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Big update on my problematic Honda CB350RS: Finally running great

19th February 2025, 15:16 by Kanad Kalasur

the bike's at 11,540km(1200kms post engine reassembly) on the ODO. Never been happier since the purchase. Pulls nicely on all the gears.

BHPian DocOn2Wheels recently shared this with other enthusiasts:

Quote from BHPian that_sedate_guy:

Hey, mate, glad to see you back at it. I happened to notice two engine gaskets stacked on top of one another. That is usually never the case because it defeats the whole purpose of a gasket.
Also, when doing this kind of work, wear thick jeans and mandatorily wear industrial safety shoes. Engine parts can be razor sharp and can slice off a toe before you even realise what happened. Stay safe, bro.

Good luck!!

Always some guidance from your side, I'm pleased! I read both of your private messages but couldn't reply to them as I don't have the permission to do so. Moreover I was busy in some other stuffs; one such stuff is my preowned 2011 Honda City of which I might be posting something in the future. An email notification to your private message reminded that something important has been put on hold for so long. I haven't even been able to go through the progress on your friend's R15.
About that double gasket- it's as it is. It consists of two thin sheets rivetted together as was confirmed when I unboxed the new one.
Before I start I would like to say- Surely We'll be....... somewhere, sometime in the future!!

The big update- How's it going!

Even before completely assembling the engine I got the CAT delete. Please let me justify this with all the troubles I had with this bike!

https://www.youtube.com/shorts/lVQVTsKolkk

Topped it up with 1L of normal mineral oil from Honda and the other 1L I used from the previously used one because I had planned to change it after 500Km and also because the bike had been run only 1200km after the previous oil change.
This is how it fired up!

https://www.youtube.com/shorts/GFdecKCP-TA

Just 40km of riding post engine reassembly this was the condition of the brand new spark plug.

https://www.youtube.com/shorts/4K8XyCl-7Kk

This indicated that the combustion isn't proper. I was always doubtful about the 02 sensor that this might be causing a rich air fuel mix by sending a faulty signal as the air filter was almost new but then MIL was not on during riding and also the deposition was not uniform all around. It made me wonder whether something is wrong with the fuel supply.

The new spark plug which I showed wasn't the company recommended(MR6K 9). Although it was NGK and had same dimensions it wasn't with the same model number. So I thought to change it and switched to the Iridium ones- NGK CPRP8EAIX- 9 @ 10,407km on the ODO.

At the same time I thought to check the fuel supply system and I thought to take it from top to bottom starting with the fuel pump.
This is how I dismantled the fuel pump. @10,407km on the ODO.

https://www.youtube.com/watch?v=H2b9vhUCvxc

With the fuel filter cleaned and the spark plug upgraded to iridium I covered 560Kms(400 on a small trip and 160 to my home). Reached home where already delivered Ngage Powerparts performance air filter was waiting to be installed. From here onwards everything has been done at home itself with the assistance of my younger brother(whose membership application was denied by Team BHP and also he's in 8th standard) and my niece.
At home I inspected the spark plug again and to my dismay it looked exactly the same as the previous one, unfortunately I couldn't take any picture of it.
Installed the performance air filter @ 11,030km on the ODO. Big disappointment- nothing changed to the spark plug condition.

(I really don't like the sticker quality from Ngage, water seeped inside just in the first wash. It was a wise advice by my brother not to stick it on the tank.)

This setback again provided me with an opportunity to further activate my frontal cortex neuronal synapses. Through my research(not in the lab obviously) this is what I found out:
(Note- Please watch the spark plug video with sound)
1. Uneven dry carbon deposition on the insulator tip(white spot on one side)- This is due to faulty fuel injector which is unable to inject fuel in a mist form which causes improper distribution and uneven air fuel mix in the combustion chamber leading to complete and incomplete combustion areas inside the combustion chamber with white spot being on the side where combustion is proper.

2. Sand like crust formation on the tip of ground electrode- This is an interesting one- it happens due to engine oil entering the combustion chamber in minute quantity in particulate form which burns and forms that crust. This can happen due to low viscosity engine oil, slightly faulty valve oil seals, slightly out of spec piston rings.

For the first problem- Having cleaned the fuel filter I moved on to clean the fuel injectors @11,060km on the ODO. This is how we did it:

https://youtu.be/jxrtd2ACFCE?si=kGKowL8RVK44MPCY

That relief; that relief of a proper diagnosis and rectification. It's a completely different sensation only DIYians can relate! Deep down I always knew there is something wrong with the fuel supply as the bike has spent quite sometime standing. Even before I took it home it had been standing for more than 5 months as the manufacturing was in October 2022(I was too stupid and desperate to enquire before booking) and I took the delivery in March 2023. Next time it was standing for another 2 months in the ASC as I've mentioned in my first post of this thread.
This was the condition of the spark plug after riding 60 kilometers post fuel injector cleaning.

During this time the bike was my father's daily commuter.
One problem which has been there with the engine is that there is slight noise from the top end(at the level of rocker head cover) of the engine which goes like- 'ghad-ghad ghad-ghad.' It is evident while running at a constant speed with the engine RPM constant. Best heard(felt) when the bike is running around 40kmph on second gear or around 60kmph on 3rd, beyond the mentioned speeds on the same gear it vanishes. It's neither evident while accelerating nor while decelerating. I assume it is because of that minor play in the camshaft bearing about which I mentioned in my previous post.
I switched to Motul 300v 10W40 @ 11,144km on the ODO. I know it is of slightly higher viscosity but I preferred it because I thought something of high viscosity might help reducing that noise.

Post 300km of riding the initial impression with Motul 300v is impressive. That noise I mentioned has reduced to such an extent that it is not bothersome anymore.

While my father was still using it for the daily commutes, @ 11,181km I inspected the spark plug again and could see the beginning phase of carbon deposition in the same fashion as earlier. Not again!!

Next day morning, the first thing I did was to take it out for a small spin of 40kms on the highway. Rode enthusiastically redlining it a few times on first and second gear. Came back and inspected the spark plug right away. To my amaze that slight deposition vanished. That day I realised lugging the engine is not a myth, atleast not for me! Of late I had adopted a habit of not shifting early and redlining atleast once whenever I drive my car and that day I got a proof of why I was doing the right thing. I always advocate downshifting!

Read so many positive reviews about Liqui Moly injector cleaner. @11,226km on the ODO added 60ml of it to a tank full of petrol. I did this to ensure proper cleaning of the fuel system and as I'm switching from a faulty bike to a DIY repaired bike I can't really comment on the performance gains and change in throttle response.

300ml bottle, sufficient for 70L of fuel.

There is one more problem apart from the spark plug blackening and the noise from top end. If I twist the throttle by about 60 degrees or more with a jerk from idle, the engine hesitates momentarily and then jumps up to the input RPM. That hesitation is momentary and doesn't affect day to day life usability. It's just something which is there. This doesn't happen on gradual throttle operations. It's my assumption that the Throttle position sensor needs a reset. I would really appreciate a guidance in this regard.

Currently the bike's at 11,540km(1200kms post engine reassembly) on the ODO. By far it's running great. Never been happier since the purchase. Pulls nicely on all the gears.
Maybe it's a placebo effect of going CAT-less(anyway I'm a dog person), adding performance air filter and iridium spark plugs I feel the bike behaves free now. It feels like it is behaving better on lower speeds at higher gears and picking up the pace on all the gears. Take my words with a pinch of salt as I have been a faulty bike owner so my comparisons will be based on that case scenario itself.

I'll keep you guys posted about the further updates.
Till then Happy riding!

Miles to go before I sleep, miles to go before I sleep!