Topic: 76 750A runs rich no matter what I try

[Chuck Hahn]

Here the situation. She has always ran rich ( belches black smoke ) and new plugs are sooty black after just 10 miles. 

Here is what I have done so far.  Moved the clip from the center groove to the second one down..still rich.  Moved it all the way to top notch..same results.  Turned the bottom screws all the way in and no change.  Turned then screw as far as 4 turns out and no change.  I have a colortune and watched it as I turned the bottom screws and it still has the yellow rich color.

Do I need to rejet it with smaller pilots and mains?  I didn't write down the sizes ( wish I would have now ) but I believe the bike has always been stock configuration. 

Also, I tried to use my gauges and sync them.  I have a service manual and for the life of me I cant get any of the cylinders to come even close number 2 without the bike starting to buck like mad and stall.  Help me please!!!!  Also, the floats are at 14.5 MM per the manual.

[salukispeed]

Start with the basics. Is it a stock air cleaner and did a mouse fill it with a nest. or someone stuff a rag in the intake kind of stuff. I had critters fill my Goldwing air cleaner to the top with stuffing from a chair in a weekend and made me nuts and almost late for work. .  Have you gone through the entire tune up list? If you leave the gas turned on does it over flow from the hoses under the bike. The bike should run fine with the stock jetting and needle position You can bench sync those carbs to #2 by  setting #2 on the floor with the speed screw adjuster and then adjusting the rest to match before assembling  back on the bike. Is the choke working properly and opening all the way.  Just some thoughts??

[Chuck Hahn]

Bench synced before installation.
New orings on the pilot screws.
New bowl gaskets.
Float hts at 14.5 MM
New air filter.
New from the dealership  airbox boots that I found at a dealership in Montana.
Supple carb to engine boots.
None of the pilot needles  tips are damaged.
No over flow from the carb throats or the over flows themselves.
Stall preventer works when clicked into gear.
Did the selinoid check per the manual  and it passed.
Moved the clip on the needles from center to second from top..no change.
Moved clip to top notch..no change.
New plugs..sooty after just 10 miles.
Good hot looking spark all the way around.
What have I missed here?
Choke plates all move fully to full choke and full open and don't hang..thought of that too.
Pumpers all work.
Carbs were 24 hr dipped in Berrymans prior to reassembly.
No left over parts.

[raymond10078]

+1 on the choke idea - is the choke opening - i.e, - have you seen the choke butterflies going horizontal?

2nd idea is the air filter itself.  I bought an EMGO (or another non-Honda) filter, and it was way too restrictive.  Could try running without an air filter to see if it runs better.  I later bought a K&N (single kind that fits in the stock airbox) with no issues.  Others have reported good luck with K&Ns as well.

3rd idea is the air filter housing - are the vents clear?

[Chuck Hahn]

Yes on the openings clear.

Yes on the chokes working right.  Hooked the carbs up and made sure the slides snapped back and actuated the choke 4 or 5 times to be sure they were working properly. Then installed the upper part of the airbox and tightened the clamps. Then set the new filter in the lower half and secured it to the upper half with the 2 10MM bolts.

I am at a loss as to whats the deal here. I mean I understand carbs pretty well seeing I have 6 other bikes and do all my own carb work on them also without problems.  This is my first Honda and its got me stumped for sure.

Ive been doing carbs on all my vintage Suzuki GSs and my 73 Yamaha TX750 and never a problem..Berrymans dip for 24 hrs, new orings, bench sync, install  and gauges for the vacuum syncing and not so much as a problem with any of them except this Honda...scratching my head here and rubbing myself a bald spot!!!

[raymond10078]

What about that air filter?

Otherwise - what about your ignition?  Spark plugs caps measure about 5k ohms?  End of spark plug wires OK.  Most snip off about 1/4" to get to good clean copper wire.  More to check - but just wondering about a weak spark.  The service manual has a spec for a spark distance - could check that.

When you set the float - were the float springs compressed - or just touching?  I'm don't recall how other bikes set their floats - but our Honda's have to just barely touch the float tips - without compressing the float springs.

[Chuck Hahn]

Good hot blue spark from the new plugs so I assume that means they are good and sparking hot enough.

And , like I said, new everything.  Filter included. OEM out of the box.

[salukispeed]

Muffler plugged up with something?? Maybe Mice again? Has the engine been apart?

[raymond10078]

correct heat range/spark plugs?

[Bodain]

You say it's running rich. Black oily plugs and belching black smoke.

OR it's just brurning oil. Ring and or valve seals.

[Chuck Hahn]

Bodain....no oil on plugs.  New plugs and gapped them at .030.  Rode 10 miles and took plugs out to see what they looked like.  Black sooty but not oily if that makes sense.  Colortune also was showing the rich yellow color on all cylinders.

I currently have all the bottom pilot screws all the way in and its not belching the black smoke as bad but it still does it..especially if I blip the throttle a bit.  theres no rhyme or reason the bike should even run with all the bottom pilots screwed all the way in..and by that I mean till they lightly seat and stopped turning easily. But it still runs and drives like its getting plenty of fuel to operate normally.  I took it 20 miles and was getting on and off the throttle just trying to make it stall or something and it never did...just responded and took off like you would expect it too..and this is with the screws ALL THE WAY IN!!!!

So thats telling me something is really worn out and out of specs???  Maybe the needles all need replaced so I got some adjustment control again?? Did the guy I got it from douche these up..I don't know. 

