High idling-throttle cable problem????

[Db7gtgrigio]

I have now done nearly 1000km on the 1974 DD 3.5 I bought just before Christmas and loving it now I have fixed the clutch and installed a new cam belt. Next issue is the very high idle 2500-3000rpm.

The front LH carb has about 3-4mm free play at the throttle cable although the adjuster is screwed right in and there is no jam nut. The rear RH carb has ZERO free play even thought it also has no jam nut and the adjuster screwed right in.

I removed the RH cable and measured it. Total length is 953mm. 80mm of inner cable is exposed so the sheath is approx 870mm long.

Both RH and LH cables say Venhill on them. Bike was purchased from NLM by previous owner and he did basically nothing other than a service in the 8 years and 800km he owned it.

Does anyone know the correct throttle cable lengths?

The other issue is that the idle speed austerity have absolutely no effect on the bike. I removed the RH card and dropped the slide into the bore and then screwed in the adjusting screw to see if it raised the slide, but it did not. Very strange, what am I missing????

Thanks all.

[unreal]

Just a thought but are the slides in the right way round? I seem to recall one of the exploded diagrams showing them the wrong way.
Simon

[Db7gtgrigio]

Flat end of the slide is towards the intake side NOT the air cleaner side, I think that is correct?????

[EVguru]

I might just forgive Venhill for this one.

The plastic block on the twistgrip that the cables plug into comes in two versions, with different depths of recess for the cables. It sounds like you have the shallow version.

It is possible to drill the holes deeper, buy my advice is don't! It's quite easy to destroy the block by doing so and I've not seen them as a replacement part.

It was problems with Venhill cables that got me into making my own. I had a number of clutch cables with incorrect inner and/or outer lengths and one where the cast on nipple pulled straight off.

Their throttle cables also use too thick an inner wire to properly suit the Verlicchi twistgrips.

I'd pull the ferrules off the end of the cable and cut the outer casing back a little. I've done that for someone at the AGM campsite.

A reversed slide would result in a lot of slack cable and around a 5000rpm idle.

[Daddy Dom]

Sounds like you've got lots of good tips to go on with.

For my 2c, when I went through my throttle cables last year I gave them a proper oiling. The change in throttle-action was (of course) like night and day. I simply hadn't realised how stiff and dry they had become and my riding pleasure increased dramatically as a result. It's the little things!
DD

[texaskitty]

The throttle cables on my 75 Sport are probably the originals. The cables are of different lengths, the longer one being for the right, or rear cylinder carb. The total length of this cable is 871 mm. The total length of the sheath is 781 mm.

Total length of the shorter cable is 805 mm; total length of that sheath is 715 mm.

If you push each cable right into the sheath at one end, there is 82 mm of exposed actual cable at the other end, then there is the nipple at that end.

Both cables run from the throttle to the left of the steering head; then one on top of the other below the left front petrol tank mount, then above an earth connection, then the right cable crosses over between the top, large diameter frame tube and the smaller frame tube below it, then on the inside of the high tension cable going into the black box ...

[Ralph]

My Strada is near the same but I have just by a whisker enough free play to get away with it.

[Db7gtgrigio]

Thanks Texaskitty that is just what I needed to know and the cable routing info is very useful as well

Surprised my cable is so different from an original

Cheers

[EVguru]

I'm not in the least surprised that a cable is the wrong length. It's all too common. I think only the Japanese achieved good quality control on cable lengths.

I route the cables above the brake lever on a Sport for the smoothest largest radius curves. Some factory brochures show this arrangement. It doesn't work so well for the electric start bikes as the starter button become hard to find.

[Db7gtgrigio]

Removed carbs to clean and rebuild and astonished to discover I have 2 x VHB25BS

Surely I should have one VHB25BS (Sinistra = left) and one VHB25BD (Destra = right).

The S carb mounted to the forward or left cylinder appears to have the slide reversed so the carb could be fitted with the fuel banjos on the inside and the enrichener lever on the outside. Reversing the slide does not allow it to bottom properly. Surely this must be a big contributor to my high idle problem??????

Remember this was a bike sold by NLM to the previous owner, who did basically nothing to it. Just a bit surprised this was not picked up.

Suppose I'm on the lookout now for a VHB25SD.......if anyone has one in any condition please let me know.

In the meantime, would it be OK to extend the fuel line, put the slide back in the correct way, and install the S carb on the Front cylinder. Yes,mths choke lever would be difficult to access but the bikes should run Ok......

[MickeyMoto]

Both carbs are the same. One faces forward and one backwards. The chokes are on the outside, fuel banjos inside. If you swap the right to the left it will be turned through 180 degrees and will still be correct.

[EVguru]

The left and right designations simply indicate on which side of the carburetor body the idle stop and mixture controls are located.

That's just an accessibility issue.

I'm confused about a slide being in backwards. You originally said that you had no cable slack on one carb and only a little on the other. Reversing the slide raises it up, so you'd have considerable cable slack. It also results in a very high idle and the bike would be horrible to ride.

[Db7gtgrigio]

Sorry for confusing everyone my concern I had wrong carbs and incorrect slide orientation was a load of codswallop......brain seizure.

I have now very carefully cut back cable outers with my Dremel and have achieved 3mm slack at cable adjusters. I also checked the float height and discovered it was massively out. Dellorto spec said 24mm +/- 0.5mm. Front carb was 29mm rear carb was 31mm. Corrected this and immediately the throttle stop screws became effective. The high fuel level must have made the bike way too rich because it is now running much better and revs cleanly. I synced the slides and bike going pretty well. I am still struggling to get it to idle below an indicated 2000rpm however I suspect that is inaccurate tachometer and in fact idle is lower than 2000rpm.

The idle mixture and sync is not perfect but very acceptable so I am pretty happy

Went for a twisty road ride with a friend in a 1974 Ducati 450 Desmo, which I rode for about 30 miles. Nice bike, great handling but no better than Morini and no faster than Morini and the engine vibrates a lot more than Morini. The owner paid 3 times the amount for his Desmo than I paid for my 1974 Sport, and I think the Sport was the better bike.......old Ducati prices are amazing!!!!!!