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Old 05-06-2017, 01:39 PM   #1
[JP]
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Default Sucking and not responding..

Hello gents... it's me again!

So.. the damn Shovel is putting up a fight this year, after been such a good girl last year. It's on thing after the other.
Got a new one... this one has developed since I got that regulator burnt.

So.. 76 Shovel, kick only, SU carb

She's running fine when riding about, no problems at all, pulls like a train, can do 70mph easily etc..
However.... slow speeds.

going to try to explain this as best I can, how it happens.

3rd gear (or any gear), riding along, let go of the throttle and let her slow down..
she slows...slows... when she's going really slow I can start hearing a wooosshhhhh sucking air noise.
open throttle gently and nothing.. just the woooshhh seems to be more, the bike will not go anywhere, it even just cut out once, but most of the time just nothing happens.... unless I pull the clutch in or
blip the throttle and pufff cloud of smoke out the exhaust and she's back to life again and ready to go as long as I accelerate...

Seems like she doesnt like very low revs - but this shit never happened before.

Now. the wooooshhh sucking sound I thought was coming from fuel cap, but now I think it's coming from the carb.

trying to get my head around it for tomorrow.
could it be an air leak? the carb is sucking air from somewhere?
Any ideas? anyone experienced this before?

thanks!



I have just taken the SU off and fitted a S&S shorty super E to try out tomorrow and see if the problem goes away..but... I'd like to keep the SU, yes I know not everyone likes them...
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Old 05-06-2017, 02:02 PM   #2
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Default Re: Sucking and not responding..

SU's are a far far better carbs than an S&S boat anchor,...
when the sound was heard, did you try removing the fuel cap ??....
the vent can be blocked and cause negative pressure in the tank starving the carb of fuel. if you are using fatbob tanks the top balance pipe may be crushed as well that would cause the same negative pressure.
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Old 05-06-2017, 02:35 PM   #3
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Default Re: Sucking and not responding..

Yes, I did several test runs like that.
cap screwed in and undone, it didnt seem to make such a difference that I'd say that was the problem.
maybe slightly better, but it still happened then and again, with the cap unscrewed.

the tank is just an alien tank.

I'm going to take her out tomorrow with the S&S on it, just to see if it makes a difference, then I'll go back to the SU if she keeps doing the same.
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Old 05-06-2017, 02:49 PM   #4
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Default Re: Sucking and not responding..

maybe check the fuel line, the filter & the petrol Tap screen & rubber ''o'' rings for a blockage,....
the new ethonal fuel we are forced to use can fuck up rubber and plastics internaly,
it sounds like fuel starvation so worth a quick check,,,,
they do need a good supply of motion lotion to keep running well
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Old 05-06-2017, 08:50 PM   #5
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Default Re: Sucking and not responding..

Is it possible the tank is not venting, thus starving the carb?

Next time it does that, reach up and loosen the right-side fuel cap. See if that helps.
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Old 05-07-2017, 10:40 AM   #6
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Default Re: Sucking and not responding..

Well.. it was the goddamn carb!

She run absolutely beautifully with the S&S carb, even that problem I had of juddering at slow speeds is gone.
I have ran the SU for the last 4 or 5 years, never tried anything else different and today..what a difference! riding at slow speeds is a doddle..

think I might be ditching the SU and keeping the super E.
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Old 05-07-2017, 11:17 AM   #7
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Default Re: Sucking and not responding..

Quote:
Originally Posted by [JP] View Post
Well.. it was the goddamn carb!

She run absolutely beautifully with the S&S carb, even that problem I had of juddering at slow speeds is gone.
I have ran the SU for the last 4 or 5 years, never tried anything else different and today..what a difference! riding at slow speeds is a doddle..

think I might be ditching the SU and keeping the super E.
Good that it's fixed sir, my pan hated the Super E, ran like total ass on it. So I got a link and it's the same. Bike runs like a train! maybe give the SU a once over before you ironclad the choice!
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Old 05-07-2017, 12:25 PM   #8
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Default Re: Sucking and not responding..

you have oil in the can?
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Old 05-07-2017, 01:14 PM   #9
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Default Re: Sucking and not responding..

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you have oil in the can?
No oil, Rivera advises not to use oil, use a splash of wd40, and it had some in it.
the tickler pump is sticking as well, so I guess it's probably due a rebuild.

but even so, never my Shovel ran so well at slow speeds.
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Old 05-07-2017, 10:03 PM   #10
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Default Re: Sucking and not responding..

I'm not a SU guy but had friends who loved them. My recollection is that the oil also dampened the movement of the slide so that it wasn't jumping around. Is that your juttering?
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Old 05-08-2017, 04:31 AM   #11
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Default Re: Sucking and not responding..

Quote:
Originally Posted by joe49 View Post
I'm not a SU guy but had friends who loved them. My recollection is that the oil also dampened the movement of the slide so that it wasn't jumping around. Is that your juttering?
Actual SU carbs use oil in the dashpot. Rivera Primo SU's recommend WD40 in there.
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Old 05-08-2017, 09:18 AM   #12
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Default Re: Sucking and not responding..

Basically the damper unit has to have oil in it.
look here
http://sucarb.co.uk/technical-h-type...retter-diagram
This diagram calls the moving part the piston, I said slide.
No oil or maybe low oil, no dampening.
Dampening unit is like a shock absorber.
What I remember was the guy's ran ATF in them.
I'd ask them but they are RIP.
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Old 05-08-2017, 11:59 AM   #13
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Default Re: Sucking and not responding..

That diagram is for an SU carb. Rivera licensed that design and tweaked it some. To non-SU people, they appear the same and people use the terms interchangeably, but an SU and a Rivera are different animals. Basically, one was for a car, and the Rivera unit is bike-specific and a bit more modern.

