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Author Topic: 1977 Honda 750 Supersport  (Read 6220 times)

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Offline reliv77

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1977 Honda 750 Supersport
« on: October 05, 2012, 05:44:57 AM »
My newly acquired 1977 Honda 750  Supersport has some issues. The Bike will go into a High Idle at will and it has a slight Head Gasket Leak. I am in Cleveland Ohio. Looking to see if anyone knows a good mechanic in the Cleveland or surrounding area.
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Offline flybox1

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Re: 1977 Honda 750 Supersport
« Reply #1 on: October 05, 2012, 07:01:29 AM »
you can fix the high idle issues yourself.
how bad is the gasket leak? 
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Offline Old Scrambler

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Re: 1977 Honda 750 Supersport
« Reply #2 on: October 05, 2012, 07:42:09 AM »
Tell us a bit more..............how many miles............how long had it been parked before the recent startup..........completely original or.............???

The high idle is likely one or more of the carb-slides hanging up.......may be from old fuel so its an easy fix with carbs still on the bike.

The leaky head gasket should be thoroughly investigated because few of the head gaskets actually leak..........its usually from dried-up internal seals below the cam tower........after you have cleaned the motor, observe where the oil is coming from and report back..........if it is the head gasket you may choose to live with it............if its a seal, it will only get worse.  Do some searching on this forum (google) about F2 and F3 top ends.....We are here to help.......
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Offline reliv77

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Re: 1977 Honda 750 Supersport
« Reply #3 on: October 05, 2012, 01:10:48 PM »
The Odometer read about 4k but it is not the original Odometer. No idea how long the bike sat. When I drained the Tank the Fuel looked clean. I put in new fuel. As far as the Head Gasket, maybe I am referring to something different. I am talking about the top of the Engine that is held on by Philips Head Screws. There is just some minor leaking  of oil after I ride the Bike. The Bike is very Cleanand Stock looking, so I am guessing it has low miles on it.
Can you tell me how to investigate the carb-slides hanging up.
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Offline TwoTired

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Re: 1977 Honda 750 Supersport
« Reply #4 on: October 05, 2012, 01:37:45 PM »
You can do valve cover gasket replacements with engine still in frame.  (But, you can't completely remove the valve cover without hacking on the frame or taking the engine out.)

High idle could be carbs needing vacuum sync.  Or there are intake/induction air leaks.  Or maybe it just needs a routine 3000 mile tune up.  I'd start with that.
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Offline flybox1

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Re: 1977 Honda 750 Supersport
« Reply #5 on: October 05, 2012, 02:17:15 PM »
new set of allen bolts and a re torque might be all you need  ;)
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'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

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Offline reliv77

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Re: 1977 Honda 750 Supersport
« Reply #6 on: October 05, 2012, 04:40:13 PM »
I think I will try a new set of Allen bolts and a re torque and see if that works on the Oil Leak. Question, Would I need "Honda Allen Bolts" or could I find them at a Box Store or some other place.
If I go a step farther, and try and replace the Cylinder Head Cover Gasket, the Cylinder Head Cover Philips Head Screws are all I would have to remove to replace the Cylinder Head Cover Gasket? From the Post from TwoTired, it sounds more involved.
Still looking for some help on the carb-slides hanging up. If i could get some more details on that.

Thanks for the replies. Bear with me. I have never worked on a Motorcycle Engine before.
If it was a 1971 Ford Thunderbird, I could tell you where every bolt and nut are at.
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Offline Old Scrambler

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Re: 1977 Honda 750 Supersport
« Reply #7 on: October 05, 2012, 04:42:29 PM »
Welcome......your a fast learner.......Yes, that is the valve cover and it appears you already have allen-head screws.....If they are stainless steel, they are prone to losen so re-install with some blue locktite......be sure to check them all.

