1980 MTD 918 - 'Ol Rusty!

I've thought about electric pumps too but don't like the idea off adding electronics unnecessarily especially when the Briggs style pulse pumps are so cheap plus they're easy to swap out on the trail if needed. An electric pump has no reference to demand so it will try to pump the same regardless of engine rpm, they might work great though so maybe you could be the test horse to find out!

Brianator wrote:

I've thought about electric pumps too but don't like the idea off adding electronics unnecessarily especially when the Briggs style pulse pumps are so cheap plus they're easy to swap out on the trail if needed. An electric pump has no reference to demand so it will try to pump the same regardless of engine rpm, they might work great though so maybe you could be the test horse to find out!

I mean in theory you could hook it to the stator using a second diode, and then also to the crank wire off the ignition so it pumps full when cranking, but yeah a pulse pump would probably be more reliable

RichieRichOverdrive wrote:

Sweet little honda! Funny, the only 390 I've been around was in my shop because it needed the valves adjusted. That thing would about pull your arm out of socket before I fixed it! The delco alternator should be a nice addition, I had one in budgie for a while but never really used it- the 6hp didnt need a battery and the 18hp had it's own charging system.  As for the electric pumps, it really depends on the carb. I've seen them work with some and some it floods out like crazy. Doc Sprocket did say that a good carb should hold back 5psi of air when you turned it upside down.

Someone told me once that it was a common thing to put a big harley carb on a suzuki samurai back in the day, but the stock fuel pump would overpressure them something fierce. They would add a return line after the pump with some sort of fuel filter in the return line. The filter in the fuel line would add just enough resistance to keep fuel in the carb, but not so much to where it would overpressure it. You might try something like that.

Funny, I have that kind of return line setup on my Honda Odyssey; had to change out the fuel pump so I put a bigger one on it and for the return line to the tank, I stuffed a Chinese carb main jet drilled out a bit bigger. Never had an issue with fuel to the carb other than making a turn as the fuel sloshing all to one side of the tank lol.

Will definitely try the return line again on this build!

MightyRaze wrote:

In the mean time, if your charging is 6amp or less on that engine.  I've seen some guys use these on clone engines.
Kohler 233959 | Diode, 6 Amp Harness

Ohhh is that seriously all it is? I've been trying to figure out what amperage coil I got, I only have 1 white wire coming from the recoil starter area and it's not too thick of a wire tbh. Maybe I got the 3A version?
So that diode would just go in series with the coil and out come a half wave rectified DC.

Brianator wrote:

I've thought about electric pumps too but don't like the idea off adding electronics unnecessarily especially when the Briggs style pulse pumps are so cheap plus they're easy to swap out on the trail if needed. An electric pump has no reference to demand so it will try to pump the same regardless of engine rpm, they might work great though so maybe you could be the test horse to find out!

I'm down for that! My plan is to have the original tank as the main fuel source, and my buddy suggested I make the original Honda tank the "reserve" tank.

I'll get some pics tomorrow hopefully, but I bought some 3/16" steel plate from my metal store, notched out some existing bolt holes and sat the Honda on top for now to mock everything up. Looks like the hood will close without any modifications, but the output shaft if awfully close to some idler pulleys.

Red Stag has the same 1 wire 3 amp charging system. I extracted the diode from the ignition switch box that went in the trash. I have the arrow pointing to the R or rectifier terminal on my ignition switch.

Silver_Pharaoh wrote:

Funny, I have that kind of return line setup on my Honda Odyssey; had to change out the fuel pump so I put a bigger one on it and for the return line to the tank, I stuffed a Chinese carb main jet drilled out a bit bigger. Never had an issue with fuel to the carb other than making a turn as the fuel sloshing all to one side of the tank lol.

Thought you were talking about the minivan for a second there

@TechnoChicken ohh that explain's the whole why is there a carb on a Honda van thing.....ooooh

Crazy_Carl wrote:

@TechnoChicken ohh that explain's the whole why is there a carb on a Honda van thing.....ooooh

Yeah lol them fuel injection systems are rubbish, you get double hp with a briggs carb

Crazy_Carl wrote:

Red Stag has the same 1 wire 3 amp charging system.  I extracted the diode from the ignition switch box that went in the trash.  I have the arrow pointing to the R or rectifier terminal on my ignition switch.

Thanks for the pics!

TechnoChicken wrote:

Silver_Pharaoh wrote:

Funny, I have that kind of return line setup on my Honda Odyssey; had to change out the fuel pump so I put a bigger one on it and for the return line to the tank, I stuffed a Chinese carb main jet drilled out a bit bigger. Never had an issue with fuel to the carb other than making a turn as the fuel sloshing all to one side of the tank lol.

