Author Topic: Need help.....VHB carb question  (Read 620 times)

Offline robertx901

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Need help.....VHB carb question
« on: January 20, 2023, 04:18:08 PM »
Hey everyone, question for you about VHB 29 carbs.

I got my V700 up and running, but having an issue with the fuel mixture screw on the right carb. I'm using VHB 29 carbs that I bought on ebay.

The left carb seems ok -- positioned the left carb fuel mixture screw out 2 turns. When I open the screw from 2 turns out (at idle, after warmup) the revs go up, just what I would expect.
But right carb doesn't seem right. The bike, at idle and after warm up, wants to stall unless the right fuel mixture screw is in all the way. If I back it out from there the bike wants to stall.

I switched the fuel mixture screws between the two carbs, the left one remains fine, the right one is still an issue. That would seem to indicate that the fuel mixture screw isn't the problem?

Something to do with the pilot jet? Doesn't seem like the jet needle or needle jet would be involved?

Any advise on what would cause the right carb mixture screw to be acting funny be much appreciated. Thanks!


Offline Don G

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Re: Need help.....VHB carb question
« Reply #1 on: January 20, 2023, 05:32:14 PM »
Blocked idle jet passage most likely, pull it apart and give it a soak in MR Clean or some such household cleaner. Keep an eye on it to see if the cleaner is affecting the alloy, you will know by the colour that its turning, black is not really good, also it may foam as well. Soak over night or so and blow out the passages. Check on this old tractor for the appropriate cleanser.  DonG
Of course you would want to strip the carb first and have a gasket kit in hand, as well as a set of new enricheners x2.
« Last Edit: January 20, 2023, 05:37:13 PM by Don G »

Offline pehayes

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Re: Need help.....VHB carb question
« Reply #2 on: January 20, 2023, 05:57:22 PM »
'Choke' plunger not fully sealed?
No tension in the cable.  Must be some slack.  Remove the plunger and turn it over to ensure that the little rubber disc is still there.  Reinstall.  Make sure the cable exterior sheath goes slack when fully down.  Pull the cable dust boot up and out of the way for testing operation.

Patrick Hayes
Fremont CA

Online TOMB

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Re: Need help.....VHB carb question
« Reply #3 on: January 20, 2023, 07:35:52 PM »






Also, did you switch the main jet with the pilot jet locations?

They share the same thread pitch.

The inlet ports were the same size as the later Ambo-Eldo BUT the valves were much smaller so they didn't flow correctly Guzzi came up with a fix by installing reducers into the intake ports so the flow would flow better.

Also, the V700 came with carbs with the fuel bowls on the side of the carbs (I can't remember but the intake track may have been smaller also)-The VHB style the fuel bowl is underneath the carb.

You can find a picture of the inserts in the V700 parts book.

Im sure others will chime in with additional info.

TOMB
« Last Edit: January 20, 2023, 07:57:53 PM by TOMB »
TOMB

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Re: Need help.....VHB carb question
« Reply #3 on: January 20, 2023, 07:35:52 PM »

Offline Scout63

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Re: Need help.....VHB carb question
« Reply #4 on: January 20, 2023, 08:34:11 PM »
Eyeball the idle jet to see if it is clear.  Don’t rely on cleaners or compressed air.  Run a #78 drill bit or .016” guitar string through it. I would then start the tuning procedure over for both carbs after checking valve clearance cold and ignition timing.
Ben Zehnder - Orleans, MA USA

Offline Don G

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Re: Need help.....VHB carb question
« Reply #5 on: January 20, 2023, 10:59:32 PM »
Just cuz the jet is clear don't mean that the drilling in the carb body is, and 99% of the time that is the fault. DonG

Offline robertx901

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Re: Need help.....VHB carb question
« Reply #6 on: February 06, 2023, 04:14:30 PM »
Update: I took the carb off, found that the passage in the carb body was blocked -- just like you guys thought. I fixed that, put the carb back on and......the bike starts up fine and the fuel mixture screw is operating properly. A friend at the community garage I belong to helped me fine tune the carbs and my guzzi is running smooth and wants to go out and play. Thanks again for your help :cool:

Offline Tom

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Re: Need help.....VHB carb question
« Reply #7 on: February 06, 2023, 04:48:48 PM »
Just remember to run it.  Don't lug the engine.  It'll rev and likes it.  It's not a Harley. 
From the Deep Deep South out in left field.  There are no stupid questions.  There are however stupid people asking questions.  🤣, this includes me.  😉

Offline robertx901

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Re: Need help.....VHB carb question
« Reply #8 on: February 06, 2023, 07:09:40 PM »
Thanks Tom, I haven't ridden it yet, or any other old Guzzi's so wasn't sure if I should baby it or not.

Offline moto-uno

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Re: Need help.....VHB carb question
« Reply #9 on: February 06, 2023, 10:54:31 PM »
  I just love these success stories  :thumb: . Peter

 

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