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Rcwrecker

Rcwrecker

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Got her running and everything seems okay except she bogs down at full throttle, have done some research but am getting varied answers, you guys are always Spot on so please can you tell me where I'm going wrong/ what I need to do
 
Perfect reply…

So, bogs down as in it noses over and looses power or simply stops building RPM as if never coming up on the pipe?
 
Shad0man said:
Perfect reply…

So, bogs down as in it noses over and looses power or simply stops building RPM as if never coming up on the pipe?
Click to expand...
Noses down and loses power , will stall if I don't let up ,if I do let up runs fine again until I try and give full throttle.
 
First thoughts are fuel starvation on the big end … particularly since it will recover if you let up on throttle.

Others may offer a different path.

If mine, I would start by making sure that the fuel tank is able to breathe and that a vacuum is not being created within it on the big end.

Often while idling and under moderate power the issue won’t be evidenced.
 
You are welcome…

Sounds like you have a cool project.

I should have asked. Is the RC new to you or simply a new issue?

If it is new to you and you have not done so.

1. Inspect the spark plug and gap
2. Fresh gas with proper mix
3. Confirm that the baseline carburetor low and high speed adjustments are correct. I’d start with the the high speed 1/8-1/4 rich and once the issue is resolved you can lean it out again.

I look forward to your progress.

Enjoy.
 
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Gotcha

If you did not do so check the items I mentioned above. Particularly the carburetor low and high speed settings. Doing this insures that your rig will remain safe while this issue is being resolved. If the items all check out fine I come back to it being a fuel delivery issue.
 
Thanks again ☺️ have been trying to run as rich as possible, I guess it's just tweaking the carb , barely touched the low end screw beyond suggested settings, will follow your advice on other things 😎
 
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I understand the term and the mechanics of POP pressure however, I personally have never checked it on my RCs. I have cleans rebuilt the carburetors so maybe I have been lucky. Is there an easy way to test the POP because I suspect he is wondering the same.

Also, you me reference 20psi. I just did a quick search with Walbro and I am seeing 10-12psi. Why do you suggest the increase?

Thank you
 
Shad0man said:
I understand the term and the mechanics of POP pressure however, I personally have never checked it on my RCs. I have cleans rebuilt the carburetors so maybe I have been lucky. Is there an easy way to test the POP because I suspect he is wondering the same.

Also, you me reference 20psi. I just did a quick search with Walbro and I am seeing 10-12psi. Why do you suggest the increase?

Thank you
Click to expand...
10-12 psi should be a reset pressure. Walbro stopped giving standard pop pressures years ago. mainly due to many different applications that the same carb can be used on, requiring different settings. Typically, I find them north of 30psi which is too high for most applications, save for smaller displacement engines running carbs that are a bit on the big side.
Anyway, I think I covered most of this in the carb sticky so I'll be brief.
In a diaphragm carburetor there is no float to keep a constant fuel supply. The diaphragm and fuel inlet needle are what controls this function. Higher pressure means less available fuel to the jets. High rpm lean issues can be because of this. Conversely too much fuel (excessively low pop pressure) will cuse too much fuel and the inability to control fuel setting with the jet screws. It all needs to be set correctly.
20 psi is a good general rule of thumb to shoot for. Reset (when the fuel needle closes) should ideally be 10-15 psi. I try to shoot for 10 psi as this gives a nice open and closed range and should flow adequate fuel for most, even ported smaller cc engines. (As a side bar even my saws up over 100cc get set to 20psi pop pressure. It's really a goldilocks setting.)

Checking pop pressure is pretty easy. You'll need a way to pressurized the carb with a gauge attached.(mity vac) It is a wet test, ie the carb needs fuel In it to test it.
Remove the metering cover and diaphragm to reveal the fuel inlet needle and lever. Pressurize the carb via the fuel line slowly. You should see it build up, then stop and start to fall. Once it stops and starts to fall is your opening pressure. More commonly refused to as pop pressure. The gauge will co tinge to fall till the fuel inelt needles seats again. This is your reset pressure. I don't get suoer hung up on reset. Around 10 typically good.
I don't and do not reccomend going over 30 psi, it too high and either the metering lever spring will need replaced, or it will need clipped. Do this in small increments. A little change in spring height can have quite a large effect. I don't advocate clipping springs, but I have tons of springs laying around and hundreds of carbs for parts. Most don't and I haven't been able to find the kit walbro use to sell for fine tuning carbs, so clipping the spring becomes nessisary.
 
Rcwrecker.

