120 replies to this topic

[DarkHand]

Been messing with my carbs this weekend and made a few discoveries! I haven't had the CRX running in over a year so I didn't test my ideas (want to change the oil and do a tuneup before trying to start it after all this time), but if all this stuff turns out to work, I'll do everything over again on my other carb and completely document the process.


For one, has anyone who has devacced had any problems with the throttle sticking open? If you have a hand vacuum pump, with the car off draw vacuum on the secondary diaphragm and open the throttle. The throttle opens and won't close! The diaphragm is strong enough to hold the throttle plates open by the secondary linkage. This seems potentially dangerous to me... When you're devacced, part of the process we've been telling people to do involves connecting the secondary diaphragm to venturi vacuum. If the vacuum ever managed to be strong enough, one could run into the potential problem of being stuck on full throttle. Definitely not good. So has anyone run into this?

With a little research, I found a way to eliminate the vacuum diaphragm and convert our carbs to mechanical secondaries using just two zip ties! The carb is already basically a hybrid between vacuum and mechanical secondaries as it is, connecting the mechanical part of the secondary linkage to the normally vacuum controlled part is all that's necessary. The secondary then opens and closes at the correct time, completely mechanically.


I was also removing every extraneous diaphragm and attachment from the carb. The choke and its diaphragms, secondary, AC, float bowl vent, everything. But I found that by removing the throttle control diaphragm, you lose the use of the idle control screw! The screw actually uses the diaphragm linkage as support; remove it, and the idle speed screw is useless. The canadian and Accord carbs have a little adjusting screw on the back of the carb with a black plastic knob on it to control their idle, while we have the screw on the front.

I discovered that our carbs also have this other adjusting screw! It doesn't have the plastic knob on it, and the screw head is blank; there's really no way to grab hold of it and turn it since it was never really meant to be used. It's just a placeholder screw, but it does have a tension spring on it to hold it's adjustment, and it does work! I plan on finding out the size of the threads, buying a longer one, and adding some kind of knob to the end, making a new idle adjustment screw!


With all the extra addons removed from the carb, it's very easy to rebuild, too. Pulled it apart, cleaned it out, blew all the passages clean, replaced the float valve and the accelerator pump diaphragm. At the bottom of the float bowl is the power valve. It's a little brass jet with a button in it that opens and closes to let additional fuel into the primary throat. It's normally open, and only closes when the emissions boxes detect certain conditions. That's why the port that controls the power valve is capped off when performing a devac. I removed it and tried to blow compressed air through one side. No matter how much pressure I put on it, I couldn't get any air to flow through it whether the little button was pressed or not. It was totally frozen in the closed position. I pulled the power valve out of another carb and tested it, and it worked great. With pressure on one side, pressing the button let a strong blast of air through it with no problem. This meant that the other power valve wasn't working at all. The valve isn't part of any rebuild kit, so there was no way to replace it. It's really just a jet with a valve in it, so I decided to remove the guts and make it a simple jet, since without any emissions equipment it was now always open anyway. I got lucky and found a good method to remove the valve mechanism and spring from the power valve without damaging the nozzle, turning it into a simple jet that won't freeze up and cause problems.


All this stuff isn't tested though... I plan to install my now heavily modified carb on my car this weekend and give it a shot to see how it runs. If the results are good, I'll do everything over again on one of my other carbs and take step by step pictures... to document Devac 2.0!

Edited by DarkHand, 08 June 2008 - 08:53 PM.

[anassa]

Wow that seems like some very interesting stuff. it would be very nice of you to take pics and document your testings and findings, it would definately be very helpful. . . use that stock carb to the full potential, i wonder how much power could be made with the stock carb if u totally modified it like that - get the power of bike carbs without putting on bike carbs??? ahaha that would be fun.

[badpenny]

awesome, keep it up. We just got to see if it will pass emissions.

[DarkHand]

You know, I've been thinking... Why am I not posting pictures when there's a whole world of minds out there? I may not have tested these changes yet, but I can still post my thought processes.

So here we go!


Here's a look at a fully decked out US carb on the left, and the stripped down 2.0 version on the right. It's almost as small as the Canadian carb now!



Here's a shot of the regular idle control screw in the foreground, and the 'new' idle control screw in the background. This is on the emissions equipped carb:



Another shot, this time with the normal idle control screw removed, on the test carb. You can see the new idle control screw more clearly in this shot, and how it pushes on the throttle linkage just like the 'old' control screw, only in a different location. On this carb the screw was frozen pretty badly so I had to grind the normally round head square to be able to loosen it up with a wrench.



Moving on to the mechanical secondaries!

