Print Page | Close Window

Carbs suck?

Printed From: guzziriders.org - moto guzzi forum
Category: Technical
Forum Name: Small Blocks
Forum Description: V35 up to V750 including Breva750, V7, V9 and new V85.
URL: http://www.guzziriders.org/forum_posts.asp?TID=11773
Printed Date: 28 Mar 2024 at 10:01
Software Version: Web Wiz Forums 12.03 - http://www.webwizforums.com


Topic: Carbs suck?
Posted By: Tony G
Subject: Carbs suck?
Date Posted: 14 Sep 2020 at 15:13
So I've the old air filter housing out, and found a 1989 filter wedged in place. new one ordered.
Cleaned carbs, found plenty of grot and blown out filters.
   Fittered plunger style chokes. Started up out of curiosity, still dose not like choke so would point to rich mixture.Left hand carb ( when sitting on bike ) sucks plenty of air, at idle but stalls if I put the choke on. Right hand carb sucks very little air at idle and the choke makes no differance. 
  when the left hand plug cap is pulled the engine nearly stalls but the right hand plug makes no differance. both carbs suck air when revved. Any ideas 


-------------
I'll get their soon



Replies:
Posted By: c13pep
Date Posted: 14 Sep 2020 at 16:30
Had exactly the same on the Monza and only cured by replacing both plugs but am replacing the caps as well 

CHRIS 


-------------
you can`t have any fun in a straight line

Monza
Honda CB77 project



Posted By: Tony G
Date Posted: 14 Sep 2020 at 17:53
Thanks Chris ,I'll at those to my list SmileSmile

-------------
I'll get their soon


Posted By: chrispy
Date Posted: 14 Sep 2020 at 19:00
My bike starts quite well ,
I have noticed that you require next to no choke on these bikes starting from clap cold,
If I touch any choke it will stop the engine .I have only used choke a couple of times when bike has been stood for a week or so ,even then I only need choke for a second or two.
have you adjusted the cable free play so both carbs slides are moving together from lifting off the idle stops ,it can be done with carb balancer gauges, or if you have the filter off try the peg trick by putting half a wooden peg resting on the carb slide sticking out of the end of the carb,then as you twist the throttle you can see the pegs start moving, they should obviously move in unison,great visual aid for getting the carb slides in balance.

Cheers
Chris


Posted By: Richard Hyatt
Date Posted: 14 Sep 2020 at 19:05
If the left plug cap removal makes no difference than something is not right on that cylinder.
Can you swop the plug cap and plug to the other side , then run it and see if youve 3xported the fault to that side


Posted By: Tony G
Date Posted: 14 Sep 2020 at 19:08
I did a quick visual look with the carbs of the bike. The right hand carb dose slide befor the left. 

-------------
I'll get their soon


Posted By: Tony G
Date Posted: 14 Sep 2020 at 19:22
I was toying with that idea I' do that the next few days 
  Thanks all


-------------
I'll get their soon


Posted By: Brian UK
Date Posted: 14 Sep 2020 at 20:30
Well you do need to synchronise the carbs first. Both should open or close at exactly the same moment. Adjust the cables until they do, then see if it's improved.

-------------
Brian.

Better 5 minutes late in this world than years early in the next.


Posted By: AdrianW
Date Posted: 15 Sep 2020 at 10:26
Tony,
As Brian says you need to synchonise the carbs first.. With mine I replaced the cables (I do this on any bike new to me) and adjusted them until I could hear them both "plop" down together. You probably need the air cleaner / pods out of the way to hear this properly.

I had already refurbished the carbs at this point (new needles, needle jets & float needles) and was lucky enough to borrow a vacuum carb sync tool to finish the job.
Tickover is a bit high when hot but the plugs are a lovely colour and it runs well - one of the few success stories with my bike so far......

Cheers,
Adrian
Bristol UK


Posted By: iansoady
Date Posted: 15 Sep 2020 at 10:28
It probably goes without saying but if they're that far out make sure you wind the throttle stop screws right out before doing as Adrian says. Obviously this means it won't idle but at least your cables will be properly synchronised.Then when you do a proper synchronisation using carbtune or whatever you can tweak the cables to suit.


