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MVVS 116 CARB SETTING PROBLEM

Old 03-01-2010, 04:44 AM
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aguillamot
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Default MVVS 116 CARB SETTING PROBLEM

Dear Pe,

We have been fighting against the carburetor of this engine in order to set the needles properly, during two months with three different MVVS 116 engines, in a work bench and in the plane, on the ground and in the air.
Let me to explain our experience.

Starting with the factory settings H 1 turn and 5 minutes (maximum rpm less 200), L 45 minutes, we put the engine up-side down, in a work bench or in the plane, and the engine run rich because when WOT the engines needed some time to burn the gas and didn't reach the rpm as when the engine is right-side up. We closed the L needle 5 to 5 minutes till we had a good response, it meant a total amount approximated of 20 minutes, but when we put the engine right-side up the engine quit when quickly WOT. At that moment, we managed opening or closing the H needle but without success. The solution was to opened the L needle slightly in order to have a crispy response without quitting but when we put the engine inverted again we found same problem, lack of response; it happened when flying in knife edge motion as well. This happens on the ground and flying. After two months trying to investigate the different solutions we have throw the towel; we do not find the needles commitment , up-side down versus right-side up.
We have checked the tank, we have changed the factory hose by 4 mm Tygon, we have put a balsa box, we have used a velocity stake, we have opened the hole of the filter to 3,5 mm, we have used a felt filter, we have put baffles in the cowl and nothing clearly worked.

Is it absolutely necessary to use the hose than comes with the engine from the factory?
Does the felt filter in the tank do some effect?
Does the balsa box work in this situation?
Is it possible to substitute the carburetor for another less critical (it is understood that this carburetor was designed for carts used always right-side up)?
Is it necessary to guarantee always a minimum of 4 mm of line tube from the tank (filter, inside tubing and connections)?

Sorry for such amount of questions but please understand that we are desperate because of so much time trying to get the proper settings.
Thanks in advance and best regards,
Andrés Guillamot,
Old 03-01-2010, 05:25 AM
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pe reivers
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Default RE: MVVS 116 CARB SETTING PROBLEM

Dear Andres,
You should follow the general carb setting instructions. Reliable idle first, then top end without backing off to rich! This is glow engine practice, and not suitable for petrol (gas) engines.
The idle needle should be AT LEAST 1/2 turn open (30 minutes) From that setting, tune the H needle for best rpm, on the rich fall-off edge, but without loosing rpm!
Then check for good throttle response, but do not close the L-needle beyond the 1/2 turn open limit.
Check 1/2 throtle engine setting for best running. This is difficult, because the engine when set too lean, will sound rich! Change settings for best running using the L-Needle, but again, do not close beyond 1.2 turn open.
When done, readjust the H-needle to best rpm, rich fall-off edge. Set the throttle servo stroke lower to the point where the engine just starts to loose rpm, and use exponential (about 40%) in the throttle curve.

You definately need to use a static pressure tube to the carb. Nothing else will take care of a constant fuel reference pressure inside the carb. This is not open to discussion. The item is covered at my forum. www.prme.nl/forum . With the static tube in place, and engine tuned well, there will be no difference in running upside down. If there still is difference, the engine is tuned too rich!
All WB typewalbro carbs are made for Kart uses. MVVScorrected the carb for airplane use with their conjet system.

In the forumyou candownload the Walbro maintenance manual, where rich/lean fall-off edges are described for carb adjustments.
You did not state which propeller and muffler you use. We have had good results with menz28x14, Xoar 26x12x3laminated, up to 29x12 and 30x10.
I fly mine with a 29" three blade Mejzlik shortened to 27x12x3 and MTW TD75 canisters, well baffled.
In our club there is a second 116 on a Swiss Trainer, running a 28x12 prop / MTWTD110 canisters.this propis too small and rips.

Old 03-01-2010, 06:12 AM
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aguillamot
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Default RE: MVVS 116 CARB SETTING PROBLEM

Dear Pe,
First of all, thanks a lot for your prompt answer.

We have been working with MTW TD75, KS 88 VS-5 R canisters and eventually with Bison pits style. Propellers: Mejzlik 28x10x2 (6.300 rpm), Biela 28x10x2 (6.150 rpm) and Mejzlik 30x10 (5.850 rpm) in Madrid which is 700 meters altitude.

We should recognize that the H needle has ben set very slightly rich and the L needle to have the best response up-side down probably 25 minutes or slightly less. We will now work as per your suggestions.
By the way, I forget to comment you that in the first engine we had, during last summer, we checked the static pressure tube that we knew from your website but we didn't find any improvement probably due to the fact of our mistakes tuning the engine well.

Something about the big hose that comes with the engine?

We are going to follow your suggestions this weekend and I will tell you our experiences.
Thanks again for your help and best regards,
Andrés,
Old 03-01-2010, 07:27 AM
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pe reivers
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Default RE: MVVS 116 CARB SETTING PROBLEM

MVVS supplies the engine with a piece of fuel line. As long as you can tune your engine rich with the H-needle less than 1.5 turn open, the fuel line is thick enough.
Just open up the L-needle some more, and start with 3/4 open.
Old 03-09-2010, 04:56 AM
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aguillamot
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Default RE: MVVS 116 CARB SETTING PROBLEM

Dear Pe,
Last weekend we were working in the bench with one third engine after breaking-in. We started with L needle 45 minutes and H needle 50 minutes. the engine performed perfectly right side up burning 1 liter of gas. When we put engine up side down, it was doubting and lasting to reach the maximum rpm when we pulled the throttle so we closed the L needle 5 minutes because at half throttle the engine seemed rich, one of the two cylinders were burning too much gas and running in four stroke. after closing only 5 minutes the L needle the engine run perfectly with fast acceleration. we wasted another liter of gas.
But when put the engine right side up, again it quit when WOT, just at the end.

We tried shortening the stroke of the sick even losing 100 rpm, using 40% exponential curve, using a curve by points but all unsuccessfully. the only thing that seemed to work was closing partially the hole of the carburetor with a finger.

Summarizing, up side down, L needle needs to be closed 3-5 minutes (aprox. 40 minutes total), right side up L needle needs 3-5 minutes opened, all with H needle 50 minutes opened. There is no common point that works both sides, there is a commitment between both sides, if you want to run perfect right side up, inverted runs rough.

I am wondering whether a filter in the intake of the carburetor will help because we realized that putting a finger in the intake, closing slightly it in order to avoid entering a lot of air suddenly, it worked.
Could you be so kind to let me know your suggestions about the filter?

Is it possible that the carbon fiber sheets inside the carburetor need some breaking in in the sense to get them much more flexible. I am asking myself it those parts are working properly when they are new.

Thanks a lot for your help.
Best regards,
Old 03-09-2010, 06:35 AM
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pe reivers
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Default RE: MVVS 116 CARB SETTING PROBLEM

You got theLow needle about right,But need to adjust the High needle richer to get WOT right. The idle needle contributes a lot to the mixture at WOT, so be careful there. Any small changes with the L need also changes to H.
I run my engines with air filter. That may be of influence.
The reeds have nothing to do with it, unless broken, in which case the engine will be hard to start and idle.

edit:
The L needle has a very steep taper, so it is very sensitive to small corrections. When the setting is about right, 1/64 (one minute) changes will be about right if you do not want to over-correct.

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