Topic: Speedo not accurate

[Scooterhead]

I have a Honda cb350four with an inaccurate speedo reading,it says 70 when really it's about 60.
Has anyone experienced the same.

[rocket johnny]

   my 76 k6 shows 55 when its 50 .  i think that is fairly common

[PeWe]

Changed front wheel tire/wheel dimension? My CB750 K6 -76 has better accuracy than I thought. Show around 52 when driving 50kmh, less than 5% wrong. New tire 100/90-19

[Scooterhead]

My speedo is about 15% out

[MD]

Changed front wheel tire/wheel dimension? My CB750 K6 -76 has better accuracy than I thought. Show around 52 when driving 50kmh, less than 5% wrong. New tire 100/90-19

I'll agree with PeWe,

I had a truck that was 5mph off at 55.  Changed to oversize tires and the speedometer became accurate.  Look at the stock size tire and see if you can get one with higher side walls.

-MD

[Scooterhead]

My cb350f is all completely stock apart from the exhausts
They 4 separate stainless pipes and I think they are sports pipes because they are quite loud and it sounds like a bigger bike they are baffled as well
The  tuning is taking a white to get right and I am getting there.the main jets are 78 with the needles set to the middle notch
I think it is running weak bright white porcelain plugs can I get this bike right with this set up

[flybox1]

What intake?  Pods, airbox?
white plugs indicate lean, but dont just change your main. 
start with the idle circuit, and work up.
assuming your bowl fuel level is correct:  Idle plug chop - adjust your air screws to get tan plugs.
If you can tune out the lean-ness, go to the next larger pilot jet and repeat.

[Scooterhead]

Ok is the pilot jet for idle and small throttle and main jet for open throttle because I have slight tan at idle and white at high throttle

[Scooterhead]

Having just got back from working away I am having another go at tuning the bike
I have tried to dial out the hesitation by turning the fuel air screws in but it still got bad hesitation if I turn the throttle to do an overtake
I haven't checked the float bowl level because I don't know the best way to do it
Do I check them with the engine off or on,at idle or with throttle
My main jets are Kevin 78 do i need to go bigger to get rid off this hesitation,it's strange because when I turn the throttle gradually there is little hesitation

[TwoTired]

Lecture deleted by request

Nobody is going to lecture me

[BomberMann650]

TwoTired, what are those Mods to the throttle slide cutaway angle you mention?

[TwoTired]

Lecture deleted by request..

Nobody is going to lecture me

[Scooterhead]

The bike is all stock apart from aftermarket pipes which are loud
The bike runs quite well,if I turn the throttle slowly in every gear you can hardly tell there is a problem,but if I am in 5 gear at say 4K revs and I open the throttle moderately fast she stumbles but eventually sorts out quite bad sometimes.is this the pilot or the main?
The bike sounds like a bigger bike than 350 .are the exhaust the problem as everything is stock

[Scooterhead]

Just to add to my last comment what should the plug chop look like at wot and idle

[PeWe]

Ignition OK?
My bike got much better response when I advanced the setting that was too late.

[TwoTired]

Lecture deleted by request..

Nobody is going to lecture me

[Scooterhead]

Thanks two tired do I need to change main jet only if so from 78 to what

[TwoTired]

Lecture deleted by request..

Nobody is going to lecture me

[Scooterhead]

Thanks but I bought the bike with them on
I am going for a tan colour spark plug I have just turned th air fuel screws in a bit more

[Scooterhead]

Hello two tired
My bike is all stock apart from these exhausts 4 separate loud sounding ones no markings on the little begets
The head ports have Been smoothed out
There is just something not right the spark plugs look lean at wot there is a black ring the core is white and the ground is slightly tanned
I am new to this but I'm listening and learning and I think I might be lean so which jet should I change?

[TwoTired]

Lecture deleted by request..

