Help needed. Do I have a carb problem ?

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JustMike
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Help needed. Do I have a carb problem ?

Post by JustMike »

I am hoping that some of the more knowledgeable owners can help me out here as my head is getting sore.
I am in the UK, and I recently bought a 79 CBX and from day one it hasn`t run properly.
As soon as I fired it up I knew something was wrong with it. It was taken home from the garage on a trailer, not ridden.
It was bought from a supposedly reputable garage who were supposed to be servicing the bike before I got it.
Oil level wasn`t even touching the minimum mark, chain was hanging loose, swing arm bolt was spinning free as was rear engine bolts.
Talk about a bunch of cowboys.
I am not afraid to get stuck into the bike to get it running properly and am trying to eliminate things as I go.
The spark plugs are new. I have swapped over the ignition triggers. I have just put in a brand new spark unit. And so far no change in how she runs.
The engine starts fine on choke but doesn`t warm up on choke or it fouls plugs, and also there is no high tickover to keep revs up.
Engine has a notable roughness to it when I rev it up and at time black smoke can be seen from the exhaust indicating running rich.
When I ride off she picks up reasonably well but there is a rough patch around 3K rpm which sort of clears.
Once I get the speed up between about 3500 to 5K rpm on a steady throttle the engine sings nicely. But from 5K rpm the engine starts hunting and holding back.
It is a similar feeling to towing a large trailer with the car and you can feel the trailer snatching at the tow hitch.
Revving the engine up past 5K rpm is a nightmare, it is like it has gone onto 5 cylinders. But once I reach 7K rpm she starts to clear her throat and although still a bit rough will then take off and run to the red line.
The end of the exhaust can is all black and sooty and on checking spark plugs they are showing beige in the centre electrode although dark, with sooty around the outside indicating a bit rich.
But is the black smoke when reving in neutral and the sooty exhaust due to unburnt petrol going into the exhaust because of misfiring, or due to the carbs being wrong.
The carbs were professionally stripped and rebuilt so should be okay, but the bike sat for 3 years or so afterwards.
Before I got the bike it had a fuel leak so the garage sent it to their residential expert in their other shop so he could fix the leak. If this is the guy who left engine bolts loose, then god knows what he`s done to the carbs. Hopefully some of you very nice people can offer me some ideas on what to check next.
Hopefully I`ve left nothing out.

Regards
Mike

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Re: Help needed. Do I have a carb problem ?

Post by Larry Zimmer »

Hi, Mike. Welcome to the 'club'. While I am no expert (and we do have a few in the organisation) it sounds to me to be a major carb issue. I'm thinking you will need a tear-down/cleaning by someone who most definitely knows what they are doing. Should be able to find someone in UK who qualifies. Many a 'professional' seems to not handle CBX carbs well. Hopefully, one of the guys here will have a recommendation. Dave, Mike, Mel Watkins -- can you help?
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Re: Help needed. Do I have a carb problem ?

Post by JustMike »

Hi Larry, thanks for the welcome.
I used to own a CBX back in the 80s so do actually know something about them. But I`m not wanting to go too far into this without some ideas kicking about in my head first.
I have just been checking the coils for bad connections etc and find nothing. And I get no shocks from the coils while engine is running so probably no shorts happening there.
The engine ticks over like a watch at bang on 1K rpm.
Starting is good but rough until warmed up.
As mentioned the carbs were professionally rebuilt and then the bike lay for about 3 years.
Before I got the bike they found a fuel leak from the carbs and ordered in new seals to fix it.
Now no fuel leaks but the question is, what did the mechanic do while inside the carbs.
I have just sent off for a float level gauge just in case, but I fear I`m going to have to strip the carbs and have a poke around inside.
I`m capable of doing it, just don`t want to have to lol.


Mike

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Re: Help needed. Do I have a carb problem ?

