Sticking carb slide?

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tony.mon
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Re: Sticking carb slide?

Post by tony.mon » Wed May 30, 2018 11:25 am

jchesshyre wrote:
Wed May 30, 2018 9:56 am
tony.mon wrote:
Mon May 28, 2018 2:36 pm
You could try popping the tops off the carbs and measuring the spring lengths.
Specs are in Haynes.
Can't see this anywhere in Haynes or Honda manual...
Can't help ATM as I'm not in UK.

Some years ago a chap called Benny Hedges found a difference in spring length after he accidentally trod on one. He posted up about it, but I can't give you any more clues than that.

Just a thought, you've checked that the needle isn't slightly bent, have you?
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Re: Sticking carb slide?

Post by jchesshyre » Wed May 30, 2018 11:28 am

tony.mon wrote:
Wed May 30, 2018 11:25 am
jchesshyre wrote:
Wed May 30, 2018 9:56 am
tony.mon wrote:
Mon May 28, 2018 2:36 pm
You could try popping the tops off the carbs and measuring the spring lengths.
Specs are in Haynes.
Can't see this anywhere in Haynes or Honda manual...
Can't help ATM as I'm not in UK.

Some years ago a chap called Benny Hedges found a difference in spring length after he accidentally trod on one. He posted up about it, but I can't give you any more clues than that.

Just a thought, you've checked that the needle isn't slightly bent, have you?
Ah no worries. The needles are brand new (well, NOS!) Honda ones and definitely not bent.

Just to clarify, I have sorted the hanging revs issue, it's just a hesitation on large throttle openings (worse in higher gears) that I'm trying to eliminate now.

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tony.mon
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Re: Sticking carb slide?

Post by tony.mon » Wed May 30, 2018 11:33 am

Didn't Mikstr find that the fixed needle jet was worn on a set he had? Not sure how you'd check that.
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jchesshyre
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Re: Sticking carb slide?

Post by jchesshyre » Wed May 30, 2018 11:38 am

tony.mon wrote:
Wed May 30, 2018 11:33 am
Didn't Mikstr find that the fixed needle jet was worn on a set he had? Not sure how you'd check that.
So did I! Eyeballing them with a torch showed a slight ovalling of them. This was the reason for changing my carbs in the first place. It was causing richness around 3-4k rpm, due to what I believe is known as a wet mixture (badly atomised fuel). This was confirmed when I ran the engine with the airbox lid off and could actually see droplets of fuel emerging around the needle!

Could a very slight leak at the inlet rubbers cause a hesitation in power with large throttle openings?

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tony.mon
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Re: Sticking carb slide?

Post by tony.mon » Wed May 30, 2018 11:47 am

No, it would have an effect, if any, at small openings but at full draft wouldn't have much of an effect.
To prove this, unplug the carb balance tube.
It runs horribly at lower revs, then ignores it until six or seven and gives you full beans suddenly.

You could try assembling the carb into the rubber with a light smear if silicone just to check, but I don't think it will make a difference.
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Re: Sticking carb slide?

Post by jchesshyre » Wed May 30, 2018 11:53 am

Damn... it's most noticeable at higher gears, WOT, around 4000 rpm. It sometimes does it around 7k as well.

My carbs and carb settings are now completely stock. Only thing that isn't is that I have Fuel silencers (with baffles in) but I ran them for many miles without this issue. My spark plugs are both a nice tan colour on the tips.

So possibly a slide movement or ignition issue? Would a coil beginning to go cause this?

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tony.mon
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Re: Sticking carb slide?

Post by tony.mon » Wed May 30, 2018 11:57 am

Find a nearby local with a bike that's running right and swap bits starting with plugs and coils, then ECU, then carbs to see what's making the problem.
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Re: Sticking carb slide?

Post by jchesshyre » Thu May 31, 2018 9:33 pm

I've found the issue, and thankfully it's not some obscure electrical gremlin.

This looks like it's alright, yeah?

Image

Is it balls!!

Image

I'd only checked it on the outside, without looking at it inside out - they look completely fine on the outside! It doesn't look as if it goes all the way through, although I can't completely tell, but there's at least one more crack like this and surely this is likely to be causing the hesitation? Turns out both diaphragms are a bit perished-looking where they meet the slide body, as are the other set I have:

Image

Is this age? Ethanol? Lack of use by previous owners? My money would be on the latter.

Fortunately I have a third pair whose diaphragms are much better. They have third lift holes drilled in them (otherwise I'd have used them already) but I've blocked them up and the epoxy is curing as we speak...

It's a shame a new piston+diaphragm is ONE HUNDRED AND EIGHTY pounds.

Thanks all especially Tony for your suggestions. I'll re-post tomorrow once they're back in the bike and I've ridden it!

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Re: Sticking carb slide?

Post by jchesshyre » Fri Jun 01, 2018 12:51 am

...awaiting the morning...

Image

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Re: Sticking carb slide?

Post by jchesshyre » Mon Jun 04, 2018 9:34 pm

Well the bike's running has definitely improved now and is almost perfect! However I still have this weird thing where the power hesitates with large throttle openings. It feels as if the engine is briefly gasping for breath (but that breath could be air, fuel, or spark!). It's not consistent - going downhill off a roundabout earlier I went all the way through the first three gears at full throttle (well full in 2 and 3!) and it didn't hesitate, and pulled really well without stumbling. But it possibly is worse when under more load - higher gears and slightly uphill. I can't totally work out what combination of factors causes it to happen, but I think it's when going from large throttle to closed and back to large again - for example when re-applying throttle after changing gear under hard acceleration.

