Stalling on medium-to-full throttle


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fquaade
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Stalling on medium-to-full throttle

Post by fquaade »



Hi Wing friends,

My 88 have suddenly started not stalling when I go hard on the throttle (medium to full throttle). When doing so the engine does not pull with full power and does not run smooth. Releasing on the throttle it springs back to running smoothly.

I can get it up to speed while running and sounding right, by going gentle on the throttle and only go 1/3 to 1/2 on it.

The issue appeared quite suddenly on the highway, but the bike was running well until that.

I did change the spark plugs and both idle and main jets recently (200km ago) and it was running very well after that.
I looked at the plugs today, but they seem right and not burned or anything.

My own thought is clogged main jets (that how it acts to me) but that would be weird as I changed them to brand new very recently. Alternatively a clogged air filter, but the sparks do not look sooted or anything like that. And again it appeared quite suddently.

Im tempted to pull the carb and investigate, but though others might have easier things to try or help me diagnose before I dive into pulling the carb (once again).

Any ideas or similar experiences?

Thanks :-)


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John K
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Re: Stalling on medium-to-full throttle

Post by John K »

My 98 acted that way a few years back

Turned out that the fuel petcock had a SMALL tear in the diaphragm. I do mean real small

Replaced the fuel petcock diaphragm and while there replaced the fuel filter also

Be OK since

Best of luck
John K
fquaade
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Re: Stalling on medium-to-full throttle

Post by fquaade »

Thanks John - thats a good lead; I will investigate tonight.

Were you able to find the crack by visual inspection?
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Rambozo
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Re: Stalling on medium-to-full throttle

Post by Rambozo »

You can confirm by checking fuel pressure while riding. That will also check fuel pump, lines and filter.
fquaade
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Re: Stalling on medium-to-full throttle

Post by fquaade »

@Rambozo how do I check fuel pressure while riding?

I did inspect peatcock diaphragm and no damages - it seemed fine.

I did inspect and cleaned fuel filter.

Neither fixed the issue though.

I did notice that when cranking throttle and stalling it does backfire slightly.

Anyone else have an idea on what to look for?

Thanks🙏
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Rambozo
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Re: Stalling on medium-to-full throttle

Post by Rambozo »

Just tee in a pressure gauge and hang it on the bike somewhere.
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paseandoconhonda
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Re: Stalling on medium-to-full throttle

Post by paseandoconhonda »

From what you say it seems like it doesn't have enough fuel when you demand it. It could be the petcock, or the suction hose that acts on it allowing the fuel to pass through. Cracks in the membrane are usually very small and can be seen with very bright light from behind or pointed at the sun.
At night and at 100 it is not noticeable.
FM-USA
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Re: Stalling on medium-to-full throttle

Post by FM-USA »

Another thought, the bogging occurs to both carbs at the same time. So both blocked jets seem unlikely.
Vacuum would be 1st thought, low fuel psi 2nd..
As others said, psi check but also do a fuel flow check into a jug.

HOPE YOU FIND IT
If so, post here.
When I do one thing, I'll sidestep a little & learn many things.
fquaade
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Re: Stalling on medium-to-full throttle

Post by fquaade »

Thanks for all the valuable input.

@FM-USA - you say that bogging occurs to both carbs at the same time. I was wondering how to diagnose that myself, so what makes you conclude that?

Also - while I understand the concepts of Vacuum, low fuel PSI and @Rambozo´s suggestion of tee-ing in a gauge can you please let me know how where exactly to measure and the best way of de-bugging/problem solving.

Much appreciated :-)

Thanks.
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Re: Stalling on medium-to-full throttle

Post by FM-USA »

It's been over dozen years so... but back then I pulled the carbs & found a large (3/8) hose with a hole in the elbow.
It's located on the left intake front & below the matt.
IF it's there, my fix I bent a 3/8 copper tube, cut short legs, file/sanded the sharp edges smooth & inserted using WD-40 type lube.
Same issue is the smaller hose rearward of the large hose.
The #4 cylinder theres the petcock vac hose. Remove left lower fairing panel you'll see it.
I've never had fuel delivery issues, exact symptoms unknown. So I relate them from cars for diagnosis.
Have you checked the tightness of the 2 "carb to intake" boots? I found both were loose.
.
Lastly, when your bogging occurs will a slow throttle roll-on increase power? If so more than likely the accelerator pump is the issue. Mine the diaphragm got stiff/hard. Carbs need to be pulled.

.
When I do one thing, I'll sidestep a little & learn many things.
fquaade
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Re: Stalling on medium-to-full throttle

Post by fquaade »

Thanks again,

I will check the hoses mentioned if I end up pulling the carb again (which is likely).

Yes I checked the carb intake boots and they are tight.

Symptoms are that if I only deliver slight on the throttle the engine runs fine and pulls as it should - and I can get the bike up to highway speed. The issue shows on more powerfull accelleration (eg overtaking or so) - then is stalls. If I release a little on the throttle and it runs fine.

I checked accelerator pump and it seems fine - delivers the squirts as normally. Also I think it only comes into action on instant throttle-increase and not over longer time of heavy acceleration. Thanks for the lead though.

I am stull unsure of the best way to du a fuel PSI check but will investigate.

I will keep you guys updated on my progress. Thanks.


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