Wet Plugs

[bcware]

I have adjusted the float height in 1mm increments from something like 22mm to 32mm and my plugs are wet on cold starting. Using or not using choke is not changing anything.

As I increased the float height from 22mm to 32mm I would occasionally think I had solved the problem (by then I am sure the engine is hot), but the results were never consistent, so I kept increasing the height. All I seem to have achieved by reducing the fuel in the bowl, is a lean mid and high range. My plugs, especially the left one--the low one when on the side stand, clutch side--, seems to be worse than the right one, but I have experienced this on both sides.

I have also toyed with adjusting how much the float needle is allowed to open. Letting it only drop open a small amount seemed to help, but again, my results are never consistent. How much are the float needles supposed to open? This is something I have never read anything about or heard mentioned in any manual.

By the end of the day I think I have everything sussed out and the next morning: wet plugs!

Facts:

Emgo cheap pods
high flow mufflers
2 up on pilot jets
3 up on main jets
Diaphragm needle height is on the 3rd notch counting from the bottom; the bottom being opened maximally.

 

[bcware]

I think I figured this out.

Another user, 01ps, made a detailed post on his carb settings after switching to a similar setup. He mentioned that he actually lowered his main jet diaphragm needle to the leanest position. This prompted me to give it a try and I developed a theory.

First, I reset my float height to 26mm. Next I lowered that main jet needle all the way. The result? She fired right up without issue, but ran quite lean in the mid range (obviously).

The theory? Pod filters and freer flowing exhausts increase air velocity and thus vacuum inside the carb. Larger main jets provide a larger hole for fuel to flow into the carb. Some combination of these two factors is siphoning fuel out of the main jet and into the venturi at any float height and at very low--starting--rpms.

Lowering the main jet needle is effectively plugging the hole at low rpms and preventing the flooding. In order to compensate for this low needle height a much larger main jet is required than would otherwise be expected. This also coincides well with 01ps, because he said he was running lean with a 150 main! He ended up drilling his own mains to 160.

Here is a link to his post

http://www.xs400.com/forum/showthread.php?t=5241&highlight=wet+plugs

Any thoughts?

Looks like I need larger mains.

 

[drewpy]

good theory, seems about right too

 

[new kid on the brat]

just for theoretical theory.... pod filters and free flowing exhaust does increase velocity wich does increase vacuum with the venturi effect!! but a more restrictive filter will increase vacuum in the carb also!!

so....... at wide open throttle is your needle even in your main jet?

with a two stroke i have always started with a main jet that performs well at wide open throttle!!
and then you can adjust your needle height to the correct mixture at mid throttle and optimum throttle response!

now these vacuum carbs react differently and i tried an experement with mine. i have not changed from my factory jets as of yet...... my two into one gave me a slight hesitation at mid throttle but was fine at wide open throttle. after i added the pods i lost more mid and the top end also......too much air right?..... so i wrapped about a 1/4 of my pods with masking tape and they got even worse at mid and virtualy no topend. all the while it starts great and runs great if your gentle and don't rev very much. like chugging at 1/4 throttle.

so are the round pods actually chocking my engine out? it bucks and pops like it is too rich!!! i understand that the oval filters flow more air and are not recomended for the 400.

does altitude affect the carb on a street bike like it does a carb on a car?? we used to have a spare set of jets we would take with us when we went to the high desert..... 300' to about 5000'.. a lot less air up that high!

 

[bcware]

I agree with the general method of tuning you suggested, but the quirkiness I experienced is only happening on cold starts and very low rpms.

So, I use the main needle to block the main jet at low rpms and I am going to increase my main jet to richen the mixture at mid and high range. The stock main jet needle height causes flooding on cold starts at any float height.

Lowering the needle a single notch has solved all of my problems. The only thing left is to determine whether the largest jets available (160 so I have seen) are large enough to overcome this restriction I have imposed. I will find out Tuesday

 

[drewpy]

there is also a concensus that pods attached directly to the carbs prevent the diaphrams from operating properly.

Its the main reason I'm keeping the inlet pipes and attach the filters to these.

 

[xschris]

The cheap emgo pods are horrible. The large oval pods that mikesxs has or uni filters are the best. or keep it stock.

 

[bcware]

If I can't get the bike sorted properly I will definitely consider upgrading to a higher quality filter or even reverting to stock.

In the mean time I have started the bike every morning without issue and ridden it at very low rpms and I have not experienced any drama aside from the brick wall I hit at 2500 rpms

 

[new kid on the brat]

my bike runs great like i said, if you keep it under 1/4 throttle.... maybe you should try smaller pilots as those essentially richen the whole throttle spectrum!

i made my own foam filters for my shadow yesterday and i mistakenly used a foam that had very little airflow and it hit about a 2500 rpm wall also. i almost went over the bars. ha ha ha that was a rush!!!

i changed foam and she screams again!!

 

[bcware]

Are you using the stock air intake? I have done quite a bit of testing and I will report additional findings tomorrow when I can make some noise; it's too late right now to rev the engine...

 

[new kid on the brat]

i have removed the crossover air intake boot for now. just strictly pod filters on the carbs.

 

[bcware]

What brand are you using?