Engine bogging when idling after 10 minute runs.

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Dashz

Dashz

Well-Known Member
Messages
179
Location
Spain Andalucia
Hi there. I have noticed that when the engine is hot (after 10-15 mins running and being ripping full throttle) if I drop the throttle to idle at any point the engine dies instantly.

When it bogs down it feels and sounds like the idle screw is set lower or the engine is running rich.

The idle screw is not the issue (it doesn’t move a hair, also, letting the car rest for a couple of minutes makes it idle nicely again)

I thought that it might have to do with running a very rich high speed needle but Im now using stock settings… This doesn’t happen in my Baja, not even after running a full tank straight away and it uses the same Walbro 1191/1107 carb with same settings.

The engine in this rig is bigger though 36cc compared to the other 29cc.
 
RcJunkie13 said:
Ok well first I would suggest throwing away that Rovan 36. But I would start by replacing the insulator block and all gaskets
Click to expand...
I’ll put a zenoah 32 in a near future, the point is that this engine is brand new lol… And no leaks anywhere around the gaskets.
Also the insulator block is a cnc piece and gaskets are new
 
Last edited:
Just a thought: Check to confirm your fuel lines are connected properly. Had a similar issue but this was after a rebuild. I have the Rovan 36cc engine too. I did not connect the fuel lines to the correct ports. The line with the filter inside the tank goes on the bottom of the carb. After 10 minutes of run time, your fuel level in the tank will not be the same. If you see lots of foam or bubbles in the prime pump bulb, chances are the lines are backwards.
 
could be heat soak from engine to the carb mate,
you say you're using an alloy insulator, if its a rovan one then probably wont have a delrin spacer to reduce heat transfer between the insulator and the carb,
tell tale sign is an empty bulb on the carb when hot,
with you saying that 10 mins cool down and it runs fine again thats my suggestion (y):D
 
spents said:
could be heat soak from engine to the carb mate,
you say you're using an alloy insulator, if its a rovan one then probably wont have a delrin spacer to reduce heat transfer between the insulator and the carb,
tell tale sign is an empty bulb on the carb when hot,
with you saying that 10 mins cool down and it runs fine again thats my suggestion (y):D
Click to expand...
Is that the “ptfe kind of fat gasket thing” that I didnt install because I didnt want to re-adjust the throttle linkage? Lmao…

And yes, the bulb is empty after a while and Im definitely not running the engine lean.

You might be right in the spot. Then fitting this in should fix the issue while keeping the metal insulator no?
 
I used the white plastic spacer on both 36cc engines between the carb and aluminum spacer. The Rovan I have is the all aluminum limited edition verion, the white spacer was used on that.
20211125_090911.jpg

The second 36cc engine came with the white plastic spacer but had a crack in it. I replaced that with the aluminum one and used the white plastic spacer that came with the aluminum spacer. Not much of a change on linkage, just a throttle end point change was needed.
20211125_090720.jpg

Thus far, I have not had any issues with the 36cc except when I connected the fuel lines backwards.
 
Bandit2013 said:
I used the white plastic spacer on both 36cc engines between the carb and aluminum spacer. The Rovan I have is the all aluminum limited edition verion, the white spacer was used on that.
View attachment 80070

The second 36cc engine came with the white plastic spacer but had a crack in it. I replaced that with the aluminum one and used the white plastic spacer that came with the aluminum spacer. Not much of a change on linkage, just a throttle end point change was needed.
View attachment 80071

Thus far, I have not had any issues with the 36cc except when I connected the fuel lines backwards.
Click to expand...
Thaaaat same thing yes 👍🏼
 
Dashz said:
Is that the “ptfe kind of fat gasket thing” that I didnt install because I didnt want to re-adjust the throttle linkage? Lmao…

And yes, the bulb is empty after a while and Im definitely not running the engine lean.

You might be right in the spot. Then fitting this in should fix the issue while keeping the metal insulator no?
Click to expand...
yes, as bandits pics show above, fit the plastic spacer and all should be well again (y):D,
and as bandit said, just readjust the linkage if needed or just the end points if that will work,
 
I just added the ptfe gasket and now it’s even worse it happens After a couple of minutes.
Already sprayed WD-40 into the gaskets and no leaks or issues there.
I might just have got a lemon carb, Ill replace it entirely with a new one jus to see.
 
Dashz said:
I just added the ptfe gasket and now it’s even worse it happens After a couple of minutes.
Already sprayed WD-40 into the gaskets and no leaks or issues there.
I might just have got a lemon carb, Ill replace it entirely with a new one jus to see.
Click to expand...
double check everything mentioned above before ya splash out on a fresh carb (y),
tank vent and splits in lines etc,
clunk still connected,
lines the right way round,
also check that the ptfe gasket has the hole for the pulse from engine to carb in the right place/orientation,
could be a duff carb, but rule out everything else first (y)
 
spents said:
double check everything mentioned above before ya splash out on a fresh carb (y),
tank vent and splits in lines etc,
clunk still connected,
lines the right way round,
also check that the ptfe gasket has the hole for the pulse from engine to carb in the right place/orientation,
could be a duff carb, but rule out everything else first (y)
Click to expand...
All of the above is fine.
I found a thread from a guy that had a similar issue with the very same setup; Low Rpm Rovan 36cc It happened for him straight away not after some time but the behaviour of my engine is exactly as shown in his videos.
I believe he simply swapped a new carb in and call it a day.

Last thing to try before getting a new carb is retuning the lsn in mine as it seems it has been running rich with the default tuning, I discovered this thanks to a post from @RcJunkie13 in that thread I linked.
 
I leaned out both needles as according to Rovan I had them very rich.
Now it seems to last longer without suffering this issue like 15-20 mins driving like crazy.
The carb is barely warm throughout the entire session, so this might be an issue with the engine itself or the carb, but Ill live with it.

If it gets worse Ill get another carb or throw away the engine if a new carb doesn’t fix this.
 
As an update: It turns out the 29cc engines don't like the 1107, I swapped a new 1107 in (Brand new and genuine Wb) and again faced same issue, I have seen some people on youtube having the exact same issue.

This carb runs too rich for <32cc engines, might be the bigger venturi or the fuel pump but in order to get decent low end power and not having the engine die idling after a full speed pass I had to lean the carb so much that I had no more thread left for the idle screw to lower the idle and engine started doing that metallic clinky noise that indicates the engine is too lean.

Just to prove this I swapped in a cheap rovan carb which I believe they are 668 clones and … boom, problem solved, idle is now solid and no bogging even near the end of a full tank running non stop…
 
Rep732 said:
Dump the aluminum isolator I had the same issue with my rig if you wanna stay with a billet isolator get the one obr offers as that worked good for me
Click to expand...
I fixed the issue by simply fitting the ptfe insulator and changing the carb for a smaller one. But be sure if at some point this repeats Ill toss the metal insulator.
 
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