throttle overrun?

Technical Help Forum

throttle overrun?

westtexwing 07-22-2008, 7:25 PM

Recently got bike running (gl500) cleaned carbs, new plugs , cleaned out petcock filter etc. Bike is starting to really rev well but now seems to rev high after letting off gas and pulling in clutch t o shift. Also has slight popping on deceleration.

Any thoughts appreciated.

thois forum has helped an old rider and old bike get back into it.

Thanks

Re: throttle overrun?

Anonymous 07-22-2008, 7:35 PM
Sound like the carbs are't closing.
Check throttle cables at handlebar and carb. Check routing of cables, no kinks or the such.
Carb linkage sticky?

Re: throttle overrun?

westtexwing 07-22-2008, 8:03 PM

thanks,

Throttle returns fairly quick. How will I know witch way to adjust down at the carb?

Re: throttle overrun?

Anonymous 07-22-2008, 8:12 PM
look for an air leak somewhere between the carbs and the engine, this will cause backfiring and slow throttle response

Re: throttle overrun?

Anonymous 07-22-2008, 8:15 PM
On my 81 the carb end of the factory cables are set up like this.

The one that has no adjustment is the closing cable, the one you can adjust (2 nuts on it) is the opening cable.

With no cables connected the carbs should snap closed with authority when operated by hand.

Does the bike do this while in neutral when you rev it?

Re: throttle overrun?

Shep 07-24-2008, 6:04 PM
I've found several causes for this.

1:Sticky cable usually the B cable and near the carb body/bracket holder(Check routing and near carb)
2:Bad Air cut-off valves(Can be bypassed)
3:Incorrect Float heights(Carbs off to check.should be 15.5mm from perpendicular)
4:Out-of-sync carbs(Sunc them)
5:Throttle cable mechanism sticky at carb body.Flood with rust penetrating oil and activate repeatedly.May require carbs off to check properly.

HTH :)

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Re: throttle overrun?

NstyDevil 07-25-2008, 10:06 AM
i was thinking this morning that i've got the same issue... overrun, and popping... overrun means it's too lean, popping means it's too rich... GAHHHHHH

i'll be watching this thread closely.

__________________

'80 CX500 Deluxe
approx 80k on the odometer

Re: throttle overrun?

RichNCT 07-28-2008, 10:00 AM
Popping can also indicate too lean. Mixture too lean to burn in the combustion chamber, but builds up some in the header or muffler then pops whenever it becomes burnable. That's two indications of lean, go for three?

Born to be relatively wild

Re: throttle overrun?

Shep 07-28-2008, 2:27 PM
Remember also with these bikes it's not uncommon that someone has mixed up the Primary and Secondary main jets.
The 78s go into the carb body.
The 112s or 115s go into the Brass Hex Holder.

Also you on thes carbs you Screw the idle mixture screw IN to Enrich the mixture and OUT to make it leaner.

See also here,
Carbs

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Re: throttle overrun?

mcreviver 07-28-2008, 7:49 PM
Always use a ight touch when screwing in the idle mixture screw. Too tight and you've ruined the carb. It won't idle right and the rpm hangs up on deceleration.

Ron in PA

Re: throttle overrun?

RichNCT 07-29-2008, 4:53 AM
"The 112s or 115s go into the Brass Hex Holder."

Or in the case of the CX650E, the 118s go in the jet holder. heh heh heh zoom zoom zoom

Born to be relatively wild

Re: throttle overrun?

Shep 07-29-2008, 5:08 AM

RichNCT wrote:
"The 112s or 115s go into the Brass Hex Holder." Or in the case of the CX650E, the 118s go in the jet holder. heh heh heh zoom zoom zoom

Rich.Just out of curiosity do you know anything about these 115 jets.I recently bought a set of carb re-build kits from GeorgeFix in the USA.They came with all the stuff and new 78 and 112 jets but also had some new 115s in them.I would just like to know when and why would the 115s be used in a CX500 and what effect would they have e.g more power?

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Re: throttle overrun?

RichNCT 07-29-2008, 9:34 AM
I don't recall what the GL650 had, and maybe the CX650C is jetted a little differently. At some point I'll take a look, I believe I have both those carbs in the shed. So the answer is no, I don't know. Was the CX500 jetting different depending on whether the carbs had an accelerator pump or not?

Born to be relatively wild

Re: throttle overrun?

Shep 07-29-2008, 12:16 PM

RichNCT wrote:
I don't recall what the GL650 had, and maybe the CX650C is jetted a little differently. At some point I'll take a look, I believe I have both those carbs in the shed. So the answer is no, I don't know. Was the CX500 jetting different depending on whether the carbs had an accelerator pump or not?

