Help needed. Do I have a carb problem ?

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

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Just for giggles replace your slow jets with New ones , not sure what exhaust you have ? may even go to a # 38 slow jet, what the heck you got to loose at this point , sounds like Carbs to me leaned out stumble, My bike would only run with choke on when purchased , Replaced all jets, Did you run a compression test?

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

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The jets are all standard. The exhaust is a 6 into 1, but the misfire is there with the original standard exhaust.
The misfire can be heard from about 3,000 rpm up.
I have not done a compression test but the engine is sound and makes good power when used in anger.
Today I had a bit of a head to head with a Suzuki GSX1400 that my mate owns. I wont incriminate myself by saying what speed we were doing lol. But when the CBX got its throat cleared he didn`t have enough power to get past me (his words).
Not bad going for a 40 year old bike vs a 15 year old one. So I know the motor is producing good power.
You can hear the misfire by rolling on the throttle in neutral but I`m just struggling to pinpoint what or where it is.


Mike

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

Post by wyly »

JustMike wrote: Today I had a bit of a head to head with a Suzuki GSX1400 that my mate owns. I wont incriminate myself by saying what speed we were doing lol. But when the CBX got its throat cleared he didn`t have enough power to get past me (his words).
Not bad going for a 40 year old bike vs a 15 year old one. So I know the motor is producing good power.
Mike
for a 40yr old bike the cbx has nothing to be embarrassed about it still holds it's own with most new bikes...and the only cars you need worry about are mostly in the "supercar" category and how often do pull beside one of those...I did have Nissan GT-R try tempt me into race :roll: I declined a beat down and pretended I wasn't interested :lol: ...
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 ?

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JustMike wrote:The jets are all standard. The exhaust is a 6 into 1, but the misfire is there with the original standard exhaust.
The misfire can be heard from about 3,000 rpm up.
I have not done a compression test but the engine is sound and makes good power when used in anger.
Today I had a bit of a head to head with a Suzuki GSX1400 that my mate owns. I wont incriminate myself by saying what speed we were doing lol. But when the CBX got its throat cleared he didn`t have enough power to get past me (his words).
Not bad going for a 40 year old bike vs a 15 year old one. So I know the motor is producing good power.
You can hear the misfire by rolling on the throttle in neutral but I`m just struggling to pinpoint what or where it is.


Mike
If you were closer i would let you put my carb rack on your bike, It would be one way to eliminate Fuel as problem, Can you make a Video i just put my stupid smart phone on my belt and did a short run to hear exhaust, These bikes do haul A$$ this was my first maiden run , I was not even pushing 5-6000 rpm LOTS of throttle to be had , But maybe you could do one so we could hear and help , Greg https://www.youtube.com/watch?v=L9Y-CvWRw1Q

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

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Hi Greg
I have actually thought about doing a video of the exhaust note while riding.
My wife is on holiday this week so planned on getting out on the cbx for a run. I could get her to use her phone cam to record it.
I had my mate trying to hear it while following me but he said it sounds fine.
Another loves standing at his door listening to bikes blasting down the hill away from his house, it`s about a mile long hehe. But he said it sounds fine (and he`s a mechanic).
When riding it I can hear it and feel it.
But on Monday I was chatting with a mate about it and showed him some videos on youtube and said to him, now that you hear how a proper running cbx sounds listen to this, and started the engine.
Then he heard the misfire. He also picked up on it as he watched me ride past his house on my way home.
So it is definitely there.
Swapping carbs is definitely the way to go in an ideal world. But this is one big problem that we have. It isn`t easy to just lay your hands on bits to swap over and make comparisons.
I do have a couple of things I want to try so I`ll see how it goes. But who knows, maybe there is something I`ve missed on the carbs, but the jets are clean and all the passageways blasted out with carb cleaner so I`m stumped.
I listened to your video. Your bike sounds sweet. I`m jealous lol.

