Smokey rebuilt 350

[royhall]

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?

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.

[royhall]

Thanks for that information. Problem remains that the three pots where the readings are apparently correct smoke, smell of unburnt fuel and are blackening the plugs alarmingly. Those three pots are clearly running super rich, with No.4 being the worst even though it has the best reading? The mechanic at the mot station said he could smell it running rich before he started the test.

A brief history: These carbs came as a refurbished set from Gerben in Holland. They gave trouble immediately and were sent back to Gerben who went through them again. They were better but not right so I sent them to Harper's who stripped and cleaned them and fitted the Cruzinimage kits. They were decent for a while then got smokey. At that point I wrongly diagnosed the smoke as an engine issue due to the carbs having been professionally built three times. Problems were found and rectified on the subsequent strip down, so that at least was not wasted. These carbs have been ultrasonic cleaned at least twice by two people that know what there doing and all new internals fitted.

At this point I'm not sure the emissions readings are helping. It starts from cold without choke or throttle and idles immediately. That is not what Honda's do. It runs okay until the engine get properly warm then it bogs down. It is obvious from the symptoms that it's super rich. I am ready to abandon this set of carbs and find some more. I could really do with borrowing a set just to make certain that it runs well on known good carbs before buying any more. Not sure I can do much more with this set. Today however, I am going to make a fitting to check the actual float/fuel levels with a clear tube. Kevski has given me a measurement to set them to that works on his 350.

I think this is why bikes end up dumped under a cover at the back of the garage. Will report back with what I find.

[Laverda Dave]

Good luck with it Roy. So frustrating when you rebuild an engine twice over and the cars three times only to find the same problem persists. I'm sure you'll get there, at least its the carbs and you rectified some engine issues. All is not lost, hope you find some spare carbs to try.

[kevski]

Roy, i have my original jets and float needles if you wish to try them in your carbs to see what results you get, they are not worn my bike has only 5 and half k on it. Send me your address if you wish to try them out, my new set came from 4 into 1.

[royhall]

Thanks Kev will let you know. Are the new valves in yours genuine or pattern?

Sent from my Nexus 6 using Tapatalk

[kevski]

The valves in mine are pattern, i had to lap them in a touch, the ones that i would send to you will be the originals along with the original jets.

[royhall]

Just dug out of my ever growing stash of bits, four used CB350F carb bodies that look in good nick. After I check the float levels later today I think I will give Matt Harper a ring see what we can do.

[K2-K6]

Have you tried running it without the air filter Roy? And are you confident there is no impairment to the filter box entry?

Years ago I had a look at a bike that was doing something similar and the air filter,  which had just been put in new, was not flowing properly.  Never did figure out why it wouldn't flow air at the right volume.  It defied logic and was replaced without any further issues.

It doesn't deal with the odd carb on no3 though.

[royhall]

Checked that early on. As it takes its air from under the seat, I thought the plastic seat base on the repro seat may be bending down and blocking the vent, it wasn't. Will run it without the filter though, didn't think of that. The air filter has been common all though so who knows. Will let you know. Wouldn't that be tough to live down.

[royhall]

Just checked with the air filter out and the seat up and it is just the same. At least that's another link eliminated. The air filter smells quite strongly of petrol though, again indicating rich running. Just asked the question about the emissions readings and they are for CO.

Checked the float heights with the clear tube method. Pot 1- Can't check (flooding),  Pot 2 - On the bowl crease (good),   Pot 3 - Top of the screw threads (nearly overflow),  Pot 4 - Bowl crease (good). I think Pot 1 is flooding due to it being way too high, and the extra ventilation is allowing it to flood. Stopped doing it when I removed the tube. A mixed bag really, all plugs are black with Pot 4 (the worst one) wet with petrol. Strange how the height on the worst one is correct? Carbs out again time. Matt Harper has offered to ultrasonic them again and check for cracks and corrosion etc. Gerben has sent me some Viton seals and stainless clips. I am also sending my 4 spare carb bodies so he can pick the best of the bunch. I don't think Matt likes to be beaten by carbs, appears to relish the challenge. Well I wish him the best of luck.

Off the road again for now until Matt waves his magic wand. One day you never know!!

[royhall]

Well here we are 3 months later and bike still smoking badly on pot 4. The carbs went back to Matt Harper for another go as the float valves were a bit leaky. All that's sorted now and pot 4 is no different. I have also tried a set of carbs lent to me by a kind gentleman off a bike that is known to run okay. Same result so that's the carbs ruled out. Just ran it to hot in the garage and the plug from 4 has come out black and oily. Not sure where to go from here, so will re-cap what I have tried.

1. The engine ran fine after the 1st rebuild for 200 miles.
2. At this point cylinder 4 started smoking and it got so bad it wouldn't really run as it was filling the street with smoke.
3. Stripped down the top end as I was suspecting it had been bored to the wrong tolerance.
4. Had the bores re-done to 8 tenths of a thou (although they were okay the first time) that eliminated pistons and rings.
5. Re-did the valve guides that were reamed to new tolerance and the valves checked for wear.
6. Reassembled the engine using all genuine Honda gaskets and seals.
7. Carbs rebuilt again due to leaky float valves, another set of carbs tried. That eliminates the carbs.

Certainly looks like the top end is coming apart yet again unless someone can make a suggestion for something I have overlooked. This time I'm going to have to look for cracks/distortion/holes etc as that oil is getting in somewhere. Any ideas before I get a can of petrol and burn the wretched thing down to the ground.