Sticking carb slide?

Need advice on which oil to use or which tyre best suits you? Share your topic and get help here.
jchesshyre
Posts: 590
Joined: Wed Jun 15, 2016 9:09 am
Location: Chester, Cheshire

Re: Sticking carb slide?

Post by jchesshyre »

...I've ruled out a tank vent issue by going for a run with the tank cap open (I'd always thought it was impossible to get the key out when the cap was open but now I know how!) - the issue is still there.

It seems to get worse when the bike is hot, indeed it's more or less not there at all when cool (not even fully cold, just cooled for two hours after riding). It gradually starts to manifest and get worse as the bike warms up. Do ignition coils that are starting to go bad show more symptoms when hot? I recall reading that this is the case before.

I've taken the liberty of ordering two good condition coils + HT leads off ebay since this needs to be ruled out. Worse case I have two spares - they're not expensive in the scheme of things!

Have tested the ignition pulse generator, TPS and ECT sensor - all in spec.

It's annoying me because normally I'm pretty good at tracking down faults, and also because aside from this the bike is running/pulling incredibly well.
User avatar
AMCQ46
Posts: 16535
Joined: Mon May 11, 2009 4:54 pm
Location: Worcestershire / Warwickshire border

Re: Sticking carb slide?

Post by AMCQ46 »

from what a few people told me, the actual fuel tank vent is in the filler cap, the pipes in the base of the tank are drains incase you overfill.

simple way to check is to ride with the tank filler open ... just don't have it full and brake too hard 8O
AMcQ
jchesshyre
Posts: 590
Joined: Wed Jun 15, 2016 9:09 am
Location: Chester, Cheshire

Re: Sticking carb slide?

Post by jchesshyre »

AMCQ46 wrote: Mon Jun 11, 2018 10:32 am from what a few people told me, the actual fuel tank vent is in the filler cap, the pipes in the base of the tank are drains incase you overfill.

simple way to check is to ride with the tank filler open ... just don't have it full and brake too hard 8O
Tried this yesterday and no joy : /

I think the one consolation I have is that identifying the issue as only happening when the bike's hot does help to narrow it down, slightly. I hadn't noticed this before because it only happens at full throttle and I don't use full throttle when the bike's cold, of course. However yesterday the engine was basically warmed up (had ridden for an hour two hours previously) but the bike had nevertheless cooled down a bit, and in these circumstances the issue did not start happening until I'd been riding for twenty mins or so.
User avatar
VTRDark
Posts: 20010
Joined: Sun Mar 18, 2012 9:24 pm

Re: Sticking carb slide?

Post by VTRDark »

What you describe is a way to determine if a jet size is too large or small.
1- Top end (full throttle / 7.5k to redline ) Select Best Main Jet
Best Main Jet must be selected before starting step 2 (needle height)!

To get the best, most even top end power (full throttle/after 7500 rpm), select the main jet that produces the highest top speed / pulls hardest at high rpm. If the bike pulls harder at high rpm when cold and less hard when fully warmed up, the main jet is too large. Install a smaller main jet and retest until you find the main jet that pulls the hardest at high rpm when fully warmed up If the bike doesn't pull well at high rpm when cold and gets only slightly better when fully warmed up, the main jet is too small..
This must be done first - before moving on to the other tuning ranges. In order to properly tune the midrange and low rpm carburetion, THE MAIN JET MUST FIRST BE PROPERLY SELECTED after 10 to 15 minutes of hard use!
Do not pay too much attention to the low-end richness when you are changing main jets - you still need to be using the main jets that produce the best power at high rpm. You will deal with the low-end / cruise later - after step 2.
http://www.vtr1000.org/phpBB3/viewtopic ... 31&t=14214
==============================Enter the Darkside
jchesshyre
Posts: 590
Joined: Wed Jun 15, 2016 9:09 am
Location: Chester, Cheshire

Re: Sticking carb slide?

Post by jchesshyre »

Yeah, I mean the fact that it only happens once warmed up did make me think of a rich condition, but I'm running stock main jets. However (a) I guess I don't know for sure that someone hasn't drilled them out and (b) I am running a slightly freer-flowing exhaust (albeit with baffles in) which I do know can paradoxically lead to richer running with these bikes rather than the expected leanness.

However, my plugs don't show signs of sootiness - they are a nice grey with a hint of tan - so I'm not sure.

I should maybe try 172F 175R just to rule this out though I guess.

Btw, although, as previously described, changing carbs didn't get rid of the issue, I used the same main jets when I swapped the carbs as the carbs I was putting on had DJ main jets in. So if it is a main jet issue it would have been carried over when I changed the carbs over.

