carburater blues

This is seancycle, I just found this site as of 4/15/05 and have carb issues on my '96 KTM 620RXC LC4. I have a Delorto 38mm (PCM?) and I don't think it is as great as people are saying. But to make things worse, I just bought a Holley Quick Silver by Edelbrock off Ebay for $20. (thinking that was going to solve all my problems until I see what you guys are writing about the Edelbrock). The Deloroto is great for stomping on the gas (much like the Deloroto's I ran on VW's), but the idle circuits really suck!- they don't regulate for beans! Comming off freeway speeds to stop idle speeds, this thing is always sticking on high idle, header pipes are bluing on the exhaust and bike is "hunting" or light "surging" at 55mph+. Please tell me this is a carb tuning issue because I'm starting to have flashbacks of horror from my earlier volkswagen days. Brief history of the bike: I'm 3rd owner with 3600 miles on bike., Ist owner- old fart with too much bike sold it to coworker. 2nd owner coworker blasted around in the mud and dumped ita couple times and left it in the garage for long periods of time. Then I got it. It kick started well. I ran quickly 300 miles on it and the carb started acting up. Took the carb apart and found the fuel line rotted and clogged it up. I took the fuel tank and pitcock apart and cleaned them. Reassembled and added an in-line screen type fuel filter. I still have light hunting all though it is still pulling strong. Header pipes seem quite blue to me and I am getting about 75 miles before I hit reserve on the 2.5 gal tank. What do you guy's think? I'll wait to test the Edelbrock (looks like it is going to make a nice book end). What is it exactly that is so hated about the QuickSilver? Do you guys have any tuning tips for me? I do most of my riding on the highway with cross-over tires and geared with different sprockets than stock. I'm also looking for a larger fuel tank. Your input is sincerely needed. Thanks!

FWIW, I'm no expert on the dellortos or the ebrocks, but I know several people have reported great success using Mikuni BSTs on LC4s of your vintage. They've picked them up for cheap off ebay and such. That said the BSTs are CV carbs and some people have had issues when using them for MX. But this shouldn't be a problem for your type of riding.

I'm using a Mikuni TM40 on my 2000 with good results. If cost is no issue the ultimate answer is the Keihin FCR.

IMO, the best bang for the buck in a big tank for your model is the one offerred by IMS. It doesn't fit the later models too well but should fit on your 96 pretty well.

Do some searches here and on ktmtalk. You'll find lots of carb info.

Your dellorto and quicksilver will make good bookends , if your on a budget pick up the mikuni bst 40 oem on late model lc4s , they work fine unlike the quirky dellorto and brick with a couple of holes in it quicksilver.


Really appreciate the help!

My 95 620RXC came with the Edelbrock - absolute crap - no jets, can you believe it?! I got a used Dellorto off a Duke and it's a world of difference; it's run great for 2-1/2 years (with the exception of some very recent minor problems). Mine has always had a steady idle and no surging at steady speed, although it does pop a fair amount on deceleration. I've got 45 pilot, 175 main (probably too rich), needle on lowest clip. My bike has a Holeshot pipe, opened-up airbox, 3000' elevation. You can buy rebuild kits pretty cheaply he also has a complete stock of jets. I would buy a needle & seat at the same time just as a precaution. The Mikuni is probably a better choice in the longrun but the Dellorto might be worth some playing around. BTW, are you sure it's a 38mm? Mine is a PHM40.

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