Topic: Gummed up pilot jets

[Bduck72750k]

Bike: 1974 CB750K     Oil type:Castrol conventional 15w40 (first change at about 450 miles with very fine shards)
Now has about 700 miles on odometer after complete rebuild (stock rebuild motor to include new chains, pistons, rings, decked heads, etc with help of Hondamans book).
Carbs are completely rebuild (cleaned as per Hondamans book) and all original floats, needles and Keihin brass. Carbs are 657a i believe, and will attach picture. Im running 110 main jets and 40 pilot with a steel dragon performance air box and 4-1 carpys exhaust with baffle in but not actually running any packed fiberglass in it. Havent done a formal plug chop but final seem to have it mostly dialed in and plugs look good (d8ea) and carbs are synchronized with Carbtune pro (thinking of maybe hooking it back up to confirm still good sync). I had a lot of help trouble shooting when jetting and getting a good idle and air/fuel mix. Currently 1 turn out on all four carbs.
I commute with it almost daily (30 miles one way) and joy ride evenings and weekends. My only complaint is closed throttle to 1/4 throttle is just bogging when its hot, and i have checked out the pilot jets several times after finding that they seemed 50% clogged (roughly) the first time, so i subsequently have checked a time or two since and seemed to again see that they were slightly clogged. Seems like a good improvement after cleaning them. I have a good tank and have drained it before to ensure no debris. I also have a brand new petcock, lines and i currently run 91 octane non-ethanol.

Any advice?

[Hoosier Honda]

May sound stupid but are the fuel lines you installed actual fuel hose and not just rubber hose? Just a thought. Seems weird the jets would gum up that fast with non ethanol fuel. Something is dissolving if they are clogging.

[Deltarider]

You may consider a socalled maintenance dose of a fuel system cleaner @ every tank fill.

[Bduck72750k]

I have used other octane levels with ethanol. But the last two fill ups are strictly non-ethanol. I have brand new 5.5mm honda fuel line that i believe i got from Yamiya. What would you recommend for a fuel additive. Today i will pull the pilot jets again to see if they are actually clogged or not.

[Deltarider]

First of all: it is very difficult to arrive at a view position, where you can actually see the hole clearly as a round hole. Sometimes it looks like there's a spiders web in it. Well, there isn't, it's a trompe l'oeil if you will pardon my French. It took me quite some time to make the pic below of a #40 slow jet for instance.
I guess all fuel system cleaners are more or less the same. Brand is not important. In Europe we have Tunap, Forte, Redex, Holts, Wynns, just to mention a few. Some folks mix their own brew of some lamp oil (= kerosene), naphtha and maybe some alcool. An easy way to blow air through the slow jets in situ is: drain the floatbowls, turn the big central idle knob thus that the carb slides are down and then kick a few times so the down going pistons suck air through the slow jets. When needed (seldomly) for cleaning I use some stranded copper wire which is softer than the brass jets are made of. Always worked for me. But I haven't had clogged jets in years. In this forum there's a lot about carbs, but I'm one of those that believe in: '90% of fuel issues turn out to be electrical', in other words: ignition.

[Bduck72750k]

I do have a brand new advancer, timing plate points and condensers all tec brand. It has the spring “mod” HM talks about on advancer unit, and timed perfect. I should go back and triple check timing (ive done this several times) and honestly would love to consider electronic ignition this winter. I also have a new OEM harness and a purpose built moto black box controller in it that does all my custom buttons. Honestly will probably do an m-unit very soon. Im sure my A/F mixture is probably not perfect, but it seems like 90% there, and im leaving it alone probably for the remainder of the season. I really need to plug chop at 1/4, 1/2, 3/4 and WOT. Probably will perform this over the winter at a local Harley shop that has a dyno.

[Deltarider]

[...] Honestly will probably do an m-unit very soon.[...]

I have no idea what you expect of that. The answer for your issue, is not buying stuff, I mean not necessarily, but a proper diagnosis.

[...] I really need to plug chop at 1/4, 1/2, 3/4 and WOT. [...]

Well, good luck with that! It's a method from the theory book, but I haven't seen many success stories.

[...] Probably will perform this [...] at a local [...] shop that has a dyno.

That sounds better.

[newday777]

I have used other octane levels with ethanol. But the last two fill ups are strictly non-ethanol. I have brand new 5.5mm honda fuel line that i believe i got from Yamiya. What would you recommend for a fuel additive. Today i will pull the pilot jets again to see if they are actually clogged or not.

Did you happen to add inline filters? I didn't see any but figured I should ask as they have been problematic.
Also looking at your air filter, did you put on a bracket to hold the carb weight from bouncing?

[goodtryer]

i currently run 91 octane non-ethanol.

