Carburetors in the test - YSN PHBH 30 against Dellorto PHBH 30

YSN PHBH 30 against Dellorto PHBH 30 in the test - the big comparison

With us scooter drivers, the tried and tested is popular. Mainly because there is often a wealth of experience with established components that can be drawn on. This also includes the Dellorto carburettors in the PHBH design, which have been known for decades. Hundreds of empirical values are circulating for this carburettor, which can be helpful when adjusting for a wide variety of engine concepts.

Unfortunately, Dellorto has not devoted itself to the production of carburetors as usual in recent years and the popular fuel atomizers are only sporadically available.
Of course, it is only a matter of time before the seemingly anachronistic mixture conditioners fall victim to cutbacks at Dellorto and are thus completely put out of production.

In order to satisfy the demand for the popular PHBH carburetor, another source had to be found.

One of these sources is called YSN. The manufacturer from the Far East bowed to the original and resurrected the PHBH.

Like probably many of you, I am always a bit skeptical when it comes to replicas of original parts. Especially with carburetors. After all, manufacturers of other derivatives have shown in recent years how it is not possible and you screw up a bag full of problems on your beloved vehicle that you would not have without this component.

The PHBH 28 was the first carburetor that YSN produced in this design. At the time, we ran a few tests with this carburetor to find out what we might let loose on our customers.

To do this, we compared a Dellorto PHBH 28 to a YSN 28. The Dellorto was tuned on an engine and the tuning on that engine has been ridden on the road for many miles and has proven itself.

In order to be able to compare the design of the YSN one-to-one, all relevant components from the Dellorto carburetor have been transferred to the YSN carburetor after the comparison run on the test bench. So slide, nozzle needle, mixing tube, adjusting screws, float, float needle, auxiliary, main and choke nozzle.

So if the YSN PHBH does anything differently than the Dellorto PHBH due to its design or manufacturing, then that effect would be seen on the performance measurement graph and experienced on the road.

When comparing the two runs directly, nothing was seen - no difference in behavior; which is pretty good. The test drive with the YSN on the road was also unremarkable - so that's good too.

The comparison, i.e. the components with the same specifications from the YSN carburetor implanted in the Dellorto, brought the same result. So we know that both the components used by YSN and the carburetor itself are the Dellorto template and don't cause confusion.

Enriched by this wealth of experience, we have decided to include YSN carburetors in our range.

Soon after, we sent an inquiry to the manufacturer as to whether they could also offer the coveted PHBH with a 30mm passage.

It took a while, but finally samples of the 30mm carburetors arrived.

As with the 28mm PHBH from YSN, I took a close look at the sample of the 30mm version.

Of course, the testing of the samples also includes collecting and documenting all data.

While the 28 YSN works perfectly, the 30 YSN had some teething problems. In addition to various small things such as the wrong mixing tube, a wrong choke nozzle, open channels which disabled the choke and the engine then does not start when cold and float needles that were not spring-loaded, there was the problem that the slide could not be opened completely. The pattern of the 30 carburetor only allowed a slide opening of 28,5mm.

While the YSN30 carburetors were already being traded elsewhere with the lower passage and the problems listed above, after a few contacts with the manufacturer we decided to cure the teething troubles.

Identifying and fixing the open channels in the choke system only required an email and two pictures.

We had to do more to solve the problem with the slider. A total of 3 samples of the carburetors with different approaches have gone back and forth between Taiwan and Germany. We sent an original Dellorto PHBH30 and Dellorto mixing tubes and float needle valves to YSN as a sample and after almost 4 months of sample tests, Skype appointments and waiting times, the YSN30 carburetor was just as we had imagined.

We then tested the final sample of the 30mm YSN carburettor in the same way as the 28mm PHBH before and we came to the same conclusion again. The curves run congruently and the engine runs unobtrusively when driving and without any difference to the Dellorto PHBH30.

When ordering the 30 carburetor, we also decided to equip the carburetor according to our specifications.

Idle jet 55
Main jet 125
Mixing tube AS266
Jet needle X2
Choke jet 70
Float needle valve 250
cable choke

We deliberately selected this equipment based on experience, as it gives us a very good starting point with many engines.

With many engine concepts you start with a usable set-up for the first test drives and the necessary changes are limited to a few tweaks to the nozzle box.

At 250, the float needle valve is significantly larger than in the series and covers a wide range, which extends to the use of a 190 main jet. We cannot recommend a larger float needle valve over 300 in relation to the usual concepts with shifting scooters. The high weight of the large float needle and the large bore often require a completely different set-up in the lower partial load range; concerning the slider, needle and mixing tube. If a fuel pump is used, the float needle valve should never be larger than 280. The pressure generated by the fuel pump can otherwise simply push open the float needle valve and cause the carburetor to overflow or lead to ambiguous results when tuning.

Usually, the YSN30 requires main jets in the 120 to 150 range. The basic equipment with the 250 float needle valve also offers other concepts significant security.

On our Test engine with 62mm king shaft and 244 Quattrini For example, one of these YSN carburetors also ran. Here the carburetor cross-section was sufficient for a power output of over 40 hp.

So it's still there - the well-known but new companion - PHBH30