Hitchcocks Forum

Hello fellow Bulleteers.



My Bullet (std 350) has been hesitating and misfiring at low rpms under load (about 1/8 throttle). I cleaned out the carb several times with compressed air and carb cleaner, paying particular attention to the pilot jet, but it made no difference. I also checked the rubbery bits connecting the carb to engine and air filter for leaks - nothing doing. Then, on a whim, I tried refuelling with 97 Octane fuel. Initially she started but was trying to idle far too slowly and kept cutting out - I increased the idling speed with the throttle stop screw - and now she behaves faultlessly with no more misfiring/hesitation.



I'm a bit of Bullet newbie, could other Bulleteers advise me: should I just use high octane fuel from now on? Or do I need to try to find the underlying problem?



Here's the spec of my bike: 2001 cast iron 350 Bullet. 5000 kms. Short bottle silencer. Standard air filter. VM 24 carb with 100 main jet, 27.5 pilot, and 2 Slide.



The misfiring/hesitation started after I tried fitting a conical air filter. I didn't like the hissing noise, and there seemed to be no meaningful increase in performance, so I switched back to the standard air filter. That's when the problem began.

Stick with the 97, use it in all my bikes with no problems surfacing, stay away from Ethenol mixes, motorcycles give good MPG, no need to count pennies buying fuel

The higher octane (premium) fuels of well known brands tend to have added detergent additives for fuel system cleanliness. The less expensive fuels tend not to. This is more applicable to EFI systems than carbys, however it could still have an affect.

Bit of production detritus from the new filter could have ended up inside the air passage feed for the pilot jet and despite attempts to clear it is still remains.

I would not waste money on high octane fuel in a motorcycle with a compression ratio as low as found in a 350 Bullet.

My experience is that putting high octane fuel in a Bullet isn't a waste of money -- the extra MPG more than makes up for the extra cost. But it doesn't make the bike run any differently either.

I suspect in your case it was the fiddling with the idling that made the difference, not the fuel. What I would do:

• go back to the air filter you prefer and, make sure it's clean
• leave the idling as it is now
• check that you've got the correct jetting for your combination of air filter and silencer

And take it from there. By all means check to see if you do get better fuel consumption from high octane fuel, but I don't think that's your problem here.

On up-hill riding I found my 500cc (iron) Bullet, year 2007 with sidecar, would bang a bit, pinking I presume. Somebody said it neeeded the 97 octane in. That seemed to cure it.

Does that make sense? -Chris

High octane fuel burns slightly more slowly. This lets you do two things. 1) Run higher compression ratios and 2) Advance the timing further before you experience detonation (pinking).

As Bullets are not generally cursed with high compression ratios unless you have gone to some effort to make this the case, if you're experiencing pinking, it's almost certainly because the ignition timing is too far advanced. Running more advanced timing alongside a higher octane fuel to prevent it pinking ought to slightly improve performance but I suspect in this case, such gains are likely to be marginal and possibly difficult to notice. The other thing is that not everywhere sells higher octane fuel so if you've set up to run on it, get "caught short" and have to use standard fuel, you'll have to keep the revs down.

One additional consideration is, as has been mentioned, you need to watch the ethanol content. Ethanol has a very high octane rating -it's why they run trials bikes with stupidly high compression on dope- so some high octane fuels, especially the cheaper ones, can have a very high ethanol content. This is fine in so far as it goes but it also has a lower energy density, so you can stop the pinking but then find yourself running lean. Or dissolving your feul lines.

There comes a point where it is just easier to set up to run on standard pump fuel.

High octane fuelmakes no difference to my Iron 350; I've tried it a few times.
It certainly does to my Jap bikes though. They pink on the standard stuff if you get enthusiastic with the throttle.

Ed,are you sure? That would require an improvement of pretty much 9% in your MPG before you were even starting to be in profit.