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Message started by Michael L on 08/05/14 at 14:43:08

Title: Pilot jets
Post by Michael L on 08/05/14 at 14:43:08

It looks like I have finally found a dealer who can provide me with the jets that I need.. Especially the pilot jet was hard to find.. But they've got 3 different kinds of pilots, and since I don't have any jets in hand to compare with, I don't know which one is the correct one..

I've made this picture of all 3 of them. Can someone identify the right size I need for the bs40 mikuni???

I read the carburetor guides, and thought I would go for a 152,5 main, and a 52,5 pilot. What you guys think?

Title: Re: Pilot jets
Post by engineer on 08/05/14 at 17:42:01

The jets I use in my 2005 have an overall length of 14.00 mm

The outside diameter of the threads is 4.82 mm

The diameter at the end on the wider cylindrical part is 3.75 mm

And my model has no holes in the side of the jet.

Hope this helps. (I bought my extra jets from Lancer on this forum)

Title: Re: Pilot jets
Post by Michael L on 08/05/14 at 22:41:28

Thank you for your precise Info!

Then it seems it would be the one in the middle, although the conical top is only 3,5.. Think i may need to take out the jets and have a look afterall..

Title: Re: Pilot jets
Post by LANCER on 08/06/14 at 05:05:27

The pilot jets you want are:

Mikuni N151.067 (non bleed type-no holes)
Mikuni BS30/96 (Bleed type-holes)

They are 14mm long and 4mm diameter at the thread base.
Both are listed for OEM CV carburetors, both will work just fine.
They retail for up to $6+ each now.

http://www.sudco.com/Catalog37Digital/index.html#/218/zoomed

Title: Re: Pilot jets
Post by Michael L on 08/07/14 at 07:11:10

4 or 4,8 ? :P ..Could there be differences in the carbs through the years? Mine is a 1999.

I talked to this guy at a nearby motor shop, and he asked me: "why do you wan't a bigger pilot?" I said: "my plane is heavy in the back".. then he said: "mikunis are not for aircraft use.." ..moving on :D

he said that most of the time you could just get it right by adjusting the airscrew, and that the pilot jet almost only decided the idle mixture.. I kinda trusted him because I know his experience in the garage, but then again, the thumb screw on the left side, that's where you should adjust your idle speed..?

Title: Re: Pilot jets
Post by Dave on 08/07/14 at 07:34:57

The Pilot jet only affects mixture up to about 1/8 throttle. The pilot circuit has two different paths....one bypasses the adjustment needle and flows without adjustment, the other circuit passes through the idle mixture screw. The adjustment screw fine tunes the mixture at idle - but the size of the pilot jet controls the mixture though the entire 1/8th throttle motion. The size of the pilot jet therefore has a lot more influence on the mixture at the low throttle settings....then the screw does.

With the engine at a low idle and all warmed up, turn the idle fuel mixture screw in until you hear the engine begin to slow down....that is too lean for the engine to run well. Then back the screw out until you hear the engine speed reach the maximum.....that is the ideal mixture setting for the idle. If you continue to back the screw out.....you should hear the engine speed slow down. Mikuni claims that if the best idle speed is reached at 1.5 turns out from seated - the Pilot Jet size is ideal. If you can turn the idle mixture screw all the way in and you don't hear the engine slow down....your Pilot jet is too big. If you need more than 2.5 turns out to reach maximum rpm....you pilot jet is too small. Any more than 3 turns out and the screw is no longer doing anything - as the needle has backed out from the seat enough that it is no longer restricting the flow...and backing the needle out farther will not increase the flow.

It might be difficult or impossible to actually get the speed perfect at 1.5 turns out - I generally don't increase the pilot jet size if I am less than 2 turns out.

Setting the Pilot Jet size is the first thing I do when in the jetting process. The next step is then to find the right main jet size by doing some full throttle runs, then adjusting the needle jet setting for throttle openings between 1/8th and 3/4 throttle.

Dave

Title: Re: Pilot jets
Post by Michael L on 08/07/14 at 07:49:48

Good info, I'll give it a try.