Tuning Carburetors For Throttle Lag & Hesitation

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In this video we are back on the KZ400 build to finally get some carburetor tuning done for these mikuni VM30 carburetors. With the help of our friends over at @DNAHighPerformanceFilters we have this motor breathing right. The next step is to dial in what we can before we go on our test ride.
But we have a problem... When you give the throttle a quick twist, it hates it.
Join me as we use a few techniques to pinpoint what needs to change in order to make riding this bike more enjoyable and respond quicker to what throttle inputs we give it.
ENJOY!
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[@BabaYaga6677]

Hey man keep these videos up its been helping me alot and teaching me alot of stuff you cant find by simply looking it up

[@georgesteffens7489]

Wish my dad and I had kept an old 1975 CB500T years ago. What I’ve learned, a lot from your channel, would have helped us with that bike. Something so satisfying about getting ‘er dialed in!

[@sthildas4857]

Great practical advice in trying to tune it plus the range of options..

[@michaelsorokin1548]

Restoring a midnight special here soon and finding your channel was the most fortunate thing that could happen. Appreciate your time and effort.

[@davidguest6051]

Wow. Who knew you need to oil the air filter. Not me. So helpful. Your videos always have some tiny bit of info that I never knew about. Has anyone ever come out and said thankyou. Well, I will be that guy. From all us expert & backyard mechanics....Thankyou. Thankyou for sharing your knowledge and expertise. Years of your servicing motorcycles, and you freely hand over that knowledge to us. Wow!. Thankyou. Cheers. D.G. from Canada...eh?

[@ethantabor79]

Thank you for making these videos! You are an awesome source of information on these bikes. Ive been building my own 75 kz400 for almost a year now and im down to the final steps. Carb tuning with vm36s on it now. This helps a ton! Thank you! Cant wait to see this one on the road.

[@colinculverwell325]

I've been down that road myself with the 3 cylinder Yamaha RD I built. Used oem Yamaha RD Mikunis. I got the main jet about right and from about 2/3 throttle the thing really took off. But on decel and small throttle openings it would surge and stutter. Messed around for ages with pilot jets, needles and settings but in the end changed the slides from 2.5 to 2.0. Issue disappeared straight away. Seems like we get used to changing jets but I don't hear many stories of people swapping slides which for some coukd well be the answer.

[@jimkoney4200]

I used to own a 1973 Honda CL 350. I did my own tune-ups. I learned a lot from your carb tune video.

[@TheMotorcycleMD]

That's awesome!

[@snake_eyes_garage]

One of my favorite bikes I've owned was a KZ400. I bought it with "bad carbs", prior owner gave up. Rebuilt the carbs but had the hardest time getting rid of this stumble. Wish I could take this video and go back in time 35 years. 🙂 I swapped in Mikuni's and got it running well enough to ride it to the shop, and have a tech show me what you went through. Then he said, 'you can spend weeks dialing them in... now you have something to do when you're bored.' Nice. It was a great bike but (now I know) was lean on full throttle. Those air filters would have helped that.

[@vmax4steve524]

Bought myself a suzuki VS1400 that had been stood for several years, carbs gummed up. Bought a carb rebuild kit and have just spent the last two months getting it to run right. Finally I raised the needles one notch and bingo, everything is great. If anyone has ever tried to tune the carbs on a VS 1400, well it's one bitch of a job, everything is hidden under the seat and tank, front cyclinder carb under the tank and rear cyclinder carb under the seat and a cable to sync between the two, everything has to come off for every single adjustment as you can't access anything with them fitted, total nightmare.

[@tedking9793]

Good topic Cody. One step at a time! LOL and many steps. Too many times customers want to change two or more things at once...

[@michaelanderson3771]

Super helpful Cody. I keep spreading the word of your stuff on the shadow riders page and your stuff is super helpful and real easy to follow even for the newbies.

[@TheMotorcycleMD]

Thanks man! That means a lot!

[@vic2095]

very nice video, I wish for more! Especially 4 carbs in line setups! BTW: I knew raising the needle would help at very beginning of video, so satisfactory to watch :D

[@atombombsgarage]

Thanks for all your videos man. I always learn something new from them

[@garyguyette9739]

Hold Sh**!! Cody!!! This popped up on my suggestions. Great video homie!

[@TheMotorcycleMD]

Thanks man!

[@rudeliorodriqueziii1090]

I think we all have gotten in touch with our pyromanic side from time to time.

[@scottaspect]

Try using some bleed type needle jets, they work a lot better on a 4 stroke. The primary type needle jets delivered stock in Mikuni VM's are more suited for 2 strokes.

[@MrNiklas1967]

Good video

[@TheMotorcycleMD]

Thanks for the visit!

[@kellysmallwood6205]

Colertune works pretty good

[@j1nguyen]

Can you make a video about main and pilot jet differences? When to change them? I have a scenario where my idle is good but once I give it throttle, esp if I throttle fast, the bike bogs and eventually dies.

