Carbs are off again. What now?

[Its been a long time]

Picking up here from my comments in the what did you do today thread. Current state of play with my bringing a 77 650D back from the dead is that everything seems absolutely fine but the engine fires but won't run. The only place left to look is in the carburettors. I looked through the carbs back soon after I first got the bike. It was clear that previous owner had been in there not long before selling the bike. Carbs were clean and tidy with new brass ware but mostly the wrong sizes for a 77 650D. Typical of aftermarket kits I would say. So I cleaned and blew through all the visible air and fuel passages. All were clear. I fitted correct brass ware and checked the floats (look very recent) and diaphragms, nothing found.

So this morning, the carbs are off again. First thing I found is the fresh clean fuel from yesterday is the colour of tea. I conclude the fuel is eating the plastic fuel lines. So they're going to be changed. There's a little bit of the tea stain in the float bowl. But not much. The time delay between refuelling and starting the motor was minutes. I doubt the tea stained fuel is a significant issue on this occasion. But glad I found it. Fuel -

 

[Its been a long time]

Next thing is check the float heights. These were found six months ago to be 25mm. I fitted new seats and needle valves. They're fine.

Today the floats are still 25mm. Question - I measured with the floats depressed lightly on their seats. Not depressed the float height is 30mm. Am I measuring correctly? If not, that could well be my problem. Picture -

Screenshot of the manual. Am I doing this right, or do I let the float rest on the needle valve just under it's own weight? The difference is 5mm.

 

[jaybar6]

I thought the float height was 28mm? (guessing as I sit on my sofa, with no info at hand) Is that manual for an earlier model?

 

[Its been a long time]

I thought the float height was 28mm? (guessing as I sit on my sofa, with no info at hand) Is that manual for an earlier model?

It's the TX650 manual with supplements for 650C and D. As per screenshot it's 25mm plus or minus 2.5mm. I need to know if I measure with the float resting on the needle valve under it's own weight or do I press it lightly down. The difference is 5mm. So it's important I get this right. Thanks.

 

[jaybar6]

Picking up here from my comments in the what did you do today thread. Current state of play with my bringing a 77 650D back from the dead is that everything seems absolutely fine but the engine fires but won't run. The only place left to look is in the carburettors. I looked through the carbs back soon after I first got the bike. It was clear that previous owner had been in there not long before selling the bike. Carbs were clean and tidy with new brass ware but mostly the wrong sizes for a 77 650D. Typical of aftermarket kits I would say. So I cleaned and blew through all the visible air and fuel passages. All were clear. I fitted correct brass ware and checked the floats (look very recent) and diaphragms, nothing found.

So this morning, the carbs are off again. First thing I found is the fresh clean fuel from yesterday is the colour of tea. I conclude the fuel is eating the plastic fuel lines. So they're going to be changed. There's a little bit of the tea stain in the float bowl. But not much. The time delay between refuelling and starting the motor was minutes. I doubt the tea stained fuel is a significant issue on this occasion. But glad I found it. Fuel -

View attachment 332169

The colour is strange! I can only conclude that there is old dried out gunge fuel from the reserve that has mixed with the new fuel.

 

[Its been a long time]

The colour is strange! I can only conclude that there is old dried out gunge fuel from the reserve that has mixed with the new fuel.

Not really. The fuel was only put in there less than 24 hours ago. I think the fuel is eating the fuel tubing. I have some different stuff to use now anyway. Thanks.

 

[member43148]

Measure float height to the float top NOT Compressing the needle spring.
Floats just resting in place.

 

[member43148]

And.. suspect the fuel is getting dirty from something in the tank ?

 

[Its been a long time]

Measure float height to the float top NOT Compressing the needle spring.
Floats just resting in place.

Thank you! I'm going to clean up the carbs again and reset the float 5mm lower. Thanks again.

 

[Its been a long time]

And.. suspect the fuel is getting dirty from something in the tank ?

I used a temporary plastic fuel tank on the bike. Fuel was new and used within minutes of topping up the temporary plastic shop tank. Otherwise, yes that's the obvious place to look.

 

[jaybar6]

It's the TX650 manual with supplements for 650C and D. As per screenshot it's 25mm plus or minus 2.5mm. I need to know if I measure with the float resting on the needle valve under it's own weight or do I press it lightly down. The difference is 5mm. So it's important I get this right. Thanks.

you are correct with the 25mm, I don't know about how you measure it. sorry!

 

[Adamc]

It's the TX650 manual with supplements for 650C and D. As per screenshot it's 25mm plus or minus 2.5mm. I need to know if I measure with the float resting on the needle valve under it's own weight or do I press it lightly down. The difference is 5mm. So it's important I get this right. Thanks.

Float should be resting under its own weight. Measure from the deck height edge of the carb body without the gasket in place to the top of the float.
No pressure on the float.

 

[Its been a long time]

Float should be resting under its own weight. Measure from the deck height edge of the carb body without the gasket in place to the top of the float.
No pressure on the float.

Thanks Ads. Just done it like you said. It's 24.5mm. That's as close as I can get it. That's a significant difference. I'm hopeful we're closer to a runner now. Just buttoning the float bowls up.

 

[Adamc]

Thanks Ads. Just done it like you said. It's 24.5mm. That's as close as I can get it. That's a significant difference. I'm hopeful we're closer to a runner now. Just buttoning the float bowls up.

Oh make sure both sides of the float are equal height too.

 

[Its been a long time]

Oh make sure both sides of the float are equal height too.

Done

 

[Its been a long time]

Bonus points for getting the mangled screws out of the tie bar and putting cap head screws in. Got some new JIS bits and it's quite remarkable how they will successfully grip onto a previously mangled screw head. (Mental note to oneself, buy a couple of new float bowl drain plugs ).

Also done, suspected bad plastic fuel tubing replaced with reinforced PVC. All fuel and air passages blown with carb cleaner and compressed air. All is good.

 

[Jim]

With 'em resting under their own weight.... jus' to throw another voice out there.

 

[Its been a long time]

With 'em resting under their own weight.... jus' to throw another voice out there.

 

[Grimly]

Also done, suspected bad plastic fuel tubing replaced with reinforced PVC.

I'm a user of that stuff but it comes with one proviso - it won't last past a couple of years with modern fuels stiffening it up.
It eventually cracks and splits, which isn't good news.
Dirt cheap, so worth replacing it every two or three years.
I just wish Tygon wasn't so bloody pricey, or I'd be using that, and job done.

 

[mrtwowheel]

You don't mention any fuel filters. Should use fuel filter with your plastic tank and fuel tank. Like, why clean carbs and then not use filters? Not saying that filters will stop that coloring, but it will stop the larger parts.