Engine rebuild, idle problem from camshaft?

[Som]

Hello,
Last year I rebuild the engine of Buddy (VW Westfalia 74). I order the big bore cylinder, (96mm) from AA piston. When I remove the engine, I realise that's a CB (72) so I need to open more the head for the new cylinder. I also ordered a new camshaft (SCAT C25) and bearing for the engine.
I also change the Empi 32/36 progressive carburetor for a Dual Weber 40mm IDF.
Now I have a problem, when it's on idle, sometimes it goes to 2500rpm alone and I can't adjust it. Normaly it's a vacuum leak but I look and I didn't found it.
Maybe de duration of my cam is too big? 238 at 0.050
The valve on the head are a little bit smaller then the 1800 because it was a 1700 originaly. I have 39.3mm Intake and 33mm exhaust.

What could I do?

[SGKent]

check the brake booster. check your linkage.
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Som]

[SGKent]

my opinion is too much cam and too much carb for a street car, especially a bus.
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[germansupplyscott]

[orwell84]

I have never run a C25, but have read up on others that have. I never got the impression that the C25 was a “big cam”. As mentioned, it’s not so much the cam itself but the combination. The more you deviate from stock, the more time and figuring need to go into making it work.

I am running a 2l T4 with a Webcam 73, original 34mm Solex carbs, rebuilt mechanical/vac advance distributor, a crappy 4 in 1 EMPI exhaust with CR set to factory specs.

I would consider it overcammed, under-carbed, with valves on the small side. The stock carbs alone probably leave a lot of power on the bench. But it just runs so well…lots of oomph moving off and on hills. It has more top end than I have the nerve to use. It idles smoothly at 950 rpm. I set out to build a reliable stock plodder with a little extra to get out of the way. So far, so good.

Keep at it, I’m sure you can make it work.

[richparker]

[Zed999]

No power under 2,500 sounds about right for that cam in a small bus engine even if the CR is right. I had a C35 in a 2l type-1 engine but that had a crank that could rev. It was very powerful from 3500-6500rpm but under 3,000 it was a dog. You live and learn. I'd accidentally built a Beetle engine for a bus. lol

The valves aren't small IMO I have 1700 heads on my 2.4L with HEAVILY worked original seats, 42mm valves and a stock cam. OK revs are limited, but it's a heavy camper not a drag car. This engine was a reaction to the C35 one above. It might not have the max HP the 2L did, but at 1500rpm it has 50HP where the 2L probably had about 10. It's a joy to drive.

Best you can do I think is fit the smallest venturis you can find which would help the low end a little, but really... it's the cam. And maybe the CR.

As for the carbs, we have people in the UK fit 40's with 28 vents to their stock 1600's. I don't know why they would do that but they say they are happy.

There will be a way to get the best out of your engine, but like myself I think you're going to struggle at lower revs whatever you do. Might be best to bite the bullet and rebuild with a stock cam, it will be much nicer to drive.

[germansupplyscott]

[SGKent]

Rich, it is all about the column of air that has to stop and reverse direction every time the intake valve opens and closes. A smaller venturi helps preserve the vacuum and gives the air column more speed at lower RPMS than a big venturi. It's the same principal of a kid on a swing. It is easier to push a kid already moving than to push a kid from a dead stop. A smaller mass is easier to push than a larger mass. Add to it that the longer duration camshaft needs a higher RPM to oscillate the air properly. The column can't exactly stop so it slams into the back of the intake valve and builds pressure before it reverses itself. If the valve opens at that point it can take advantage of that pressure. If the carb venturi is too wide then the air column moves to slowly to build pressure at low rpm.

Too many people are only interested in bragging rights. I've seen so many people boast about their engines only to see what dogs they are in real life compared to a well tuned engine. These are utility trucks that need torque, not top end RPM like a race car going thru the gears while holding a high RPM. We didn't give hoots about how well the race cars idled. They weren't driven at an idle. They didn't sit at stop lights.
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Jetfxr69]

I put a scat25 in a stock ‘77 2L FI engine for my buddys bus. we have since been trying to find what we assumed was a vacuum leak cause it just wont tune at idle. But he just ran it on a 2 hour interstate run at 70-80mph. He said it just flys down the highway and even passed a few cars ( something I cant do).

wont use that cam again, but depending on what your after, works great. again, were FI, not carbed, so this is useless info.
_________________
You can't be a real country unless you have a beer and an airline. It helps if you have some kind of a football team, or some nuclear weapons, but at the very least you need a beer. Zappa

‘77 westy Seamus
‘76 tintop Crusher
‘77 westy The Judge
‘72 tintop bastard westy Hudson

[SGKent]

each single duration camshaft has an RPM range it works at. It is that simple. The long duration camshafts do not work at idle RPMS well regardless what anyone tells you.

To get around the problem Honda came up with an innovative solution in their engines in 1989, called the VTEC engine. Variable Valve Timing & Lift Electronic Control System

They mounted multiple lobes of different durations on a camshaft and engaged them using oil pressure and cogs at different RPMs. That way a docile cam duration lobe can be used at low RPM for idle to middle range RPM, then the torquer cam duration lobe comes in to pep it up at mid RPM's, then the semi-competition duration lobe kicks in to keep the engine strong at high RPMs. Best of all worlds. At the same time the plenum and intake runners are changing sizes to keep the air volume at the perfect velocity for the RPM to get the most air into the cylinders one can get at any RPM. More air and more fuel equal more power. We in the 1970's single cam engines are limited to the ONE cam duration that works best for how we want to drive our bus. If we want to fly down the freeway at 5,000 RPM passing people that is our choice but expect a poor idle. Or we can play nice around town and maybe a little better. I personally use the WEBCAM 142 because it runs really strong from idle to about 4500 RPM then it starts to slowly taper off. I can hit redline in 3rd gear and have easily had it up to 75 - 78 on the freeway but only when passing. I do not like pushing a 50 year pushrod engine like ours that hard. Today cars have 6, 8, 9, 10 speed transmissions so you can drive 90 mph at 2000 RPM. The MDX has a top speed capped at something like 132 mph on N.American models. I think the RL was 140 mph. Shit happens really fast at those speeds. The energy stored in the tires alone spinning that fast can almost cause brakes to glow, let alone adding the mass of the car.
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Xevin]

[SGKent]

[Som]

Thank's all for the comment, I have a CR of 7.8, I don't know if it's good with this Cam.
I'm new in the Aircooled family but I want to learn.
There is a way to run Buddy with this cam? maybe I will need to stay over 2500rpm, I have a cut-off rotor in the distributor of 4500rpm, I will not break the motor.
If I adjust the valve loose (0.006 intake and 0.008 exhaust) maybe it will help?
Also I need to change the venturi for 28, I didn't look inside the carb but I think it's easy to change?

[Wildthings]

238° is less than a Web 142 (247/242°) which I ran a copy of for years. 96mm is long 7% larger than the 93mm pistons of an 1800, so there again not much change from stock. Maybe I am missing something, but I would think you should be able to make you combo work fairly well.

[richparker]

[Jetfxr69]

[germansupplyscott]

[richparker]