Sean shared good information however, in all my years I have never had to tweak my POP off pressure. I have replaced diaphragms and springs during carburetor rebuild but that is all.

FYI, the POP off pressure is the pressure required to move the carburetor needle out of the seat so fuel can flow. Based on what you shared this does not sound like the specific issue that you are having as you are able to meter the fuel via the low and high speed needles.

I’d encourage you to focus on the simple and somewhat obvious items at this point. It’s a new rig and for you to blindly open the carburetor and make tweaks I think is premature.

Here is a description of the POP off operation as shared by another for your reference.

The pop-off pressure is the pressure at which the needle valve will open thus letting the fuel to enter the metering chamber. The value of this pressure is a function of the engine, power output and other factors and it will directly affect the air-fuel mixture that the carburetor will deliver to the engine. It is true that the mixture adjustments are done by the HI and LO screws but if the pop-off pressure is too high, it can lead to fuel starvation especially at high RPM. Such a situation will cause engine overheating and possibly lead to a seizure.If the pop-off pressure is too low, the carburetor will have a flooding tendency especially at low and mid RPM. It will also cause difficulties in restarting a warm engine.
Seandonato73 said:
10-12 psi should be a reset pressure. Walbro stopped giving standard pop pressures years ago. mainly due to many different applications that the same carb can be used on, requiring different settings. Typically, I find them north of 30psi which is too high for most applications, save for smaller displacement engines running carbs that are a bit on the big side.
Anyway, I think I covered most of this in the carb sticky so I'll be brief.
In a diaphragm carburetor there is no float to keep a constant fuel supply. The diaphragm and fuel inlet needle are what controls this function. Higher pressure means less available fuel to the jets. High rpm lean issues can be because of this. Conversely too much fuel (excessively low pop pressure) will cuse too much fuel and the inability to control fuel setting with the jet screws. It all needs to be set correctly.
20 psi is a good general rule of thumb to shoot for. Reset (when the fuel needle closes) should ideally be 10-15 psi. I try to shoot for 10 psi as this gives a nice open and closed range and should flow adequate fuel for most, even ported smaller cc engines. (As a side bar even my saws up over 100cc get set to 20psi pop pressure. It's really a goldilocks setting.)

Checking pop pressure is pretty easy. You'll need a way to pressurized the carb with a gauge attached.(mity vac) It is a wet test, ie the carb needs fuel In it to test it.
Remove the metering cover and diaphragm to reveal the fuel inlet needle and lever. Pressurize the carb via the fuel line slowly. You should see it build up, then stop and start to fall. Once it stops and starts to fall is your opening pressure. More commonly refused to as pop pressure. The gauge will co tinge to fall till the fuel inelt needles seats again. This is your reset pressure. I don't get suoer hung up on reset. Around 10 typically good.
I don't and do not reccomend going over 30 psi, it too high and either the metering lever spring will need replaced, or it will need clipped. Do this in small increments. A little change in spring height can have quite a large effect. I don't advocate clipping springs, but I have tons of springs laying around and hundreds of carbs for parts. Most don't and I haven't been able to find the kit walbro use to sell for fine tuning carbs, so clipping the spring becomes nessisary.
Click to expand...
Great write up .. thank you
 
Thanks mate,was going to do due process today but weather said otherwise, will follow all guidance.one point is ,it has been suggested that it might be low screw needing leaning but I'd prefer not to do that in a new engine (unless totally necessary)
Rcwrecker said:
Thanks mate,was going to do due process today but weather said otherwise, will follow all guidance.one point is ,it has been suggested that it might be low screw needing leaning but I'd prefer not to do that in a new engine (unless totally necessary)bit of a pita because for whatever reason can't upload videos
Click to expand...
 
It will work out just fine!!!

One step at a time…

Create your to-do list and check and verify each step … in the end the path may take you to Sean’s suggestion regarding the POP off pressure but this is not where I would begin my journey.

In fact, Sean enlightened me too which was very cool.

In any case.

You have a cool toy, a good approach by asking, and your not being frustrated is pivotal.

Takes care
 
Shad0man said:
It will work out just fine!!!

One step at a time…

Create your to-do list and check and verify each step … in the end the path may take you to Sean’s suggestion regarding the POP off pressure but this is not where I would begin my journey.

In fact, Sean enlightened me too which was very cool.

In any case.

You have a cool toy, a good approach by asking, and your not being frustrated is pivotal.

Takes care
Click to expand...
Thanks so much fella 😎😎😎😎😎
 
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