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October 1st, 2006, 02:54 PM   #1
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Making Popcorn?

I just finished putting my '93 FE501 back together. I did my annual tear down and cleaning process. I did however install a new Big Gun Exhaust system. Starts rather hard and spits, sputters, and then stalls. I removed the carb, cleaned, and reinstalled. Carb is a 38mm flat slide dellorto. When running, I have to turn in my FM what seems way too far, to idle at all. When cracking the throttle, it pops and such through the exhaust. Idle speed is very eratic and engine will stall as soon as load is applied. I was told that I should not need to re-jet whith this exhaust set-up. And yes the valves are set proper. Confused About jets. One is a #50, and the other is a #33. Please shed some light on my issue. I'm sure I'm over looking something.

Thanks,
Opie '93 FE501, '00 250sx, and I would love a new speed triple if y'all could help me convince the wife!
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October 1st, 2006, 03:26 PM   #2
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RE: Making Popcorn?

Opie,
Put the old exhaust back on the bike,if it still has the same issue you do not have a jetting problem.If the problem goes away you will have to jet youre bike for the new exhaust.If you have the same problem with the old exhaust then you need to understand why youre engine needs a overrich mixture to run and has an unsteady idle. Most likley cause incorrect valve timing and /.or bent valve,causing vacumn drop and air leak.
Do a leak down test first and check for any air leaks on the intake and exhaust side..good luck
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October 1st, 2006, 03:38 PM   #3
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Opie,

I'm going to assume the following: Fresh gas, fresh plug, exhaust joints sealed with a quality high temp silicone sealer, the little fuel filter screen beneath the fuel inlet housing on the carb is clean, your vacuum line to your fuel pump is properly attached and in good condition IE no cracks causing an air leak, and that your fuel pump is funcition properly.

I would guess that the #50 is a starting jet, and the #33 is your pilot jet.

You say that have to turn your FM(?) in too far to keep it running. Are you talking about fuel mixture screw or idle speed screw?? Because the more you turn the Fuel mixture screw (that's the screw on the engine side of the carb with an internal spring) the less fuel you will be putting to it. But, if it is the Idle speed screw (the big screw with the external spring) that you are turning in then I can under stand what you are saying.

Now then, all things being equal and you just replaced the exhaust, then it is quite possible that you will have to turn the FMS counter clockwise (out) to deliver more fuel at idle. It is also quite possible that you will have to raise your needle a clip position or two as the new big gun is probably flowing more than your stocker. By the way, why did you replace the stocker??

Try this: Find the FMS and turn it all the way in (clockwise),LIGHTLY seating it, and keep track of how many turns in it went. If it was only a half turn or so this could be a big part of your problem. Then turn the screw out 2 & 1/2 turns. Start the bike and set the idle with the idle speed screw at around 1500 rpm, this is just a smooth normal idle. Then try turning the FMS screw in until the idle starts to drop off, then back out until you reach the highest idle speed. Keep note of how many turns. Then keep going out with the FMS until the idle starts to drop off again. Take note of how many turns, and then set the FMS half way between the point at which you achieved highest idle, and when the idle started to drop off as you richened the mix. I'm not sure about the flat slide delorto, but, with the round slide I found that it needed at least a #38 pilot jet with a 501. If you get to 3 turns out and the idle doesn't drop off, or it takes that many to get the highest idle, then that is an indication that you need a bigger pilot jet.

Now that you've got the idle mix set correctly........ IF you try and open the throttle and it dies try lowering the cliip on the needle, thus raising the needle, two positions and see if that doesn't clear things up. Also, if while decelerating if the bike is popping that is also an indication that the needle position is set too lean.

If this doesn't help drop me a line and we'll see if we can't get it sorted.

Hope this helps,
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October 1st, 2006, 04:36 PM   #4
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Thanks guys.
First, the exhaust was replace because of an unfortunate tree incident. Too damaged to repair, stock replacement very $$$$ and hard to find, big gun new on e-bay cheap.

second, All is well.. fuel lines, boots, vacuum, proper seal @ flangrs, etc....

third, yes the fuel mixture screw had to be @ 1.5 turns out. Lean I Know. I expected to have to fatten mixture, but i couldn't get an idle unless idle speed screw was in so far as to raise slie up .5 cm or so.

I did not know about the clip position. Lowering the clip increases fuel?
What is the correct jet sizes for my setup? ( sea level)
Thanks again gents.
I will keep on truckin' and figure this out.

Opie
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October 1st, 2006, 04:50 PM   #5
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Hey Opie,

Yes raising the needle also known as lowering the clip positon does richen the mixture. This can and will make a marked difference in how the bike runs.

The reason I ask about how come you replaced the stock exhaust is because my stock exhaust on my 94 501 broke inside and made for less than stellar performance to say the least.

By rasing the slide 5mm you are gettig the bike to idle with the needle. Did you happen to notice how far it was open before?

How does it run with the choke on? That hasn't come up yet.

I'm betting that with a #38 pilot and the FMS out at least two turns out you should be able to get a good idle to 1/8th mix. But just for the heck of it, try opening up the FMS to 3 turns out and try it.
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