Wicked Stick

Wicked Stick

Well Known Member
Just thought I'd pose this issue to the collective minds out there.

I co-own an RV-4 with an O-320 Lyc. in it. It has a std carburetor, Vans airbox with K&N round filter, slick mags, wooden prop, prestolight starter and only 2 primer lines (rear cylinders only)

My Query is: "Why is it so hard to start and why is such a different technique required to start it compared to a Grumman with exactly the same engine model I used to own" ? The Grumman was easy, winter time was 1.5 to 2 shots of primer and it would start up in about 5 seconds after hitting the start button.

The RV-4 seems to be very different on technique for starting. Cold, 1 shot doesn't do much and 2 shots of primer seems to flood the rear cylinders, while nothing is getting to the front. I've tried "no primer" and then as it starts to turn over, I pump the throttle once or twice while its turning over and sometimes that gets it started, while other times it does not. When it's a hot start I never prime it and it starts up sometime easily, and other times not without a fight.

Things I've already checked: Impulse mag has been removed and overhauled recently, timing is spot on as I get nice even 50 rpm drops on both when checked at run-up, and I get the same when checked at idle. I've also recently replaced the spark plugs as well.

I've heard (myth ?) that a hi-speed starter turns over an engine too fast and does not allow the impulse couple to work right ? There have been times when it starts up if I just "bump" the starter switch when it's nearing TDC or when someone hand props it after it won't start in a normal manner or simply cranking it over.

Or, do you think it is carb/intake related... It does not seem to be timing or spark related in my opinion and it runs great and smooth once it starts. On shut down, I get the normal (very slight rise) when pulling the mixture at idle.

I've been tempted to try an electronic ignition just to see if that solves it, but wanted opinions on elswhere to look first.

Thanks,
 
Two things to check:

Make sure the primer nozzles are clean. Sometimes they foul up.

The other thing to check is to make sure that the primer lines are distributing fuel evenly. When you remove the nozzles to clean, try the primer and see if they are all squirting evenly.

The primer system can be reworked so that all lines are of equal length and are teed off of the same point. That helps to distribute the flow evenly.

Vern
 
Dave
I have no primer installed and just give it 3 full pumps with the throttle before engaging the starter when cold (maybe more if really cold). Might be worth a try. Works well for me.

Fin
9A Flying
0-320 D1A. LSE Plasma III, one mag and Sky-Tec starter
 
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Finley Atherton said:
Dave
I have no primer installed and just give it 3 full pumps with the throttle before engaging the starter when cold (maybe more if really cold). Might be worth a try. Works well for me.

Fin
9A Flying
0-320 D1A. LSE Plasma III, one mag and Sky-Tec starter
Click to expand...

Fin,
No disrespect intended but this is not a good thing to do.

It can lead to an induction/air box fire very easily.
When you pump the throttle, the accelerator pump shoots fuel straight up into the induction manifold part of the engine sump.
It hits a flat surface and then drops straight back down through the carburetor into the airbox.
If the engine has a back fire while this fuel is laying there (common with a cold slow cranking engine)... you have yourself an engine compartment fire.

The very best way to prime is with a primer system.
Since many of us with RV's don't' have one, the next best way is to pump the throttle only while cranking. This will tend to pull the fuel through the induction manifold to the cyl. instead of it dropping back down though the carb.

As for Daves' problem...

One difference compared to the grumman is the wood prop. You don't have the inertia from the prop weight to help get it through the compression stroke that the metal prop provides. This extra speed helps the magnetos put out a higher spark voltage.
Assuming that the primer system is good I would be looking at the ignition system. An engine will still run well with worn (large gap) plugs and weak mags, but starting it (particularly when it's cold) is another story.
As mags get higher in time, the internal timing on them can drift which causes the output voltage to drop off. A good indicator of this happening is needing to re time your mags to the engine during routine maint.
If the mag timing has be readjusted a number of different times, it is possible for the mag internal timing to have drifted enough to cause hard starting, but the engine will still run fine after it is started.
 
hard starting

Some other things to check on hard starting lycomings. Make sure you are starting on the left impulse magneto (check your P lead wiring to make sure when you are in start mode the left magneto is not grounded) Another thing to check is the lag on the magneto itself, look on the data tag. Aerobatic magnetos have a different lag than the standard, and they make starting more difficult. We experienced this on a Citabria we had in a Aero Club ship. Also you may want to move the primer lines to cylinders 3 and 2 as this is where I have seen most factory installed primers are located, they pull manifold pressure off number 4. Hope this helps.
 
rvbuilder2002 said:
Fin,
No disrespect intended but this is not a good thing to do.
Click to expand...

