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carb heater

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Re: carb heater

Postby Anonymous » Tue Feb 10, 2015 10:14 pm

Posted by: Gary on 09:37:48 12/17/14 Wed

Steve, sorry did not see the 1 before post until today, wow lots of work done,
I would of thought you should still obtain the correct tick over regardless of the above work, should be easier to obtain it unless the set up is not correct.
If you put your hand over the inlet rubber and turn the prob, it should suck your hand like a prostitute with no air leaking noises, does it do this? Its the best test to check the inlet

Re: carb heater

Postby Anonymous » Tue Feb 10, 2015 10:14 pm

Posted by: Steve on 13:10:57 12/17/14 Wed


We did test for air leaks and all passed. We checked around carb rubber and also inlet. Carb rubber is brand new.


The engine passes all those test except the idle. Engine is very smooth at anything above 950RPM. No hesitation on applying power. At 950RPM the engine runs fine but if I do anything to take it below that RPM it starts to stutter (for example turn off one Mag while it is idling).

As a check, we changed the plugs, plug leads, both Mags and checked over the dizzy caps and rotor arms. All were in 'as new' condition' and changing them made no difference.

The only thing I can say is that I have not yet managed to warm the engine up completely. Other than being flown back from maintenance which showed no problems, it has only been ground run so far and in this weather it has been impossible to get the oil temperature above 40-50 degrees without risking the CHT temperatures going too high.

Re: carb heater

Postby Anonymous » Tue Feb 10, 2015 10:14 pm

Posted by: Gary on 19:37:46 12/17/14 Wed

Steve, when I had an inlet issue the symptoms were
Poor idle, rough at anything below 900 rpm
Crap at starting
Unable to push the choke in after start up
Symptom of a duff mag drop on the left hand side
Engine failure x2 on finals
In flight and high tick over smooth and good.
The near exact to what you are saying. The above led me to the left mag issue, turn off the mag at tick over and rough as a badjets Backside, above 900 and no notable issue.
I stripped the carb 3 times, stripped the start carb, replaced all seals, left hand mag, left hand plugs, left hand leads, left hand dizzy, left hand rotor testing in between each change out, i could not find the fault.
After 2 engine outs when going to tick over (would not quit static) i would not fly it again. What hit me was on the 3rd day on cold start up, after a couple of mins I was able to pull the choke without the engine cutting out. This is a no no, so i knew instantly in was an inlet fault as the motor would die if any choke was pulled when running, then I pulled the carb off and did the suction test, i heard it sucking air, turned out to be sucking under a jubillee clip, a tiny split. Fitted a new rubber, tested the suck, all good and it ran ad it should, no mag drop smooth idle at 600 rpm etc and if you pull the choke when running it cuts instantly.
So I still think you have either an inlet issue or carb set up or leak issue. The ignition is a shadow you are chasing
All assuming you have good compression and valve train set up correctly

Re: carb heater

Postby Anonymous » Tue Feb 10, 2015 10:14 pm

Posted by: RogerLewis on 11:16:37 12/17/14 Wed


I have to agree with Gary.

When an engine is released from service one should be confident that it is 100% fit for flight. There are a number of indicators that reflect the health of an engine and a smooth low rpm idle is one of them. If this cannot be achieved the the cause should be identified especially during the 'running in' period. As Gary mentioned, the cause could be as simple as a failing carby rubber - easy to replace but has the potential of an engine failure at a later date.

You may want to consider seeking the assistance of someone who is familiar with all the vagaries of the engine. In the meantime, I have included a list of 'indicators' that may be of assistance:

1. 4 good equal compressions with no unusual metallic noises
2. No tendency for the engine to go tight when hot. You can check for this after running the engine at 1200 rpm for 2 mins or watch the propeller kick back after shut down - or both.
3. No oil leaks
4. The engine should be able to run smoothly at very low rpm
5. The engine should be able to go from idle to WOT without hesitation. WOT rpm should be around 2800-2900 rpm
6. At WOT there should be a drop of 25-50 rpm when hot air is applied.
7. Main gallery oil pressure shoul be in the green segment, vary with rpm and only drop into the yellow at idle.
8. At 2000 rpm there should be no drop in rpm during tbe ignition test.

This is a list from memory and I used a similar one to pre-flight engines prior to maiden test flights. Sometimes I accepted a below par indicator but only after determining the cause.

Re: carb heater

Postby Anonymous » Tue Feb 10, 2015 10:14 pm

Posted by: fj27 on 16:56:35 12/17/14 Wed

About cold starting prior to anything don't forget to check the good setting between ignition modules and magnets.

Re: carb heater

Postby Anonymous » Tue Feb 10, 2015 10:14 pm

Posted by: Roger on 15:44:19 12/18/14 Thu

Thanks - that is a good reminder although I do recall that the engine will not be able to run smoothly at very low rpm if the settings are not correct. I will check again to make certain.


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