Enrichment Well Pitting and Corrosion

So I was doing a carb rebuild on a set of Hitachi carbs and after cleaning decided to check the enrichment circuit for leakage. I installed the plunger assemblies minus the rubber cap and sprayed some brake clean at the top of the shaft so it would dribble down the shaft into the enrichment well. The #4 carb is leaking quite a bit, as brake clean fluid enters into the throat of the carburetor almost immediately.

All of the plungers have been cleaned / polished and inspected under high magnification, and I tried one of the other plungers in the #4 carb and got the same results. When I inspected the enrichment well under high magnification, the edge of the sealing hole for #4 carb is pitted from corrosion.

The bottom of the enrichment well is tapered, and the sealing hole has absolutely no bevel at the sealing lip.

So, I am wondering if anyone has some good advice on how to repair this.

 

You could use lapping compound on the end of the plunger to dress the hole until it has an even surface, then clean the passage out thoroughly with spray carb cleaner.

 

is it really a problem though? rarely do you read on here of someone not being able to make the idle lean enough, that's what this would cause. with the plunger up and the throttle closed fuel is drawn through the tiny jet in the bowl. with the plunger down but leaking, i'am not sure there's enough vacuum to draw fuel up.
K-moe's lapping sounds good but maybe use a spare plunger since the plunger will get lapped too, unless that's what you want.
what about the cap that goes over the plunger that can't really be a vacuum seal?

 

I liked this idea, but I was worried about lapping the plunger also and then needing a new one. I did try the lapping compound by covering the plunger with heat shrink, but it just was not doing enough cutting. I then tried applying double stick tape to the plunger and sticking 1500 grit to that. The plunger assembly was then installed with a piece of vacuum tube on the top to help rotate it back and forth, and this worked well on the other 3 that were leaking just slightly. On #4 I had to step down to 600 grit and work up to 1500. Here is a better pic of #4, but it still doesn't really show all the pitting on the sealing edge of the hole. As of now none of them are leaking when tested with brake cleaner.

I questioned that myself and not really sure. This all started with a very slight hanging idle only when the bike reaches full operating temperature and normal tune-up procedures did not help. The hanging idle is not very bad, but may take about two to three seconds to drop back to idle speed. I suppose I imagined that some gas or air could be drawn into the engine through the leaking plungers, particularly under high vacuum conditions such as when the throttle is suddenly closed and the engine is trying to return to idle. Blipping the throttle, performance, all seem good otherwise.

And I certainly did not miss that boat. Color tune is a Bunsen burner blue but will not reach yellow even at 4 turns out with the pilot mixture screws. The carbs have been rebuilt including new throttle shaft seals with only about 2K miles on them or about 2 years ago. However, on that go around I neglected testing the enrichment circuit for leakage. I plan on changing from a #40 pilot jet to a #41 pilot jet this go around and do another complete rebuild / cleaning on the carbs hoping not to overlook anything.

So as I understand it these are just dust / water seals for the Hitachi and the carb relies entirely on the plunger to seal the enrichment circuit. They are original so probably time to hit Len up and get some new ones. It certainly would not seem to matter if they leak air as the enrichment circuit is already open to atmospheric pressure under the diaphragm.

 

what seal is stopping that brake cleaner? there's two, one on the point and the larger one that touches the lip your working on. If you lower, by lapping, the larger seat, the gap just gets wider because the smaller point is touching it's seat. Now we need to know if both seals need to be closed or are they redundant?

 

A leaking plunger valve can happen, and it should cause a rich condition. You say that you can't get the Colortune to go "yellow" (orange), indicating a rich condition. With a leaky plunger valve, you should easily be able to get rich. The inability to do so may indicate a partially clogged pilot circuit.

Bumping the choke on slightly should get you to yellow/orange on the Colortune............

 

Guess I don't quite understand this. I was thinking the only point of contact that seals the enrichment circuit is where the plunger contacts the hole in the carb body, the smaller hole shown in the pictures. Therefore, if the edges of the hole in the carb body are not perfectly smooth, the hole is out of round, or if the plunger is not smooth or out of round, then the result of the two mating surfaces would not seal 100%.

I do get yellow / orange when bumping the choke on

Totally agree, but I think everyone knows the difficulty of ensuring these tiny passages are clean within the carb body. On this cleaning event, I drilled an old pilot jet to match the straw on the carb cleaner. I then plugged the idle air screw and the pilot mixture screw and blew carb cleaner into the modified pilot jet. I can look at the 3 holes in the carb throttle bore and see a very robust stream of carb cleaner exiting from all 3 holes.

I also used a flow rate test on the idle circuit before cleaning to check if it was clogged - it is a cheap setup but I was able to ensure that the carb body idle circuit opening exceeded the flow rate of the hole in a pilot jet.