Nobody is going to lecture me

[Scooterhead]

Excellent thanks very much for that explanation you are a guru
Is the factory setting for air,fuel screws 7/8 turns out and is it important for it to run smoothly when at idle

[Scooterhead]

There are two metering pathways for fuel entering the carbs.  Which is dominant, is determined by throttle position.
At idle throttle position, the pilot circuit is dominant. This consists of an air jet, a pilot jet with its incorporated emulsion tube, and an air metering screw.
When the slide is lifted (opening the throttle), there is a sudden change of carb throat pressure which results in drawing less fuel from all the fuel delivery orifices in carb.  The response by the engine, due to lack of fuel drawn, is hesitation or stumble before the throttle valve section of the carb can take over the fuel delivery chores.  What is needed is more fuel for the inrush of air into the carb throat by the lifted slides.  For this reason, the pilot circuit is deliberately set over rich, but not so rich as to immediately foul the spark plugs with soot.  Since the engine isn't expected to spend its existence idling, to clean the plug deposits, operation above idle should heat the plugs to keep them from fouling.  Back to carb metering circuits.
As the slide continues to lift, the fuel delivery chore transitions to the throttle valve.  The throttle valve consists of the slide to vary inlet air availability, the slide needle and needle jet to vary the fuel delivery commensurate with the varied air input, an emulsifier tube to froth the fuel before carb throat delivery and an air jet to meter the air being frothed with the fuel. The throttle valve dominates engine mixture delivery from about 1/8 to 7/8 throttle positions.  At full throttle slide positioning, the main jet provides and limits maximum fuel delivery into the carb throat via the same throttle valve delivery path.

Carbs are not smart or adaptive to engine breathing characteristics.  If you change induction or exhaust characteristics form what Honda engineers used to determine carb metering sizes, the carbs can't deliver what the engine needs to run properly.  To restore the carbs to actually meeting what the engine needs,  there are three known methods:
One: keep changing/ juggling the internal fuel metering orifices until you get lucky, 
Two: take the machine to a dynamometer where the engine can be loaded, and the exhaust monitored for fuel mix.  Then make corrections to jets as appropriate to achieve best power and optimum fuel usage.
Three: learn to read plugs, find a test track, insert clean spark plugs, and operate the machine under max load and the same throttle setting.  Then hit kill switch, pull in clutch, stop and pull plugs to read combustion condition during the preceding operation.  I start with full throttle operation first, setting the max fuel delivery the engine will ever need.  After main jet is determined, 1/2 throttle operation is tested (under load) and the slide needle height adjusted.  Then the slide needle taper angle is checked at 3/4, and again at 1/4 throttle.  If you are lucky, you won't need a custom needle taper.
Lastly, the pilot air screw is adjusted to provide the following engine response:
Mark your throttle so you know where one half twist is located.
Drive the bike as slow as you can in top gear.  The engine should be very near idle revs.  Now quickly open the throttle to 1/2 position.
If the bike stumbles, turn all four pilot screws inward about 1/8 turn (assuming factory settings made prior) and repeat the test.  Do this reiteratively, until the engine picks ups smoothly and reliably.  (it won't be fast).
Don't be tempted to turn the pilot screws in any farther so that even more throttle twist can be accepted, as this will just take the spark plugs closer to fouling out during idling periods.

I guess there is a fourth method; have someone else fix the carb jetting for you.  But, getting what you pay for might not be what you wanted.

Hope this helps,

Hello twotire I looked at my exhaust today as I am struggling to get this thing right and they do not appear to have any baffles meaning they are straight through .Is this my problem
Bearing in mind that the intake is all stock ,the valves ,timing and points are all spot on what would the probable jet sizes be considering the straight through exhaust.
Ps is it normal to have non baffled exhausts

[Scooterhead]

Hello flybox1 I have just learned that my exhausts are non baffled 4 singles,everything else is stock
What would be the probable jets sizes now for this

[TwoTired]

Lecture deleted by request..

Nobody is going to lecture me