Mike

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

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Mike i reread your post , Take your mixture screws out to 2 1/2 ,and then try 3 that would be to the limit of the 25 slow jet . These bikes were extremely Lean from the factory if everything is in perfect condition even your throttle plate shaft felts and absolutely perfect new seals and new Carb insulator rubbers they just about run lol..Give it a try ..Also recheck your Carb rubber clamps tighten . Greg

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

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Hi Greg.
The screws are set at 2 turn for now and the plugs are a nice tan colour with a hint of black around the edge.
Starting is first touch of the button and when warm tickover is bang on 1,000rpm.
Throttle pick up from tickover is fine and the misfire starts to rear its head above 3,000rpm.
But this is what puzzles me. If the carbs have still got a blockage somewhere in the primary jets which is the range where the misfire occurs, it is hiding well. and yes it could be just one jet that is causing the problem.
Before I stripped the carbs at the end of last year there was a flat spot starting around 4,500rpm that didn`t clear until over 7,000rpm. That is gone now and the choke is also now working where before it didn`t.
Every time I took plugs out they were always black and often fouled causing the bike to run on 5 cylinders. Black smoke was always seen coming from the exhaust too.
So the engine is definitely running cleaner than before.
So what is going through my head is that if the flat spot from before which was like hitting a wall at 5,000rpm, has gone, but there is still a misfire which seems to be all through the rev range from around 3,000rpm. What could it be?
You mentioned the carb manifold rubbers, they have been replaced by new ones. I also have a stock foam air filter. All jets are standard originals as are the slide needles.
I`ll definitely be grabbing a video to see if that provides any clues.

Mike

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

Post by wyly »

This may not help you at all but I had a similar problem and I added SeaFoam to a full tank and by the time I got through a tank of fuel the problems disappeared.
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 ?

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I just took this photo Greg.
The 2 plugs on the left are from before I stripped the carbs and the 2 on the right are from after reassembly and a test run a week ago.
Still a touch on the rich side I think, but loads better than the black sooty things I used to have.

Mike

7819

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

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Hi Wyly.
My mate suggested similar yesterday. So just waiting for him to finish work and give me the name of the stuff he uses.
There is always the possibility I have missed a bit of dirt and I`m like 98% there. So running some additives through the system might just finish the job.

Mike

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

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Mike ok i see what your describing, With out seeing your plugs , the black around the thread base maybe caused from running sitting and idling revving or even accelerator pump charge , But , everything you are describing i have battled with myself (Midrange) that is right were you are at that RPM , Every time it is the Slow circuit , Can you see your Choke throttle shaft on your carbs ? we all have seen after rebuild how the blades on the choke can be sticky and remaining partially closed , But you really should go 2 1/2 out first being it is just a simple adjustment , It can always be turned back to 2 turns. This may have been asked already Your mixture screws have new rubber O ring and washer and spring ? Greg

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

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JustMike wrote:I just took this photo Greg.
The 2 plugs on the left are from before I stripped the carbs and the 2 on the right are from after reassembly and a test run a week ago.
Still a touch on the rich side I think, but loads better than the black sooty things I used to have.

Mike

7819
Ok just seen these , That plug on the left looks like oil and is fowled , Your motor ever been rebuilt ?

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

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Mike i reread your post again lol,,you stated you never ran a compressing test ,,and you have 27 k miles "not a lot" your right about it could be just one cylinder giving you all this grief , But your Valve stem seals may be dried out and needing replaced that could be contaminating that cylinder spark plug , Put a new plug in that cylinder and run it for around 10 minutes , Let it sit and cool down for a hr, and then check it for wetness on the base of the threads . Greg

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

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I`m not aware of the motor having been stripped Greg.
It has only had one owner from new who lived in the Minnesota area and then the bike was imported to the UK. Current mileage is 27,000 miles.
But the 2 plugs on the left are from before I stripped and cleaned the carbs end of last year and the 2 on the right are from last week.
So yes I was always fouling plugs before, but not now.
There is no black smoke coming from the exhaust any more.

Mike

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

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Gearheadgregg wrote:Mike ok i see what your describing, With out seeing your plugs , the black around the thread base maybe caused from running sitting and idling revving or even accelerator pump charge , But , everything you are describing i have battled with myself (Midrange) that is right were you are at that RPM , Every time it is the Slow circuit , Can you see your Choke throttle shaft on your carbs ? we all have seen after rebuild how the blades on the choke can be sticky and remaining partially closed , But you really should go 2 1/2 out first being it is just a simple adjustment , It can always be turned back to 2 turns. This may have been asked already Your mixture screws have new rubber O ring and washer and spring ? Greg
When I get a chance I can try turning the screws out a bit and see how it goes. The carbs were fully stripped and rebuilt 4 years ago and to my knowledge all O-rings and seals were replaced.
Before those 2 plugs on the right were pulled I had been running the engine hard and then back into city traffic for a few miles to get back home. So I put the sooty ring on the outside down to the the slower riding.

Mike

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