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Author Topic: won't rev past 6000rpm???  (Read 18089 times)

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Offline Hush

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Re: won't rev past 6000rpm???
« Reply #25 on: July 02, 2011, 10:53:53 PM »
Don't panic, Hush is here. ;D
Firstly mark the position of the electronic pick-up plate with a felt tip that won't rub off, make a mark on the plate and a corresponding one on the engine casing, think about this for a minute, when you go to put the plate back in you simply line up both of these marks and your timing is set again.

Right, the big nut is simply there to turn the motor over as the little one is too small and would snap off if you were setting the timing and needed to crank the motor by hand a few times.
Hold the large nut, it is really a bit of a fake, undo the small one, you will find it is actually a bolt.
The large nut should now come off easily (don't think anything will be holding it on now), slide the auto advance unit from the bike, there is a keyway on the shaft so you cannot mix up where it goes back on. Clean it and retrace your steps to reassemble.
Any probs give me an email....Hush. :)
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I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!

Offline Hush

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Re: won't rev past 6000rpm???
« Reply #26 on: July 09, 2011, 03:02:47 AM »
How did you get on? ::)
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I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!

Offline ak58lp

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Re: won't rev past 6000rpm???
« Reply #27 on: July 11, 2011, 07:33:51 AM »

Not good and I don't know what to try next.

I spent the money on new rubber tees between the carbs, had a struggle getting them apart to replace and also getting back together.
Removed all carb parts and soaked in Pinesol for 2 days, flushed with water, and blew dry with compressed air.
Clean. clean, clean all parts.
I also replaced all carbs parts with a new kit ....(brand new jets, float valves, O rings, needle jets, etc)
Did a bench synch as posted on another forum

Bike will run smooth on take off but still hits that annoying wall at 5000 rpm....still stumbles a bit with hand on the throttle lightly but not as bad. Also I notice now if I hit the throttle hard it gasps for a bit and then takes off. The accelerator pump rod looked fine and acc tubes were completely blown out with Pinesol and compressed air. So I removed the air box and found the one side was coming loose. Silconed it back up and sealed that air crack. Same thing

I took off the side cover you mentioned and had a look at the ATU. I pulled the small nut off and the phoney hex nut. I didn't pull the whole ATU out as it seemed to be on there really tight. I did pull out the lobed piece on the end and could see the pivot points and the weights. It was a bit rusty but the pivot points and springs are free as a bird. Shot a lot of PB Blaster in there, cleaned it up and greased those pivot points.

I haven't taken it out yet but I doubt it will make a difference as the ATU seemed fine.

The only other things I can think of are:

-clean gas tank ( I also have an new inline filter in the fuel line too now)
-set Pilot Screws as per book noting rpm increase/decrease
-put cover back on air box that was removed long ago
-drain overflow tubes from air box below again and try to get bottom overflow reconnected to air box again..tight fit

-take shotgun to bike
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My Bike - 2001 Honda ST1100
Wife's Bike - 1982 650 Nighthawk

Offline ak58lp

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Re: won't rev past 6000rpm???
« Reply #28 on: July 11, 2011, 07:40:18 AM »
In summary here's what I have tried so far.

-new air filter
-drained rubber hoses near the kickstand which were FULL of water and crap (helped a bit)
-removed the air filter cover and used the washer mod (helped some too)
-cleaned tank
-added Seafoam
-replaced rubber tees between bottom of carbs
-soaked carbs in Pinesol for days, new carbs parts (jets,float valves, needle jets, O rings, etc)
-hand cleaned carbs and flushed again
-blew dry with compresed air
-bench synced carbs
-sealed air box side that had a crack in it
-cleaned ATU pivots and greased
-cleaned and added hydro electric grease to coil connections
-new plugs and wires 2 years ago.


