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Carb problem

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The Hurricane
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Carb problem

Post by The Hurricane on Tue 20 Nov 2018, 9:52 pm

I have a problem with one of the carbs where I have to set the air mixture screw to 5 turns out to get the spark plug looking the biscuit colour.
I have had the carb out and checked the jets, cleaned them out and blown through with compressed air and checked for any leaks or cracks and can't find anything. The other side is perfect and is set to just over 1 turn out. 
Has anyone had a problem like this before and if so I would be very grateful for your help.
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RossObey01
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Re: Carb problem

Post by RossObey01 on Tue 20 Nov 2018, 10:43 pm

I had a similar problem with my bike only running on one cylinder. I stripped the carbs to check for blockages no end of times and could only resolve it by fitting new carbs.

I eventually tracked it down to a partially blocked pilot jet. Each time I stripped them I did each carb individually, which meant when I held the jets up I could see light and knew they were good. But it wasn't until I checked both jets next to each other that I saw one was slightly blocked and although it let light through, not nearly as much as the good side.

That was despite blowing it through with cleaner and air, in the end it needed to be physically cleared with wire.

So I guess all in saying is make sure 100% the jets are clear.
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eternally_troubled
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Re: Carb problem

Post by eternally_troubled on Wed 21 Nov 2018, 7:56 pm

That sounds like good advice, thought make sure you have some *very* small wire and use it rather carefully (you don't want to enlarge the hole...).
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The Hurricane
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Re: Carb problem

Post by The Hurricane on Thu 22 Nov 2018, 7:10 pm

Cheers for your reply guy's. 
I will get the bike back together this weekend and see what the plug looks like. I will update over the weekend on the outcome.
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The Hurricane
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Re: Carb problem

Post by The Hurricane on Sat 24 Nov 2018, 7:45 pm

I had a new pilot jet in my toolbox and put that in and fitted the carb on the bike and started her up, she wasn't running right, so took the plugs out and turned the bike over and the good cylinder was blowing out fuel and the one which was giving trouble had nothing coming out. I checked the float bowls and the left one which has been giving me trouble was nearly half of the right side, so carbs out again and bowls off and checked the float valves on both and looked ok. I put the carb back together and before fitting back on the bike filled the carb with fuel and then drained each bowl and both were the same level of fuel. So hopefully when I get time in the week, I can checked the plug out method to see if fuel is coming into the cylinder. 
I have had these carbs off the bike so many times now, it is starting to get frustrating.
What I can't workout is why the float bowls would be different levels as the pressure of the fuel coming in pushes the valves down to fill the float bowl and when full, the floats push the valve up to the hole where the fuel is coming in. The floats feel nice and free, so can't see them getting stuck.
Any help would be much appreciated.
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ANDYC
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Re: Carb problem

Post by ANDYC on Sat 24 Nov 2018, 8:49 pm

Is the small plunger in the float valve needle free? You could swap the floats and valve needles and see if the problem moves.
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The Hurricane
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Re: Carb problem

Post by The Hurricane on Sat 24 Nov 2018, 9:24 pm

I checked the float needle plunger and it moved freely.
I am going to change the float needle, as this is the only thing I can think of that would cause the float bowl not to fill to the correct level for the fuel to get sucked up the pilot jet.
Any thoughts on my mine, as I do go down the wrong road at times.
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eternally_troubled
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Re: Carb problem

Post by eternally_troubled on Sat 24 Nov 2018, 10:22 pm

It is certainly worth changing the float needle, just in case. Did you check that both the floats 'float' in a similar way? (i.e. that neither of them has a hole!)
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The Hurricane
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Re: Carb problem

Post by The Hurricane on Sat 24 Nov 2018, 10:32 pm

I checked that they both sat at the same level and they both moved up and down freely. I will take the floats out and see if there are any cracks in them.
Many thanks for your help.
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eternally_troubled
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Re: Carb problem

Post by eternally_troubled on Sun 25 Nov 2018, 2:10 pm

Best of luck. As Andy said, I think it might be worth swapping them over to see if the problem follows the floats or the carb bodies - at least this might give you somewhere to start.
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The Hurricane
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Re: Carb problem

Post by The Hurricane on Sun 02 Dec 2018, 9:11 pm

Got back to sorting the carbs again today. I put new float needles in and got them back on the bike and they both over flowed with fuel. I then took them off again and checked the float height that is in the manual and that seemed good. I put them back on the with just the carbs and no air box and tried starting the bike and fuel was coming out the back of the carbs and filled up the carb and the whole lot went into the cylinders. Another oil change will have to be done once I get it sorted, that's hoping I do.
I am lost now as the floats move nice freely and the needles shut off ok and measure 13.7 in height from the base of the bowl seat. 
If the float needles shut off the fuel coming in, then there shouldn't be fuel over flowing into the cylinder and my garage floor. 
This is getting to the point of doing a Basil Fawlty on the bike soon.
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ANDYC
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Re: Carb problem

Post by ANDYC on Sun 02 Dec 2018, 9:41 pm

That's unusual,  it could be worth checking the float jets I guess. As you rightly say new needles should close off the fuel supply. 
The fuel tap is shutting of the supply unless the engine is running I assume. If not this may be adding to the problem.
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Jameshambleton
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Re: Carb problem

Post by Jameshambleton on Sun 02 Dec 2018, 10:02 pm

Refit the carbs, and tap them as you're filling them up with fuel, the floats often get slightly stuck until
the pivot pin is "lubricated" with petrol. Tapping them will help
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The Hurricane
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Re: Carb problem

