Author Topic: Still bogging... (Read 4075 times)

GreenHornet74 · « **on:** May 07, 2011, 03:38:52 PM »

As you may or may not know I purchased a 75 cb750 and currently trying to get this baby running puuurfect. So far these are the tune ups I have done: oil & filter, cleaned the oil tan & pump screen, new air filter, adjusted valves, cam chain, drive chain, installed new Dyna S ignition & did timing, new fuel lines, and last but not least I just got cleaning the carbs, setting the floats, and syncing the carbs. But for some reason the throttle response lags. Am I running too lean. It has 105s on the main jets, stock air box, and original 4-4 exhaust(baffles removed). Any thoughts on what I should try next?
Thanks!

Roach · « **Reply #1 on:** May 07, 2011, 03:54:22 PM »

might wanna try putting some baffling in that 4 into 4

GreenHornet74 · « **Reply #2 on:** May 07, 2011, 04:34:08 PM »

Unfortunately the PO did not have the baffles for them. Will those muffler fiberglass blankets work?

Patrick · « **Reply #3 on:** May 07, 2011, 04:38:30 PM »

Is it bogging or lagging? Where in the range are you having issues? What do your plugs look like? What color are they? White to very light is lean. Very dark to black is rich. Richness can cause your bike to big under acceleration. Trouble at idle to about 1/4 throttle would likely be the small jets. Bogging or flatness in the mid-range is usually the needle and bogging at high throttle is the main jets. So where are you having trouble?

Did you reset your floats. Mis-adjusted floats can cause a rich or a lean condition as well. More info is necessary for a long range diagnosis.

Patrick

GreenHornet74 · « **Reply #4 on:** May 08, 2011, 05:43:48 PM »

Ok so I tried to mess with the air mixture screw and I think I made it worse. It is at 1.5 turns out. It has a hard time staying at idle unless im constantly fiddling with the throttle. Another thing I noticed was that sometimes the engine would rev up to 2500 rpm or so then it would go down to idle. Also exhaust 1 seemed to be less hot than the the rest but I could still feel exhaust come out. Ive been working on this bike for a couple weeks and its getting frustrating! Ahhh I need a beer.
Heres a pic of the plugs....

Patrick · « **Reply #5 on:** May 08, 2011, 06:34:56 PM »

You need to go back to your carbs. If no. 1 pipe is not as hot as the rest that is because it is not firing. Plug No 1 in your picture does not appear to be getting fuel. No 2 is running rich, nos 3 and 4 look like is is running mean. When you cleaned the carbs did you pull out the jets and the emulsifiers and make sure all the holes in both were clear? How did you set your synch? Nos 2, 3 and 4 seem to be getting spark, have you confirmed spark on no. 1? Put a plug in the cap and ground it to a head bolt and turn the engine with the starter. See is you get a healthy blue spark.

How did you perform the synch. Pull the carbs again, check and make sure all orifices are clear and do a bench synch. That should get it close enough to run on all four. Only then worry about fine tuning it with the air screws.

Patrick

GreenHornet74 · « **Reply #6 on:** May 08, 2011, 09:18:01 PM »

When I cleaned the carbs I pretty much took every part apart and cleaned it with brake cleaner. I made sure that every jet was cleared of any debris. I then bench synced them, got it running, and proceeded with the carb sync using a emgo vacuum gauge. I eye balled the floats to 26mm from where the float gasket sits. I just checked the spark and both 1 & 4 gets sparks. Now whether it was fat/bright, im not sure since ive never done this before and my other honda is at my folks home. But there were definitely sparks going on. Since I had a long day tinkering with this bike I am throwing the towel and tomorrow I'll check the float levels. Which brings me to my next question. I'm going to re adjust the floats again but I want to check to see where they float via clear tubing attached to the drain hole. Where should the height be? How many mm's below the bowl? I saw a pic of a guy checking the height and it looked like it was almost a centimeter below where the gasket sits. That seems too low no? I'm so confused, thanks to you guys I feel like I'm getting closer though. I can feel it!

ekpent · « **Reply #7 on:** May 09, 2011, 04:42:44 AM »

Agree with Patricks comments-back to those carbs.Unsnap the float bowls and visually see how much gas is in them as that #1 plug does look thirsty.As for baffles the cap on the end of the HM341 pipe is really just called a diffuser,it is not a baffle per say like the HM300.Most of the baffling on the 341's are built into the different chambers inside the pipe.Keep at it and she will roar.

