The bike is running well and has been for ages. The only minor issue I find a bit ****ly is an acceleration issue. The bike has just clicked over 73-74K and meticulously maintained (read babied )

When cold and you roll on the throttle alittle too quick (not snapped open) the bike dies then lurches forward under power, you sort of have to gently roll to avoid it. However this issue considerably lessens once the bike is warm. If you have the choke slightly 'on' weather the bike is cold or hot the issue dissappears completely. It sort of like the bike is too lean maybe???? I honestly dunno.

I have tried winding out the idle mixtures but no difference except it uses waaaaay more fuel so have returned these back to the one & half turns out. The bike starts easily weather it's hot cold or freezing and idles beautifully around 1k once warm. The plugs indicate the are burning beautifully and are all equal. The air filter is clean and I use the higher octane 96 fuel (the highest avail here) I balanced the carbs about 3k ago and still seem to be in balance by the nice even 'pur' at idle.

Even when warm and cruising at highway speed if you crack the throttle for a top gear over taking manovure the bike reacts with a sluggish hesitatancy (almost like its 'bogging' like a two stroker does when overloaded in the wrong gear) I always have to drop back to fifth to make the bike get up and move quickly. If you roll the throttle on the bike picks up speed easily but not quickly. Even a few mates have had a go think it very sluggish for big bike on the throttle 'roll on' but, is as quick as lightning if you drop a few cogs and give it the gumbo! Around town riding is good with no noticable issues unless you crack open the throttle like a clown, so not really an issue.

What do guys think, time for a carb strip and clean? a timing issue maybe? I know it's a bit of a nightmare getting these carbs out, but does anyone think it's worth it or should I a run some sort of fuel cleaner through it?? I have been reluctant to do this as I don't know how corrosive or damaging they can be on older rubbers, plastics etc.

I know with any of my old VT 250's with any acceleration issues, the first port of call was to remove the fuel bowls and check the little mesh filters in the inlet as these blocked up easily. I haven't looked yet but do these bikes have these or just the main filter in the tank. I have checked the tank filter some time back and it was nice and clean.

Any thoughts, ideas, recommendations or am I just expecting too much from the bike? Remember it's the CBR 750 model too

Cheers, Andy

 

Nope normal at least with my 2 bikes anyhow ...... sluggish until totally warmed up
Yeah the 1/3 choke routine helps a bit until you forget to pull it back

As for the highway etc ............. well the good stuff starts to happen up around
8k so if you work in that power band you should not be experiencing those kind
of hesitations ........... basically between 8 and 10 is where the ***** & giggles is !

 

Cheers Sprock, yeah it does get up and howl around 7500 right through to 10 or so, and no hesitations then, it just howls it head off.

Tootling back and forth to work I like to just roll on the herbs so revs tend to only reach 5 - 5500 at the most, unless passing. Anyway I'll try leaving the choke on for longer as per your post. The ole girl runs as cool as too, barely making the 'normal' temp range, apparently it's fairly typical of the 750's. Cheers, Andy

 

Octane is a flame retardant. Ethanol added to the fuel also retards the flame. With E-10 or E15 high octane fuel, you will have a crappy burn at high RPM. These bikes run fine on 86 octane.

The octane was added to fuel to stop pre-ignition in high combustion engines by reducing the flash point. You simply don't need it, it may be hurting you instead.

At high RPM you need a fast burn and the 86 works fine.

Poor roll-ons can be caused bu to much ethanol in the fuel. Find another pump and try the 86.

 

I think probably the issue here is that it's a 750.

Please report back when you have bought a 1K, if that doesn't work for you try a 1400 Ninja

Loving that rear view mirror and welcome aboard.

 

My Owners manual says 91 octane. I am lucky enough to have a friend who sells 92 octane with no ethanol in it.

Am I mistaken or is ethanol bad for bikes of this vintage?(more than 10% ethanol anyway)

 

Lucky for us we don't have that ethanol based fuels (yet) just the choice of 91, 96 (& in some cities 98). After asking around about fuel system cleaners, I will now look at runnning some type fuel system cleaner through the bike in the next week or so. It will be interesting if it makes any difference or not.

Hey Kiwi TK, your probably right, you can't beat cube's for punch. Bigger is always better in the long run. hopefully, all going well I will look at getting a bigger honda(of course) in the future, but the the 750 is a good work horse for the meantime. Cheers

 

^ WOW! Please send me some. The stuff we have here sucks.
The bike falls on its face at take off like a 2-stroke.....blub..blub..blub...blub....VAROOM!

 

A mate runs his modifed Hyosung 650 R on the 98 when he can get it. It makes a big differance to the bikes performance over the 96. The bike really changes how it's power is delivered, it goes from from the man Dr Hyde into the beast jeckel (or is the other way round, should paid more attention at school eh) down low and makes a big difference on the tight twisty hill work.

The 91 is a sad affair, even our Honda car (yep Honda all round - cars, bikes & even the lawn mower has a honda motor!) won't run on it properly, it's a pig to start in the cold and burps and farts for a while before coming right.

 

'Octane' (actually just an improper word we use for Anti-Knock Index (AKI)) is not a flame retardant. Flame speed is essentially the same on all grades of pump gasoline. AKI merely indicates a fuel's resistance to forming certain intermediary chemicals as compression increases. Higher-AKI fuels make less-detonation-prone intermediaries.

Actually, propagation rates are higher with the alcohols. This is one of the ways in which engines (like turbo Subarus) can be tuned to mitigate the BTU reduction of alcohol blends.

More likely the issue is carburetion, to include the possibility that, since stoichiometry with alcohols is a richer fuel mixture than with gasoline, it's experiencing a quick lean condition. Or maybe the carbs just aren't responding quickly enough?