That could be it.

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Re: throttle overrun?

I'm going to GL 08-05-2008, 6:49 PM
Hope you don't mind that I shake the cobwebs out of this thread with a full-on hijack.
I simply can't help but ask how in god's name could, a motorcycle of all things, possibly run right WITHOUT and accelerator pump? How could there be enough enrichment to cover lean miss at tip in? Especially in cold temps. Surely I'm missing something here, but I swear I can almost hear the backfire through the carbs now......

Thinking out loud here> Was considering the OPPOSITE today when looking at carbs I just got. I was pipe-dreaming of some sort of scheme to mod the thing for adjustable accel pump shot. Seems it could help for winter riding and or to cover other issues with carbs (etc.) until proper repairs could be made.

1982 GL500 "When the going gets weird, the weird turn pro" - Hunter S. Thompson

Re: throttle overrun?

Blindstitch2002 08-05-2008, 7:48 PM
The first two or three years of the cx500 didn't have accelerator pumps. Mine doesn't and seems to accelerate decently but I am working on the thought of picking up a set of carbs with an accelerator pump to test the difference. I'm sure most bikes before 1980 didn't have and accelerator pump and ran fine.

1978 Honda Cx500 Maggot
1979 Honda Cx500 Custom
1980 Honda Cx500 Deluxe Couch Project Bike

CX500 Factory Service Manual
Courtesy of Randall-in-Mpls

Re: throttle overrun?

Shep 08-06-2008, 1:53 AM
Good explaination here,

http://faq.ninja250.org/wiki/How_a_carburetor_works:_Carbs_explained

I can't really see a need for an accelerator pump?

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Re: throttle overrun?

I'm going to GL 08-06-2008, 4:58 AM
Nice! Great link Shep

Weird...It seems funny that I'm kind of starting over since getting into the bike thing, so many automotive things, however similar, flat-out DO NOT relate/apply to bikes stuff (DUH!). Accel pumps are good example - spent countless hours figeting with pumps and pump cams, sometime making my own to get certain things done (heavy cars going FAST).
Sorta cool though, some times makes me feel like a kid again - humbling to say the least.

1982 GL500 "When the going gets weird, the weird turn pro" - Hunter S. Thompson

Re: throttle overrun?

Shep 08-06-2008, 7:37 AM
I do know a lot of the US CX/GLs that people have picked up have had them removed over the years with no apparent change in performance.Bit like the Resistors in the Plug caps and the limiter on the idle screws.I think the a lot of these things were over zealous emisson rules etc in the 80s.

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Re: throttle overrun?

Blindstitch2002 08-06-2008, 9:01 AM
Shep your a walking library.
Where do you store all this knowledge?

1978 Honda Cx500 Maggot
1979 Honda Cx500 Custom
1980 Honda Cx500 Deluxe Couch Project Bike

CX500 Factory Service Manual
Courtesy of Randall-in-Mpls

Re: throttle overrun?

Shep 08-06-2008, 2:17 PM

Blindstitch2002 wrote:
Shep your a walking library.
Where do you store all this knowledge?

In the,"Chip" on my shoulder(Very Zen)

School report:
Paul is a very well balanced child.He has a chip on both shoulders

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Re: throttle overrun?

senile_seinen 08-06-2008, 3:05 PM
Accelerator pumps are necessary where there's a big plenum between the carburetor and the intake valve - usually a long intake manifold run. When you open the throttle rapidly, air rushes through the carb into the plenum faster than the rate of change of fuel flow through the carb jets. Result: momentarily lean mixture and a flat spot in acceleration. They're especially useful if the jetting on the engine is very lean as they can dump a shot of extra fuel in to momentarily richen the mixture to improve acceleration without materially affecting emissions or fuel economy.

Unless you jet a CX really lean, I'm not sure why these would be necessary. I guess that's what Honda did with these bikes as emissions rules tightened. If you richen up the jets a little, you can certainly disable the things. And yes, I think a bike with accelerator pumps on 2" stub manifolds is silly. On the upside, mine work fine, and I doubt anybody has ever been through these carbs.

1981 CX500 Custom

Re: throttle overrun?

Shep 08-06-2008, 4:17 PM

senile_seinen wrote:
And yes, I think a bike with accelerator pumps on 2" stub manifolds is silly. On the upside, mine work fine, and I doubt anybody has ever been through these carbs.

do you mean like this,

CX carbs 1

CxCarbs2

HTH :)

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