32 replies to this topic

[sonscar]

Would running out or too much fuel affect the vacuum gauge?The motor is just a pump?Steve..

[Ethel]

The converse could be true - if it's recording an air leak that's bypassing the carb,

[Kevybmini]

I’m at a loss, lowered the fuel pressure and it still the same - runs fine for ages in the garage revving it ect. Drive 1/3 mile and it starts - vac gauge all over the place and have to pull over. 20 seconds then drive back home. 

[Ethel]

That sounds like a dashpot issue. Is  there oil in the damper tube? Damper damping? Spring springy? Communication ports  (holes by needle & through rear gasket face) communicating?

[Kevybmini]

Had the carbs stripped today and blew out the jets and checked everything. So odd

 

dash pots are fine - could anyone suggest why it’s only when the engine is under load. Thrash it in the garage with no issues 

[Ethel]

It will need to be under load to lift the piston. At idle the revs rise without needing much extra power so the throttle has less effect than piston.

[68+86auto]

Latest conclusion following much much messing about. The fuel pressure is too high so going to turn it down to 2psi. Was chasing not enough fuel but think it’s too much and flooding the engine. Update to follow when it stops raining this weekend. Thanks for all the replies

Get rid of the regulator and get the correct pump. Regulators cause issues. To reduce pressure they reduce flow.

[68+86auto]

Had the carbs stripped today and blew out the jets and checked everything. So odd
 
dash pots are fine - could anyone suggest why it’s only when the engine is under load. Thrash it in the garage with no issues

Check the ignition system.

[Kevybmini]

Might change the plugs again, 

[Kevybmini]

It will need to be under load to lift the piston. At idle the revs rise without needing much extra power so the throttle has less effect than pistonah right - thanks

Ah right thanks 

[cal844]

What coil do you have fitted?

[Kevybmini]

What coil do you have fitted?

Aldon dizzy and 3 ohm flame thrower 

[Kevybmini]

No 1 spark plug is very white if that makes any sense. No 2 normal 

[Cooperman]

With my twin H4 carbs on my 'S' I run at 3.5 psi from my twin Facit pumps.

[imack]

No 1 spark plug is very white if that makes any sense. No 2 normal

Possibly running excessively lean at full throttle, causing the exhaust valves to overheat and bind in the guides, preventing them closing and engine dies. Lack of compression so won't restart. Valves cool sufficiently after 20-30 seconds and free off adequately in guides allowing them to close again. This would account for vacuum gauge readings too.
If the above should be the cause, the valves and guides will need replacing and the cam and followers will likely be wrecked as well.
Have you had it set up on a rolling road since modifications have been carried out?