Request for assistance - Dellorto 40mm on Ducati 900 Replica

[Blacklightning]

Evening All,

I'm running in the rebuilt number 146, Ducati 900 Replica (MHR).

Have now completed 550 miles.

At around 350 miles a slight fault has started with the carbs. When off the gas the bike will not always return to normal idle speed - 9 times out of 10 she will settle around 2k rpm.

Blipping the throttle doesn't often sort it out.

Yet occasionally it will drop back to c1k rpm.

When starting from cold (twice) she will happily sit at c1k rpm.

She was perfect when first set up and running the first 350 miles without problem so the carbs have been perfect.

Both slides appear to be returning positively to the stops.

I think (don't know for sure yet) that it is the front cylinder running faster, not both carbs from feeling the exhaust gases from the silencers at c2k rpm.

Throttle cables free and returning.

So, I am beginning to suspect that I might have a little dirt in the air screw which is artificially enrichening the mixture.

Does that sound possible.

I plan to run a couple of tankfuls through with redex, I've had good results with other carburettor bikes using that.

Any other thoughts on what to check?

Regards

Stuart

[Craig in France]

I am beginning to suspect that I might have a little dirt in the air screw which is artificially enrichening the mixture. Any other thoughts on what to check?

Hi Stuart,

Also suspect the air passage that comes in from the front of the carb. It supplies idle air and any slight blockage here will produce the problem you describe.

(And check your float heights).



HTH

Craig

[Blacklightning]

Thanks Craig,

I'll get the compressor and air line out and blow them through. Thanks for the extra tips - I have some detailed Dellorto diagrams of the carbs so will have some homework tonight.

Though no carb specialist, I kind of suspect dirt/obstruction/dirty fuel as the bike has been running perfectly as a Swiss Watch with a lovely even 1000 ish rpm tickover solid and reliable.

Dad did always teach me to think it through - and she was running perfectly...so rather than start adjusting everything the right thing must be to track down what has happened to cause the issue and try the fix one stage at a time.

I'm going to cheat though - blow through those passages at the front you've pointed me to, clean the airscrew tip and blow the channel and redex in the tank all at one go......

You chaps have kept the enjoyment of riding a Bevel a good secret.....my goodness she is such fun to ride. On a short section of uphill twisties today that I've now ridden three times I had to haul it in towards the end of the section - looking down I saw 60 mph plus - no wonder, these tight series of bends are normally 40 - 50. A real hoot.

Thanks for the help, advice and encouragement once again.

Cheers and keep you posted.

Regards

Stuart

[Craig in France]

I have some detailed Dellorto diagrams of the carbs so will have some homework tonight.

If you have the Dell manual, Stuart, the idle circuit is described in section 3.4.1. Quick scan below.

Have a look at fig 18. The "calibrated passage" (as Dell call it) is arrowed 1. Spraying some carb cleaner down it may very well clear any minor blockage, but resist poking a bit of wire down it. It is "calibrated" i.e. reduces in size, so poking around with a metal whatever could do damage.

You chaps have kept the enjoyment of riding a Bevel a good secret.....my goodness she is such fun to ride.

[Blacklightning]

Hi Craig,

I don't have that manual - it looks helpful - quick question - where best to get hold of one?

Ebay? Amazon? or the Dellorto distributor in the UK in Reading?

S

[Craig in France]

I don't have that manual - it looks helpful - quick question - where best to get hold of one?

Free PDF download here:
http://www.motoguzziclub.co.uk/tech/del ... _guide.pdf

Hard copy from UK Carbs (or whatever they call themselves these days ... ). It's the "Guide 1.1" you want.

http://www.dellorto.co.uk/merchandise/p ... ectionID=8

They're also selling them on eBay:
http://www.ebay.co.uk/itm/Dellorto-A-gu ... _562wt_976

[BevHevSteve]

Wouldn't it be nice to have people support This Website by supporting those that support you... Yes we stock all the various DellOrto manuals and guides as well as just about everything DellOrto you could use for your Ducati..

