Help with engine and clutch

[Matthijs]

Hello everybody,

I just stumbled upon your website and hoped you could be of help.
I have bought a couple of go karts to have fun with my friends but I can't get them to run properly.
They are retro go karts that weigh about 100kg or 220lbs. They have a Subaru Robin EH17-2B 170cc engine.
These are its specs: Robin America EH12-2, EH17-2, EH25-2 Service Manual (Page 5 of 79) | ManualsLib
So 3,5hp at 1500 rpm, 4,0hp at 1800 rpm and 6.0hp at 2000rpm
They have a 90mm (3,5") Amsbeck centrifugal clutch.
They ran real bad so I have replaced the clutch linings and springs (I've tried different springs and in the end, a go kart shop advised me to use springs that engage at 1800rpm). I have also replaced the governer style throttle with direct throttle.
Changing the throttle style worked wonders because I couldn't get the setup right with all the different springs and such.

The go karts use a belt drive and the belts kept snapping. Then I found out they were a bit loose so they were slipping a lot, causing them to get damaged. So now I've put more tension on the belts, stopping them from slipping. Now the clutches are starting to overheat. On one clutch, there were chunks of clutch lining missing. I replaced it with an original amsbeck clutch lining which didn't work, it still overheats.

Now the internet tells me I should check the clutch bearing.
But really I am wondering: Do I have the right engine at all? To me it seems like the clutch kinda worked before with 2000rpm because the belt was slipping. But now perhaps the clutch is just slipping and creating tons of heat? The go karts are rather heavy and, because the rpm is so low, the ratio between the clutch pulley and the drive pulley is about 1:3 (I'm going to check this tomorrow) and the tyres are 11".
If the engine isn't right, it feels weird because we bought the go karts from an old go kart track.

What would you guys advise me to do?

Thanks for reading,

Matthijs

 

[Denny]

Going to need pictures of your drive set up and the karts. Sounds like someone threw the years screwed with the setup and gear ratios.

 

[Matthijs]

Thanks, I just went to make some photos.
I took the clutchliners and weights out. It seems greasy but that's just from trying to get the darn thing off, which I couldn't do. Before it was bone dry. Since it's running on a ball bearing you'd expect it to spin freely without the belt on it, but it doesn't so that seems to indicate the bearing is done.
I ran the engine for a few minutes to see if the clutch would heat up due to the bearing creating friction. It did warm up a tiny bit, however the exhaust started to glow red from the heat so I guess that's another problem....
Below are some pictures of the setup

Governer is now always pulled open by this spring


Throttle cable is connected directly to the governer which is connected to the throttle by a linking rod.


The Amsbeck Centrifugal clutch without the insides.

 

[Denny]

I’m guessing that setup is not factory and the ratios are not even optimized for that kart. Some pictures of the kart would be helpful also.

 

[Matthijs]

 

[Denny]

That’s an old consession kart. I don’t know what kind of drive system it had originally. Probably had a 2:1 reduction box on the engine. You have your work cut out for you if you want a usable kart. It is probably a late 60s to early 70s model. See if you can find a makers name on the frame anywhere?

 

[Matthijs]

Yes according to the specsheet of the engine it has a 2:1 reduction inside, so while the engine itselfs revs up to 4k, the output shaft revs up to 2k. According to the specsheet that is. I haven't measured yet, but considering the topspeed, it seems about right.
I can't find a makers name anywhere on the frame. It has about 20 layers of paint on it as well so it would be hard to find. It seems somewhat DIY though. They had 9 and I've bought all of them.

I know some of them have rather new engines. I've checked yesterday and they are all the same (all with the 2:1 reduction).
Funny thing is, I have driven these karts years back at the track where I bought them from (the guy retired) and whilst they were never tuned equally, they never had the problems they have now. The clutch is really stuck to the output shaft and the driven pulley can't really be any bigger so it seems that the ratio has always been like this.
I'm going to check if I can fiddle with the idle air-fuel mixture to solve the overheating exhaust/engine. Also it idles quite high so perhaps I can fix that as well.
I'm buying a pulley puller set to see if I can take off the clutch and replace its bearing.

Any tips from you guys how to go about getting these things to run right?

 

[jmaack]

Look at the side of the engine. where the pto would normally come out isn't there. I wonder if it is internally reduced?

 

[Matthijs]

It's internally reduced. It's connected to the camshaft

 

[Denny]

That’s one of those crazy camshaft drive engines we were just talking about a few weeks ago. Back in the mid 70s I rode some karts just like that when we went to Wisconsin Dells. I don’t remember what kind of drive they had though.

 

[Matthijs]

That's cool!

 

[Matthijs]

I've got a little update.
I've replaced the bearings of the clutch (two 6006 2rs bearings). The old ones were pretty bad.
Yesterday I mounted the clutch, set the idle and went for a test drive. It runs great. highest speed I went was 50km/h or 31mph.
The clutch did get pretty hot (can't touch it without burning your fingers) but not smoking. Still I feel like it should be colder., what do you think?

