Author Topic: Carb fun.......(TT?,HondaMan? (Read 5936 times)

TwoTired · « **Reply #25 on:** October 07, 2009, 11:32:02 AM »

Quote from: midnight08 on October 07, 2009, 10:59:47 AM

When the bike is off, I can open the throttle then let go completely and hear the throttle slide "click" shut.

No you can't. If the engine is still running, the slides will never close completely. Most likely the click you are hearing comes from the idle stop screw on the stop arm. If a slide does close completely, you have a dead cylinder and a cool head pipe.

Quote from: midnight08 on October 07, 2009, 10:59:47 AM

I know they are opening and closing completely.

If it closes completely, where does the oxygen needed for combustion come from to keep the engine running?

Quote from: midnight08 on October 07, 2009, 10:59:47 AM

however, I went to a mechanic down the street from me to see what he thinks as i am almost completely stumped by this... He listened to it and thinks that when the bike is hanging onto the Revs, if you shut it down with the kill switch without manually turning the throttle back, he can hear the slide click shut when the bike is shut down. so his and my thinking is that when there is no vacuum in the carbs, the slides are clicking shut perfectly fine. however, whenever they are under vacuum, the throttle slides are hanging open ever so slightly until either you manually turn the throttle back, or you shut off the motorcycle and the vacuum leaves the carbs.... in my mind, this signifies that the synch must be off and causing higher vacuum in one of the carbs which is ever so slightly keeping that slide up.... I'm not 100% sure though. the only way to determine it is to synch the carbs. I even lubed the throttle "bar" where it connects to all of the slide rods.

The only reason why you can use slide carbs is because the intake flow is pulsed. The periods between pulses relieve the side pressure on the slides allowing them to reposition.

Why haven't you sync'd the carbs yet? And, why would you expect it to run properly without a carb sync?

None of this explains poor fuel mileage or fouled plugs, though. That usually means more fuel is being delivered than you have oxygen available. (There can be other reasons. But, scrupulous attention to carb cleaning or corrective attention to PO modifications often cures that.)

J.Webster Designs · « **Reply #26 on:** October 07, 2009, 11:40:12 AM »

I should have reworded those statements... Of course, if the slide closes completely, there would be no air entering through the carb throat.

I haven't synched the carbs yet because I have been battling this rich mixture problem. I don't have a synch tool so to have them synched is going to cost me about 70 bucks. I want to at least try to get the fouling problem under control as i will probably have to take the carbs off resulting in having to re-synch them if i disassemble. which will cost me another 70 bucks. I know i know, I should just get my own manometer, but I am a poor college student right now and im trying to balance monetary priorities.....

is anyone else thinking that the float height is a little high along with the extremely retarded timing is causing the fouled plugs, extremely high fuel consumption?

J.Webster Designs · « **Reply #27 on:** October 08, 2009, 04:43:27 AM »

J.Webster Designs · « **Reply #28 on:** October 08, 2009, 11:59:44 AM »

J.Webster Designs · « **Reply #29 on:** October 11, 2009, 02:40:40 PM »

i took the carbs off of the bike today and re-checked the float heights and reset them. The float heights were around 25mm. i reset them at 27mm to make sure that the rich condition is not due to float height. almost all of the floats were "tweaked" so i straightened them out and set the float heights. I have not put the carbs back on yet as i am hoping someone may come along with something else to check before i put the carbs back on the bike.

I also checked the plugs after i re-did the timing and they are no where near as bad as they were when the timing was set way retarded. however, they are still sooty.

HondaMan · « **Reply #30 on:** October 12, 2009, 08:03:17 AM »

This sure sounds like blocked (or partially blocked) air emulsifier feed passage problems. This is the tiny air port into the mainjet's holder (actually called the "emulsifier tube") area. It starts at the air horn of the carb, and runs into the very top of the emulsifier chamber, next to the needle jet. It's REAL hard to see (if you're my age), needs a light in the hole. Here's some pictures of me cleaning one out with a flexible mechanic's wire: the guitar string will be too stiff to make the bends required to push the white crud through the hole. I did not remove the needle jet in this particualr carb, as I was just taking pictures of the process: if there is much crud in the passage, the stuff won't push through if the jet is in the way.

