Idle circuit running lean after mods Need advice

[Fairlyodd45]

I had my stock carbs completely rebuilt from top to bottom. All jets, needles and seats, floats, emulsion tubes, fuel and vent tees have been replaced with NOS Mikuni. My bike has been modified with Delkevic 4 into 1 exhaust and I am running individual K&N pod filters. I am having a major issue with the idle circuit lots of popping at idle and I can't get the idle to settle down it's acting like I have a major vacuum leak. I've checked everything that would be suspect for vacuum leaks and everything checks out. I tried upping the size of my pilot jets to 45 but it just ran super rich and wouldn't idle at all, so I went back to the stock 42.5 and now it's running way too lean even after adjust the air/fuel mixture screws to almost full out still getting the popping and unstable idle. I ordered the stage 3 kit from 6 Sigma that is supposed to rectify this issue, but am very leery about physically modifying my stock carbs since they are in NOS condition. If anyone has any suggestions I could sure use the help because I'm at my wits end with this issue. Thanks in advance.

[DiverRay]

When the carbs were rebuilt, did they replace ALL the seals, like the throttle shaft seals, and the caps for the vacuum ports? Those are the two big problems as our bikes get older. With your mods, you should have gone up at least one size on the main jet.
Now for the stuff we need to know, what year is the bike AND what filters are you using? A lot of the pod filters can block some of the holes you can see in the back of the carbs. If the holes, vents AND jets, are partially blocked the bike will not run properly.

[Fairlyodd45]

When the carbs were rebuilt, did they replace ALL the seals, like the throttle shaft seals, and the caps for the vacuum ports? Those are the two big problems as our bikes get older. With your mods, you should have gone up at least one size on the main jet.
Now for the stuff we need to know, what year is the bike AND what filters are you using? A lot of the pod filters can block some of the holes you can see in the back of the carbs. If the holes, vents AND jets, are partially blocked the bike will not run properly.

Yes all the seals were replaced along with the fuel tees which are now high quality brass and both of the vent tees were replaced with NOS Mikuni. I went up two sizes on the main to 145 and the pilot jets to 45.5, but found going up two sizes on the pilot jets was a mistake because it ran so rich I couldn't adjust it out and the bike wouldn't idle, so I put back in the stock size pilot jets and it now runs very lean at idle with all the symptoms of a major vacuum leak Popping at idle and unstable idle when at running temp. I've sprayed every inch of those carbs and around the boots to check for leaks and there isn't any. The bike is a '79 running the stock BS34-II 2H7-10 carbs. I am running K&N filters that don't block any of the ports so that's not an issue.

[Larrym]

I've sprayed every inch of those carbs and around the boots to check for leaks and there isn't any.

I've checked everything that would be suspect for vacuum leaks and everything checks out.

IMHO, wrong method to ID or locate "vacuum leaks." ( •_•)

Dunno how many farking times I've heard this from peoples and then I've gone over IRL wit' my own DIY smoker and SHOWN them MULTIPLE vac leaks.... (－‸ ლ)

Sumpthin' like shown here-

Not sayin' yur prob actually IS a vacuum leak but iffin' we's gonna move forward we GOTS to be sure... ( •_•)

[DiverRay]

I would go back down to one size on the main and stock pilot jets. Also, what gas are you running? These bikes are MADE TO RUN 89 octane, NOT premium! Higher octane gas burns SLOWER, and will cause carbon buildup in a stock engine. I don't know your location, but if you have ethanol free gas, USE IT! These bikes were produced before the introduction of ethanol, and "gas" with ethanol is NOT good for them.

[DEEBS11]

Did you sync the carbs?

[DiverRay]

Thanks Deebs, I didn't think to ask that, as it's a "given" for me.

[Fairlyodd45]

Did you sync the carbs?

Yes I did and they synced perfectly which really surprised me.

[Fairlyodd45]

I would go back down to one size on the main and stock pilot jets. Also, what gas are you running? These bikes are MADE TO RUN 89 octane, NOT premium! Higher octane gas burns SLOWER, and will cause carbon buildup in a stock engine. I don't know your location, but if you have ethanol free gas, USE IT! These bikes were produced before the introduction of ethanol, and "gas" with ethanol is NOT good for them.

