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de-inked
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Joined: September 03, 2010
Posts: 12
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 Posted: Wed Aug 04, 2021 12:59 am Post subject: lumpy power when cruising |
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my bug has been sat for a few months, so I took it for a 30-mile-cruise...
did the usual checks (oil, fan-belt, tyres etc) then set off...
about 5-miles-in I noticed the engine felt lumpy when at cruise speed... ie when accelerating it pulls like a train, I hit my cruise speed, back off, then as it cruises along the power delivery doesn't feel smooth... I've never had anything like it with previous vw engines so I'm asking - where to start looking to fix?
And here's a pic as I know we all love a pic!
Type 1 engine, 1776, twin webers
TIA |
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flat4olsen
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Joined: February 20, 2014
Posts: 342
Location: Denmark, Europe
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| Posted: Wed Aug 04, 2021 2:18 am Post subject: Re: lumpy power when cruising |
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Blocked idle jet. When cruising you at low rpm and load, you fuel is delivered by the idle jet. When accelerating, your carbs are fed primarely by the main jets, so you won´t feel the blocked idle jet
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Type 1 1968, Lotosweiss. 2109 oxyboxer engine
Early Bay 1970, Montana Red. Under construction
Last edited by flat4olsen on Wed Aug 04, 2021 3:38 am; edited 2 times in total |
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de-inked
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Joined: September 03, 2010
Posts: 12
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| Posted: Wed Aug 04, 2021 3:33 am Post subject: Re: lumpy power when cruising |
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Thank you - will give them a look  |
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oprn
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Joined: November 13, 2016
Posts: 12730
Location: Western Canada
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| Posted: Wed Aug 04, 2021 5:40 am Post subject: Re: lumpy power when cruising |
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Those air cleaner elements let in a lot of dirt, get some pre-filters on there and save yourself a lot of carb/jet cleaning and protect your piston rings.
Oh, and I would start with the right carb. You could well be dumping sludge from the engine crankcase down that one with your breather. No car manufacturer to my knowledge does that. Just the VW aftermarket people, all others vent the crankcase BEFORE the air filter or AFTER the carb to prevent messing up the carb.
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We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age) |
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FreeBug
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Joined: March 12, 2012
Posts: 4278
Location: deepest, darkest Switzerland
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| Posted: Wed Aug 04, 2021 6:53 am Post subject: Re: lumpy power when cruising |
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| oprn wrote: |
Those air cleaner elements let in a lot of dirt, get some pre-filters on there and save yourself a lot of carb/jet cleaning and protect your piston rings.
Oh, and I would start with the right carb. You could well be dumping sludge from the engine crankcase down that one with your breather. No car manufacturer to my knowledge does that. Just the VW aftermarket people, all others vent the crankcase BEFORE the air filter or AFTER the carb to prevent messing up the carb. |
IIRC, the late-model (1303) plastic air filter has the breather dumping into the lower half, so downstream from the filter, and upstream of the carb. I don't remember about oil bath, can't find the full image in my head... |
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de-inked
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Joined: September 03, 2010
Posts: 12
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| Posted: Wed Aug 04, 2021 8:08 am Post subject: Re: lumpy power when cruising |
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| oprn wrote: |
| Oh, and I would start with the right carb. You could well be dumping sludge from the engine crankcase down that one with your breather. No car manufacturer to my knowledge does that. Just the VW aftermarket people, all others vent the crankcase BEFORE the air filter or AFTER the carb to prevent messing up the carb. |
I did think the location of the breather a bit odd when I got the car (but has been running fine til recently so I figured dont mend what aint broken...!)