You have to remove the emulsifier tube (aka mainjet holder) and carb slide (to get the needle out of your way) so you can push out that needle jet (the little brass tube where the needle slides up & down to meter fuel), to allow the wire to push the crud from the air hole into the passage, so it can be cleaned out (and take note of which way those needle jets come out: they have a top and bottom side!). It's tricky, but do-able. It's a common problem on these 750 bikes that sat and dried out without preparation, and makes the bikes run rich (with enormous torque!) in the mid-to-upper RPM ranges, fouling plugs in short order.

BTW: this activity will not mess up the balance of the carbs: they were designed to be removeable from the faceplate and reinstalled into those forks again without rebalancing (common misconception). Just don't mix up the slides and carbs!

J.Webster Designs · « **Reply #31 on:** October 12, 2009, 09:09:06 AM »

from what you are describing, that sounds like what i have going on.... after about a second or two of full throttle, the thing picks up and scoots quick when it gets to higher RPM...

so let me get this straight, when i pull the main jet holder (emulsifier tube) and the slide, there is still that little brass ring in the center of the carb where the main needle goes through. this brass ring has to come out in order to clear the passage way? how do i go about removing the ring?

J.Webster Designs · « **Reply #32 on:** October 12, 2009, 11:00:57 AM »

anyone know?

david 750f · « **Reply #33 on:** October 12, 2009, 11:56:58 AM »

Try a wooden dowel, tap gently. Should come out easily.

http://www.salocal.com/sohc/tech/carb/dspg_mgs/rmvndljt.htm

J.Webster Designs · « **Reply #34 on:** October 12, 2009, 04:34:29 PM »

so do i need to actually take that little brass ring out? its not a jet holder.

HondaMan · « **Reply #35 on:** October 12, 2009, 07:22:51 PM »

It's about 3/8" long, with a larger diameter section in the middle. One end is bigger than the other, too, so it only should go in one way. It is held in (pressed to final depth, actually) by the emulsifier tube when you screw that back in, later. You have to push it out from the slide side, then make sure the hole is real clean when you go to reinstall it. Push on it with wood things, so you don't distort it, and tap gently when removing.

Spanner 1 · « **Reply #36 on:** October 12, 2009, 07:55:48 PM »

So, reading back on page 1, apparently you set the static timing on a Dyna ignition system to fire with the advance mechanism turned to full advance ?....could that be right ?....is that the instructions with a Dyna ?...... sounds weird to me.

J.Webster Designs · « **Reply #37 on:** October 12, 2009, 09:02:09 PM »

yes, that is the instructions from Dyna. you static time with the advance mechanism fully open and time it to the full advance marks that are about a half inch to the right of the F mark.

HondaMan · « **Reply #38 on:** October 13, 2009, 07:27:50 AM »

They make you do that because the triggers "fall behind" at higher RPM, due to the small size of the trigger magnet... $:-\$

Then, it makes the idle advance a little much, like an extra 2-4 degrees. On the 550, this sometimes makes for an engine that does not want to settle in RPM when going back to idle, so you have to increase the spring tension on the advancer to force the issue a little bit. On the 750K3-onward, this is not so noticeable: on the K0-K2 it can sometimes be annoying.

J.Webster Designs · « **Reply #39 on:** October 13, 2009, 03:51:05 PM »

i tore the carbs apart again today and checked the emulsion tubes... everything is good. i ran wire through them for about 1min each just to be sure. checked all other passages as well. all is clear. as I was putting them back together it dawned on me that I have yet to check the needle clip position (don't ask me why i never did this because I'm asking myself the same thing....) I took them out and they are set in the 4th down from the top (5 slot needle) 2nd slot from the bottom. im thinking that i need to raise the clip up at least one notch and see if that leans me out and puts me in the ballpark. HOWEVER......Lucky for me... the #1 carb has obviously had water in it at some point because the little screws that hold the needle in and hold the slide rod are nice and rusted. not only that, but the PO did a lovely job at rounding out the Phillips screw heads, drilled them out slightly and broke off one head completely. I will be running over to a local shop tomorrow to see if a guy i know there has any ideas on how to get these things out and replaced..... hopefully i will be able to get this done before i plan on leaving Thursday for daytona.... if not i will have to pack up some extra spark plugs.... do any of you guys have any ideas on how to get those little screws out of the slide? (one with a broken off head, and the other with extremely goobered Phillips slots and partially drilled out.....)