I'm using a 50/50 mix of 92 Octane Shell premium with 110 octane avgas. I have buddies who are pilots and they get me 5 gallons whenever I need it, so lack of octane isn't the issue. The bike is very responsive at throttle up and pulls strong after 1/4 throttle. The issue is the idle circuit. The carbs are very lazy about returning to idle once the bike reaches running temp usually getting stuck around 1500 RPM and I have to rev her up to get her to settle down and that doesn't always work. I'm going to park the bike until I get this issue resolved the last thing I need to do is burn a hole in my new pistons which will happen if I keep running her her hard with the lean mixture. Thanks for your suggestions guys. Hopefully this stage 3 kit I ordered will fix this issue.

[bikerphil]

I would be suspicious of the new needles and emulsion tubes, if they are even of the slightest difference from the original, it will cause problems. If you have the old ones, carefully compare them with each other and/or revert back to the old ones and give that a try.

[DiverRay]

YOU ARE NOT USING THE PROPER FUEL!!!! These bikes were designed to run on LOW OCTANE gas! Please switch to a regular grade fuel unless you KNOW that the engine has had high compression pistons installed. You WILL ruin the engine very quickly with that mix. And just so you know, Shell has some of the worst additives for engines out of the pump. I'm 70, and I've been working on I.C.E. for most of my life, so this is not just "something from the internet". I've seen the inside of engines that ran only Shell.

[Fairlyodd45]

I would be suspicious of the new needles and emulsion tubes, if they are even of the slightest difference from the original, it will cause problems. If you have the old ones, carefully compare them with each other and/or revert back to the old ones and give that a try.

I purchased all of the parts personally. These are all NOS Mikuni parts, not cheap Chinese knockoffs. Every single part is legit so no that isn't the issue either, but good thinking outside the box I'm impressed.

[Larrym]

I am having a major issue with the idle circuit lots of popping at idle and I can't get the idle to settle down it's acting like I have a major vacuum leak.

now it's running way too lean even after adjust the air/fuel mixture screws to almost full out still getting the popping and unstable idle. .

These engines use a "Waste Spark" ignition system which means that each cyinder gets 2 (two) sparks with each at a different time during the 4 stroke cycle. (*′☉.̫☉)

When the mixture is too rich to completely burn... the SECOND spark happens just at the right time to ignite any UNBURNED fuel/air and you get the POPPING most people usually associate with a "Lean" condition in an engine that DON'T got the waste spark system. (☉_☉)

When one or mOaR of float needles/seats ain't actually metering the fuel level to the right height in the fuel bowlz, (usually overflowing and regularly found in the Taiwan carb kits...) and the fuel level is WAAY too high? (O_o)

SO much fuel is dumped in that you'll GET that popping along with spark plugs that might look "lean" at first glance, but are actually CLEAN. As in gas is a SOLVENT and the electrode/anode have been washed clean. (O_O)

BTDT. (_Oo)

[Fairlyodd45]

I've considered setting up a jig such as this to check the fuel level in the bowls, but normally if the level is too high you would end up with fuel seeping out of the vent tees which in this case isn't happening. However I'm willing to keep an open mind and at least give it a shot since I have nothing else to lose at this point considering I have well over $1500 tied up in this set of carbs that can't even get out of the driveway without pissing themselves. I knew I should have gone with a set of flat slides for this project, but didn't do so do to the cost which in hindsight would have been the best solution considering what I already have invested in this stock set. I ordered a 6 Sigma Stage 3 Kit and am going to install it to see if this rectifies the issue as they claim it will. These carbs are extremely fussy when it comes to any sort of modification with air flow or exhaust back pressure and I would have normally set her up on a dyno to tune them properly, but I no longer have that option in my area. Thanks again for the suggestions and I'll keep you all posted with my progress.

[Fairlyodd45]

By the way if you guys are looking for a person who does a great job at refurbishing your old tired looking carbs give this gentleman a sub at Total Motorcycle Parts. You can find him on Facebook and eBay. What I sent him looked like a pile of junk, but what I got back looked like NOS. Definently worth the $500 for his services.