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38mm delorto off idle problem

S

sweet41k

Joined Aug 2003
27 Posts | 0+
Fresno, CA USA
I have a 95 FE600E that I bought several years ago. I took it out for the first time last weekend on a trail ride in the mountains. I cleaned and blew out the carb before going. It starts great cold, idles great, runs great above 1/4 throttle, but just blubbers terrible from off idle to 1/4 throttle. I've heard this common and hard to get rid of. Does anyone have any ideas or modified carb specs needed to correct this? I'm looking for the easiest way to fix this problem. The bike runs shifts rids and looks great except for this concern. I've heard that switching to a TM Mikuni works fine too, but what about jetting specs. I want a simple solution even it cost a little to be right. I already tried raising and lowering the neddle and adjusting the pilot screw with only minor improvement. Please HELP.
Steve
 
When you stripped the carb did you remove the atomizer jet? This is the jet that the needle slides up and down in, you will see some very small holes if these are obstructed it will not emulsify the gas properly.

You could also experiment with the fuel height.

Regards

Sparks.
 
Yes, I did check the needle jet to be sure all the little holes in it were open and they were. I really don't think float level is going to change anything because it's real bad. At times the engine will even die as you open the throttle if stopped and idling. I could find nothing plugged up at all in the carb or any of the jets. That's why I'm sure there is a problem in the jetting. I've just heard so amny stories about how these Delortos can't be fixed and parts are hard to come by locally. I also noticed that some Berg's come with a round slide Delorto, but mine is a flat slide Delorto. Are the round slide Delortos better. I have access to one off of a 98 FC501 that I could try if it's a better carb.
Steve
 
The only difference between the flat slide and the round is the flat slide pulls the air easier it's more aerodinamic.
When you say it blubbers can you define the problem with a better discription. it is either to rich or to lean one or the other.
Have a look at this site, I have put it on thread to sixdays it might help you out.
www.ducatimeccanica.com/dellorto_guide/dellorto_2.htmly
When you stripped the carb did you check all the air passages were clear in the carb body?.
I had to completely rejet the Dellorto that is fitted to the Sherco 4t that wasn't a two minute job but with persiverence I got there.
Check out the dyno report on my web site before and after to see what can be gained by a correctly jetted carb

Regards

Sparks
www.uk-motoplat.com

Steve.
 
I've never been able to get that carb to run good on a four stroke if trail riding and a smooth idle is important. Sparks is right, throttle response is much better though. Is a 2 stroke style of carb without a separate idle circuit and an air screw somewhat controlling the pilot mixture. But other than a bit of instability on the low speed circuit, it should run fine. Check that grease or air filter oil didn't drip into the air jets in the carb mouth. 95-96 Bergs were blessed with that carb. Earlier models had the round slide Dellorto as did 97-03 bikes.
dan
 
Sparks, the Ducati link in your last post was not a good address. DSDucati, I think it's running lean because it dies at times when opening the throttle from idle, but that's not a definite. Raising and lowering the needle made little if any difference.
Steve
 
Hi Steve,

Take the y off the end of the web address I don't know how that got there.
regarding leanness and richness it can give you same the problem, one of the faults on the sherco 4t was it would cut out dead from time to time the same as your problem and it was running to rich pilot jet and slide are the ones to alter at this throttle opening.

Regards

Sparks.
 
Sparks, I do have a question in regards to the idle mixture circuit. The web site doesn't depict a specific Delorto carb model. Is the Delorto flat slide adjuster screw an air screw or a mixture screw. They work backwards from each other and that might help me make some better tests. I was really hoping to have somebody tell me that the Mikuni flatslide is an easy swap and runs perfect with specific known jetting. I would then just buy a carb and the jetting nedded and be done. I don't mind working out the bugs though as long as they can be corrected. Did I understand DSDucati to say that the Delorto round slide models were better with less problems than the Delorto flat slide models? And I would think that the jetting specs for the 40mm Delorto on a FC501 would be very close to working good on a 600. Would you agree?
Steve
 
