Mikuni Carb - The Sub EGR valve - Servicing

[BradMph]

Below for you Mikuni Carb Owners is the Sub-EGR valve. This valve refeeds exhaust back into the carb for reburning any possible left over fuels after it's first trip into motor. These valves tend to get very carboned up with black soot to the point it will cause a gas peddle to stick. The valve will get stuck in the soot and lodge itself in it's mounting and cause the gas peddle to have a strange sticking feeling. These valves are very easy to clean and should be checked occasionally.
Simply remove the valve and lightly clean all the carbon from the valve shaft. If you have a bottle brush to fit the opening the valve cylinder fits in, great. Push it in and clean the opening as well before returning the cylinder.
This entire line can build up with carbon like a clogged blood vessel. It goes all the way through the head and can completely seal up after years of use. I clean mine with a coat hanger to remove the soot buildup thru the head. The carb and intake line can do the same exact thing too. Clean as much as you can out of the trail and reinstall you're valve. Service the throttle arm and make sure it moves the sub valve normally when completed.

egr_sub valve.gif

[pennyman1]

Definitely good info for those still running the Mikuni carb.

[irotagrup]

I am going to try this, I just put
My 82 power ram 50 back together with a no jet valve head, but now I am having problems with the car sticking about halfway to almost full throttle.

[pennyman1]

Glad to see you are back Irotagrup!

[irotagrup]

Good to be back! Foxy lives again!!! The stick was a bent bracket. Lol

[SubGothius]

Below for you Mikuni Carb Owners is the Sub-EGR valve. This valve refeeds exhaust back into the carb for reburning any possible left over fuels after it's first trip into motor.

That's a common misconception; the actual purpose and function of any EGR valve is to lower combustion temperatures by diluting the intake charge with inert (already-combusted) gases without affecting the fuel-oxygen ratio, thereby reducing NOx emissions formed at high combustion temps, which in turn lead to smog.

[Traven1188]

That's a common misconception; the actual purpose and function of any EGR valve is to lower combustion temperatures by diluting the intake charge with inert (already-combusted) gases without affecting the fuel-oxygen ratio, thereby reducing NOx emissions formed at high combustion temps, which in turn lead to smog.

It can't hurt to also note that the desired effect of the addition of the inert gases is to ensure that ignition occurs at the proper time, thereby reducing the high temps that allow oxides of nitrogen (NOx) to form. The lower temp also prevents detonation and allows for more advanced timing.

[xboxrox]

BradMph, glad you posted about the sub EGR ~ do you or the fellas here have more detailed instructions on cleaning out the EGR passageways with a coat hanger type tool..? I will need to remove my Mikuni carburetor soon to rebuild it & was thinking of removing the EGR also to clean out the carbon... I am not sure where or how many openings there are to drill with the coat hanger..? My assumption is all the orifices that need cleaning will be where the EGR is bolted onto the engine..? I also assume the intake manifold has no holes or passages in need of carbon cleaning..? Also, how far must the coat hanger be inserted to know the passage is completely clean 'n open..? Or, is there a feel for knowing when your done (as in there will be more freedom of movement of the coat hanger when it's reached the end of the hole and hit the sweet spot)..? TIA for any info...
<---- goodbye carbon