MasterChief750 · « **Reply #8 on:** May 09, 2011, 06:14:45 AM »

id get a float level gauge or make one and get them spot on. i had idle issues until i did that

wrenchmuch · « **Reply #9 on:** May 09, 2011, 07:09:17 AM »

I don't think brake parts cleaner makes a good carb cleaner . It cuts grease and flushes brake dust of of parts . Petroleum distillate cleaners generally work the best but not all are equal in strength . Aerosol carb cleaner is good for flushing passages to see if they are clear but there is no substitute for a soft wire pushed through the air passages of the carb followed by a blast of carb cleaner . On #1 its likely no fuel in the bowl or blocked slow jet . Does it come alive when the throttle is opened ?

goaarongo · « **Reply #10 on:** May 09, 2011, 07:14:57 AM »

+1 for everything listed so far. You might check out this link for float height and carb rebuilding info - I have been going back to this site for years, every time I take some of these carbs apart. http://www.salocal.com/sohc/tech/tech.htm

I thought your bike came with either 110 or 120 mains, so 105 seems small. But all kinds of variables exist there, including the altitude where you live. (I think higher altitudes need smaller jets...). You might also want to ensure that the clips on your needles are all set at the same height, and that there is no pitting or damage to any needle. I recently had one cylinder that was rich, and a damaged needle was the culprit.

flybox1 · « **Reply #11 on:** May 09, 2011, 07:43:23 AM »

Quote from: GreenHornet74 on May 08, 2011, 09:18:01 PM

I'm going to re adjust the floats again but I want to check to see where they float via clear tubing attached to the drain hole. Where should the height be? How many mm's below the bowl? I saw a pic of a guy checking the height and it looked like it was almost a centimeter below where the gasket sits.

Per HondaMan: 3 to 4mm below the bowl gasket seam.

GreenHornet74 · « **Reply #12 on:** May 14, 2011, 02:59:05 AM »

Ok, Its been kinda stressful with finals as I'm finally graduating.... Today I re cleaned the carbs with carb cleaner this time and compressed aired the hell out every hole! Then the ignition would not turn on. Turns out the PO by-passed a burnt fuse with aluminum foil so I replaced the fuse. I checked the float levels via home made manometer and turns out all carbs where barely getting any fuel. Re adjusted the floats, no carb overflow leak pheww...... Tomorrow I will bench sync and then proceed with the vacuum sync. I am hoping this was the problem. Well, I guess I will post tomorrow with the results (crossing fingers). Another note, the gas tank looks a little dirty, nothing too extreme, but the petcock filter looked decent. Should I still run an inline filter?

dave500 · « **Reply #13 on:** May 14, 2011, 03:23:51 AM »

got a multi meter?check the plug caps resistance aswell,always double check ignition before doing the time consuming carbs.

Bodi · « **Reply #14 on:** May 14, 2011, 04:39:23 AM »

The needle jet emulsion tubes iare often skipped in carb cleaning because they don't come out without persuasion. Did you remove these and clean all the tiny cross holes? Also, Hondaman has posted some suggestions for modifying these cross holes on some bikes (I think).

Patrick · « **Reply #15 on:** May 14, 2011, 06:46:18 AM »

BTW, the emulsion tubes that Bodi and I have referred to are the parts the main jets screw into. Those DO come out. (Just to be clear what we are talking about. Of course, he called them emulsion tubes and I called them emulsifiers but he is from Canada and I am from Texas so we have a language barrier). When you remove them you will see the holes we are talking about.

Patrick

GreenHornet74 · « **Reply #16 on:** May 14, 2011, 08:33:48 AM »

Yes, I removed everything but the choke mechanism. Made sure every hole was clear of any debris. I also checked the needle position and every clip was 4th from the top (or second from the bottom). I think thats stock recommendation? Thanks for the ignition reminder, I will clean and re gap.
This may be a dumb question but should I lightly lube the carb piston slide or is this risky and not necessary?

