Help on carb tuning...

[Alpha]

Hi All,

I need help...

I have recently cleaned my carbs...using the carb cleaner spray you get at a spares shop, but now I have a problem, where my 503 now idles at +- 1350 rpm and when I accelerate she is slow to pick up revs but then just as she gets to 3000rpm she bottoms out as if she is flooding...

Can anyone help or maybe let me know what could be the problem..

Heeeeellllpppp!!!!!!!!

Fly safe

[Kalahari]

This rather sound like a piece of dirt that came loose from the Carb Cleaner that got stuck in a jet somewhere, it rather sound like fuel starvation than flooding, if it was flooding you probably would have seen fuel dripping out of the small PVC pipe under the bowl, that fact that she is slow to pick up revs sound like a blocked fuel jet, that is why at 3000revs the mixture become too lean and she will bottoms out!

[Morph]

One thing that does puzzle me is why the idling is down as well. Could be fuel restriction feeding the carbs or a crack in the vaccum pipe that operates the fuel pump. This is the pipe that connects from the engine to the centre bottom of the fuel pump. Do you have a backup electric fuel pump? If you do switch it on and see if the engine comes to life.


Did you take the carbs apart when you cleaned them?

If not, take the airfilters off and look into the carbs. Get someone to move from minimum throttle to max and watch the slide movement. Is it going from the bottom all the way to the top, or does it stop half way? If so then this is your problem

Otherwise you are going to have to look at all the jets, fortunately they are all accessable from the float bowl side.

See pic. Remove the float bowl

Remove the main jet and the needle jet, it would probably be one of these. Check and clean. If this still does not work then you are going to have to strip the carbs completely and clean them out.

[Alpha]

Hi guys,

Thanks for the advice, I will take a look at the needles etc. However one more question, could it maybe be the carbs are not synchronized?

[Kalahari]

There must be a VERY BIG difference between the carbs to have this effect if it is sync related and the symptoms will not ba what you experience In my opinion, no this is not a synchronisation issue, this is most probably an obstruction somewhere in the fuel path.

Did you check the plungers on the choke cables if they are in their correct postion, are'nt they perhaps stuck in the wrong position?

[nickjaxe]

Did you fit the plastic slides with the needle and clip the correct way around???


Nick.

[Duck Rogers]

Did you fit the plastic slides with the needle and clip the correct way around???


Nick.

My initial reaction on reading the post was that he replaced the white plastic retainers back in the wrong way, but then he doesn't say whether he took the carbs apart or not only that he "cleaned" them and I decided to shut up because the post is a bit ambiguous and lends itself to hundreds of questions before a diagnosis can be made..
If the carbs were taken apart and re-assembled, I would bet a few bucks that is what the problem is.

[Alpha]

Hi All.

Duck, please accept my hummble apologies for the vague post in this regard...just a tad frustrated as I was supposed to have an awesome fly away this weekend and I am still learning and by people such as yourselfs asking me questions I learn what to ask and post.

Ok Yes I did take the carbs apart and when reassembling all the elements together I made sure I put the plastic slides and needles and clips the correct way round. You can only put them in one way without forcing anything.

Cleend the jets etc....setup the carbs airscrew and timing screws as per the manual....but when I quickly accelerate now and also in the rev range of about 3500 to 4000 rpm...it seems as though there is a fuel starvation or flooding, not sure which...

Thanks for all the advice

[Duck Rogers]

No need to apologise.

Ok Yes I did take the carbs apart and when reassembling all the elements together I made sure I put the plastic slides and needles and clips the correct way round. You can only put them in one way without forcing anything.

True, but you can put the white plastic retaining cup in wrong by fitting it below the needle. Go have a look again. You should have the plastic retaining cup ON TOP of the needle and clip.
Will post a picture soon

[Duck Rogers]

Like so........

[Alpha]

Hi All,

Thanks for the advice, today it seems the problem is resolved, I replaced needle jets, jet needles, float needles and filters, all seems fine, although I max out rpm at 6100! Is that ok?

Thanks again!

Gary

[Morph]

perfect

[nickjaxe]

Which tach is that on....some of them can be a good few hundred RPM out either way.

Nick.