I've found the same thing happens right up at the highest revs as well, but hadn't noticed before because I don't tend to rev it all the way to the top (like I do with my CB500!). It almost felt like a rev limiter but wasn't because it was at about 9 or 9.5k.

I can't see how it is a carb issue - I have now got totally different carbs (including, now, different slides) from before. And the fuel tap diaphragm is fine.

When I had the spark plugs out the other day they were literally the best colour I've ever seen them! So there's not a mixture issue.

Could a restricted fuel tank breather cause this symptom? I've checked at the tank and the hose and both pass air but it did seem quite hard to blow through, but then I've got no comparison and maybe that's just what the breather's like.

I'm guessing next I need to test the coils and if that doesn't yield anything try someone else's ICU (uk13iker...? ).



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VTRDark
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Re: Sticking carb slide?

Post by VTRDark » Tue Jun 05, 2018 12:25 am

It's not consistent - going downhill off a roundabout earlier I went all the way through the first three gears at full throttle (well full in 2 and 3!) and it didn't hesitate, and pulled really well without stumbling. But it possibly is worse when under more load - higher gears and slightly uphill.
So is this from when going from heavy braking /slow down and then back on hard on the throttle.

It might be the carb breathers. The two pipes that run through the middle inbtween the two carbs. Pull these out so they dangle down or at least so there is not such a sharp bend where the pull through the holes in the side brackets. You might be flooding the front carb under hard deceleration.
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Re: Sticking carb slide?

Post by jchesshyre » Tue Jun 05, 2018 7:28 am


VTRDark wrote:
It's not consistent - going downhill off a roundabout earlier I went all the way through the first three gears at full throttle (well full in 2 and 3!) and it didn't hesitate, and pulled really well without stumbling. But it possibly is worse when under more load - higher gears and slightly uphill.
So is this from when going from heavy braking /slow down and then back on hard on the throttle.

It might be the carb breathers. The two pipes that run through the middle inbtween the two carbs. Pull these out so they dangle down or at least so there is not such a sharp bend where the pull through the holes in the side brackets. You might be flooding the front carb under hard deceleration.
Unfortunately this isn't it. It doesn't just happen after braking and in fact until recently I'd removed those hoses altogether (but have tried with them on again on the off-chance that that was the issue - it wasn't!).

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Re: Sticking carb slide? SORTED (I think)

Post by jchesshyre » Fri Jun 08, 2018 9:34 am

Well I've deleted my last speculative post about this as I think I've found the bloody problem.

When I crashed last year I had a replacement (used, of course) fuel tank which included a petrol tap. I compared the visible condition of the diaphragm in this new tap and in my existing one. The diaphragm in the new one looked better so I decided to use this tap. However, I had a pattern fuel tap repair kit lying around so (for some reason) decided to replace the smaller rubber part (plunger) in the tap, but not the actual diaphragm. I've previously posted (http://vtr1000.org/phpBB3/viewtopic.php?t=40973) about these kits and that I'd found them useless as the rubber that the diaphragm is made of is far thicker than the OEM diaphragm and just doesn't work. Who knows why I still decided to use the plunger bit in this new tap.

Anyway...I've just had a ride with the other petrol tap on and the problem has gone! If I operated the faulty tap off the bike I could see the plunger moving just fine, but it did seem to spring closed far more quickly than the other tap, so I don't know if this was somehow the issue or if that part wasn't sealing against vacuum properly. Discussion here viewtopic.php?t=15128 seems to suggest that it is a problem if the tap closes too quickly as at full throttle there's very little vacuum to hold the tap open. This does sound rather like it might be what my problem was...

But my advice is do not buy kits such as this https://www.ebay.co.uk/itm/112136577816 as (IME) they just do not work.

Is there any satisfactory way of disabling the vacuum operation of the tap so that it is just a manual tap? If not, then I might have to splash out £50 on a new 'COVER SET C0CK' from Honda to make sure these issues are properly sorted and don't come back.

*edit* just seen AMCQ's post so will maybe try one of the OEM-quality kits he mentions first - half the price!

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Re: Sticking carb slide?

Post by sirch345 » Fri Jun 08, 2018 7:34 pm

Wow you got there at last :clap: HURRAY you must be made up :D

Very good information in this thread for future peeps with similar problem,

Chris.
A closed mouth gathers no foot. :thumbup:

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Re: Sticking carb slide?

Post by jchesshyre » Sun Jun 10, 2018 6:47 pm

Well...I'm sorry to say the issue isn't sorted. I spoke too soon. It's maybe better but not gone completely.

I've now actually made the fuel tap free-flowing (as per this http://www.akhara.com/nc30/fueltapmod/index.html which seems to be a very similar if not identical fuel tap) and the issue is still there.

Generally the engine pulls really well, the problem is really only noticeable at full throttle. It's a hesitation (quite an abrupt one) around 6k sometimes or around 7.5-8k and also, as I've said before, if changing from large to small then back to large throttle openings. And it's more noticeable in higher gears, definitely. I'd say it actually never does it at part-throttle, only WOT.

Just in case it's a fuel tank venting issue, how does one go about checking this? The longer part of the vent hose is clear, but what's the easiest way to check the tank itself is venting properly? If it is this, it's only a marginal problem as I'm not actually getting full-on fuel starvation.

Could valve clearances being out cause this symptom? I adjusted them all to spec 17,000 miles ago which I know is just over the service interval but really don't expect them to have gone out in that time.

I'm really clutching at straws here, but could the fact that I removed the foam inside the airbox snorkel have caused this? It was all perished so I thought I'd get rid of it. I can hardly believe this would cause this, but I do know how sensitive these bikes are to any airbox changes so I'm not ruling it out!

I'm really struggling to not get a bit despondent about this and don't really know where to try next.


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