TEA-20 starting problems - part III

Ok, well we've some progress, but still some problems. We've finally got the awkward beast running, though I have to hold the choke out else it backfires (through the carb air intake!!!)and immediately dies. However we've had it running long enough to adjust the timing via distributor, and that seemed to help. We've looked at adjusting the settings on the carb, and the govenor, with so-so effects, but we feel pretty close now.

A couple of things we've noticed - plugs are new, but quickly get sooted up (poor mixture??) and also the fuel pipe is wrong (it looks like a homemade one, and runs round the front of the tractor, rather than the rear, so we're going to replace that), and the final thing is the exhaust seems to get really really hot. I know they do, but this does seem excessive. Does this point to anything?

So there we go - thanks to all the tips so far, we've got it going (to an extent!!) - hopefully you can point out how we might get to the next stage.

Any help, very gratefully received as ever.....

First of all. If I understand you correctly, you have got the engine running long enough to adjust the timing. This is not the way to do it.
The centrifugal weights starts to advance timing at very low speed, so when it idles the timing is advanced already. The way to do it is when the engine is stopped.

I will give you the correct procedure, but I need the engine number and distributor number.
The engine number is located above the oil filler cap, and a little forward.

Then, take a look at the numbers below.

Type 1:
Engine number S1E to S8995E
Distr. model D3A4
Distr. number 40132

Type 2:
Engine number S8996 and onwards
Distr. model D3A4
Distr. number 40146

Type 3:
Engine number S1E to S8996E
Distr. model D3A4
Distr. number 40146

Type 3 is actually a Type 1 engine with the type 2 distributor, as a Lucal Replacement distributor.

Please tell us what combination you have, type 1, 2, or 3.

I have a very strong feeling that you have too late timing. Both the sooting, bad running, and hot exhaust indicated this. In addition, setting the timing at idle speed will 100% sure fool you to believe you have a more advanced timing than you actually have. So, it is pretty many circumstantial evidences that you may have too late timing.

Best regards, Bill

Ta, Matt

The exhaust manifold getting really hot is indicative of late timing and/or too lean a mixture, and that can be caused by the retarded timing and/or an air leak around the carb metering system. Now if the plugs have dry sooty fouling and you have an air leak around the metering section of the carb, you have to over rich the mixture(either via the choke or by increasing the power jet opening) just to get it to run, causing your situation.

The most likely culprits for the air leak are the throttle shaft, the connect flange between the carb and the intake manifold, and the intake manifold to cylinder head connection. To check for leaks get the engine running and then CAREFULLY spray starting fluid around the the aforementioned locations. If you hit the leaky area, the engine will speed up when the starting fluid gets sucked in.
The fuel pipe while not OEM is something to deal with later as that is not the source of your problems unless it's not providing sufficient fuel.

If it were me, I would make sure the timing is correct (not just close) and also make sure that the centrifugal advance mechanism is working by noting that the spark timing advances when the engine rpm increases. Then check for the air leaks as described above. Do these check sytematically and check for proper operation after you change anything, writing down the results for future reference. Don't just willy nilly start changing everything and then try to check. You'll never get to the root cause of the problem and you won't learn much in the process.

I think we"ll start with the air leak principle - that"s come up a few times and seems to point to the problems we"re having.

Is there a particular check to ensure that the timing is spot on rather that just close enough? We"ve had the distributor rebuilt completely, so I would hope that the centrifugal advance mechanism is ok.

Will report back any findings.

Thanks again for your advice, Matt

If you have it handy and wouldn't mind forwarding it on, I'd be very grateful.

Thanks, Matt

Cheers, Matt

I don't know the Spec on your Engine but someone
should have it.

JMHO

Matt

Hot exhaust = lean mixrure.

(At least it does in aircraft. My TEA20 doesn't seem to care too much!)

You sure that Zenith carby isn't sucking air somewhere?? Last time I had a problem requiring the choke partially out, the carby was sucking air due to wear.

Send me an email before you buy a replacement timing chain. It may not be the chain - more likely worn crank shaft and cam shaft sprockets. John (UK) is a wonderful help - and knows the problems I had!

And the fuel line definately runs behind the fuel tank - not in front!

So I guess it's possible that we have worn rings and a lean mixture!

As for the carb, it's probably something we need to check again now we can get it running for an extended period of time. It's had a rebuild kit, so a new main gasket and a manifold gasket, so it shouldn't be leaking air, but you never know. If it isn't the gaskets, where else might it be worn?

Yes, I'm ordering a new fuel line today!! No more messing about.

Matt