as mentioned above the moded 2 stroke vhsb 38 carb that was oem in these bikes was far better than the phm round slide carbs.
when i switched to phm 40 i really missed the tons lighter flatslide feeling and the way faaster responce-the only gain was in smoother operation.
by reading the symptoms i think that
either your float height is incorrect (it greatly affects idling)
or the litlle hole that the ait goes in at the idling circuit is blocked
or the idling jet is big
or there is some quantity of oil in to your intake rubber boot (that came out of the breather tube)

post your jetting please
 
in your carb the "screw" controls the amount of air going into the idling circuit.
the more srewed in the richer the mixture becomes-on the contrary phms are the opposite, the more csrewed in the leaner mixture becomes.

sorry to miss that but i forgot to ask if your idling speed is correct?? (1600-1700rpm)
 
If your adjuster screw is at the rear of carb it is air, if it is at the front it is fuel.
In this case if you havn't got a Dellorto dealer local it is going to be difficult to obtain the required parts and not knowing if you require leaner or richer jets and before you know where you are the money you are paying out could go towards a carb already sorted.
If there is a carb on offer that comes correctly jetted this could be the way to go in this instance.
It was easier for me because I had access to the jets I required, Dellortos have never been the easiest carb to set up but it can be done.
Do you have a local tuner that runs a dyno and do it the way i did it's alot more accurate.

Regards

Sparks.
 
Been a while since I had my 96 with the flat slide so I'm not sure if this can be done or not, but if the slide is in a carb backwards it will run like you are describing.
dan
 
Hi

The idea of the web site was to give you some idea on which jets to alter, and the under standing of which part of the carb is giving you problems
If it's just off idle pilot jet or slide cutaway. The slide cutaway is something people always over look.
But without a gas annaliser you don't know which way to go.

Regards

Sparks
 
Sparks,
I'm very familiar with round slide carbs including modiying the cutaways. I'm just not sure about doing anything to the cutaway on a flat slide. Flats and Rounds both work the same, the flat slide models are just more efficient supposedly. Being a
Delorto is just another complication to the matter because of lack of available tuning parts locally or from friends. That's last issue is why I would like to switch to a Mikuni or Keihin carb if it's a easy conversion. There has to be some buys out there that have done this and have a basic starting point as far as jetting specs. I do know a guy that has a dyno with gas analyzer, but it would still cost quite a bunch to get it dialed in. It would just be complicated and time consuming if the Delorto was used even for him because of the tuning parts situation. He already has all the Mikuni and Keihin tuning parts.
Steve
 
By far the easiest and cheapest route is to simply bolt on a 40 round slide from a newer model FE600 unless having the ultimate in performance is a big issue. I changed my 96 400 and 96 501 to round slides. With the little 400 I didn't like the loss in throttle response and went to a Mikuni pumper designed by Sudco for a race spec XR400 and was very happy with the results after jetting work. Installation wasn't easy and required machine work on the intake bell. 501 had plenty of snort so a little smoothness from the round slide didn't bother me. Would bet a 600 would be ok as well. Peter at HMS probably has a half dozen or so lying around.
dan
 
Hi steve,

I'm only giving workable options, at the end of the day it's your call, but if you can't obtain the parts it's a no go, so from what you have said a Keihin or Mikuni looks the way to go. Good luck.

Regards

Steve.
 
DSDucati,
I talked to and bought some parts from Peter at HMS a few years ago, but I can't find phone number or email address for him anywhere. Can you send me this info or post it here, please. That's a good idea.
Steve
 
No problem, Peters # is 505-870-4807. If you can't get him at the shop PM me for his home #.
dan
 
I have never been a fan of the semi flat slide 38 mm Dellorto carburetor and therefore have very little tuning data.

Personally,
I would encourage you to purchase @ the very least a PHM 40 mm Dellorto as opposed to purchasing tuning Brass for the 38.

Hope this helps.

Sincerely,
Dale
 

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