Vm29/cb750 dohc (I know.....)

When doing a bench sync, all the slides had the same gap using g a small drill it. When running engine with vac sync the gauges have about 7"hg difference and runs poor. Would that indicate a vac leak?

That "7" is pretty a sloppy sync. A vacuum leak..could be if you're showing low measurement on one or two. Although a twist bit only gets you in the ballpark, dynamic adjustment really required. These have basically the same "adjustments" as the KZ900. Was goofing around this morning looking at that Dyna 2000 ignition. Seems to be problems associated with those when used on the 79-up CB Series. Unlike the other versions of the Dyna S and 2000i, your pick-ups run in oil. Does this aftermarket ignition work well with the original carbs or was it added just recently? What was the problem with the original ignition bits? They are super reliable, weak point on these are the rotors/brushes. Stators rarely fail unless hit on the cover.  

i have had everything as it is for about 8000kms and then went through just the motor keeping all the same components as is right now. put another 8000kms on with no problems aside from failing charging system. you called it!! i went with the vape system with perminate magnet and swap the carbs. was still running normal with stock carbs/air box and getting 5L/100kms (200km to work round trip) wanted to be able to have pods and the mechanical connection of fuel control and not cv. i am kinda doubting this decision but from what results i can see so far it will be worth it. and it finishes off the look. 
i did check for vac leaks with propane torch all around the boots till the point where was getting a little scared! it didn't make a lick of difference on idle quality. i was very careful to get all the slides to the same amount of drag on drill bit. like you said "ballpark"
just don't make sense to me.
will changing the air mix screw change the vacuum sync? i didn't check that if it is a factor. i did get them all the same vac reading and the idle was sooo much better, just black plug fouling.

You seem to be getting good MPG, just black plugs which points to a rich condition but not rich enough to give bad gas mileage. Can you post some pics of the plugs, I noticed you did not post any.
 

sorry if i lost you in my rant. its hard to get out all the info at once. in the right order also. that was all on the original carbs. the vm rack is only problematic at idle and taking off from a stop it will sometimes misfire/studder but after 1/8 throttle it gets gone. i haven't put many miles on the vm's until i get pilot right.
if you can picture holding a lighter up to a spark plug and it gives it that black carbon build up covering everything, thats it. they aren't wet at all just lots of carbon.

Sounds like valve guide seals to me.

you might be right by all means, i really can't say no. not trying to be rude but i do find it hard to believe since this problem came when i put the vm rack on.
i am just wondering what kind of vacuum the z900/1000 pull at idle. does anyone use a vac sync or the mercury style. if i can't pull a strong enough vacuum then i might pitch the idea.....after i try new exhaust of coarse! it might even be a factor as well. the p.o. had replaced mufflers and had to cut the head pipes to do so. head pipes are double wall. he cut the support for the inside wall out and now it rattles under certain rpm range (at hwy speed) and it is really quiet mufflers on it. maybe too much back pressure and not enough flow is my thought.

While looking through your posts I didn't see pics of your plugs. That would help.

Benz1991 wrote:

you might be right by all means, i really can't say no. not trying to be rude but i do find it hard to believe since this problem came when i put the vm rack on.
i am just wondering what kind of vacuum the z900/1000 pull at idle. does anyone use a vac sync or the mercury style. if i can't pull a strong enough vacuum then i might pitch the idea.....after i try new exhaust of coarse! it might even be a factor as well. the p.o. had replaced mufflers and had to cut the head pipes to do so. head pipes are double wall. he cut the support for the inside wall out and now it rattles under certain rpm range (at hwy speed) and it is really quiet mufflers on it. maybe too much back pressure and not enough flow is my thought.

CV carbs require a good vacuum signal to operate. They also adjust to engine operating conditions leaning out the fuel mixture if needed so I'd rule that out. They really are excellent carbs for a stock motor. On my bike the plugs would foul out in 100 miles due to bad seals leaving me stranded on the side of the road making me change them to get home. The plugs should tell the story. 
BTW too much back pressure can make it run rich as well. Jetting can help that as long as the engine is in good running condition. 
Steve

i will get a pic of plugs soon.
can anyone tell me what vacuum the 900/1000's pull at idle?

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I'm getting 20-22

 

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