P-70 Pops on first start
05-23-2005, 11:39 AM
#1
Thread Starter
Join Date: Feb 2002
Location: Raleigh, NC
Posts: 426
Likes: 0
Received 0 Likes
on
0 Posts
P-70 Pops on first start
Matt,
I have a P-70 installed in an older BVM sabre with Bypass. On the first initial start (each time) I set the trottle trim high, then place the throttle to full to start the start sequence. The propane valve opens immediatley and you can hear the propane rush into the engine, the starter spools the engine with no ingnition, then disenganges. On the second spool up, there is so much propane, I get a big pop, (scares the heck out of you if you are not ready for it).
I then pull everything down and go for a second start, this time it lights off beautifully and no other problems.
I have Tried:
1- venting the propane tank just before start to relieve pressure
2- placing just a little Propane inthe tank
I hate to change the valve values as it lights off so nice the next try.
Let me know whatcha think
Anthony Wiencek
Raleigh, NC
I have a P-70 installed in an older BVM sabre with Bypass. On the first initial start (each time) I set the trottle trim high, then place the throttle to full to start the start sequence. The propane valve opens immediatley and you can hear the propane rush into the engine, the starter spools the engine with no ingnition, then disenganges. On the second spool up, there is so much propane, I get a big pop, (scares the heck out of you if you are not ready for it).
I then pull everything down and go for a second start, this time it lights off beautifully and no other problems.
I have Tried:
1- venting the propane tank just before start to relieve pressure
2- placing just a little Propane inthe tank
I hate to change the valve values as it lights off so nice the next try.
Let me know whatcha think
Anthony Wiencek
Raleigh, NC
05-23-2005, 12:48 PM
#2
My Feedback: (9)
Join Date: Dec 2001
Location: Tomball,
TX
Posts: 442
Likes: 0
Received 0 Likes
on
0 Posts
RE: P-70 Pops on first start
Anthony,
Im no Jetcat expert, but I have a p-70 on a kangaroo and also have a buddy that has one in a bypass on an f-22 that I help him with
The propane valve should not open until the starter motor spins the motor up around 5k-7k rpms. If the propane is releasing into the motor before it spins. I would suspect a faulty valve or ECU. If the valve was not shutting properly I would suspect that it would leak propane constantly. So I would lean a little towards a faulty ecu. But since you say that is starts the second time no problem, I think you just confused the start sequence a little in your description.
Next, I would like to ask how you have your onboard propane tank mounted. Vertically or Horizontally? If horizontal, it tends to want to let liquid propane into the system which will cause a serious pop if not flame on start up. If you cannot mount vertical, Then at least try to get the tank tilted up a little. After I fill my on board propane tank, I always purge any liquid from the line. You don't have to open the manual valve alot. Just enough to get the liquid out.
On both mine and my buddy's I have adjusted the start gas parameter down to about 40%. On your first attempt to get light off you are getting to much propane and the mixture is to rich to achieve proper ignition. Becuase it is a fresh charge of powermax the pressure in the tank is a lil higher. When you go for your 2nd attempt it lights smoothly because the pressure is less and less propane is being injecting in the turbine.
On my second start of the day without refilling the onboard propane most of the time it starts. If not.. i shake the nose of the plane a little to stir up the onboard gas tank and it lights off no problem. I really feel that if you adjust your start gas %, bleed any liquid propane in the lines, make sure your start tank is not horizontal that your problem will be gone. I hope this has helped you some and Im sure matt will chime in as well.
Im no Jetcat expert, but I have a p-70 on a kangaroo and also have a buddy that has one in a bypass on an f-22 that I help him with
The propane valve opens immediatley and you can hear the propane rush into the engine, the starter spools the engine with no ingnition, then disenganges
Next, I would like to ask how you have your onboard propane tank mounted. Vertically or Horizontally? If horizontal, it tends to want to let liquid propane into the system which will cause a serious pop if not flame on start up. If you cannot mount vertical, Then at least try to get the tank tilted up a little. After I fill my on board propane tank, I always purge any liquid from the line. You don't have to open the manual valve alot. Just enough to get the liquid out.
