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luddite
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1,814 Posts
Discussion Starter #1
ok so it's not turbo lag but that's what it feels like!

I just got back from a week end trip to the vosges & whilst there, going up the grand Ballon d'alsace in the hairpins the bike developed a bizarre fault. I could do with some help trying to pin it down before I either spend huge amounts of Dosh that I don't have or do something drastic myself using skils I don't have, to attempt to remedy it.

The Symptomes; shut down the throttle (going into a very wet hairpin for example!) round the apex & snap the throttle back on in either First or second gear (depending how slow the nobber in front was going) & the bike takes a pause before anything really happens, then the power comes on all in one go, so, having narrowly avoided falling into the apex cos the power didn't come on when I open the throttle I then nearly chuck it all sideways cos the power has come on too fast for a very wet, very cobbled(!) hairpin bend...

my first thoughts were a) altitude, b.) humidity & c) crappy fuel.

a) though we were over 1000m (3200ft) I don't believe this is high enough to affect the engine. I've also ridden the bike higher than this in the past & never had this problem. carb icing is also out of the question as it was 17°c (62.5°F)

b.) we were in cloud so humidity was high, we'd also ridden though drizzle, mist & fog all day. could it be humidity in the cdi connections, HT leads, plug caps or even coils?

c) last fuel stop was in a crappy cheap supermarket, but everybody else had also fuelled here & only I had the problem.

That evening I swapped over the cdi's ( to make use of the telltale rev counter dip if the aft cdi is dicky. I'd had no rev counter dip during the problems, so if the problem reoccured the next day & still no rev counter dip, haveing swapped the cdi's then that would suggest the problem lies elsewhere) & sprayed wd40 on all the electrical connections I could get at easily (it was dark, could & raining & there was no shelter)

but the weather was so apalling the next day we forwent any further hairpin strung summit topping country lanes & remained on more major roads. Humidity was again a big possible problem but the problem didn't reoccur 'till late in the day when we were back on dry roads & large doses of full throttle were required, less blatent but still discernable. Playing with it I reckon that it only happens when the throttle goes all the way shut & is opened agressively, then the power seems to come on in 2 stages... could this be a problem with carb balancing / synchronising? throttle cable? or is it more likely to be an electrical problem?

I also wondered if it was a sort of pre seize symptome as the oil level was very low that evening despite my having checked & topped up the level only a couple of days ago. she never usually uses oil... or maybe that's just due to the fact that it's a 22yr old bike with 124000 (77000miles) & that we'd done 4 hours of autoroute @ +/- 140km/h (85mph) before even arriving at the hairpin stuff...?

I'll check the oil level again tomorrow morning & see how much it's used in the run home today.

any pertinent thoughts?

ps oil level fine when checked this morning. so no use of oil on the return trip (not on autoroutes so running at 90 - 120km/h with occasionel sprints "slightly faster"...
:rolleyes:
 

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Golam Rosewater
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1,444 Posts
The turbo lag feeling sounds very much like lean running, check carb to engine rubbers and carb to airbox rubbers, or spilt carb diaphams ?
 

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luddite
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1,814 Posts
Discussion Starter #3
I had split airbox to card rubbers on an xj650 many...many years ago but that just prevented it ticking over...

I don't think that would make it lag like that ONLY when soliciting power quickly, would it?
 

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Registered
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This is just a guess but given it only happens when the throttle position is altered I would look at the carb diaphrams.
If one is starting to fail then the higher altitude would excacerbate the problem. The turbo lag is because the mixture is too weak becaust the diaphrams arnt doing their job but once air fuel mix starts flowing correctly (after the lag) the diaphrams job is done so the symptoms disappear.
 

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luddite
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1,814 Posts
Discussion Starter #5
This is just a guess but given it only happens when the throttle position is altered I would look at the carb diaphrams.
If one is starting to fail then the higher altitude would excacerbate the problem. The turbo lag is because the mixture is too weak becaust the diaphrams arnt doing their job but once air fuel mix starts flowing correctly (after the lag) the diaphrams job is done so the symptoms disappear.
I had a long chat with the mechanic at the bike shop I use & what you're saying ties in with what he thinks too. He says to strip the carbs & inspect the diaphragms cos either one's porous or there's a wee split.