Here's the underside of the carb, with the part of the linkage in question pointed out:



There are two pieces involved, the long gold piece of linkage that physically moves the secondary plate and is normally controlled by vacuum, and the small square against it that is mechanically controlled. Here's a picture with the throttle partially opened, and the mechanical part of the linkage starting to move. The two linkages are pointed out, making them a bit clearer. You can see that the long gold piece of linkage (that's vacuum actuated) hasn't moved, but the mechanically controlled piece is starting to move:



Here it is at full throttle. The secondary is still completely closed, but the mechanical part has moved away completely:



So the mechanically controlled part of the linkage is moving at exactly the right time, and exactly the right rate to optimally open the secondary (The linkage has a cam cut into it to do just that). It's a hybrid mechanical/vacuum secondary, designed to mechanically open the secondary when vacuum is applied to the secondary diaphragm, which is controlled by the emissions boxes. The only problem is that we're devacced! There's no vacuum without the boxes, and my recent experiments have made me nervous about applying raw vacuum to the secondary diaphragm (I found that it can possibly cause the throttle to stick open). So what's needed is a way to make the normally vacuum-controlled part of the linkage obey the will of the mechanical part without using any vacuum. And I think I've found a way:



Zip ties! One zip tie on each piece of the linkage with the ties intertwined. This connects the two parts of the linkage together, binding the vacuum-controlled secondary plate to the mechanically controlled (and properly actuated) linkage.

Here's another shot. You can see how the two ties are connected a little better. You can also see how I've got the throttle partially opened, and the secondaries are still closed:



This is exactly what you want; you don't want the secondary to open perfectly in sync, you want a progressive opening. This mod opens the secondary exactly as Honda intended, it just does it without vacuum! Here's a shot at full throttle with the secondary wide open, no vacuum required!



I'm out of picture space, so the final mod is in the next post!

Edited by DarkHand, 19 February 2008 - 01:32 AM.

[DarkHand]

Continued from last post:



Finally, I went inside the carb and started cleaning it up and rebuilding. Found that the power valve was stuck closed, preventing a good amount of fuel from reaching the primary throat. The power valve is normally open except under certain startup, low rpm and coolant temp situations, all decided by the emissions boxes. With no emissions boxes to be found, the valve should always be open. Because of this, I decided to mod the stuck power valve to always be open by removing the internal valve.

Here's the power valve at the bottom of the float bowl inside the good carb:



And here's it is out. It's basically just a nozzle with a valve:



I didn't take a picture, but there's an elongated actuator on the underside of the top plate of the carb that reaches down and presses on the button on the power valve. It's normally pushed down all the time, but applying vacuum to the power valve port on the carb lifts the actuator up and cuts off fuel. Since this will never happen without emissions boxes, and since the valve was stuck closed and I had to open it anyway, I removed the guts from the power valve with:



A file! I filed off the top of the valve in order to access the guts. The power valve is brass so it's very soft and easy to file. Checking as I went, just a few minutes later I was through to the guts, halfway through the top part of the valve. Here's a shot of an in tact valve, along with the filed valve, and the plunger that was removed (Also removed the little spring and the button, but I dropped them on the garage floor, never to be seen again). You can see that there's still a good amount of the top left, which is important. The top of the valve acts as a hex nut, you screw the valve into the float with a 6mm socket. There's still plenty of hex area left to do so:



The power valve is now in a perpetually open state, with no more chance of the valve getting stuck:



And is then cleaned up and reinstalled in the test carb:



So that's what I've been doing! Like I said, I still haven't tested the carb out yet, but I don't really see any glaring problems with any of these changes. The power valve is the scariest change to me, but the tiny little nozzle on the bottom of the valve is untouched, so the same amount of fuel should be going through it as before. The idle screw is neat, but I'm sure I'm not the first to have noticed it, and it really doesn't change anything other than help make the carb even simpler than before by being able to remove the idle control diaphragm. The mechanical secondary will probably be the biggest change, I think the regular devac method doesn't put enough vacuum on the secondary diaphragm to open it any significant amount... If it did, my tests show that the throttle could potentially stick open. Having a functional secondary is going to be a biggy.

Edited by DarkHand, 19 February 2008 - 12:50 PM.

[anassa]

hmm interesting, now i just wish that i was so mechanically inclined to be able to debate and help your thought process, but all all i got a say is: nice! I almost want to try it right away with my car, but of course its not currently running.. but i should be able to find the darn key this week to test my normal devac... anyway test your theories!! If it works it would be very cool, and if it turns out to work well then I will be the second person to do it <-- called it for anyone else who want to do it too. oh and btw it seems like we the will have our carb VTEC! lol

Edited by anassa, 19 February 2008 - 12:52 PM.

[anassa]

hey DarkHand any news?
as soon as i find the vac leak and get my car running, i will try to find a extra carb, see if i can mod it accordingly to what you said and see what problems. if any do, arise.

[EuphoricBlue]

Hmm, I missed this post earlier. But damn. You beat me to it!

I looked at much of this stuff on one of my carbs because I want to install a turbo. So I was looking at devacing and making everything mechanical.

I too noticed the binding secondaries thing. But the carb no longer does that for some reason. I'll have to look into it later.

I'd have to examine the valve thing more to form an opinion on that. I might be worried about running rich with all the guts missing out of it.

[DarkHand]

hey DarkHand any news?

None yet, haven't had any days much above freezing yet since the last post... Winter can end any time now! Haven't even cranked the CRX in over a year now, want there to be a little warmth before giving it a shot. Mainly so I can get out there and change the oil first and not freeze to death in the process. It was nearly 55 on Sunday but I wasted that whole day on my crazy $800 tool shopping spree.

