Kz750ish carb advice

Seems like I need bigger jets and bigger carbs....

I doubt if you need bigger carbs on what is a mild state of tune. you could lose a lot more bottom end than you gain on the top.

Think of the 'signal' a carb gets when the throttle is part opened...the difference is like like sucking a drink through a drinking straw or a hosepipe. Instant throttle response and pick up might be compromised if you over carb it.

The late GPz750 and 1100 both share the same 34mm carbs...you need to be at quite a high state of tune before your carb size is a limiting factor in my opinion.

Tyrell Corp wrote: I doubt if you need bigger carbs on what is a mild state of tune. you could lose a lot more bottom end than you gain on the top.

Think of the 'signal' a carb gets when the throttle is part opened...the difference is like like sucking a drink through a drinking straw or a hosepipe. Instant throttle response and pick up might be compromised if you over carb it.

The late GPz750 and 1100 both share the same 34mm carbs...you need to be at quite a high state of tune before your carb size is a limiting factor in my opinion.

Thanks. I will give it a go with what I have and go from there.

Jeff, what settings did you end up using on your vm24 with a 750 engine combo? what main jet pilot and needle clip setting? I have the same carb engine set up on the bike a just baughtm 1976 kz 650 with vmm with a 1982 ltd 750 engine, just baught itm needs a. Carb clean and sett up asap

Well things changed a bit. The VM24's are going on another 650 I just picked up. Besides that my elevation is at almost 4500 feet so jetting may be very different....sorry I could not be much help. Good luck!

iam at 4100 ft elevation, if you where going to do that combo, what did your research suggest as a starting point?

Well its been 8 years since my bike was running but I had purchased a dynojet kit for the the k&n filter and went between the stock airbox and pods. I can see what jet sizes the kit has but the dynojet numbers are differt than normal jet numbers. So basically I didn't do the research I cheated.

On my KZ650 I'm running stock jetting with the airbox and just a V&H exhaust at 5,000 feet. VM24's should be fine for a 750 upgrade IMO.

Regarding jetting, IMO many get a little carried away, you need to bare in mind that a carb does have some ability to allow for extra cc's in it's basic function. If you pull more air through a carb because you have extra CC's, it also draw in more fuel with that air. If the engine is remaining stock other than the overbore and was jetted correctly before hand then the changes required will be minimal.

My recently acquired KZ1000A2 has the 1075 kit and the PO had, IMO, got carried away with the jetting thinking the extra capacity was a big deal, as a result it didn't run well. returning closer to stock has made a huge difference to starting and idling. Being at altitude seems to have a big effect on idling and slow running, I think the thin air is more noticeable a low rpms and so it's easy to go too big on pilot jets. I've found keeping the pilot jet relatively small and running a bigger main jet so you don't get the engine too hot on the top end has worked well on a number of machine's carbs I've modified. I have a Honda XR650L, they come super lean from the factory, but with the altitude I could only go up one size on the pilot jet, I jumped two sizes initially because I had some other mods too, but it would bog when accelerating, two sizes more on the main jet worked fine.

Personally if it was me I'd get it running with stock jets first to see how far out that was before jumping to any conclusions. I'm not personally a fan of the dyno jet kits, I like to just buy the individual jets, based on how running with stock jets was working and how they feel. The dyno jet kit can throw in too many variables at once, if you change everything in one hit and don't get the result you hoped for, it's difficult to know where you went wrong.

One thing at a time, then move on.
Steve

It's tempting to change every thing at once as those carbs can be awkward to remove and them being 4 of them it's relatively a lot of work each time, but on carbs in general I've seen it advocated many times to change things in stages because different components work at different throttle openings it is possible to start with pilot jets and work up from there through the other systems so you don't get a couple of wrong sized or set components compounding problems while at the same time becoming very difficult to diagnose..