GreenHornet74 · « **Reply #17 on:** May 14, 2011, 06:44:27 PM »

Ok guys heres the status..... I suspect the coils or wires to be bad. Do they die slowly or instantly? I am asking because I after wiggling the connections it seemed to run better. Took it out on the road and runs way better than before. Now I'm just worried about the coils/spark wires. Any thoughts?

Patrick · « **Reply #18 on:** May 14, 2011, 07:10:24 PM »

Check your spark plug caps. In fact, don't check them at all. Yank the the caps off, trim bakl the wires about 1/8 to 1/4 inch (to expose clean copper wire), and screw the caps back on. If you lose a coil you will lose one and four or two and three, not just one. Three of your cylinders appear the be firing, so your coils are working. They will not be intermittent. They will work or not, no in between.

Simple stuff, only the start looking for bad parts.

Patrick

BrianAdair · « **Reply #19 on:** May 14, 2011, 10:21:46 PM »

Not trying to thread jack,
I'm going to pay close attention to this thread as I am currently having the same problems...

and have had my carbs off so many times I'm sick...

Mine are clean for sure, and re-built with Keyster brand kits, today I pulled the main jet needles out and replaced with the stock ones as I read on here that the keyster brand weren't very reliable, and was thinking this was the problem for making my engine idle up on it's own to like 2k rpm and not wanting to come back down.
I have 125 main jets, they have been bench synced, and the Emgo vac gauges that I have say that they are all dead on... set the floats and re-checked 26mm. I have played with the air screws all the way out to 3 turns, I do have crappy emgo pod filters on mine though, so maybe that most of my problem. even replaced the manifold boots with new ones, thinking they were sucking air, which one of them was. I'm going to play with my timing a bit, as mine is slightly advanced, but my engine is not stock, bored to 849cc, ported polished head, hot cam, hd valve springs, Manley stainless valves, Kerker 4 2 1 header (removed wrapping).

Mine acts like it is rich at times on idle, but then bogs in 1 st gear until you reach 2k rmp then it smooths out and pulls hard.

Good luck GH74, hope you figure it out, and hope I can get some tips off of this thread also.
I'm frustrated and at a loss

BrianAdair · « **Reply #20 on:** May 16, 2011, 08:56:39 AM »

mine was idling up on it's own due to the timing advancer, I had oiled it before and made sure it was free, but the spring tension was a little loose, so I tightened the springs. Now it idles back down, and does not idle up on it's own, I still feel I need to lower my main jet needles one or two nottches, as I have them all the way up right now, but it's running good and ridable now. You can just tell that around 3k to 4k that it's a little rich.

GreenHornet74 · « **Reply #21 on:** May 16, 2011, 09:49:10 PM »

I cut back a bit of wire off the spark plugs and cleaned the boots. Runs fine but I need to take this thing on the highway again for further diagnosis. I checked the spark plugs again after the "re adjusting" and they all look very similar. A bit on the lean side but, I'm just glad they all look the same. 1/8th of a turn in on all air screws should do the trick? Another thing I noticed was that rpm gauge gets a little bouncy above 5k. Any cures for that besides a new cable? Doesn't bother me much. As long as it does not affect the performance. I'm about to graduate college so I'll be in debt for for the rest of my life or so lol!

HondaMan · « **Reply #22 on:** May 16, 2011, 11:02:57 PM »

