78 kz750 twin help

hi all havent posted for ages , hope your all enjoying the riding season in the usa , we are lucky here , ride nearly 12 mths of the year , sometimes hot sometimes bloody cold
any way i have finally got the twin ready to fire up have done complete rebuild , engine , carbs , re wired the coils re the coil mod on the forum gave me great spark , it cranked up 2 kicks today but is only partially running on the right cyl ? pull the plug lead off r side and hardly notice the diff do same on the l side and it stalls , the carbs wont tune via the idle screws except to have them screwed out 3 to 4 turns , on the right side it pops till you screw it out at least 3 to 4 turns i know this isnt right , have put on new carb rubber manifolds etc , done a comp test had 155 to 160 an both cycls hot
where do i look first , have checled timing with light ,its good , new points condensor , coil mod gave me from about 11.5 volts to well over 12 now , good blue /orange spark , strongest i,ve seen it do for years , where do look first , any help appreciated , i think it may be the carbs ?
sorry about the long post
cheers graemeB)

You may have a vacuum leak somewhere.
Is the hose between the two intake manifolds on the bottom connected?
Did you use some kind of sealant on the manifolds where they contact the head?
Have you set the float levels?

I installed NOS (New Old Stock) intake manifolds on my 750 twin and had to take them back off and apply sealant to fix the same problem.

Post edited by: steell, at: 2007/09/23 08:37

grace1 wrote:

...the carbs wont tune via the idle screws except to have them screwed out 3 to 4 turns , on the right side it pops till you screw it out at least 3 to 4 turns i know this isnt right...

There's alot of stuff I would suggest, but this is the thing in the post that stood out. Yeah - that's not right. The way you describe it suggests the float height is wrong, or the carbs are gummed up (or otherwise dirty) somewhere int he pilot system. Can you get "Seafoam" fuel additive there? I had a similar situation even after adjusting floats, and I ran half a can of Seafoam in a tankful, and it cleaned out my pilot system...

The ideal thing to have is a vacuum manifold with 4 gauges. Each boot has a port to connect to. You can tell a lot about the carbs,valves'& general engine condition from these. If those cyls are equally low but steady. then you might have a head gasket problem or a valve timing issue.If they bounce the needles the you have valves not seating fully. At my work (cars) I will do a comparison running comp test. That is run the engine with the comp gauge on the problem cyls then on the strongest one. Sometimes the cranking comp test won't detect weak valve springs,or bent valves etc.

Also if you choke those weak cyls with your hand slightly & they clean up then you definitely have a carb issue.

Post edited by: outatimeoutlaw, at: 2007/09/23 08:59

Post edited by: outatimeoutlaw, at: 2007/09/23 09:03

thanks guys you are great
steel yep used a sealant on the new manifold rubbers
the hose is connected between the 2 manifolds
bisque ; what is seafoam add mate is it a cleaner type additive ?
apart from the guages is there a quick and easy way to check for vacume leaks re soapie water or something ?
probally should invest in a set of guages , as far as i know i got the floats right , how do you do the clear tube test for checking your bowls ?
appreciate the help , i will remove the new mainfiols and re seal again steel cover all bases , means i will get it right one day
it is so discouraging its been a constant problem ever since i got it back from the so called mechanic
have just joined a australian branch of the vjmc and have a vey good mechanic by trade with us so he may win this as a job this week ,have even contemplated sendinding the carbs to wiredgeorge and gettting them done right
cheers better get some sleep local time 12.00am

grace1 wrote:

thanks guys you are great

apart from the guages is there a quick and easy way to check for vacume leaks re soapie water or something ?

Spray WD-40 or similiar all over the manifolds. If the idle changes (as the light oil temporarily seals the leak) you know you have a leak.

probally should invest in a set of guages , as far as i know i got the floats right , how do you do the clear tube test for checking your bowls ?

You would install a clear hose on the float bowl drain. Depending on the float bowl you may have a nipple or else you have a screw that needs to be removed and you jam the hose in the screw opening. Hold the clear hose next to the bowl and turn on the gas. Don't move the hose around...look at the fuel level and compare it to spec in manual, it should be a hair below the carb body/float bowl mating surface, usually 2-4 mm.

appreciate the help , i will remove the new mainfiols and re seal again steel cover all bases , means i will get it right one day
it is so discouraging its been a constant problem ever since i got it back from the so called mechanic
have just joined a australian branch of the vjmc and have a vey good mechanic by trade with us so he may win this as a job this week ,have even contemplated sendinding the carbs to wiredgeorge and gettting them done right
cheers better get some sleep local time 12.00am

thanks for the advice all
have been flat out at work , will try again on sunday arvo 'see what happens ,
i,ve allways had trouble with the right cyl tuning the pilot etc had the carbs put in a bath at a carby place in town and blown out but i guess that dosent mean it dislodged the blockage , tuning pilot is it allways going to mean a carb prob or maybe am i looking at the too obvious
cheers graemeB)

Take the carbs off, flip them upside down, and if you have the brass floats set them at 1 " (25mm will work) between the bottom of the float and the carb bowl gasket (while holding them upside down).

I did this, then checked the fuel height using a clear tupe epoxied to the bottom of a spare set of bowls, and the fuel level was right in the middle of the specified range.

That enabled me to screw the pilots back in to where they were supposed to be(instead of three turns out).

Post edited by: steell, at: 2007/09/29 08:31

thanks steel

ok i hope this all makes sense , i resealed the new manifolds , checked the float level as steel suggested , spot on 25 mm , used wd40 spray in generous amounts as it idled it made no differnce to idle , pulled carbs down and blew out with air , did make a little bit better to tune r/h pilot screw , i really need to get a vacume guage to see what is happening ,
something i have found is i am getting a slight boot of the r/h plug cap sometimes , have tried another coil , no difference , swapped the spark plug caps over still the same ??
could it be the coils or another thought is , is the coil mod we have read of on this forum is it compatable for the twins as is for the z 4cyl,s
i wonder ? someone told me the twin has a different firing sequence etc ?
am trying to find another set of bs38 mikunis to bolt on and see if it resolves the issue , it now runs smoother on that side but the pilot is still out 3 to 4 turns ,too much i know , have also altered the needle setting up one notch didnt seem to alter anything .
any ideas
thanks for reading this , hope everyone has or is having a good weekend riding ,
ride safe everyone
graeme