Dellorto rebuild

[NYK]

Eurocarb will rebuild a pair of DHLA for close on £1000, which I think we will all agree is expensive. When I rebuilt my engine I stripped my carbs and replaced all seals, gaskets spindle bearing etc plus gave the bodies a damn good clean.

I’ve been setting the engine up this week and I can see from the 4 channel manometer that cylinder 1 has greater airflow than 2. My understanding is that one is meant to be able to twist the shaft to balance this out. Seems to me that this is guaranteed to ***k them up.
I’m really loathed to spend a thousand pounds to put this right. I really can’t see that it should be costing a grand to rebuild these carbs as all they seem to replace is those parts I’ve already replaced.
Any suggestions?

[lotusfan]

Presumably you fitted new spindles and refitted the original throttle butterflys. Sounds as if you did not quite get the butterflys to close equally when you did the rebuild. To correct this you could proceed as you suggest by twisting the throttle spindle but it is a bit hit and miss and difficult to judge how much elbow grease to apply.

For condiserably less than £1000 you could remove the offending carb and reposition the offending butterfly at the cost of new fixing screws. Did you follow the instructions in Des Hammill's book about holding them up to the light to make sure both butterflys were shut?

How far different are the readings you are getting between 1 and 2? I too have Dellortos which I rebuilt and although they are not exactly balanced I am very happy with the tickover and pickup. During the inital tune up I did twist one throttle shaft and was lucky but moving the butterfly a bit is the the way I would do it again if I had to.

[Craven]

This myth of twisting the shaft to correct air flow came from way back when very long service carburetors fitted with somewhat weak brass spindles would twist. If you try and correct airflow other than this you will of course change the relative progression between barrels.

[NYK]

Presumably you fitted new spindles and refitted the original throttle butterflys. Sounds as if you did not quite get the butterflys to close equally when you did the rebuild. To correct this you could proceed as you suggest by twisting the throttle spindle but it is a bit hit and miss and difficult to judge how much elbow grease to apply.

For condiserably less than £1000 you could remove the offending carb and reposition the offending butterfly at the cost of new fixing screws. Did you follow the instructions in Des Hammill's book about holding them up to the light to make sure both butterflys were shut?

How far different are the readings you are getting between 1 and 2? I too have Dellortos which I rebuilt and although they are not exactly balanced I am very happy with the tickover and pickup. During the inital tune up I did twist one throttle shaft and was lucky but moving the butterfly a bit is the the way I would do it again if I had to.

One of the replacement spindles was a tight fit, pretty sure it was faulty and I re-used the original. Yes I did the holding up to the light thing and at the time was pretty happy with them. Here’s a photo of the balancing, not the final setting but does show the difference. Number 1 on the right then no.2 and 4 on the left.

[mbell]

Do the carbs happen to have sure bleed screws?

[NYK]

Do the carbs happen to have sure bleed screws?

Just checked, no they don’t

[lotusfan]

Dear NYK

You don't say how the tickover is, lumpy or smooth? and have you set the slow running mixture screws yet? I ask because your manometer readings are similar to mine, maybe a little worse, I would set it so that the average of 1 and 2 is the same as the average of 3 and 4. It would be nice to have all 4 equal but I'm sure many pairs of carbs are only equal-ish.

I don't know how EuroCarb would do it but I wonder if some carb rebuilders use some sort of airflow test to make sure both barrels are balanced. Does anyone know?

[NYK]

Tickover is not very lumpy but certainly not silky smooth, I have set the mixture screws but need to revisit the timing. I absolutely would not part with a thousand pounds if they did not run some sort of bench airflow test and quite honestly it they can’t provide some sort of print out proving performance then what is one paying for. Like I said a thousand pounds to rebuild a pair of carbs where the replacement parts cost is well under £200 pounds is a lot of money.