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My Bike - 2001 Honda ST1100
Wife's Bike - 1982 650 Nighthawk

Offline cb650

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Re: won't rev past 6000rpm???
« Reply #29 on: July 11, 2011, 10:55:40 AM »
Did u try it without the air cleaner?
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Offline ak58lp

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Re: won't rev past 6000rpm???
« Reply #30 on: July 11, 2011, 11:14:48 AM »
Not yet, but I will also try it with the air box cover back on too.
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My Bike - 2001 Honda ST1100
Wife's Bike - 1982 650 Nighthawk

Offline Hush

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Re: won't rev past 6000rpm???
« Reply #31 on: July 12, 2011, 12:47:56 AM »
I had the same model as yours a few years back (very sorry I sold it) they have a very strange shaped gas tank, you have cleaned the tank out which I had to do too.
I'm wondering if the air hole in the gas cap is blocked, this causes fuel starvation at a certain speed as the carbs cannot get gas flow.
To prove/disprove this you can ride the bike like you normally do then flip the gas cap open the first knotch so the tank can breath and the carbs get good gas flow, try it, on our SOHC4 bikes this is a very common problem and so easy to check.
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I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!

Offline ak58lp

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Re: won't rev past 6000rpm???
« Reply #32 on: July 12, 2011, 12:15:20 PM »
I will try all of the great suggestions noted above. Every day I find articles online with folks with the exact same problem. Just found this.

http://www.sohc4.net/?p=323

Seems like this was a known issue on the 1980 model and they fixed the problem with a new air cover complete with tubes that connect the banks of carbs together. From there the bank is tied to the air cleaner box, which my 82 model does have. Other posts also talk about very finky air problems related to the CB650 carbs.

I am getting closer but no luck so far!!

Pictures from original Honda article.

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My Bike - 2001 Honda ST1100
Wife's Bike - 1982 650 Nighthawk

Offline ak58lp

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Re: won't rev past 6000rpm???
« Reply #33 on: July 13, 2011, 06:22:26 AM »
I removed the air filter, hooked up the over flow hose on the bottom of the air box, drained the over flow tube, put air filter back in, put air filter cover back on, completed drained and rinsed gas tank, added fresh gas and still this runs like crap.


It seemed to make a difference draining the overflow tube and then I could run it past 6 grand but only one time.

The only thing I haven't tried is running without the gas cap. Also I have yet to take it on a longer ride than a few miles but I doubt that will help either.

I have ran out of time, money and patience with this. I really hoped to get it working as the bike is in great shape otherwise. We also wanted to make sure it was running great before we sold it next year or 2.
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My Bike - 2001 Honda ST1100
Wife's Bike - 1982 650 Nighthawk

Offline Hush

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Re: won't rev past 6000rpm???
« Reply #34 on: July 13, 2011, 03:23:38 PM »
I'm really not sure what difference the overflow tube would have for the bike's performance, maybe if the carb floats were set too high but then it would be bogging all the time and you would notice the gas leaking out.
Maybe try that gas cap trick as it may have the same effect of allowing the carbs to breath but from the top of the tank as opposed to from the breather.
I'm pretty much stumped on this but it does not seem to be a huge unsolvable problem and no doubt with some trial and error it can be cured.
Any other SOHC4 guys in your area?
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I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!

Offline ak58lp

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Re: won't rev past 6000rpm???
« Reply #35 on: July 14, 2011, 07:52:02 AM »
Thanks everyone I really appreciate the help.

I tried removing the gas cap, did the plug chop test (tan plugs) and also removed the inline fuel filter.

I finally gave in and took it to a local mechanic who works on old bikes ( most big shops here in Ontario won't touch old bikes). Right way he said the wires should be copper and not steel ( I bought a set from a hardware store for a car 2 years ago as they were cheaper..ya I know :), asked about how I cleaned the carbs (as most people he recommends ultrasonic cleaner) and noticed other things with the gas tank being clean etc.

So I hope he can figure this issue out and I will let everyone know. 2 weeks of beating my head against the wall is too much.


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My Bike - 2001 Honda ST1100
Wife's Bike - 1982 650 Nighthawk

Offline davesee

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Re: won't rev past 6000rpm???
« Reply #36 on: July 14, 2011, 05:36:21 PM »
i've been reading through the thread and was about to suggest that this might be an ignition issue. where did you take your bike? i'm visiting ottawa and rebuilding my engine here, and couldn't work the block off the base and took it to byward motorcycle repair, and the guy seems great.