On both mine and my buddy's I have adjusted the start gas parameter down to about 40%. On your first attempt to get light off you are getting to much propane and the mixture is to rich to achieve proper ignition. Becuase it is a fresh charge of powermax the pressure in the tank is a lil higher. When you go for your 2nd attempt it lights smoothly because the pressure is less and less propane is being injecting in the turbine.
On my second start of the day without refilling the onboard propane most of the time it starts. If not.. i shake the nose of the plane a little to stir up the onboard gas tank and it lights off no problem. I really feel that if you adjust your start gas %, bleed any liquid propane in the lines, make sure your start tank is not horizontal that your problem will be gone. I hope this has helped you some and Im sure matt will chime in as well.
05-23-2005, 02:07 PM
#4
RE: P-70 Pops on first start
Hi Anthony,
It is almost certainly too rich of a propane mixtureon start up. That is why the second start is better, the pressure head in the tank is lower, probably because of the temperature drop in the tank as a result of the first start. I would dial down the percentage duty cycle on the starting gas by 10-20% and try again
In addition, make sure the glow plug is very hot, by having the element pulled out properly, and the voltage at the top of the heat range for the plug you are using.
Good luck
Matt
It is almost certainly too rich of a propane mixtureon start up. That is why the second start is better, the pressure head in the tank is lower, probably because of the temperature drop in the tank as a result of the first start. I would dial down the percentage duty cycle on the starting gas by 10-20% and try again
In addition, make sure the glow plug is very hot, by having the element pulled out properly, and the voltage at the top of the heat range for the plug you are using.
Good luck
Matt
05-24-2005, 07:37 AM
#5
Thread Starter
Join Date: Feb 2002
Location: Raleigh, NC
Posts: 426
Likes: 0
Received 0 Likes
on
0 Posts
RE: P-70 Pops on first start
OK guys, looks like we will attempt to lower the propane values. To answer one of your other questions.........
The propane tank is vertical.
I did not notice in the manual description on how to lower these values. I will try tonight and report tomorrow.
Getting ready for Fentress this weekend.
The propane tank is vertical.
I did not notice in the manual description on how to lower these values. I will try tonight and report tomorrow.
Getting ready for Fentress this weekend.
05-24-2005, 10:40 AM
#6
Senior Member
Join Date: Oct 2002
Location: Chatham, UNITED KINGDOM
Posts: 143
Likes: 0
Received 0 Likes
on
0 Posts
RE: P-70 Pops on first start
I have a similar problem with a trim Sabre, I solved it by fitting a computer fan in a tube and blowing air from the air intake through the by-passwhile going through the start process. it is possably back pressure and the gas is igniting in the by-pass in front of the engine.
Just a thought.
Tony
Just a thought.
Tony
05-26-2005, 08:07 AM
#7
Thread Starter
Join Date: Feb 2002
Location: Raleigh, NC
Posts: 426
Likes: 0
Received 0 Likes
on
0 Posts
RE: P-70 Pops on first start
Ok Guys,
I made some adjustments the other night. The ECU was originally set at 80% for gas flow. I lowered this to 60%, went to start and it popped. Lowered to 50% and would not light off, back to 60%, and it would not light off again. Then to 70% and it lit off nice.
The only issue was I was not refilling the tank each time to simulate the same situation.
I have left it at 70% for now and will try it this weekend.
I too have used a blower through the intake, doing this, the engine will make one attempt with no light off, then it cycles again and lights off pretty.
I may just have to vent the gas tank prior to each start.
Thanks guys.
Anthony Wiencek
I made some adjustments the other night. The ECU was originally set at 80% for gas flow. I lowered this to 60%, went to start and it popped. Lowered to 50% and would not light off, back to 60%, and it would not light off again. Then to 70% and it lit off nice.
The only issue was I was not refilling the tank each time to simulate the same situation.
I have left it at 70% for now and will try it this weekend.
I too have used a blower through the intake, doing this, the engine will make one attempt with no light off, then it cycles again and lights off pretty.
I may just have to vent the gas tank prior to each start.
Thanks guys.
Anthony Wiencek
