Carb help? Show me the ropes

[Squiggles]

Im looking for someone to show me the ropes when it comes to dismantling, cleaning, and rebuilding the carb for one of my gn250's

Have got two of them to do, tried by following the manual but didnt have much success as there's a fair bit in it that i didnt fully understand, and thus i failed to cure the problem with very hard starting and bad running

Anyone willing to show me the ropes for a few beers / donations to race funds and so forth :)

Stephen

[Pancakes]

I've been reading lots about carbs over the last year and still wouldn't touch one! Everythings so interconnected, I'me sure there will be people happy to help tho'. Jaycar does a EGO kitset so you can test your work if that helps.

[Squiggles]

*bump* to the top :D

[98tls]

What part/parts cant you follow mate.....carbs are not exactly rocket blah blah blah......

[xwhatsit]

Is it a proper slide-type carb, or one of those awful CV-type things with the diaphragm?

If it's a slide-type, I can show you -- I'm no master re-jetter or anything, but I know how to strip and rebuild carbs, and didn't we meet while I was setting my pilot mixture?

[Squiggles]

diaphragm type :(

[Max Preload]

Im looking for someone to show me the ropes when it comes to dismantling, cleaning, and rebuilding the carb for one of my gn250's

Have got two of them to do, tried by following the manual but didnt have much success as there's a fair bit in it that i didnt fully understand, and thus i failed to cure the problem with very hard starting and bad running

And you traced the hard starting etc to the carb how?

The reality is carbs give the least trouble of any of the engine peripherals. As long as they're clean and undamaged there's very little to go wrong. I would suggest you look more at compression as an issue.

However, this (http://oldmanhonda.com/MC/Rcarbs.html) site carries some of the basics of carburettor operation.

[Squiggles]

Bike was running, albeit very poorly beforehard, with seemingly two idle speeds, one @ 3500 when warm, one @ 1500 when cold

Discovered rubber boot had a wee rip in it and replaced that accordingly, bike ran well initially after my attempt at a cleanout (which i did at the same time), then seemingly flooded, still had a very poor idle after 5 minutes riding after the cleanout (i was probably imagining that it was running any better)

Tappets are set perfectly, Doubt compression as she ran fine before (with the odd bang start as the battery was well past its used by and wouldnt hold charge) I have a new battery for her now also


The "As long as they are clean and undamaged" is what im looking for help in, having not done it before unless its blatantly obvious that somethings wrong i will most likely miss it :pinch:

[xwhatsit]

CV carbs, there's a wee diaphragm that I'm sure you encountered. These frequently give trouble, leak, perish etc. One of the reasons I'm happy with my pumper round-slide.

What did it look like? Maybe buy a new one of those?

It could very well be damaged, considering it's a rather elderly GN by now, plenty of ham-fisted mechanics such as myself could've been in there. Check float height, try and get some compressed air through the pilot circuit (there's all kinds of internal passages that you can't see, they can block up).

You've got a couple of GN250s, no? Tried swapping a known good carb?

[Max Preload]

I'd be happy to come and explain and show you the ins & outs but I'm a little busy this week. Perhaps one evenng during the week? PM me.

[Squiggles]

CV carbs, there's a wee diaphragm that I'm sure you encountered. These frequently give trouble, leak, perish etc. One of the reasons I'm happy with my pumper round-slide.

What did it look like? Maybe buy a new one of those?


First one was perished a wee bit at the edges so replaced it with a good one from the spare carb



It could very well be damaged, considering it's a rather elderly GN by now, plenty of ham-fisted mechanics such as myself could've been in there. Check float height, try and get some compressed air through the pilot circuit (there's all kinds of internal passages that you can't see, they can block up).

You've got a couple of GN250s, no? Tried swapping a known good carb?

None are known good carbs, as for the rest, thank you for listing what im asking help for ;) :D

[Squiggles]

I'd be happy to come and explain and show you the ins & outs but I'm a little busy this week. Perhaps one evenng during the week? PM me.

will do tomorrow when im not soo sleeepy :sleep:

[pete376403]

http://www.thegsresources.com/gs_carbrebuild.htm
9 pages of carb how-tos. While this is a GS Suzuki specific site the info can be applied to just about any conventional carb.

[Defiant]

Ahhhhh....the Constant Velocity Carb.....i know them very well....I can help you depending on where you are...pm me.....but the one thing i will say is that those carbs have a idle circuit that affects the starting and if clogged (which if you havent cleaned it properly WILL be blocked).....the circuit is only pin size.....and there is also the enricher holes by the butterflies.....Hmmm pm me and i can show you or talk you thru it.....they are easy once you do it once.....the magic word with carbys is TRIPLE.....as in TRIPLE CLEAN them......clean them once then again and then again once more...

