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 :confused:)

[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.

[vifferman]

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.
Well then ignore my comments about idle speed. But popping on deceleration is usually a sign of a too lean idle mixture (when you throttle off, usually only the idle circuit is in play), although if it's running REALLY rich, some unburnt fuel can get into the exhaust and ignite.

[sammcj]

Well then ignore my comments about idle speed. But popping on deceleration is usually a sign of a too lean idle mixture (when you throttle off, usually only the idle circuit is in play), although if it's running REALLY rich, some unburnt fuel can get into the exhaust and ignite.

It does often backfire / pop on deceleration, Asked KG about this when they were working on it and Kev said 'nah it's fine, sounds good too doesn't it!'

[mnkyboy]

When it's idling does the exhaust output smell rich? (slightly sweetish)

What does the sparkplug look like?

Did the shop adjust the carb or did they just put it in?

[98tls]

Fwiw i would say its flooding as in running to rich,Have you replaced can...if so then start it from cold and run your hand round the join from header if you feel any air then thats the source of your backfiring.Take it apart run a bead of high temp silicone and clamp it up.As for the Dyno comments:laugh:Ive an old Nsr framed Honda single in the shed,when it doesnt run right should i A sort it B take it to a Dyno:wacko:If mine i would take the carb to bits and work backwards from there.Easy really,still chuckling at the 'dyno' posts.

[avgas]

The 600 bore is a cunt of a thing. I was quite thankfull that with my "good" gb the previous had only done a 450 kit (or something). Is it a bore or a 600 engine swap?
If its getting temperamental check a few things.
Float on carb isn't stuffed - i had one do weird shit
YOU MUST CHANGE PLUG TO IRIDIUM IT IS LIKE GOLD!
Battery terminals to be tight (and connected at ALL times)
Choke off, engine warm - engine should give 1000+ rpm. If not adjust idle screw.
Dyno would be the best bet. Get everything to do with the carb balanced and reliable

[sammcj]

Right thanks for the info guys.

To answer a few questions:
-It's been bored out to 600cc+ not an engine swap.
-The carb was replaced at this time and the jets were re-done (I think bigger main).
-Battery terms are tight as a ... thing thats tight.
-Theres no way it would idle at 1000RPM, 1300 Yes until it pops and stops.

What I will do next:
-I will check for leaks around the headers (good idea, I didn't even think of this).
-Check the plug.
-Smell the exhaust (not for too long I hope).


Would the Iridium plug make a difference? If so, is there a particular model you'd suggest?


I'm down south Fri-Mon so it'll have to be early next week :'(

[sammcj]

Update:

-Replaced the plug with an NGK DPR8EiX-9.
-Big up's to T.W.R (http://www.kiwibiker.co.nz/forums/member.php?u=4185) for giving her a good look over for me and adjusting valve clearances etc...

She's running a lot better, more power, sounds smoother etc...
I think she's still running a little rich and she does still pop and stop on idle but not nearly as much.

[T.W.R]

Once I've got this house shifting lark sorted I'll give it a thorough going over for you :niceone:

Isn't too far off but there's still a wee bit to be sorted... it's definitely a lot sharper than it was.

You'll have to post a piccy when the wheels are done though :shifty:

[ThumperHeaven]

Hi ya
Can you tell me where you had your GB borred out to 600cc? I have a 500 and want to explore what this takes / costs. Are you happy with the result?
Cheers
Matthew

[sammcj]

Hi ya
Can you tell me where you had your GB borred out to 600cc? I have a 500 and want to explore what this takes / costs. Are you happy with the result?
Cheers
Matthew

I got Kevin at KG Motorcylces here in CHCH to do it.
I personally don't think he was committed enough to making it run correctly, he stuffed around and took a long time to do each stage BUT it did only cost $1400 (including making up an exhaust).

You'll need -

-Bore out
-Sleave
-Make sure you have a good clutch (I put heavier springs in mine)
-Replace exhaust (muffler should be enough, I'm running stock headers)
-Carb jets increased in size

it is 100% worth doing, you go from having a cool neo-classic thumper to having a fast neo-classic thumper.

I personally think you could find someone that'll do a more thorougher job than KG did, but you'd be wanting to put $1600 - $2000 aside if you're not planning on doing any of it yourself.

I know the block was bored by Hills Engineering and they have a very good reputation.

[ThumperHeaven]

Cheers - thanks for the info. Meeting a mechanic this week in Wgtn to discuss so at least now I can sound like i know what I'm talking about (sort of :)

[bsasuper]

Dyno shops have to make money so they charge a arm/leg because people are willing to pay for a few more hp.

[sammcj]

Right, Got her booked in at Dynoworx / HondaCountry next wednesday.
I'll let you all know how the dyno-tune of the carb goes!

[The Pastor]

carbs, easy to tune - yeah right!

[sammcj]

renegade master - carbs, easy to tune - yeah right!

[sammcj]

I'll be at Dynoworx Ashburton tomorrow at 9AM... Wish me (/ my wallet?) luck

[sammcj]

I'm back from the dyno - Results here:

http://www.kiwibiker.co.nz/forums/showthread.php?p=1129547869#post1129547869