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Cursing issues at 40mph


PeterCS
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had my engine rebuilt last year due to compression issues. Good compression now.

got the engine professionally (supposedly) tuned up this week - starts well, idles well, and is fine if accelerating. But the car jerks annoyingly is just cruising on suburban streets.

Set up - 74 / not a tiki / manual choke / all new ignition components / electric fuel pump.

 

I have spent enormous time and money to get this car running properly and am a bit frustrated.

Next step?

PeterCS

74 2002 BMW Inka

82 315 Baur

 

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Just to start off the discussion...during part throttle cruising at relatively low speeds, the gas supply through the carb is coming from the idle jets, not the main jets.  So you might want to check the idle jet sizes to see if they're correct.  And "correct" depends on other engine variables such as compression ratio, cam, igntion setting etc.

 

There may also be a vacuum leak somewhere that is small enough not to upset the air/gas ratio under acceleration or high speed, but will upset the mixture at a steady, low speed.  You can check for vacuum leaks with a can of carb cleaner (or an unlit propane torch) sprayed around possible leak sources.  (Just be careful doing this around a running engine)   If the idle speed momentarily increases, you've found your leak.

 

mike

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25 minutes ago, PeterCS said:

And a Weber 32/36 carburetor.

The engine rebuild included new larger pistons.

Might this mean that I need different jetting in the carb?

thx,

PeterCS


And was the carb (a.) new, (b.) freshly rebuilt, or (c.) “the same old carb you’ve had forever”?


When were the fuel filters last changed or cleaned? Is the electric fuel pump new?

 

Regards,

 

Steve

 

 

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2 hours ago, PeterCS said:

had my engine rebuilt last year due to compression issues. Good compression now.

got the engine professionally (supposedly) tuned up this week - starts well, idles well, and is fine if accelerating. But the car jerks annoyingly is just cruising on suburban streets.

 

You have a manual choke, so you can try this quickie-test:

 

When the jerking occurs, pull the choke cable out a bit -> that’ll richen the air/fuel mixture (by closing the choke flaps) and - if it smooths out - it likely points to a lean jetting condition. -KB

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I vote carb issues.  Jetting... float level...

 

EVERY engine wants slightly different jets, so the piston size matters in theory,

but in practice, it doesn't affect things as much as individual engine and carb variations.

 

But timing comes into play, too, especially if there's a vacuum- 

advance distributor on there.

 

t

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The car has an electric pump because I put in a tii engine. 
I restored this car 15 yrs ago. It has never driven well. So I broke down and had the engine rebuilt during the pandemic. Was hoping that it would solve the problem. 
the carb was new 15 years ago an I doubt that it has more than 1500 miles on it. I think my intake manifold is standard. 
keep the ideas coming. 
thx, 

PeterCS

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2 hours ago, PeterCS said:

The car has an electric pump because I put in a tii engine. 

Tell again what you have?  A 2002Tii car or a 2002 that was originally with a carburetor?

The Tii engine is just the bare engine fitted with a carburetor and associated downdraft manifold?

The fuel pump is the Tii pump or another low pressure electric pump?

 

Edited by jimk
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