Re jetting

[seb421]

The only way you are going to know is to try it. I ended up moving a clip position on mine and thought that maybe it was a bit much and wanted something in between, so I ended up shimming the rear carb to richen a tad more than the front. The principle behind it with Hawks write up and the rear being shimmed more than the front. Sounds like your getting there. I think in your case with the full system the 50's is the right move. I'm going back down to the 48's on mine. It's just a little to rich and too hard to get the mixture spot on.

I don't know what revs you where at where the flat spot is. You say the middle so I presume about 7 thou which is right at the top of the needle circuit, so your mains are on they way to being full on. Sounds like your in that overlap zone where it's switching circuits. What mains have you got in. It may be worth considering dropping one size on one of the carbs. It's a quick easy check compared to adjusting needles.

But then there's a little voice in my head saying no. The mains are good so leave alone. Get the needle heights right and then move onto the pilot. Which is the way Factory Pro say to tune CV Carbs. Start at the top and work you way down.

A black-art, black art-indeed. It's not always that straight forward. I would love to have my own dyno. Don't Halfords sell them. Gunsen dyno tune

(:-})

its flat soft spot is around 5k mark

come the weekend or if i can be arsed mid week i will put the needles back on the 4th clip and see what it does, then try the 6th clip see what that does, then try needles on 5th clip again but with 48 pilots

that should pretty much help iron it out i think mate

[VTRDark]

So at 5 that's the exact opposite. Get you needles in the best possible position but treat both carbs as individuals, they don't have to be the same. You may find that leaning the needle on one of them will do the trick. Or lean them both and richen one up a tad with a shim. The rear should be a tad richer than the front.

(:-})

[VTRDark]

From what I understand and have researched, I have put together in laymen's terms a basic write up on how the CV Carbs work with regards to jetting.

The main jet which screws into the emulsion tube is the fuelling for the top end 7.5 thou rpm upwards at 3/4 throttle to (WOT) wide open throttle. Different size main jets have a larger or smaller hole for fuel to flow through. The larger the hole, the richer it is.

The needle in the slide controls the midrange 5 thou to 7 rpm 1/4 to 3/4 throttle. the needle height determines how rich or lean it is. With adjustable needles (standard Honda needles are non adjustable) The lower the needle is it leans it out and the Higher it is richen's it. The needle is tapered and goes inside a hole in the side of the carburettor main chamber, so as the slide opens and closes under the vacuum from the diaphragm the taper opens or closes the gap in the hole. So to richen move the clip towards the pointed end and to lean it out move the clip towards the blunt end.

The pilot or slow jet as it's sometimes known controls the bottom end from idle & 2 thou to 3 at 1/8 to 1/4 throttle opening. As with the main jet, the size of the hole in the jet determines the amount of fuel flow. The larger the hole the more fuel that flows.

The pilot works in combination with the mixture screw setting. There is a channel inside the carb that links the two. Turning the mixture screw (or to be more precise a fuel screw on these bikes as it controls fuel flow) Turn outwards/anti clockwise to richen or inwards/clockwise to lean it out. This opens or closes the gap in the channel linked between the two and gets the bike idling smooth with no fluctuations.

There is a slight overlap between between the pilot, needle/slide and main jet and it's a case of getting an even balance and appropriate air fuel ratio between them all.

The float works like a ballcock in a toilet cistern. The fuel gets sucked from the tank and into the carb float chamber, which is like a middle ground holding area for fuel. If the float had a hole or was broken then there would be no control on the amount of fuel going into the carb and it would flood. The VTR float height is non adjustable.

Here's a rough guide to how the individual carb circuits cross paths.


This may help to get a better understanding to what is going on. I hope.

(:-})

[scott02464]

That's a good clear explanation Carl!

Going on what you have said I think I'm well on track with what Iv done so far.

On the dyno what gear do they 'Wang' the throttle open and at what rpms?

