35cc Carb Adjustments
09-01-2007, 09:09 PM
#1
35cc Carb Adjustments
My fellow modeler has a MVVS 35cc with the new lite ingition on a profile 3D plane. He has the MVVS tuned pipe with the MTW header to reduce weight. The engine has about 2 gallons of 30 to 1 gas through it and we had started trying to get the carb adjusted per Pe's directions. We are getting a very good idle and high end but the mid range is 4 stroking from just under the high end on down to idle. Almost sloppy 4 stroke sound. When we try to lean the low end needle and readjust the high end needle per Pe's instructions to correct the 4 stroking we loose the good transition from low to high. Is the tuned pipe causing this problem? What are we doing wrong?
09-07-2007, 10:32 AM
#3
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RE: 35cc Carb Adjustments
How long is the header and what prop are you running? It seems to me like a mis-match between engine load and tuned RPM range outside the engine sweet spot of 7000-8500 rpm.
BTW Gaines,
Muffler arrived, Hope to answer your last mail tonight.
BTW Gaines,
Muffler arrived, Hope to answer your last mail tonight.
09-07-2007, 05:50 PM
#4
RE: 35cc Carb Adjustments
More Corrected information!
Pe,
He is running the MTW header that is 22 mm diameter by about 185mm long measured at the center of the exhaust flange. He cut the MTW you made up for him to the about the same length as the original MVVS heavy header.
He is running the Bambula laminated Beech 20 x 8 prop. We tached it at 7100 RPM full throttle this morning. He flies 3D so spends most of his time in the midrange of the throttle and of course he needs the clean throttle response for 3D.
This problem just seemed to have surfaced over the last few flights, so don't know what might have caused the change in performance.
Would a 25mm header and pipe be better on this engine?
Looking forward to your email on the engines.
Pe,
He is running the MTW header that is 22 mm diameter by about 185mm long measured at the center of the exhaust flange. He cut the MTW you made up for him to the about the same length as the original MVVS heavy header.
He is running the Bambula laminated Beech 20 x 8 prop. We tached it at 7100 RPM full throttle this morning. He flies 3D so spends most of his time in the midrange of the throttle and of course he needs the clean throttle response for 3D.
This problem just seemed to have surfaced over the last few flights, so don't know what might have caused the change in performance.
Would a 25mm header and pipe be better on this engine?
Looking forward to your email on the engines.
09-11-2007, 05:16 PM
#5
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RE: 35cc Carb Adjustments
The problem may be related to the ratio L and H needle.
As you know by now, good running can be achieved with a lean L-needle and rich H-needle or vice versa. If the running gets too rich in midrange, it is a rich L-needle combined with lean H-needle. The cure to look for is to lean out the L-needle, and readjust the H-needle until good transition is regained. If you are a daring kind, you might want to experiment with the fuel lever height inside the regulating carb section.
Lower the lever slightly, and your top end will get leaner so you have to open the H-needle more. Right now it slipped my mind what it does to midrange. If it makes the condition worse, just bend the lever the other way. [8D]
The 25mm header I shipped today may improve the situation as well, since it improves power over the total range
As you know by now, good running can be achieved with a lean L-needle and rich H-needle or vice versa. If the running gets too rich in midrange, it is a rich L-needle combined with lean H-needle. The cure to look for is to lean out the L-needle, and readjust the H-needle until good transition is regained. If you are a daring kind, you might want to experiment with the fuel lever height inside the regulating carb section.
Lower the lever slightly, and your top end will get leaner so you have to open the H-needle more. Right now it slipped my mind what it does to midrange. If it makes the condition worse, just bend the lever the other way. [8D]
The 25mm header I shipped today may improve the situation as well, since it improves power over the total range
