Motorcycle Repair: apparent intake leak, 1978 hondamatic 750, intake leak

Question
BACKGROUND: Bike is 1978 hondamatic 750. Am original owner after buying it as a new leftover in 1980. 48k miles on it.

After 2 mechanics worked on it for the last 6 months (I had other projects to get rid of) for "hard to start and
rough idle problem" I now have it back.

Last one rebuilt the 4 carbs with kits and set it all to
specs.Still idles rough. At 55 mph, I note that it is not
pulling as it should. About an inch of choke pulled out
causes improvement..same at idle. Indicates to me possible intake air leak.

Thought the "insulators" were cracked, so I sprayed the insulators with carb cleaner and got no change at idle.

However, I sprayed the fittings on the head where the insulators attach,  (#1,3 &4 cyl) and the engine idle
rpm goes up significantly...indicating to me, either the fittings are loose or cracked and cause an intake leak. Need to pull the plugs and look for a white, lean plug next I assume.

Options appear to be: grind down a wrench thin enough to get at the nut/fitting, loosen the insulator (hose clamp holds it tight) and try to tighten 1 and 4 to see if it matters.

Problem is, it is a REALLY tight fit with carbs on the engine.

Opt 2: take it all apart to where I can get to the fittings with the carbs off and tighten all 3. It does
not appear to me to be an option to ride the bike with
the choke out an inch all the time.

QUESTION: If I take it all down again...and risk damaging the now "age hardended" insulators a third time...How are those threaded "collars" (the part the insulator attaches to with the large nut and that is threaded into the head)
attached?

A tapered pipe thread? "O" ring--I would think not? Sealed somehow originally?

Suggestions on "tightening them" and "sealing them" would help me here if you could.

Should I take them out and put JB weld on them and put them back in? They have not been out in 28 years....what are the odds they will come out again or need to be taken out again? Looks like a sealer would work...even if they are cracked.

I have found no local "old timer" yet that knows about them. The local Honda dealer has no clue.Your help might save me some aggravation (as if I have not had enough!) and some time.

Also, autos had a shift activated solonoid that pulled on a little throttle when put into gear. Mine stopped working about 4 years ago, and part is not avail. Vacuum diaphram is ok but elec switch appears not to work. Not a big deal,
but if I had a part, I could put it on while I had things
apart. Anyone know of a source for said elec (used or not)
activated vacuum unit?

Thank you, Greg

ANSWER: Greg, it sounds like an air leak.  Those fittings in the head do not come out.  I've never seen anyone take them out or needed to take them out myself.  They are supposed to be a permanent assembly with the head casting. Unless someone has messed with them, I'd be amazed if that's where the leak was.  I've seen those intake isolators leak as they shrink with age.  Try replacing the original clamps with hose clamps.  I've seen where those clamps pinch the isolators and cause an air leak. You may be able to close them out with a little more clamp force.  

I've not tried to purchase any recently but it looks like they are still available.

Regards
Rich

---------- FOLLOW-UP ----------

QUESTION: Rich, thank you for the reply. The insulators, while showing up on websites as "orderable" are not available..no matter where one tries to get them. An error in a database.

The fittings have threads on them (mine do) and do NOT appear in the Honda fiche. They might come as part of the head, but are not shown anywhere. I have been told: there is an "O"ring there and 2) there is a gasket there. But, either way, it is "thought" there is something there to seal it. I have spoken to 6 older Honda guys...all are like you and never had occassion to take them out. Never checked them for leaks. But they are threaded into the head. Strange way to do it. They insulators have never been taken off of the fittings.....carbs have been removed from the carb end of the insulator. Guess I am back to sq 1 and will have to take it all down to carbs off and then try to tighten/seal the threaded fittings. Problem is...I won't know if it did any good until I then put it all back and get it running.

I ran into a repair shop in Delaware today. Guy heard the bike run and said "probably need the carbs rebuilt." Then I told him the story I told you.

He offered to take the carbs off, check out what the other guys did, check the float levels and jets and put the guages on the carbs and set them...said it would run about $370 on the outside. I left $300 with the guys that rebuilt the carbs for parts and a little labor (they said they had 11 hours into it...I can believe it, they took them off twice they said.)

Seems like the old bike is getting too expensive to run any more. And this guy had never heard about the solonoid activated vacuum pull on for the idle step up when it is put in gear. Are you familiar with that aspect of the automatic use?

Funny how no mechanic I have spoken to has ever had to take out/tighten up the fittings the insulators attach too. Must just be a Greg thing.

Thanks again. Hope you have another answer. Greg

Answer
Sorry you're having so much trouble.  I repair bikes for friends and family as a hobby anymore but $370 for a carb rebuild seems pretty steep.  It takes about 20 minutes to get then off, and an hour to take them apart and clean them. Another 45 minutes to put them on and synch them and you're done.   I guess I don't charge $65 a hour either so maybe it's reasonable.  

I don't specifically recall the fast idle feature but it makes sense.  When you drop it in gear it puts more load on the engine at idle so the idle would need to be raised to keep it from dying.

Regards
Rich