What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

RV7/io360 hot weather issue on the ground...

steve91t

Well Known Member
Hello all! My dad has owned his RV7 for 8 years now (had 300 ish hrs on it when we bought it) and we?ve had a hot weather issue from the start. The PO, the guy who built it, said that once in a while it needs the fuel pump when on the ground to help prevent vapor lock.

So it?s an IO360 with dual P mags.

During NC summers and on the ground, it runs great while warming up. But once warm, like after a flight, we have problems. Yesterday was a good example. A buddy of mine and I flew it to a grass field glider airport where I fly the tow plane. 10 minute flight in the morning, then it sat in the sun all day while I towed. At around 4 pm (over 100 degrees on the field), I jumped in with a friend to give him a ride. I did a cold start procedure and it fired right up. We took off and flew around for less than 10 minutes at 1500 ft and at about 20? and 2400 RPM. Came in and landed. Now I needed to do a quick turn around since one friend was getting out and the other was getting in. Hot starts with such a quick turn around are nearly impossible with this thing. So I decided to keep the engine running. I had it runnng at about 900 RPM and leaned out. Friend A jumped out and friend B climbed in. He was just about in when the engine started to die. It went from running smoothly then it sounded like I had pulled the mixture to off. That quick. I turned the fuel pump on, shoved the mixture in and added throttle. I just barely kept it alive. From there it was running like **** and there was nothing that I could do to make it happy. I told my buddy that we had to hurry up and go. I had to keep it at about 1300-1400 rpm just to keep it running. As soon as I added power for take off, it smooths right out and runs perfectly.

So we fly 30 minutes to get BBQ. Land and shut it down 45 minutes later I did a hot start, short taxi, and took off. It ran fine on the ground. Flew 30 minutes home, low pass, and landed. Taxing in, the engine was idling ok, but surging. Again, this has to do with the hot weather on the ground issue.

It just had an annual and the mechanic (familiar with RV?s) insulated the fuel lines to try to help his problem. But it made no difference. Everything I?ve read says that you might need the fuel pump to help with vapor lock until the cool fuel is pulled through the lines then you don?t need it. Our issue seems to be different. It?ll be idling just fine then all of a sudden it?s trying to quick and it won?t stop until you either take off or shut it down and let it cool. If it actually quits, it won?t restart until it cools.

Again, this is only an on the ground issue. Like vapor lock. But how could a 10 minute flight with just a few minutes of idling cause this? Something else is going on and we can?t figure out what. The problem seems to be getting worse.

I?m sorry this was so long, I wanted to give as much detail as possible.

Any help with be appreciated.

Steve
 
Gascolator

Try blast cooling a shroud around both the mechanical fuel pump and gascolator, if you have one. I'd also consider removing the gascolator, as it's a perfect little oven for your fuel.
 
This is a pretty common problem. Suggest you search and will find several ideas. I had most success with smaller injectors, stronger spring in spider and a fuel return system to provide cooler fuel before the servo.

Also suggest that you get your idle mixture dialed in. I like the method of adjusting to the lowest Map with the engine fully warm.

Larry
 
I’ll find out if a gascolator is installed.

We do agressively lean at idle.

The spider spring would be an easy thing to do. Not sure why that would make a difference, but it’s worth a shot. Any adverse effects of the spider spring?

Tell me more about this return line? So it’s cockpit controlled? You crack it open with the fuel pump on so it allows circulation of cool fuel? How big of a job is that to have it done?
 
Last edited:
I'm running an IO360 with .024" injector orifices and a 4-pound spring in the fuel divider and it behaves perfectly well on 100LL and acceptably well on 91E10 in west Texas temps. I do not have a gascolator, nor an engine-driven fuel pump, and all my fuel lines are insulated with a double-layer of firesleeve.

The return valve you are asking about is the Airflow Performance purge valve, it's a simple three-way valve placed at the inlet to the fuel divider that, when activated, will isolate the fuel divider and reroute all the fuel to a return line back through the firewall and back to your fuel tank. The idea is that in the event of shutdown-heatsoak-hotstart routine, you would use this to precool the fuel system and remove the FWF heat in the fuel and fuel components prior to start. I have it installed in my 9A and hotstarts work beautifully with that. My hotstart procedure is as follows...

