2-stroke carbs USUALLY have a brass spray tube sticking up from between 4 and 10mm. Stay clear of this type of carb, it is possible to jet them in but would require a total different set of jets and won’t be listed below.
Where the needle comes out as the slide is raised, a brass spray tube should stick up protruding into the main carb hole, if the brass spray tube is flat to the carb casting then the carb is a four stroke type. To identify a two-stroke carb, look down the main carb hole. All information given below is presuming the carb is a two-stroke type carb. Today newer versions have come along so we have updated this information from the older days of the 80's and 90's. These carbs over the years have mainly been Amal and Dellorto carburettors with sizes ranging from 22mm to 39mm in tuned engines. These carbs have come and gone depending on fashion or availability at the time. Lambrettas over the years have used various carbs. This is MB's way and should set your engine for a long life.
#Dellorto phbh 28 main jet how to
Different people and companies suggest different methods of how to run-in. I will try to pass on my knowledge to help make your job much easier without complicating the issue. Jetting is very misunderstood and can take years of experience to set a carb correctly. Today there are a number of aftermarket Twin Tank conversions and long range tanks available, these tanks holding extra fuel helps with head of fuel so some engines may flow fuel well these days - BUT always check these tanks fit with our MB inlet manifolds and carbs used.
#Dellorto phbh 28 main jet full
Tuned engines tend to use up more fuel per gallon (especially TS1-RB type engines) a good way to help this problem, would be to have a Twin Tank Conversion by having your petrol tank and tool box modified, this will increase full capacity to approximately 13 litres. Also if cable run against the float bowl fuel will leak. It has been known for the push in needle valve to come loose and petrol will come out of the over flow pipes so check this if fuel leaks. We haven't found the need for different floats, needle valves or needed to alter the floats. We have always found these carbs as they come from the factory that they flow plenty of fuel for any tuned engine. Genuine carbs are not bad at supplying fuel but the pattern carbs are not so good - because of this MBS do not use Kiehin carbs any more! So many manufacturers now make copy the PWK type carb, we've found even if you do manage to drill out the float valve or the holes either side of it fuel flow doesn't increase! The internal hole feeding it is far too small, when the carb is modified then the fuel flow is good enough for a TS1. Some recommend drilling out the float needle valve, we don't recommend these as they never let the float valve seal and when the fuel tap is turned on fuel leaks everywhere. Fuel flow can be adjusted by bending the float arm, we see this tip on forum threads but only helps the problem.
But on a TS1 or high revving or powerful engine the engine can need more fuel than the carb can give! PWK's don't have removable float needle valves or smaller floats or larger float bowls as does the other carbs mentioned. The down side of the PWK type of carbs is the fuel flow is slow, these are excellent on mild or low revving engines and usually work fine. PWK Type carbs, Kiehin, BGM, Stage6, OKO, Koso
None converted carbs will get fuel starvation below 3/4 of a tank, (mainly on fast high revving engines).Ī word of warning! Using an Amal power-jetted carb on a TS1 engine could result in fuel starvation at high rpm as the carb is at an angle and where the Power Jet is would suck air! Convert the carb to a none power jet type. A word of warning! We have found that all flat slide Dellortos have a fault from the factory and require what we call a blue print modification.
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