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GCV160 questions...

4626 Views 42 Replies 5 Participants Last post by  DavidBoren
I plan on turning up the governor on my GCV160 to ~3500 after I get a new blade, and I have a few questions regarding the GCV160 engine...

1a. Can the GCV190 carb be installed in place of the GCV160 carb?

1b. If yes, can one retain the Auto Choke System?

2. Can the GCV190 cam wheel be installed in place of the GCV160 cam wheel?

From what I can tell, the GCV160 and the GCV190 both use the same timing belt, valves, and rockers... but the cam wheels are different. I am hoping the GCV190 cam is larger [either in duration or lift, or both] , but still is a direct fit in place of the GCV160's cam wheel. There is a PDF on how to adjust the valves, so I am too worried about that part of it.

As mentioned earlier, I am going to turn the governor up... can one advance/retard the cam wheel? The cam wheel and timing belt both have teeth.
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Honda GC's aren't like car engines... if you change, advance or retard the cam wheel, it's going to run bad or not at all. the gcv190 carb may fit, but being for a larger engine, may run too rich and pull down performance. going off memory on the GC's i've tore down, the duration and lift is the same. and even if you did change the duration, it will run bad if you don't change the ignition timing, which is virtually impossible... unless you were to get an offset flywheel key which do not exist for that engine.
as far as the lighter blade goes, contact the people you bought it from and ask if they know the maximum RPM, or blade tip speed it can be run at... centrifugal force is very strong, and is also proportionate to the mass of the object.
Thank you for the response.

I probably need to get it into my head that the little Craftsman mower is not a racecar. Lol. But it is an internal combustion engine, so certain principles remain nearly universal... although some things do not scale in a linear manner.

I, myself, appreciate torque over horsepower... I like the mechanical leverage of a long stroke crankshaft... I generally prefer overhead valve architecture... but, BUT, what I have is the smallest possible displacement, shortest possible stroke, overhead cam GCV160.

I could just get a bigger mower, but I am not going to do that. Since I don't have the raw torque, I have to go for average HP. I know I am going to raise the governor speed, and I really don't want to run out of fuel. Thus, my interest in the GCV190's carb... I don't know if a 13% increase in RPM's justifies installing a carb from an engine with 19% more displacement, but I really don't want to run out of fuel.

It is disappointing that the cam duration and lift is the same between the two, I wonder why they have separate part numbers. Actually, they dont. Huh. I could have sworn my original search(es) shown different part numbers for the GCV160 camshaft pulley and the GCV190 part. They apparently use the same cam wheel. That simplifies things, I suppose.

Good call on needing a new timing pickup on the flywheel if one was to advance/retard the cam. I am probably not going to mess with any of that since there is only one cam profile available. I guess I could still try retard this cam a tooth or two, since I am raising the governor speed... but I'm probably not going to. If the GCV190 cam had more duration, I would have been willing to advance it a tooth or two in an effort to keep torque where I want it. I think it would have been cool to see the difference between a small cam retarded a couple teeth versus a large cam advanced a few teeth. But, oh well.
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Sweet. Just ordered the 0650.

Thank you
After doing a little math, a 5% increase in jet size may have actually been a little conservative... I probably should have went up 10%, and ordered the 0680 jet. As it turns out, I would probably need to spin my '160 to about 4K to average the same air/fuel requirements as a '190 at 3500rpms... that would be a ~15% increase in average engine speed.

I am dubious of revving to 4000rpms with an aluminum cylinder, and nothing is forcing me to spin the motor that high. I don't have uber-grass that is exceptionally hard to cut. It's just my morbid curiosity and desire to tinker. Trying to match the air/fuel load of the '190 @ 3500rpms is a completely arbitrary goalpost.

Might actually need that bigger carb, if I do decide to chase 4000rpms. Even if I can put a large enough jet in the '160 carb, I don't want to suck the bowl dry... carbs aren't really my thing, so I don't know if bowls running dry is really a problem... this whole mad scientist experiment is actually an attempt for me to better understand such things.

If I am increasing the main jet size 5-10%, should I also increase the pilot jet size an equal amount? A lesser amount? More than I increase the main jet? Does the pilot jet size even matter that much since it is low throttle operation, and the GCV160 has Auto Choke, and the pilot isn't adjustable anyways. Lol.

