Forum

[wilf]

A couple of weeks ago I posed the question: What benefit is to be gained from fitting our hosts sports pancake air filter (or words to that effect). Now I know it's daft, but I've been tinkering around with my speedo and have got it somewhere near accurate, but now instead of clipping along at a respectable fifty-five MPH indicated, I find I'm dawdling at a true(-ish) forty-five. It's all in the head, I know, but I'm getting quite a complex about it. So, once again is there any actual improvement in performance in fitting a freer-flowing air filter. The bike has a sporty exhaust which was on the bike when I bought it. She's a 2005 Iron Barrel 500.
Thanks in advance for any comments chaps.

[Barry_Q]

This is going to sound a bit silly but: At full throttle. Is your engine gasping for breath? If it's not gasping for breath. You don't need a better air filter. OK. I don't use this criteria for my own Enfield. It chugs around perfectly happily doing 50-55mph on the original air filter.

[wilf]

Hmmm, at full throttle things begin to get a bit frantic. Engine revs freely (no, clutch not slipping.) road speed rises to sixtyish, but I wouldn't want to hold it there for more than a few seconds. Until I "adjusted" the speedo I was happily cruising along at an indicated Fifty-five, and could wind her up to an indicated seventy, but as I say, not for long. Don't think she sounds out of breath. Any thoughts on fitting a bellmouth?

[wilf]

By the way Barry, is your speedo particularly accurate?

[Tim NZ]

IF your bike is vibrating frantically at +60mph, then check that ALL motor mounts are tight.


Over advanced ignition timing can and does cause harsh vibration...


Any change to exhaust or air filtration WILL require adjustment to carb settings: what Carb and what main jet?


While the 'pancake' air filter is often an improvement over the stock item, it is by no means the optimal arrangement.




The Speedos are woefully inaccurate and are very poorly made. It is important to keep the workings lubricated with a LIGHT spray of a Light, non evaporating lubricant. (NOT 5.56)


Only 10% out for a new speedo is about normal, but am interested in hearing what you have done to the speedo to improve it??? Every one I have had apart has been totally worn out and beyond redemption.

[1950s Bulleteer]

Have you done a plug chop to check the mixture? It is normally required to put a bigger main jet in to allow for the greater amount of air from a free-er flowing air filter. If the mixture is too weak you will lose power, the engine may overheat and pinking can result.

[wilf]

I'll certainly check the engine mountings, though it's not really vibration that I'm getting. Just plenty of revs and not much else. Sometimes I think raising the gearing would be the answer, but I don't want to be pottering about on B roads in third. Pretty sure the timings good as no overheating problems and bike starts and runs fine in all other ways.
I adjusted the speedo by following one of our chums (sorry, can't remember who) recent tips:remove speedo glass, remove needle and replace, t'other side of stop, then gently bend needle over stop. After two attempts my speedo is much more in touch with reality when checked against a mobile phone app. The crazy thing is, I was quite happy with my bullets performance until I did the speedo thing.

[Barry_Q]

Wilf. I have absolutely no idea how accurate my speedo is. The biggest pain is that it's a KPH speedo with a converter gearbox on the back (So it reads MPH). With the graduations being closer together, it can be tricky to read. Having said that. The engine is quite happy between 4000-4500rpm in top gear. If anyone wants to work out what the speed it. Please feel free. Now. Just how accurate is the tacho?

[Thack]

Barry_Q asks: " At full throttle. Is your engine gasping for breath? If it's not gasping for breath......"



How on earth can you tell? That's a serious question: exactly what signs do you get that the engine is power-limited by the air filter?



Personally I don't think you can possibly tell whether the power is being limited by the air filter, the diameter of the throttle body, the intake valve timing, or whatever else, just by riding it. You need to experiment, preferably on a dyno, to find out.



To answer Wilf's question: if the sports air filter has less resistance to air flow, then the engine will run weaker at high rpm / large throttle openings. This is NOT what you want so you should consider up-sizing the carburettor jets to compensate. H's will advise. Then - IF the air filter was a significant limiting factor - you will probably enjoy slightly improved performance (and more intake noise, unfortunately, which I really dislike).

[Barry_Q]

Well Thack. I did say it sounds a bit silly. It's very hard to quantify it in real terms. It's just something you get a feeling for.