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Dellorto PHM 40 KTM 620

A

azzad

Joined Jul 2009
31 Posts | 0+
Hi all, I know I am not talking Husaberg but I believe the KTM and Husaberg share some similar tech and so far I have not gotten any decent info from anywhere else regarding the Dellorto.

I have a 97 KTM620 super comp. It comes stock with the Dellorto PHM 40 and the following jets:

Main Jet 195J 195
Needle Jet DR272
Idle Jet 45
Needle K51 2nd from top clip
Slide 40
Starting Jet 45

It has a full Staintune Exhaust and a modded airbox.

I have only had the bike for a 3-4 weeks and have given it a thorough service, clean and tidy. Valves have been set and ignition timing set.

I use a tech edge Wideband O2 sensor (ask me if anyone is interested in one of these they are very affordable) for tuning and have been able to get this thing sorted apart from idle to 1/8th throttle. Idle is all over the place and the mixture jumps around with it, when cruising it is an absolute pig at these throttle positions hunting and surging.

Can anyone suggest anything for me to try as I am about to pluck the carb again and give it another thorough clean and check. I am interested in what drilling the air bleeds achieves?

Is there any downside to running a slightly lower float level?

Regards
Dazza
 
I would start with replacing the needle jet and needle. They wear out quickly.. The settings for my 98 600 are:
main jet-170
Pilot jet-33
Needle K51- clip 2nd from top
Needle jet-DR 272
Start jet -42? ( I dont remember)
 
Don't know where you are or how you ride it but the pilot and main jets both seem pretty big.
Mine's running a 175 main and a 33 pilot and is still a little rich.
I've also dropped the float level a little bit cos when I set it using the arms parallel to the body method it tends to overflow.

SC
 
I like Dellortos and the 195 is about what I used. They are easy to jet. When riding pull the choke on and if it goes better your main jet is too small. If you turn the fuel off and it goes better it is too rich. Now have the bike idle and too the fuel tap off. Listen if it gets better while idleing for a short time (till the fuel runs out) you may find your float is out or too rich pilot. Replace the needle and needle jet as said by Coastie because they do wear quickly. Check for air leaks then set the air mixture. You will then find out if the pilot jet is too big. I don't think the super comp has a counter balancer.... am I right? Also the dellortas are really good but not the best at idling... they are racing carbs. When going slow and you need to have your finger near the clutch. A lot of people struggled with the no counter balancer bike if not used to big four strokes and never shutting the throttle. The bike is bullet proof though and would outrun a 600 Berg in open fire road, but when it got tight .....
 
Thanks all for the replies.

I use the bike for my daily and have come from a 91 DR 350, so yes this has been quite a big jump, this bike is a beast in comparison and has no trouble in lifting the front wheel with throttle input only. I took the DR for a quick spin last night and never realized how hard I had to ride it to make it go.

I got interupted when typing last night and forgot to add that it has a new float, needle and seat, needle and I am waiting on the needle jet.

The jetting is std for the 620 and according to my O2 sensor it is pretty close, maybe a little rich up top but I can live with that.

You are correct it doesnt have a counter balance shaft; plenty of good vibes :D

The reason I asked about the float level is my does spill occasionally and I thought I might have been imaging that it idled better just after turning the fuel off.

Thanks again; I will hopefully get some more tuning time this week and report what I find.

Dazza
 
hey dazza whats yer o2 sensor tool yer using sounds like a piece of kit id be intrested in for all the same old reasons lol cheers man
 
This is what I am using: http://wbo2.com/2j/default.htm

I have been using it with a rig stuck in the exhaust but I am going to weld in a bung and make it a bit more permanent.

I have also made up an LCD display for it for about $20 from a local electronics store rather than buy one of theirs.

This will tell you exactly whether you are rich or lean at all throttle positions. I have marked my throttle so I know where I am at and you acn actually see the transition between primary jet etc.

All up it cost me $300 Aus to buy and I can use it on any of my bikes or cars (diesel included).

Regards
Dazza
 
There not very big over here in Oz; not even a dealer in the capital city I live in.

Dazza
 
Ok with the float level lowered I get a much better consistant idle and idle mixture; I havent had a chance to ride it yet.
 
So after doing some more riding the problem still exists.

I have a few primary jets so I went up to a 50 and this made it worse then down to a 40 this made it better.

I was dubious of going to far away from std so I started looking for other cause it might be running rich. I thought the starting circuit might have been leaking so I made a gasket up to blank this off and problem was still there.

I am still waiting on a needle jet but I am going to try and chase up a smaller primary again.

Dazza
 
http://wbo2.com/2j/default.htm looks like an interesting tool.

In my experience the Dellortos won't give a consistent float level. Others have installed Keihin needle and seats to solve the problem, In frustration, I ultimately installed a complete FCR on my 501.

Steve
 
Hello. just my thougth. If you are using a wideband on a singlecylinder engine, the probe must be placed as close to the exhaustport as you can, becouse on lower rev you get clean air sucked back from the end of the exhaust, making the mesurement unsteady offen lean, I have used some wideband in diffrent rides and the hardest to get god readings is singles. check my gallery there is some pics. I did a adapter to put my lamba in, and i hade prefered to have it more forward but i didnt want to mess up my acra pipe to much. The low speed shouldent be so hard to get right even without a wideband. Ive never done jettings on dellorto, but ive heard they had very big problems with the quality on them, that bores and pasages could be very rough and uneven so somethimes you need to drill some passages and so . i dont know any more than that. just some experianced husaberg mecanic in sweden that told me that.

Regards
 
Thankyou for your input.

I did have the O2 in an adapter in the tailpipe but I have relocated it as close to the head as I could get it now. I will have a look at your gallery.

This is where I am picking up that it was infact rich not lean like I first thought. Sparkplug tells the same story.

I am now down at a 35 primary and it still shows rich so I am sick of waiting for my local supplier to get back to me regarding the needl jet and I will try and chase one up elsewhere.

I really dont want this thing to beat me so I am going to perserve with it for awhile yet.

Regards
Dazza
 
Thanks, I have been using a local shop that works on older Ducatis and they source their gear from Gowanlochs, I am going to see if Jaydee have them or else I was going to go overseas.

I am down in Adelaide.

Dazza
 

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