The other symptom I've noticed is that if I'm giving it full throttle at high-ish revs, and slightly close the throttle, the bike feels briefly like I've totally shut the throttle rather than just slightly - there's a weird hesitation then as well - before the power delivery comes back again, which it definitely didn't do before this problem started happening.
User avatar
sirch345
Site Admin
Posts: 21672
Joined: Mon Aug 25, 2003 10:35 pm
Location: The West Country.

Re: Sticking carb slide?

Post by sirch345 »

This is a very interesting thread, although that is most likely not your opinion right now :wink:

I'm impressed with all the effort you're putting into tracking this problem down, I hope you get there very soon,

Chris.
jchesshyre
Posts: 590
Joined: Wed Jun 15, 2016 9:09 am
Location: Chester, Cheshire

Re: Sticking carb slide?

Post by jchesshyre »

YEEEEEESSSSSSSS thank you VTRDark!!!

I know I've already put a post saying 'it's definitely sorted' but now it really and truly is. It feels completely different above 7k rpm and races towards the redline like it used to, rather than feeling a bit tired up there, and all the full throttle weirdness I was getting has gone. And this was with the bike fully warmed up.

This has been annoying but (a) I'm relieved it's not something electrical or engine-related and (b) I've learnt something new in carb tuning - what top-end richness feels like.

I'm afraid I've been unscientific and changed two things but at this stage I just wanted to get the problem sorted.

I swapped my main jets for 172 front 175 rear and I also changed the slide springs for the ones off my old carbs. No massive visible difference between the springs although the ones I've put in were maybe 1 cm shorter (they're all stock though - AFAIK Dynojet ones are quite a bit shorter).

I've visually examined the jets I took out (which are Keihin stock ones) and there's no obvious sign that they've been drilled. I know I should be scientific and put in the 175/178 ones that I know are good, so that I know whether it's the size change that's improved things or whether there was something up with the ones that were in there. I've tried 'measuring' the bore size of the ones I took out vs my known good 178 jet using tiny drill bits but don't have one of a size that reveals anything - they're either much smaller than the orifice or don't fit at all.

If the richness was due to the sizing rather than the ones I took out having been modified, I wonder why I was running rich on the stock sizes. I know that having a freer flowing exhaust system could do this but I'd kind of be surprised if this was it, since I just have a pair of Fuel end cans with baffles in - it's not a race system or anything. However, Factory Pro do suggest 172F 175R mains in their jet kit, which I put down to the needle profile being different but actually at the top-end where the main jet really comes into play the needle surely is fully raised and not affecting things anymore. When I asked them why they specify these jets rather than 175/178 they gave me an extremely curt answer along the lines of 'we've found this works best'.





User avatar
Wicky
Posts: 7895
Joined: Sat Feb 11, 2006 2:43 pm
Location: Colchester Essex
Contact:

Re: Sticking carb slide?

Post by Wicky »

Get it on a dyno to confirm evrything is as it should be and post the printout
It may be that your whole purpose in life is simply to serve as a warning to others.

ImageVTR Firestorm and other bikes t-shirts
jchesshyre
Posts: 590
Joined: Wed Jun 15, 2016 9:09 am
Location: Chester, Cheshire

Re: Sticking carb slide?

Post by jchesshyre »

I would so love to do this! How much does a dyno session cost, roughly, on average? Bit skint at the mo but I'd be well interested to get one done.
Wicky wrote:Get it on a dyno to confirm evrything is as it should be and post the printout
User avatar
VTRDark
Posts: 20010
Joined: Sun Mar 18, 2012 9:24 pm

Re: Sticking carb slide?

Post by VTRDark »

Weyhey...fingers crossed. End cans shouldn't make that much of a differance especially with baffles in. A full system really changes things though. Saying that, mikstr has noted a differance between low level and high level exhausts but we are talking extreme fine tunning here and with a highly modified engine. Also I noticed a improvemnt with low end power when I put the longer SP1 Arata cans on with tapered links so I woudn't rule end cans out totaly. FYI Factory Pro and Keihin jets are the exact same. The factory Pro needle profile is totally diffrent and they also supply 50s for pilots. Strange how you never got a more informative response from them. Maybe they have had enough of VTR's after Mikstr's latest deallings with them :lol:

Every bike will be slightly diffrent and require subtle changes from another one so for FP to say 172F 175R mains is what works best is bit of a bold statement. If that was the case they wouldn't supply a multitude of main jets in their kit. Altitude, climate conditions, quality of fuel, wear & tear plus the diffrent mods all make a differance. Something else Factory Pro suggest is to replace the front emulsion tube with the same as the rear if one has persistant richness at cruise that can't be got rid of by other means. Note this is the equivelent of the HRC aproach which uses a diffrent method by blocking one slide hole as in Hawks guide. So one size does not fit all so to speak.