-------------
Ian
1952 Norton ES2
1986 Honda XBR500
1958-ish Greeves/Triumph in progress


Posted By: Tony G
Date Posted: 15 Sep 2020 at 10:45
Thanks for all the helpful info. I'll check in the next few days and report my findings.

-------------
I'll get their soon


Posted By: iceni
Date Posted: 15 Sep 2020 at 12:22
Not wishing to hijack the thread, I’d be chuffed if I could revert from EFI to a carb on the little Benelli!


Posted By: Brian UK
Date Posted: 15 Sep 2020 at 12:29
Anything is possible I've been told.

My response is usually "Try striking a match on a jelly".


-------------
Brian.

Better 5 minutes late in this world than years early in the next.


Posted By: i24
Date Posted: 15 Sep 2020 at 17:45
Originally posted by chrispy chrispy wrote:

have you adjusted the cable free play so both carbs slides are moving together from lifting off the idle stops ,it can be done with carb balancer gauges, or if you have the filter off try the peg trick by putting half a wooden peg resting on the carb slide sticking out of the end of the carb,then as you twist the throttle you can see the pegs start moving, they should obviously move in unison,great visual aid for getting the carb slides in balance.
Cheers
Chris


My procedure for this:

  • Take off both carbs, and adjust the idle adjust screws until both slides are exactly the same gap from closed. Use a 1mm drill bit as a feeler gauge. Also set the idle mixture screws the same (2 turns out).
  • Connect the throttle cables, while the carbs are still loose. Balance the carbs on top of the frame so you look into them and see both slides at the same time.
  • Adjust the cables to both slides start to move at exactly the same time when you twist the throttle. Also set the free play in the cables to about 1mm - but exactly the same on both carbs.
  • Then reassemble them onto bike.
  • Start the bike and make small adjustments as as necessary. But make sure that you turn the screws and adjusters by exactly the same amount on each carb.
If the carbs are clean and working properly, the bike should run nicely! Replacing worn or damaged throttle cables is a good investment.



Posted By: Tony G
Date Posted: 15 Sep 2020 at 19:16
Brilliant advise. Thanks.
   EFI to carbs, I had a similer thought with a car I had. and another thought at one time convert from petrol to diesel. I did'nt get round to the efi which is theoretically doable but probably not as efficient?
   As for petrol to diesel, I sold the petrol and bought a diesel.
once more thanks for advice


-------------
I'll get their soon


Posted By: Ken-Guzzibear
Date Posted: 16 Sep 2020 at 08:29
the choke on these carbs is a cold start often only needed for a very short time not a choke as such the o ring on the choke wears as does the bottom of the plunger

-------------
The Older i Get, The Better I Was


Posted By: Dennis menace
Date Posted: 16 Sep 2020 at 13:07
If you do all that has been suggested to the carbs and you still have a problem with one cylinder you might want to replace the condenser on the faulty side. I had a good spark on both sides and the the carbs seemed OK but the exhaust was cold on one side. Turned out to be the condenser but be warned I had two faulty NEW condensers from a well known Guzzi supplier before I got one that worked. I found this out by swapping the old, good condenser to the other side and that exhaust pipe heated up. The bike runs well now but does require choke for a few minutes before it is warmed up. I have plunger type chokes.
Dennis


Posted By: iansoady
Date Posted: 16 Sep 2020 at 14:28
Originally posted by Brian UK Brian UK wrote:

Anything is possible I've been told.

My response is usually "Try striking a match on a jelly".

If you dunked it in liquid nitrogen it would probably be rigid enough.....


-------------
Ian
1952 Norton ES2
1986 Honda XBR500
1958-ish Greeves/Triumph in progress


Posted By: Brian UK
Date Posted: 16 Sep 2020 at 14:40
I think it might just be a tad too cold to produce a flame then.

