OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk GV150 tuneup help needed

I have a GV150 here. It's on a Vulcan (superswift) babybob.

I have a Superswift contractor base that i want to fit the motor too. I think they will be a good match.


I pulled the carb apart on the motor, cleaned it all out, emulsion tube was covered in crud.

I think i have the linkage all worked out. Perhaps too much pull on the spring as its revving a bit hard.

Just ondering what the specs were for the adjustment screw on the back of the carb. Is it a mixture screw?? Low speed or high speed.

I cant seem to get it to either idle right, or not hunt at revs.


Can anyone help??


Cheers, Bob.

The usual source does not have a manual for a GV150, only for a GV100 or a G150. Some of the literature suggests it is the same carburetor. However, the GV100 illustration shows someone adjusting the pilot screw while the carburetor is on the engine, which doesn't sound as if it is on the back of the carburetor. Here is the GV100 download URL:
http://www.honda-engines-eu.com/en/engines/models_range/GV_range/GV100/shop.jsp

Here is the G150 download URL:
http://www.honda-engines-eu.com/en/images/1004.pdf
This one says just set the pilot screw to a standard 1 and 5/8 turns, and you're done. That sounds a lot more like a screw that you can't access when the engine is running.

Thanks Grumpy.

I will see what i can do.

I think i had the screw out over 2 turns.
You can sorta get at it with the air cleaner off.

Its not running too bad, just popping a bit and the spring needs looking at as it revs too hard.

Got back into this one today.

Well got it out, it was in the way. Started it up 2nd pull.
Had another GV150 on a Victa base that I got from the scrap yard that had a broken rod.
Thought it might offer an answer but the carb has been messed with and had a fair whack of dirt in it, it does look clean in the fuel bowl.

Still cant work out this pilot screw.
The G150 manual says 1 5/8
The Gv100 manual says 2 3/8

I have no experience with side valve Honda carburetors. My experience with OHV Honda carburetors so far has been that the pilot screw is just an idle mixture screw, and it is quite insensitive: you need to be wrong by more than half a turn to have an effect that I can even notice without using instruments. (I tend to watch the tachometer, let it settle for a while, and maybe find a difference of 10 rpm for a quarter of a turn of the screw. I sometimes do that at around 1500 rpm rather than the specified idle speed of 2000 rpm, to increase the sensitivity.) The idle jet provides the main restriction in the idle system, the pilot screw seems to be mainly an emissions control adjustment.

If you have a problem under load or at maximum engine speed, it won't be the pilot system. If it won't idle, look first at the carburetor to port gasket, then secondly at the complete pilot system, especially the jet. Blow some carburetor cleaner through the pilot screw system of course, but the problem is usually that the jet is obstructed.

Perhaps the other carb was not messed with. It had an extra spring on next to the govenor spring and no cutout spring so someone had been fiddling with it.


I wound the screw in on it and it was out 2 1/4. So I went with that. But its probably a bit more as Im not sure I could get the screw on the mower done up seated. Using a phillips head screwdriver sort of like a bevel gear on the top of the screw. It wasnt doing the screw any favours.


Pics will explain it.
The slot in the base of the air cleaner housing is a bit forward of the screw.





I wound the idle screw right in.
The pilot seemed to be better so I wound the idle out until it was idling at a good speed. That was back past where it was. Strange. It will idle and picks up clean to full revs. But it goes past full revs and screams util the choke comes on.
So it will still need a bit more work. I think I might take the carb off again and check the gaskets as suggested. Also tackle the screw again, I think it might need to come out another 1/4 or more. At least I will be able to wind it in and get an accurate count.
The carb should be clean as a whistle inside, I cleaned it out twice back when I was first messing with it.


I would rather not used the grubby carb if I dont have too.
Ive got another GV150 here thats got no carb or exhaust on it, id like to have a crack at getting it going.
Once this motor is running right its getting swapped for a Tecumseh thats on a 19 inch supaswift contractors base.

If you are supposed to adjust that pilot screw with the carburetor installed, I suspect you are meant to do it either from above by using a universal joint on a socket extension, with a screwdriver bit attached:


or from in front with one or other of these:



If the engine over-revs that can't have anything to do with the idle (pilot) system - on a 4 stroke it sounds like a governor problem, not a carburetor one. Interesting that the other engine had a second governor spring fitted, as if it had governor trouble and the tenant made an improvement. Also, I notice the GV150 has an air vane governor, very much like a second and later generation Briggs one, but with a complicated and fraught-looking vane pivot. It sort of all comes together if there is a friction or binding problem in the governor vane or linkage. The vane pivot looks like a good candidate for causing trouble when its really old and corroded:


If you want to look at pages from the illustrated parts list, it is available (free) here:
http://www.ereplacementparts.com/ho...ine-parts-c-37657_37658_38010_38030.html


On a different subject, why not clean up your dirty carburetor anyway, since you have another engine?

Hi Guys, its always great when you have the right tool for the job!
I must get myself a universal joint on a socket extension, with a set of screwdriver bits. Could come in handy for a few of my projects. Thanks for posting the pic.