Thought you were talking about the minivan for a second there

Lol naw I have and FL250 over at my dad's house, put a new Mikuni 23mm VM carb on it. I was mid tuning it doing plug chops and such to get it just right when I moved out. I miss that dune buggy, super fun to ride

Heres some pics of the motor sitting in it's place:



Had to move the tractor outside tonight plus im working tomorrow so hopefully Saturday night I can get to working on it again.

For pulleys, what's a good setup?
I'm wondering if I can take the stock pulley off the transaxle and put it on the engine, then grab a 6" pulley from Princess Auto for the trans?

Not likely, the motor probably has a 1" keyed shaft (hopefully not tapered?) and the trans probably 5/8" keyed but could also be splined.

A 1:1 pulley ratio will give you a good balance of speed (should get you 10+mph) while keeping a useable low first gear but be aware that the 2300 trans uses second gear for reverse so you need your clutch working perfectly so you can feather it when needed.

Nice to see you making some progress!

Brianator wrote:

Not likely, the motor probably has a 1" keyed shaft (hopefully not tapered?) and the trans probably 5/8" keyed but could also be splined.

A 1:1 pulley ratio will give you a good balance of speed (should get you 10+mph) while keeping a useable low first gear but be aware that the 2300 trans uses second gear for reverse so you need your clutch working perfectly so you can feather it when needed.

Nice to see you making some progress!

Sorry that's what I tried to say but the forum glitched and just posted the quote, I will second that thought, but again try to get the pulleys as big as possible (within reason) 6" pulleys on the front and rear is an excellent setup, you get lots of grab while also having a decent disengagement and controlled slip so you get a smooth clutch release

Brianator wrote:

Not likely, the motor probably has a 1" keyed shaft (hopefully not tapered?) and the trans probably 5/8" keyed but could also be splined.

A 1:1 pulley ratio will give you a good balance of speed (should get you 10+mph) while keeping a useable low first gear but be aware that the 2300 trans uses second gear for reverse so you need your clutch working perfectly so you can feather it when needed.

Nice to see you making some progress!

Thanks! Yes the GX390 despite coming from a Honda generator, appears to be a straight shaft so that's cool!

TechnoChicken wrote:

Brianator wrote:

Not likely, the motor probably has a 1" keyed shaft (hopefully not tapered?) and the trans probably 5/8" keyed but could also be splined.

A 1:1 pulley ratio will give you a good balance of speed (should get you 10+mph) while keeping a useable low first gear but be aware that the 2300 trans uses second gear for reverse so you need your clutch working perfectly so you can feather it when needed.

Nice to see you making some progress!

Sorry that's what I tried to say but the forum glitched and just posted the quote, I will second that thought, but again try to get the pulleys as big as possible (within reason) 6" pulleys on the front and rear is an excellent setup, you get lots of grab while also having a decent disengagement and controlled slip so you get a smooth clutch release  

Got a line on two 5-3/4" pulleys in Toronto for $25 each vs Princess Auto.
Hopefully I can pick them up this week and they will fit without issue!

Quick update on the build!
I've been working on it off and on the past few week, but I was stuck at home with covid and didn't really feel like messing with the tractor much.

I did manage to get the wiring started - got the kill switch hooked in and the electric start coil wired.
Amazon had a new switch in the warehouse deals and I found a wire harness that works with it since mine was rusty and buggered up.



Pics of the diy mounting plate for the GX390, I should have ordered it a few inches longer but oh well.


Any one have any ideas on the muffler? Its currently blowing into the glass headlight, and even if I cut and reweld it to exhaust out the side, the heat by the light is still gonna be real bad...

Just cut the pipe off the flange then build your own however you see fit! What's important is to keep it tucked somewhere it won't get caught up on things and can't  pinch your leg or foot between it and the ground in the event of a roll over.

Brianator wrote:

Just cut the pipe off the flange then build your own however you see fit! What's important is to keep it tucked somewhere it won't get caught up on things and can't  pinch your leg or foot between it and the ground in the event of a roll over.

Easy enough, any complications with just welding a 1"pipe to it or something? Should it have a few twists for back pressure?

Also, any idea how the clutch used to be hooked up? Looks like maybe a spring went from one hole to the 1/4" bolt?
The pulley in the middle swings back and forth the top middle one is an idler from what I can find online...

