Need help with rupp Tecumseh hs40 tuning

[bikesandcars]

When I first started working on the minibike it didn't run at all.

First thing I checked was spark, it had none. After doing research and trying to fix what was there I assumed the condenser / coil was bad. I ordered a Mega Fire II ignition and a new coil and that seemed to solve that problem, nice hot spark.

After I had spark it still wouldn't run, so I ordered a reproduction hs40 carburetor and now it starts / idles like a champ.

I'm in the process of getting the governor hooked up, but before that I'm trying to test it running.

It idles good, but when I give it gas it accelerates briefly, then chokes out and dies wetting the plug. Are there some recommendations for screw settings for this carburetor?

 

[buckeye]

Aprox 1 1/2 turn out from just closed. Don't close the jet too tight, it will bung up the needle.

 

[bikesandcars]

Aprox 1 1/2 turn out from just closed. Don't close the jet too tight, it will bung up the needle.

Thanks. That's where I started but it's acting wayyyy too rich. wetting the plug and stalling the engine.

My arms are getting tired and I need to clean the plug every 2 stalls.

Both H and L screws are 1.5 turns out

 

[buckeye]

Turn them in a bit to maybe 1 1/4.
Or there may be a air leak.

Got any pictures?

 

[bikesandcars]

Turn them in a bit to maybe 1 1/4.
Or there may be a air leak.

Got any pictures?

sure, here's some pics

The governor is very "wiggly". I re-set it per the manual instructions and it seems to work (limits the throttle anyway).

The high speed mixture is adjusted at 1/2 turn out for it to run right! that can't be right.

Is it the angle I'm testing it at?

I looked closer at the plug, it's not fuel that's coating the plug it's oil. .... it's fouling on oil really bad, which might also explain why it's so smokey. It seems to have OK compression so my first guess is valve guides. I checked the level. Any thoughts?

side note, I remember now why we put this thing away 20 years ago... there's nothing more frustrating than a hand-starting engine that doesn't run right

 

[bikesandcars]

so I had it running, then it did it's usually load-up shut off thing.

I cleaned the plug and can't get it started anymore.

I checked the compression, 60 psi... I'd expect about 120 or so, so it looks like it's time for a rebuild.

That's a real shame because I don't really have the desire to spend another $100 to make this old Tecumseh engine new again.... but I have over $100 invested in it now with the ignition and carburetor... I feel like I'm between a rock and hard place with this stupid engine

 

[buckeye]

Well, there ya have it.

Another thing, looks like the carb doesn't sit level so that will jack you up too.
Look on the bright side. Should be good for another 40 years when you are done.:thumbsup:

 

[markus]

remember that the rupp HS40's have a ball bearing supported crankshaft, you have to pull the seal at the crankshaft output side and remove the C-clip on the crank in order to pull the sidecover off the motor.

 

[71demon340]

i used .010 over rings file fitted to my stock bore hs40, just used a hone to get a cross hatch runs good now!!

 

[oldfatguy]

try gapping the plug a little tighter---.025---

there are a few things that you can check before you go ahead with a rebuild.

first make sure that there isn't too much oil in it and that you are using 30 weight oil.
Then take the breather apart and clean it and the filter.
If it still smokes after that pull the head off and check the valves to see if they move side to side in their bores, a little is OK but over 1/16 of an inch or more shows that they are worn. Check the valve lash gap with the piston up on the compression stroke . Then check the piston to see if it rocks front to back in the bore. If it seems too loose that means the cylinder has a taper worn in it and should be rebored to rebuild it right.. Also check for deep scratches in the cylinder. The things that killed most mini bike engines is they were run without an air cleaner or with dirty oil . If that all seems good then take the crank shaft and piston out to make sure that the rod journal isn't scored or worn out and that the crank isn't worn where it rides in the block behind the flywheel. If all the parts look good then just put a set of rings in it and a new head gasket.

 

[jrzmac]

I think you might need new rings. You should be up over 100 for the compression, not 60.... and oil on your spark plug, thats not good. Is it smoking a lot?