Looks like the '160 comes with a 0350 pilot jet... and they offer 0380 and 0400 pilot jets. I am thinking that +5% on the pilot jet, and +10% on the main jet would be a good place to start, but I don't know $#!+...
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Thank you. It is good to know that I don't have to worry about the bowl running dry.

In the name of science, I think I am going to try the larger 0400 pilot jet, instead of the 0380. Having already ordered a new main jet that, in hindsight, may not be big enough... I will overcompensate by getting a pilot jet that may end up being too large. See where that gets me.
The Honda website has the net power listed at 3600rpms, which is well above where they wish people to operate these machines... 3000rpms is the recommended operating speed to reduce warranty claims and maintain a reputation of reliability.
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Safe is a subjective word. Lol.

Honestly, catastrophic failure of a lawnmower is less spectacular than mentos in Dr Pepper, so I am not too worried about exceeding what they recommend as the maximum safe operation speed.
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That being said, I do not aim to waste this little motor... and I am trying to do this "right"... assuming there is a correct way to exceed the manufacturer's recommended maximum safe operating speed by nearly 30%. Lol.

Anyways, I am probably going to order that 0400 pilot jet, and install it at the same time as the 0650 main jet. Then just tune the governor until it runs well with those carb jets, whatever RPM that may be [it will be checked with a tach].

Are Honda pilot screw threads relatively universal across their small carbs? I keep seeing these hand-adjustable pilot screws intended for go-karts and dirt bikes...
Funny story... so I kind of took tabora's 0620 main jet example and assumed it was what was in my GCV160. It is not.

I actually went out to the garage and looked up my exact model... it, in fact, has either a 0550 or 0580 from the factory. So I jumped the gun when I ordered the 0650, assuming it would have a 0620 sitting in there right meow.

My original intent was to just install a GCV190 carb, and it just so happens that the GCV190 comes with either a 0620 or 0650 from the factory... nailed it!

So, the 0400 pilot jet is probably going to be alright. Hopefully I can find an adjustable pilot screw...
Oops. Oh well. We will see how it goes...
Let's talk Emulsion Tubes... where the magic happens...

Changing jets is all well and good, but that main nozzle is ultimately what is going determine how close one is to optimal air/fuel mixture at any given rpm. The good news about push mowers is there is really only one speed they operate at when in use, so there is not a lot of mid-range/transitional tuning... so the main nozzles can be relatively simple in their design.

But how are they [main nozzles] measured/labeled?

How does one determine which nozzle to choose? Is there a rule of thumb for emulsion tubes... like less holes for more rpms, or whatever?
16166-Z8B-901 is what shows up for the GCV160LA1 S3B NH1... it's number 9 on the hondaparts carburetor diagram.

16166-Z8B-841 is the GCV190 part number for its emulsion tube... what Honda calls a Main Nozzle.

I will take a set of calipers to both and see what the actual difference is. It is interesting that the larger displacement motor has the numerically smaller emulsion tube... either the part numbers are completely arbitrary, or it is somehow referring to the outside diameter of the tube, itself.

A larger diameter emulsion tube would provide more of a restriction between the outside of the tube and the inside of the bore [where the fuel actually flows]... less fuel, smaller displacement... explains why the GCV160 has the '901 emulsion tube, and the GCV190 has the '841 main nozzle.
Yeah, GCV160LA1 S3B NH1 is on the barcode sticker on the back. It's on a Craftsman M250 push mower, if that means anything.

Did Honda actually put a closed loop PCV system on the GCV's? The breather tube appears to lead to a bowl inside the air box... to feed crankcase oil vapor back into the combustion chamber, I suppose.

Does the carb/intake actually provide vacuum to pull crankcase gas through this system?

Could one simply put a valve cover PCV filter in place of the breather tube? Assuming that it doesn't interfere with the throttle linkage? I cannot guarantee the factory air box and filter will continue to be used, so this breather system may need to change, as well.
I figured as much. Thank you.

I'm seriously considering running a little conical dirtbike airfilter, and thought it would be pretty slick to have a matching, although smaller, conical filter next to it on the breather. If I am feeling squirrelly, I could even possibly modify a crankcase breather cover with a valve cover breather kit.

By the looks of it, the breather hose is just inserted through a hole in the breather cover, and is left unsecured inside.
The Honda/Keihin "constant velocity" carb is an interesting piece to use on a lawn mower, me-thinks.

