Dellorto Oddities

GregT

GregT

Hero member
Location
Christchurch NZ
Some of you may remember me asking about suppliers for Dellorto brass replacement pieces for a chap around the corner from me.
The pieces were sourced and the carb set went to a local "carb specialist' - who I'd never heard of. Anyway, job done, But the owner spotted something and brought them to me for an opinion.
He'd noticed that on one slide the brass plug at the lower end of the accelerator pump ramp was missing...Leaving a hole in the slide. We agreed that this was not desirable, but as we're in NZ and getting a replacement slide ain't easy, I made and fitted a brass plug. No probs so far...Anyone else found a slide with no plug ?

Once the set was reassembled I noticed that they would not move in sych. The outers in this set moved with no lost motion but there is a noticeable lag from the center slide. Once the lost motion is taken up, they're in synch.
No loose mechanical joints, no adjustment - it has to be different length lift cables.
He's got the cables which came out of them and a full set of new went in, so I suggested he try swapping cables till he had a set which worked correctly.
IMO the guy who did his carbs should have done both the plug repacement and sorted the lift cables...but hey, I'm an old cynic.
Anyone found this problem ? Am I right thinking it's the short lift cables differing in length ? Any quick fix ?
 
Greg,

I'm assuming your talking about throttle slides... :D

All cables the same length (well, they should be), it's the choke cables that have the inner one shorter than the outers.  The later rods as used in the RGS are more durable than the earlier cables. 

Try shifting the actuater arms (under the top carb cover) on the shafts.  Loosen the screws a little and you can shift the arms through about +/-5? movement.  Then there is the possibility that the brackets holding the carbs together are bent/warped/fucked in one manner or another.  Check the adjuster arms on the linkage shafts haven't been tampered with, a slight bend in one or the other direction drastically alters effective arm length, which has great influence on throttle lift action.

Never come across a missing brass plug...

HTH,
piet
 
GregT said:
He'd noticed that on one slide the brass plug at the lower end of the accelerator pump ramp was missing...Leaving a hole in the slide.
Click to expand...
Greg, I'm pretty sure the brass plug seals the hole where a light spring is in place to exert minimal pressure on the needle, once in place. No prob to fit a new one, but if there's no spring in there, it's not doing anything other than filling the hole. I have noticed that the springs compact with use and become ineffective as slides wear.
 
Piranha Brother 2 said:
Greg, I'm pretty sure the brass plug seals the hole where a light spring is in place to exert minimal pressure on the needle, once in place. No prob to fit a new one, but if there's no spring in there, it's not doing anything other than filling the hole. I have noticed that the springs compact with use and become ineffective as slides wear.
Click to expand...

Hmm, 3 brand new slides. The two with plugs fitted didn't seem to have any spring loading on the needles. The plugs however did encroach on the needle holes to the point that they limited the needle free movement - so I copied this.

Thanks for the clarification Piet. I'm too used to jap carbs where if an arm is screwed to a cross shaft, it's designed not to move...We'll have a look at it again and see if the outers can be tweaked one way and the inner the other direction to eliminate the difference.

I didn't charge him for what I did as I was of the opinion he'd been screwed by the guy who did the job.
 
sfcpiet said:
..  Check the adjuster arms on the linkage shafts haven't been tampered with, a slight bend in one or the other direction drastically alters effective arm length, which has great influence on throttle lift action. ..
Click to expand...
+1
Often, I've had to re-twist a set of external lever arms to get an outer carb to sync again with the centre carb.
Just a slight twist in the flat lever arms can throw out the available movement left in the adjusting screws.
Why these lever arms can get twisted so bad is just another bloody DellOrto mystery    :(
  Mark
 
All cables the same length (well, they should be), it's the choke cables that have the inner one shorter than the outers.  The later rods as used in the RGS are more durable than the earlier cables.

Can the later rods be installed as a swap from the cables? If so, availability? Seems like most strand cables stretch over time and use and this would cause uneven throttles..the rods more reliable.
 
PHF-ROD.jpg


Part number 11003?
 
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