1" pipe should be fine, as long it's either the same size as original and short or a touch bigger and long you'll be fine. The only backpressure that needs to be worried about is excessive backpressure and why I feel bigger pipe when long is important because of the friction created insode the pipe. Engines needing backpressure is more of a myth than a fact, the less backpressure the better BUT keeping the pipe within proper sizing for VELOCITY is extremely important! Length plays a big role in the tuning department for timing sound waves to hit the valve at the exact right moment to help with exhaust scavenging but maybe that's a little extreme of a topic to touch on for us so I'll shut up about it now! Lol.

That's a toughie as it looks like an interesting setup. I'd guess one of those holes is for the linkage rod maybe? Hard to tell, can you post more pics trying to show the whole setup and the surrounding bits of tractor? Whats that rod running along the frame behind the pulleys? What moves and what's stationary. Worst case Ontario I could come down soon if we can't figure it out

Brianator wrote:

1" pipe should be fine, as long it's either the same size as original and short or a touch bigger and long you'll be fine. The only backpressure that needs to be worried about is excessive backpressure and why I feel bigger pipe when long is important because of the friction created insode the pipe. Engines needing backpressure is more of a myth than a fact, the less backpressure the better BUT keeping the pipe within proper sizing for VELOCITY is extremely important! Length plays a big role in the tuning department for timing sound waves to hit the valve at the exact right moment to help with exhaust scavenging but maybe that's a little extreme of a topic to touch on for us so I'll shut up about it now! Lol.

That's a toughie as it looks like an interesting setup. I'd guess one of those holes is for the linkage rod maybe? Hard to tell, can you post more pics trying to show the whole setup and the surrounding bits of tractor? Whats that rod running along the frame behind the pulleys? What moves and what's stationary. Worst case Ontario I could come down soon if we can't figure it out

Alright sweet, I'll slap on some pipe hopefully this weekend!

For the clutch, yeah I'll snap some more pics, if not you aren't too far from me so that would work for me  

Parden if it was mentioned, but that looks to have a variator on it?

MightyRaze wrote:

Parden if it was mentioned, but that looks to have a variator on it?

I don't think it was? What's a variator do?

Variator pulley is used in a varidrive belt set up.  Typically an engine belt goes to a double pulley that has a center flange that can slide up and down or side to side depending on the amount of pressure that is on it.  The other side of that pulley goes to the transaxle.  It works like a centrifugal clutch, but instead of speeding up with rpms, it speeds up with pressure.

The arrow does, does that pulley.



does it look something like:



It allows for more speed control.  If that is what it is, it will allow more speed control between your gears. I don't remember seeing a lever for speed control.  I just looked back and yeah, I see you're "speed lever".  Maybe that added info can help with maybe finding an old manual or something for your tractor.

MightyRaze wrote:

Variator pulley is used in a varidrive belt set up.  Typically an engine belt goes to a double pulley that has a center flange that can slide up and down or side to side depending on the amount of pressure that is on it.  The other side of that pulley goes to the transaxle.  It works like a centrifugal clutch, but instead of speeding up with rpms, it speeds up with pressure.

The arrow does, does that pulley.



does it look something like:





It allows for more speed control.  If that is what it is, it will allow more speed control between your gears. I don't remember seeing a lever for speed control.  I just looked back and yeah, I see you're "speed lever".  Maybe that added info can help with maybe finding an old manual or something for your tractor.

Hmm you know what, that speed lever is on my tractor! I couldn't figure out what it really did because when I moved it, it also actuated the brake (that's what the rod you were looking at was attached to Brian) so I adjusted the nut on that speed control lever so it engages the brake and when I disconnected the rod from the speed lever and brake assembly, it now acts as a parking brake essentially.

So I think I understand the variator from what you described, it's like a cvt but instead of RPMs forcing the belt to be squeezed out for higher speeds pressure via the speed lever forces the belt to the outside of the pulley for huger speeds right?

Good catch @MightyRaze! I knew something fishy was going on there but couldn't put my finger on it...

You're right @Silver_Pharaoh it is like a CVT and you're so very close... the lever controls the pulley which is balanced by a pair of very strong springs. That pulley looks to be in terrible shape and I'd be surprised if the center isn't seized, you have a 4 speed and the clutch is already right there so doing away with the VariDrive isn't a big deal even if a little engineering is required.

Your tractor is from 1977-1980, this must be one of (if not) the earliest example of MTDs VariDrive...

Brianator wrote:

Good catch @MightyRaze! I knew something fishy was going on there but couldn't put my finger on it...

You're right @Silver_Pharaoh it is like a CVT and you're so very close... the lever controls the pulley which is balanced by a pair of very strong springs. That pulley looks to be in terrible shape and I'd be surprised if the center isn't seized, you have a 4 speed and the clutch is already right there so doing away with the VariDrive isn't a big deal even if a little engineering is required.