J.Webster Designs · « **Reply #40 on:** October 13, 2009, 07:41:50 PM »

Spanner 1 · « **Reply #41 on:** October 13, 2009, 08:23:54 PM »

With all the double-checking you have done without success, I think your main jets altho' stamped 107.5 have been drilled-out to some unknown size, were they in the bike already ? My mains were stamped 120 , drilled and I didn't know until I got new ones and compared an actual 120 to what was drilled to about a 150 !! Had all kinds of rich/ foul symtoms with the '150's' ....

J.Webster Designs · « **Reply #42 on:** October 14, 2009, 05:00:00 AM »

once i figure out if these needle settings do the trick, then i will look at my main jet. you very well could be right. i have a set of stock 110s that i know are good.

HondaMan · « **Reply #43 on:** October 14, 2009, 07:21:41 AM »

Umm...you may be over-thinking this problem.

When the carbs get disassembled, and slides removed, they frequently do not get vertically aligned properly, because no one seems to know they need this step...

So, loosen the top ring on every carb, about 1 full turn. Pull the throttle all the way open, let it close, pull it open again and hold it there, and snug down the rings. Normally I do this while the carbs are off the bike, so if one of them is hanging up against the grommet on the cap it can be nudged by finger to straighten it out.

The little foot inside the carb's slide, where the vertical rod slides back and forth a little, is designed to allow for this misalignment in production. When the carbs are assembled, this rod is slid forward or back to center the rod in the grommet, when new. Over the years, the grommet wears a little oval around that original position and the foot wears a little notch in the home spot. When the carbs are disassembled and cleaned (and the foot is usually overlooked), the foot moves out of this notch, making it less than vertical where it comes out of the grommet, and it drags a little bit. If 2 of them drag, the throttle won't close, despite the spring, by itself. If you add some cable drag, it's even worse.

So, try the alignment of the rods. Also, add a little slack in your throttle cable setup: if the cables have some wear in their sheaths, they can drag if the slack is all adjusted out: not a good practice. When installing new throttle cables, always adjust for zero slack (do not tension the cables, just remove the slack) with the handlebars pulled all the way to the right. After 1000 miles, do it again. After that, if you remove the slack again, be very careful: the sheaths are wearing and will create drag upon the sides of the cables, which can cause throttle hang.

99.6 ft-lbs of 1st-gear torque can be hard to stop at 1500 RPM!

J.Webster Designs · « **Reply #44 on:** October 14, 2009, 07:43:58 AM »

Hondaman.... I will definitely do that upon re-install. but don't you think i should move the needle clip up one position to lean out the mixture a little? the plugs are still nice and soft sooty black. i do not think that the tuning and the hanging onto revs are attributed to the same problem so i am dealing with them as separate problems. ( figure out the rich problem, then the hanging onto revs problem)

they are pretty fouled and this is without the filter installed. so if i install the filter the rich problem is only going to get worse....

J.Webster Designs · « **Reply #45 on:** October 14, 2009, 10:41:13 AM »

UPDATE: got the two rusted/drilled out/broken screws out of the slide. replaced the screws and moved the needle clip up one position on all slides. will begin reassembly after my two tests today......

Hondaman or TT, if you get this in time, lend me your thoughts on moving that needle clip up a position (stock location "middle" position) since all the passages are free, and the plugs are still sooty black on all four cylinders. The mains are 107.5 and slows are 40. idle mixture screw is turned out to 1 3/4 and still sooty.

TwoTired · « **Reply #46 on:** October 14, 2009, 10:58:30 AM »

I haven' t worked on your style carbs, but assume the functional behavior is the same as other SOHC4s of the era. If they have specific quirks, I won't know about them.

However, I'd look into whether the needles and throttle valve orifices are stock, or aftermarket or worn. That entails measuring them against known good Honda parts, or comparing numbers (part numbers, or measurement numbers that I don't have available. I think it was Bob Wessner that fixed his rich running 750 by putting the stock needles, emuslsion tubes, and throttle valve orifice components back into his carbs. I recall others, too.

I favor knowing what I have, over just changing things 'til it works. But, if you just want to take a wild stab, then lower the needles deeper into throttle valve orifice until new spark plugs show proper color when the throttle is used between 1/4 and 3/4 positions.

(I assume you have eliminated any possibility that the carb inlets are unobstructed by overly restrictive filter media.)

J.Webster Designs · « **Reply #47 on:** October 14, 2009, 11:17:45 AM »

Quote

I favor knowing what I have, over just changing things 'til it works.

