2002 FC550 lots of popping on decel/dellorto carb

olpace · Jul 2, 2012

I was looking in my paperwork and I show that stock my main jet should be a 190, when I cleaned my carburetor I had a 200 main, the rest I believe were stock but cannot be sure about the needle jet I don't remember looking at it. anyways my bike runs good and doesn't (Backfire) or what I would consider a backfire like on harley which is very noticeable however it does a $@#$ load of popping on full throttle decel. The guy I got it from was running pure 110 octane leaded race fuel in it, I now have it mixed half and half with the 110 and 93 pump gas, is it running too lean or too rich? Im not sure which way to adjust my fuel mixture screw or if I should run it at 1 1/2 turns and move the needle? Thanks in advance, yall have been of great help to me!

olpace · Jul 2, 2012

Also this is running with only 1 petcock turned on, runs great this way, will flood and foul the plug if u open both of them at the same time.

zaga · Jul 3, 2012

Hi

This bikes are made for 98 RON, but you can run them with 95, it depends on how hard you are riding.

The octane should not make a difference on the decelaration poping, and you can have some leak on the exhaust, that will suck air in to the exhaust and that makes that poping.

Try to set the mix screw to the most high revs at idle, then set the idle with the idle screw.

The rule is, you have poping in the range of revs were you have jetting problems, so you will know what jet to set up. So if you have lots of poping on decelaration on high revs, its the Main Jet.

Also that thing with the petcock doesn't make any sense, you shoud have constant level allways, maybe you have a problem there, you have to set it to close when the arm is horizontal.

:cheers:
ZAGA

olpace · Jul 3, 2012

Ok, that makes sense so im thinking I may need to go back to a 190 main jet and try that, I will also check my exhaust bolts etc for leaks..... yeah on the petcocks, I can turn one completely on (doesnt matter which one), and it will run like a scalded ape, idle great etc... but if I turn both of them on it will only idle as soon as you try to give it gas it starts doing a lot of sputtering, lugging, popping and then will stall out and foul the plug. clean the plug, turn only 1 petcock on and everything is back to normal... this makes no sense to me either other than getting waaay too much fuel, could this be due to the 200 main jet as well? possibly an impropper float adjustment? as far as adjusting my mixture screw, im at about 1 3/4 turns out right now and approx 5 turns out on the idle screw, should I adjust my mixture screw while its idling? turn it until the bike revs to its highest point and then idle it down with the idle screw? Where should I have the idle screw set at when I start adjusting the mixture screw. I just didnt want to get it too lean or too rich and mess it up, forgive my ignorance. I am mechanically inclined, but I am not familiar with the bergs.

Thanks again for everyones help!

zaga · Jul 4, 2012

Hi
I will try to answer your doubts.

I think your 200 MJ might be too much, but this things you have to try, and if I remember between 200 and 190 you have at least the 195, but I think you also have the 198 ?? don't remember. Go to http://www.dellorto.co.uk/default.asp and check it.

The leaks are not only on the head, it can also be where the parts of the exhaust comes together, use silicon (wurth-RTV-red one).

The MJ has nothing to do with the float level, and it doesn't matter how many gas you have going to your crab, when the float gets to the point of closing it closes. thats it. So if it doesn't closes you check it, level and that litlle valvle that goes under the arm, thats the one that closes the gas.

You adjust the mixt screw with the bike idling at normal speed, you have to waite a few seconds for the revs to change. Just start from were you are. If it doesn't change try a different revs at idle, if nothing, check the oring of that screw. After you get that you may whant to change it a bit, with riding tests (this will influence very low revs) or if another setting is best for starting.

On a 02 bike you may whant to refresh the carb, the needle if its not ok (check it), the needle jet (can be worn and you can't see it) and check the float valve.

:cheers:
ZAGA

olpace · Jul 5, 2012

Ok, update, since I have cleaned the carb the bike runs fine with both petcocks open so that issue is resolved. I think I have my mixture set at a happy medium (1 3/4) seems to be what it likes best at this time, however I only use 1-3rd gear and sometimes not all of third, the bike revs quickly with no hesitation and pulls strong, but I cannot say what its doing on the top end as I have no where to run it that fast. Now as far as the popping everything is tight at the head and ther is some sort of blueish silicon sealant, you said to seperate the exhaust and put red (permatex??) rtv sealant on it and stick it back together? I am assuming you mean where the springs hold it together? the popping sound is almost a sound as if there was raw fuel getting into the exhaust and igniting but there are no burn marks on the muffler/exhaust to confirm this theory however I thought the other evening riht at dark that I might have seen a small flash pop out, again this could revert back to me needing to play with different main jets..... thanks again for your help brother! :mrgreen:

zaga · Jul 5, 2012

Hi
You told before that you had poping at high revs decelaration, that is why we've been talking about MJ.

In simple terms when you open the throtle you use first the Pilot Jet (PJ) wich is fine tuned by the Pilot Screw (PS), after the major influence will be of the needle and needle jet, this will be from 1/4 to 3/4 (its were most of us uses the bikes), after 3/4 it will have major influence of the Main Jet (Mj). Offcourse this is not exact and the influences will mix a long the throttle opening.

So, by what you are saying your bike runs clean with no hesitation, so your jetting must be good.

This bikes have some poping specialy with a more open exhaust like the FC and a cam like the FC, but as a rule you can use is, were you have the poping its the rev range that you have more jetting problems.

Also some people say when you have poping, you have too much gas, but some times its the other way, you are too lean and you are getting too much temp out on your exhaust, or for example you have the wrong ignition timming.

The other thing that I was saying was, sometimes you have a leak on your exhaust and that can cause it also. For that you can use exhaust paste to seal it, but you can also use a good high temp silicon, the one that I like more for that and for the engine is WURTH super rtv (the red one, there are several, but this is more high temp.). You have to try to seal it on the head, after the curves (where it goes 2-1) and where is goes to the mufler.

Hope it can help

:cheers:
ZAGA

2002 FC550 lots of popping on decel/dellorto carb

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