[pete376403]

Pedants like me would suggest that. in regards to carbs, CV refers to Constant VACUUM, not velocity.

[Defiant]

Sorry but I am correct CV stand for Constant VELOCITY.....The slides are operated by vaccum but it is the air speed(velocity) thru the carb that justifies and determines how far they open they are spose to be more economic and smoother and were designed to be used in all elavations on bikes(ie countries) because they compensate for different air pressure and atmospheric conditions without major tuning(in most cases)......have dout and tuned these carbs for more than a few years.

[SOHC]

hey people.

I have been looking at my bike and thinking that it would look way better with the AIRBOX off...

So here I am reading up about carbs etc.

I have a GB250 with a keihin VE carb. which is quite hard to get guff on till I found that Harley Davidsons use the same style.. learned a whole bunch really fast.

I also discovered the "choke" circuit in my carb was staying open due to the cable being sticky... Now I understand why it was being erratic. every start up was different.

So I am going to get a few different main jets etc and get tuning...

Also I made a mod to the pilot jet screw adjuster. on my carb and the harley version the screw is under the carb at the engine end. READ, hard to a screw driver in there, actually you can get a normal one in there at alll....

I made a knob on the lathe and soldered it on.... looks really good!

Any body want one. I will put up a post and pic of it soon.

Carbs...

R.

[pete376403]

Sorry but I am correct CV stand for Constant VELOCITY.....The slides are operated by vaccum but it is the air speed(velocity) thru the carb that justifies and determines how far they open they are spose to be more economic and smoother and were designed to be used in all elavations on bikes(ie countries) because they compensate for different air pressure and atmospheric conditions without major tuning(in most cases)......have dout and tuned these carbs for more than a few years.
Carb experience? Ok let me say "me too"
I'd beg to differ on the constant "velocity" - you say the air speed is the same regardless of throttle opening? Also - it's not the air speed through the carb that determines how high the slide lifts - the vacuum on above the slide determines this. And this in turn controls how much air (and thus fuel) goes into the engine. This idea has been around for many years, starting with the SU carb. Stromberg called them CD (ie constant depression) which is another way of saying vacumm, but certainly ot another way of saying velocity.
Wiki says this: Variable-venturi, in which the fuel jet opening is varied by the slide (which simultaneously alters air flow). In "constant depression" carburetors, this is done by a vacuum operated piston connected to a tapered needle which slides inside the fuel jet. A simpler version exists, most commonly found on small motorcycles and dirt bikes, where the slide and needle is directly controlled by the throttle position. These types of carburetors are commonly equipped with accelerator pumps to make up for a particular shortcoming of this design. The most common variable venturi (constant depression) type carburetor is the sidedraft SU carburetor and similar models from Hitachi, Zenith-Stromberg and other makers. The UK location of the SU and Zenith-Stromberg companies helped these carburetors rise to a position of domination in the UK car market, though such carburetors were also very widely used on Volvos and other non-UK makes. Other similar designs have been used on some European and a few Japanese automobiles. These carburetors are also referred to as "constant velocity" or "constant vacuum" carburetors. An interesting variation was Ford's VV (Variable Venturi) carburetor, which was essentially a fixed venturi carburetor with one side of the venturi hinged and movable to give a narrow throat at low rpm and a wider throat at high rpm. This was designed to provide good mixing and airflow over a range of engine speeds, though the VV carburetor proved problematic in service.
So we'll have to agree to differ on this.
However I believe the real place you'll find CVs is the drive shafts of front wheel drive cars .

[Defiant]

http://www3.telus.net/dougsimpson/CVcarb.html

http://www.google.com/search?rls=com.microsoft%3Aen-US&hl=en&q=constant+velocity+carbs


Well.....looks like we do disagree...I have no interest in turning this thread into a "i know more than you" thread........take a look at the sites above(i rest my case).....do your own search if need be.....I have worked with bikes and cars for more that 15 years and have my company of customers that have never been mislead so what you seem to know interests very little....I was merely offering to help the thread starter.......next time you see me on the road lets see whos carbs are better tuned huh?.........PS, i dont remember saying the air speed was constant and you who types so much should know that even a cv carb has a butterfly that is cable operated.......the vacuum you speak of is created by the air velocity(air speed) running past the rear venturi and causing negative air pressure(low air pressure/vacuum) resulting in the slide lifting thus opening the slide which in turns lifts the NEEDLE jet to deliver fuel from the fuel bowl via the EMULSION tube....otherwise know to the LACKY'S as the fuel jet......HD also refer to their own carbs as being constant velocity carbs as do hitachi, mikuni, Zenith and a host of others.......by the way CV in a front wheel drive vehicle is ALSO named as a constant velocity joint........I do need to comment that your response greatly reflects something i have seen on another carbs site.....????....i hope you didnt copy and paste....