Your tractor is from 1977-1980, this must be one of (if not) the earliest example of MTDs VariDrive...

What are everyone's thoughts on removing/bypassing the varidrive, using the "speed control lever" as a parking/handbreak (for hills maybe?) And using the clutch pedal as just that leaving the old brake pedal to be used as throttle?

Seem feasible?
I don't think I'd loose any speed by removing the varidrive right?

I also did find the manual online for the MTD 918, it definitely is a varidrive and it has some pics of the setup, but it's an old scanned copy so not great quality, but just enough to see the belt routing and the fact that I'm missing 2 large springs. It does list belt sizes though too.

You would essentially end up in the middle of the road for speed where the variable pulley is at it's 1:1 ratio but you could actually gain speed because you could easily choose your own pulley ratio and only have to figure out the clutch and belt length. As someone who owns 2 modified variable speed tractors I can confidently tell you that the amount of messing around requires alot of patience if you stray just one little bit away from a completely stock setup.

The springs are balanced to work with each other and without them you have a problem, MAYBE they can be found? Can you send me a link to the manual, I want to see if the parts are the same as some I have. Is the variable pulley in working order? The center sheave should spin and slide back and forth smoothly.

When it comes to VariDrive you'll probably be stuck with me for help for the most part, noone else wants to mess around with it and I'm one of only two people I know of that's successfully ran modified VariDrive. In your case, I'd advise it's way cheaper and easier for 2 pulleys, a belt and a spring to bypass it but if you want to go the VariDrive route I'll help as much as I can, I even have some parts from your tractors successor (same tractor the wheels came from), a 1982 MTD built Craftsmans GT18 but it had a vertical shaft engine.

Brianator wrote:

You would essentially end up in the middle of the road for speed where the variable pulley is at it's 1:1 ratio but you could actually gain speed because you could easily choose your own pulley ratio and only have to figure out the clutch and belt length. As someone who owns 2 modified variable speed tractors I can confidently tell you that the amount of messing around requires alot of patience if you stray just one little bit away from a completely stock setup.

The springs are balanced to work with each other and without them you have a problem, MAYBE they can be found? Can you send me a link to the manual, I want to see if the parts are the same as some I have. Is the variable pulley in working order? The center sheave should spin and slide back and forth smoothly.

When it comes to VariDrive you'll probably be stuck with me for help for the most part, noone else wants to mess around with it and I'm one of only two people I know of that's successfully ran modified VariDrive. In your case, I'd advise it's way cheaper and easier for 2 pulleys, a belt and a spring to bypass it but if you want to go the VariDrive route I'll help as much as I can, I even have some parts from your tractors successor (same tractor the wheels came from), a 1982 MTD built Craftsmans GT18 but it had a vertical shaft engine.

Here's the link:
MTD 918 Manual

I'm leaning towards scrapping out the varidrive for simplicity's sake, if for some reason I want more speed I'll swap the transaxle pulley for a smaller one haha.

I'll keep the parts though, everything I've taken off I'm keeping in case I need them later on.
Maybe I'll swap to the varidrive later on down the road

You'll need to replace the trans pulley regardless if you're scrapping the VariDrive, the groove is designed for 11/16" wide belts and regular 5/8" belts don't tend to grip them so well. How fast you want to go? A 6" in the rear and a 6" on the engine should get you to about 11mph with 25/26" tires, put an 8" on the engine and you should see 15mph. I wouldn't go much more extreme than that, apparently 2300s don't like being oversped TOO much although I don't understand why after seeing inside of one.

Thanks for the link!

Brianator wrote:

You'll need to replace the trans pulley regardless if you're scrapping the VariDrive, the groove is designed for 11/16" wide belts and regular 5/8" belts don't tend to grip them so well. How fast you want to go? A 6" in the rear and a 6" on the engine should get you to about 11mph with 25/26" tires, put an 8" on the engine and you should see 15mph. I wouldn't go much more extreme than that, apparently 2300s don't like being oversped TOO much although I don't understand why after seeing inside of one.

Thanks for the link!

No problem!

Ahh shoot, I already bought a 6.75" OD pulley from Princess Auto, the 6.75" was cheaper than the 6.25" so I said what the heck. Pulley on the transaxle is about 7" OD.

The Princess Auto pulley can take A or B belts in addition to 4L & 5L. Seems "B" belts are 21/32" wide so closer to 11/16" than 5/8" maybe that'll be okay for now if I can find one?

Yeah sitting on 25" tires for now, I'm not sure on top end speed, this isn't gonna be a racer.... Yey maybe lol. Think I'm good with 20Kph or about 10Mph. Still need to see how she handles before I go cranking up the speed.