|
Author |
Message |
Rob2810 |
This post is not being displayed .
|
Rob2810 L Plate Warrior
Joined: 05 Mar 2019 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
redeem ouzzer |
This post is not being displayed .
|
redeem ouzzer World Chat Champion
Joined: 06 Oct 2015 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
Rob2810 |
This post is not being displayed .
|
Rob2810 L Plate Warrior
Joined: 05 Mar 2019 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
Grubscrew |
This post is not being displayed .
|
Grubscrew Scooby Slapper
Joined: 23 Dec 2018 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
Hong Kong Phooey |
This post is not being displayed .
|
Hong Kong Phooey World Chat Champion
Joined: 30 Apr 2016 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
bugeye_bob |
This post is not being displayed .
|
bugeye_bob World Chat Champion
Joined: 05 Sep 2013 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
Teflon-Mike |
This post is not being displayed .
|
Teflon-Mike tl;dr
Joined: 01 Jun 2010 Karma :
|
Posted: 06:03 - 06 Mar 2019 Post subject: |
|
|
GSX750F... the old tea-pot.. oh-kay.... tough as old boot oil-boiler motor, I keep using the word 'old'.... hmmm, tea-pots and kettle's perhaps!
Right, first thoughts, were 120 mph? Where's he doing that then? Shortly followed by, so how fast does he want to go? Which is to suggest old adage before looking for a solution, make sure you actually have a problem.
Back to the owld.... I has to go check specs, 'cos I seem to recall that the thing was no tarmac-rippler.. well, like eva! Specs suggest that it has about 95bhp, which sounds about right for last of the line pre-water-cooled motor. Specs also suggest it has a top-end of somewhere between 130 and 140.... from a well fettled and prepped "press" bike, put through the traps in close to ideal conditions by a practiced pro..... run-wot-you-brung scores tend to be rather disapointing compared to the mag reviews, with typical examples of the breed in the hands of typical riders... even in the more favourable conditions of a sticky track..... So? a genuine 130'ish' would be more reasonable, 120... yeah that sounds a bit asthmatic, especially if thats the usually rather optimistic speedo reading.
BUT.... like I said, before looking for a solution, make sure you have identified the problem!
Before pulling carbs apart and 'stuff'.... check the tyre sizes! an over-sized front could give a 10% difference, and at that sort of speed that's more than 10mph.
Next up; the fugly fairings are 'supposed' to aid aerodynamics.... and they probably do, but.... without any at all, 95bhp isn't going to get you far past 120mph...... which begs next query, before pigging with jets an-stuff... has any-one 'foy-t'ad' the thing? Or put a tall or flip screen on it?
And follow on, if it's not been stripped naked... how large a fella are you, and are you getting 'tucked' out the wind-stream... and back to top... where are you trying to do 120? It can take a bit of winding up to get the last few mph out of almost any bike... are you sure it got the room?
And that begs the next conundrum... is it on stock cogs? If it's been down cogged for acceleration, it'll top out early. If its been cogged up, for more relaxed cruising, it will likely struggle, even more, to find the last few mph on the scale.
IF all of that is checked out and eliminated first.... my NEXT suggestion is the clutch... as you approach topping out, and the wind resistance is reaching the max force the engine can make... the clutch can slip... A-N-D the jerkiness of it letting go, then biting again, CAN feel a lot like a fuel block/starvation....
And its an oil-boiler.... what oil is in it? When was it last changed?
If car oil has been used... there's often copper based friction modifiers in there... bit like coppa-slip brake grease, fine on cars and even in cars with in-sump gearboxes where the oil would pick up phosphur bronze from the syncro-cones anyway.... b-u-t, not so great on a bike, with a wet-clutch sat in the oil, where you don't really want the fibre friction plates picking up low-friction additives so they dont have any friction!
And on the tea-pot, that actually begs another ponder-point; I seem to recall a common bug-bear in selector forks, and particularly, I think 3rs gear often not staying engaged, which oft down to knackered/bent/worn selector forks.... which are usually a bronze based alloy.. coppa-slipping the oil as they wear.... does it shift easy and stay in all cogs, under gross load? I would likely be dipping fingers into old engine oil... then cursing cos I forget to let it cool first! But smearing it on nice clean white kitchen roll, looking for the glint of gold and worn selector fork metal in the fluid.
So... starting with the obvious, simple and easy:-
Has the bike been layed up for winter? Have you dumped the fuel in the tank? Over-winter layup condensation on the inside of the fuel tank, will collect, and settle, the petrol floating to the top.
Following down, has any-one fitted an after-market fuel filter? These will often air-lock. My advice, if some-one has added one, is to dump it. They are oft more hassle than they save. But check the pipes for periushing, check hose clamps, check that the hose isn't kinked or pinched when any-ones taken tank off.
Working down... hmmm... carbs is scary and delicate... likely culprit by as said, I;d be in no hurry to have'em off.
Back to fuel tank and pipes. You dont say what year the thing is, and they made them an awful long time... earliest not so fugly faiuring models go back into the late 80's ISTR, so you have a bike that at it's youngest is over a decade, at its oldest over three, most likely somewhere in the middle, around 150-20.... so what state is the tank in?