A few comments to think about:
1. You mentioned that you rebuilt the carbs. So, first question: were they Keyster parts? If so, the float level must be 24mm from the gasket's mounting surface (i.e., with gasket removed), because the Keyster float valves are too stiff and cause a low bowl condition by about 2 mm. If the float valves are Honda, use 26mm instead.
2. The #3 plug in your picture (if #1 is on the right) above indicates that cylinder has a vacuum leak (i.e., if your spark plug boots are all within 500 ohms of each other). If your hoses are hard, you can either soften them with wintergreen oil and xylol overnight (50/50 mix works fine), and/or use wider hose clamps on those hoses to seal the leaks. If one leaks, it's a good bet the others do, too.
3. Bodi is right: the emulsifier air bleed holes can be opened up a little, and it really helps with ethanol-laced fuel. Drill the lower holes out to .035", try it and see how it goes, if not enough, try it at .037". The upper holes should probably not be drilled out past .033" unless you are at high altitude (>5000 feet) on a regular basis. The upper ones are usually .025" to start. HOWEVER - this mod is a 'last step' after all the other things are fixed: it will not fix the other problems.
4. Having the last baffle out on HM341 pipes will cause a flat spot at about 2500 RPM if you try to snap the throttle. Also, keep in mind: this bike has no accelerator pump (like most carb'd bikes of the era), so the throttle should not be suddenly snapped below 3500 RPM in any case, lest it drop dead lean and fall on its face: entirely normal. If you're into that sort of riding style, keep the revs on tap (like me), running steadily above 3800 RPM all the time. It keeps the plugs cleaner, improves the MPG (really!), and keeps the power readily available. You'll learn to hate it with those last baffles missing, though, as this is where the cam starts to go resonant and the pipes start to peak. The HM300 pipes are more open, so the cam peak moves upward: the resonance doesn't start until about 4500 RPM on those. (And, it's a much sweeter sound! IMO...)

GreenHornet74 · « **Reply #23 on:** May 22, 2011, 09:48:57 PM »

I did not re build them, just took everything apart and re cleaned them. Im not sure what the difference between the float valves are, Im guessing they are the honda type since after I set them to 26mm they aren't leaking. Someone told me that I could spray wd 40 around the hoses while the engine is running and if the idle fluctuates then there is a leak. Tried it and no leaks. Did not have time to drill the emulsifier tube. I took it on a 500 mi trip today and it seems to be running significantly better than before. I think trimming back the spark plug wires might of solved some problems. I plan and using a dremel tool and installing new spark plug wires. The only casualty on this trip (keep in mind this bike was sitting for 3 yrs) was an oil leak from the oil pan. Thanks guys for all the help!

PS: Btw this summer my cousin and I will be ridding coast to coast on our CB 750s. I will have to make a new post on the trip with pics n' all!

HondaMan · « **Reply #24 on:** June 08, 2011, 11:44:38 AM »

Quote from: GreenHornet74 on May 22, 2011, 09:48:57 PM

I did not re build them, just took everything apart and re cleaned them. Im not sure what the difference between the float valves are, Im guessing they are the honda type since after I set them to 26mm they aren't leaking. Someone told me that I could spray wd 40 around the hoses while the engine is running and if the idle fluctuates then there is a leak. Tried it and no leaks. Did not have time to drill the emulsifier tube. I took it on a 500 mi trip today and it seems to be running significantly better than before. I think trimming back the spark plug wires might of solved some problems. I plan and using a dremel tool and installing new spark plug wires. The only casualty on this trip (keep in mind this bike was sitting for 3 yrs) was an oil leak from the oil pan. Thanks guys for all the help!

PS: Btw this summer my cousin and I will be ridding coast to coast on our CB 750s. I will have to make a new post on the trip with pics n' all!

With the black baffles removed on the HM341 pipes, it makes a lean moment at about 2000 RPM on the K4-K6 engines. This can make it feel boggy if the throttle is snapped a little too much. Also, the #3 (or is it #2?) plug in the picture above shows that one is too rich. This won't usually be from the carb mixes, rather more often from vacuum leaks around the hoses, at the head.

The air screws: set them at 1 turn. Their range is 7/8 turn to 1-1/8 turn, and never should be 1-1/4 or more turns out on the K0-K6 bikes. It will foul plugs like mad at those wider settings.

Check the spark advancer, too: make sure the timing advances like it should. On the K4-K6, full advance should be in by 2200 RPM, worst case.

If the bug continues, and you don't find new baffles, try raising the float levels a bit. First try it at 25mm (raised +1mm), but don't go higher than 24mm or the bowls will leak when the bike is on the sidestand from the fuel lying against the gaskets.

Don't overlook the use of the ND X24ES-U sparkplugs: they provide a natural torque boost right at 2000-4000 RPM, which is often perceived to be the "bog range".

If you take the engine apart: advance the cam 3 degrees. You won't recognize the bike afterward: it will feel like you bored it to 811cc or something.

News:

Author Topic: Still bogging... (Read 4075 times)