Morning All, Okay so now that the mighty KTM is finally running with some reliability, it's time to sort the finer issues out. I'm finding that since i got the headwork done the tuning is out pretty badly, it's backfiring nicely on the overrun, and is a bitch to start from cold (it was always a 2 or 3 kicker), i reckon it's way too rich. I've downloaded the instructions and followed 'em, dropping the needle etc, but i think i need someone who has access to a range of jets etc and knows how to use 'em. So the question is, who in NSW, Vic, SA or southern QLD knows how to tune the Dell'Orto PHM carbs and doesn't mind working on a KTM? These carbs came fitted original to early Ducati's, Moto Guzzi, CCM, Husaberg etc. Dyno tuning is prefered if possible.
My Guzzi Sport 1100 has PHM40's on it, and I have spent a lot of time playing with the jetting, so I will give you some pointers. First of all you need to get the idle jetting correct, one of the "problems" with delorto's is that they have much more adjustability in them than most, so are "harder" to tune thanks to this, but getting it right will reap benifits. Delorto use the idle jet to set two ranges in the carby opening, they are the pure idle, slide on the idle stop, and the transition from this range to the start of the needle jet, both of these are additionally influenced by carby slide cut away. Is the bike stuttering and hesitating just off idle? In my expereance it is in the area of idle jetting that most delorto's are out in, but an added complication is that idle mixture is influenced to a great extent by valve clearances, wider clearances will make the bike act like it is jetted too rich, and visaversa. So the first step is to give the bike a good service and set the tappet clearances as close to where that will be normally be, before doing any jetting changes. Let me know where you are at and I will talk you through the tests and adjustments. I am off on a mainland trip for three weeks, starting on wednesday, but I will be taking my laptop with me, so I will intermittantly check on progress
Someone will probably correct me if/when I am wrong, but it sound like you are running too lean. When starting from cold, you generally need a richer micture than normal, that is what the choke is for. Too lean, and it will be a bugger to start. How much difference does using the choke provide? When you have the thing running, does it become more stable as it warms up? Or does it start to bog down? If it bogs down more after warming up, it is running rich. As for the back firing. I assume you mean popping on deceleration, and not actual backfiring(burn your airfilter type stuff)? I noticed that when I put a more open pipe on my bike (leaning the mixture), I was getting a lot more popping noises.
G'day Andt, Thanks for the help, but be warned, when it comes to carbs, if it's not an Amal or an SU i'm stuffed. But here goes! The bike is a 660 Rallye, and has pretty much an open xhaust all the way through, complete with megaphone and a muffler which is really just for looks. I had the backfire issue down at wombeyan caves the other day which was very on then off the throttle, when shutting off i was getting very impressive backfire with flames almost a foot long out the pipe, which i reckon has to be fuel burning in the exhaust. When i put the engine together it had the standard head mods and required a simple cold start procedure of, choke on and kick through a few timesthen jump on it, the engine would start and run in a few kicks, wait a few secs then taake off the choke, ride away. When hot it was just a case of kick through a few times then jump on it. It'd fire straight away. Now when cold, put on the choke and it'll chuff once per kick, take off the choke and it will fire after a few kicks, if not the choke on again til it chuffs then off and kick. When hot it's like usual. At all times do not touch the throttle though or you're screwed and it floods. The bike used to have no flat spots but was very peaky, but thats the naature of the beast. Now when out of gear and i rev it slowley it has a flat spot just off idle and bogs down, i'm thinking slide maybe? When riding you can't feel it but the engine is more manageable, it doesn't feel like it's bogging down or anything, in fact it pulls like a 14 year old. Valve clearances etc are all good as the engine has just been nailed back together. Traditionally these bikes run a bit rich, but this is now a bit extreme, it used to rumble through the exhaust on overrun with the occassional pop, now it's full on canon shots, the coppers are gonna love me
Hey olddog,i will have a look what jets ,needles are in mine,its had the same cyclinder head work as yours,my bike ran fine after rejetting.....the dellorto has being replaced now with a 39mm fcr,a liitle bit of stuffing around but has given it a good hit down low,just to bad these things weigh as much as a f250,and are just as wide.
Have a look at the bottom of the choke plunger,there is a rubber bung that gets hard and develops a depresion over time,these can be pried out with a pin,not super hard but takes a bit of time and turned over to give a better seal for a few more years,make sure there is free ply in the choke cable when it off,common problem in Laverdas and Ducatis.
Good evening all.I visited JAYDEE MOTORCYCLES last year and discussed lc4 starting issues and was told tuning on the dyno is the go.He goes to the trouble in making his own needles and I think he would be a good start.They are located outside melb at New Gisborne.0354281331.While Iam here my crank goes back in soon and is there a desirable float clearance for a 80 mm crank for which one of you wise people might know.ALL THE BEST.
Crank float should be betwen 0.03mm to 0.12mm. Be very careful as you measure this up, measure it several times before you finally fit up the inner races.
G'day John, thanks that would be apprciated. I don't spose you'd be interested in selling it? I thought about your suggestion to change carbs before but thought i'd leave it as close to original as i can get it. Bad manners and all!
It is strong I am of the opinion that form should follow function, if it works well, then it looks good to me The reverse to this is the "Hardly ridable" point of view, it doesn't matter how well it works, as long as it looks good, not for me
Hey Olddog, I may be your man I mean girl, I have 2 x 41 mm pumpers on my shelf (almost new) I used to have on my duc bevel superbike. I also have a large range of jets and needles, springs, slides and gaskets, from memory somewhere lost in my shed. I do believe I can tell you how to tune your carb and get the beasty under control. If your interested I could mail you up a carby, and all the bits I have etc so you can play with em and work out what works. The jetting that is in the carbs now for a 900 ss but will be very close for 660. What main is in there now? You better shoot me a pm. We can chat.
Sorry to go of topic but...........Sylvia you wouldnt happen to have a 39 or 41 fcr carby in that shed aswell that isnt being used.
Mmmmm yes that looks like mine, althoiugh i'm not using a bell mouth. Could you get a side on pic? The side that has the mixture and idle adjust? I'm running the bike at the moment, but will yank the carb on saturday and get the jet sizes etc. Thanks for the help Sylv!
