hesitating at constant speed

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her.XT
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hesitating at constant speed

Post by her.XT » Sun May 13, 2018 6:54 pm

hello
I'm still working of my (girl)friends bike, 1990 XT 3TB.
I did a carb overhaul which I hoped would solve the problem. Unfortunately it didn't.
During the overhaul (cleaning and changing of gaskets and all critical parts) I noticed a lot of dirt on the internal fuel filter. It has been changed, now its clean.

The problem:
Motor starts good. Takes gas very good, accelerates nice.
Driving at constant speed is the problem. Motor hesitates, wants to die.... put some gas and she goes.

Any idea what could be wrong?
Thanks

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Mezo
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Re: hesitating at constant speed

Post by Mezo » Mon May 14, 2018 7:55 am

Its always a good idea to have an inline fuel filter (between tank & carb). Have you removed the petcock & checked to see if the filter on the petckock is free of crap? it could be broken where the filter has detached itself, and while your there it may be prudent to flush the tank.

Now i know you say you have cleaned the carbie, but how good was it? there is a post on here somewhere where a member thought he had cleaned it thoroughly but it wasn't sufficient, he found the tiny passageways was full of varnish from stale fuel that had been sat for years, he ended up using mig welding wire to clear the passageways out (scraping out the varnish).

It does sound like fuel starvation to me.

Mezo.

her.XT
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Re: hesitating at constant speed

Post by her.XT » Mon May 14, 2018 6:21 pm

Hello and thanks for your answer!

I really think the carb is clean. I checked all the canals and air was flowing easely through all of them after the cleaning.
I found a lot of dirt on the small filter inside the carb.

I didnt check the petcock! I will do it tomorrow evening and let you know what I found.

her.XT
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Re: hesitating at constant speed

Post by her.XT » Mon May 14, 2018 9:34 pm

petcock looks clean to me, see pic;
https://i62.servimg.com/u/f62/19/91/07/25/img_3111.jpg

But looks like its missing a piece, right?
The white filter is on the reserve ouput, which should be lower than the other output.
I think I hear something in the tank. I need to empty it completely and have a look. Will do that tomorrow.

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Mezo
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Re: hesitating at constant speed

Post by Mezo » Mon May 14, 2018 9:42 pm

Yep one tube has come off, some are plastic & some are brass, either way its letting crap at the bottom of the tank go direct to your needle filter & is why i say its prudent to have an inline fuel filter.

Image

Image

Mezo.

Hodgo1981
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Re: hesitating at constant speed

Post by Hodgo1981 » Tue May 15, 2018 1:43 am

her.XT wrote:
Mon May 14, 2018 9:34 pm
petcock looks clean to me, see pic;
https://i62.servimg.com/u/f62/19/91/07/25/img_3111.jpg

But looks like its missing a piece, right?
The white filter is on the reserve ouput, which should be lower than the other output.
I think I hear something in the tank. I need to empty it completely and have a look. Will do that tomorrow.
And its actually the main pipe that has come off, which would mean you have no "reserve". so you might have a rude shock when you flick to reserve and there is no fuel left.

Thankfully re-manufactured petcocks are for sale everywhere... I cant vouch for quality of any particular brand or location to buy from though.

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Re: hesitating at constant speed

Post by her.XT » Wed May 16, 2018 1:23 pm

In fact, the longer pipe of the petcock was in the tank.
I fixed the petcock. In facts, a additional fuel filter is a good idea that needs to be considered.

The cleaning of the carb didnt solve the hesitating motor at constant speed. It's OK for a daily use because its quite soft. So I'm thinking of leaving the carb this way for the moment.

I am thinking of checking the manifold. It could have a hole or a small crack. I's still the first manifold, so its almost 30 years old and very rusty...
Any good ideas how I could check if its still sealed or if it has cracks?

What about sandblasting the manifold to remove the rust and maybe paint it with black high temp color. Did any of you do it?

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Re: hesitating at constant speed

Post by Hodgo1981 » Thu May 17, 2018 1:01 am

I'd say it is almost DEFINITELY the inlet manifolds leaking air.

Every yamaha XT or TT I have bought has had a leaking manifold.
Its a cheap and easy replacement.

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