 

[bikesandcars]

try gapping the plug a little tighter---.025---

there are a few things that you can check before you go ahead with a rebuild.

first make sure that there isn't too much oil in it and that you are using 30 weight oil.
Then take the breather apart and clean it and the filter.
If it still smokes after that pull the head off and check the valves to see if they move side to side in their bores, a little is OK but over 1/16 of an inch or more shows that they are worn. Check the valve lash gap with the piston up on the compression stroke . Then check the piston to see if it rocks front to back in the bore. If it seems too loose that means the cylinder has a taper worn in it and should be rebored to rebuild it right.. Also check for deep scratches in the cylinder. The things that killed most mini bike engines is they were run without an air cleaner or with dirty oil . If that all seems good then take the crank shaft and piston out to make sure that the rod journal isn't scored or worn out and that the crank isn't worn where it rides in the block behind the flywheel. If all the parts look good then just put a set of rings in it and a new head gasket.

Thanks, I'm not gonna give up! It just gets so frustrating when you're yankin yer arm off! Great advice and I really appreciate it!

I might need to lean on you guys for a support group until I get this figured out

 

[bikesandcars]

I think you might need new rings. You should be up over 100 for the compression, not 60.... and oil on your spark plug, thats not good. Is it smoking a lot?

I agree, new rings at minimum. I'll take the head off and give it a good once-over.

Also, the governor seems really floppy, is it supposed to be nice and tight or a little sloppy when the engine is off?

Oil was some kind of blue thick funky stuff.... I replaced it with straight 30 wt. I generally run 15/40 diesel fuel on older stuff because of the extra protection for the cam...but I'm trying to follow all specs until I get this thing figured out.

 

[The Restore Kid]

Nooooo usually the first culprit in low compression is the valve clearance.. Just routine maintenance in a small engine requires pulling out, and re gapping the "valve lash" as the valves and seats burn away, the valve lash tightens up, till the valves will not even close at all...

If you are at low compression pull the head and see what the valves look and act like before building anything..

 

[bikesandcars]

All will be revealed shortly (drum roll please) :hammer:

any comments on governor? Maybe that is shot too! do the shafts get loose or is there a bushing that would allow the governor to move around?

 

[bikesandcars]

Well, I have some bad news...

The valves are "wiggley" when they are opened up (by rotating the piston). They seem to be a little wobblier fore/aft than side to side. I'm getting probably just around 1/16 total displacement (which seems like a lot to me)

I checked the valve clearance and it is OK, (.011 intake, .015 exhaust). The seats seem OK, not burned, and there is no carbon in the breather. They may be just serviceable.

The piston however seems sloppy in the bore and the bore is noticeably scored on the "front" side of the engine (opposite intake / exhaust) and the piston is visably looser fore-aft than side to side.

In my opinion I will likely need a .020 over piston and a bore/hone just to get it running. The valve wobble I'm not sure about and could use some more advice on.

Is it scrap yet?

 

[71demon340]

mine was bad like yours, i just honed it and filed down some .010 over rings, i used a valve stem seal on the intake valve, new gaskets and it runs great!! I couldn't really find a shop to bore it and really the engine would only see a few hours of run time a year anyway.

 

[71demon340]

Tecumseh 40016A
Intake Valve Seal, ohh60. this is what i used on my intake valve stem.

 

[The Restore Kid]

Shewww yeah it probably needs some rebuilding then.. Hone it out and find a piston somewhere.. maybe.. :laugh:

I might have one in a good used motor but if the bore is blown out you'll need over sized stuff..

The governor is fine unless you can physically see blown apart plastic gears or something.. It is supposed to flop around easily.. The engine running puts pressure on the internal parts and thats what causes resistance.. If it's not bolted to anything and the motor isn't running it just flops in the breeze..

 

[bikesandcars]

I found a .020 piston / ring set at ruppparts.com, that plus the cost of gaskets, a new air cleaner (mine is missing) and other standard rebuild parts will be setting me back around $170 all together if I pull the trigger. If I want to add new oversized valves or get bronze valve guides for a ream / insert job it will be on top of that.

I've changed my mind for a little on how to approach this rupp. Right now the entire bike needs redone... it's rusty, greasy and nasty all over and I just want to have it running so I can use it a little. I think I'm going to put in a $120 predator 212 engine in a non-altering way (not changing the frame or hard parts). If I can pull that off and I enjoy using the bike then sometime in the future I'll probably pull the trigger on a full rebuild and restoration including the HS40.