83 Seca 900 bogs down.

I don't know where you get the 5 turns out @chacal ? Did I miss something?
Also, please forgive me, you have your cv carb theory wrong. Slow lifting of the slide results in rich mixture, not weak. Hence my question about showing us the bottoms of the slides in case someone has enlarged the air passage.

@MrSeca , are you certain you checked the progression holes and passages @chacal mentions? I don't see how you can perform a service on these without? And also - you didn't respond to the question I posed - you did remove the mix screws didn't you?

Lastly, well nearly, @k-moe suggested starting with 2.5 turns out for these screws, I would agree with this, maybe even 2.75 turns.

And, actually lastly, recheck your float levels again, if non of the above works.

 

You see this comment "only really happen at the higher speeds." Well, if all your screws are reset, you did clean them and check fuel flow through the passages, and no- one has doctored your slides, I would get a set of standard needles, used ones if you can, provided they're good.

Essentially, at higher speeds and loads the progression circuit does less, and the needles do more. Also, a low fuel level in the float chamber translates to more air mixing in the emulsion tube - hence a weaker mixture.

 

Yes; if the idle circuit passages are entirely clean. If they are not, then they will not be able to deliver the additional fuel needed during transition as the slides lift, resulting in a weak mixture. Remember that the idle circuits provide the same function as an accelerator pump does in addition to maintaining fuel flow at idle.

 

Yes, MrSeca responded to my question of why his Colortune attempts weren't working:

Well, what I was referring to is what k-moe stated:

Pilot circuit that doesn't / isn't able to "deliver the goods" during this transition will cause a lean mixture until the slides / main fuel circuit "catches up".....which is the issue that MrSeca said he was experiencing:

It is the "quick cracking" of the throttle where one might expect to experience issues related to a deficient pilot fuel circuit, although as many have pointed out (correctly), other factors could also cause the same problem (modified slides, incorrect needles, etc.). My recommendations were due to the fact that his pilot fuel circuit seems to have some issues, and those issues could also be the cause of the "bog" when snapping the throttle open. "Pilot" or "idle" fuel circuit is a little bit of a misnomer; it is active throughout the rpm range, although it predominates during low, slow, or steady engine speeds/loads, especially up to around 4000 rpms.

 

Hmm, well they indeed do work during transition (hence I call them progression holes and passages), but the OP states that while at speed he has the stumble when opening the throttle - now "at speed" could mean they are still working, or, at higher speeds, doing nothing or very little. Damnit - just realised, they will allways be working to some degree, since there will allways be a vacuum, even at wot. However, it will be small amounts due to the size of the orifices.
Anyway, I digress. The accel pump feature once off progression (and during to a degree) is taken care of by the hole in the bottom of the slides. It is callibrated to limit the speed of rise of the piston/slide. If it goes up fast you get a weak mixture.

 

Missed your reply @chacal ...
Re the 5 turns out, @MrSeca wasn't riding the bike with the screw 5 turns out, but yes agree there must be something wrong tomget this far out on the colortune. (And yes I had missed that...)

Edit to question your reply, but I don't want to make an issue of it:

↑
Also, please forgive me, you have your cv carb theory wrong.
Well, what I was referring to is what k-moe stated:

↑
Yes; if the idle circuit passages are entirely clean. If they are not, then they will not be able to deliver the additional fuel needed during transition as the slides lift, resulting in a weak mixture.

This was after your post....^

 

Yes, he didn't indicate that he was, but.....the same thought applies. Which is why I recommend (to him anf others) when you suspect an idle circuit "clogging" issue, then one way to verify is by using the choke a little bit, since it provides an extra dose of fuel which can mask the lack of fuel thru a clogged idle circuit. Not a sure-fire diagnosis, but sometimes it's a helpful "clue", which is important when there could be multiple causes for the same observed problem........of course, this assumes that the enricher (choke) circuit is also not clogged, which can also happen, especially if the idle circuits are clogged. So really the first step is to verify that the choke circuit is operating okay, and then, use a bit of choke on the freeway cruise and see if it eliminates the crack-the-throttle / bogging issue.

 

Thank you everybody for giving feedback. I did try Chacal's suggestion and turned on the choke/enricher while on the freeway. I still had the issue. Keep in mind, it's not a HUGE issue it just has the subtle hesitation after I crack the throttle and THEN it accelerates.
Also keep in mind that I broke the rack and ultrasonic cleaned, chem dipped for 24 hours, and then ultrasonic cleaned again all 4 carb bodies. I'd be very surprised if pilot circuit is clogged but I could definitely be wrong.
A couple other things: since I did the carb rebuild the bike has been harder to start and a couple of times it would just die when I pulled up to a stoplight. Wasn't doing this before. Also, when I initially start the bike to warm it up only full choke works where as before I was able to keep it idling at half choke and when I rev it a little bit it has a similar stuttery type of reaction when you start to lose fuel and have to change to reserve, however, once it warms up, the stutteriness (is that a word?) goes away. Just to check, I sprayed starter fluid around the carbs and intake boots to see if there were any leaks and none were detected.

 

I hate to be brutally honest, but the first step is to strip the carb bodies and soak them in a good carb dip, then verify that the passages are clean with a cheap can of carb cleaner.
After that the rest is gravy.
When in doubt go back to the beginning.

 

I will adjust the air screw mixture and try that first. Thanks

 

Just for confirmation, are the valve clearances in spec, and were they rechecked after changing shims?

 

Last time I checked AND rechecked was last May.

 

Chemically cleaning and ultrasonically cleaning doesn't guarantee the progression circuit is not blocked - you have to squirt carb cleaner down there (with eye protection - ask anyone who's done this, almost guaranteed to get you in the eye). The beauty of it is, you have 4 carbs to do it to, so you get a good comparison on flow rates.
But anyway, I would set all screws 2.75 turns out to see, this is easy. Then recheck float levels. See if you can get some used needles? After that I'm afraid its strip rack time...