Things to consider: The belt was slipping again so I've got to put some more tension on it.
When I give the idle screw just a quarter of a turn the wheels start turning already (with the wheels of the ground) so the springs might be too weak.
I'm off work in a few hours and will go and adress these things (put more tension on the belt and swap out the springs for stronger ones)
I couldn't do this yesterday because the clutch was so hot.

Wish I could just change the drive ratio because I'm okay with it running slower. Could try to add another shaft with two pulleys to increase the ratio but everything I do I have to do with all 9 go karts so I do need to think about money a bit

 

[JimD]

Where are you located? I would be interested in looking at the clutch on the engine. You are right if it was working properly it should not be that hot. You are engaging way to high, You should be getting springs to engage at 800rpm to 900rpm. How about giving me the measurement of the crankshaft that the clutch is on. I want the exact diameter and the length as well as the size of the drilled and tapped hole. You are using the correct cog belt. Is it a AX or a BX?

 

[Matthijs]

Hey Jim
I live in Europe (The Netherlands), If you want I can make some more pictures for you, just tell me what you need to see. I'm not sure what the idle speed of the engine is. I'll get some batteries for my tachometer in a bit and check it out. Then we'll be able to decide what springs to get instead of just messing around. The clutch is mounted to the camshaft which has a diameter of 20mm exactly. The clutch is secured to the shaft with a key and a bolt (axially). The belt is an AVX13x750. As I'm writing this I'm doubting if this is the right belt. When I replaced it the last time around I just grabbed one I had laying around but I think it's actually from my old Mercedes (it's a new belt though). I'll check the other belts to see if this is the correct size, although it does fit pretty well.

In a few hours I'll have the info for ya

 

[JimD]

DON'T SEND ME THE CLUTCH, I do make house calls so you can send me a boat ticket (hate big planes but use to be a pilot). When the engine is turning 1,800 rpm then the jackshaft is only turning 900rpm so that is why you have to go to a much weaker spring. Try and get stainless steel springs because they will take more than twice the heat of a music wire spring.
Looking at the larger pulley most likely you are using the correct belt since it is riding on the top of the "V" of the pulley. Go back to the clutch people and request a clutch that is engaging at the 800 to 900 range. Should work fine once you have the correct rpm dialed in.

 

[Matthijs]

Hehehe you wish!
It's really hard to find parts for these clutches though. The only place I could find that sells springs is a place in Germany.
This place
When you scroll down you can see the different springs they have for this clutch. I bought the 1800rpm springs. They come in sets of 4 but I only put two in the clutch. Perhaps the crankshaft drive engine needs 4 so it engages at 1800rpm and mine now engages (theoretically) at 900rpm?

 

[JimD]

I have to see what the set up of the springs looks like to give you the correct answer. If each spring went to a shoe to hold them in to give you the neutral then the two shoes without spring are ALWAYS engaged to the drum which means they are in a slip mode anytime the engine is running which mean you have a clutch you can use to cook your dinner. Yes, it is going to get HOT and never have a chance to cool down. Once you generated that much heat the two springs you have now are fried from the heat and no longer have the strength to hold back the shoes they are attached to because they have been annealed (lost their temper). I will try and see a picture of what the clutch looks like to verify what I just wrote is correct.
Maybe Joe Biden might give me the ambassadorship to the Netherlands and I can make a house call while visiting the embassy. Never been past Ireland and England.

 

[ezcome-ezgo]

You'll probably need to negotiate that deal through Hunter.

 

[JimD]

Saw a picture of the clutch. You might need heavy weight to lock up the clutch fast and the spring to match the weight for the 900rpm engagement. Yes it is a well built clutch and I am sure it isn't cheap because the Germans do make quality and over built the design so it last a LONG time. I have a feeling the shaft coming out of the 2:1 gear box is rather short. When you put the clutch on you might want to machine and extension to the shaft so the bolt and washer holding the clutch on puts pressure on the shaft NOT on the clutch housing. When you tighten everything down without the belt on the pulley must free spin easily with no binding of any kind. Hopefully the engine mounting plate is slotted so you can move the engine back to put pressure on the belt. If not you have to raise the engine with washers so you can to it is we are only talking a little movement needed.

Otherwise get your Dremel out and take the engine off and get comfortable. Put in a good carbide burr in the Dremel and elongate the holes at least 40 mm. This will give you plenty of slide to get the right tension on the belt.
Once you give me the shaft length I can give you some other alternatives. How much was the German clutch? That will tell me what I would do in your case.

 

[JimD]

Ezcome-ezgo -- do you still have his number?, might be worth a try for good International relationship. I still in a learning mode so I am always open to adventures in international business. I have read where he has gotten some nice deals.