CB750 Yerf Dog Kart

[quickbird144]

Hello everybody. Checking in with this custom Yerf dog Kart I picked up a couple days ago. PO didn't know too much about it so had to do some research. Front end is from a Kawasaki Mojave atv. Frame is a Yerf dog. Honda CB750 engine. Learning more as I go. Runs but carbs need a run through. Got quite a few plans for it and hope to gain some knowledge from here as well.

[mrdeadman1]

Just keep an eye on those welds, lol looks like a whole lot of fun

[Kartorbust]

Looks like they welded an extension on the engine sprocket, supported by what looks like a pillow block bearing to get it to the axle. At first I thought it was a jackshaft, guess not. Hopefully it holds.

[landuse]

Originally Posted by Kartorbust

Looks like they welded an extension on the engine sprocket, supported by what looks like a pillow block bearing to get it to the axle. At first I thought it was a jackshaft, guess not. Hopefully it holds.

That is the first thing I noticed too. I had to look o see if there was a supporting pillow block on that shaft extension. That engine puts out a lot of torque and if the shaft isn't supported things are going to bend real fast

Otherwise it looks good from what I can see with my limited experience. I hope you have a lot of fun with it

[Duceduce]

horrible carbs to tune and sync at least the ones I had were!! My cb750 was jammed into a Suzuki let 230 ... it was insane .. I would take them to a place that does sonic carb cleaning if they are really bad. It’s hard to get all the little ports in them clear of gummed up old fuel. Where are you from ?I’d love to put mine up against yours and see how it does lol!!

[itsid]

Yeah that contraption will cause some headaches in the very near future.

I so hope the extension shaft wasn't welded to the engine shaft..
if it was, I'd cut it off and build a proper jackshaft instead,
if you want to try that way first.. get a second pillow block and support the shaft
on one more point (ideally close to both ends)

I'm inclined to say that the shaft is supportet that way because the weld was crooked and the shaft doesn't run true...

Anyways, the carbs are a bit delicate I hear,
but frankly.. most of the problems come from improper fuel and air filtration.
If you rely on cheap undersized paper air filters (no oil soaked foam prefilter)
no wonder you collect dust in your carb,
if you don't use a fuel filter at all, or reuse a dirty one over and over again w/o changing it occasionally,
no wonder you collect grime, right?

I'd also install a fan horizontal in front to the engine on the swingarm pointing up.
That engine is an aircooler afaik and you do not want it to overheat. an additional oil cooler might help as well.

'sid

[quickbird144]

That rear setup definitely is no good. I plan on adding a fan eventually. I'm sure some more fabrication would be involved to change that rear axle?

---------- Post added at 09:03 PM ---------- Previous post was at 08:10 PM ----------

Originally Posted by Kartorbust

Looks like they welded an extension on the engine sprocket, supported by what looks like a pillow block bearing to get it to the axle. At first I thought it was a jackshaft, guess not. Hopefully it holds.

I'm hoping to change the way the engine drives the wheels. The PO said he had issues with they bearing. I guess it was on the outside of that plate and kept pulling away. So he swapped it to the inside and welded it to the engine cage.

---------- Post added at 09:05 PM ---------- Previous post was at 09:03 PM ----------

Originally Posted by Duceduce

horrible carbs to tune and sync at least the ones I had were!! My cb750 was jammed into a Suzuki let 230 ... it was insane .. I would take them to a place that does sonic carb cleaning if they are really bad. It’s hard to get all the little ports in them clear of gummed up old fuel. Where are you from ?I’d love to put mine up against yours and see how it does lol!!

I head these carbs can be a pain especially without the factory air box. There's a guy that'll rebuild them and jet them properly with oem parts for about $400. Still debating on that but they all definitely need a rebuild.

I'm in Florida. Have any info on your build?

[quickbird144]

You guys were right about that shaft. Welded straight to the gear. And I think the axle shaft is bent on the driver side. That back wheel wobbles.

[Kartorbust]

Hopefully you can pull that welded sprocket off the engine and get a new one on there. I'd probably extend the whole swing arm for it.

[itsid]

^^that!

if he didn't remove the retaining nut on the engine sprocket,
then you're pretty much screwed

"straight" as in straight or in just?
Since frankly whoever made that decision was maybe dull enough to just wing that weld
and the extension itself is what wobbles.

Disconnect the chain for a minute and run the engine in first at idle just to see if that extension is straight or not.
That also gives you the opportunity -once you killed the engine again-
to see if you can simply pull it off the splined shaft that should hold the sprocket.
(I think I see a grub screw on the pillow block bearing holding you back, so take care of those first)

If you can, there's no need to make a new jackshaft IMHO.. that might just work with a second pillow block.
One can actually be fittet directly to the sprocket cover,
the outer one just has to move closer to the chain driving sprocket IMHO.

Not too sure that gear ratio is serving you well.
As a base: the same ratio as the bike had is a good starting point
(since at best you compensate the higher weight with the smaller wheel)

But since your wheels are fairly big and the kart is fairly heavy... maybe a few more teeth will serve you better *shrugs*

axle will be tough, since frankly an inch is just not enough, 1.25" might not be either
and you won't find many hubs for a european kart axle (50mm [~2"]) to fit an ATV rim...

One thing you can try is to move the wheels as close to the bearings as possible
(or the bearings to the wheels of course which means welding )
that way you might get away with a flimsy axle.


'sid

[quickbird144]

I appreciate all the insight guys. Very helpful. I'm trying to come up with ideas for the rear axle setup now. Maybe even some kind of irs. Not afraid to weld just not that creative lol.

Also an update. The wobble is infact the axle shaft. The shaft welded to the sprocket actually spins straight and true. Also they removed the nut holding it on before welding that shaft onto it! Guess they thought that one over.

If I were to do some kind of swingarm would I need to bring the whole axle back and level with the engine, build from there? Not having the axle under the engine or could I still make it work?

[itsid]

great news
So only a new axle and a few bearings to stiffen that rear..

'sid

[Duceduce]

Originally Posted by quickbird144

That rear setup definitely is no good. I plan on adding a fan eventually. I'm sure some more fabrication would be involved to change that rear axle?

---------- Post added at 09:03 PM ---------- Previous post was at 08:10 PM ----------



I'm hoping to change the way the engine drives the wheels. The PO said he had issues with they bearing. I guess it was on the outside of that plate and kept pulling away. So he swapped it to the inside and welded it to the engine cage.

---------- Post added at 09:05 PM ---------- Previous post was at 09:03 PM ----------



I head these carbs can be a pain especially without the factory air box. There's a guy that'll rebuild them and jet them properly with oem parts for about $400. Still debating on that but they all definitely need a rebuild.

I'm in Florida. Have any info on your build?

Ahhh that’s to bad I’m in Canada ... my build is a cross between a manco deuce ,Yamaha Worrior , Polaris XC, and parts from a few other machines but all it really is a manco deuce with a two stroke Polaris XC 700 motor in it ... tons of fun

[quickbird144]

Alright so hoping maybe I can get some ideas. Got a new axle put on. 1" solid steel "deluxe" from gokartsusa. All was well until I got on the happy pedal. Bent the axle on the drive side. The axle is held in with four pillow blocks, 2 on each side. I'm thinking the rear wheels need to move back behind the engine just a tad instead of being infront. Maybe an ATV axle of some sort? What you guys think?

[Kartorbust]

Joe-405 uses a Banshee axle on his ZX12 Grudge racer. An atv axle will hold up better and longer than a standard go kart axle. It should also give more options for wheels.