2 for the Price of One (High Idle Speed and Faulty Thermostat)

[fast al gordo]

wrong ballance of carbs can cause very high idle too. usually in combination with extremely slow decrease of RPM after closing the throttle

I turns out the carbs were'nt fully seated into the carb rubbers, pusing down on the carbs caused the idle speed to fluctuate between 2k and 4k. Refiited the carbs properly and she'll now idle around 1k to 1.5k.

Next jobs is balance the carbs,any know what flow rate they are supposed to be pulling. The workshop manual just says to balance to the line on the tool, but doesn't state what number the line on the tool represents.

[ventYl]

always seat the carbs with airbox detached. with B4 seating the airbox is quite easy (except of getting drain hose to be routed correctly) - compared to 1st gen B6. and if you can't seat it no matter of what you can suspect that the reason is that carbs are not being seated properly too.

there's no defined level of vacuum as there can't be any. you are measuring against atmospheric pressure which is undefined. you'll simply follow the instructions in the manual and the ballance will be correct - it is correct if all cylinders create equal vacuum at defined engine speed. pay attention to ballance them really properly (preferably use callibrated gauges) and try to get the ballance as close as possible. this small displacement engine is very sensible for ballance setup and vacuum leaks.

[fast al gordo]

always seat the carbs with airbox detached. with B4 seating the airbox is quite easy (except of getting drain hose to be routed correctly) - compared to 1st gen B6. and if you can't seat it no matter of what you can suspect that the reason is that carbs are not being seated properly too.

Really? It was taking me around 20 mins to get the airbox on previously, even with refitting the carbs I found it quicker and easier to put the airbox on first. Now that I've done it once and know how far the carbs go into the rubbers, it'll take about 5 mins.

Carbs are now balanced, well better balanced than they were before. Engines sounding better and it'll rev right up to the redline.

It also turns out the rad fan is working, it was a loose connection from where a replacement fan was spliced into the loom.

Next job is get the refurbished calipers back on and she's good to go.

[ventYl]

i've done it several dozens of times. it takes no more than 30 seconds to place airbox inside including placing drain hose the way it can be routed correctly.

if you are connecting the carbs with airbox connected I wonder how do you connect throttle and choke wires?

[fast al gordo]

i've done it several dozens of times. it takes no more than 30 seconds to place airbox inside including placing drain hose the way it can be routed correctly.

if you are connecting the carbs with airbox connected I wonder how do you connect throttle and choke wires?

I've wondered that myself...

[Gouraami]

I must agree with the others here, I cannot see how you could put the airbox on first, the carbs need a firm push to seat on the intakes.

Put a little rubber grease on the intakes when pushing the carbs on, makes it a lot easier!

[ventYl]

i've found out that the easiest way is to plug carbs into adapters with throttle and choke wires disconnected and choke lever unmounted. after carbs are seated, connect throttle wire (it goes easier without choke lever installed) then connect choke lever and then choke wire itself.

then you should be able to connect airbox. open the clamps as much as possible and optionally apply some oil to inners of rubber adapters. it goes easier when seated under angle and then re-seated straight once carbs are half-in. sometimes airbox to frame mounting holes are not aligned properly, usually it means that carbs are not pushed to the limit.

[bdouvill]

wrong ballance of carbs can cause very high idle too. usually in combination with extremely slow decrease of RPM after closing the throttle

100% ok with you ;-)
Plus I noticed wrong tension of the throttle cable increase this phenomenon... this is true at least on my bike :D

[Squishy]

If you think putting airbox on the 400 is hard... you should never try a 80s bikes with airbox stuck inside the frame (airbox gotta go first, then force carbs between airbox and engine).

I'd rather fit the airbox on the 400 10x, then 1x on a GPZ 900. Not even kidding.

[ventYl]

1st gen B6 is the same cup of tea. you have maybe up to 2 cm of space to slide carb rack inside.

[fast al gordo]

It appears that I've been everything ass backwards.

But it's all working now!

[Squishy]

1st gen B6 is the same cup of tea. you have maybe up to 2 cm of space to slide carb rack inside.

2cm? I wish the gpz 900 had even 1cm.
In fact there's -2cm, and you have to compress/violently bend the intake rubbers.