4

I'm working on a custom built trike based on a 1600cc Air-cooled VW engine.

I'm a specialist auto-electrician and these engines are a bit before my time so I'm struggling to work out what is wrong.

The engine has a Solex carb which requires two 12v feeds that are both present. Is has various vacuum ports that are blanked off.

The distributor doesn't have vacuum operated advance/retard. The points look new.

The engine runs fine when cold, leave it overnight and it runs, revs and drives perfectly.

When it is warm it has no power you can barely pull away, it also back fires extremely bad while accelerating.

The owner seems to think the engine has recently been rebuilt.

What would be causing this and why would it do it when hot?

Newbie Noob
  • 2,792
  • 11
  • 23

2 Answers2

2

This engine can be prone to detonation, which can be aggravated by lean mixture and hot spots in the cylinder. I would check out timing as well.

If that is not the issue, then I would be looking at the spark intensity (voltage) with a spark tester (that is adjustable to give voltage indications).

I find it interesting that there is no vac advance...how does the timing change for higher power draws?

Is there a centrifugal advance for the timing, which is perhaps binding a bit?

Poor timing and hot spots with an air cooled engine are frequent causes of poor operation at high engine temps. Lean mixture can cause higher than normal cylinder temps, but the fact that the engine runs OK when cool discounts mixture as being a primary issue.

mongo
  • 2,115
  • 10
  • 17
1

There were two things that I done that fixed this issue:

The automatic choke was well out of adjustment so I adjusted this and then readjusted the fuel mixture to suit.

There was still a problem that made me lean towards a fuelling issue, my theory was that the fuel was heating up where the fuel pipe runs across the exhaust manifold and where it had custom manifolds to suit the trike frame the carb was very hot so I rerouted the fuel pipe and made a heat shield for the carb and this cured the remaining issue.

Newbie Noob
  • 2,792
  • 11
  • 23