Hi, I got a 1985 FZ750 and all she does now is starts up fine and I take it for a small lap around the yard and it boggs down and the only way to keep her going is having it wide open on the throttle and that's just keeps it at a huffing pace / crawling speed I have so far tried the following and no change:
Shim's checked Carbs Cleaned 3x , all parts are smooth Floats adjusted to rich and lean no change in bikes attitude Air mixture screws are out 4 turn's at the moment were at 2.5 and 3 with no change Took off gas cap and ran it changed fuel filter changed alternator changed starter fully charged (newer) battery New spark plugs Changed pickup coils Tested spark against frame Compression test (cold) 1cyl: 120psi , 2: 110psi, 3: 105psi, 4: 110psi Spark plugs are wet with gas and black Choke doesn't seem to work or noticeably work for that matter Engine is timed correctly cleaned air filter synced carbs rigged up my timing light to check firing and it "seems normal" but I recall earlier the light would flash weird as if the computer was firing at random times and some long pauses
things I notice are: Fuel pump is pumping (seems) It drove when I first started trying fixes, but it was cutting out on low end but seemed fine higher speeds. my blood pressure is rising bike seems to act different each time its started and seems to work easier on cooler temps
A couple of things I've picked up on is that it starts fine but bogs down after a while. One thing that springs to mind is that it could be fuel starvation. It may be worth finding out if you are getting enough flow from your tank first. In the past I've had the small fuel filter in the tank get dislodged and obstruct the flow of fuel causing the symptoms similar to what you describe. Therefore I would disconnect the fuel lines from your tank to your fuel pump and let the fuel flow into a fuel container to check that its flowing enough fuel, if that's ok then I would then check the flow after your fuel pump (disconnect the pipe where it fits onto your carbs) by putting the pipe into a fuel container and turning your ignition on to see if the pump is flowing enough fuel. Not much to go on but at least it may be a start by ensuring that it's not fuel related. Good luck.
If you don't crash, how do you know what your limits are ?
Sounds like a fuel problem as Wheaty mentions, not enough fuel flow at lower revs but enough to start , then revs high meaning fuel is being pumped to the carbs, yet lack of power, could be a blockage in the flow to carb or carbs, maybe not enough pressure from the fuel pump, a fact that fuel tanks can hold so much rubbish even after cleaning time and time again, air jets are normally 2 1/4 - 2 1/2 turns out, they only work at the lower range as mains work at higher range, Have recently been told Esso petrol don't use ethanol which for older machines has to be a good thing,
( a friend of mine had a similer issue he did everything you have tried the last time (x3) he cleaned the carbs and renewed the tap seals he noticed the fuel pipe was slightly obstructed , just enough to cause symtons you mention, upon inspection he found a samll piece of rubber from a tap seal, once removed all was fine and happy chappy,) you mention no change when floats ajusted, unless they sink,they do all float? stick with std settings, if the fueling is right i would surgest ign timing could be out, being that you have checked all the coils igniters etc, wet plugs fuel fouling plugs = irratic sparking = ignition , good hunting, test & test you'll get there
Thanks for the info, I am gonna test the bike without the pump I think to see if that solves the issue by using an elevated lawnmower tank or something strait to the carbs and go from there next is checking if the floats float (didn't think of it).
I'm thinking it's fuel problem weather it's the pump / pump relay / gas tank clogged outlet..
I just wanna get it running! I'll post if it fixed or not.
Well its not the tank or the pump but I did notice that it seems to be flooding because when It gets stuck in the bogging situation I cant go past 1000 rpm (huffing) at throttle wide open but if I let the throttle down as much as I can before engine cuts out it will slowly come back to life where i can rev it then when I rev it it puts out black smoke a bit then back to normal. Is the black smoke oil or just too much gas?
I checked the floats and they float in gas. I polished the float valve and needle just in case it was getting caught. The needle valve has a ring around the tip (maybe from the hole of the valve) is this normal? I ordered a new set of needle valves in case its the problem.
so I tried the bike again but same thing.. Is it normal to spray a mist of gas with the airbox off when reved? I notice its drinking the gas quick too from my homemade temp tank but could be float needles although it seems like a lot of gas going in.
BTW one of my main jets is plastic not brass like the rest .. is that OK?
right, main jets really need to be brass as original, yes they do wear the rubber valve float needle , check the size of the main jets and are correct size is in the book, if you have after market filters then usually go up a size or two on the mains to try and iron out the hesitation mid range, no you dont need to add any fuel into the carbs, it seems to be flowing enough by the sounds of it, so you know it's getting fuel to each carb, don't polish the float needles or valves at all, have you balanced the carbs after trying the mods they need syncronising for optimal perfromance,
fit the new stuff, check the size of the main jets etc, check height of the needles in each carb, and balance the carbs, when the carbs use pod type filters they really mess up the carburation, thats usually the cause of mid range hesitation as i mentioned, std airbox with performance filter are better, but we all have to deal with what we have, are you using the std exhaust? all you have to remember is what you have done and what you will be getting after sorting it , smiles all round
Main jets are all 110 seems to be ok there even the plastic one. I will balance the carbs again. It looks like the original exhaust but I'm not 100% all I know its a 4 to 1 and the plate that had a logo is worn off air box is std but there is a k&n filter in it. I cleaned it but didn't put oil yet on the filter I might just buy a regular one seems like it works better with the air box off except under load. would you recommend drilling main jets a size or two bigger?
