Fuel pouring from carby

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cooperplace
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Fuel pouring from carby

Post by cooperplace »

I'd like advice from the group. My 1982 900S2 has sat around for some years, and today when I tried to start it, on turning on the fuel, it poured out of the RHS carby. It had a pair of brand-new Dell Ortos about 2 yrs ago, hardly run since. Turned out the float was half full of petrol. I put in a float from one fo the old carbies (looked fine), still flooded petrol on the floor. If I take the float bowl off and hold the float up manually, it seals fine.
What should I do next? Thanks.
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81mhr900ss
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Re: Fuel pouring from carby

Post by 81mhr900ss »

I strongly suggest removing the carb, you can leave the slider and top hanging in the bike, take the bowl off and turn the thing upside down on a table top and measure the float height as described in the manual. It's really easy to adjust with the carb on a table in front of you. It is possible that you have a lump of varnish plugging something and causing the float to stick.

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http://www.thisoldtractor.com/dellorto_ ... etors.html
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Craig in France
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Re: Fuel pouring from carby

Post by Craig in France »

cooperplace wrote: Fri Apr 10, 2020 3:59 am What should I do next? Thanks.
Very, very simple. Buy a new float valve from Steve ...

https://store.bevelheaven.com/Dellorto/ ... Valve-250/

... and install as per the instructions above.

A wise man would do this with both carbs.

You might also consider buying one of Steve's float height gauges. Or make your own. P.s Can't find these in his on-line shop; so best ask.

The reason for the failure is that the tips of the float valves go hard with age/when not used. Given the length of the bike's lay-off, you should probably allow for a complete carb clean sometime in the not so distant future.
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BevHevSteve
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Re: Fuel pouring from carby

Post by BevHevSteve »

Thanks Craig - the #250 float needle valve is for PHF carbs. For PHM carbs the #300 float needle valve is used.

https://store.bevelheaven.com/Dellorto/ ... Valve-300/

And, I am out of stock on the float gauges but some vernier calipers will do the job well. Adjust float height to 18mm +/- 0.5mm
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81mhr900ss
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Re: Fuel pouring from carby

Post by 81mhr900ss »

Always dangerous to make assumptions but as the bike had new carburetors only two years ago and has only been very lightly used, I didn't think it likely that the float valves would have aged and hardened. It's more likely that something is jammed in the carb fuel valve. The float full of fuel should never have happened, especially with a new carb but mistakes are made, even by Dellorto.

It's easy enough to check the 17.5 to 18.5mm float height with a small steel ruler.

Please report back cooperplace!
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Craig in France
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Re: Fuel pouring from carby

Post by Craig in France »

81mhr900ss wrote: Tue Apr 14, 2020 11:27 am I didn't think it likely that the float valves would have aged and hardened.
You could be right; but every spring I have to replace float valves in Dell'Orto carbs, float valves that have stopped sealing in less than 4 months of inactivity. And judging from reports on other forums, I'm far from being the only one.

That said, I get the impression that the phenomenon is becoming less of a problem than it was a few years back. It has been suggested that Dell'Orto have changed the material they use to make the valve tip. Dunno. Steve may know more than I.
81mhr900ss wrote: Tue Apr 14, 2020 11:27 amIt's more likely that something is jammed in the carb fuel valve.
Good point. If someone has been careless about reinstalling the floats, it is possible that they catch up on the side of the float bowl. A sharp tap on the side of the bowl with a screwdriver or similar is often enough to release them.
hedton
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Re: Fuel pouring from carby

Post by hedton »

I had trouble with my MHR Mille 1985.The front cylinder was flooded with fuel.
After some investigation I found out that the RH fueltap (The vaccum controlled fuel tap) was the problem.
The diaphragm (membrane) was leaking, so the fuel went through the vaccum hose (the one that goes to the inlet manifold.
I threw away the fueltaps and mounted the older fueltaps without the vaccumpipes.
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Re: Fuel pouring from carby

Post by BevHevSteve »

I recommend that anyone with a bike that has a vacuum tap to toss it, plug the vacuum port at the manifold and install a pair of mechanical fuel taps...
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Re: Fuel pouring from carby

Post by hedton »

I fully agree.
And put on syncnipples that you can run with rubbercaps.
cooperplace
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Re: Fuel pouring from carby

Post by cooperplace »

The (white) float on the front carby was full of fuel, so I tried replacing it with a spare black float I had, but it seems they're not compatible, even tho' both are from PHM40s. So now I got a new white float, and fuel no longer pours from the carby. Starts and runs, but on 1 cylinder only: the back. Both have good blue spark. I pulled the front carby off and am trying to clean it.

If anyone has any advice on how best to clean these, I'd be grateful.
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Craig in France
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Re: Fuel pouring from carby

Post by Craig in France »

cooperplace wrote: Sat Jul 25, 2020 11:05 pm The (white) float on the front carby was full of fuel <snip>
Yup, that would certainly do it! :-D

Small comfort, I know; but you're far from being the only one to have had problems with white floats - or at least a certain batch of them. Plenty of similar postings on Laverda and Guzzi Forums. The fault was splitting down the seam.

Btw, be aware that the floats come in different weights. Originally 10g and 14g, but I see that Eurocarbs these days list 3 in the black series (7.5g/10g/14g); and Steve A. lists 2 others (8.5g and 9.5g). So advance with a certain amount of caution 8) . I think 10g is correct, but please don't take my word for it.
cooperplace wrote: Sat Jul 25, 2020 11:05 pmIf anyone has any advice on how best to clean these, I'd be grateful.
Ultrasonic bath seems to be the preferred method these days, but you can still do it the old-fashioned way with carb cleaner. The most important thing - which ever method you use - is to make sure all the galleries really are clear afterwards. Here's one way:

1. Remove the pilot jet and the mixture screw.
2. Using a can of carb cleaner with an extension tube fitted, put the tube up the hole where the pilot jet goes. Cover the mixture screw hole with a finger and squirt cleaner while looking for a stream coming up into the venturi, just in front of the back edge of the slide.
3. Now put the tube in the mixture screw hole. Cover the pilot jet hole with a finger and squirt cleaner whilst looking for a stream coming out between the slide and the engine.
4. Now put the tube into the little air hole under the main carb air intake (not the "middle" one: the one on the side). Squirt, and look for cleaner in the venturi.

This latter is the most important. This drilling is stepped inside and crud loves to accumulate there ...

And obviously: renew all the seals and O rings.
cooperplace
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Re: Fuel pouring from carby

Post by cooperplace »

I'm happy to use u/sonic, as I have access to one. If anyone can point me towards a good guide on disassembly and cleaning of PHM40s, I'd be grateful.

It starts and runs on both, but like a dog, backfiring, etc.

Thanks
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BevHevSteve
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Re: Fuel pouring from carby

Post by BevHevSteve »

I have written a comprehensive guide on how to do rebuild a PHF carb and it's available via the link below
https://store.bevelheaven.com/Digital-I ... tructions/
19 pages, 3673 words, 30 images....

For PHF carbs you need this one:
https://store.bevelheaven.com/Digital-I ... tructions/
19 pages, 3570 words, 30 images....

To properly do a carb sync I wrote another manual here
https://store.bevelheaven.com/Digital-I ... s-Digital/
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cooperplace
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Re: Fuel pouring from carby

Post by cooperplace »

Hi Steve,
thanks, I purchased one,

Peter.
cooperplace
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Re: Fuel pouring from carby

Post by cooperplace »

Hi Steve,
that guide is great, thanks. I pulled both carbs apart, used an u/sonic bath to clean up, reassembled. Starts and runs perfectly now.
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