GPz1100B1 engine will not rev - Carb problems.??

[Big Fluff]

Just been out on the maiden voyage this morning to get an MOT (passed).
First noticeable thing (apart from how sweet it rides) was that it simply coughs and splutters under anything more than 3500/4000 revs, below this it's fairly responsive.

Engine is GPz1100B1 with UT cams and carb conversion. Cam timing and valve clearances are spot on (checked and confirmed).
The carbs are off the old Z1000J engine, which was running pod filters, so I removed the small 'Ledar' screw in grub jets from the rear of the carbs. The carbs were completely dismantled and thoroughly cleaned though not ultrasonically. I've also checked that the diaphragms are seating properly (which they are) and appear to be in excellent and serviceable condition. New 130 main jets were fitted, air screws 1½ turns out, middle needle notch, and I'm running the standard 1000J airbox with a new air filter.

Ignition system is Dyna-S (a proven good unit off my old Saxon) and standard Kawasaki coils with new leads, caps and ND plugs. The ignition (both fully advanced and static) is bang on so I'm happy with that.

Weird how it pans out though..... It'll tick over perfect, throttle response is instant and it'll rev right through to 9000 rpm statically. Under any load it'll cough and splutter, so I though if it'll rev through statically then the revs should climb under light throttle load.? No chance.... it refuses to go past 5000 rpm.

Any pointers lads I'm sure it's down to carburation but I've been spoilt with the Saxon only having one large bucket for a carb and you'll know far more than I will.

[Al]

Standard J carbs have brass jets pressed into the inlet side but i have not seen them to be removable unless very determined.

If its had a dynajet kit fitted for the sake of the pod filters this involves; drilling a larger relief hole in the base of the slides, a different needle to compensate for mid range mixture and one of the inlet jets mentioned above (the smaller one i believe) is enlarged slightly with a drill supplied in the kit.
The standard needle has the 'square within a square emblem stamped on it and possibly the number 50 depending on which model they were originally fitted to.
You will need an electron microscope to see them though.

AL

[PAULJAC47]

Hi Will,Are you sure coils are good? not breaking down when hot,get them hot with a hairdryer and see if makes a diff,are you using standard Ht leads or the ones for Dyna coils?are you sure the advance unit is retuning and advancing every time?is the fuel cap vent clear? if you are running a vacumn tap is the diaphragm unspilt?recently i helped a local lad with his cbr600 race bike,he had all sorts of probs with it,turned out the powder coat had partly isolated the engine earth,it ran fine off load,are you sure genny and rectifier are giving out a heathy output,good 12 volts to coilsy,sorry if i am doing the sucking eggs routine,only tryingb to help,good looking bike by by the way..Cheers Paul J

[Taffus]

Sounds like your not getting enough petrol under load above 4k revs. Had similar when I got my B1 and it went away when I fitted a pingel fuel tap

[Pigford]

Will, is it RPM (revs) related - or THROTTLE position/opening......


If you get to 4k then open the throttle just a bit, does it bog down....... or is it as the throttle is agressively opened up wider

If its a defo stop at 4k then more likely ignition.... if throttle opening is causing it, then fuelling (probably)

[Yellow]

Had similar problems with a Z400F a few years ago.
Turned out the carb diaphragms had got porous.
They looked good bug gave the same symptoms as yours.
Replaced all 4 (pricey) and she ran like a good one again...

[Big Fluff]

Guys - Thanks for the replies and tips.
I think first off, I'll make sure the tank vent is free then go for a coil swap.
It's pissed down here all day so we'll see what comes in the week.
Will keep you posted and thanks again.
Will

[j.b]

have you tried sealing the airbox Will, where the new rubber manifolds slot into it? maybe the extra air getting in could cause an issue, i'm probably wrong but could be worth a go with some plasticine or putty just to check mate

[big green bus]

If the carb's have had a induction kit fitted it would have had the slide holes drilled out as per the instructions on those kits, this might cause some prob's
just a thought.

[Big Fluff]

Hi Will,Are you sure coils are good? not breaking down when hot,get them hot with a hairdryer and see if makes a diff,are you using standard Ht leads or the ones for Dyna coils?are you sure the advance unit is retuning and advancing every time?is the fuel cap vent clear? if you are running a vacumn tap is the diaphragm unspilt?recently i helped a local lad with his cbr600 race bike,he had all sorts of probs with it,turned out the powder coat had partly isolated the engine earth,it ran fine off load,are you sure genny and rectifier are giving out a heathy output,good 12 volts to coilsy,sorry if i am doing the sucking eggs routine,only tryingb to help,good looking bike by by the way..Cheers Paul J

Paul

I can't say for sure that the coils are good, but even when it's cold it's just the same symptoms. The leads are standard copper core and are pushed firmly into the coil spikes.
The advance/retard mechanism is working perfectly too.
The vacuum tap is brand new and also working perfectly (even tried it on prime).
Engine, frame etc. all earths are good with big earth wires everywhere so I'm 100% sure it's not that either.
Output from the alternator is also good, with a healthy 13 volts.