Go here: http://www.riveraengineering.com/SUI...-0001LORES.pdf

From Page 1: Note: Do not oil in the dampener. [sic] Once a month remove the dome cap & lightly spray WD-40 inside on the piston shaft.

JP mentions in post 9 that he has a Rivera.
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Old 05-09-2017, 02:21 AM   #14
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Default Re: Sucking and not responding..

Not quite clear
he has a Rivera or not?
(Rivera advises not to use oil. is what he said, maybe reading instructions and applying that to all SUs?)
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Old 05-09-2017, 05:21 AM   #15
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Default Re: Sucking and not responding..

yes... I do have a Rivera.

SU and Rivera are different.. although all the Riveras are made by SU just downt the road from me (I know the owner) and then shipped to the US where Rivera makes their own alterations.
Been trying to convince SU to actual come up with their own design of a motorcycle SU, obviously using my shovel as testing plant haha

I've ridden again and I'm sold on this S&S carb... cruising slowly is piss easy and idles perfectly. I think this year I'll ride S&S.... then order a rebuild kit for the SU and play around with it again towards the end of the season.
have a couple of rides planned to europe end of this month and next so don't want to mess around with the SU.

only thing with the S&S is if I crack open the throttle in 3rd gear, lowish revs, when its picking up speed it kind of hesitates twice and then its ok.
I have also found that hesitation when doing constant speed 65mph or thereabouts, seems almost like a misfire but with no banging, kind of a split second stoppage on power.
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Old 05-09-2017, 10:09 AM   #16
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Default Re: Sucking and not responding..

"with the S&S is if I crack open the throttle in 3rd gear, lowish revs, when its picking up speed it kind of hesitates twice and then its ok." JP
Increase accelerator squirt.
"I have also found that hesitation when doing constant speed 65mph or thereabouts, seems almost like a misfire but with no banging, kind of a split second stoppage on power." JP
Try one size smaller intermediate jet.

Might want to disassemble and clean it also.
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Old 05-10-2017, 01:35 AM   #17
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Default Re: Sucking and not responding..

Hmmm
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Old 05-11-2017, 02:28 AM   #18
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Default Re: Sucking and not responding..

Quote:
Originally Posted by joe49 View Post
"with the S&S is if I crack open the throttle in 3rd gear, lowish revs, when its picking up speed it kind of hesitates twice and then its ok." JP
Increase accelerator squirt.
"I have also found that hesitation when doing constant speed 65mph or thereabouts, seems almost like a misfire but with no banging, kind of a split second stoppage on power." JP
Try one size smaller intermediate jet.

Might want to disassemble and clean it also.
Thanks Joe, I'm going to order some jets today, yesterday was a nigthmare of a day!

When I experienced the above (on the S&S, not the SU, seems like we moved from the SU to S&S now haha) I only had a teardrop cover with no air filter. So maybe was the fact of having no air filter in there that was causing that sputter.

Anyway, yesterday decided to put a velocity stack on the carb as don't really like the teardrop cover.
deal lord... what a load of crap the bike was running.... struggled with it on a short ride, definitely would need some jetting to use the stack, or maybe just ditch the stack. then to top it all, on the way home a seat spring broke and a bird shat on me!!

Got home took the bowl out to check the jets and have a 72 main with a 0.295 intermediate.
Reading about these seem to be the standard size for a stock Shovel, so can only assume my sputter at speed was due to having no air filter in the teardrop cover.

I'll order some jets today and have a play around.
Also what I found was if I had the accell pump too far out, to the setting where the engine is responsive when blipping the throttle on idle, then she would not start. I'd have to use choke. if I have the acell pump screw further in, then she start fine first kick.
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Old 05-11-2017, 11:33 AM   #19
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Default Re: Sucking and not responding..

Quote:
Originally Posted by [JP] View Post
Thanks Joe, I'm going to order some jets today, yesterday was a nigthmare of a day!

When I experienced the above (on the S&S, not the SU, seems like we moved from the SU to S&S now haha) I only had a teardrop cover with no air filter. So maybe was the fact of having no air filter in there that was causing that sputter.

Anyway, yesterday decided to put a velocity stack on the carb as don't really like the teardrop cover.
deal lord... what a load of crap the bike was running.... struggled with it on a short ride, definitely would need some jetting to use the stack, or maybe just ditch the stack. then to top it all, on the way home a seat spring broke and a bird shat on me!!

Got home took the bowl out to check the jets and have a 72 main with a 0.295 intermediate.
Reading about these seem to be the standard size for a stock Shovel, so can only assume my sputter at speed was due to having no air filter in the teardrop cover.

I'll order some jets today and have a play around.
Also what I found was if I had the accell pump too far out, to the setting where the engine is responsive when blipping the throttle on idle, then she would not start. I'd have to use choke. if I have the acell pump screw further in, then she start fine first kick.

I had all those same problems with the S&S, call me archaic, but I went to a linkert and my pan literally runs like a steam train. I had the same problems with starting. I turn the accel up, the bike won't start, turn it down bike starts but then sneezes through hard accel in 3rd.. I think they're a real good carb, BUT you need to get it spot on.

My link is running spot on for both pots and the bike pulls hard through the gears... I'm content but I appreciate some people especially with shovels want a bit more kick to go with the more power.
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Old 05-11-2017, 03:49 PM   #20
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Default Re: Sucking and not responding..

A lot of times, a carb without a cover or a carb with a velocity stack will try to pull the fuel mixture out of the carb inlet instead of feeding the fuel into the engine.

You might try blocking the wind off the front of the carb with your leg or hand when your riding the bike and see what happens.
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