Looking back at your original post, you say you sorted a vacuum petcock. Seems like a good place to look.
Replaced it with a brand new one. It activates when it should (i.e. the old "chuck a hose on it and suck" test). Surely there couldn't be much more that it could do...
Can't help thinking @Arquebus is right and it's more likely to be a fuelling issue as that is what you've played with.
You describe this as a petcock, is this the main feed of fuel from tank to carbs? I'm confused a little because you talked about a tank breather being a problem - do you mean the return to the tank?
I reckon you're right. It just seems odd to me that unburnt fuel is still getting through. I'm going to check the earth situation tomorrow and start re-tracing my steps (again) to make sure I haven't done something galactically stupid. The vacuum operated fuel tap - could be using the wrong terminology, just what it said on the box. The diaphragm failed in this tap, causing fuel to bypass the carb and head straight into the cylinder, causing a sump full of fuel. Should have just put a manual fuel tap in from the factory! The tank breather (the bottom hose that vents to atmosphere) was pinched at one point, causing pressure build up in the tank. This was obviously more pressure than the fuel tap/petcock was designed for so it pushed fuel past it and out of the main carb feed. This happened after the new tap was installed.
Well now, it's possibly irrelevant. It was listed more so to answer @Arquebus' question regarding whether the tank was venting properly or not.
The expansion in the tank occurs with the carbed SSs......the tank breather on them is mainly to stop a vaccum forming in the tank, but it also releases pressure.........at what pressure it does this is largely dependant on whether it is dry or wet from fuel slosh. It should release at approx 4psi, but I have tested them up to 12psi....that's enough pressure to open float needle valves, once that starts a siphon can get underway because lazy carbed SS riders don't turn the petcock shut. The carbed SS pump should run at approx 4psi max....but 3 - 4 is OK. The air cut off diaphragms on these carbs can become weak or fail; and the choke needle assemblies can wear. Plus it isn't hard to mis-assemble the choke mechanism where it links to the choke needle assemblies. If the OP has been playing around with fuel hoses and pulling them off and putting them on; the hoses if old-ish can have deteriorated enough to produce small crumbly pieces of rubber which goes straight down the fuel line to the carbs.......some can past the little filter into the float bowls, others will eventually block it. How about float assemblies being worn or incorrectly set......has the OP played with them?
Not sure about the SSs, but my Monster doesn't have a manual petcock for me to shut off. Float height was reset as per FactoryPro instructions to 14mm. I'm about at the stage to pull the carbs off again, so I will be going back over everything. The needle valves showed no obvious signs of wear and the float height was set at 14mm as per FactoryPro's recommendations with this set-up. I'll be looking at the fuel hoses too, but most are almost new. I just can't figure out how it can foul plugs if it's a fuel starvation issue.
!4mm could be a problem..........it is far too weak IMO..........14mm is only a starting point...... Mine are at 12.5mm and could do with being at 12mm........however, because the fuel level in the float bowl is part of the pilot circuit it can seriously affect low speed running..........sometimes it can be adjusted out with the pilot screws....mine are at 3.75 turns out. The main jet needle doesn't come into play until you are approaching 4000 rpm IIRC.......see if the slides lift when you open the throttle........I'm wondering if the diaphragms are OK or is the little O-ring missing from the diaphragm covers? Just as a matter of interest, what are the pilot screws set at? How many turns out?
Diaphragms are in good condition (have checked them under light for holes or cracking) and the O-rings were replaced when the carbs were apart. They certainly lift under throttle. Pilot screws are set at 3 turns out. Have had them half a turn either way and noticed no difference to the current problem. I can't help thinking that richening the mixture is the last thing I need given the plug situation?
It is far more likely to foul the plugs if you aren't actually getting out on the bike and just keep starting it trying to solve the problem...........plus using the choke to start it..............it may not be getting hot enough to burn off any fouling. Sorry if we are touching on things you have already tried and suggesting things that may not be the answer........just trying everything I can think of...... Are the choke needle assemblies properly hooked into the choke slider bar or is the bar sticking so the assembles don't close properly?
Hey, not at all! I really appreciate all the suggestions! Best I can tell, it's just that the bar is sticking. I can close the choke by hand too, and have been to avoid it getting stuck open.
When the engine won't run above 4000rpm, what is the misfiring like? Is it what used to be called '8-stroking'? (a 2 stroke engine will 4 -stroke)........or is it banging and popping? Black smoke suggests it is over-fuelling..........which could mean the choke is stuck on........perhaps you should take the choke bar off and inspect the choke needle assemblies.......IIRC you can get at them with removing the carbs......the assembly pin should be sprung loaded so the pin goes back fully. I have several here from carbed SSs and the needle is black plastic..........some are very worn, some have the 'metering' tip broken off.
Sounds logical, but assuming I'm not miles out with the carb specs, would that not raise the idle? As it stands it doesn't want to idle without throttle. The misfiring sounds like it's only running on one cylinder with some pops and bangs. I've tried removing plug leads to see if it changes and it doesn't seem to make a difference. I can take a video in the morning if it helps.
If on one carb the needle tip has broken off or the needle is stuck / worn, it would make it smoke from one side, obviously and it could possibly mess the idle up so you need the throttle to clear it...... ...however, a few years ago mine went through a similar misfire..............turned out the balance screw had somehow jumped around. Did you split the carbs when you cleaned them?.......if so, I assume you got the linkage back together correctly? If I were you, I would try increasing the tickover rpm so you don't need to use the throttle and then try balancing it......drop the tickover as things get better. You can do a rough balance check while the engine is not running without removing the carbs (but it best to have them off).........take the top of the airbox off and remove the air filter, grab a small torch and look through each carb throat so you can see the bottom of the butterfly..........is there a gap between the butterfly and the carb throat? Are they the same on each carb? If not, check the throttle stop / idle screw and turn it until you can see a gap.............grab a long-ish piece of lockwire and form a loop in one end........(tie a length of string on the loop so you don't drop the wire right through) poke the straight end so it goes under the butterfly (put a small kink in the wire to get it past the emulsion tube) adjust the tickover and balance screws so both carbs have the same gap using the wire as a feeler gauge.
I've got access to a carb balancer, however I didn't split the carbs when I had them apart... Balance was done approx 500km ago but couldn't hurt to re-check. I'll get hold of it ASAP and have a play. Cheers
I have a Honda ST70 to which I fitted a Daytona 150 engine. After a lot of trouble with the first Carb I bought I splashed out on a genuine Keihin PE28 recommended by Daytona. They recommended for that carb a 130 main jet a particular needle (can't remember the code) and a 30 pilot. That's where I started. What I got was exactly what you described. It would start on the choke tick over nicely and as long as I hardly opened the throttle would gently accelerate As soon as I opened the throttle it would cough splutter and bang and cut out. To get it running nicely I ended up with a much fatter needle a 105 main and a 38 pilot. So just because your kit says jets of that size if you rule everything else out maybe try smaller mains or drop the needles or both