Post by The Hurricane on Sun 02 Dec 2018, 10:04 pm

I have been using a bottle to feed the fuel with a hose attached to the hose going to the carb as it is a pain the backside to keep taking the tank off. As far as I know the fuel tap on the tank is a continuous feed when the engine is running with a vacuum hose attached to the cylinder head.
Either method should still have the needles shutting off when the bowls fill up.
At the moment I maybe missing something that someone else can pick up on. 
There are a pair of carbs on eBay that I might buy to see if I get a different result, that's as long as they are a good pair off carbs.
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Crash- Elmit
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Re: Carb problem

Post by Crash- Elmit on Sun 02 Dec 2018, 10:39 pm

have you tried leaving the float bowls off, running fuel in the same way you are doing, but manually
close the floats to see if that stops fuel flowing
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ANDYC
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Re: Carb problem

Post by ANDYC on Sun 02 Dec 2018, 10:43 pm

You beat me to it.
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eternally_troubled
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Re: Carb problem

Post by eternally_troubled on Sun 02 Dec 2018, 11:09 pm

^  just what I was about to say too!

This will involve making mess with petrol so you should be slightly careful - mind you, it sounds like you have some previous experience with this!
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The Hurricane
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Re: Carb problem

Post by The Hurricane on Sun 02 Dec 2018, 11:18 pm

Great idea of leaving the float bowls off. I will try this in the week and let you know the outcome. 
I will tap the bowls when fitted back on. 
These two ideas will hopefully solve my problem.
This forum is great for help and I really appreciate everybody's input.
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cb500rider
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Re: Carb problem

Post by cb500rider on Mon 03 Dec 2018, 12:22 am

Sometimes the float can become stuck or not move freely enough due to a scum like build up within. You could roll a small piece of ultra fine sandpaper and scrape the inner wall where the pin part of the float moves, and then spray good quality carb cleaner to flush out any remnants with a quick blast of compressed air for good measure. This can help to stop it potentially sticking.

Have you inspected the carbs rubber diaphragm for holes/tears which can be total pain trying to fit them back exactly back in place, but just work on the float bowls first with the above mentioned suggestion. Also, you can use a G-string guitar wire is actually strong & slim enough to poke through any hard build of crap within the jets, and finish easily with Carb cleaner & can of compressed air.

Finally, for good measure get an inline fuel filter with if I remember correctly an 8mm outer diameter for the fuel line that is appropriate for a 500cc bike, as the slightly smaller version of them will eventually cause fuel starvation while running the bike on the road nearing 60mph for a while. This will help to avoid rust particles & crap potentially entering the carb's bowls to avoid plugging up the jets!
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The Hurricane
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Re: Carb problem

Post by The Hurricane on Mon 03 Dec 2018, 7:46 pm

Well on trying the float bowl off method it appears that the new float needles are the cause of the problem. 
I touched both bowls so they close off the supply and fuel was still dripping out at a fair rate. I then put the old float needles in and they closed off the fuel. I checked the new needles to see why and it appears that when you locate them in the slot on the float, the plunger sits against under pressure in the slots and does not let it hang freely.
So to try and cure my problem no.1 I had of a fuel getting to the left cylinder and the cause of a float needle being the problem, this then doubled my problem in another way.
So searching for another set of float needles Tourmax do them and at a price of £11.14 each they don't come cheap. David Silver want £20.60 each plus postage. The one's I bought originally came in gasket kit for £9.75 each. 
I must say thank you for your help so far, as I have had nothing but problems with this bike since I bought it back in August and it was in much need of some tlc. It has been a real pain in the backside and hopefully I will get it back on the road soon, as this is the final problem that has stumped me at times.
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ANDYC
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Re: Carb problem

Post by ANDYC on Mon 03 Dec 2018, 8:08 pm

At least you have identified the problem, and it's not insurmountable. 
I have a pair of known good ones if that helps. Otherwise I would recommend replacing them with original ones as you have already had problems with pattern ones.
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The Hurricane
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Re: Carb problem

Post by The Hurricane on Mon 03 Dec 2018, 8:37 pm

How much would you want for them?
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ANDYC
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Re: Carb problem

Post by ANDYC on Mon 03 Dec 2018, 8:54 pm

Nothing,  PM me your address and I'll post them out to you when I get a chance.
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eternally_troubled
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Re: Carb problem

Post by eternally_troubled on Wed 05 Dec 2018, 8:08 pm

Glad to hear that you managed to find the problem.

I'm a big fan of pattern parts, but only when they are made to the right pattern!

I have found this with other bikes and cars too - sometimes the makes of the pattern parts make assumptions and use 'that'll do' type solutions which completely f*ck things up.

The good thing is that the majority of parts are allright; you just need to be slightly careful (especially on ebay, especially when buying the cheapest option).
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The Hurricane
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Re: Carb problem

Post by The Hurricane on Wed 05 Dec 2018, 8:48 pm

Hopefully now I can sort out the original problem of having to turn the air mixture screw out 4-5 turns for the plug to look the right colour. I have tried running the bike and upping the revs slightly on the adjuster and screwing the air mixture screw all the way in and then screwing back out again till the bike sounds right. This appears to be about 1.5 turns out. When I check the plug it is whitish in colour, which to me is too lean.
I have changed the pilot jet and given the carb a good spray through and then blown through with compressed air.
Any advice very welcome

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