 on: July 01, 2015, 09:24:44 AM »
First: the mechanic in question is just the guy who's filling out the safety inspection for the bike.  He doesn't work on the bike nor repair bikes. 

Second: the bike was reving at 3000 rpm after the inspection.  I was able to adjust the idle screw and now it's much better, reving at 1200 rpms.

I had it out today and i noticed that while riding at approx 4500 rpms it starts to sputter/lose power.  I'm guessing that the carbs need to be synced and checked for leaks.

Btw it was AWESOME to get out for a ride.  It's been 14 years since i rode her last.... legally lol!!
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1974 CB550 Four

Offline Vinhead1957

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Re: 1975 CB550 won't start ** now rev's too high
« Reply #12 on: July 01, 2015, 01:46:25 PM »
Those pesky orings on the intake manifold! 
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Offline cnd_guy

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Re: 1975 CB550 won't start ** now rev's too high
« Reply #13 on: July 01, 2015, 02:51:42 PM »
That's what I'm thinking!!
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1974 CB550 Four

Offline flybox1

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Re: 1975 CB550 won't start ** now rev's too high
« Reply #14 on: July 01, 2015, 02:59:56 PM »
Quote from: cnd_guy on July 01, 2015, 09:24:44 AM
I had it out today and i noticed that while riding at approx 4500 rpms it starts to sputter/lose power. 
this is the transition between pilot jet needle jet and main jet.
recheck and clean these....especially the emulsion tubes.
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'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
77/78 cool 2 member #3
"Knowledge without mileage equals bullsh!t" - Henry Rollins

"This is my CB. There are many like it, but this one is mine…"

Offline eigenvector

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Re: 1975 CB550 won't start ** now rev's too high
« Reply #15 on: July 01, 2015, 04:28:43 PM »
Yeah, my thoughts exactly.  The mains need to be scrubbed down.
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Rob
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Offline cnd_guy

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Re: 1975 CB550 won't start ** now rev's too high
« Reply #16 on: July 02, 2015, 04:36:56 PM »
Okay, thanks guys!
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1974 CB550 Four

Offline Deltarider

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Re: 1975 CB550 won't start ** now rev's too high
« Reply #17 on: July 03, 2015, 01:44:42 AM »
Before you go at the needles and their jets (which has become almost a folklore here in this forum) I suggest you first ride a tank empty with some stuff added (here we have Forté and Tunap, I believe overthere it's called Seafoam). Easy to do. Make sure you ride with all possible throttle openings. My experience is that, if there still are openings, such an additive can help. If it's clogged up, sensitive hands are needed and NO materials that can damage. I would use stranded copper wire which is just a bit softer than brass.
« Last Edit: July 03, 2015, 01:46:48 AM by Deltarider »
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