Post by spencer »

I am far from an expert, but since it is a '79, it just occurred to me that whoever overhauled the carbs could have mixed up the primary jets. Did it ever run correctly after the overhaul? I don't even know what the typical symptoms of switching the jets are, so this idea may be way off, but I think it is possible to do it, so it may be something to check.
SCH Rochester, MN

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Re: Help needed. Do I have a carb problem ?

Post by JustMike »

Hi Spencer. The carbs were overhauled by a professional so I would presume they were done correctly.
They were done long before I got the bike and presume it ran alright.
If I am going to have to go into the carbs I will be checking what you suggested for sure.


Mike

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Re: Help needed. Do I have a carb problem ?

Post by EMS »

JustMike wrote:Hi Spencer. The carbs were overhauled by a professional so I would presume they were done correctly.

Mike
Two dangerous assumptions: 1. "professional" 2. "done correctly"


Other than myself (within limits) I would trust probably only two or three guys in the U.S. to do CBX carbs correctly. And I think there are a few more CBX guys in the U.S. than in the U.K.

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Re: Help needed. Do I have a carb problem ?

Post by JustMike »

[/quote]

Two dangerous assumptions: 1. "professional" 2. "done correctly"


Other than myself (within limits) I would trust probably only two or three guys in the U.S. to do CBX carbs correctly. And I think there are a few more CBX guys in the U.S. than in the U.K.[/quote]

So very true.
As a rule I never let anyone work on my bikes. But in this instance I`ve had no option as the work was all done before I got it.
Now I am in a hole because I don`t know what has been done to it either correctly or wrong.

Mike

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Re: Help needed. Do I have a carb problem ?

Post by daves79x »

Hello Mike. Sounds like a carb issue for sure. Does the bike have the stock airbox, or pod filters? Need to know that first. The carbs have to come off either way, be thoroughly checked/cleaned and reassembled according to what you have, stock intake or pods. With pods it will never carburate completely smoothly, but better than you describe. Give us some more info on that and we'll see.

Dave

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Re: Help needed. Do I have a carb problem ?

Post by JustMike »

Hi Dave.
The bike is completely standard except for a 6 into 1 exhaust that I fitted a few weeks ago. But, it was running the same with the original exhaust, just that the new one being louder I can now hear the misfiring better.
The air filter is a new standard foam one. I don`t like those pods so won`t ever use them.
I am hoping to replace the HT leads this week. Just to rule them out.
So far it has been a process of elimination, and I am now thinking as well that it must be carburation.
I have a float gauge ordered in preparation for doing that and I`ll be no doubt having to pull all the jets to make sure they are clean.
As I tried to explain previously, the carbs were stripped fully and rebuilt. But before I got the bike someone else was in there and I have no idea what he might have done.

Mike

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Re: Help needed. Do I have a carb problem ?

Post by herdygerdy »

Hi JustMike,

Certainly understand your pain and frustration with your new ride, especially as you probably have very fond (albeit distant) memories of your earlier experiences with a much sweeter running CBX.

I have to agree totally with Dave79x, Spencer and EMS etc who are suggesting persistent carb problems. Sadly, when "spanner twirlers" with, ahem, "more ambition than skill" get their grubby mits on them, lord knows what can and does happen. I and many others here have seen incredible 'crimes against carburetion'.

These old gals have been around near on 40 years now, so the risk of wannabe specialists (with little or no real world experience on how to set them up correctly) having their way with these bikes is VERY high.

Re your comment "...The carbs were overhauled by a professional so I would presume they were done correctly.", with the greatest respect, my only response is..."presumption is the mother of all stuff-ups"

There are definitely folks with great experience and reputation accessible through here in your neck of the woods who can assist.

But...

If you 're-frame' the problem as an opportunity to really bond with your newest member of the fleet, then it sure sounds like you would be more than up to the task of solving each and every issue yourself. Of course, we here on this forum would be only too happy to be 'virtually' looking over your shoulder on this journey.

