Help needed. Do I have a carb problem ?

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

Post by JustMike »

Dave, I wasn`t happy with how much fuel was collecting in the jar so tried something.
I drained the bowls one at a time and then turned the tap on to just let the petrol flush through.
After doing all six I have left them sitting with the fuel turned on for the last 3 hours and there has been a massive difference.
So I will leave them as they are till morning and if no change I think I`ll try them on the bike.


Mike

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

Post by JustMike »

Well I fired the beast up last night, first time.
Choke works but no high tickover, but that doesn`t concern me.
Once warm she settles to a steady 1000rpm tickover and revs nicely when opening the throttle.
I will get it road tested once I get it all back together, but to be honest I`m thinking it still isn`t right.
Rather than annoy the neighbours with me revving the engine I just locked the shed up till today when I go back out.
Time to go buy some stuff to rig up a coil bypass so that I can try that as well.


Mike

steve murdoch icoa #5322
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Re: Help needed. Do I have a carb problem ?

Post by steve murdoch icoa #5322 »

A tempered congratulations.....i think?

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

Post by JustMike »

Thanks Steve, I hope to get an idea today.
Got nothing done yesterday as I had a bitch of a migraine so wasn`t in the best mood for working on the bike. More likely to make mistakes.
Hopefully I`ll get some time to check it out today once everything is bolted back together.

Mike

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

Post by JustMike »

Well, after all that the misfire is still there.
Not had it out on the road yet, but there is no need as just revving in neutral shows it up.
And to top it all I was wondering why I always had oil on my chain. I suspected a possible leak from the gearbox seal.
I need a new oil cooler pipe. I found a nice little pool of oil on top of the air box and a tell tale line of oil running down towards the sprocket area.


Mike

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

Post by JustMike »

Well that's the coil bypass wired in.
The bike runs so I must have done it right lol.
Hoping to get it out tomorrow for a road test to see how it runs after doing the carbs and the bypass.

Mike

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

Post by JustMike »

I thought I should update my post with whats happened so far.
I stripped the carbs and cleaned them. I also replaced a couple of float bowls which were leaking fuel from split overflow pipes. Put CBR600 coils in with new HT leads. Put on a bypass relay to feed the coils straight off the battery.
The spark unit was replaced by a new modern one. I replaced the pulsers with another set, which made no difference.
As it happens I didn`t get the bike fully reassembled and road tested and winter set in.
Last week I got her finished off and took it for a run.
So it would seem that cleaning the carbs did some good as my choke now works as it should and the flat spot in the mid range 5 -7,500rpm seems to be gone now.
But the misfire I`ve been getting is still there and it now looks as though I`ve been thinking I had one issue causing a problem when in fact one may have been hiding the other.
So sitting at a steady throttle/speed the engine sounds great. But when I open the throttle it sounds like I`m dropping a cylinder or maybe 2?
It is difficult to describe. The nearest I can get is if you imagine how a cbx just loves to scream when revved. But when I open the throttle that scream stops and suddenly I`m not on a cbx but a Ducati.
Unlike before though the engine will rev a lot more easily all the way to the red line making decent power. But there is definitely something not right and holding it back.
I was thinking maybe a faulty spark plug so thought to hell with it and bought a new set.
When I pulled the old plugs they were all showing a nice tan colour on the electrodes, so carburation is fine. They have always been black and sooty and black smoke visible from the exhaust when starting up.
When I put the new plugs in and fired it up I can still hear the rough running.
I read elsewhere on here about a poor charging system can cause misfires at high revs but according to the ampmetre the battery is charging okay.
Is there something I`m missing maybe ?


Regards
Mike

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

Post by NobleHops »

Sorry to guess, but my guess is that you’re experiencing 90% of all electrical problems, IOW, the carburetors aren’t right.
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Re: Help needed. Do I have a carb problem ?

Post by JustMike »

A guess is better than nothing NobleHops.
If it is still the carbs then it must be well hidden from me.
I had the jets out and they are clean. I blasted cleaner through all the holes to make sure they were clear.
The injectors were all working when I tested them. Float levels were all set and rechecked. Mixture screws are all set at 2 turns out.
Jet sizes are standard and slide needles are too.
The bike starts easily and runs at 3,000rpm if I keep the choke on. tickover is rock steady at 1,000rpm.
In neutral pickup from tickover is clean but as the revs rise there is a roughness which can be heard from the exhaust.
Holding the throttle steady while riding and the exhaust note is sweet. Try to accelerate and the note goes flat like it drops a cylinder or 2. Or as I suspect maybe 2 half cylinders if that makes sense.
But the roughness is right through the rev range. As soon as I ease the throttle off the misfire is gone.


Mike

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

Post by steve murdoch icoa #5322 »

Just a guess here.
Sounds a bit similar to a cracked coil problem that i had on my '81.
Were the coils in your new CBR setup tested before being installed?

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

Post by daves79x »

I found something on an '81 I was working on over the winter that may have been similar. The bike started great and idled well. But it was dropping #1 cylinder at anything above idle. Pipes were all hot at idle, but after a ride, and not letting the bike idle again, #1 was cool. Kind of opposite from the usual blocked idle passages. I then checked for any electrical issues, but only dropping one cylinder is not usual. Nothing I did/swapped around changed anything. New plug did nothing. Being #1, I could get the carb bowl off and check everything on the bike. Nothing wrong. I blew through all passages, still nothing. I finally swapped the carb top and vacuum piston from a spare set and viola! Fixed. After investigation, I found that someone had sanded/machined the vacuum piston enough so that it was not picking up when the engine called for fuel. So there's that.