Thanks.
 

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Premium Member
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6,922 Posts
If it is the diaphragms, then these guys - NRP-carbs.co.uk - should be able to sort you out with new ones at a bit less then genuine ones from Honda.

Edit: Stopped being lazy and had a look for you. For an 87 - 95 model Transalp the diaphragms are £32 each - though not sure about whether the dreaded VAT is included nor what the postage would be like.

As a comparison, David Silver's list them at £138 including VAT!!! Part number - 16111-MF5-841

And bike-parts-honda.com (French outfit) quote €181.53!!



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Registered
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As a comparison, David Silver's list them at £138 including VAT!!! Part number - 16111-MF5-841

And bike-parts-honda.com (French outfit) quote €181.53!!

For a thin bit of vinyl ,,,,,,,,,,,,,,,, your aving a laugh ain't ya.
Rip off:rolleyes:
 

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luddite
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1,814 Posts
Discussion Starter #8
If it is the diaphragms, then these guys - NRP-carbs.co.uk - should be able to sort you out with new ones at a bit less then genuine ones from Honda.

Edit: Stopped being lazy and had a look for you. For an 87 - 95 model Transalp the diaphragms are £32 each - though not sure about whether the dreaded VAT is included nor what the postage would be like.
brilliant, thanks Lutin. erm... on their site there's a "HONDA XL600VK-X TRANSALP '89-99 LOOSE DIAPHRAGM" @£32,64 or there's a "HONDA XL600VJ-VT TRANSALP '88-96 MAIN DIAPHRAGM" @ £38.40

Mine being a '91 XL600V M Transalp (at least it's an "M" as far as I can make out) it fits into either of theses categories but what's the difference between a simple "loose diaphragm" & a "Main diaphragm"? which should I order?

:confused:
 

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Premium Member
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brilliant, thanks Lutin. erm... on their site there's a "HONDA XL600VK-X TRANSALP '89-99 LOOSE DIAPHRAGM" @£32,64 or there's a "HONDA XL600VJ-VT TRANSALP '88-96 MAIN DIAPHRAGM" @ £38.40

Mine being a '91 XL600V M Transalp (at least it's an "M" as far as I can make out) it fits into either of theses categories but what's the difference between a simple "loose diaphragm" & a "Main diaphragm"? which should I order?

:confused:
Erm, you've got me there. Best bet would be to drop 'em an email I suppose.



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luddite
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Discussion Starter #10
well I mailed 'em a posed the question, got a mail back from Andy saying "I've simplified that bit of the site, loose diaphragm is if you fit it, t'other one is if we fit it to the slide for you..." or words to that effect, so I ordered them today, in theory I'll be getting two carb diaphragms for less than the price of one from Monsieur Honda France!:thumbright:
 

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Premium Member
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well I mailed 'em a posed the question, got a mail back from Andy saying "I've simplified that bit of the site, loose diaphragm is if you fit it, t'other one is if we fit it to the slide for you..." or words to that effect, so I ordered them today, in theory I'll be getting two carb diaphragms for less than the price of one from Monsieur Honda France!:thumbright:
Sounds like a result to me. Top stuff. :thumbup:

I'm presuming that the originals are past their best?



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luddite
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Discussion Starter #12
I'm presuming that the originals are past their best?
I won't know 'till I pull 'em out, unfortunately I have a time limit, I have to be in Grenoble (or thereabouts) on sunday with the bike so I'm hoping the diapnragms get here with time to fit them before I go, if not I'll have to ride it like it is for this trip & do it afterwards. i'd rather replace them befor I leave but I'm not going to strip the carbs down till I've actually got the things in my hand, just incase they don't get here in time.

my experience & everybody I'v spoken to suggests that one or both carb diaphragms are either porous our damaged. As far as I'm aware they are the originals which would make them 22yrs & 124000 (77000miles) old so I'm adding 2 & 2 & hoping not to come up with 7 & 3/4...
 
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