Honda GB air/fuel mix + good/bad days?

[sammcj]

Alo' All.
Another question from someone unskilled in engine tinkering (but learning!)

My GB (600cc~) suffers heavily from having good and bad days (/starts?) with performance, weather does not seem to effect it but I don't think she likes cold days as much.

For example on Saturday I went for a ride, it wasn't pulling that hard (still went OK) then I parked up for an hour or so and when I started her up again I could definitely feel the increase in power and smoothness.

About 6 months ago she was bored out from 500cc to 600cc~, Carb was replaced with a mint spare and ignition was fully checked over.

I heard someone say something about "Power Valve" but I thought that was only for 2 stroke engines? - If not, tell me more!


Next question is around the Air / Fuel mix.

I'm pretty sure she's running a bit rich (is this a problem?), she blows a bit of black when she's starting (first 3 mins of cold running~) and the exhaust is quite sooty black on the inside.

I know where the adjustment screw is on the carb (it's a bugger to get to), is it easy for me to adjust this and tell the difference?
If so, in or out for leaning it out? What's the best way to do this (take her for a ride up the road after each adjustment?).


Another engine characteristic I have is that she often 'pops and stops' apparently this is typical of big singles, but it can do it during down-revving which causes it to jerk around a bit.

[koba]

Cool bike.

Take it to a place with a Dyno and get them to set the carb up on the dyno. Making the engine bigger will alter its fuel needs, you can get it close by feel with lots of experiance but its worth the money to just go and get it sorted.

[The Pastor]

yeah it can only be done by feel/indepth knowledge or on a dyno. its $120ish for the run or about $600 to get it tuned.

[vifferman]

The "pops'n'stops" thing can happen with v-twins too - it's common with the VTR1000, and easily fixed by adjusting the idle speed (and mixture too, IIRC )

[sammcj]

yeah it can only be done by feel/indepth knowledge or on a dyno. its $120ish for the run or about $600 to get it tuned.

$600 = Ouch!

[The Pastor]

$600 = Ouch!

well you can get the base run done and do it yourself, but it'd probably wont be right

[sammcj]

So I'd still need a wide-band o2 sensor for measuring air/fuel ratio correct?

[sammcj]

and if she's running a bit rich, do you think perhaps making a minor adjustment to allow a bit more air into the carb would be a good simple step to correcting this DIY style? (change filter type to pod style as I don't think the stock sucks enough air in).

[The Pastor]

well the dyno shop will have an02 sensor.

did you rejet the carb when you bored out your bike?

[sammcj]

Yeah, KG motorcycles here in CHCH did it, but I'm certain he didn't use an o2 sensor, also he had a lot of problems along the way that took him a long time to figure out so I must say I've somewhat lost confidence in him.

[The Pastor]

get it on the dyno then, its the only option

[The Pastor]

post up your printout too, would be useful to see it

[sammcj]

OK noted, will do but might not be for some time yet.
Thanks.

[vifferman]

Yeah, KG motorcycles here in CHCH did it, but I'm certain he didn't use an o2 sensor, also he had a lot of problems along the way that took him a long time to figure out so I must say I've somewhat lost confidence in him.

Are you sure? I thought dyno runs were always done with an O2 sensor to get the Air/Fuel ratio, which is usually graphed on the chart as well. Kinda pointless doing a dyno run without checking that the fueling is correct.

Anyway, regardless of that, you can try altering the idle mixture, as long as you only make small adjustments (say, a quarter turn out on the screw) and record what you did each time, so if needs be, you can put it back how it was. You'll then have to determine if a change is better or worse than the previous setting. If you're not sure, you can always go back to how it was, then repeat, or else make a bigger change to see if it's better or worse.

If it's popping an stopping, that's usually an indication the mixture's too lean, but this can also occur if you've got a leak in the intake manifold or somewhere in the exhaust. It's also more inclined to do this if the idle speed is slightly low - try going up 100rpm, see if this helps.

[sammcj]

KG did the bore-out and carb replacement etc...
No dyno-tuning done.
It's definitely not the idle speed, it does it on deceleration, standard idle is 1300RPM, I've got it about 1500RPM to keep it going as often as possible.