SOHC.co.uk Forums > CB350/400
Smokey rebuilt 350
royhall:
--- Quote from: K2-K6 on May 18, 2018, 09:44:38 PM ---What a pain Roy, but hopefully you're closer to eliminating all the things until you get on top of it.
As Hairy says, it's worth running a bit more to evaluate the pipe and if it will clean up . Although that black plug is worrying and as you say, suggests you've got too much of something burning in there.
What about getting a emissions test for each pipe once it's warmed up at mot test station. If you can get a decent readout for each then at least you can make a more fundamental judgment as to what's coming out of that cylinder versus the others.
Or, pull the carbs and switch the main jet from that #4 over to another cylinder to see if the problem moves?
--- End quote ---
That emissions test at the MOT centre was a very good idea. Tonight I did just that and the readings on 3 pots were pretty high and 1 pot they were low. The readings were as follows: No1-3.002 No2-3.050 No3-0.084 No4-2.800. Neither me or the MOT tester knows what the readings should be but pots 1,2,and 4 appear to be running rich with pot 3 lean. Pot 3 is the only one that does not smoke. I know it's rich as it starts first prod without any choke, very un-Honda like. Does anyone know what the correct emissions should be on a 350F. Cheers.
K2-K6:
Are they readings for either hydrocarbons "HC" or "CO" Roy?
If it's CO, then a good aim point is 1% (it's usually expressed as percentage even if not marked as such on printout) below 1% the exhaust starts to smell more carbon monoxide,eee and much less of unburnt petrol as it's a more efficient burn condition.
I'm trying to find if bikes have a specific level so will post if anything found.
Currently petrol cars pre cat equipped are max 1200 ppm for HC, I'm seeing avg around 100 actual for currently well setup motor.
And for CO, max limit of 3.5% with current avg actual of 0.65% for same engine.
It certainly gives you a lead to get a feel for what your cylinders are doing, and hopefully a path to examine.
K2-K6:
Looking further into bike specific CO levels, it seems the aim point (for non accelerator pumped) carbs, is 2 to 4 % so your 3 cylinders appear to be sitting right in the middle of it. That doesn't necessarily say running correctly overall though.
If it were in front of me I'd try to find what is causing the low number three reading as it looks like the measurements are for CO. You could start by adjusting the idle screw on that carb to see if the idle circuit gives you any response as it looks impaired. Looks like it's burning almost nothing at tickover.
If it's been synced on this offset it can give a overall poor setup. It's this area I'm getting at when discussing syncing as one error here can cause you to put an undesired offset in place.
If you can answer that number three mixture, then get it to parity you could then aim with the idle screws to get it close to 2% at idle for all four cylinders. In other words, untangle the primary error then you've more room to manoeuvre in desirable setup.
If that makes sense.
Nigel.
andut:
No experience on bike emissions, but an old school car engine on carbs would typically be around 2% to 4.5% CO at idle and I see no reason why a smaller engine would be much different. Cyl#3 reading would suggest a problem, either air screw adjustment or blocked idle jet if readings taken at idle, but I would expect you to notice a miss or hesitation ? If you strip the carbs, suggest you give them a good blast of air through all of the cross drillings in the bodies, emulsion tubes and jets (including the air bleed holes in idle jets)- may be worth getting a set of jet drills to double check jets are the size they say they are just in case someone has been tinkering although a larger jet would obviously not be causing your apparently lean cylinder.
Andy
K2-K6:
I agree Andy, Don't see any reason for it to be different for engine size.
My post with current levels of car engine is for fuel injected, although about 28yrs old and fairly crude, it does have the ability to work with a lower baseline setting and still give a stable idle plus additional enrichment when wacking the throttle open. So explains the baseline of 1% versus 2% for carb fed engines.
http://blankeindustries.com/exhauxt-gas-analyzer-products/technical-bulletins/motorcycle-airfuel-mixture-adjustment-guide/
Above link gives a reasonable overview of desired levels and what you are looking at.
Don't know your arrangements with the test station Roy, but if you sort the no3 problem and look at it again it could be worthwhile recording the "turns out" idle screw position to obtain both 2% and 3% readings so you have some scale to play with for setup.
Interesting to judge the higher rev reading and assess the main jet mixtures as well.
I know you have indicated concern about cruzinimage kit before, but those numbers for the three cylinders look impressively accurate in delivering CO readings almost bang on aim and tightly grouped to boot.
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