Thanks for the link.

I am pretty sure that it is not meant to be adjusted on the motor.


None of those things would fit, its in a hell of a spot.
The 1/4 drive wont fit though the slot in the air cleaner base.
The 90 deg screwdriver wouldnt work as you need to get a full 45 deg swing to get another bite at it.
That ratchet type setup would probably work if you could get it in through the hole but i doubt you would.


I suppose the deal would be to have a modified metal cover so you could get access.
I had thought about removing the air cleaner housing and fiddling while running, but that sort of takes away from what I am trying to achieve. It needs to be right with the restriction of the air cleaner and its housing.



Nothing wrong with the vane pivot. The one I stripped (broken rod) had the number 6 type.


I think the issue is cable drag.
Item 17 does not have that many teeth, a slot for choke, then a slot further back for high speed antoher for low. If you pull the cable full forward to choke it is stretching the govenor spring. I am sure that if the cable was light, the govenor spring would pull back on the throttle lever and get it to notch in the high speed position.

Perhaps the tennant spring was something along these lines. Perhaps its the reason the cap let go on the rod too. Theres a bolt and a half in the sump. Bore and piston are fine. There is some damage in the crankcase, will need to strip it. Some bits busted off the bottom of the crank case breather setup by the look of it. I should be able to rebuild it, but dont have a carb etc.




This motor has been sidelined again. Pulled the blade plate off it and its a short shaft with a long boss on it.
So the motor would be for a Victa or a SB or the like.
Might be going in the mini hot rod i want to build.


The carb less motor has real good compression, spark, and the right length shaft for the Commercial Supaswift base I had picked out. So I will rip the head off and look inside, check the valve clearances. Then clean up that carb etc and get it together.

Not having the engine in front of me, I don't know what you mean by cable drag. Vane governors produce very small forces - operating through one wire link is about maximum for them. If yours is supposed to move the inner part of a Bowden cable, I think it is set up incorrectly - there is no way it can reliably generate that amount of force, especially since the efficiency of Bowden cables is highly variable (as well as always being low). On a really old engine like that, if it is actually operating the vane governor through an ancient Bowden cable, it is no surprise that the engine scattered. Also, since the governor spring opens the throttle while the vane closes it, double governor springs is a good way to get the hot metal flying around even without a sticky mechanism.

Running the engine with the air cleaner housing in place, but no element, seems pointless to me, especially at idle. I think the suction created by the element would be greater than that created by the housing. I'd be looking for a way to hold the element in place without the housing, to do the idle tuning job. Or, if that really wouldn't work, I'd just attach a tachometer, then adjust the pilot screw in quarter turn increments by stopping the engine each time. You'd have to wait for the idle speed to stabilise after each restart, but it should work eventually.

I dont have a wide enough shot to show how the throttle link works.

If you put the parts diagram together in your head that will give an idea. Keeping in mind what I said about about only 3 detents.
There is a lever on the side under the air cleaner housing (item 16). Perhaps it should just be that lever and no cable.
The drag of a cable makes it impossible to feel the detent for full speed. Perhaps there is meant to be no cable.

I would need to find an old HR21 fitted with the GV150 originally to find out what cable if any they had originally.

It definately does have a keeper for the outer of a cable.
Perhaps it should have a cable similar to the GXV motors. Rather than the solid core spiral wound cables most mowers use.
I am not sure how hard it has to push to get the motor to shut off.



I was not running the engine while adjusting. I was adjusting and then running like you suggested.
It runs the same filter as the GXV120. The housing is different due to the manfiold going 45 deg and the carb being beside the engine. The GXV120 has a 90 deg in the front, this has a 180 deg at the rear.

So, the gear sector and cable you were talking about, are on the opposite end of the governor spring from the governor and carburetor. You are talking about how to set the amount of tension in the governor spring with the speed control lever. Is your concern that you are overspeeding the engine because the gear sector, Item 17, does not apply the choke until the control lever (item 16) has already applied too much tension to the governor spring? Hence when you start to open the choke, the engine over-speeds, but you can then bring the speed down by continuing to move the speed control toward slow?

What operates the choke linkage - is it one of the functions of Item 21 or 22? It sounds as if you have an adjustment/timing problem in the relationship between the control lever (Item 16) and the lever/link that pulls the choke.

Perhaps I should go and take a couple of extra pictures. Theres details that the diagram does not show up.

21 and 22 are the different cutout/stop switches. This motor has 21 with the spring. Perhaps the other has 22 without spring.

17 is fixed, 16 piviots. Right above the 7 in 17 there is a downward indentation.
18 trips the choke.
Below the - before the 16 there are 3 holes in the front edge of the throttle arm for the govenor spring. High med and low goverened high speeds. The other end of the spring goes over the pin on the butterfly arm on the carb. Then wire link to the vane.


