anyone with Dellorto carb experience

[Trevor]

I have been running a 4.3L Rover engine in my 40 which has run very well for a number of years. Recently, it started to run rough on idle with backfiring when you back off or maintain a trailing throttle (full acceleration is fine). When I started to investigate, I found that the Malpassi fuel regulator was no longer regulating and that fuel pressure was more than 10 psi (max of my measurement gauge).

I have rebuilt the regulator (a plastic pressed-in bush had fallen out of its seat causing the inlet valve to slip). It now regulates ok again and I have reset the outlet pressure to 3 psi as required for the Dellorto 45 DRLA carbs. However, the engine is still running rough and appears to be rich. Any ideas if the over pressure could have damaged the carbs and what should I be looking for before I start to take things apart. I am thinking float bowl needle valves / float level may be the culprit.

 

[Trevor]

nobody? nobody at all??

 

[Garry]

Trevor,
I have never worked on Dellotoro's, but some of the others may have. Try posting this same question as an engine running problem and see what comes of it.
Garry

 

[Andrew Robertson]

I am thinking float bowl needle valves / float level may be the culprit.

double check fuel delivery and float level for sure. Float level will have a major impact on idle and transition fuel and the commencement of the main circuit.

Cheers, Andrew Robertson, New Zealand

 

[Cliff Beer]

Trevor, the dellortos work very similarly to the webers, not a lot of difference at a basic level.

I doubt the prior over-pressure could have actually damaged anything internally. However, you may have a stuck float. In other words, the fuel pressure coming out of the float valve may have moved the float up to a point where it sticks.

Have you taken the dellortos off and drained/cleaned them?

 

[Trevor]

Thanks Andrew and Cliff for your input.

I have taken 2 of the 4 DRLAs apart so far. No problems with the floats but have found two other problems; a plugged air balance jet connecting the two rear carbs and a loose post on the throttle linkage assembly which has probably caused the carbs to be out of sync (throttle openings not in sync). Working my way through each carb and taking the opportunity to clean up the external surfaces of the castings as well; 14 years of accumulated grunge.

Fingers crossed that this should solve the problems.

Cheers,
Trevor

 

[Cliff Beer]

Thanks Andrew and Cliff for your input.

I have taken 2 of the 4 DRLAs apart so far. No problems with the floats but have found two other problems; a plugged air balance jet connecting the two rear carbs and a loose post on the throttle linkage assembly which has probably caused the carbs to be out of sync (throttle openings not in sync). Working my way through each carb and taking the opportunity to clean up the external surfaces of the castings as well; 14 years of accumulated grunge.

Fingers crossed that this should solve the problems.

Cheers,
Trevor

Trevor,

Sounds like you're on the right track. Certainly, the prior flooding of the carbs could have dislodged all kinds of dirt and debris, which then settles in odd places when the fuel level subsides. If you're checking that the jetting is consistent and everything is clean and buttoned up then you'll probably be OK when it comes time to start her up again. Incidentally, a jet guage can be handy when going through the carbs...for where some hack has previously drilled out jets rather than acquiring the right size...just a thought.

 

[Trevor]

Amazing what a bit of metal polish and elbow grease can do!