[@NubsWithGuns]

Now I know what the problem with my mini bike most likely is, thanks. It has a small industrial engine on it(212cc hemi head predator)and I have that problem with it just wanting to stall if I give it a handful from idle. Stock style carb with a fuel screw on the back' But raising.the idle makes it mostly go away, and after I've ridden a while it doesn't do it sometimes. I had wondered if it was a fuel pressure thing before. Gravity fed and the stock fuel tanks are known to not flow and vent well.

[@jakubwojciechowski4183]

Great job. Did you go for the road and started to work on main jet size and then middle range? That’s very interesting. Cheers

[@Roaddog420]

I always wonder what the logic is for ditching the factory airbox. I have never seen an airbox that restricted air flow more than the slide(s) itself. I can understand changing the filter but every bike I have seen with the pod filters always runs worse than the factory airbox.

[@Lepasfin]

would it be a good idea to use a wideband ?

[@pd8559]

If I fully gun the throttle on my small displacement single thumper carb bike it bogs and quits. But it doesn't have an accelerator pump design so no big squirt of fuel into the carb when gunning the throttle. Other than that it's fully tuned and I don't gun it off idle when on the streets so I just ride it without issues so far. My plug was black as night when on larger idle jet so I've backed off to where I run now. I'm only a step above factory which is lean for EPA requirements today.

[@kawasakichopshop2759]

im working the same kinks out of a 440...first i think your main is too big...you may want to try a product made by Thunder products...its called UFO ultimamite flow optimizer....they fit under your slides and smooth out the flow...better fuel atomization...the VM slides like to tumble the air flow....so far this has been the only thing that has improved my off idle stumble...as it does increase and improve the air flow it also richens everything way up...but as i said its the one thing that has helped with my stumble....as you stated the obvious your air filters are causing this problem...your getting too much air too fast. great video and i know exactly what your going through

[@TheMotorcycleMD]

This is an interesting read! I will look into this product if I can't iron this stuff out with what I have on hand. Thanks man!

[@terryfennell1575]

I hadmaconie on mine not a lot of good also found if you use engine oil on air filter it last longer and they run better

[@cbrider726]

Wow your good man . Just dont burn your workshop down lol . Carbs a real pain if you cant set them up . My old FZR750 caused me many problems until i found a Yamaha racing team enigineer and he had it sorted in a coulpe of hours . 👍👍👍

[@tedking9793]

Your experience is a good reason most shops don't want to do carb tuning, especially on a non-stock set up. Even your Factory race tech took a couple of hours. Carb cleaning is one thing but tuning and changing and testing all take time.

[@cbrider726]

Your so right . I have been working with bikes for over 30 years and still find that seting up carbs can be so frustrating . Differant jets and engine wear .Modern exhoust systems make thing even more complicated . Trying to remove carbs can drive you crazy @@tedking9793

[@seanhall4098]

I've got a 77 kz400 with the cv carbs, I got it running good enough with the stock jets. Took me a week to finally figure out what model I had lol. I guess in late 77 they converted to cv carbs. Wild goose chase.

[@TheMotorcycleMD]

Dude the model line up for these bikes is nutty. I literally had to call Kawi Inc. and find out hahaha

[@cbrider726]

Just a quick question . Why would a bike rise and drop in revs on tick over . ????

[@miguelpagansr6128]

I have a weird situation on my Honda express2, sometimes at idle it runs well and all of the sudden the idle would go up on its own. It’s a 2 stroke engine with new seals, gaskets and more, any thoughts? Thanks. Before I forget, still running the original carburetor and I have the air fuel mixture screw set at 1.5 turns out with the needle in the number 3 position which is the middle.

[@matthewwooliever1785]

Check for air leaks. Mist starting fluid around seals. Quick and easy check/fix. Rule it out along with compression and other base variables.

[@benderbender1233]

🤘

[@bigal7561]

I'm a member. Have a 75 Honda CB 360t that I did a full carb overhaul. I've replaced the mufflers and put the combo ret/reg and elec ignition system. No vac leaks, and vac synced carbs. Just touch the starter and she starts and purrs. Problem is when your running and you give it some throttle it hesitates and and has a bit of a choke. Carbs are running rich as the plugs get charred. I've adjusted the fuel/air back and forth. The only thing I've not done is check the valves after I set them at the get go. Help

[@TheMotorcycleMD]

Hey man! Send this question over to the Members email. I try not to spend too much of my time in YT comments and I don't want to lose track of members that need some help.

[@Colormanify]

👍🏻

[@user-zn8ep7ls2p]

My it kind weird I release the brakes the bike starts moving I mean fast without I turn the throttle

[@whistlindixiesmallengine2085]

I'd run a 2 into 1 intake

[@jeromewilliams2678]

🇯🇲👌🏾💯👍

[@cbrider726]

BTW dont bother with the color tune kits are waste of time . I have been around bikes for over 38 years and gave up on this crap . You are far better to use your own skills .

[@TheMotorcycleMD]

Noted! I might do a video for fun. Me vs Colortune hahaha

[@cbrider726]

You will win lol@@TheMotorcycleMD

[@user-yt1zn9sz5b]

​​@@TheMotorcycleMDPlease do it. I was just about to order the Colortune, but this video and the comments on it makes me think twice.

[@NubsWithGuns]

Could swear I learned about carbs with my ears and not colors😂.