Walbro HDA-120 on 346xp? Better than Zama EL17b?

[LuckyRookie]

Before I get into this question, I should start by saying I have an HDA-120 from a 262xp that I swapped the shafts/plates on with an HDA-199 to get a carb with larger venturi size on my ported 262xp. So, I now have a HDA-120 sitting around which has the shafts and linkages from a HDA-199 that I'm considering putting to use. So here is the question: Does anyone have any information on how a HDA-120 compares to a Zama EL17b? or a HDA-159a for that matter? I can tell from measuring the bore on the throttle side that there is virtually no difference in diameter between the three, but what I'm really looking for are the jet sizes. Does anyone know where to find this information?

My tentative plan was to use the modified HDA-120 on a 346xp OE rebuild I am working on, but I was hoping with all the experienced users on here someone would be able to tell me whether or not I was wasting my time fiddling around with this HDA-120. Thanks in advance for you help.

 

[Ronie]

You can look up your carb here, https://web.archive.org/web/20050202114126/http://wem.walbro.com/walbro/group2.asp?FamilyName=HDA, it only give the jet part number but you might be able to look it up. It also give the venturi size and according to that site the 199 is larger.

 

[LuckyRookie]

Thanks for the reply @Ronie I wish that those diagrams actually listed jet size for the carbs in question. The HDA-199 definitely has the largest venturi and was why the original swap was made to get that carb into my 262xp. The enigma to me remains whether there is any functional difference between an HDA-120 and an HDA-159 or a Zama EL17b. I have to believe that there is some difference between the HDA-120 and HDA-159 because it seems odd to me that Husqvarna would put functionally identical carbs in both a 62cc saw (262xp) and a 45cc saw (346xp OE), but I've certainly been wrong before...

 

[huskihl]

Internal jet size doesn’t matter as long as the h and l screws are adjustable (within reason, at least).

 

[LuckyRookie]

Well, the 346xp has been ported and there have been lots of reports in the past of people having trouble getting a stock carb to keep up with a ported 346xp at WOT. So, I was just curious if I would be gaining anything over the HDA-159/Zama EL17b by running the HDA-120 or whether I should simply get a larger carb. In the end, I'll probably just have to see how it runs, but I was just curious if someone had tried this before or had any words of wisdom they could share to ease my journey.

 

[huskihl]

Well, the 346xp has been ported and there have been lots of reports in the past of people having trouble getting a stock carb to keep up with a ported 346xp at WOT. So, I was just curious if I would be gaining anything over the HDA-159/Zama EL17b by running the HDA-120 or whether I should simply get a larger carb. In the end, I'll probably just have to see how it runs, but I was just curious if someone had tried this before or had any words of wisdom they could share to ease my journey.

It’s more than likely a tank vent or fuel system issue than a carb issue if the stock carb won’t keep up.

 

[huskihl]

Well, the 346xp has been ported and there have been lots of reports in the past of people having trouble getting a stock carb to keep up with a ported 346xp at WOT. So, I was just curious if I would be gaining anything over the HDA-159/Zama EL17b by running the HDA-120 or whether I should simply get a larger carb. In the end, I'll probably just have to see how it runs, but I was just curious if someone had tried this before or had any words of wisdom they could share to ease my journey.

I’d compare the venturi size of the 120 to the others. If it’s larger, one might assume that it would flow more air. And then it’s pretty easy to get more fuel by either adjusting the jets out, or drilling a jet hole bigger