In the high RPM position the govenor spring is in tension and the indent in the slot. Below a certain spot there is no govenor tension due to the oval hole/wrap on the butterfly end of the spring. So it is spring/vane goverend at high RPM setting and perhaps the top 60-80%, below that you only have idle set by the stop screw. So to me that would say that the motor is designed to run at either idle or full speed nothing in between.

Choke position is above high speed. Quite a few degrees, when the engine is running you can move the lever up past the high speed detent over revving the engine and leave it set there without the choke coming on. The choke does come on as it should at the end of the levers movement.

Perhaps the movement so far past the high speed detent before full choke engagement is to put extra tension on the govenor spring to ensure that the throttle butterfly stays open for more reliable starting. At high speed perhaps the spring tension is not high enough to stop the butterfly 'flapping' with the air pulses.


What I was getting at is that with probably almost any type of control cable used on a mower it is not possible to 'feel' for the correct spot for the engines high speed throttle setting without looking at the side of the air cleaner and using the sticker on the lid and the lever as a refference.

On another note, I was looking around yesterday for the next victim to drag into the shed and I spotted another GV150 on a mower half way down the driveay. Its on an old rusted out sidethrow pope chassis.
Better get that one in the shed and check it out.

I follow most of that Bob, but I don't understand why you can't drop to the middle position governor spring setting. If that gives you a sensible speed (like 3,000 rpm) just before the choke closes, it would be operating like a modern Honda: past the speed control lever detent the choke is on, just before that detent the choke is open and the engine runs on maximum governed speed (3,000 rpm). If you want to you can set intermediate speeds between 3,000 and idle (2,000 rpm) but I currently use 3,000 rpm for mowing, and 2,000 for emptying the catcher or wheeling the machine around between grass patches. The choke detent may be part of the secret ingredient for making it work: it jumps between full choke and full speed with no choke, so you don't expect smooth operation between the two.

Has every GV150 you've seen, had the governor spring in the highest speed position? If so, have you figured out why?

Here are some late additional comments, now that I've finally looked at the service manual.

First, here is how you tune the pilot screw:


The doctrine according to Honda, is you adjust it with the air cleaner housing removed.

Here is the doctrine on setting up the governor:


Incidentally one of the interesting things I noticed is that the GV150 has an oil pump. It might be a good idea to clean it out and check that its input and output are clear. You access it from the bottom of the engine - no need to open the crankcase.

With regard to the engine speed being hard to manage between the high speed position and the choke position, perhaps that is why Honda switched to a more elaborate system on the OHV engines, using a very strong detent on the speed control lever between "Fast" and "Choke", as well as a screw-adjustable speed stop on some models.

Hi everyone,don't know if I'm in the right area here.I have a gv 150 honda mower ,runs well except for the oil leaking out of the top crankshaft oil seal which floods the points area.I have replaced the oil seal twice but still leaks ,have done plenty oil seals before but first time on this model,this has me boggled.anyone please help.

Here is the instruction page on installing the top bearing and oil seal:



Here is the instruction page on cleaning and checking the top bearing:



Oil seals work unless one of four faults exists:
Fault 1: The seal - especially its sealing lip - is damaged or the shaft has a non-round or rough surface.
Fault 2: The seal is eccentric to the shaft.
Fault 3: The shaft is too small relative to the seal.
Fault 4: The outer support ring of the seal does not fit the housing or the housing has not been cleaned properly, so leakage occurs between the two.

Expanding on Fault 1, the shaft needs a perfect, ground surface where it runs against the seal. If it is pitted, scarred, or otherwise damaged, sealing may be ineffective. Also, you cannot cure a rough shaft by reducing its diameter, since unless this is done on a lathe, you will always end up with the shaft eccentric to the seal. Even if you use a lathe, the seal can only tolerate a rather small clearance to the shaft - depending on seal type, it can be as little as 0.003" undersize from nominal shaft diameter. (Seals with springs around the lip may accept 0.020" undersize.)

Expanding on Fault 2, if there is wear in that upper ball race supporting the crankshaft, the shaft will wobble about. The maximum momentary eccentricity normal oil seals can stand, and still seal, ranges from only about 0.0015" TIR for low pressure types without springs, up to perhaps twice that for higher pressure types with springs. You deal with this issue by making sure there is no wear in that top ballrace.

Expanding on Fault 3, the sealing lip will usually create a wear groove in the shaft over a long period of running. A new seal will then not work effectively because the shaft is too small and the seal lip does not touch it properly. You deal with this by installing the new seal slightly higher or lower on the shaft so the lip does not coincide with the wear groove in the shaft.

Expanding on Fault 4, you need to be sure the housing is clean and undamaged before you press the seal into it.

Post-edit: I should have included Fault 5: Installing the seal backwards. Seals are usually uni-directional. If they have lips on both sides, normally one will be the oil seal and the other, just a dirt seal which will not hold under pressure.

Best information I've seen in a long time.Very much appreciated thankyou so much and take care.

roebuck, please let us know whether you now succeed in getting that oil seal to work. When this is resolved we will be able to close this thread.