[Craig in France]

Wouldn't it be nice to have people support This Website by supporting those that support you... Yes we stock all the various DellOrto manuals and guides as well as just about everything DellOrto you could use for your Ducati..

Steve.

EVERY time I go to the effort of checking your website to see if you have any specific item for sale. And this time was no exception. So yep, I went here:
https://store.bevelheaven.com/dellorto-carbs/

Where there is NO mention of the fact you stock the manual.

Nor is it listed here ...
https://store.bevelheaven.com/misc-dellorto-parts/

Nor it is in the 6 pages of items listed here:
https://store.bevelheaven.com/carb-fuel-related-etc/

So I reckon I did ok by you. But if you think not, please say so and I will disappear like a summer breeze.

[BevHevSteve]

In the BOOKS AND MANUALS section

https://store.bevelheaven.com/dellorto-manuals/

Maybe I should put them in the carb and fuel system section as well?

[BevHevSteve]

Hey Craig - thanks for pointing this out to me. I just added a manuals sub-section to the carb section. Ya know, I tend to think I have everything worked out on the website - but it sometimes takes someone slapping a 2x4 across my forehead to make me see that there is something lacking for me to see it........

[Craig in France]

No worries, mate. Happy riding!

[Blacklightning]

Evening All,

I guess I'm going to do more of this as I run her in, learning the hard way....well it turned out to be restorer error. I must have over tightened the manifold nuts to the head as the rubber manifold gasket failed, splitting around the perimeter and baring the steel insert - so, air leak in a big way.

Replacement fitted this morning, re-fitted carb and gently nipped the manifold and set the carb vertical using a spirit level (anorak) and she is perfect once again - completed 100 faultless miles.

So now at 1200 miles running in, have "almost" managed to keep her below 4,500 for all of that - certainly 95 plus%.

Two oil changes completed and getting ready for the third.

Having slackened, relocated and re-tightened the left hand clip on it slipped through the previously tight top yoke....

Chain needed three adjustments till the grease came out and she settled down.

Front carb came loose twice on the manifold. Rotated clamp 180 degrees to get a long screwdriver on it from the other side below.

Blue lights indicator on dashboard has stopped working as has the right hand indicator indication light on the dashboard, I have a spare for the blue lights indicator but I don't have a spare for the indicator - so will probably have to do the "led" fix.

Clutch adjusted to run fine, so long as you snick neutral before coming to a complete standstill - that's a no-no and can't get neutral that way...

But pretty much all else is just superb....can't see anything coming loose.

Bike is brilliant, love it to pieces. Have done a 200 mile run, comfortable and enjoyable. Love the roadholding, she is at home best on fast sweeping A class roads here in the UK, once the roads get tighter and twistier you need to slacken off the fuel supply.

Drives beautifully, pulls like a train, sounds divine and looks the business - yep, I really love it 1200 miles down the track. <> <> <>

Stuart

[machten]

Great work Stuart! Anything you have left is "tuning & fettling". Don't be afraid to give ashort squirt up to 6500 now. It helps bed the rings in IMHO. I'd have done that after 700km.

Kev

[tricatcent]

I am just running in my 75 900ss, and I am having the same problem with the idle speed. I am at just 400 miles. I will check the same things and see if I get the same results. I lowered the needles a notch. That has helped a lot with the rich running. I think my atomizes may be worn out. My needles only have three grooves. Is that correct?

[Blacklightning]

Hi,

I have had a second manifold rubber fail on the front head, of course with the weight of the carb on it and the angle of the manifold it is where the most problematic location sits I guess.

I suspect that the replacement manifold gaskets may not be quite as good as originals - but having said that, when I have taken the two originals out of the box of leftover bits, sure enough one of them has failed in exactly the same place, the inner seam around the metal plate has split.

I deffo did NOT overtighten this time either, just nipped enough to stop the carb opening up the gap around the manifold rubber.

I had to make a special 13mm spanner to fit inside the fairing and frame to do the job insitu.

Now I carry spare manifold rubbers and the spanner in the tool kit.

Best of luck.

Stuart