Hi folks

[Seandonato73]

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.

Great write up .. thank you

for the past several years it's been a common issue with walbro carbs. We've witnessed many complaints with the same symptoms. Low, no power on top end. Runs fine at idle to mid rpm. Stumbles, stalls, return to lower rpm/idle it's OK again. Certainly not a cure all, but easy enough to check and set and won't hurt the performance of the engine. We've been down this rabbit hole quite often, to the point where guys have thrown new carbs on to have the same issues.

 

[Rcwrecker]

for the past several years it's been a common issue with walbro carbs. We've witnessed many complaints with the same symptoms. Low, no power on top end. Runs fine at idle to mid rpm. Stumbles, stalls, return to lower rpm/idle it's OK again. Certainly not a cure all, but easy enough to check and set and won't hurt the performance of the engine. We've been down this rabbit hole quite often, to the point where guys have thrown new carbs on to have the same issues.

Thanks fella,is there a better substitute carb or something?my baja 5b clone has a walbro spiral diaphragm without any issues but unsure of the carb on this one (am assured is k320 engine and relevant clutch n carb ) everything else on my rig is really assuring...
This rig also doesn't seem to take off until got but does lovely then (except top end bogging) thanks to all of you, you always seem to hit the nail on the head

 

[Rceverywhere]

Was curious what pop pressure was and the search for the site gave 10 pages of response mostly about pressure so it didn't help and I gave up, then forgot to Google search it, thanks for asking and for relearning us.makes a hole lot more sense now, and as most forum sites the search is useful for wasting time

 

[Seandonato73]

I thought I did a run down on it in my carb sticky, but may not have gotten around to it. Just been too busy to dedicate time to tutorials.

Thanks fella,is there a better substitute carb or something?my baja 5b clone has a walbro spiral diaphragm without any issues but unsure of the carb on this one (am assured is k320 engine and relevant clutch n carb ) everything else on my rig is really assuring...
This rig also doesn't seem to take off until got but does lovely then (except top end bogging) thanks to all of you, you always seem to hit the nail on the head

As per walbro rovan get all their carbs from walbro. The 1191 is the same spec as an 1107. So really nothing wrong with it per say. It's just a generalized issue we've seen with them.(stock carbs) I don't know why, and some engines it doesn't seem to matter.
I'm a fan of the spiral diaphragm, but I also run pump gas and couldn't care less if it has ethonal in it. Just another thing I don't have to deal with. I think @Rep732 didn't care for them. They can be tricky to tune if you don't have the metering lever just right with the included gauge. I don't think they have quite the movement of the regular metering diaphragms. Mind you this is speculation on my part, I have nothing to back up that notion other then playing with them. I use them in o.p.e. that I work on as well with good results.
Found the email from walbro. Quite informative guys.

 

[Rcwrecker]

Thanks fella