I ask this because when Iv been out testing what changes Iv made, I have tried putting it in 6th, slowing down to 2-2.5k rpm then opening the throttle fully. This will make the bike feel like its 'labouring' (as if it's in the wrong gear) to about 3.5k rpms then start pulling properly and strongly.

Is this normal?

If I put it in 3rd then do exactly the same it just starts pulling straight away. No noticeable flat spots.

I hope this makes some sort of sense

[VTRDark]

It sort of makes sense but what speed are you going in 6th. This is the hardest thing to check on seat of the pants tuning cause to test the mains you need to be in top gear max speed.

You talking about a big change from 6th high speed down to the other end. Maybe the storm needed time to recover and catch up. After all it's a carb and not injection. At lower speeds 6th gear 2-2.5k IMO is too high a gear for the bike. it's gonna take it's time to pick up from there. Don't forget your speed and what gear your is relative to each other.

I've not seen a dyno run done but I have heard it. And they give the bike a hard time and push it to it's limits through all the gears. Before going to a dyno, make sure your chain is adjusted and lubed properly and your tire pressures are set. Also make sure that all your exhaust seals have no leaks. Check out some of the dyno runs on you tube.

(:-})

[scott02464]

Yeah it did seem a silly thing to do at the time tbh as with my riding style (and prob everyone else's) I'm never realistically going to be doing them rpms in top gear. I will have geared down, as you know 2.5k rpm is a slower pace and would require a lower gear.

I must say tho, when out testing Iv hit the limiter in 4th and 5th but not in 6th. There's no roads fast (or safe) enough to do it round here.

I do have a 14t front sprocket too which will have altered the ratios of what gear as to what speed.

Yeah mate I'm going to get it in tip top condition before the dyno, I do have a slight leak in the rhs link pipe that needs nipping up.

[scott02464]

Well here's the results.....
What you guys think?

[lloydie]

respectable 102bhp
looks like you need to drop your needles down a little .
what set up have you on the bike ?
cans/exhaust
air filter
coils
jet kit

[scott02464]

respectable 102bhp
looks like you need to drop your needles down a little .
what set up have you on the bike ?
cans/exhaust
air filter
coils
jet kit

I have K&N filter mate, blue flame straight through cans, standard coils.

Iv not put a kit in mate, I put 180&185 mains (Keihin) and shimmed the standard needles up with washers (3mm front and 4mm rear)....

Front mixture screw is 2 turns out and rear is 2 1/4 turns.

[VTRDark]

That looks very good Scott. So is that with just your tinkering or did the dyno guy do make some adjustments. You should be well pleased with mate. Lovely straight torque curve.

(:-})

[lloydie]

That looks very good Scott. So is that with just your tinkering or did the dyno guy do make some adjustments. You should be well pleased with mate. Lovely straight torque curve.

(:-})

torque what chart are you looking at

[scott02464]

That looks very good Scott. So is that with just your tinkering or did the dyno guy do make some adjustments. You should be well pleased with mate. Lovely straight torque curve.

(:-})

Thanks a lot mate it was just with my tinkering, he didn't touch the bike apart from putting it in the machine.

He's made me feel a bit deflated tbh and tried selling me a dynojet kit saying its 'way out' ??

[scott02464]

That looks very good Scott. So is that with just your tinkering or did the dyno guy do make some adjustments. You should be well pleased with mate. Lovely straight torque curve.

(:-})

torque what chart are you looking at

The torque was 64 mate.

[lloydie]

That looks very good Scott. So is that with just your tinkering or did the dyno guy do make some adjustments. You should be well pleased with mate. Lovely straight torque curve.

(:-})

Thanks a lot mate it was just with my tinkering, he didn't touch the bike apart from putting it in the machine.

He's made me feel a bit deflated tbh and tried selling me a dynojet kit saying its 'way out' ??

you dont need a jet kit
maybe drop your needles a little

[VTRDark]

The top one (power) that's the torque init. I'm looking forward to your one on Saturday. That will be the first dyno with lager airbox. Should be interesting.

(:-})