Dellorto air noise - top vent

[miked]

I wonder if anyone can shed some light on the above please. I am more familiar with Webers.
I am chasing down a few faults for a friend. The front carb is making a chuffing air noise. Sounds like a small steam engine. I first thought it was the O rings to the head since the nuts were not that tight. I changed them and restarted with more intent on locating were the air noise was coming from. I found it to be from the jet top litte cover on the front carb. I blocked the front vent with my fingers best I could and the noise diminished. Revs rose. Found both cold start mech solid on both carbs. Levers won't move. Lifted both float bowl top covers. Looks like the front cold start valve is stuck slightly higher off the seat possibly.
I will attempt to disassemble and free tomorrow.
Can anybody give some advice. The front two spark plugs showed a lot leaner than the two rear. Assume this stuck valve is allowing air but not fuel due its incomplete position.
Cheers Mike

[miked]

Just found this statement on another car forum.


"The choke on the Dellorto is not like the Nikki - it's basically a controlled vacuum leak and makes a loud hissing air sound when it's open. Go to gruntled.com and look at the Diagram for where the choke lever is (it's basically a little round o-ring kinda piece of metal on the top of the carb that you can move side to side)"


I must also add that i found the vac pipe on the servo diaphram knocked off. Perhaps this explains the plug colour, certainly on number 1 cylinder.

[mark030358]

Hi Mike,
The choke or enrichment device on a dell or to is a brass cylinder with a rubber seal at its base. The cam lifts the cylinder upwards and it closes under spring pressure. I “may” have a spare one, ill look tomorrow. TBH I never ever use them.
Cheers
Mark

[miked]

Thanks Mark

I have the brass tops off. Will try and get the valve free in the morning. Absolutely solid. Think it is blasting grit. Will let you know if I need one.

Cheers Mike

[512BB]

I suspect that most people with Dellorto carbs will be running about with items that look like the carb top on the right, I was. I could move the enrichment lever to any position and there it would stay, the parts were so gummed up.

After dismantling and a wizz through the sonic, I polished the brass parts with brasso and reassembled. A little bit of grease on the cam and light oil on the spring and hey presto, the mechanism works like new, and now the lever snaps back of its own accord. At the same time, new needle valves were fitted. On examination of the old valves under a 10x lens, a round groove had been worn where it contacts the valve seat, not visible with the naked eye. This was obviously the cause of fuel leaking out of the trumpets, non seating needle valves, now cured. A very satisfying and worthwhile job done.

Leslie

[miked]

Thanks Leslie,
I just came in for a brew after spliting them down, polishing and greasing. They now snap back with vigour.
So thanks for your post. Yes, just as you say.
These were full of blast medium. Went through me when trying to release. Scratching the sides of the piston. Really stuck. I would have been happy with gum.
Polished up now.
Crimes against Lotus and Dellorto. Grrrrr
Cheers Mike

[miked]

Sorted, noise gone. When you pull the choke they both hiss but silence as they close. You live and learn.

[mark030358]

great result ...