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-   -   Honda Activa: Engine idling & stalling issue caused by faulty "O" ring fitment (carburetor) (https://www.team-bhp.com/forum/motorbikes/186962-honda-activa-engine-idling-stalling-issue-caused-faulty-o-ring-fitment-carburetor.html)

Major Update to the Scooter's riding experience

Quoting my own post from the initial review posted in the Page 1 (see the part in italics):

I haven't updated the thread regularly but I used to inform BHPian interc00led regularly on how she performs whenever I use her.

When I last updated the thread the odometer was at 1400 kms. Now my BIL has come to Hyderabad for further studies so he is using the scooter regularly and the odometer as I write the thread is 2733 kms. I am happy that the scooter is being used at least.

Problems faced:

1. Erratic idling - Feels just like it is choking to death or I am not supplying fuel and trying to run the scooter on air;

2. Switches off automatically - when I slow down for a traffic signal. It felt like my scooter has auto start/stop system.

As we were discussing what could be the issues on WhatsApp, both of us decided to meet up and do the carburetor cleaning to see if the above problems solve.

So the yesterday evening we both meet up and on my way to meet him I experience what it could be if a scooterist is hit by an RTC bus all thanks to my silly scooter that thought I am slowing down for a traffic signal so it abruptly switches OFF at the very moment when I needed engine power to get out safely. It was my luck plus presence of mind of the bus driver that made him brake in time else I would have been in the hospital. :Frustrati

So the problem now needed to be addressed on an emergency scale.

While he arrived, I opened the engine cover and let it open to cool so working is easier.

PS: Since I was assistant in this DIY, I couldn't click many images or details of the work done. What came out was a revelation and a shocker.

"Size matters* :D"

Why I have put this here, it'll be self understood by the images I post hereon.

Odometer at time of job


Screws to be removed to open the body


Engine cover removed partially


Engine bay


Another angle


Zoom'ed in on the Carburetor


Body removed


Body kept aside


Close-up View of the engine area


Carburetor removed


Taken for cleaning


Another angle


Butterfly valve


Fuel Screw


Deformed 'O'-ring in the lower end of the fuel screw


New 'O'-ring purchased


New 'O'-ring fixed on the fuel screw


Air filter post 2600 kms


Air filter part number and price


*'O'-Ring - Deformed one vs Good one

• As I put the quote of Size matters before the images, the proof is in put down. The idiots @ Honda engine assembly plant did the wrong assembly when manufacturing the engine (read carburetor). Idiots!
  
  
• The actual way to fit that fuel screw is the 'O' ring comes, then comes the spring; then the metal washer and after that at the end 'O' ring needs to be put.
  
  
• 'What the idiots @ Honda did was put the 'O' ring first after the spring on the fuel screw and after that the metal washer. So whenever there was adjustment done to the fuel screw, it kept pressing against this 'O'-ring deforming it. Manufacturing or Assembly Defect!!!
  
  
• Interc00led and I were in surprise when we opened the carburetor for cleaning. Good that we met to clear this issue else it would have been suspense for life or till something big would have happened.
  
  
• A small sized 'O'ring has created so much havoc in performance and drive-ability. Size does matter!!!
  
  
• Post the job when we started the scooter the idle was super smooth and acceleration was unbelievably smooth and vibration free. This is what I was looking for when I was buying the Activa.
  
  
• The scooter has done 100 kms post the job and both me and my BIL are happy. It doesn't stop at the signal and the drive is silent and smoother.

At the end of the day I am relieved and can't thank Mr. Shoeb aka interc00led for helping me always with anything related to automobiles. Thanks once again.

Excellent diagnosis Sir. clap:

This wasn't an easy spotting in any way. I also faced the exact same issue way back in 2009, in my friend's Honda Aviator, and she ended up replacing the entire carburetor assembly after the mechanics failed to get to the root cause. The new carburetor was fortunately trouble-free for the rest of its service life.

Regards,
Shashi

Many thanks for sharing Anurag! Considering the popularity of the Activa, I'm moving your immensely helpful post to a new thread so that other Activa owners can easily find it.

My wife's Activa is facing a similar issue of stopping abruptly or when idling. Let me see if this is due to the O ring. Thanks for the clear and descriptive post.

This is a common issue with Keihin metal flanged carburetors. (Carburetors with rubber intake hoses are less prone to this idling issues) The poor idling is due to air leak in carburetion. The air leak can be at 1. Air screw 2. The carburetor flange 3. Carburetor top 4. Idling screw. The idea is to have no vacuum leak anywhere on the carburetor .