Throttle and mixture full forward.
Activate purge valve (cockpit control via cable).
Electric fuel pump on.
Wait 60+ seconds - during this time fuel is flowing from the tanks forward through the servo and the line to the purge valve and back to the tank, removing heat from those components that would cause fuel to boil.
Mixture to ICO, throttle closed plus a crack open
Deactivate the purge valve
Crank the engine and push mixture to mid-range as the engine catches. Every engine is different and it will take a while to figure out the sweet spot on yours, but with mine a hotstart is just as easy as a coldstart using this technique.
 
... It just had an annual and the mechanic (familiar with RV?s) insulated the fuel lines to try to help his problem.

Can you guys elaborate how that insulation is done? I have a similar problem and would like to try that trick. thanks
 
Can you guys elaborate how that insulation is done? I have a similar problem and would like to try that trick. thanks

http://www.aircraftspruce.com/catalog/appages/aqfiresleeve.php?clickkey=4118

buy this and install it over the existing lines with safety wire ties on the ends to hold it in place. If it's not convenient to remove the line to slide this over the hose, then buy a larger size and cut it lengthwise, wrap it around the line, and use safety wire every few inches to hold it in place.
 
Can you guys elaborate how that insulation is done? I have a similar problem and would like to try that trick. thanks

I?m not sure exactly what he did but I?ll tell you it didn?t make a bit of difference.

I just talked to him. He has another RV7 in his hanger with the bypass. He knows exactly what it is and how to install it.

So the plan is to remove the gascolator if it?s installed and install the bypass.

What?s funny is he also has an RV8 there without a bypass. He called the owner and asked if he has hot start issues. His answer was ?nope, because I know that whenever I shut it down, I?m there for at least 30 minutes!? I thought that was funny.
 
Can the bypass valve be cracked open on the ground with the engine running?

No, it's meant to operate full-open or full-closed - and as soon as it's open to the bypass line, that goes all the way back to the tank so there's zero pressure left to open the fuel divider and all flow to the injector lines.

To do what you're thinking of would need one of the EFI solutions where fuel is delivered via electric pump all the way to the injector rail, with a bypass regulator at the far end of the rail that returns the excess fuel back to the tank. That design does truly keep cool fuel to the injectors all the time.
 
You can?t crack the valve just a little? Otherwise this thing won?t help my scenario I described in my original post.
 
You can?t crack the valve just a little? Otherwise this thing won?t help my scenario I described in my original post.

No. This valve will not help your situation, trying to pass X amount of fuel FWF and returning Y amount back to the tanks while sending Z amount to the fuel divider. You will need an EFI installation for that.

Sorry, but there's no "easy button" on this one.
 
Can the bypass valve be cracked open on the ground with the engine running?

Depends how you set it up. My return is pre-servo, not post servo. I drilled an orifice that would flow about 8-10 GPH through the return circuit with the return valve open. I designed it this way to insure that enough flow would be remaining from the fuel pump to support full power on the engine if I accidentally left it open, which I have done far too many times. The mech fuel pump will flow 35-45 GPH, so I have plenty of margin at full power. My injectors are in the primer ports and I will get stumbling when I go to idle on final and like to have to return open on landing to help reduce this when the ambients get hot.

My return starts at the FI servo, not the fuel pump to help take more heat out of the fuel. However, my situation is a bit unique and need to shed more heat due to the injector locations on the hot side of the baffles.

Larry
 
Last edited:
IO360 hotbstart

Ibhad my share of problems starting after a lot of stuff trials and errors installed a slick start.

She starts every time hot or cold

Alot of folks have Ideas but putting enough spark on the plugs helps the engine start

Cold starts. Fuel oump on for about 2 seconds
Mix rich theottle 1/4 open firesnoff on about the secound blade

Hot starts
Blip the fuel pump a nani second
mixture idel cutoff
Throttle about half open
Crank as reduce throttle toward idle as engine fires at some point during the throttle reduction slowly put mixture in

Thats it works fine if the battery is good

Pull a couple botton plugs and check for led deposits. If you see leadnin the plugs lean aggressively on the ground

Check injector nozzles for trash. It will cause your 4!cylinder engine to really miss behave

Hope part of this helps
 
Back
Top