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Jan 15, 2020, 09:36 PM
Still gassin' it.
Quote:
Originally Posted by modeltronics
Maybe I found the problem. There is a groove in the carb barrel that a screw rides in. This cams the carb barrel in and out a little as the throttle is rotated. The grove in this barrel looks slightly defective at one end. This would be the end that the screw would be in at low throttle. It is slightly wider at this end. That would allow the barrel to move in and out more at low throttle. I looked at the barrel in an ASP FS70 and 90. The groove is a constant on those engines. From what I can tell the part number is 70813F. It looks like the carb is the same for the 70 and the 80. Just Engines and Mike Goes Flying does not have the part. Now I just have to try to find the part.

I tried to take some pictures of the defect. I had the camera very close to the part and the pictures came out bad but maybe you can see what I am looking at.

Pete
I don't think that is it... I grind those grooves all the time. But I would have expected the wear to be on the other side of the groove (not the "full throttle side" but on the right side of the groove).

Is the spring still in? there should be a fairly weak spring on the bottom of the barrel-hole.
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Jan 16, 2020, 05:53 AM
Registered User
Thread OP
Yes, the spring is still in there. I can feel the spot in the grove as I rotate the barrel.
Jan 16, 2020, 05:57 AM
Still gassin' it.
Probably that engine has been mounted on rubbers, and spent a lot of time idling….
Or it has been a hardening issue.

Anyways, I have not seen that before.
Jan 16, 2020, 06:24 AM
Registered User
Quote:
Originally Posted by 1967Brutus
Probably that engine has been mounted on rubbers, and spent a lot of time idling….
Or it has been a hardening issue.

Anyways, I have not seen that before.
No Bert, this can be the result of too low spring force.
Each time when in the problemfull position so expanded spring you sometimes can see the axial movement of the barrel. The groove will wear out at that location by vibration. It sometimes happens when the pushrod linkage has an axial movement and delivers some axial force to the pushrod linkage/lever/barrel in that position. I mostly use a straight pin in the lever and no (quick)link.

Cees
Jan 16, 2020, 09:05 AM
Dieselized User
gkamysz's Avatar
The problem with the barrel is several things. I would say it was large clearance in the groove initially only leading to more wear. I really don't know why the springs were used as they are almost never strong enough to overcome intake pressure at low throttle in a four stroke. The barrel sees a variable pressure from the intake stroke and this pulls it in and out. This is quite apparent in some engines. It also makes some engines very difficult to tune when it affects idle mixture.

OS manages to make barrels from aluminum with no springs and they do not wear.
Jan 16, 2020, 09:34 AM
Still gassin' it.
Quote:
Originally Posted by gkamysz
The problem with the barrel is several things. I would say it was large clearance in the groove initially only leading to more wear. I really don't know why the springs were used as they are almost never strong enough to overcome intake pressure at low throttle in a four stroke. The barrel sees a variable pressure from the intake stroke and this pulls it in and out. This is quite apparent in some engines. It also makes some engines very difficult to tune when it affects idle mixture.

OS manages to make barrels from aluminum with no springs and they do not wear.
I can say from experience and having experimented with it (not on purpose but as a side observation) that the required springforce depends on the groove clearance: on my FX46 the groove having a couple of tenths of a mm clearance did not cause issues with the Original spring and the barrel did not move sideways (you can notice that by the mixture going a bit leaner when you push the barrel inwards).
When the groove was modified, it suddenly became an issue, but only a marginally stronger spring allready completely solved that issue.

On the aluminium OS barrels: I have noticed that the groove in the barrel is very wear resistant. But I have seen wear on the retaining pin that rides in the groove, and that creates similar issues. I have fixed a few by installing a spring (usually from discarded carbs from worn or broken engines).
Jan 17, 2020, 01:32 PM
Registered User
Thread OP
I have not run the engine again because it is cold and raining here. The part I want is impossible to find alone. I ordered a new carb from Just Engines. I can see ASP parts are starting to disappear. I will report back on the RPM wandering on the low end after I get the new carb.
Thanks All,
Pete
Jan 18, 2020, 11:09 AM
Registered User
AA5BY's Avatar
Hi Pete,

As to magnets, I've used them as small as 1/8 dia x 1/16 thick and they trigger fine. The thinner can also be stacked if the ring offers more meat.

FB on the piston stop you have made and for others needing a stop, it can be as simple as a 1/4" wood dowel chucked in a drill and filed down so it just grips the hole threads as it is screwed in,

Mounting the pickup can be either pretty or not. One of my conversions has the pickup actually mounted to the engine mount rather than the engine.
Jan 18, 2020, 03:59 PM
Entropy is happening!
Jim.Thompson's Avatar
Quote:
Originally Posted by AA5BY
Hi Pete,

As to magnets, I've used them as small as 1/8 dia x 1/16 thick and they trigger fine. The thinner can also be stacked if the ring offers more meat.
.........................
That is what I have done, fitted two small ones stacked.
They don't need much of a magnetic field to trigger.
Jan 18, 2020, 04:48 PM
Registered User
I'm using a 1.5mm dia x 2mm tall magnet on my conversion. Works fine and easily fits the prop hub.

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Jan 18, 2020, 05:11 PM
Registered User
Thread OP
I had no feel for how strong the magnet needed to be. After receiving the RCEXL unit I saw the hall sensor was an Allegro 3144. After looking up the specs on the 3144 I saw the operate field was 70 to 350 gauss with a typical hysteresis of 55 gauss. All of this is at room temp. After reading that I had no idea of the field produced by my Ebay magnets. I was concerned that I might not have enough magnet. Now after running the engine I know it works and was probably worrying about a non issue. Now if I can just get my new carb in the mail to see if that fixes the idle RPM wandering.
Thanks for the help and comments.
Pete
Jan 23, 2020, 05:29 PM
Registered User
Thread OP

OS Surpass 52


Iím still waiting for the ASP FS80 carb from Just Engines. So, I decided to spend some time with the OS Surpass 52. I have a friend up the road with a lathe in his garage that let me make some rings for the magnet. I turned 4 rings and brought them home. My plan was to use a 2-56 set screw on the rings to hold it in place. After looking at the set screw I realized I didnít have an allen wrench small enough for it. I have no idea of what size it takes but it is small. I had enough room to use a 4-40 so that is what I used. I got the engine all timed yesterday and the weather was good enough today to run it. I put a 12X8 prop on the 52 Surpass. It started right up very easy. I leaned the engine per Bertís suggestions and it runs great. Top end was around 9K RPM. Here is where it gets interesting, the low end. I let it run at about 1.5K RPM as I walked to the mail box and back. It ran that way but didnít sound like it would run for a long time that way. It just didnít sound happy. It is very happy to run for a long time at 1.8K to 1.9K RPM. I donít think I could get it running like that with a glow plug. At around 1.9K it is very stable and I think it would run all day that way. One advantage I can see for CDI is the low end. It is a lower RPM than with glow and very reliable.

I will report back on the ASP FS80 as soon as I get the carb in the mail.

Thanks again to all who have helped me with this project.
Pete
Jan 23, 2020, 07:11 PM
Registered User
AA5BY's Avatar
Great report. Sounds like you are having fun with them.


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