sticky carb

[Dru]

Latest fun and games has been the engine faltering when trying to accelerate; put foot down and it sort of coughed, spluttered a bit, and eventually made up its mind to speed up. Ran fine at steady throttle opening...

So I had a look at the carburettor, and found that the piston was a bit gunked up and scored, and not running smoothly up and down.

I cleaned up the inside of the suction chamber and the sides of the piston with Autosol, which seemed to help; it runs and accelerates smoothly now.

Small questions;

<a href="http://www.flickr.com/photos/belvedere/3861866712/" title="SU jimmy by Dru Marland, on Flickr"><img src="http://farm3.static.flickr.com/2676/386 ... 26595a.jpg" width="500" height="333" alt="SU jimmy" /></a>

the base of the piston is fairly badly pitted, as you may see from the picture. Would it be worth lapping it to improve the airflow, do you suppose?

And that little black doughnut thing on the base of the piston; what's that for? -just to stop it clunking too much when the piston drops? It does look a bit tatty...

-and is it better to let a bit of oil go over the sides when topping up the dashpot, or does the piston operate better when it is scrupulously clean?

...another thing I noticed while I was in there, was that the gasket between the air filter mounting and the carburettor inlet was sticking out quite a way, thus

<a href="http://www.flickr.com/photos/belvedere/3861866698/" title="improving the airflow- before by Dru Marland, on Flickr"><img src="http://farm4.static.flickr.com/3440/386 ... 980b_m.jpg" width="240" height="160" alt="improving the airflow- before" /></a>

...so I took a scalpel to it, so that it is flush with the bore. Which can't do any harm, at least.

<a href="http://www.flickr.com/photos/belvedere/3861866704/" title="improving the airflow - after by Dru Marland, on Flickr"><img src="http://farm4.static.flickr.com/3456/386 ... 2952_m.jpg" width="240" height="160" alt="improving the airflow - after" /></a>

[Alec]

Hello Dru,

don't make a habit of using Autosol, or any other polish. Use a solvent cleaner only.
The pitting is not worth bothering about and the 'little doughnut' is the final stop, so as not to have metal to metal.
Just lightly oil the piston rod then top up after reassembly.

Alecl

[bmcecosse]

Well done with the strip-down. As Alec says - best to NOT use any abrasive in there - just clean it. Extra oil does no harm and the black doughnut is there to hold the piston slightly open - so some air can get through initially. Your strip-down pics don't show or mention the spring - was there one in there ?

[Dru]

Yes, the spring was there, but out of shot

Thanks, Alec, too! Point noted about abrasive; the piston was scored with several vertical lines from top to bottom, and there was a gratey sort of feeling to the sliding motion, and the Autosol seemed like a good idea at the time. I'll just clean it next time... if there is a next time (strongly suspects there will be a next time... )