Scott,
No disrespect taken, I expected a comment such as yours and you may well be correct. So if anyone feels uneasy about priming with the throttle then don't do it! My experience tells me different. I started my Vari-Eze this way for many years (Cont 0-200 with no primer), hand started it so it often backfired and I never had a problem. If my memory is correct using the throttle for priming was the recommended procedure for the 0-200 Vari-Eze. I have never had an issue with my RV, it starts beautifully and has never even backfired. Each to his own!!

Fin
9A Flying
 
DO NOT PUMP the throttle. It can easily cause a fire. Some ideas for you.

I have seen two fires in Archers because of this pumping technique. This is very serious obviously and can cost you a lot. It is also less likely to get your engine started than correct priming. Here is where I would start.

A.) Ignition:
Check plugs and make sure they are all good. I would then get the Mags timed and checked if you use Mags. This is inexpensive and probably your most likely problem area in a carburetted engine. In my view you should use at least one Electronic ignition as it helps in a lot of ways that I won't go into here. I use a Lightspeed system and I start first time after 4 pumps of prime on my 0-320 everytime. Once you are sure this area is good, look at the induction system.

B.) Induction:
Take off your airbox and filter where it connects to the bottom of the carb.
Now get someone to pump your throttle once to see if you can see it pumping fuel up into the carb correctly. It will leak down on you now, which is a good sign..:) Clean it appropriately. I am assuming it work fine as you do eventually get it started from what I can tell. Now check were the induction tubes leave the sump and head up to the cylinders. Verify that there are no leaks around them. If you have leaks it causes leaning. Different year 0-320's have different recommendations for fixing leaks here. This is generally easy to do whatever the solution. Now move up the tube and verify that there are no leaks around the rubber intake hoses and then up at the cylinders around the intake gaskets to the cylinder. Once you are good here, then you are done with the intake inspection.

C:) Priming system.
When the cowl is off, get someone to pump your pimer. Its critical to check for leaks here. Firstly leaks mean fuel dripping around on things such hot exhausts and cylinder components etc.. This can happen easily as I found out at my annual this year. Where a leak did not exist a week ago, a simple bump from your hand when changing a plug can cause one this week. Make sure you have no leaks and that your primer system is working. You can take out the top plugs before you pump it and verify by the smell etc..

Once all of these things are good and there is no air problem, I can't think of any other reason why you would not start quickly. Again, an electronic ignition makes a big difference here in my mind.

Please note, this is advice based on my experience and not much more. Please take it as that.

Hugh.
 
I am willing to bet that those engine fires were due to flooded engines.

A pump or two should not provide enough fuel to engulf an engine.

Any resultant fires were probably failed attempts to light an engine that was already flooded because it was over-primed and then accelerator pumped to boot!

I never use a primer in the Citabria and it will always start after days of sitting with a pump or two of throttle (while cranking!). Today I proved it once again.

Anyways, Dave... we need to put one of your P-Mags in the -4! Send the Slick from the -4 out for service and put that in your -8!

Your problems will be solved!

My two!

:) CJ
 
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You certainly could be right about the flooded engine causing the fires. The two people who had this problem certainly like pumping that throttle.

The problem of course is that if something is making it hard to start and someone believed that pumping the throttle more than the two times you mentioned was the right way to go, they could find themselves in trouble. Whatever works for people and what they are comfortable with is what they should do of course, but I like reducing the risk of fire both in the air and on the ground and if you have a primer system and understand your engine, its the better way to go in my book.

H.
 
I have seen this in one Cessna, The problem was that the mag impulse pawls were gummed up and would not drop out and catch the capstans on start sometimes(just sometimes, not all the time). You can tell if this is happening by rotating the prop through by hand with the mag switch off when it won't start or is hard to start and listening for the impulse click sound. (be very careful turning the prop as the engine could kick over or even start if the mags are not grounded or if the mag switch is on, or even from compression, always assume that when turning a prop the engine will start or kick over and take the necessary precautions, too many people are killed by props) If you are not familiar with hand propping tecniques, then get someone who is. If you don't hear the click, then the pawls are stuck closed in the impulse. Just remove the impulse mag and clean the pawl area good and it should start working again. (retiming will be necessary) I washed the Cessna impulse assembly with mineral spirits and disolved the gummy stuff then reoiled the pawls. The pawls should move in and out easliy with no binding or tendency to stick.
 