Hmm, I missed this post earlier. But damn. You beat me to it!

I looked at much of this stuff on one of my carbs because I want to install a turbo. So I was looking at devacing and making everything mechanical.

I too noticed the binding secondaries thing. But the carb no longer does that for some reason. I'll have to look into it later.

I'd have to examine the valve thing more to form an opinion on that. I might be worried about running rich with all the guts missing out of it.

I never had a problem with the throttle sticking on the road either, but I only had the Civic on the road for a very short time after the devac, before the timing belt broke. The diaphragm is definitely strong enough to overpower the return spring and hold open the throttle, but I don't know if the vacuum from the port we use for devac is strong enough to actuate the diaphragm. Which is a lose-lose situation: If it's not strong enough, the secondary won't open. If it is, the throttle will jam. I had a theory for a while about poking a hole in the secondary diaphragm, bleeding off vacuum to prevent it from staying open, but that wouldn't work... It seems like it would work in the garage with a vacuum pump... you could apply vacuum, and then the hole would bleed it off and the throttle would close. But in a running car at full throttle, that vacuum is being applied constantly. Even though it's bleeding off it's being regenerated all the time, leaving you right back where you started, in a feedback loop. You can't let off the throttle to decrease vacuum and let the diaphragm bleed it off because you're stuck on full throttle!

I'm still iffy about the power valve too, I keep having to reassure myself about it. There's a tiny little nozzle at the bottom, the only thing I was able to clean it with was a single strand of copper wire from a piece of electrical cord. That jet is still in tact, and the valve is always open after a devac anyway... Applying vacuum to the power valve port actually closes the valve under normal circumstances. It seems like more fuel can get to the nozzle without the guts in the way, but I'm hoping that won't cause any problems... Whether .1ml or 100ml of fuel is sitting above the nozzle, only so much can go through at once.

Edited by DarkHand, 05 March 2008 - 07:40 PM.

[bambbrose]

Keep us updated on your findings. I'm very interested in what you come up with. If the secondaries are indeed malfunctioning like you mentioned then I would assume that on most devac'd setups they are just not opening. I say this because people would notice it if it stuck fully open, and wouldn't necessarily notice it if it wasn't opening all the way.

[DarkHand]

More carb work!

To recap: Since the regular idle control screw becomes non-functional when you remove the idle control diaphragm, I have to use the idle control that the canadian/accord cars use, which is normally unused when this carb is on our cars.

Here's the regular idle control in the front, and the alternate idle control in the back:



As you can see, the screw in the back is just a placeholder. It's a flat round head that's practically impossible to turn. So I needed a replacement that was longer and easier to adjust, and I came up with this:



A 40MM long M5x0.8 bolt with the head ground down so it can bottom out on a wingnut, which is glued down to act as a handle (the wingnut was glued with blue threadlock in these pics but I got impatient and later used 5 minute JB weld ). An aluminum spacer approx. 1cm long to take up the extra length of the new bolt (I just ground down a longer one I had on hand until it fit), and the tension spring from the original blank adjusting screw.



Voila! Now the idle can be easily adjusted by hand. I still needed to shorten the spacer in this pic so the spring wasn't quite as squished.



I also made a block off plate for the float bowl vent using 16ga sheetmetal and the original o-ring, since I've been removing every unnecessary part from the carb. One less vacuum hose to worry about!



I considered filling the entire opening with JB putty, but the small bronze vent above the center of the plate in the pic also goes straight to the float bowl. Filling the opening with putty would have blocked this opening as well, which I didn't want to do. The plate seals off the old vent diaphragm opening, but keeps this other vent open.

Today is supposed to be a whopping 74 degrees for a high, after a good few weeks of 40 degree weather. I'm going to try to leave work early today, swap in the new carb, and give 'er a test!

[anassa]

sweet! can't wait to here the verdict.

[DarkHand]

Well I can't test the drivability of the secondary mod, but for the most part the carb works great! Idles smoothly, revs strongly, looks like the rebuild went well, and the power valve mod doesn't seem to have caused any huge problems. Not having a choke is more annoying than I thought though... I just couldn't get it to start without choking it with my hand and having someone else start the car. I'll give myself some more time to try to get used to it, but I may reinstall the choke equipment. In fact I might try to buy/install a Canadian manual choke!

Carb didn't want to idle below 1200 rpm or so until I pulled back on the throttle linkage. I've never had the test carb running until now, looks like the main return spring isn't very strong. I'll try to see if I can tighten it up by winding it around the linkage an additional time. If not I'll swap another one on there.

I had forgotten that the secondary diaphragm is permanently attached to the throttle cable mount! I kept it on there for the initial test:



Afterwards I took care of that with the Dremel and the grinder:



Much better!

So I still need to fix the throttle return, and figure something out for the choke. Other than that it's looking pretty good!

[DarkHand]

Darn thing really is the size of a canadian carb!

[yuriy89]

Darn thing really is the size of a canadian carb!

Does the vacum lime from the front of the carb goes 2 dizzy? Thanx.