One cylinder running too lean

Gorankh

Gorankh

Well-known Member
Joined
Jun 2, 2020
Total Posts
69
Total likes
3
Location
Oslo, Norway
My left cylinder is running lean and I can´t figure out how to fix it.
- I measured fuel volume in the bowels, both had 37ml + some spill. I adjusted float height to 25mm from 26mm. Before both were running lean, now only the left side is running lean.
- I have cleaned both carburetors several times. Replaced o-ring and kept original brass
- Carb are bench synced, throttle is synced and idle spedd adjusted. The mixture screw on left carb 1 1/2 turns. Right side 1 1/4 turn.
- When I cleaned the carbs last time i noticed that it was harde to blow air through the pilot jet on left side. I have replica pilot jet but did not use it, the holes are smaller than the original one.
- No problem to start the engine when cold with choke open.
- When engine warm and choke closed -> better throttle response but bit sluggish at full throttle and high rpm.
- Compression about 150 on both sides.

Any advice will be very appreciated

IMG_2149.jpg
 
A guy here in Norway recommended me to use B7ES, better for our climate. He know his stuff, been racing with CB350 for ages.
 
At idle, check each carb by grabbing each INDIVIDUAL carb (by the idle screw area) and rev each side in turn. Do they rev and the fall the same way?
 
Middletons said:
At idle, check each carb by grabbing each INDIVIDUAL carb (by the idle screw area) and rev each side in turn. Do they rev and the fall the same way?
Click to expand...
When following your instructions the right side (good mix) revs faster than the left side (lean). It is especially sluggish at beginning. It's why i think it's either the pilot jet or primary main that doesn't deliver enough fuel.
 
The pilot jet was clogged, I was able to unclog it with a guitar string. It improved things but still not perfect. I have a new from a repkit but that one has smaller emulsion holes. My guru here in Norway suspected that PO had drilled bigger holes in mine because the looked bigger that they should be. What do you think. Will bigger emulsion holse let in more air and hence lean the mix?
IMG_2154.JPGIMG_2155.JPG
 
wow. those holes do look quite large.

you have nothing to loose by trying the replica pilot jets. yes, the original brass is preferred, but if you don't have it...

If it were me, I'd install those replica pilot jets, re-tweak idle speed and idle mixture screws, then try to get each carb to rise and fall equally as well as adjust for equal exhaust pressure/pulse. make sure the throttle cables are nice and loose during the adjustments so as to not influence the idle.
 
Those are the OEM pilot jets. The difference between them and the replicas is shocking.

Personally, I would leave the OEM jets in, but that’s just me.

I’ll ask the silly questions:

- Are you positive your valve lash is set correctly. I was chasing a rich idle issue for weeks before realizing my valves were set dead on. Cleaned up 80% of the issue.
- Have you followed J-T’s procedure for setting the idle sync and idle fuel mix? It’s well written. If you haven’t, I’ll try to dig it up.


Ed
1972 Honda CL350
 
Ribrickulous said:
Those are the OEM pilot jets. The difference between them and the replicas is shocking.
Click to expand...
But I think in this case the holes have been drilled bigger, they are not even round


Ribrickulous said:
- Are you positive your valve lash is set correctly. I was chasing a rich idle issue for weeks before realizing my valves were set dead on. Cleaned up 80% of the issue.
- Have you followed J-T’s procedure for setting the idle sync and idle fuel mix? It’s well written. If you haven’t, I’ll try to dig it up.
Click to expand...
What do you mean by "Valves were set dead on"? It´s only some weeks ago last time I checked valve clearance.
 
I will try the replica and see if it fixes the issue. Will report when I have done it and tested.
 
Looking closer (i.e. not on my phone) they do seem large, but obviously that's just eyeballing it.

See this thread for my comparison: https://www.vintagehondatwins.com/forums/showthread.php?590-Proper-OEM-Carb-Gasket-Kit

The intake and exhaust clearances are .05mm and .1mm, respectively (check me on this, but I'm 99% sure that's correct). My left intake valve was a little on the loose side, and I was never able to get the carbs sync'd, and thus the idle circuit dialed in correctly (fuel mix screw had no impact on engine speed, all the way out or all the way in).

Just a thought.
 
I think I may have solved the carb issue once and of all. I had kept the original needle valve till now. They looks abused so I gave it a try and replaced with replica I had. Guess what, the mixture is not lean anymore. I should have replaced them in the first place but thought it was best to keep the original brass. Both the pilot jet and needle jet are replica, rest is original.

IMG_2164.jpg
 
I celebrated too quickly. Today I discovered that the engine hesitates a bit at 6000rmp. I can´t actually feel the hesitation when riding the bike, It´s only seen on the tachometer. It jumps up and down around 6000 rpm for a short while. When in neutral I can hear cough (weak, you can barely hear it on the video).
I didn´t have this issue a couple of weeks ago but had a lean mixture that is now solved. I don´t use inline filters and did try with tank cap loose.

Do you think it´s carb issue or could it bee electrical (points, battery, coil)?
On think I should mention is that the bike sat outside for 10 days, mostly rain and humid weather. Could it be water condensation in the tank? I remember it was a common problem where I live on old cars.

 
This may just be the tachometer sticking since you don't feel anything while riding. There's a small bushing the needle shaft rides in and it can get dried out or collect dirt causing it to stick.
If your plugs are looking good and there's no symptoms while riding I wouldn't be terribly concerned. Engines and carbs behave slightly different when under load than unloaded in neutral.
 
I did replace the primary emulsion tube because the original in the carbs were beaten up. Look at the pics in one of my previous post. I installed a pair from a replica kit. Could it cause the issue I’m describing?
 
66Sprint said:
Swap them and see if the trouble side also swaps.......
Click to expand...

No difference. Also rechecked points and valve clearance. Starting to think maybe something is wrong with my tachometer. Seems like Jim is right about tachometer is sticking.
 
You are right on the use the original Brass parts in Carbs whenever possible, but yours were clearly used , abused, and beaten up by the PO.
On the Tach Pull the Cable out and clean it in kerosene and then pour some thru the cable housing and work the cable in & out a few times to loosen any old dried up grease inside it.
Then coat the cable with a light Moly Grease and re-install.
I've seen lots of cable operated clocks fixed by doing this.
 
Yendor said:
On the Tach Pull the Cable out and clean it in kerosene and then pour some thru the cable housing and work the cable in & out a few times to loosen any old dried up grease inside it.
Then coat the cable with a light Moly Grease and re-install.
I've seen lots of cable operated clocks fixed by doing this.
Click to expand...

Thanks for great advice, no more sticking tachometer
 
You must log in or register to reply here.
Back
Top Bottom