Jersey J

[phil le brocq]

Having had it's initial post rebuild run last week with a fuel tap leak, I've been running up the bike today checking carb balance which is pretty well spot on but I've got a problem with the motor holding on to its' revs when you initially shut the throttle. I'm pretty sure it's carb related as it has improved by winding out the pilots to three turns. I'm running the J carbs with a 80's ledar kit minus the air correctors (which were never fitted) which ran fine on the J motor but I'm now running a late GPZ1100 motor with the J ignition and carbs. Before I splash out on a dynajet carb kit is there any reason why the J pick ups/advance retard unit fitted would a contribute to the problem. I'm aware a dyna ignition or similar would be better but is it required to make it run as I have to stop spending at some point if I wish to keep all of my favourite body parts!

[tlc]

Do your carbs have the extra shut off diaphragms and could these be a cause?

[phil le brocq]

Ummm? I have been stripping carbs for quite a while, I've even stripped a set of CBX carbs which is not for the faint hearted but you've got me this time. please please educate, shut off diaphragms?

Phil.

[Pigford]

Are manifold rubbers good - no cracks

[phil le brocq]

how I like the wife. brand nude, Ooop's sorry, brand new

[tlc]

Phil. The diaphragms can be seen here under the circular plate held by the three screws.
When I ordered rebuild kits it was recommended that I change these at the same time.

[phil le brocq]

Thanks for the pic, easy when you can see what your looking at. I'm pretty sure my problem is carb related so I'm going to order a dyna jet kit and give them another going through. I'll check the diaphrams while their stripped.

Thanks again, Phil.

[Al]

Phil at the risk of looking like youre stalker i have copied these bits * from the 'search forum' facility.
Might be worth checking whether TDC is correct for the ignition setup you have. As they wear they wear retarded which together with any weakness or air leaks will hold the revs up and make for a thin and wispy mix. If there is a shim washer at the base of the moving advance unit, i have found it better to remove it as a few iv'e seen have split and jammed the A&R unit from opening properly.
I think i heard you start the bike up the other day and last weekend so i am guessing no back pressure in the exhaust. Might be worth looking into.

*Roughly; CV's work best with standard airbox give or take. You can get a K&N for the standard airbox. Radical or incorrect valve timing can supress inlet vacuum giving problems with flow characteristics, it can help to set the two inner carbs a little richer, you can 'pre-load' the springs above the slides to stop them opening too quickly (not recommended) slower opening of the throttle often results in increased power delivery, a weaker mixture can give better power delivery also (right up to the point of detonation) but care is needed here, air leaks around the inlet stubs are a common failing, and so it goes on.


*CV's are difficult to get right with individual filters ( pods or ram airs) they really need the original airbox to generate enough back pressure / resistance to lift the slides correctly.
That said, if the idle mixture is set correctly they will pop and spit back untill fully warmed up. Does choke even them out or kill the idle?

*Use a set of vacuum gauges to set the balance of the four chokes with the engine stone cold. Bend the tangs on the choke bar but make sure each choke assembly is correctly seated with the choke lever off.


*As Rob says above, some small changes in cam timing amongst other things can explain differences in idle vacuum. A much lower value than 27 may give rise to poor idleing but i suspect yours' is as regular as anything. 22 springs to mind as a basline value for standard set-up.

*Did you silicone seal the new rubbers onto the head?
Are the carbs clinically clean inside?
Have they been ultrasonically cleaned.
If not have you removed the filters which sit immediately above the float needle jet seats?
You dont need a vacuum tap or vacuum arrangement to make them work.
So long as you have all 4 vacuum take-offs' on the bodies blanked off and there is a prime position on the tap which delivers full flow you'll be OK.
Is the valve timing more or less correct.
Cams can move easily within the hyvo chain and mess stuff up very easily.
If the timing is a little retarded that will supress idle vacuum and lead to poor idling and poor pickup off idle.
You mention that all plugs are sooty. This doesn't necessarily mean that it is running rich. It may be a severe missfire that leads to blackening of the plugs. It could still be lean. If it is then use of the choke will correct it temporarily.

*Will be interested to see the compression figures as well.

*For range; i'm using standard air-box with K&N and free exhaust, Unitrak head and cams on 1170 HC pistons and made these changes;
Mains 130++ i think
Pilot screws are an average of 3 turns out (from 2 3/4 to 3 1/4)
I also use another spacer between the diaphragm spring and vacuum slide to slow the slide down a little.
Dynamic fuel level is 4 +- 1mm below float bowl to body mating surface with gasket removed.


AL

[phil le brocq]

Thanks for taking the time to compile that lot. My initial reaction is the vacuum levels, These were particularly low, under 10 which suprised me, I'm a marine engineer and set up carbs on a regular basis and gives credence to the ignition timing related idea that has been nagging me. I'm using the GPZ motor including cams with the J2 advance retard and pick ups. The carbs I cleaned (ultrasonic) a couple of years ago and have stored since, They do spit back at tickover but they always did on the J motor and ran fine above that. The standard airbox I haven't seen in 25 years but has never been an issue. What would you suggest as a first move?

Phil.

[Al]

With only 10 didlybars it would be hard not to come to the conclusion that the cam timing was out.
Which 1100 Gpz motor is it by the way?? A or B
I would flick the cam cover off doing all that was humanly possible to preserve the existing cam timing (not necessarily that easy) and have a good look see.
Confirm that cams are round the right way particularly if its got vernier wheels.
Have a measure up on TDC and see that the timing marks align correctly within the RHS cover. If its the TEC pickups then there is probably no adjustment. I have recently altered that situation with a set of those by dragging the holes if i remember because of wear in the A&R unit giving a falsely low static timing value (too retarded leading to too much range at full advance).

AL

[phil le brocq]

99.9% sure cam timing is ok, I spent enough time setting it and worry about such things to a point of distraction. Motor I believe is the last model, shim under bucket model (85?) but was acquired from a local breaker having snapped a chain so was rebuilt around a set of crankcases from usedkawasakispares.com fitted with my J2 ignition, a real mix up. Next please?

Phil.

[Rich]

Pilot jets too small or fuel levels too low

[phil le brocq]

I'm still worried about the vacuum levels being so low but could one carb fuel level being low cause the problem? as I did do a repair on a carb float post in No2 which snapped when I originally stripped them which ties up with my orignal thoughts of lean running.

Phil

[big green bus]

From you original post you said the rev's were hanging on, on my bike with a unitrac motor it would do that, it turned out just to be tick over mixture, this was wrong and would not tick over very well, so I turned the tick over up a bit and the revs would hang on terrible, but if I lowered it, it would cut out. fiddled with the mixture screws until until I sorted it, this is probably not your problem, but I thought I would let you know before you start spending money, mine also ran a z1000j ignition no problem

[phil le brocq]

Thanks for that. It sounds exactly like the problem I'm suffering because it does improve and get worse when you adjust the tick over and I improved things a noticible amount when I adjusted the pilots. It's also an interesting point that you're running a J ignition which must prove the point that they are compatible. Although i'm still concerned about the vacuum values, I'm so 50/50 between carbs and ignition I'm coming round to the idea of just finishing putting it together and see how it runs under load and crossing each bridge as we reach it. At least I'll have a bit more info to throw at you guys if I still have a major issue.

Phil.