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Newbie Carb Idler Question

jianelli

jianelli

Tuned and Synch'ed
Joined
Oct 22, 2011
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Location
Lincolnville, ME
My '81 CX 100 LM is running poorly up to 3000 or so. coughing and farting from 1000rpm up and at idle. I adjusted the idle mixture screw, which helped but did not fix the problem, so I am thinking I need different jets.
My inexperience with this shows up in that I don't know how to tell what is on there now, is it stamped on the part somewhere?
Do I buy a range of parts and see what works best? (a 50, 54, 57, 48...) or is there a "best guess?"
 
Size is stamped on the face of the jet. First I'd check that the idle jet isn't blocked, the air passage from the adjuster is clear, and that there is no water in the fuel. Also verify the float level is correct. If low, the idle circuit doesn't get fuel.
 
Thanks, I may be over my head, but do I remove the jet and look for blockage? or blow it out with air?
I've put 4 or 5 gallons of gas (93 oct) through it in the past week so I don't think it is water...
No idea how to check the float level..
Thanks again. John
 
jianelli said:
Thanks, I may be over my head, but do I remove the jet and look for blockage? or blow it out with air?
I've put 4 or 5 gallons of gas (93 oct) through it in the past week so I don't think it is water...
No idea how to check the float level..
Thanks again. John
Click to expand...

Since you are asking these kinds of questions I believe you may very well be in over your head. Your options are to locate a Del Orto manual, read through it then ask specific questions or find someone that is a mechanic. Hopefully you can find someone that will teach as they repair.

BTW, if you remove the jet, you can just try to look through it to see if there is blockage.
 
Thanks,
So I have a mechanic looking at it and he took out the original 55 pilot jets (they were clean) and put in 50's (euro stock spec...). No change in the problem & maybe it is a little worse.
.... I may need a better mechanic... Any other ideas? The plugs were blackish when I pulled them... I am using K&N air filters and exhaust pipes that are little more restrictive than the stock exhaust....
 
Needle and atomizer tube may be worn. '81, square slides or round slides? Think guzzi switched that year.

Square slide: as far as I now delorto doesn't make the accelerator pump any more, which doubles as the atomizer. But if it were the atomizer it would run crappy to redline... or maybe not..? Try new slide needles.

Round slide: Change both the needles and atomizers. Can't always see the wear.
 
Thanks, it is the round slide and I ordered the needles and atomizers from mgcyccle, according to the stock specs from greg benders site...
I really appreciate the help. John
 
So I brought it over to the best mechanic in the area and he put in the new needles and atomizers and still could not get the problem solved. We are now replacing the rubber connectors as they might be leaking (32 years old...). If this doesn't work I don't know what to do... Is there a carburetor person you all recommend that I could send it to? Anyone know of a guzzi expert in Maine?
Thanks,
John
 
If the inlet rubber replacement doesn't work, I don't know anyone in Maine. I can only think of the guys at Seacoast in Derry NH. They are probably more familiar with FI so I'd call them before bringing the bike over.
 
Well $400 later the problem is still there. New inlets, new needles, new atomizers...I also tried putting on a more free flowing exhaust and at best it was the same, possibly worse.... The pilot jets are 50's now, should I try something smaller? 45? or larger 60? It still runs great at 3000 rpm and above... Not so great in town...
Thanks for any help.. John
 
How may turns out is the idle mix screw? 2 and a half turns is ideal. If less, smaller jet, if more larger jet. However, it sounds like there are other issues as well. What position is the needle? If you want to make the mix richer, raise the needle, to make it leaner, lower the needle.
 
