Honda P50 owners I could use some help

I have finally had the time to finish up my Honda P50 project. I have done a lot of work to this one to get it to where it is at. From having custom o-rings made for the carb, making repairs the the wiring so that everything works to doing a top end overhaul.

It starts and runs well at idle and but once I run it up in speed it starts to misfire and sputter. If I open up the Air Screw, from the stock setting, it gets better but then I lose the bottom end and it starts to misfire. It will actually stall and die trying to get it going.

I have an original service manual and have put all the carb settings to the factory specs. I have cleaned and cleared out all of the passages in the carb.

Here is my question... The service manual says my main jet should be a #55 there is a #62 in place. I have another carb (the newer style) and it too has a #62. So I have to ask if anyone out there is running a P50 and knows what the main jet size is in yours.

The plug looks a little dark so it looks like it is running rich. I can purchase the #55 main jet but it is overseas and costs a small fortune to get it mailed here. Just want to verify if I have the right jet and the carb has issues or I have the wrong jet and need to get the right one.

Thanks for any help.

Re: Honda P50 owners I could use some help

Perhaps the previous owner upjetted to compensate for lack of tune and leaky gaskets.

Re: Honda P50 owners I could use some help (plug chop)

Mark Booth /

Here is the update.

It was 55 degrees 2 days ago and I took a long ride and kept making adjustments to the carb. I did a long run at full speed and it will clear out and wants to stay running smooth so it must be something else. Maybe a short intermittent in the ignition system.

Today there is 2 inches of snow on the ground and it does not look like it will warm up till Spring so I will winterize it and put it away for the Winter. I think this Winter I will order the better PC50 Valve Springs and install them for better top end. It will be safer too I am told. And could be the cause of the miss fire too. The Valve Springs are so weak you can install them with your finger.

If anyone has a chance to see what they have in their carb just to lay this to rest I would appreciate knowing the Main Jet size you are running.

Here is the plug after a long full speed run for those that are interested. I think it looks just right.


Re: Honda P50 owners I could use some help

Mark Booth /


Anyone know what main jet they are running in a stock Honda P50?

Re: Honda P50 owners I could use some help

Plug looks lean to me. Fix any air leaks and that should fatten it up. If there are no leaks to fix. Then look into up jetting.

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Re: Honda P50 owners I could use some help

Andrew Fleetwood /

Did this question ever get properly answered?

I have struggled to rebuild the carburettor on my P50 which was very broken and corroded. It has taken me months to realise that there are two different carburettor types on the P50 and they take different jet sizes.

Most of the information on the internet is incorrect (nosurpise there).

I finally found a reliable source of information here;

From this I realised that my P50 has the B type carburettor and I needed a size 62 main jet and 35 idle jet.

Then I discovered that the correct main jet in size 62 is made of unobtainium. I had to saw a size 60 jet in half through the thread to give me just the emulsion tube which could be screwed home,and then saw down some 8mm Keihin jets to squeeze in on top.

That worked,surprisingly. And what I then found by experimentation was that mine only runs correctly on modern fuel with a size 65 jet. 62 is too weak, and 68 is too rich. These engines appear to be extremely sensitive to jet sizing.

The extreme sensitivity to jet sizing, and the erroneous information all over the internet explains why so many folks struggle to get these running correctly. But you will need a Dremel and patience to cut jets down in order to have a choice of sizes to try out!

Hope the information helps someone!

Re: Honda P50 owners I could use some help

why couldnt u just drill to 62 four stroker?

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