rich running

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Scottish888
Posts: 207
Joined: Wed Feb 07, 2018 1:47 am
Location: Edinburgh, Scotland UK

rich running

Postby Scottish888 » Wed Apr 22, 2020 1:15 pm

First run out with my ducati with its rebuilt engine, it starts easily, gets off choke within a minute to idle fine.
When riding it, the bike will not run well above 1/4 throttle. Gassing it up a long hill, gives nothing, just splutters like it is too rich.
I can ride ok if using less throttle.
Just stripping the carb (again) the needle was in the middle, so will try on the top notch, the plug was sooty. Jets are all clear, carb is clean.
Dellorto VHB 29A.
Any tips?

Jordan
Posts: 983
Joined: Fri Dec 24, 2010 11:29 am

Re: rich running

Postby Jordan » Wed Apr 22, 2020 1:18 pm

Try without air cleaner.
Check enrichener (choke) plunger fully closes.
Check float height.

ranton_rambler
Posts: 275
Joined: Sun Jun 04, 2017 11:33 am
Location: Stafford UK

Re: rich running

Postby ranton_rambler » Wed Apr 22, 2020 1:48 pm

Are you happy the ignition advance is working properly?
Is the engine and carb set up with standard specification? If it won’t go past 1/4 throttle it can’t be main jet, more likely atomiser size or needle. If you hunt on ‘net you can easily find Dellorto needle profiles and with a bit of measuring you can see how much throttle gets you onto the tapered part of the needle.

Scottish888
Posts: 207
Joined: Wed Feb 07, 2018 1:47 am
Location: Edinburgh, Scotland UK

Re: rich running

Postby Scottish888 » Wed Apr 22, 2020 2:33 pm

Just checked the carb,
jets look clear, float height is ok and closing off. filter is new.
Checked choke plunger, is is seating fine when closed and operates ok.
Not tried the ign advance yet but it was set statically, it is the ducati eletronica system.
Will give it a run with the needle on lowest position and see what difference it makes.
Thanks

blethermaskite
Posts: 133
Joined: Thu Mar 01, 2018 1:06 am
Location: northern ireland

Re: rich running

Postby blethermaskite » Wed Apr 22, 2020 3:12 pm

Its a long time since I threw the last vhb carb in the bin :) (I really don't like them) but just check the choke plunger........I think if my memory is correct? there is a little rubber sealing disc in the bottom of that plunger, if it is damaged or hard with age it won't seal properly and will cause all sorts of weird mixture faults.
Stay well,
Cheers,
George

Scottish888
Posts: 207
Joined: Wed Feb 07, 2018 1:47 am
Location: Edinburgh, Scotland UK

rich running?

Postby Scottish888 » Wed Apr 22, 2020 8:49 pm

Thanks all for the advice, I stripped and cleaned the carb, all looked ok with nothing sticking.
The choke plunger is seating ok and free enough, there is a rubbber seal in it and likely it is hard as it will be original.
I moved the needle to the lowest position, bike started fine, off choke within a minute and idling.
Took it for a run, there is a long hill near my house so ideal to test. Bike would not rev beyond 4500..5000 was sputtering then nothing, just totally bogging down. Had to go up the hill in second as did not want to lug it up in third.
Not checked the plug yet, will see in the morn.
Not sure if this is fuel or ign.Really seems like a fuel side issue but middle or lower needle made no difference so maybe not?
If ign what can be done? it is electronic. Not checked it with a strobe but any advance will be done by the ign controller.
Happy to dump the Dellorto, I have had good results with OKO flat slide carbs on other bikes.

Thanks again

Duccout
Posts: 261
Joined: Wed Feb 05, 2020 1:20 pm
Location: Essex UK

Re: rich running

Postby Duccout » Wed Apr 22, 2020 9:41 pm

It is very hard to find the cause of something like this, which could be ignition or carb related. Is the plug new? Have you checked to see if there could be an air leak at the manifold rubber spacer? As the bike has been laid up for a while the carb could be internally corroded. I doubt moving the needle will have any effect. Sooty plug...... I wonder if the float needle is seating properly?

You will either get lucky and find the cause easily, or go nuts chasing your tail.

Jordan
Posts: 983
Joined: Fri Dec 24, 2010 11:29 am

Re: rich running

Postby Jordan » Wed Apr 22, 2020 9:57 pm

I don't know what I'm doing wrong, but I get fantastic reliable performance from my VHB.
If anyone wants to discard theirs, please let me know.

Scottish888
Posts: 207
Joined: Wed Feb 07, 2018 1:47 am
Location: Edinburgh, Scotland UK

Re: rich running

Postby Scottish888 » Wed Apr 22, 2020 10:01 pm

Thanks Duccout,

The rubber spacer is original but looked ok, will check it again tomorrow.
Float seems to seal ok with a blow test when apart. Could be a lack of fuel rather than too much.
More stripping and testing tomorrow.

Regards

graeme
Posts: 705
Joined: Sun Mar 25, 2012 12:00 am
Location: Tasmania Australia

Re: rich running

Postby graeme » Wed Apr 22, 2020 10:01 pm

Bin the VHB and use a modern carb.
Unless they are new you will be forever chasing problems

Graeme


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