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MVVS 45 - won't pump gas, fixed but a new problem

Old 12-02-2007, 11:26 AM
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Miketc
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Default MVVS 45 - won't pump gas, fixed but a new problem

I have a MVVS 45 mounted inverted H9 260. Last flight back in April or May, the engine cut out. Landed safely but since then I have not been able to get this one to start. Engine was running smoothly on a pipe with no visible problems. The engine will not suck fuel. There is a good spark on the plug, the engine turns fine against compression. The engine has more than 2.5 + gallons thru it.
Let's see what have I done:
1) Checked and cleaned the carb.
2) Cleaned out fine mesh filter under the diaphragm. (removed a tiny amount of gritt)
3) Fuel pump diaphragm looks new.
4) Cleaned out the mesh filter under the Float diaphragm. (Removed the needle, closed off the other and sprayed with carb cleaner)
5) Checked the reeds (Looked new, a small space under one of them, hair line gap between reed and housing when looking up against the light)
6) Float diaphragm looks new.
7) Cleaned out the 1st fuel filter, second has a Sullivan screen type, looks new.
7) Fuel flows fine when the fuel pipe is off the engine.
8) Turn the prop thru compression, no fuel flows.
9) Primed the carb with a separate line.

After all this, not even a burp from the engine.
L Needle set at 2
H set at 1.75

Your help is needed..
Mike




Old 12-02-2007, 12:32 PM
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pe reivers
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Default RE: MVVS 45 - won't pump gas

Mike from Kuweit,
have you checked the crankcase pulse line from crankcase to the carb? (leaking, kinked, nipples sound etc.)
Your country is hot, so it may be leaking?
Old 12-02-2007, 02:34 PM
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Default RE: MVVS 45 - won't pump gas

Hi Pe, yes done that, I pushed some air thru when I had the reads out for inspection.
The pipe is firmly in place, I cannot remove it from either end.
The carb is facing down, engine is inverted.

Question, I have a NIB MVVS 58 (for a comp-arf 2.3 under construction) engine.
I appreciate that the carb is not the same, but is it worth swapping out and trying this carb on the MVVS 45?

By the way, the MVVS 35 in my Edge 540 is still going very well.
Running 6700 on a Mejzlik 20 x 10, still running a little rich, a little black spots under the plane.

Regards,
Mike
Old 12-02-2007, 04:08 PM
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Default RE: MVVS 45 - won't pump gas

As a test you might do that. I'm afraid that tuning will suffer, though I am not sure. A larger carb needs higher rpm, so smaller props to perform well. You may run out of steam with the reed induction. I have tested the reeds up to 8000 rpm on a 58cc, and they still did the job.

The carb not pumping may be due to a hidden leak, or you may be in need of a membrane kit. Can you pressure test the carb for pop-off pressure, and see if it leaks somewhere?
Old 12-03-2007, 10:52 AM
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Default RE: MVVS 45 - won't pump gas

Hi Pe, can you explain how to "pressure test the carb for pop-off pressure, and see if it leaks somewhere?"
Is this something I can do without special "equipment"?

Thanks for the support.
Mike
Old 12-03-2007, 12:50 PM
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Default RE: MVVS 45 - won't pump gas

Quite shorthand:
I use a bicycle hand pump, a pressure line with check valve and a pressure gauge with added end fuel line connected to carby fuel inlet. Fill the end line with gas, and pump away. Nasty things always show up, surprises included.
Old 12-03-2007, 12:55 PM
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Default RE: MVVS 45 - won't pump gas

Thanks for the support. I will give it a go.
Old 12-11-2007, 03:44 PM
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Default RE: MVVS 45 - won't pump gas

any news yet?
Old 12-13-2007, 11:56 AM
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Default RE: MVVS 45 - won't pump gas

Bought a replacement carb kit. Fitted new diaphragms and gaskets. The carb is getting fuel now. I reset the both needles to 1 & 3/4 turns. Not yet had a chance to run the engine, maybe some time this WE, time permitting. I will let you know either way, but it looks promising. Thanks for the support.
Old 12-15-2007, 12:15 PM
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Default RE: MVVS 45 - won't pump gas

Pe, fixed the problem.
Engine is pumping gas now but,
I had a second plug holder fail.

I was running the engine on the ground, making tuning adjustments to the carb.
The engine would not settle down, it had an intermittent hiccup at full revs.
I cut the engine to check the carb settings when I noised the plug lead was not tight.

I attached some photo's. ( Set up on an internal canister)
The engine is running sweet, no issues with transition.
Wide open on the ground is 7080 before dropping back to 7960 rpm and stable. ( Set up on an internal canister)
Idle is 1350 rpm, it does drop a little then picks up.
Not sure the carb is fully set up.

I find it quite bizarre that I have had two of these fail on the same engine.
I swapped out the plug holder for a spare and the problem was gone. The plug is fitted tight against the head.
Your thoughts on this would be appreciated?
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Old 12-15-2007, 01:27 PM
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Default RE: MVVS 45 - won't pump gas, fixed but a new problem

The plug sows that your top end needle can be leaned out slightly.

The breaking of the tapered plug boot land is vibration dependant. I do not know how you fitted the engine, and wether the HT plug cable is looped and supported to allow free engine movement without loading the plug boot. The land is stressed, while the rest of the lower boot is not. When exposed to excessive vibration, it will fail in time.
Now, it is hard to define excessive vibration. Low vibration frequencies can have quite a large amplitude before becoming excessive, while high frequency have near invisible amplitude and will wreck anything that is subjected to them.
Your application seems unhealthy for the plug boot, so you have to change something. I would suggest a stay to the (foam isolated) plug lead, that vibrates with the engine, and a loop in the lead between the stay and the ignition unit.
Old 12-16-2007, 01:44 PM
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Default RE: MVVS 45 - won't pump gas, fixed but a new problem

Pe, thanks for the feedback, I have attached a number of photo's to show you my setup. I hope they help!

Vibration, while setting up the low speed, the engine was vibrating (somewhat) +- 1100 rpm.
I then adjusted the idle to between 13 / 1400 rpm. It does drop a tad, but not much, 50 rpm or so then speeds up.
No vibration at the high end. I am going to remove the prop and check it for balance. The prop is a Mejzlik 22 x 10, with no visible damage or nicks.
I took some video on my phone, need to down load it tomorrow at work. I will post the footage for you.

"Wide open on the ground is 7080 before dropping back to 6960 rpm and stable. ( Set up on an internal canister)" had to correct to "6960"
On the high end, I will try to lean it by 5 or so min's.
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Old 12-16-2007, 02:52 PM
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Default RE: MVVS 45 - won't pump gas, fixed but a new problem

Hi Mike,

I do not see you exhaust system, please take its foto.
Jan
Old 12-16-2007, 03:31 PM
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Default RE: MVVS 45 - won't pump gas, fixed but a new problem

Janch, some of these were taken when I originally set the plane up.
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Old 12-16-2007, 05:42 PM
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Default RE: MVVS 45 - won't pump gas, fixed but a new problem

Mike,
You might consider tying the high tension cable to the cylinder (with tie-wrap and appropriate isolation of course). That will reduce the free cable length that swings on the plug boot. Also lead the HT cable directly to the back, so you can make a loop between the engine and ignition box.

I notice that you gave no cooling baffles. This is not too good! See http://www.prme.nl/forum/viewforum.php?f=18 for ideas and information.
Old 12-17-2007, 12:21 PM
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Default RE: MVVS 45 - won't pump gas, fixed but a new problem

Thanks, will give it a go before the holidays.
Happy holidays to you all.

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