So...getting back to basics, some useful thoughts for you to ponder....

1. Are the valve clearances adequate? Getting all as close to .005" / 0.13 mm is indeed a worthy goal. Is the tension on both cam chains set correctly?

2. Is compression good and even across all cylinders?

3. Are you actually getting 12V across all coils? (measured between the black/white wire that jumpers across the back of all 3 coils and earth). I have seen a 3 volt drop from measurement across the battery + / - compared to what is arriving at the back of the coils. This will give weak start, difficult starting and a host of other running issues. An ignition coil relay is a low cost bypass of this issue. PM me if you need help with that.

4. Are the igniters behaving correctly? In an ideal world you would have access to borrow a set from a known sweet running CBX to help diagnose the root cause.

5. Are the carb to cylinder head rubbers in good order? If they are hard, there WILL be air leaks. A clue is the carb rubber clamping screws are bottomed out on the nut with no more to go. Easily fixed with a set of Viton ones from a supplier on here.

6. Float levels all evenly set at 15.5mm. I use a small steel engineers ruler to do this and it works well.

7. All 6x accelerator pump jets squirting vigorously and happily as the throttle is operated.

8. Is the choke fast idle adjustment set correctly?

9. As mentioned earlier, are the correct sized jets installed in the correct passageway?

10. Don't even think of putting the carbs back on unless the pressed in 0.35mm idle jets have been extracted, and both them AND the passageways behind them scrupulously cleaned. Many so-called 'professionals' have no awareness this is even a thing.

Rest assured, when set up correctly and fed with quality filtered fuel (run through an in line filter between tap and carbs), these carbs give years of totally trouble free service and a VERY sweet running engine.

Check out Mike Nixon's book on CBX carb rebuilding, and Randakks Cycle Shack for carb rebuild kits.

IMHO, it makes sense to start from a known and established baseline. So maybe you could consider tilting the motor (not a huge deal to do, but it just takes time and some familiarity with, and sensitivity to, the CBX architecture, which it sounds like you already have), pull the carbs and begin your journey of enlightenment to the reward of a really sweet running CBX.

The feeling of putting it back together KNOWING (not presuming) it is done right is an enormous sense of relief, esp. when you light the wick and she sits there purring like a happy kitten.

We're here to help and guide you every step of the way JustMike, and welcome aboard!

Enjoy the journey.

Cheers...Tony

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Re: Help needed. Do I have a carb problem ?

Post by wyly »

carbs are the heart of the beast and that unfortunately means tilting the engine but they need to be ruled out as the source of your problems...send a pm to cbxmel he can probably advise who are the cbx carb experts in your area if you need hands on help...the nearest CBX Specialist to you that I know of he knows everything there is to know about the CBX is Bert in the Netherlands(six center motoren)...

I've had my expensive lessons learned with "professionals" who claim to know everything but you need local cbx contacts like cbxmel who can guide you to the real local experts when required...
CBX a work in progress, still improving...GS1150EFE completed and awaiting modifications.....RD350, remnants in boxes scattered throughout the garage

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Re: Help needed. Do I have a carb problem ?

Post by JustMike »

Thanks Wyly and Tony for your comments.
I`ll do a quick run through of Tony`s comments to help paint a better picture. I have just changed the HT leads for new ones, but not yet had a chance to run the bike on the road. Hopefully tomorrow. I have also put some fuel additive in to run through the carbs to see if that helps. If that doesn`t work I am hopefully getting some coils to swap over. If that fails. It will be carbs out. I have just been going through a process of elimination. Or maybe I`ve been delaying the inevitable carb strip lol.
The bike was actually imported here from America where it had one owner from new. According to documentation from that owner the bike was regularly serviced at his local dealer with some extra oil changes between servicing intervals by himself. The engine sounds pretty good apart from the usual clutch rattle. But tickover sits at a steady 1000 rpm most of the time. Mileage is 27K, so still a young motor.
To go through Tony`s pointers.
1. The engine I believe had the shims checked and set by a garage specialising in classic Jap bike inc CBX`s. I am going by information on the receipts for work done that I got with the bike.