-------------
Brian.

Better 5 minutes late in this world than years early in the next.


Posted By: iansoady
Date Posted: 16 Sep 2020 at 16:00
But it's the match that produces the flame......

-------------
Ian
1952 Norton ES2
1986 Honda XBR500
1958-ish Greeves/Triumph in progress


Posted By: Brian UK
Date Posted: 16 Sep 2020 at 21:44
Doubt it, but it's not helping the original question.


-------------
Brian.

Better 5 minutes late in this world than years early in the next.


Posted By: Mike H
Date Posted: 17 Sep 2020 at 20:22
Originally posted by Brian UK Brian UK wrote:

Anything is possible I've been told.

My response is usually "Try striking a match on a jelly".

LOL



-------------
"Chicken nuggets don't dance on a Tuesday."


Posted By: Mike H
Date Posted: 17 Sep 2020 at 20:30
Originally posted by Ken-Guzzibear Ken-Guzzibear wrote:

the choke on these carbs is a cold start often only needed for a very short time not a choke as such the o ring on the choke wears as does the bottom of the plunger

Officially it's a "fuel enrichment device" aka "bypass starting device" and all things being correct is only really needed for cold start in very cold weather, having got all my jets sorted out (partially blocked) I next used "choke" as normally this is in summer, totally flooded it, took a while for the penny to drop why it wouldn't start (cos I'm not doing anything different). This was the VHB carb's. 



-------------
"Chicken nuggets don't dance on a Tuesday."


Posted By: Tony G
Date Posted: 18 Sep 2020 at 19:37
Mine a phbh carbs. the Carb filters have done a good job keeping the crud out. Smile

-------------
I'll get their soon


Posted By: Tony G
Date Posted: 30 Sep 2020 at 18:44
Had my bike running this afternoon. sounds quite good. although idle is high. I'll adjust as I use. I'll enjoy the end of the biking season. then finish the servicing. Thanks for all advice given.

-------------
I'll get their soon


Posted By: c13pep
Date Posted: 30 Sep 2020 at 19:29
Another success well doneThumbs Up

CHRIS


-------------
you can`t have any fun in a straight line

Monza
Honda CB77 project



Posted By: Tony G
Date Posted: 01 Oct 2020 at 08:33
Cheers Chris Fingers crossed mate.
   Tony


-------------
I'll get their soon


Posted By: Tony G
Date Posted: 05 Oct 2020 at 08:34
So after getting the bike running, and reading posts. I decided to buy a carb rebuild kit. striped rebuilt carbs. bike wouldn't start. one battery on charge overnight. next morning ,still no joy. Tank off about to take left carb off I noticed the throttle cable wasn't in the housing properly. Turned engine over. Champion. a splutter. tank back on, splutter adjustered idle screw a bit at a time. eventualy it ran again. So before going too deep, keep things simple. ( It's my new motto )

-------------
I'll get their soon


Posted By: Brian UK
Date Posted: 05 Oct 2020 at 10:33
Always check the simple things first. Don't overthink it.

-------------
Brian.

Better 5 minutes late in this world than years early in the next.


Posted By: johnno
Date Posted: 05 Oct 2020 at 10:38
Me being a very little thinker is my Ace card Lol

-------------
1100 sport corsa , Yam R1, guzzi 650tt rider


Posted By: Ken-Guzzibear
Date Posted: 05 Oct 2020 at 11:06
Guzzis are fairly simple beasties ..... when getting a fault, especially after working on it spend time looking at everything YOU touched 9/10 times you will see the issue.

-------------
The Older i Get, The Better I Was


Posted By: Tony G
Date Posted: 14 Oct 2020 at 16:40
So after patting myself on the back, I decided as it takes a few more cranks of the engine too fire up each time I start it. Splutter splutter. as if it's flooded. I'd treat my guzz too a carb rebuild. Got them from Euro carbs. The last job was new o rings on the mixture and idle screws. no splutter, just the engine cranking. when I turned the ignition off there a very loud pop! Hmm battery is on charge and kettle on.Confused

-------------
I'll get their soon


Posted By: iansoady
Date Posted: 15 Oct 2020 at 11:44
I used to get that pop on switching off sometimes. I realised that switching off caused both coils to fire and if one pot had stopped at the right point it could ignite the mixture in the combustion chamber.

