Frustrating or what?

[bod]

Well, after a very frustrating summer of trying to get my 77 GS750 running sweetly, I think I can now say it's sorted!
Way back in April, it was suggested on here that the fuel tap was at fault. I put a new kit in it - No Good! Bike shop agreed it was the fuel tap & put a pattern tap on - No Good! It was then decided a carb kit with new needle valves was required - No Good!
The bike would run for 1 mile, then appear to run out of fuel. Leave it a minute and it would fire up again?
So, it was decided that the pattern tap was at fault because the pipe came out the back of the tap & the fuel had to go slightly uphill before falling freely.
The Genuine part took 2 months to arrive & cost £85 (plus the pattern tap £35)

It seems that the fuel tap was indeed the culprit as is now running reliably.
I still think there is a big mid range flat spot before taking off at 7 grand - but thats something for next year to worry about!

Lessons learned here - Don't mess about with pattern parts, life is too short & it costs you more.

[jbs80106]

I do this exercise quite often, try to save a few $$$ which usually works out to only be a short term thing....glad you got it sorted!

[André]

I had a flat spot like this with my 650E at 6K. It gone when I change the stator, voltage was getting weak and cause a poor ignition. Mainy people here advice to chek voltage at coil.

Good luck.

[nutsandbolts]

glad to hear you overcame the issue. It does get frustrating sometimes but you feel pretty darn good when you figure it out and then the ride afterwards is a bonus.
I second that stator idea for the flat spot but I'm no mechanic or engineer.

[bod]

Thanks for the advice on getting my mid-range back! You guys are so generous with your time & knowlege, unlike the other GS forum I visit (BMW) where all you get as a reply is sarcasm or "search is your friend".

[BadBillyB]

Try raising the jet needle in the carb to the next to the bottom notch and see if it clears up....What size main jets are in the carbs? ...My 2 cents.....Billy

[bod]

Sorry for the delay Billy! I think it has the 105 main jet the bike was built with? I'm not sure if the carb kit came with new main jets, but the drive problem is the same as before the kit went in?

Been out for a spin this morning, and pottering around the country lanes with nice smooth drive between 3 & 4000 is very pleasant indeed.
But, on the open road it won't pull cleanly beyond 70mph in 5th, and you need to ease back on the throttle & gently wind it on again to get to 80 - and that takes a long time, and this country ain't big enough.
But if I thrash it through the gears it pulls past 80 ok, but this is not a very pleasant experience.

I would also say it bogs down a little when launching or when the revs drop below 3k.
But on the plus side, it now idles nicely - ONCE WARM!

Does any of these symptons still suggest the stator as the problem?

[RipRoaringFun]

Couple things, if the vent in the gas cap on the gas tank is clogged some bikes will intermittently starve fuel. I have a coffee mug designed not to spill while driving in a car and the cap of this mug has a vent hole in the top. When I put my finger over this vent hole I can interrupt the amount of coffee that is allowed to come out of the cup, which is excellent flow control when the coffee's hot. Same idea here. Dirty vent in your gas cap, intermittent stoppage of fuel flow, *maybe.* Because it sounds like you've checked all the obvious things already.

Regarding "you need to ease back on the throttle & gently wind it on again to get to 80", on some bikes when you have to back off the throttle then the revs pick up, it can indicate a 'running rich' condition. You open the throttle, it bogs due to running too rich, then you back off the throttle, and the engine is no longer overwhelmed with too much fuel and the rpms can now start to build.

Also -- what do your plugs look like, are you running an aftermarket pipe and are you running 100% stock carbs and airbox?

[bod]

Stock airbox & Mikunis! Twin pipes BUT I think they are Italian pattern.
It has fouled a few plugs & on occasion loses a small ammount of fuel through the breather.
As you say, when driving on in top, it appears rich & the more gas you give it the slower it goes.

Very interesting point with the fuel cap - will ride it with a rag stuffed in . . . You never know?

Thanks for your interest!

[RipRoaringFun]

Just to tie up a loose end, the earlier point made about gunk in the gas tank also might cause intermittent fuel starvation by blocking the outflow from the tank -- might be worthwhile checking out the petcock's condition by removing it and also give you a chance to flush the tank too.

By the way, I own a Yamaha Daytona Special that I bought in Denver, the 'mile high city,' where the air is pretty thin, and the RD400f had been jetted for that 5000+ foot altitude. By the time I got it down to where I live at sea level, the air density is greater so the Daytona was now flowing lots more air but was running lean because it had been jetted to supply much less fuel at 5000+ feet due to the thin air in Denver. So I had to rejet to flow more fuel to match the higher air density.

So it occurred to me, as England has sea-level and higher elevation locales, perhaps the reverse could be happening in your case, because you mentioned it is running stock jetting, so I just wondered (wild chance here obviously) that maybe you reside in a higher elevation and the bike was bought and jetted by the dealer in the lowlands of the UK. This is pure conjecture obviously, but it might explain why, if you're running rich on stock jetting -- maybe it was set up at the dealer for a different altitude from where you live.

If you look in most 'Parts Lists' that are the factory-supplied versions, you'll see a list of different main jets and I believe the mechanic at the dealership, during the set-up of new bikes, could select the appropriate jet based on the altitude where the bike would be run.

Good luck with it, and I'm rooting for Lotus in F1 (I drive a 2002 Esprit).

[hampshirehog]

Have you checked your engine number against the carbs? There are 4 different stock set ups for the 750 and you might have the wrong one (assuming the carbs are the originals).

I like RipRoaringFun's thoughts; however you won't need to jet for altitude over here (unless you're thinking of a bit of off-roading over Ben Nevis).

[Big T]

You mention carb kits - did they include new jets?

kits are generally vastly inferior to original parts (which don't go bad)

As you have the stock airbox and more or less stock pipes, you should check the size of the main jet, pilot jet and which notch the needle is set on (someone might have richened it up there) and let us know what those sizes are for all the carbs. Who knows what has been done in there!

Also, do you have an oiled airfilter? Maybe overoiled?

[bod]

There has been a lot of messing in the years I have owned the bike, everything has been changed except the stator - Yet this midrange void has remained exactly the same!

The genuine Suzuki fuel tap has at least made the bike predictable & reliable.

I'm not sure what was in the carb kits, but needle valves for sure. Work was carried out at local bike shop.

The lowdown is silky smooth, and it takes off at 7000 - but that midrange is like a 250 stroker . . . nothing . . . zilch . . . nil pois!

Would a faulty stator affect power over the whole rev range, or could it just affect 4.5 - 7000rpm?