Oh yeh one more thing, Diaphram springs. I bought new ones from Honda and I was suprised how much my old ones had compressed with age compared to new. I can't remember how much of an affect this had on performance but I do remember how much more snappy my slides where and both working at the same speed equally when manually pulling them both back and letting go. As for the length I do recall measuring them at the time but did I make pysical notes or only post them up on here somewhere. No idea, it was so long ago.
==============================Enter the Darkside
jchesshyre
Posts: 590
Joined: Wed Jun 15, 2016 9:09 am
Location: Chester, Cheshire

Re: Sticking carb slide?

Post by jchesshyre »

I have to say, the bike is transformed by this change. I can't really believe it. The throttle response and acceleration are better throughout the rev range, though most so at the upper half and especially the upper quarter. I should say that as well as changing the main jets I also swapped the emulsion tubes with my old ones (although I cannot see anything untoward with the ones that were in there, and they were definitely in their correct respective carbs).

I can't believe I've been riding with it like this for so long! Though, I can't put my finger on when it started misbehaving and I'd put the slightly reduced performance down to age (fast approaching 80k miles). I'm surprised that changing the main jets by one size would make such a difference, so I do wonder if the ones in there had been drilled out slightly. The carbs they came with were otherwise totally stock, however.

I'm still puzzled as to why I've had to go down a size on the main jets, assuming that is what's made the difference. My air filter (HiFlo) is approaching the 12k-mile service interval, but I really can't see this being the issue. I've never noticed any performance loss when approaching air filter service intervals before (or indeed a gain beyond marginal/placebo after changing the filter at said interval). I looked at the filter earlier when I had the carbs off and other than the odd bit of insect and plant debris it looks pretty clean.

Or perhaps the spring(s) was/were dodgy, but other than slightly different lengths (the ones I've put in, from my original carbs, are in fact slightly shorter by max. 1 cm) I couldn't detect any difference.

I know that for the purposes of scientific experimentation I should only have changed one variable/part, but this is a fault-finding exercise first and a scientific study second and much as I love tinkering I'm not about to deliberately add to the number of times I have to open the carbs up!

It'll be interesting to see if I get better fuel consumption. I also wonder if the rich running might have been diluting my engine oil a bit as I have noticed slightly higher consumption of that.

I guess I can swap my fuel tap back to being vacuum-operated now, although I might not bother as it's no hassle to switch the tap off when removing the tank, and the page I linked to before seemed to suggest that HRC suggested this as a performance mod to allow maximum fuel flow at all times for the NC30.





User avatar
sirch345
Site Admin
Posts: 21672
Joined: Mon Aug 25, 2003 10:35 pm
Location: The West Country.

Re: Sticking carb slide?

Post by sirch345 »

VTRDark wrote: Mon Jun 11, 2018 12:25 pm What you describe is a way to determine if a jet size is too large or small.
1- Top end (full throttle / 7.5k to redline ) Select Best Main Jet
Best Main Jet must be selected before starting step 2 (needle height)!

To get the best, most even top end power (full throttle/after 7500 rpm), select the main jet that produces the highest top speed / pulls hardest at high rpm. If the bike pulls harder at high rpm when cold and less hard when fully warmed up, the main jet is too large. Install a smaller main jet and retest until you find the main jet that pulls the hardest at high rpm when fully warmed up If the bike doesn't pull well at high rpm when cold and gets only slightly better when fully warmed up, the main jet is too small..
This must be done first - before moving on to the other tuning ranges. In order to properly tune the midrange and low rpm carburetion, THE MAIN JET MUST FIRST BE PROPERLY SELECTED after 10 to 15 minutes of hard use!
Do not pay too much attention to the low-end richness when you are changing main jets - you still need to be using the main jets that produce the best power at high rpm. You will deal with the low-end / cruise later - after step 2.
http://www.vtr1000.org/phpBB3/viewtopic ... 31&t=14214
jchesshyre wrote: Mon Jun 11, 2018 9:07 pm YEEEEEESSSSSSSS thank you VTRDark!!!

I know I've already put a post saying 'it's definitely sorted' but now it really and truly is. It feels completely different above 7k rpm and races towards the redline like it used to, rather than feeling a bit tired up there, and all the full throttle weirdness I was getting has gone. And this was with the bike fully warmed up.

This has been annoying but (a) I'm relieved it's not something electrical or engine-related and (b) I've learnt something new in carb tuning - what top-end richness feels like.
Good call Carl, well done mate :clap: :clap:

Chris.
Post Reply