Fluctuating idle

[sonny8l3]

Hello, I have a friend with a '74 trike that usually runs very well. It just started fluctuating at idle when rolling in 1st gear. Once then RPMs are up it runs fine. He rejetted the carb, changed the carb, changed the distributor and has run out of ideas.Any suggestions ? Thanks for your time.

 

[rhino 2]

Hello, I have a friend with a '74 trike that usually runs very well. It just started fluctuating at idle when rolling in 1st gear. Once then RPMs are up it runs fine. He rejetted the carb, changed the carb, changed the distributor and has run out of ideas.Any suggestions ? Thanks for your time.

Its a long time since i messed with VW's.....71 and 73 Bugs....But ill just throw this out for your friend..

If the spark plugs wires are ok [Not Arcing]....Under the carb is an electromagnetic solenoid/switch with just one wire running to it...That solenoid could be bad or the wire is loose or off...And that solenoid only affects idle....Once the throttle is opened it does nothing to effect running.. ,

Worth a look see.... :Shrug:....

 

[peteg59]

The idle control solenoid Bob references above will cause the engine to die at idle as it basically closes off the idle circuit inside the carb. It will not run at idle. Assuming he's running a stock, solex type, pict 3 carb?

Assuming a stock 1600 engine.

Valve lash adjusted corretly?

Is he using a SVDA distributor? 009 type can cause fluctuating and other conditions.

Plugs and wires new?

The next step, if all checks out above, is to take a simple compression test...

 

[vwbug72501]

Vacuum leak? Check condition and fit of rubber boots between center manifold and end castings.

 

[DeathBySnuSnu]

So so many different things. Careful observation could lead you in a direction to investigate.

Yes the idle fuel shut off can intermittently work and be the cause.

Carburetor low speed circuits are the most common problem.

Worn shaft fits in the carburetor body does it.

Vacuum leaks like dry rot rubber boots and metal crush gaskets.

Missing ,plugged up, or removed manifold heat and the resulting manifold cold intake.

Worn distributor where the advance dont return right.

Distributor vacuum can plugged into the wrong port.

Low compression on a cylinder.

Bad intake valve, seat, or adjustment.

Fuel pressure too high or float not set right and carb spilling over fuel down the intake.

All just for the most obvious causes

 

[grandpanystrom61]

I try to keep a log book of the work I have done, date it, and sometimes make notes of stuff I did or need to do.

At least this way I can look back at when I did the brakes, or the vacum lines, or replaced fuel lines, or any wiring crap, so at least I can keep track of it all, memory is still here, but time pass by fast one month and slower another, so a year could be yesterday or weeks ago to me, LOL.

Yes it is a process, and one can only go thru the list above and see what they find. Some are simple inspection checks, others take a bit more time, but you could find/isolate the problem in a day I would think. Getting older worn out carbs to work is a pain and hard to get parts for on some models. Hope you the best.

 

[grandpanystrom61]

So as I went over my trike, well I found bad vacum hose. It is like the shit got brittle and shrank from the heat or cold. Either way it was all crap and need to find a better brand of vacum hose to use this time. What was it, stock VW vacum line from a Shop in California.