full throttle bog

bike rides nice but it bogs out at full throttle 3/4 throttle is great. i disassembled the jets and cleaned them with marvel mystery oil along with all the other parts. i found some used pipes 4-1 sounds great i think the cleaner i used is causing the slides to stick or maybe the main jets are gummed up.

Might be to small of a main jet with the 4-1. Usually you would go up a couple of sizes. but make sure that the Fuel level in the bowls are set to spec, and there is no restriction in the fuel line, i.e. filters and petcock/ tank vent.

Sounds like to big of a main. Does it start running better when you let off the gas a little? Did the bog start after you installed the 4-1 pipe?

so i guess when i cleaned the carbs out with marvel mystery oil maybe i should have used something else. the main jets were just about to fall out of the threads on three of the carbs. also the floats were still low i guess the spring loaded thing on the needle valve does keep it closed so a forewarning for anyone adjusting their floats that it may take a few tries. i am pretty sure the 125 main jet is stock for the 1980 kz750 ltd-4 cylinder with the keihin 34x4 carburetors. it does good now i went through shelton to bremerton and back without much hesitation. i am working with a k&n drop in filter i would like to also modify the bottom of the airbox for a cold air duct that runs through the same filter.

not bad if i do say so those ldt/"tiller" handlebars had to go i would like to be able to walk again in the case of a wreck not to mention having a half of a handlebar in my stomach.

125 mains are way to big for that. You should be running something like 115 or 118 on a 750.

you may be right the dynojet stage one is 130 and the stage 3 is 136. the only thing i see that is off is the vacuum slide has 2 holes besides the one for the needle valve. the reason this troubles me is the instructions on their pdf link says to drill the slide lift hole and it has a picture with one slide lift hole on the slide.

Hi new member I myself have been dealing with jet issues on my kz 1k..... A great place to help with the right size of stock main jets
Are preformancesportsplus.cOm ... Found out that the 127.5 mains that were in my bike were way too big. Stock size in mine is a 107.5 .... So having the 125 in there is to much on that 750 .... With a 4 to 1 being a Mac..... Or vh.... With open air cleaners... I'd say try the 117.5... U can pick up new main jets fairly cheap I got three different sets of four for 38 bucks at the dealer... Just make sure to bring in one of the jets so u know u order the right one for the carbs ..... Happy hunting love the old bikes but the carbs can be a pain in the ass

The carbs on my kz750 are 34 mm each on a 77 kz1000 for example the carbs are 28mm

i have noticed it is hard to start. i lost my tach cable and i think the plugs are being coated with gas.

Agree that a 125 is the stock secondary main jet.

thanks, i will use that for reference, as though these things don't have enough power as it is. I would like to get individual filters and a re-jet but the k&n in the air-box is nice to have due to weather conditions turning colder I would like to ride it year round.