 

Well guys, I'm at the point where I'm just throwing my hands up in the air and saying WTF!!!!!. The bike has become increasingly hard to start, the plugs are all super sooty black, the 4th cylinder isn't even firing anymore even though it's getting spark and gas. I had none of these problems before the rebuild. I have no clue what I could've possibly done wrong. I had no problems putting everything back together. This is totally beyond me. Someone please help me.

 

Take a break. Do other things for a few days or even weeks. Your brain is stuck in panic-mode. It happens to all of us.
Look at her with fresh eyes and it'll all fall into place.

 

Super-sooty plugs are an indication of either a very rich or a very lean condition:

Why are my plugs carbon-fouled (dry, sooty black deposits)?:

- Carbon fouling is the result of incomplete combustion----for any reason. It is most often associated with an overly rich fuel mixture (whatever the cause), but can also be caused by an overly lean fuel mixture (or poor spark, etc.) In a lean-mixture condition, most of the un-burnt mixture gets pumped out the tailpipe, but some fuel droplets remain in the cylinder and add themselves to the next intake charge. That's not a very precise way of metering the mixture, so when it's finally rich enough for a spark to ignite, that particular charge may be too rich, resulting in incomplete combustion and plug fouling. So carbon-fouled plugs can be due to rich or lean conditions.......your Colortune spark plug will tell you for sure. If you have a light blue or white-ish flame, intermittent flame, and/or intermittent flashes of yellow within an otherwise white-ish flame, then your fuel mixture is too lean.

And by the way.........if the spark that happens to ignite this overly-rich mixture is the "wasted spark" (which occurs in each cylinder at the top of the exhaust stroke, it will occur JUST AS THE INTAKE VALVE IS OPENING ---- so the backfire pressure wave may be directed back up the intake tract!


So this would lend credence to an overly lean condition, although overly lean conditions would typically also include:

Typical Symptoms and Causes of a Lean Fuel-Mixture Condition:

- Poor acceleration; the engine feels flat.

- The engine won't respond when the throttle is snapped open, but it picks up speed as the throttle is closed. (A too-large main jet also mimics this symptom.)

- Idle speed falls after you blip the throttle, then creeps back up.

- The engine runs hot, knocks, pings and overheats.

- A lean pilot fuel circuit condition can be responsible for a creeping or "hanging (high) idle", where rpm's are very slow to return to a normal idle speed, is often a sign of being set lean. Conversely, if the idle drops way low and then (maybe) slowly recovers is often a sign of an overly rich condition.

- The engine surges or hunts when cruising at part-throttle.

- Popping or spitting through the carb occurs when the throttle is opened. Or popping and spitting occurs through the pipe on deceleration with a closed throttle.

- The engine runs better in warm weather, worse in cool.

- Performance gets worse when the air filter is removed.

- Fuel levels that are too low will cause a lean condition.

- Pilot fuel circuit that are partially or completely clogged.

- Fuel jets that are too small for your application.

- Pilot mixture screws being set too far "in".

- In cases where an overly lean fuel condition is suspected, the application of a small amount of "choke" may decrease or eliminate the symptoms.

- Here's the main reason you don't want to run lean over an extended period of time:

http://www.xjbikes.com/forums/threads/head-gasket-1982-maxim-650.85273/#post-504365

A holed piston. Notice how it's right where the plug fires (the hottest point anyway, and made ultra-hotter by a lean fuel condition).



while other overly-rich conditions would be:

Typical Symptoms of a Rich Fuel-Mixture Condition:

- Engine acceleration is flat and uneven and loses that "crisp" feel.

- The engine "eight-strokes" as it loads up and skips combustion cycles.

- The engine's idle is rough or lumpy, and the engine won't return to idle without "blipping" the throttle.

- An overly rich pilot mixture is usually the culprit when the idle drops below normal then slowly recovers.

- The throttle needs to be open continuously to maintain acceleration.

- Black, sooty plugs, a sooty exhaust pipe and black smoke from the tailpipe that stinks of unburned fuel.

- Poor fuel economy.

- The engine works better when cold. Performance falls off as it warms up or the ambient temperature rises.

- Engine performance improves when the air cleaner is removed.

- Fuel levels that are too high will cause a rich condition.

- A choke system that is slightly hung open or has leaky plunger valves. Leaky valves can be determined via a measurement of vacuum using your synch sticks (or vac gauge) --- while watching the gauge, apply a small amount of downward force on the top of the plunger valve. If it vac draw changes, the plunger isn't sealing very well. Over time a small ridge may build up on the tapered brass plunger valve surface (Hitachi carbs) that may be possible to polish out, or a deformity forms on the rubber seals (Mikuni carbs) that may be possible to reform back into shape.

- Fuel jets that are too large for your application.

- Pilot and main FUEL jets being reversed.

- Pilot and main AIR jets being reversed.

- Pilot mixture screws being set too far "out".

- Main jet needle set at too "high" of a position (on some Mikuni models), or that has "risen up" within its head cap (on Hitachi models).

- A simple test for an overly-rich condition is to remove the air filter element, and see if performance improves. A very dirty air filter will cause an overly rich condition, AND, even if the filter was in good condition, the great increase in airflow accomplished by removing the air filter will tend to dilute an overly rich fuel mixture, and thus allow you to focus on determining the cause of that situation.

 

Right on. I'm starting to wonder if my cheap rebuild kit from ebay is the culprit.

 

What are your spark plug gaps?

 

Forget that must be carburation.

 

I think someone has allready suggested this, and I suggested to get some used needles - see that chacal guy - get some bits from him. Or re-use the original jets? But still get some needles.