I had carburettor problems on my 850-T3 Cali and they all came about because the float height was wrong. The yellow Guzzi manual says turn the carbs upside down and measure the dimension from the bottom of the floats (now uppermost) to the face of the bowl flange joint. It should be 23.5-24.5 mm. I made a simple little gauge from a small piece of card with an L shaped cut-out.
I found mine were set at 18 mm which meant the bike was running rich no matter what I did with the mixture screws!!!
To adjust the float height, very carefully bend the brass arms of the floats (very carefully, I used a small pair of snipe-nosed pliers). After that it really was plain sailing. The adjustment screws for mixture and slow-running speed both worked properly and she now runs well with coffee coloured plugs.
All the best,
David.
 
jianelli said:
Well $400 later the problem is still there. New inlets, new needles, new atomizers...I also tried putting on a more free flowing exhaust and at best it was the same, possibly worse.... The pilot jets are 50's now, should I try something smaller? 45? or larger 60? It still runs great at 3000 rpm and above... Not so great in town...
Thanks for any help.. John
Click to expand...
John It sounds very much like you are suffering from "transition/progression phase problems" :sick: :sick: Have a read of this material http://www.thisoldtractor.com/guzzitech.dk/gb_en_technical_carburetor-dellorto-manual.htm

Operating ranges, scheme of phases while running
(A) 0-1/8 throttle ; idle speed screw & idle mixture screw adjustment
(B) 1/8-1/4 throttle; selection of idle jet and throttle slide cutaway
(C) 1/4-3/4 throttle; selection of atomiser and tapered needle + >>a little main jet effect
(D) 3/4 to wide open throttle(wot); selection of main jet alone

(A) .... the idle circuit and idle adjustment is set with mixture screw and idle speed screw

(B) ...progression phase, fuel mixture delivery from the idle hole is steadily replaced by mixture delivery from the progression hole, drawing emulsion from the idle circuit, and in this range choosing the correct idle jet and throttleslide cutaway is necessary. The throttleslide cutaway slightly effects the carburation up to nearly half throttle.

(C) .... high speed period , mixture delivery from the idle circuit and from the progression hole is gradually replaced by mixture from the main circuit and selection of both the atomiser and the tapered needle should then be made.

(D) ...WOT. full throttle and with all the circuits of the earlier periods operating correctly, the size of the main jet is now finally selected.


I fitted up a set of PHF30mm Round slides to a T3 with a 88mm barrels (same as yours) and could not get it to run cleanly around town and very temperamental at idle. It would even spit back sometimes when blipping the throttle!
I kept a progressive log of the jet changes etc and ended up with no cure for the mid speed issues until I read about (Guzziology?) the small emulsion tube found on some phf models. This is found in the orofice under the pilot(idle) jet and is about 20mm long has a 5mm thread hollow and several side drillings . I removed them and never looked back.
I run :128 Mains :58 Pilots :5/3 slides, with pod filters and slightly restricted lemans staintune 2 into 2s with a crossover. I should go back to 50 pilots as it is a bit insensitive to set idle.
The 5/ slides pull more juice than 6/ slides in the transition phase (off idle ie steady taking off from standing start ) The progression hole is right under the front of the skirt of the throttle slide or directly above the pilot jet tube. Not all carbs have the tubes but they all have the progression hole! My 36 mm set don't have them and are not threaded for them either.
I hope some of this helps
 
Who ever did the carb work did they:

Replace floats?

Set them correctly?

Is it the Original ignition system?

Is one plug fouled and the other clean?

Both Fouled?

Did the problem start "all at once" or have you noticed a gradual decline in performance?

Does it clear up after you get past a certain RPM range?
 
The plugs were both black and on the suggestion of bob d. here in Maine I looked into the distributor. EveryThing was very clean but the points gap was 4 thou not the 14 from the manual. Reset the points and it has run very well ever since. I might think about the dyna ignition over the winter... Any opinions? Good idea? Not worth the $180? Thanks for all the info and well wishes...
 
Well.. Well.. Well.. !!!!!! It just goes to reinforce the old pre emptive reply of:
Have you set up everything to specification.
I might think about the dyna ignition over the winter... Any opinions? Good idea? Not worth the $180? Thanks for all the info and well wishes...
Click to expand...
I suspect you may have worn out your advise allowance after that little fiasco :roll: :roll: :roll: :roll: :roll: :roll:
 
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