Thank you |
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de-inked
Samba Member
Joined: September 03, 2010
Posts: 12
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| Posted: Wed Aug 04, 2021 8:09 am Post subject: Re: lumpy power when cruising |
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| FreeBug wrote: |
| IIRC, the late-model (1303) plastic air filter has the breather dumping into the lower half, so downstream from the filter, and upstream of the carb. I don't remember about oil bath, can't find the full image in my head... |
Thanks - might go and investigate new filters etc |
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challomoner
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Joined: October 13, 2010
Posts: 1214
Location: IRELAND
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| Posted: Wed Aug 04, 2021 10:00 am Post subject: Re: lumpy power when cruising |
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| Carbs sync'd properly? |
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oprn
Samba Member
Joined: November 13, 2016
Posts: 12730
Location: Western Canada
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| Posted: Wed Aug 04, 2021 11:20 am Post subject: Re: lumpy power when cruising |
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| FreeBug wrote: |
| oprn wrote: |
Those air cleaner elements let in a lot of dirt, get some pre-filters on there and save yourself a lot of carb/jet cleaning and protect your piston rings.
Oh, and I would start with the right carb. You could well be dumping sludge from the engine crankcase down that one with your breather. No car manufacturer to my knowledge does that. Just the VW aftermarket people, all others vent the crankcase BEFORE the air filter or AFTER the carb to prevent messing up the carb. |
IIRC, the late-model (1303) plastic air filter has the breather dumping into the lower half, so downstream from the filter, and upstream of the carb. I don't remember about oil bath, can't find the full image in my head... |
Chances are that those cars had a proper PVC system and what you were looking at may have been the inlet to the PCV loop and there was a PVC valve on the intake somewhere that the fumes exited from. I am speculating here as the newest VW I ever owned was a '73 and it was so owner modified as to not have anything of the original systems in tact.
All the older cars with the oil bath air cleaner used a draught tube to my recollection.
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We had the stone age, the bronze age, the industrial age and now we are in the age of mass deception and mind control for corporate profit. (The mass media age) |
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Ohio Tom
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Joined: February 09, 2006
Posts: 1660
Location: Marshallville Ohio
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| Posted: Wed Aug 04, 2021 12:58 pm Post subject: Re: lumpy power when cruising |
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does it feel like 2 cyls dropping out at light cruise?
If so, then it's likely just a sync issue.
Carbs being out of sync will show up during light cruise.
The way to check: Engine off... grab the throttle cable and just pull on it so the carbs just barely open above idle (like a light cruise). Do both carbs open the same amount? Look at the idle speed screws and make sure both left and right carbs have lifted off the screw the same amount.
If not, adjust a pushrod to make it so they both open at exactly the same time.
That's the biggest single reason why dual carbs run like crap.
Sync is most important to good running. |
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de-inked
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Joined: September 03, 2010
Posts: 12
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| Posted: Thu Aug 05, 2021 12:18 am Post subject: Re: lumpy power when cruising |
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thanks baz76 and Ohio Tom
will check sync/balance as well |
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mikedjames
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Joined: July 02, 2012
Posts: 2742
Location: Hamble, Hampshire, UK
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| Posted: Thu Aug 05, 2021 11:30 am Post subject: Re: lumpy power when cruising |
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The other thing, with it being Weber carburettors is that when you go to cruise, your fuel demand drops, the float chamber fuel metering valve leaks and the fuel level rises one side..
you end up with one side going very rich with drips of fuel down the throat of the carb
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Ancient vehicles and vessels
1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.
1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy |
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Willin
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Joined: October 10, 2019
Posts: 109
Location: Bozeman Mt
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| Posted: Sun Apr 30, 2023 9:34 am Post subject: Re: lumpy power when cruising |
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The title to this was exactly what I was experiencing!
And one barrel was not responding to the idle mixture screw.
Pulled the carb,( several times) blew out the idle passages. Wide open. Then I ( finally)checked the carb top. Blew one way thru the idle bleed, then the other way. A blob of something came out! I think it was a blob of sealant, which I had glued the gasket to the top with. The blob was kind of floating around in that space.
Buttoned it back up. Runs great again!
Just thought I'd share. |
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