Wide open throttle (main jet) stutter

[DewCatTea-Bob]

____ Can't see the tiny-spec in your pic very well,, have you looked at it with a magnifying-glass ? _ If so, what does that little particle-bit seem to be exactly, a flake of deposit-material from-off the inside of your Mik.carb's float-bowl, or what ?
Whatever, it seems too large to have gotten through any fuel-filter/screen.
__ I've provided (below) a zoomed-in view of it, with also a white square-boarder placed around the particle in question, as well.
While the picture doesn't have enough pixel-detail to sharply see whatever the particle is, it may still be of interest to see brightened-up & expanded as extensively as I've bothered to tweak it to.


Enlightened-Cheers,
-Bob

[machten]

Having some association with the production of motor spirits, I think the chances of "bad fuel" are extremely small if it is new fuel. It's all rigourously tested before it leaves the refineries, so pretty much the only chance of contamination is in the tanks of the retail outlet. Certainly, in Australia, these are sampled and tested from the retail pump on a regualar basis. ( I should say at this time that I'm not employed by an oil company!)

Our carburation setup is pretty tolerant. If there was a wide scale fuel contamination problem like the pictures, imagine what it would be doing to injector based systems. If I had contamination like that in my carbs, I'd be looking first at other causes. I could well be wrong, but IMHO on the balance of probability...

Kev

[DewCatTea-Bob]

____ Well, I'm somewhat fairly-pleased that at least SOMEbody has bothered to post another new response to this (recently expanded) thread !
__ Anyhow, onward-forth next ...


" I think the chances of "bad fuel" are extremely small if it is new fuel. "
" If there was a wide scale fuel contamination problem like the pictures, "
" If I had contamination like that in my carbs, I'd be looking first at other causes. "

____ First, I find it somewhat disconcerting that you've quoted: " "bad fuel" " , as no-one else had posted that particular wording within any of the previous (recent) posts, so as to actually be quotable wording. _ Furthermore, nobody-ELSE had before suggested that the contaminate-particle (which Jim pictured & posted), may have come along-with the fuel itself.
So I'm left to assume that a rather brief read-through of all the more recently placed posts (on the previous-page), is probably responsible for such a jumped-to conclusion (as you've seemed to have reached).
I really doubt that anyone has actually suspected that anybody-else would seriously think that it's possible for such a large (random/unknown) particle to have actually come directly from new-fuel.
__ But still, it's of-course fairly reassuring to have gotten your above-average experience/knowledge in the petro-field, interjected into our topic here.


" so pretty much the only chance of contamination is in the tanks of the retail outlet. "

____ I agree that most all contamination (of most types) is actually sourced from any of the storage-tanks that fuel gets (or finally becomes) stored in.
Some way or another, water seems to become a common contaminate, and I've noted within some fuel-storage container-tanks such as float-bowls, that layers of what appears to be lime-deposits are coated on inside surfaces, and it can possibly loosen & flake-off (but then usually just settles at the bottom [along-with other particles which came from the fuel-tank] ).
__ But in this case, (of Jim's),, the contaminate-particle in question seems too large to have gotten through a stock filter-screen in his Duke-tank, (so thus-then it's likely not from any tank-sealer product).
So, (so far), Jim has left us to wonder what his presented particle may actually be, and whether his carb's fuel-chamber possibly has anymore of such left somewhere inside.


" Our carburation setup is pretty tolerant. "

____ It's not real likely that that very-same pictured particle was solely responsible for each & every time Jim noted his engine was starving for fuel... Probably other smaller pieces temporarily clogged-up his main-jet before finally getting sucked-through & consumed along with the fuel.
__ Such occurrences as Jim experienced, (while certainly quite rare), are not extremely unheard-of though,, as steps to avoid such have been considered in the past...
I recall that late 1974 MotoGuzzi-models which came with Amal-carbs, included a finely meshed-screen which was formed to snugly fit-around the main-jet itself, obviously to provide one-last/final filter, apparently so as to prevent such main-jet clogging as Jim seemingly experienced.
__ So in Jim's case, it seems (so far) we're left to wonder whether fuel-line type fuel-filters would have helped prevent his experienced-issue or not.
But I rather suspect that his presented particle came from inside his carb itself.


Dukaddy-DUKEs,
DCT-Bob

[JimF]

Sorry - working a lot of hours of late... lucky to get 5 hours of sleep a night.

The item looked fibrous, it seemed a little pliable but perhaps it was rigid and chemical interaction when submerged in the fuel softened it up.

I had recently had the bowl off multiple times as I changed the main jet several times during the experimentation process, but I don't recall seeing any carb component (gaskets, seals) made from similar looking material.

It could very well be that I didn't monitor or control ambient cleanliness as closely as I should have, and that my problem was entirely my fault.

I don't have any tank sealant that I can see on the tank's inside that a previous owner might have applied, and in a thousand miles this is the first instance of this kind of blockage so I think that I don't have a tank that has flaking residue on its interior walls.

The good thing is that I am now keenly aware of the potential for this to reoccur and I could more quickly diagnose and rectify it should it happen again. The bad thing is if a subsequent particulate were smaller and weighed less it may plug a smaller port/jet other than the main jet.


Jim

[graeme]

Dandruff?

[JimF]

I wish! I barely have any hair any more.

[machten]

Just to clarify my earlier post...

____ First, I find it somewhat disconcerting that you've quoted: " "bad fuel" " , as no-one else had posted that particular wording within any of the previous (recent) posts, so as to actually be quotable wording. _ Furthermore, nobody-ELSE had before suggested that the contaminate-particle (which Jim pictured & posted), may have come along-with the fuel itself.

Bob, you said this at some stage in your own thoughts..

____ As I read-through your post, I also came to suspect that your newest issue is as if your main-jet gets blocked with some small (m.jet-hole sized) particles.
It's certainly possible that you had purchased some contaminated gasoline (that previous day).

..so maybe that's what I attached to, I don't recall specifically. Perhaps it's just a use of language thing...I guess I'd call buying "bad fuel" near enough to purchasing "contaminated gasoline".

I do know that I often read things in various places that attribute things to "fuel quality", and basically, with some knowledge of what goes in to fuel quality, I sometimes find it difficult to accept what is being said if we're talking about first world fuels.

The key point of my original post was that I would think it unlikely that the fuel was the source of Jim's "cereal flake" (my words). On that, I think Bob and I agree.

Kev