As do I, I have looked through numerous posts to try and figure out what i have going on... From what i have gathered so far through digging through peoples posts, everything is stock on these carbs minus the parts that i replaces out of the carb kit that i got. (replaced items were : slow jets; same size as stock, idle mixture screws, float valve, and gaskets. all other parts are from the original carbs) the needles are 27201 needles. the ones that came in the kit have a different taper on them. The carb kit that i ordered came with needles, jets, and gaskets. The needles and main jets were not used out of the kit as i have read bad things about the needles. if this does not fix it, i will most likely go pick up new honda needles, and idle mixture screws.

Quote

(I assume you have eliminated any possibility that the carb inlets are unobstructed by overly restrictive filter media.)

The filter is not on the bike. and it is still running rich.

mrbreeze · « **Reply #48 on:** October 14, 2009, 05:36:02 PM »

I am planning(have been for too long now!!)on replacing my needle jets and jet needles. My bike runs great now as it is but it is kinda touchy when I synch the carbs. In other words.......I think these new parts can improve what I have now.When I rebuilt my carbs a few years back,I didn't use the needles or needle jets supplied with the kits (I believe K&L) from Dennis Kirk. I reused the old ones and I don't think it would be a bad choice to replace them now with OEM.I just priced them at the local dealership for $100. They come in sets....$25 each. I also priced the insulators.....$49 for a pair of A carbs and $51 for a pair of B carbs.You wont believe what they wanted for the clamps.......$84 for a set of 8 plus another $7.92 for the 8 screws!!!!!!
Anyways....I will hopefully get the needle sets and insulators before too long.They can ram their clamps & screws up their overpriced a$$

HondaMan · « **Reply #49 on:** October 14, 2009, 06:01:27 PM »

Quote from: midnight08 on October 13, 2009, 03:51:05 PM

i tore the carbs apart again today and checked the emulsion tubes... everything is good. i ran wire through them for about 1min each just to be sure. checked all other passages as well. all is clear. as I was putting them back together it dawned on me that I have yet to check the needle clip position (don't ask me why i never did this because I'm asking myself the same thing....) I took them out and they are set in the 4th down from the top (5 slot needle) 2nd slot from the bottom. im thinking that i need to raise the clip up at least one notch and see if that leans me out and puts me in the ballpark. HOWEVER......Lucky for me... the #1 carb has obviously had water in it at some point because the little screws that hold the needle in and hold the slide rod are nice and rusted. not only that, but the PO did a lovely job at rounding out the Phillips screw heads, drilled them out slightly and broke off one head completely. I will be running over to a local shop tomorrow to see if a guy i know there has any ideas on how to get these things out and replaced..... hopefully i will be able to get this done before i plan on leaving Thursday for daytona.... if not i will have to pack up some extra spark plugs.... do any of you guys have any ideas on how to get those little screws out of the slide? (one with a broken off head, and the other with extremely goobered Phillips slots and partially drilled out.....)

You'll have to drill or grind off the heads to free the "foot", then you can get to them with an extractor. If seriously rusted, a drill-out and Helicoil will fix it up. It's tedious because it's down in there, but can be done.

My "warning flag" just went up: if someone else has been in there, claiming to have "rebuilt" the carbs, the possibility looms that Keyster needles have been installed in one or more carbs. If this is true, you will NOT be able to solve this plug-fouling problem until those needles are replaced with Honda's Keihin needles. Keyster's needles do not work in the 750, period. I can find over 10 cases in this last year alone where someone has written to me with similar issues, only to find out in the end that the carbs had Keyster needles. So, the very next thing I would look at: see if the needles you have now show the Keihin "K" on them, near the clip-it's engraved right on the needles. The number should be 27201, also engraved nearby.

Next, go to Steve D's link here:
http://www.motorcycleproject.com/motorcycle/text/specs.html
and find your year and model of carb: the correct needle position will be there.

Then, put your air filter back in, and the airbox on. The air filter will cause it to lean out slightly: this is backward from how car's carbs work, because these are pulse carbs, not vacuum carbs. They work quite differently (so I have devoted an entire chapter in my upcoming book to just how these mixers work).

If you run without the stock airbox:
The carbs will run rich in the range 2000-3000 RPM without the velocity stacks in the OEM airbox. This cannot be tuned out: if you look through these forums you will see many, many, many posts about riders who have installed individual pod-type air filters and constantly battle this one: there is no way out of it unless there is a velocity stack guiding the airflow in this RPM range.

News:

Author Topic: Carb fun.......(TT?,HondaMan? (Read 5936 times)