2. I don`t have a compression tester so have not done a compression check. But for what it`s worth for now the engine makes good power when I get past the rough patch at high revs.

3. I have not yet checked coil voltages. But have been reading up on the coil bypass with great interest, and have seen comments etc posted by you and others elsewhere on the subject. As it happens I do have a spare relay sitting in the shed collecting dust.

4. I bought a used set of ignitors from a breaker and tried them, but no change. So I`m thinking that this would imply that my original ones are most probably okay. I then bought a brand new spark unit, just in case the originals were playing up. Again no change. But at least with a new unit I have removed any doubt from the equasion.

5. I have not yet checked the manifold rubbers, but if I am going to be taking the carbs out they will be closely inspected. But so far the engine seems to be running rich so maybe they are okay. Black smoke when gassing up from tickover, and the end of the exhaust needs a chimney sweep.

6. I have just bought a float level gauge. This will be the very first thing I check if I`m pulling the carbs.

7. Again, if I`m pulling the carbs I will also be checking the injector pump.

8. Choke idle is none existent. The engine does need choke to start it but I dare not leave the choke on or I will foul a plug. Engine starts from cold easily. But, I don`t want to adjust the choke until I know that everything else is fine. I did use a mirror and a torch to look down inside the back of the carbs through the air box, and the choke flaps appear to be operating properly.

9. I have seen the posts regarding the jets so will be inspecting sizes and making sure they are all in their correct places.

10. I have also seen posts and photos showing the idle jets blocked at the sides where you can`t get at them without taking them out. But, if my jets have not been tapped, then it might be safe for me to assume they have never been out.

Hopefully that lot will put some more light on whats going on. I am not going to let this beat me. And Tony, you can look over my shoulder all you want, any help I get with this will be very very appreciated.


Mike

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Re: Help needed. Do I have a carb problem ?

Post by steve murdoch icoa #5322 »

Thanks for the thorough follow-up, Mike.
If you don't want to tackle the carbs yourself, Steve Gosine [forum name Goss] would be a great guy to contact.
If you do want to take on the task, as Tony said get the manual from Mike Nixon.
https://www.motorcycleproject.com/text/booknook.html

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Re: Help needed. Do I have a carb problem ?

Post by wyly »

some minor carb fixes I've performed... running carb cleaner through two tanks of fuel...air leaking around the carb rubbers, sometimes they're not fully seated or folded over, easy to miss in the dark crowded spaces around the carbs ...but neither of those problems caused issues at the level you're experiencing...
CBX a work in progress, still improving...GS1150EFE completed and awaiting modifications.....RD350, remnants in boxes scattered throughout the garage

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Re: Help needed. Do I have a carb problem ?

Post by JustMike »

Hi Steve, I`m not worried about tackling the carbs. I`m just putting it off in the hope it is something else.
Being that it can be a big job I would rather leave it till last.

Wyly, I was given some fuel additive to run through the carbs when I first got the bike and it certainly did help with smoother running at the bottom end of the revs. The additive I have just put in the tank today is a different one which was recommended to me by a friend who owns a local garage. He said its good for cleaning the gunge out of the carbs. So I`m hoping to get out in the morning to put a few miles on the bike and see if it does help. I ran some through the carbs this evening with the intention of leaving fuel in the carbs which will hopefully allow the additive to soak in to the jets etc. If it doesn`t work I`ll be swapping the coils next. But this will be awkward as I don`t know if the misfire is across all 6 cylinders or if it is say one coil breaking down and affecting just the 2. So that's going to take me time to play around with.
Oh and something I neglected to mention earlier. When the carbs were overhauled the guy used Randakks kits. So in that instance at least he used decent parts. I have no idea what was used to stop the fuel leak before I got the bike.


Mike

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