Sometimes the carburetor flange bolts goes loose on its own.Sometimes the flange gets warped due to over tightening. In both cases the idling will be affected.

When there is no vacuum leak in carburetion the engine has to start without throttle when warm. This is the test for right setting for carburetor.

Excellent diagnosis clap:. Regarding the wrong assembly procedure, I don't think Honda assembles the carburettor but gets it as an assembled component from Keihin.Am very much sure some bonehead at Keihin messed up the assembly.

Let me give you lowdown from the other end of the spectrum, the assembly line. This kind of situation usually arises when some of the regular workers are either on leave/absent and are replaced by casual/contract labour. They are given usually simple stations such as these to man but not knowing the importance of the how and why things are done a certain way, they usually mess up. Some of the defects are rectified during testing, but some, like the one you mentioned crop up over time and are passed on to unsuspecting customers. Now there is a good chance that this defect is present in all the stock assembled in that shift. The assembly line usually has a target to complete by the end of the shift and they usually do it by hook or crook. I am not saying it is an acceptable practice, but I understand it.

I would like to add to my earlier post. The carburetor depicted is pretty new. You can see dust adhering to the central portion of the carburetor also on flange. This is due to leaking float chamber and flange gasket. For a carburetor which has done 2733 km ,this is unacceptable quality. This combined with the O- ring assembly defect speaks a lot about the quality of production of Keihin carburetors. The quality of O- ring depicted is also very poor.

Great diagnosis & super-cool fix. Never would have been fixed by a regular ASC guy except for swapping the Carburetor.

Well in my case i have a 2009 Dio purchased last year (ran almost 45K) and this is being used by my sister for a daily commute of maximum 8Kms.
Vehicle was working trouble free until 2 months back and it started having cold start issues. Could this be due to the above issue as well?
The mechanics have already done a filter change and carburetor cleaning, however it still persists.
The issue is only with the initial starting in the mornings and the scooter runs almost trouble free for rest of the day with no stalling issues.
The mechanic further advises a carburetor swap for me but I was looking for alternatives as I believe it could not be the real cause.

I had severe cold start issues. It required me to do 20 kicks with choke lever pulled.

Post this rectification it starts in the first kick
without choke being pulled.

That's great.
And yes choke doesn't help in anyway. So would this O-ring be the same for Dio as well and something which is easily available at the ASC? Appreciate if you could share the costs as well.
This is the next thing on my To-Do list once am back at my hometown :)

I have experienced similar cold start issue earlier on Keihin. If the issue is only cold start in the morning , try the following: The choke circuit has a small well inside the float chamber. The choke well gets filled through a small hole from float chamber. This hole could be blocked. Try checking this. The float chamber could be full, but the choke well could be empty due to the hole being blocked.
Another reason could be malfunctioning vacuum operated petrol tap.When you stop the scooter the engine is warm. As engine cools, the fuel in float chamber evaporates due to carburetor getting warmed. The fuel level in float goes down and may become empty also. So when you try cold starting,
the Vacuum operated petrol tap has to send down fuel fast . So the tap has to function right for easy cold start.
Also check if your float chamber drain screw is not leaky. This could drain the float and lead to difficult cold starting.
Try this : Let the engine to cool and the float fuel to evaporate . Start the scooter only to fill the float chamber after an half an hour after parking. Then see if the cold starting improves in morning.

Thanks Eko, that is too many pointers :)
I will try to follow and fix them one by one in case it's still a problem after fixing the O ring. Also from the above, the petrol tap was already checked by the mechanic and he did mention that the flow was proper, so I assume this might not be one of the possible reasons, but for others will definitely have a check.

Cheers.

Nice & helpful post. I am struggling with the choke of my suzuki gixxer which also I believe is issue in carburetor. Can some one post similar way to help fixing that.
I have been to service center multiple times but they are unable to fix it. They will just increase the idiling nothing else. And again in morning bike will have tough time to start with choke on.

Or, could have it been caused by the A.S.S. using a carb cleaner to clean the carb w/o removing the rubber O-Ring?

I don't intend to hijack the thread. Here are 2 problems with my 125.
1) Can you identify what can possibly be the cause/source of the noise in the video? Its a Activa 125. It makes this noise when idling and the engine will conk off aftera few seconds. I though its a loose timing chain but with only ~9.5K kms on the odometer is difficult.
2) The bike will not go comfortably over 55 kmph. Over that speed engine vibrates heavily. The A.S.S. says this is b/c the engine is yet to "Open-up". Has any one experienced this?

https://www.youtube.com/watch?v=GND5w3TM-iI