Cold weather stumbling - '67 Bug w/1600cc single port

1799 Views 4 Replies 4 Participants Last post by Bartnik, Feb 11, 2002

jackr

Discussion Starter · Feb 8, 2002

Okay, so at first I thought it was just that she was having issues with the cold (30-60 degree weather) ..
'67 Bug w/ 1600cc Single port engine ..
I have an 8 mile drive to work, all surface streets that takes me about 25-35 minutes in the mornings
I'll usually warm the car up for about 5 minutes before leaving (but when I don't warm it up, it does the same thing)
And what I find is that the car stumbles badly at lower RPMs.
Taking off in first, it feels like the car just loses power, sputters and then slowly catches as I gain speed.
Shifting from first to second (or second to third, etc) unless I run it hard, I get that same sputter the whole way in to work.
If I'm in 4th gear, on the highway doing 60-65 and I hit the gas, I have no power, then it kind of kicks in slowly, just like at lower RPMs.
New plug wires, cap, rotor, points (old condenser).
Just changed oil, adjusted valves, tweaked the carb (idle speed and mixture) and adjusted timing ..
Still need to replace the fuel filter, and I need to change the oil in the oil bath air filter ..
My next thought was fuel pump, but it's fairly new (only about 25k miles on it) so I'm hesitant to replace it .. Need to get a fuel pressure gauge and watch it as a next step ..
So, if it was only stumbling for a few minutes in cold weather, I'd figure it was just cranky ..
But I get the same stumbling the whole way in to work.
I was getting the problems before the tune-up, I was kind of hoping I'd take care of it with the tune-up .. Although, I wasn't driving it so much when the weather was good, so to the best of my recollection, the problems only really started when it got cold ..
Also, with the cold weather, the car likes to stall. The carb knocks down from a fast idle too quickly and for the first few minutes (if I don't warm the car up first) it'll stall every time I come to a stop. Even with warming the car up, I have to go out a couple of times during that 5 minutes and re-start the car, as it has stalled.
When I adjusted the carb, the idle was around 900-950rpms at regular idle ..
Not sure what mechanism it uses to determine when to come down from a fast idle, but I'm assuming that it needs to be taken apart and cleaned?
The carb is reasonably fresh; rebuilt about 40k miles ago (which now that I think about it isn't so fresh any more) ..
Thoughts?

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VW_Factor

· #2 · Feb 8, 2002

Re: Cold weather stumbling - '67 Bug w/1600cc single port (jackr)

Cold weather.. Wow.. I moved from the nice warm So Cal, to Northeastern Oregon.. I was running a Zenith 32NDIX carb, on my dual port motor. It didnt have heat risers on the manifold, and after only a few minutes of driving, I would literally get a block of ice on the carb. That would be my first thought, check out your intake manifold and make sure that your heat riser tubes are not plugged with carbon.. If they are.. You may not be getting enough heat to the carb, and it wont mix fuel and air correctly.. My car acted that same way.. My solution was dual webers. Get the carbs closer to the heads for heat, expensive, but well worth the money.. Got more power from it too.. Mileage went down a bit, but no matter. It runs excellent even when its 10 below.. Good luck..

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jackr

Discussion Starter · #3 · Feb 8, 2002

Re: Cold weather stumbling - '67 Bug w/1600cc single port (VW_Factor)

Well, that's the thing though ..
Just went out for lunch, it must be in the high 50s outside and it was still stumbling ..
Admittedly, I only drove about 15 minutes, but it never used to behave like this, even when it was cold ..
And 55 degrees is hardly cold enough for the engine to care .
Is there something else that could be going on to cause this sort of behavior?
Oh, and the plugs aren't new, they've been in the car for a good few thousand miles of sporadic use (about 8 months or 4k miles) ..
Already checked the manifold and tightened it to the block; it was loose and was causing problems a few months back, didn't check it for build-up though ..

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16v po boy

· #4 · Feb 11, 2002

Re: Cold weather stumbling - '67 Bug w/1600cc single port (jackr)

sound like the ever so loved solex carb acting up. i have been ther and done that many many times. you can rebuild em and tweak em but sometimes you just got to buy a new one! id try adjusting the little gold fuel sprayer in the carb. sometimes they will even fall out. but you want that stream of fuel to spray right to the edge of the venturi. that way it kinda mists it up and doesnt hesitate. if that dont work id bet 10$ that a new carb would solve it.

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Bartnik

· #5 · Feb 11, 2002

Re: Cold weather stumbling - '67 Bug w/1600cc single port (16v po boy)

You may need to adjust your automatic choke so that it stays on longer. This is real easy to do and I have an article on my web site, http://www.type2.com/~bartnik -- click on the technical articles page.
If that doesn't do it, you will want to verify that your intake air preheating is working properly. VWs originally had a system whereby there is an air duct that picks up air from under the cylinders and directs it via a paper hose to the air cleaner. When it's cold a flapper valve in the air cleaner will divert to pick up this warm air and feed it into the carb. This helps to warm the carb up and keep ice from forming in the intake.
Further, there is an intake manifold heating system set up. There is a pipe connected to the exhaust that runs up from the tin and joins up to the intake manifold. This uses heat from the exhaust to warm up the intake manifold, helping to vaporize the gasoline and to keep ice from forming. Sometimes this gets clogged up with carbon so you have to remove it and clear it out.
So I'd start with the choke, that's the easiest. Also make sure that intake air preheater is set up.

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