I have used other octane levels with ethanol.

Octane does nothing regarding gumming up your carbs. Different components are mixed into the fuel to achieve the octane levels you see advertised and this is only a measure of the tendency of the fuel to resist pre-detonation. Do not confuse octane with power or cleanliness.

https://www.exxon.com/en/octane-rating
https://www.eia.gov/energyexplained/gasoline/octane-in-depth.php
https://www.fuelfreedom.org/what-is-octane/

What would you recommend for a fuel additive.

Sta-bil Storage Fuel Stabilizer. Since I have started using this every time I fuel up, I have not had any issues with gummed-up carbs. In fact, last month I easily started a pressure washer that had been sitting in storage for more than a year with Sta-bil in the fuel. Last weekend I started a chainsaw that sat even longer. Choke, pump the primer a couple of times, and 3 or 4 pulls later it was running.
Highly recommended.

Cheers

[kerryb]

I only mention plug caps because you didn't.  The last two engines with running issues were cured with 1 or two new plug caps!  I assume yours are new, but check them.  I'm still can't believe that was the only culprit for a hot engine power loss and stall, but a month after he says it still runs great! 
I gave up on anything but a stock airbox because I don't want to chase these gremlins anymore.

[Bduck72750k]

To respond to the responses above… the M-unit was just referring to electrical in general, and my plans in the future; the ignition as well (converting to electronic ignition). They are also brand new plug caps but i can test them to make sure!  I also wasn’t sure if there was any influence with type of gas i was using, but i may add a fuel additive every so often. Lastly i dont have any brackets for the carb/air filter, and i dont have inline filters but i do remember looking into it (in forum) and what i thought i came up with was my carbs had a brass fitting with a filter in it already. Correct me if im wrong

[TwoTired]

I'm trying to understand how your unseen jets can be "gummed up".
By what mechanism?

The fuel is largely solvent based, which holds most of everything that comprises it in solution.  Until you add water to it, it stays in solution.  Dirt and rust suspended in it can settle out over time at the bottom of any reservoir holding it.  But, that ain't gum, those are particulates and will only block a jet if they are bigger than the orifice.  Which is what the filter is supposed to block when the particulates are too big to pass through the tiniest jet in the carb.

So, that leaves solvent evaporation to concentrate the solution into something that "gums".  (Which any new additional fuel would thin out and clean away when the engine runs.)

What I have seen, is when the fuel in the carb is allowed to completely dry out through evaporation, leaving a shellac like coating inside the carb reservoir, and the jet orifice blocked by the meniscus film that has hardened.  This film is often polymerized so the that the standard solvents in gasoline will not return it to solution form.  But, a good carb cleaner fluid dissolves this deposit type.

Did you allow the carbs to dry out, and not drain the bowls for storage?  Is your tank filter compromised?

Cheers,

[Bduck72750k]

I'm trying to understand how your unseen jets can be "gummed up".
By what mechanism?

The fuel is largely solvent based, which holds most of everything that comprises it in solution.  Until you add water to it, it stays in solution.  Dirt and rust suspended in it can settle out over time at the bottom of any reservoir holding it.  But, that ain't gum, those are particulates and will only block a jet if they are bigger than the orifice.  Which is what the filter is supposed to block when the particulates are too big to pass through the tiniest jet in the carb.

So, that leaves solvent evaporation to concentrate the solution into something that "gums".  (Which any new additional fuel would thin out and clean away when the engine runs.)

What I have seen, is when the fuel in the carb is allowed to completely dry out through evaporation, leaving a shellac like coating inside the carb reservoir, and the jet orifice blocked by the meniscus film that has hardened.  This film is often polymerized so the that the standard solvents in gasoline will not return it to solution form.  But, a good carb cleaner fluid dissolves this deposit type.

Did you allow the carbs to dry out, and not drain the bowls for storage?  Is your tank filter compromised?

Cheers,

Thanks for the reply, i think when i pulled the jets it appesred when holding them up to the sunlight it seemed to be partially blocked. I could be wrong, and i am absolutely not a mechanic, although i have experience with cars and some motorcycles, i have learned so much through this build. I am a licensed veterinary technician during the day, so my extra time is tinkering with the 750. I havent had the carbs dry out since rebuild and sonce running it. This is first season it has been running since the compelte build. I would say there is like 80% of this bike that is brand new. And again, my logic and understanding might not make sense, but most of my trouble shooting has been searching through HM book and my manuals, along with trying to find forum posts.

[seanbarney41]

lots of times a freshly removed pilot jet will appear blocked when you try to observe light through it.  As Delta and TT mentioned above any fluid left inside will form a "meniscus" from the surface tension of the liquid that will block the light.  A quick puff of air is all that is needed to clear this.