Something you should trust is the exhaust pipe temperature. See if one or two are not getting as hot as the others, both at idle and after a run. See if that leads you to a cylinder or two.

Something else to check is adequate fuel flow. Both to the carbs and within the carbs themselves. The air bleeds (little brass openings under the slide in the top of the carb body) have to be open or that carb circuit will starve for fuel. I've found them blocked occasionally, and check every one every time I rebuild a set. Also check that your bowl vent system is functional.

Dave

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

Post by wyly »

daves79x wrote: I then checked for any electrical issues, but only dropping one cylinder is not usual. Nothing I did/swapped around changed anything. New plug did nothing.
Dave
I have a question about that. I know next to nothing about electrical issues I always assumed if there was and electrical issue other than a plug or plug wire that two cylinders would be effected because they're sharing a coil. I thought if number one had an issue number six would as well, is that wrong? Can number one not fire while number six remain unaffected ??? :think:
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 EMS »

wyly wrote:
daves79x wrote: I then checked for any electrical issues, but only dropping one cylinder is not usual. Nothing I did/swapped around changed anything. New plug did nothing.
Dave
I have a question about that. I know next to nothing about electrical issues I always assumed if there was and electrical issue other than a plug or plug wire that two cylinders would be effected because they're sharing a coil. I thought if number one had an issue number six would as well, is that wrong? Can number one not fire while number six remain unaffected ??? :think:

I think this is exactly what Dave is saying:..
..only dropping one cylinder is not usual...

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

Post by wyly »

EMS wrote:I think this is exactly what Dave is saying:..
..only dropping one cylinder is not usual...
okay thanks that's what I thought...Dave's answer was open to interpretation, "is not usual" left a suggestion that it does happen occasionally.
CBX a work in progress, still improving...GS1150EFE completed and awaiting modifications.....RD350, remnants in boxes scattered throughout the garage

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

Post by JustMike »

Thanks for all these replies, they`re appreciated.
As you know this is doing my head in, but at least I`ve seen something improve carb wise.
When cleaning the carbs before winter set in I followed all the advice I could from on here and as many have found, there is a lot more to those things than one thinks.
I am up for the job though as I`ve been stripping and rebuilding bikes since 1970 and used to race bikes so did all my own work there too on both 4 stroke and 2 stroke.
Anyway I`ll reply to each comment in order.

Steve Murdoch, There is always the chance of buying a used coil and it is faulty. And no I didn`t test them. From what I remember the coils came off a bike that was running and was in the process of being broken for spares (2 different sellers). But on receipt of them there was no damage to be seen and they were all in good visual condition. On running the bike when first putting them on there was no noticeable difference. It might still be worth my checking though. There is always that chance you could be right.

Dave, that is an interesting one. and is also worth thinking about. Luckily I have just bought a set of carbs which I plan on fixing up as a spare set. But it also means I have some spares if I do need them.
But in 2014 the carbs were rebuilt by Steve Gosine in the UK for the bikes previous owner and after running the bike for a few miles he parked it up and sold it on to a garage, where I bought it. The garage do not have a clue about CBX`s. I knew from the moment I trailered the bike home and fired it up for the first time that something wasn`t right. An old saying I found rings very true. "If you`ve never had a CBX then you`ll never know if it is running right or not". And I think the previous owner didn`t have a clue. Anyway, I stripped the carbs and followed all the advice I could find on here and cleaned out every orifice I could find. I`m certain the carbs are now fully clean. But, have we not heard all that before ?
I have a mechanic friend with much more experience than me trying to help with ideas and he has just bought a new temperature gun which he wants to use on the exhausts. So all being well I hope to do that today. I read that they should be in the 300deg range. Would that be correct ? I was just more interested in seeing if there is one reading off. He lives 20 miles from me so the bike will have a nice run on the way out to him.
I did blast cleaner through the air bleeds and made sure it was coming out the other end. I also checked the breather pipes. Fuel flow looks steady when viewed through the clear fuel filter.

Wyly, you bring up an interesting point, and something I have been wondering and discussing with a friend.
We noticed that suddenly I have 4 header pipes which have gone a bit blue. No1 has none and No6 has a slight hint. This made us think that this may be telling us a story. My mate thought maybe it shows there is a problem with those two cylinders, No1 in particular. And then of course I`ve read that leaving the choke on for too long can cause the headers to go blue. But why only 4 pipes and not all 6. I then started thinking of how the ignition works. The coil fires a spark down one plug into the head and then it travels from the head back up the other plug in reverse.
So my question is. Can one faulty plug cause the corresponding plug in the other cylinder to break down and misfire.
I don`t know which plug is first in line so to speak, but it made me wonder if the blueing of the headers was saying No6 plug is firing first but not just right hence only the very slight blueing of the pipe causing the No1 plug to fire even worse which is why there is no blueing at all on that header.

Oh the joys. Why is life so complicated lol.


Mike

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