Standard J carbs have brass jets pressed into the inlet side but i have not seen them to be removable unless very determined.

If its had a dynajet kit fitted for the sake of the pod filters this involves; drilling a larger relief hole in the base of the slides, a different needle to compensate for mid range mixture and one of the inlet jets mentioned above (the smaller one i believe) is enlarged slightly with a drill supplied in the kit.
The standard needle has the 'square within a square emblem stamped on it and possibly the number 50 depending on which model they were originally fitted to.
You will need an electron microscope to see them though.

AL

Al
It looks like the needle jets are standard Kawasaki as there is a square within a square as you state. The number on the jet needles is 5B5.
Upon close inspection of the throttle slides, you can still see the gold pasivated coating on the holes at the bottom so it definitely looks like they haven't been drilled out either.
Maybe the best solution for now would be to reinstall the little brass screw-in grub jets in the back of the venturis and refit the pod filters and see how it runs.

Here are the little grub screws re-installed on the back of the carbs.




The jet needle position is No.3 (middle).
The pilot jets are 37.5 and the main jets are 130.
Should the little plugs be installed over the pilot jets.??

Plug installed:-


Plug not installed, and you can see the pilot jet.


I really don't like the look of the pod filters but am struggling to make a good seal between the back of the carbs and the airbox - remember the head is a B1 head so the carbs sit back and extra inch and the little rubbers I made up aren't sealing properly (small gaps here and there).

Steve - I take it you run individual pod filters on your B1 carb converted bike

[Al]

Carbs look very similar to mine are they 34mm on the engine side?
CV's need some sort of restricted air flow / reservoir on the atmospheric side to give a pressure differential or not enough vacuum is generated to lift the slides.
This could be key here.

Alloy plugs with 'o' rings round the middle must be in place below the pilot jets.

If the slides lift holes have been drilled out they would now be 2.642mm. (letter drill bit).

Cant see 5B5 in the two lists in the factory manual for jet needles.
US J 5FLZ49
UK etc J 5FLZ50
US K and M 5FL51
UK etc K and M 5Fl52

Later models J and 1000R; 5CF 58 and 5CF 59 / 5C50 and 5C48

The screwed in jets i have not seen before but if it was a Dynojet kit ~ that would be the main air jet and that would be the one to drill out to 1.067mm
As far as i know there are no air jets in the Dynojet kit only replacement main fuel jets.
Have those carbs been black at some point. Its only relevant in as much as certain models had black and some were natural colour. It might give an idea what they were off.

AL
[/u][/quote]

[pluto]

Will,
The carbs have the mixture enrichment devices on the side which I believe are to richen up the mixture when you throttle off to reduce backfiring, these were fitted to the 1000J. There used to be Ledar air corrector kits available which may be what has been fitted to yours, I would refit the air jets and try again.
Despite what you may hear to the contrary it is very possible to get CV carbs working well with pod filters and you get a lovely induction noise as a bonus.
If everything fails I have a standard set of 1000J carbs which you could substitute to check everything else is ok.
Dave

[jimmock]

Fookin 'ell Guyz.

Some serious stuff indeed.

I just love these kinda problems.

[Big Fluff]

Will,
The carbs have the mixture enrichment devices on the side which I believe are to richen up the mixture when you throttle off to reduce backfiring, these were fitted to the 1000J. There used to be Ledar air corrector kits available which may be what has been fitted to yours, I would refit the air jets and try again.
Despite what you may hear to the contrary it is very possible to get CV carbs working well with pod filters and you get a lovely induction noise as a bonus.
If everything fails I have a standard set of 1000J carbs which you could substitute to check everything else is ok.
Dave

Dave
That's what I thought... the Ledar air corrector kit. I remember these back in the 80's and even fitted a kit myself to one of my bikes back then.
I'll see how it goes tomorrow with some old pod filters on.
Thank you very much for your kind offer, and I will let you know either way
Regards, Will

[Big Fluff]

Update

Refitted the Ledar jets in the back of the carbs (as I originally received the bike), completely removed the air box, fitten the K&N's and took it out. It's exactly the same, just will not rev above 3500 rpm though if you pull the clutch in and blip the throttle it'll rev to 9000 rpm no problem.

What to do next
I'll try a different set of coils I suppose, after that I reckon ill take dave up on his offer of trying a complete and different set of 34mm carbs.

Oh the joy of resurrecting an old piece of shite