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General Category >> Rubber Side Down! >> Introduction and A fuel mixture question
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Message started by philjayny on 08/08/14 at 12:19:57

Title: Introduction and A fuel mixture question
Post by philjayny on 08/08/14 at 12:19:57

Hi! Finally have access to this amazing forum I've been trawling, reading, and learning from since I got my 98 Suzuki Savage four weeks ago.

So far, I've made a few changes to get it to road-worthy condition like removing the Honda 450 forks/wheel front end (fun fact: the axle is wide than the triple tree, which makes for all kinds of ****ery..) and replacing it with stock parts.

Now I'm hearing ticking in the engine which I"m hoping is just a valve issue, but am currently diagnosing for fear of a cam chain issue. (Verslagen, we're emailing about this, I'll keep you updated once I give the oil filter cover a closer listen.)

Last night I went out for my first highway ride (completely unintentionally might I add..) and noticed that the exhaust shoots a constant blue flame under high-speed deceleration (i.e. when I let off the throttle.) This means it is running rich correct? The reason I'm confused is that ever since I got the bike, it seems to be running rich (best idle is at .5 turns out). I switched the stock pipe for the rail-mount Dyna exhaust, hoping that would fix this, (though mostly for audio and visual benefits.) and it is still running rich.

I know a solution would be to reduce the jet size, but assuming the jet is the stock 142.5, I feel like this should not be necessary (I live in NY, at sea level), and there may be a bigger issue?

Title: Re: Introduction and A fuel mixture question
Post by Dave on 08/08/14 at 12:43:10

No, the engine runs lean when you close the throttle - the slide has dropped down into the jet needle and closed off the fuel flow, while at the same time the high engine vacuum is pulling a lot of air past the slide and butterfly. The only fuel available is coming form the idle circuit (pilot jet), and the mixture is so lean that it cannot be ignited in the cylinder by the spark plug - but it is ignited in the header pipe by the hot inner pipe.

You should jet your engine so that it runs well while the throttle is being used - you should not jet your bike based on conditions that occur when the throttle is closed and you are decelerating.

Go to post #5 in this thread....so I don't have to type all that again.
http://suzukisavage.com/cgi-bin/YaBB.pl?num=1407274988

Dave

Title: Re: Introduction and A fuel mixture question
Post by verslagen1 on 08/08/14 at 12:59:54

sounds to me that you have a petcock diaphragm failure.

pull your vac line and check for gas.
or go to tech section and test your petcock.

Title: Re: Introduction and A fuel mixture question
Post by Yoshi on 08/09/14 at 04:40:07

You being in Ny aka closer to sea level means you will run leanest on those jets, I'd bump the jets up with the dyna to 52.5 pilot and 150 main

Title: Re: Introduction and A fuel mixture question
Post by Dave on 08/09/14 at 04:55:22

485948717D73796A6B7371180 wrote:

You being in Ny aka closer to sea level means you will run leanest on those jets, I'd bump the jets up with the dyna to 52.5 pilot and 150 main

That jetting worked well for me - but I still had a small flat spot right off idle. I solved it after some trial and error, and the end result was a #150 main, #50 pilot, and 2 washers under the needle clip instead of the recommended 3 washers.

Title: Re: Introduction and A fuel mixture question
Post by philjayny on 08/09/14 at 08:30:22

Thanks for the replies! I'm a bit confused though.

I would assume that if the highest RPM at idle is reached by turning the screw almost all the way in, that means I'm running rich?

So how would sizing up on the main jet help?

Thanks for pointing me to the petcock test. Will carry it out to test the petcock for vac line leaks.

Title: Re: Introduction and A fuel mixture question
Post by Dave on 08/09/14 at 10:23:47

Main jet doesn't do a thing at idle - it doesn't really do anything until you get to 3/4 throttle.

Going to a #50 pilot will help a bit if you currently have 52.5 pilot.

Title: Re: Introduction and A fuel mixture question
Post by philjayny on 08/09/14 at 10:40:45

Got it. Thanks!

Title: Re: Introduction and A fuel mixture question
Post by philjayny on 08/13/14 at 06:50:56

I'm having trouble figuring out which Mikuni jets (main and pilot) I should use for my stock carb (i.e. N151.067 Pilot Jet or N101.043 Pilot Jet etc.)

Which one is it?

Here's a link for your convenience.

http://www.nichecycle.com/ncs/categories/fuel-air/jettting-tuning.html#cat=197