 

Well, it sounds like you have gone above and beyond the call of duty! But, something is amiss if you can't get "rich" flame color to occur, it could be too much air from the intake manifold or their vac port caps, the manifold gasket, or the throttle shaft seals, which have been replaced (so they won't be the primary suspect). The fuel level could be remarkably low, too.

Do ALL of the cylinders suffer from the inability to get rich, or is it just this one carb (the same one with the enrichment circuit issue)?

 

Replaced intake manifold gaskets with HCP1232SET4 two weeks ago, the caps are relatively new and zip ties were added along with the clamp just to rule them out. The manifolds are about 13 years old, and the built in O-ring was totally compressed so they may be iffy - otherwise they don't exhibit any cracking or signs of deterioration. I tried the propane test also, and noticed no change in idle speed.

Fuel level was set on the bench with level carbs and is right at 3mm, but on the bike appeared a bit lower. However, I could not lift the front wheel enough to level the carbs in that direction unless I remove the rear wheel. I will revisit wet set when I get the carbs built back up.

They all appeared the same - which makes me believe I am consistently wrong somewhere.

 

two seals ? yes, no, maybe?

 

Mixture screw components orientation issue?

The order of parts, from bottom to top, would be:

a) HCP895 o-ring (first piece that goes into "the hole")
b) HCP896 spring seat washer
c) HCP6573 tension spring
d) the idle mixture screw
e) the anti-tamper cap.

What is mostly confusing is the order of the o-ring versus the spring seat washer....which goes in the hole first? The answer is that the HCP895 o-ring does. The HCP896 washer primarily acts as the lower "seat" for the HCP6573 tension spring, while also keeping the o-ring firmly and securely in place.


Is it possible that the o-ring got pinched or somehow deformed when going in?

 

The way I do it is this:

1. put the spring on the plunger
2. put the washer on the plunger with the flat side toward the spring
3. put the o-ring on and slide it up onto the larger part of the plunger, right against the washer, ever so slight bit of grease just to aid in sliding
4. put the whole assembly into the bore and gently turn it down to soft-seat.... this way everything says lined up, nothing can get kinked, the spring has a flat seat, the not-quite-as-flat side of the washer gives the o-ring just a little extra 'squish' for sealing, the spring and washer make a very even push to seat the o-ring in the bottom of the bore. Plus, I don't have to worry about teensy weensy parts falling in the floor cracks

dave

 

This is true, but..........IF the enrichment well or the tube was plugged, then you would still have an "air leak" if the plunger valve was not seating properly since that circuit IS open to atmosphere.

It might get even worse, since the brass suction tube has an air bleed hole in it, just before it enters the carb body. If the well (or tube, below the air bleed hole) was plugged, then a leaky plunger valve would draw air from:

a) under the vac piston diaphragm area, and......
b) thru the small air bleed hole in the suction tube.

Although I'm going out on a limb here, the evacuation of the air pressure in the BOWL (via that suction tube) might bleed off enough atmospheric pressure out of the BOWLS to, in effect, "lower the fuel level" and thus result in an incurable lean condition? (I don't think this is correct, as the air supply to the bowls is much greater than the suction tube air orifice, but........).

 

To me it looks like: One seal (2). One taper to allow for full or partial enrichment (1).

 

I follow Dave's procedure to assemble. However, I never noted a flatter side to the flat washer - makes sense though.

O-rings were new and hardware stack-up was correct. Anti-tamper caps were not present. Kind of wish I stuck my finger over the pilot hole to see if the color changed. Am I wrong in thinking the anti-tamper caps could play a role? If say the O-rings are leaking, wouldn't it be a moot point if the caps are installed sealing the top of the pilot mixture screw well, which would then expose the pilot circuit to full engine vacuum?

The part marked "1" does not come into contact with anything in the carb body, so it is not a factor in sealing the enrichment circuit. I believe all the sealing is from "2" mating with the hole in the carb body. The tapered point I believe is just to make sure the plunger is correctly guided into the hole. The carb hole diameter is approximately 4.2mm. The plunger diameter between "1" and "2" is approximately 2.8mm tapering down to 2.5mm.

I like K-moe's thought on this, the taper between 1 and 2 could be there for full or partial enrichment.

Took me a while to wrap my head around that theory, but I finally get what your saying (head hurts now). Anyway, just double checked the brass suction tube and it is clear in both instances (air and fuel hole) on all 4 carbs.

 

We're not talking about air leaks to the mixture screw though.... The discussion is really on the enricher plunger. The mixture screw discussion is actually a sidetrack of the original question

 

your right the point doesn't do anything. as far as your hanging idle goes, i'd revisit your running sync. swap the hoses around to make sure the gauge isn't off a little and i have to say it.
don't use the YICS tool

 

Agreed; area 2 is where my old ones had witness marks from sealing the hole.