Carb tuning for the Champ

I'm running a PW50 chinese knock off carb on my 1980 Yamaha Champ. I recently swapped over the mainjet (size 75) from my stock Mikuni over to the PW50 carb. On my recent test ride, it seems to need the choke until it is 100% warmed up. After that it runs and idle off the choke. While riding if I pull the choke up I gain a little speed. This would point me to needing a larger mainjet. What could have changed from different carb models to need a larger mainjet.

I am still running the stock airbox. I did put new uni filter element in it. I would like to get a different pilot jet as well, but not sure what kind of jet it is.

Re: Carb tuning for the Champ

The uni filter is likely less restrictive .

Jets :

https://www.jetsrus.com/

Re: Carb tuning for the Champ

punkrock randy /

UNI definitely less restrictive, but i have no air filter housing anymore either. Mine used to four-stroke at the top, not no mo. Great intake sounds too🤘🏼

Re: Carb tuning for the Champ

> punkrock randy Wrote:

> -------------------------------------------------------

> Great intake sounds too🤘🏼

Sure , until you're saying 'WHAT?' to everything said to you .

In case you didn't know , it's cumulative , irreparable damage .

You can ask me exactly how I know about that^ . No , better ask my wife . (edited)

Re: Carb tuning for the Champ

I running the same airbox just a new Uni foam element in the airbox.

Re: Carb tuning for the Champ

punkrock randy /

The 49 cc intake sounds can try to diminish my hearing, but years of concerts will likely be the causative factor 🤘🏼 Cool that the filter could fit inside stock box tho, hadn’t even tried.

Re: Carb tuning for the Champ

> punkrock randy Wrote:

> -------------------------------------------------------

> The 49 cc intake sounds can try to diminish my hearing, but years of

> concerts will likely be the causative factor 🤘🏼 Cool that the filter

> could fit inside stock box tho, hadn’t even tried.

B een there , too . A little here and a lot there , all adds to the end result .

Back to the OPs problem :

Less restrictive air filter means more air . More air needs more fuel .

How much more is relative to the higher amount of air .

I think you know that .

You might try changing needle clip and idle screw positions before spending on new jets .

Re: Carb tuning for the Champ

Just for clarification, the stock air filter is a oiled foam sheet cut to fit. I bought Uni filter foam sheet and cut it to size. I didn't oil the filter as that always gets me into trouble.

I see that treatland sells a similar knock off PW50 carb. They also have pilot and mikuni main jets available. The jet I'm using a 75 is too small. I am going to buy a few different main/pilot jets just for testing purposes.

I think with a size up on the main jet this thing will be about perfect. I will not delete oil injection, as these pumps rarely fail. I have 4 other Yamaha 2 strokes and these pumps are almost bulletproof, after lines are changed out.

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