-------------
Ian
1952 Norton ES2
1986 Honda XBR500
1958-ish Greeves/Triumph in progress


Posted By: Tony G
Date Posted: 15 Oct 2020 at 17:44
Interesting, dose it course any lasting damage

-------------
I'll get their soon


Posted By: iansoady
Date Posted: 16 Oct 2020 at 10:51
Not that I know of. It's strange that some people experience it but not others. Also, sometimes it happened every time I switched on & off, other times not at all.

-------------
Ian
1952 Norton ES2
1986 Honda XBR500
1958-ish Greeves/Triumph in progress


Posted By: Tony G
Date Posted: 16 Oct 2020 at 14:43
hmm. is it worth turning the fuel taps off or leave them on. Prehaps I'll stick with turning them off.

-------------
I'll get their soon


Posted By: iansoady
Date Posted: 17 Oct 2020 at 11:26
I don't think it would make any difference - but no harm in experimenting. I think I probably left mine on so there may have been a bit of leakage.

-------------
Ian
1952 Norton ES2
1986 Honda XBR500
1958-ish Greeves/Triumph in progress


Posted By: Tony G
Date Posted: 17 Oct 2020 at 17:06
Thanks Ian

-------------
I'll get their soon


Posted By: Tony G
Date Posted: 19 Oct 2020 at 15:06
Checked fuel flow, no problem. I was starting to think ignition. Then I read a post on spark plugs, on another thread. I checked the gap. 1st spark plug was a tight .25 thou. The 2nd plug gap was too wide. 
    I've set the mixture screw out 1 turn. Idle screw all the way in, then out 1 and 1/2 turns out. bike wanted to start but spluttered. I screwed Idle in 1/4 turn the engine fired. the warmer it got the higher the revs got. After I turned idle screws out 1/4 of a turn each it idled nice. I think it's happy at 1500 revs. A bit high but with use hopefully I'll get their.
    once again thanks for advice.LOLSmile 


-------------
I'll get their soon


Posted By: AdrianW
Date Posted: 20 Oct 2020 at 12:00
Tony,
I have had all sorts of grief with my V35II..  As part of this I had a go at the VHBZ carbs. Replaced needles & needle jet / atomisers, float needles etc.
It now starts and runs fine, plugs a good colour. It idles ok at first but increases to 2k (I am not confident my tacho is all it could be) when hot. I'm happy it starts & goes and can live with the tickover at present.
I find sometimes the more you mess the worse things get..

Cheers,
Adrian
Bristol UK


Posted By: Tony G
Date Posted: 20 Oct 2020 at 13:54
Your right there Adrian. it's time to stop messing and enjoy the last of the biking season.SmileSmile

-------------
I'll get their soon


Posted By: Mike H
Date Posted: 20 Oct 2020 at 14:31
If it's like the big blocks I had, it won't idle properly until properly hot, can't warm  it up properly in the garden / shed/ garage, ride it about 10 miles with a screwdriver in your pocket, stop somewhere THEN set the idle speed. Big smile



-------------
"Chicken nuggets don't dance on a Tuesday."


Posted By: Mike H
Date Posted: 20 Oct 2020 at 14:33
PS: in other words until up to temp, it won't idle throttle shut. 



-------------
"Chicken nuggets don't dance on a Tuesday."


Posted By: Tony G
Date Posted: 20 Oct 2020 at 15:40
Thanks Mike. I had the same thought this morning. Apart from the screw driver in my pocket
Tony


-------------
I'll get their soon



Print Page | Close Window

Forum Software by Web Wiz Forums® version 12.03 - http://www.webwizforums.com
Copyright ©2001-2019 Web Wiz Ltd. - https://www.webwiz.net