rvbuilder2002 said:
One difference compared to the grumman is the wood prop. You don't have the inertia from the prop weight to help get it through the compression stroke that the metal prop provides. This extra speed helps the magnetos put out a higher spark voltage.
Assuming that the primer system is good I would be looking at the ignition system. An engine will still run well with worn (large gap) plugs and weak mags, but starting it (particularly when it's cold) is another story.
As mags get higher in time, the internal timing on them can drift which causes the output voltage to drop off. A good indicator of this happening is needing to re time your mags to the engine during routine maint.
If the mag timing has be readjusted a number of different times, it is possible for the mag internal timing to have drifted enough to cause hard starting, but the engine will still run fine after it is started.
Click to expand...

The light weight of the wood prop doesn't seem to be an issue, this thing cranks over with some pretty good speed. The internal timing has been checked by an A&P IA who overhauls mags quite a bit. He told me that if the internal timing was off, then the mag drop check at idle rpm would show a big difference compared to the run-up (1700 rpm) mag check, and the low idle rpm mag check is fine.

In my previous post, I did mention that we just replaced the plugs which were worn and oval shaped with large gaps... so I figured the new, properly gapped plugs would help but it didn't really make too much difference for ease of startup. I'm thinking that for better winter starting, I'll stick with pumping the throttle a couple of times only after the engine is turning over.
Either that, or I need to put in another set of primer lines for the front cyl.
 
ReadyRV said:
Some other things to check on hard starting lycomings. Make sure you are starting on the left impulse magneto (check your P lead wiring to make sure when you are in start mode the left magneto is not grounded) Another thing to check is the lag on the magneto itself, look on the data tag. Aerobatic magnetos have a different lag than the standard, and they make starting more difficult. We experienced this on a Citabria we had in a Aero Club ship. Also you may want to move the primer lines to cylinders 3 and 2 as this is where I have seen most factory installed primers are located, they pull manifold pressure off number 4. Hope this helps.
Click to expand...

Interesting, I didn't know that... I'll check the numbers on the mag. I also may consider making/moving a primer line for the front.
 
Captain_John said:
Anyways, Dave... we need to put one of your P-Mags in the -4! Send the Slick from the -4 out for service and put that in your -8!

Your problems will be solved!

My two!
:) CJ
Click to expand...

Hey Capt'n,
I'm at the point of getting ready to try that. If you'd like to join in with me and get it hooked up, let me know. Shouldn't take but an afternoon to do it.
Just gotta install a switch and some wire, then time it up and try it.

Perhaps we can try that one day between the 18th thru 20th ?

For those out there with some regulation knowledge... if I install an electronic ignition P-mag, do I simply make a log entry ? or would I need to go back into a small temporary phase one routine ?
 
hard start

Slow / Fast cranking speed.

The magneto impulse coupling lag angle varies with cranking speed of the engine. If the starter cranks the engine too slow or too fast, magneto firing could occur too far from Top Dead Center for effective starting. Installing a faster cranking starter may require changing the impulse coupling lag angle

If the engine has a tendency to start when you let go of the starter switch or if the engine starts better with a low battery; then the engine is firing too early in the stroke. Magnetos are timed to the engine so as to provide the spark at 20 to 25 degrees before top dead center of piston compression stroke. This timing is designed to provide engine efficiency at normal operating speeds. Since starting occurs at very low engine turning speeds, magneto timing must occur closer to top dead center to push the piston down. The objective of the impulse coupling is to delay magneto firing from 20o before top-dead-center until about 5o before Top-Dead-Center by building in a 15o lag angle into the magneto impulse coupling. This happens only in theory.

The degree of impulse coupling retard is directly proportional to crank speed. Take for example the Lycoming O-235-L2C engine. The original starter cranked the engine too fast. Lycoming Service Instruction 1362 changed the lag angle of the impulse coupling from 15 degrees to 5 degrees to compensate for the fast turning starter and greatly improve starting on this engine. (with the 5 degree lag angle the engine may have a tendency to kick-back during hand propping. Don't hand prop!)

A later starter (Prestolite MMU-4001R) was specifically designed to turn the engine slower. But be careful now, this slower starter works with the original 15 degree impulse coupling so the magneto impulse coupling lag angle should remain at 15 degrees.