On resto, I tend to POR15 the tank, as a matter of course. The cleaning in the instructions gets rid of silt and shite from the tank, the treatment puts lining on its walls stops it rusting or coming back. Costs about £50 but, done properly and diligently, using the whole kit and some cocum, saves SO many silly questions, faff and re-doing jobs, LIKE cleaning carbs, as old tank dumps old shite into nice cleaned carbs.... Treating tank also begs removing, cleaning, and insprctuing, overhauling or replacing the fuel-tap, as well as hoses including the breather.
Which is all 'hint' and stuff worth looking at, checking and at least bottoming before getting intimate with delicate diaphragms. If nothing else, thorughly cleaning the tank when you dump the old fuel is a good start.
Moving on.... normal service procedures follow... change the oil, change the filters, change the plugs; check the cable adjustments, check the tappets....
Eliminate 'so' many silly questions at source, and again, before looking for complicated solutions, be SURE you actually have properly identified the problem.
IF its still stuttering up top all that done..... then back to diagnostics, and you may have to go over some of the stuff you have looked at, like seating of the tank and routing of hoses.
Before puliing carbs, that clutch ~IS worth another visit... after you have flushed the oil. Is it a cable or hydraulic? Is it adjusted? Is it adjusted 'right'.. revisit and make sure it cant be slipping.. and in test, stu8ff the top-speed runs, try high gear and up=hill acceleration under high-load, see if you get similar symptoms pointing at the clutch, not the carbs.
Clutch is actually not all that hard to swap and overhaul, or all that expensive compared to torn carb diaphragms.... and since you are as likely to tear a diaphragm trying to tear down and clean a carbl hence make extra problems toy chuck into the mix.... discount all else first!
It probably IS at the carbs... and its likely that a float needle or three is sticking, and or the carbs are out of balence and or the chokes a bit icky.... BUT... lots of checks outside the carb before you need pull them off... check the air filter again... check the carb rubbers, look at cables check motion of butterfly's and slides.
And as Haynes warning, carb balence is the last jfinal setting up after all other (engine) service procedures.... with a set of guages, do they sinc up?
THEN it may be time to pull the carbs off.... carefully!
Check the state of the mounting rubbers either end, then drop the flat-bowls, check the float needles, check movement of needles, check float heights, then pop the tops, look at the diagphrams.. they tend to be expensive and a lot of lore about repairing torn ones with durex or superglue, which often isn't that wonderful even if it 'temporarily' seems to work.
Slides in alloy can get sticky, especially on CV carbs where full throttle doesn't mean full lift very often, and they can be a lot looser lower down than higher up, and get sticky when you open the taps.... like pushing the last few umph out of it at almost double legal limit speeds......
Again.. pre-emptive checks of exghaust are called for before stripping carbs... exhausts rot, after-market exhgausts often aren't optimal, and an AWFUL lot of presumed carb faults are often to be found in the 'zorst.. usually after a lot of head scratching and ping-fuckets from the flat-bowls, for the umptiueth time.
IE in short... DONT dive into the carbs assuming that's where problem lies... check everything else and the less obvious, First. ____________________ My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?' |
|
Back to top |
|
You must be logged in to rate posts |
|
|
bikenut |
This post is not being displayed .
|
bikenut World Chat Champion
Joined: 21 Nov 2011 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
Evil Hans |
This post is not being displayed .
|
Evil Hans World Chat Champion
Joined: 08 Nov 2015 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
Teflon-Mike |
This post is not being displayed .
|
Teflon-Mike tl;dr
Joined: 01 Jun 2010 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
stinkwheel |
This post is not being displayed .
|
stinkwheel Bovine Proctologist
Joined: 12 Jul 2004 Karma :
|
Posted: 19:23 - 07 Mar 2019 Post subject: |
|
|
Check the fuel tank breather.
What exact symptoms. Stuttering/misfiring?
DOes it do it consistantly as soon as it hits that speed or is it a bit intermittant. 'tis the season for carb icing, that would be worse with low air temperature/high humidity and after a protracted high speed run. They can even conk out altogether as you close the throttle with this issue. ____________________ “Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles. |
|
Back to top |
|
You must be logged in to rate posts |
|
|
bugeye_bob |
This post is not being displayed .
|
bugeye_bob World Chat Champion
Joined: 05 Sep 2013 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
Rob2810 |
This post is not being displayed .
|
Rob2810 L Plate Warrior
Joined: 05 Mar 2019 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
jaffa90 |
This post is not being displayed .
|
jaffa90 World Chat Champion
Joined: 06 Apr 2016 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
Rob2810 |
This post is not being displayed .
|
Rob2810 L Plate Warrior
Joined: 05 Mar 2019 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
P. |
This post is not being displayed .
|
P. Red Rocket
Joined: 14 Feb 2008 Karma :
|
|
Back to top |
|
You must be logged in to rate posts |
|
|
Old Thread Alert!
The last post was made 5 years, 21 days ago. Instead of replying here, would creating a new thread be more useful? |
|
|
|