It [the Constant Velocity Keihin carb] has an emulsion tube, which is something Weber has developed extensively to modify fuel curves... generally to provide mid-range adjustments. A lawn mower has no mid-range to adjust.

And this is not the same CVK casting/body used on dirt bikes, so to carry over that emulsion tube has to be for some economy/emissions gain. My only assumption being that literally any measurable emulsion allows smaller jets to be used, overall. I wonder if Weber emulsion tubes fit... that would be neat.

Has anyone bother re-jetting their push mower carb? Particularly a GCV160/190 carb?

The demand of a 160cc engine @ 3500rpms is similar to that of a 70cc engine @ 8500rpms... and such engines are using #80 main jets, #40 pilots. The GCV160 has a #55 main jet from the factory. The GCV190 has a #65, for reference. Both the GCV main jets seem on the lean side.

I have already ordered the #65 main jet for my GCV160, which still seems to be leaving very little margin of error, all things considered... especially if I plan on turning up said GCV160 to ~3600rpms.

Would a richer main jet, something like a #80, have any sort of cooling effect? Every little bit helps with an air cooled engine (especially one without an oil pump/cooler).
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To answer my own question, yes. You can jet the carb rich to effectively make the engine run cooler... this process is used quite a bit in aviation as well as 2-stroke dirt bikes, and is called "rich of peak".

In this regard, I may very well order a 080 main jet to try. Honda has 99101-124-xxx main jets ranging from #48 to #150, so we have options. I have found #35, #38, #40, and #45 pilot jets, and can only assume there is also a #42 available, too [although I didn't bother searching for it]. And three different emulsion tubes available, but their differences remain a mystery to me. There are quite a few different CVK adjustable fuel mixture screws out there... I hope I can find one that works, although it really isn't the end of the world if I cannot.

It is just a push mower, not a pit bike...
Interesting... it would appear ~3500rpms is about as fast as I can go with a 21" blade... according to the "revised" standard of 19,000fpm. A 21" blade could be spun to ~3800rpms using the old standard of 21,000fpm. Not sure if the blades are actually made any different between the two different sets of standards, or how significant that 2,000fpm difference really is.

Something being flung out the chute is going to hurt, either way, but I doubt the difference is truly that significant. Blade harmonics might be a factor, but even cheap manufacturering and metalurgy processes today probably produce better blades, overall, than when the standards allowed higher tip speeds.

Who actually even knows which tests were used to establish or revise these standards, anyways? They could be completely arbitraty BS numbers established so insurance companies have an excuse not to pay.
In the name of science, would increasing just the pilot jet size enrich the entire rpm/throttle position spectrum?

Pretty sure the idle circuit is always contributing fuel, and I was wondering to what extent does the pilot jet affect full throttle enrichment?
Meh, found an answer to my own question...

It appears that a typical idle circuit only contributes about 15% [at most] of the overall fuel during full throttle.

So, huge changes in pilot size (~30%) amount to quite small (~4%) changes in overall fuel at WOT... not at all a significant amount of tuning available from messing with pilot jets, alone. I doubt one would even able to notice a difference at full throttle without equipment specifically designed to detect minor changes in AFR... it MIGHT be detectable with EGT sensors, but I doubt it.
Would there be any benefits to adding Honda's little vacuum powered fuel pump to a lawn mower? The 16700-z0j-003 pump appears to be standard on some other GC160/GC190 models, as well as GX engines.

Although it provides yet another component that could potentially fail, I am relatively confident in the simplicity of the mechanism to last for what I would be asking of it. I could even isolate the pump, itself, from vibration with a creative mount utizing rubber or polymer spacers... if such measures might be remotely necessary. The generators that use them do not seem to go through such efforts to protect the pump from vibrations.

Again, I don't know if there would be any benefits... other than possibly guaranteed fuel supply on ridiculous sidehill runs? Pick a different approach. Lol. And, if the whole mower is that tilted, the pickup location of the tank could be above the level of the fuel in the tank, and no pump is going to solve that.

Would there possibly be any drawbacks associated with installing a vacuum operated fuel pump?

It's not like that vacuum signal ahead of the ventruri/butterfly is being used for anything else... nor will tapping the intake to access that vacuum signal weaken or otherwise affect the function of the carburetor downstream. So, I don't see anything wrong with delivering an ever so slightly more consistent supply of fuel... obviously the vacuum operated pump does not overpower the float/needle, given that this exact pump is mounted on various other models within the same family of engines that I am tinkering with.
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