Lean condition 2000 to 4000 rpm

[sirch345]

Seems someone beat you to it and they sell firestorm injectors on eBay

http://pages.ebay.com/link/?nav=item.vi ... 1350874825

Chris.

[Phil_H]

I am seeking advice from experienced vtr owners. I am an Efi tuner from aus. I have owned my vtr since 2007. All I have done is a set of pipes. I have done a lot of dyno work with several jet combos. The issues I am having is lean condition at low rpm when I roll on throttle say 2000 to 4000 rpm. I have experimented and fitted very large mains ie 200 to find where the main jet has most influence and I found it goes super rich at 5000 rpm, but still has a major influence on low rpm wot. I started with a dj kit, 180 185 main 4 th clip, 48 pilots stock air box and filter. The bike ran very well, but on the dyno was super rich 11.0 to 1 afr, very flat fuel curve from 5000 to rev limiter. By this I can see the air jet is correct size. I leaned it out and found to get afr back to 12.5 to 13 to 1 where it makes best power I had to drop down to 165 170. The issue then being the lean condition from 2000 to 4000 rpm region. I increased pilot to 50 but was then to rich at idle with fuel screws all the way in pretty much. I then raised needle further to clip 5 still no good. Was 17 to 1 afr and backfiring . I tried the extra lift hole made it worse and caused hesitation at 5000 rpm. Went back to stock needles and springs. This seamed to work better but did not eliminate the lean hole. I again raised the needles to the point the engine was pulling fuel thru the needle jet at idle and causing hunting. I give up then. I went back to 180 185 clip 4 and 48 pilots and just left it as is. After reading the cv tuning section I found the float height has huge influence in this case. Looking at the float arrangement from memory they are non adjustable. I know in Holley carbs etc raising float height does richen low end. As it says in the tuning guide. Has anyone else experienced this. I will keep playing till I solve it, going bigger main to solve it is just a band aid so I will work on it till its right, any advice will be appreciated.!

Reviving an oldish thread but did you solve this problem or go down the fi route?

I'm having similar issues with an otherwise stock Varadero with lean bottom & lower mid, rich upper mid & topend thats with mains that are 10 below stock, 48 pilots helped the lower end, smaller mains give a lean hole 4-5k, not sure how much a stock needle can be lifted without leaking fuel at tickover?
So far looks like rich bottom/rich top is the only way to get an acceptable midrange!
I reckon the needles are badly designed.

Dyno with 42 pilots & 158/160 mains (10 down from stock)



Phil

[8541Hawk]

I'm having similar issues with an otherwise stock Varadero with lean bottom & lower mid, rich upper mid & topend thats with mains that are 10 below stock, 48 pilots helped the lower end, smaller mains give a lean hole 4-5k, not sure how much a stock needle can be lifted without leaking fuel at tickover?
So far looks like rich bottom/rich top is the only way to get an acceptable midrange!
I reckon the needles are badly designed.

Dyno with 42 pilots & 158/160 mains (10 down from stock)



Phil

So now the needles are poorly designed? Really ?

Just as a bit of back info, I have been tuning these carbs for 17 yrs now and the first thing I will say is that the stock needles are some of the best stock units I have used.
So sorry to hear that a few of you guys can't seen to get things squared away but my bike runs just fine and has a nice fuel curve, so yes it can be done without going to any exotic bits.

[Phil_H]

I'm having similar issues with an otherwise stock Varadero with lean bottom & lower mid, rich upper mid & topend thats with mains that are 10 below stock, 48 pilots helped the lower end, smaller mains give a lean hole 4-5k, not sure how much a stock needle can be lifted without leaking fuel at tickover?
So far looks like rich bottom/rich top is the only way to get an acceptable midrange!
I reckon the needles are badly designed.

Dyno with 42 pilots & 158/160 mains (10 down from stock)



Phil

So now the needles are poorly designed? Really ?

Just as a bit of back info, I have been tuning these carbs for 17 yrs now and the first thing I will say is that the stock needles are some of the best stock units I have used.
So sorry to hear that a few of you guys can't seen to get things squared away but my bike runs just fine and has a nice fuel curve, so yes it can be done without going to any exotic bits.

Some of the best stock needles? - why, what makes you state that claim. Not doubting what you say but intrigued as to why you say it.

Look at my pretty standard setup fueling with stock needles, hardly ideal is it?
Surely, the fact there are so many running/setup issues and mods to get these bikes fuelling correctly proves the needles are far from ideal!

I've had quite a few Hondas that I have had dyno'd over the years & all have had better fueling across the rev range than this bike.
As yet, I haven't tried the slide hole mod, I will do in time but feel I'm lean in the 4-5k range rather than rich so not sure it'll be of benefit

[8541Hawk]

Some of the best stock needles? - why, what makes you state that claim. Not doubting what you say but intrigued as to why you say it.

From more dyno runs in the last 17 yrs (yes I have been running a VTR for that long) than I want to remember and also from working with folks that are in the same league as Mr. Ditchfield and what they have said about them.

The only needle that gives a clear advantage over stock are the HRC units IMHO but as they are unobtainium just save your cash, again IMHO, and what I have seen back when I had my shop and dialed in quite a few VTRs in different states of tune.