some stuff I did today was: Clean the spark plug boots / and checked for proper ohms and it seems to be pretty close to what the workshop book says the spark also is able to cross a small gap and its blue I also swapped the coils and its still the same old news it just huffs.
oh and I think I messed up typing on my last post but what I meant to mention is that when I throttle the bike and the air box is off a mist of gas is sprayed up like there is too much but I cant remember if that was normal or not?
keep the K&N filter just clean it and lightly oil it with the right oil , Dont drill main jets that,s a given, only use original jets for that make of carb, each manufacturer have their own sizing for jets, ( so for instance if Mikuni might have a 35 main and Amal will have a 35 both are totally different )
ok as for the coughing up gas back out of carbs, ignition and valve timing , have you checked the valve timing, sticking valve maybe?
when you ride it, as your traveling turn the choke on and if it picks up and wants to go better, this usually means a fueling issue,choke allows more fuel, so id go up 2 sizes on main jets from std, are the 110's over size or std? sorry cant be arsed to find and look in book right now,lol,
but you have cleaned and checked all that system inc tank clean,filter, petrol flow to carbs, so thats ok
you have checked the ign, coils, plugs, plug leads,plug caps, and sparking is ok,so that's ok, good compression as well,
has it just started with this fault or did you buy it like this ?
make sure all the carb rubbers are on from the air box to the carbs, a few on the forum have has problems fitting them with rubber hardening ,so you need a good fit on these,
Well I hate to abandon an unsolved problem but now I bought an 98 fzr1000 exup donor and I'm just going to swap engine / carbs / electrical.. I think it was more valves sticking or not sealing is what was the problem letting too much gas in. Thanks for the help welshbanjo & wheaty.
Before you swap your engine, it maybe worth just checking your valve clearances as it does seem logical that fuel spray would be pushed up through the carbs if your inlet valves are tight. Even if you swap the engine it would be worth knowing that you've got a good spare 750 in reserve.
If you don't crash, how do you know what your limits are ?
Good wise words, Wheaty, Almez, you mentioned right at the start of the post you had checked the shims, im assiming you mean the valve shims ?
as re check the valves again, it's not a five min jobby, and you might get away with swapping some over from on to another, other wise maybe a few replacement ones, or if alls well with the vales, it the oil seal rings on valves, at worst a bent valve, as Wheaty says a check of 1000 engine prior to installation, dont forget the exup 1000 will need the crucial bits and pieces, magic box, if not using the exup valve in exhaust the jetting will need ajusting to suit, why not just refurb the 1000 and use as is, and find the fault with the 750 ? , good luck with whichever way you go, let us know how you get on ,
The bike I bought was cheap .. it's not in good shape and missing tank / farings etc.. I always wanted to do the fzr1000 parts on fz750 and I found this bike for 500.. so I will swap anyway..
About the shims.. I did a valve job 2 years ago. I lapped / leak tested / and replaced shims req. (10$ each with trade). I took it off the road and it sat in the shed for a year because of a leak where the crank case sealed.. I rebuilt it this summer and timed and checked valve clearance.. all seemed ok but I didn't check valves condition.. I didn't have much time I could have it off timing maybe a little and maybe i bent a valve but and I will fix it when it's off and check it out. It's all a matter of time .. if I could only buy time!
So to remove exup all I have to do is up the Jets? Or should I swap exaust too And use the exup?
i've not had anything to do with the FZR1000 engine others on here have, what i have read everyone says on a std machine it's better to keep the exup valve in the exhaust no flat spots mid range etc, i also know some remove it when it's not maintained properly as well, it would need jetting setting up as to clear mid range issues, the 1000 head will fit the 750 so that means the exhust should fit, you might want to consider that maybe, just fit the 1000 head and exhaust headers, some also use the 1000 block + head, for 911cc big engine, but i think you have to take out the crankcase mouth to take the 1000 block, not up to date on that mod, i know it's been spoken about on the forum, you might find a thread by searching the forum, as you say a mate of mine fitted the whole fz1000 engine in his FZ750 with micron exhaust system, i have not seen it though, but i did make an offer to buy it, nearly had it but he changed his mind doh!
My FZ750 has a Remus ex system and no issues at all, performance after market ex systems are not easy to find in the UK, although you can buy new systems which in the main replacements, in the 80's Micron where the one to have, Motad ,Harris,Gibson,Devil, of course Yoshimura + Kerker, im sure there where others as well all worked well for performance,
dont forget to use the 1000 magic box in your conversion
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