Low speed misfire

[peterengland]

Ok CB550 and when I pull away seem to have a misfire, when I'm in 3rd and above there is no problem, sweet as a nut. Used to happen in all gears but have renewed points and timing spot on, filled tank and shot some Redex in so since this it seems to get better every run I have. Is it just the Redex cleaning out the carbs? Obviously trying everything before I have to remove the carbs (46A) cos they are a pain to do, 1/2 hour to remove but 2 hrs to replace the sodding things!

[K2-K6]

I always feel it's difficult to decide if reddex has actually done much in what is claimed, but one element this appears to improve is things like the float valves if they are sticking or slightly draggy at all. In other words, more reliable switching of fuel supply and consequently float/fuel level in the bowl.

Certainly it won't do any harm to run a little further and asses to see if you feel improvement is definitely there. Then accept the decision to go into it to more depth if it's not playing ball with you.

The reddex/heat cycle/vibrations may just get them to wake up for you.

[McCabe-Thiele (Ted)]

I was told by a highly knowledgeable Oil Technology Chemist (Bob Cutler)  that Redex was developed to assist in preventing the build up of carbon deposits in the engine, primarily the valves/cyliner head /piston crown/spark plugs. It does this by raising the burning temperature of fuel  in the combustion chamber preventing the build up of carbon deposits. The same person advised me that 2T mineral oil is almost as effective and cheaper. Clearly adding too much can in fact lead to a build up deposits so dose is critical.

Your engine might misfire under certain load & fueling conditions causing a brief build up of carbon on the plugs - fouling. Adding Redex can prevent that by the higher burn temperature preventing plug fouling. I have found it also cleans injectors on petrol engines and raises compression on older high mileage engines - I ran a Merc W124 series 260E that had 184,000 miles on the clock - it would start almost instantly when I used a small amont of 2T oil in the mix.

Bob Cutler started his career at Lubrizol moving to a number of firms over the decades since we left college together. In his seventies he started his own firm in the very specialized field of oil analysis based near Conwy with his son Adam.
.

https://oilanalysislab.com/lubewear-true-wear-metal-analysis-from-oil-analysis-laboratories/

[K2-K6]

Interesting link Ted.

Lubrizol as I understand make many of the addative package element that main stream motor oil manufacturer use to bring bulk base oil to their specification and performance.

[McCabe-Thiele (Ted)]

I've never understood the technology but Bob worked hard for his previous company who developed special sump plugs for large engines  in shipping fleets as well as aerospace. When analysed the plugs would tell the owner what the wear was in an engine by measuring the metal content in the oil that the plugs absorbed. Comparison with the engine metalurgic components is somehow reflected in the oil via wear.

[peterengland]

Went for a 70 mile run today and the bike was sweet as a nut apart from if I switched it off for 10 mins for a cuppa, then when it starts it misfires slightly in 1st gear at lowish throttle. Thought of pilot jets but then why doesn't it do it in other gears at same throttle opening? As it stands this is  something that I can put up with so I will unless someone has an idea...?

[mickwinf]

is it definitely a missfire or a flat spot? Carbs can be a pain to get spot on, i had a 500 that i could never get right.

[peterengland]

defo feels like a misfire

[K2-K6]

Both would be failure to burn cleanly each whole combustion charge, ignition/too rich/too lean.

If you're confident of ignition and plugs are ok (consider trying another set) and it runs ok higher rpm, then that aspect would appear reasonable.

Couple of things to try;- when you think it's going to do that on restarting, turn kill switch off and open throttle fully wide, then crank it for 5 seconds or so, then try starting as normal to see what effect that has. It should suck sir through it and mitigate if there's any fuel leaked in while standing. That could be slightly sticky float valve or maybe breather pipes not clear that could cause bowl filling to just push a little excess fuel through one of the idle jets to make a cylinder slightly wet. First try to see if it changes.

Another, as it stumbles then pull the choke slightly to see if richer improvement is evident.  The opposite to above and may indicate something to look at.

More detailed;- mark the low speed air screws with a spot of pen on carb casting, then count the turns inward each screw is set at. Record this setting do you can get back to it if needed. Then with it warmed and idling try adjusting each screw (one at a time) to guage if that carb is running clear through its idle circuit. They should each act like a small throttle with revs changing as you move them. One that's either no response would indicate a possible restriction in that carb idle circuit.