Now lets say you purchase a starter or magnetos for your O-235L2C engine. To get optimum starting performance you need to match the starter with the impulse coupling.

The same hard starting problem may occur if you switch to a faster turning light-weight starter and don't change the impulse coupling on any impulse coupling magneto. This info from SacSkyranch You mentioned in your first post it starts if you bump it over or it is hand propped, the fast turning starter could be the culprit.
 
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basics

Dont forget the basics... pull your leads off of the spark plugs and make sure they are not covered in junk/corrosion. Best
Brian
 
Wicked Stick said:
For those out there with some regulation knowledge... if I install an electronic ignition P-mag, do I simply make a log entry ? or would I need to go back into a small temporary phase one routine ?
Click to expand...

Can't say I have any great knowledge of the regs, but I asked this question to my DAR. I switched while still in Phase 1. He said changing to electronic ignition was a minor change, not something likely to change flight characteristics and only requiring a log book entry. If I had not been in Phase 1, I would have done some testing anyway, even though not actually required.

Bob Kelly
 
Wicked Stick said:
Hey Capt'n,
I'm at the point of getting ready to try that. If you'd like to join in with me and get it hooked up, let me know. Shouldn't take but an afternoon to do it.
Just gotta install a switch and some wire, then time it up and try it.

Perhaps we can try that one day between the 18th thru 20th ?

For those out there with some regulation knowledge... if I install an electronic ignition P-mag, do I simply make a log entry ? or would I need to go back into a small temporary phase one routine ?
Click to expand...

Potentially those days are good, so long as the WX is bad. I am scheduled to fly up to KLEW and visit a friend just back from Kosovo.

Let's talk about it!

:cool: CJ
 
videobobk said:
Can't say I have any great knowledge of the regs, but I asked this question to my DAR. I switched while still in Phase 1. He said changing to electronic ignition was a minor change, not something likely to change flight characteristics and only requiring a log book entry. If I had not been in Phase 1, I would have done some testing anyway, even though not actually required.

Bob Kelly
Click to expand...

I don't think all DAR's are going to have this interpretation, but I don't think that it matters any way. All A.B. operating limitations I have seen say that you have to notify your friendly local FAA office after incorporating a major change and receive approval of your flight test plan before flying (a DAR can't do it). Unless you have the newer operating limitations that allow you the sign it back to Phase 1 with a log book entry (but I am pretty sure you still have to notify them of the change, you just don't have to wait for a response before you fly. I know that airworthiness inspectors at FAA FSDO offices do not consider an ignition change to be a minor change).
If the change is made during Phase one then it is in kind of a gray area I think. I don't think you would have any problem as long as you didn't change something that is recoreded in the aircraft records, such as engine or propeller model, etc.
I believe the FAR (can't remember the # right now) they use as a definition for major change versus minor change, pertains to anything that could effect flight characteristics or "reliability".
I change to the ignition system could effect engine reliability until it has proven itself.

Typically you can just request a two hour Phase 1 flight test time and it will be excepted. You are then meeting the requirements of your operating limitations by actually doing some testing over an unpopulated area so everyone is happy.

Bottom line...go by what the operating limitations say and the by what the FAA interprets to be a major change.

I will look up the FAR they use for the definition if anyone is interested.
 
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Some DARs are now allowed to do amendments.

rvbuilder2002 said:
All A.B. operating limitations I have seen say that you have to notify your friendly local FAA office after incorporating a major change and receive approval of your flight test plan before flying (a DAR can't do it). Unless you have the newer operating limitations that allow you the sign it back to Phase 1 with a log book entry (but I am pretty sure you still have to notify them of the change, you just don't have to wait for a response before you fly.

Bottom line...go by what the operating limitations say and the by what the FAA interprets to be a major change.
Click to expand...
Scott, about 6 months ago there was a change allowing some DARs to amend operating limitations and airworthiness certificates. To perform this, the DAR must have function code 33 in addition to FC 46.
The FSDO must still be notified, but they can now hand it off to a qualified DAR.
 
Mel said:
Scott, about 6 months ago there was a change allowing some DARs to amend operating limitations and airworthiness certificates. To perform this, the DAR must have function code 33 in addition to FC 46.
The FSDO must still be notified, but they can now hand it off to a qualified DAR.
Click to expand...

Thanks Mel, I didn't know that...

So with that being the case, what is your interpretation of making an ignition system change?
Major or Minor?
 
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