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1980 honda cb650 with many weekends worth of modifications.

Offline ak58lp

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Re: won't rev past 6000rpm???
« Reply #37 on: July 14, 2011, 06:33:17 PM »
I took it to a guy called Cycle Master just outside of Ottawa (Ashton)

http://www.cyclemastermotorcycles.com/

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My Bike - 2001 Honda ST1100
Wife's Bike - 1982 650 Nighthawk

Offline ak58lp

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Re: won't rev past 6000rpm???
« Reply #38 on: July 19, 2011, 05:19:09 AM »
Sorry for the thread jack this past while CBME but I thought since we were having the same problem maybe we could figure this out.

Well I am pleased to say my issue has been Resolved!!

I finally took it to the mechanic mentioned above and he even said it was a challenge. This guy has been working on bikes for decades.
He said it was a combination of things that got it so it would run and idle good, but no matter what "it would fall flat on it's face at anything over 5000 rpm". Once he got it running right he was not sure how critical the air box cover was and since I had it at home, he placed some tape over the air box with a small opening for air. This made all the difference in the world and he was able to get the bike just below red line at around 9000 rpm on the road. I took the bike out last night and today and it has NEVER ran this good since I bought it 5 years ago. I removed the tape and put the stock air cover back on today. Ran it at highway speed right at 5500 rpm and still had plenty to pass cars. It was solid right to 7000 and still had power left.

This is what he did:

-new plugs and wires as he noted the old ones were not copper but steel. Very reasonable prices too.
-checked timing..ok
-rechecked my carb rebuild..ok
-he also swapped the coils out with new ones and it made no difference. He replaced mine back again.
-checked carb synch...ok but tweaked a little bit
-tank was clean
-said he adjusted the air gap around the pickups by the ATU?
-played with air box until he got the right combination of air and restriction

So I think the rubber air tees between the carbs made a difference as well as the new carb parts. it just needed a bit of experienced hands to get it back in synch. I was not afraid to admit at this point that it was over my head and needed someone with years of experience to figure it out. His rates were extremely reasonable and I will go back in a minute to him as needed.

I hope this thread helps someone else.

Thanks everyone for your patience and help :)
« Last Edit: July 19, 2011, 05:30:51 AM by ak58lp »
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My Bike - 2001 Honda ST1100
Wife's Bike - 1982 650 Nighthawk

Offline davesee

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Re: won't rev past 6000rpm???
« Reply #39 on: July 19, 2011, 05:33:04 AM »
thanks for taking the time to update...so many times you read a couple of pages of peoples' efforts and never figure out the problem.

enjoy the ride!
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1980 honda cb650 with many weekends worth of modifications.

Offline ak58lp

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Re: won't rev past 6000rpm???
« Reply #40 on: August 04, 2011, 02:12:35 AM »
Just an update on this. For anyone not wanting to replace these rubber tees between the carbs, it is a good idea. They are not cheap but the gas mileage on our Nighthawk has gone from 57 MPG (imperial gallon) to on average about 68 MPG now. At our gas rates here in Ontario these tubes will pay for themselves in no time. We have hit as high as 71 MPG on a couple of tanks.
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My Bike - 2001 Honda ST1100
Wife's Bike - 1982 650 Nighthawk

Offline juntjoo

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Re: won't rev past 6000rpm???
« Reply #41 on: November 14, 2017, 04:07:12 PM »
Quote from: ak58lp on August 04, 2011, 02:12:35 AM
Just an update on this. For anyone not wanting to replace these rubber tees between the carbs, it is a good idea. They are not cheap but the gas mileage on our Nighthawk has gone from 57 MPG (imperial gallon) to on average about 68 MPG now. At our gas rates here in Ontario these tubes will pay for themselves in no time. We have hit as high as 71 MPG on a couple of tanks.

This is good to read. Just digging into my 1st bike and found these broken and wasn't sure of their importance. Still working on a cheaper alternative to paying retail.
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82 Nighthawk 650..

1982 Honda Nighthawk...

I HAVE A 1982 HONDA NIGHTHAWK FFS! j/k. It's my only bike, my first and last.
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