I also went and moved the float height from the 14.5 MM stated in the OEM service manual up to 16.5 MM thinking a lower bowl wet fuel level would lean it a bit.  Right now, with the floats set higher AND the screws all the way in, the colortune is just in that area where its not solid yellow but not that good bunson burner blue I am looking for.  Its like its flickering between yellow and trying to get to the blue but not quite being able to get there..know what I mean?

[HondaMan]

Make sure the clamps on the rubber air hoses to the carbs and head are tight. If the hoses are hard, use bigger clamps, or get newer hoses. Any vacuum leaks here make the carbs mix in a lower RPM range, which is richer. The symptom you describe of 'air screw makes no difference' sure suggests serious vacuum leaks.

[Mr Freeze]

Unless you're trying to keep the bike stock, get a set of early model "roundtop" carbs and boots and be done with it.

[Chuck Hahn]

Mrfreeze..In an earlier post I stated that I got a brand new set of airbox to carb boots from ma dealer in Montana that had 1 set on the shelf out back.  Clamps are good and tight at the intake and the engine sides of the carbs and I assure you there are no airleaks..I sprayed either to check already and then RPMs didn't change.

I know my way around carbs and all about airleaks and where to check. I have dipped these carbs for a full 24 hrs in Berrymans, new orings all the way around, new vacuum lines from the stall preventer and selinoid..blah blah blah.  Still I am stuck with them as I have previously described.  The bike shouldn't even be barely running with the screws all the way in....if at all...right??? So what gives here?  I try to completely restrict everything that is supposed to meter fuel and get no responses.

[HondaMan]

Mrfreeze..In an earlier post I stated that I got a brand new set of airbox to carb boots from ma dealer in Montana that had 1 set on the shelf out back.  Clamps are good and tight at the intake and the engine sides of the carbs and I assure you there are no airleaks..I sprayed either to check already and then RPMs didn't change.

I know my way around carbs and all about airleaks and where to check. I have dipped these carbs for a full 24 hrs in Berrymans, new orings all the way around, new vacuum lines from the stall preventer and selinoid..blah blah blah.  Still I am stuck with them as I have previously described.  The bike shouldn't even be barely running with the screws all the way in....if at all...right??? So what gives here?  I try to completely restrict everything that is supposed to meter fuel and get no responses.

Can I go back in history on the bike for a minute? Specifically: was there a period of time when the bike sat, after 1994, for perhaps a couple of years, or more, with the carbs dry? Reason I ask: when these carbs have been exposed to the MTBE we used to have, then they were allowed to dry out after their anodize was eaten away by this stuff, but with MTBE fuel sitting in the carbs, it can (and often has) cause the main air bleed passage between the bellmouth and the emulsifier tube area to generate a fine, white powder inside. This stuff, once re-wetted, sets up like a stiff baking soda and partially (or even fully) blocks the main air bleed hole(s). When this happens, the carbs run rich, the air screws have no effect, and the plugs turn black in less than 100 miles. Sometimes the formaldehyde-based fuel preservers also cause this problem, which is one reason why I recommend they never be used on these bikes.

In recent years, I have repaired several sets of the 657A/B and 7A/087 series carbs that had this problem. The cure is tedious: you have to pull out the emulsifier tube and sometimes the needle jet (be careful, or those can be easily damaged and distorted) and then run a flexible wire back and forth between the bell inlet hole and the emulsifier to scrape this powder loose and out. Then it can be washed out: I use brake cleaner for this, as it seems to help dissolve it a little along the way. It is not easy to remove this "crust", but if just 25% of this bleed is blocked, the emulsifiers cannot get enough air. Even drilling out the emulsifier holes beyond .040" will not help, as the air supply itself is just not there.

[Chuck Hahn]

You may be onto the problem. Sounds like what happening here even though they were soaked in the Berrymans for a full 24 hrs..and I never take carbs out of the dip early.  Bet this stuff is so hard the Berrymans didnt  eat it up!!  In any case, I did spray carb spray and compressed air thru the ports in the front of the carbs and cone to think about it, The ones on the left ( if I am remembering right ) seemed to be less open than the right side ones.   This is the channel you are talking about right?  I can take the varbs back off and remove everything and run a wire thru the channel and see that it is properly scrubbed open,  What type of wire should i use?  Like a small guitar string?  I have a MIG welder with .030 diameter wire too.

Maybe you can message me a number so if I have questions I can call??

[Chuck Hahn]

Got busy today and ran wire up both intake ports in  the fronts of the carb throats. Pushed, scraped, poked, twisted, rinsed with carbs spray a dozen times, and blew enouigh ait thru  to fill the Goodyear blimp.  Guess what....no more black smoke.  Set the bottom crews at 2 turns out. Just a whisp of richness smoke if I suddenly blip the throttle..but thats normal as the carbs usually hit a tad rich if you do that so I am well pleased with it now.  Thanks for the help and teaching me a great lesson when it comes to this Hondamatic. As I get the time to do other things I will probably pester you guys again. Ive got 5 Suzuki GSs and one 73 Yamaha TX 750 and its getting colder..winter wrenching season is upon us.

[salukispeed]

Sounds like Hondaman was on to something big that is easily overlooked. Nice job and great tip worth keeping in the back of the memory for future use.
Thanks

[Chuck Hahn]

Yes your right Salukispeed....I would have thought the 24HR Berrymans soaking would have dissolved any fouling inside there.  Lessons learned though!!!