Look at my pretty standard setup fueling with stock needles, hardly ideal is it?
Surely, the fact there are so many running/setup issues and mods to get these bikes fuelling correctly proves the needles are far from ideal!

Yeah it looks like you have an issue. Though the only time I have ever seen a curve like that is when a bike was run without the sub-filters in the airbox and the carbs sucked in enough grit to wear out the carb internals.

So without seeing your bike it is hard to pin point the problem but it looks like you have much more than a needle issue.

IMHO you are a bit off in you assessment that there must be a hardware issue due to the many different "set ups". I guess you can see it that way. What I see is folks believing there is all this hidden HP in this engine and a bit of carb tweaking will bring massive gains and lets start but upping the mains...... all wrong but the common misconception.

Like the guy stating that he will get 20 HP by retrofitting a F.I. system........ ok good luck. Hate to bust any dreams but a dialed in system might get you 3-4 HP max.

Another Issue with the carbs on this bike is that in the world of F.I. people have forgotten the tuning rule: "The bigger the CV carb. the harder it is to get it right"
That is why things can go so wrong so fast when you start messing with these carbs. Being the largest CV fitted from the factory, they are a bit "touchy" to say the least. Also because of the rule I just stated, they are real close to being dead on from the factory or the stock bike would have major ridabilty issues.

Then there is the issue of trying to tune for HP (or like an I4) which is not the way to go with a twin, but that is another thread and I have gone on too long as it is.

I've had quite a few Hondas that I have had dyno'd over the years & all have had better fueling across the rev range than this bike.
As yet, I haven't tried the slide hole mod, I will do in time but feel I'm lean in the 4-5k range rather than rich so not sure it'll be of benefit

I agree that your curve is very bad, but I don't agree on the conclusion you have come to on the cause of your issue.
The fact that you have to run that small of a main jet tells me you are dumping fuel into the system somewhere and a different needle is not going to change things much, if any.

So I do hope you get this squared away and will help in any way I can but IMHO you are going in the wrong direction to cure your issue.

Any chance someone close to you has a set of stock vtr carbs you could pop on to see how she runs?

[Phil_H]

Hi and thanks for your input
The bike is a Vara 1000, not a vtr but similar engine/carbs albeit with a softer state of tune/smaller carbs.

The bike is nice genuine and unbutchered, low miles (25k), valves plugs etc are all good. Carbs looked untouched & spotless internally when I first removed them. Stock air filter & exhaust.
Secondary filters are still in place (although I have just fitted some home made replacements as the originals were looking grubby.... )

Any leaner on the needle has the bike coughing & surging (lean) at low revs - an issue that does crop up on stock bikes from time to time, shimming the needle up doesn't pep up or richen the 2-3.5k area as hoped.

Infact many of my symptoms tally with the op's comments, hence my post here.

Any ideas???

[fabiostar]

i think i have found the cure. open cans. 52mms links. leave everything else as honda intended pulls like a train every day..sometimes the simple answer is easier lol

[John Orchard]

Hey Guy's :-) Sorry to drag this up after so long (but I have now some info), I can't message anyone yet, I have not enough posts.

The issue of the OP can be cured by adjusting the float height (yeh I know they are not adjustable ha ha), let me start by discussing the problem with the VTR, both carb casting are the same BUT they sit at different angles to each other, hence the effective float level is different to each other (in the relationship between the fuel level verses the emulsion tube bleed holes), basically, even with the fitting of unequal emulsion tubes, the front fuel level in the bowls is 3.25mm (rough calculation) lower than the rear cylinders carb, this will cause a leaner transition from the pilots to the needle.

Honda have tried to help the situation by running the rear emulsion tube with the bleed holes 2.5mm higher (making the pilot/needle transition leaner) in the rear cylinders carb, this is not enough to balance out the two cylinders to each other.

I managed to raise the fuel level in the front carb 1.5mm by grinding the top of the float needle, from the a total length of 19mm down to 18.70, it's a very gentle hand to knock off .3mm, so the float level measurement went from 16.5 to 15mm.

This cured the lean midrange stumble and I am actually running #40 pilots @ 1.5 turns out on the mixture screws !!! Still too rich on the rear cylinder at part throttle though (which I am thinking is contributing to the bad VTR fuel consumption (still yet to do fuel testing with the 40 pilots).

My next test is to set the mixture screws: front 2.0, rear 1.0, to cure an occasional lean spit-back on the front cyl, and treat the black plug of the rear cyl. Stay tuned (no pun intended).

[tony.mon]

Something to watch out for is the likelihood of ovality in the needle jets. These bikes are getting old now, and a large bore means high pressure changes in the carb throats as the inlet valves open and close, moving the needle into frictional contact with the jet.

[John Orchard]

Something to watch out for is the likelihood of ovality in the needle jets. These bikes are getting old now, and a large bore means high pressure changes in the carb throats as the inlet valves open and close, moving the needle into frictional contact with the jet.

Good point Tony, l'll pay close attention to that.

[John Orchard]

And ..... l may consider running pilots~ front #42, rear #38 ?

[tony.mon]

You could try it. Some markets had .40 pilots, some had .45.
Most people keep them paired, so same front and back.
Sounds like you need a lambda sensor in each downpipe if you plan to set up each carb separately.

[John Orchard]

I have, that's how l know l am rich on the rear cyl (up to 4,000).