The easiest way to begin to cure the hanging-carb issue is to put some Sea Foam or a few ounces of fuel-injector cleaner in your tank.......and then go for a 50 mile or longer ride.  If that does not cure the idle problem, get the bike running and hold at a constant rpm at or just above idle....spray the manifold rubbers with WD-40 and look for immediate dry spots as well as an increase in the idle speed.......if found either tighten the clamps or replace if cracked.  BTW....are you sure you have the choke completely OFF?
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Dennis in Wisconsin
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CB750 Classic Bonneville Racer thread - http://forums.sohc4.net/index.php/topic,135473.0.html
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Offline TwoTired

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Re: 1977 Honda 750 Supersport
« Reply #8 on: October 05, 2012, 04:58:31 PM »
Allen bolts are far easier to over torque than cross head screws.  And aluminum is softer than steel.  Don't over torque in hopes of  extending hardened rubber service life at the risk of helicoling stripped threads.


For the random high idle, begin with a 3k Tune up, and vacuum sync.
Then look for intake vacuum leaks.

What do you base the "carb-slides hanging up" diagnosis upon?   You know, you can pop off the top of each carb and squirt penetrating oil on the slide bores.  This will dilute gummed carb slides, if that is the real problem other than out of tune/out of sync, or intake leaks.

Cheers,
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Offline piute

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Re: 1977 Honda 750 Supersport
« Reply #9 on: October 05, 2012, 05:49:44 PM »
   I myself had a high idle (F2)
 All my boots were hard boiled them in some green(works wonders) I cleaned the carbs 3 different times ,slides and all jets  all stayed stk. no changes,But new diapham kit instal;ed, Set sliders to 1/8" using an 1/8 inch drill bit(have sync tool yet to use) Hey why mess with a great thing there doing fine cam chain bit noisy though.Everything seems fine still,"O" all new cables removed throttle return cable (not advised if not ridden lots of miles and know when to use kill switch.
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Offline reliv77

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Re: 1977 Honda 750 Supersport
« Reply #10 on: October 06, 2012, 02:47:05 PM »
From the suggestions on this Post I think I will try the minimum:
1) Try a new set of Allen bolts and a re torque the Cylinder Head Cover. Again, are these Bolts available through Honda in Allen?  Maybe find them elsewhere? Is there a Tork Spec for these Bolts?
2) Try some fuel-injector cleaner in the tank.
3)Pop off the top of each carb and squirt penetrating oil on the slide bores.
Good for Starts?
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Offline Stev-o

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Re: 1977 Honda 750 Supersport
« Reply #11 on: October 06, 2012, 10:15:57 PM »
The socket head screws are not stock and can be purchased at a local specialty bolt company. I believe they are 6mm and various lengths. 

Try Hexagon...

http://www.hexagonindustries.com/
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Offline reliv77

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Re: 1977 Honda 750 Supersport
« Reply #12 on: October 07, 2012, 08:22:47 AM »
Thanks for the replies. Bear with me. I have never worked on a Motorcycle Engine before.

Still debating on replacing the Cross Head Screws with Allen Bolts and a re torque the Cylinder Head Cover for the slight Oil Leak. Would I likely Strip the Threads in doing so?
Also now seeing another slight oil leak from one of the eight large silver "Cap Bolts" on the Cylinder Head Cover. I do see O rings on these. Assuming they are replaceable O Rings?
I am also assuming that I can not take off the Cylinder Head Cover without first removing the Engine from the Frame???
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Offline Don R

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Re: 1977 Honda 750 Supersport
« Reply #13 on: October 07, 2012, 09:05:39 AM »
If you try to tighten the cross point screws be sure to find the proper screwdriver bit. Most of the problem people have is use of the wrong bit. They are not auctually phillips heads they are a Japanese equivalent. JIS. I usually tell people to find the screwdriver that looks perfect and then use the next larger one. You can try to tighten, usually doesn't work. Use the google search function here. Almost everything has been gone over multiple times. The FAQ, and tips and tricks section is great.
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Re: 1977 Honda 750 Supersport
« Reply #14 on: October 07, 2012, 09:32:25 AM »
Quote from: Don R on October 07, 2012, 09:05:39 AM
If you try to tighten the cross point screws be sure to find the proper screwdriver bit. Most of the problem people have is use of the wrong bit. They are not auctually phillips heads they are a Japanese equivalent. JIS. I usually tell people to find the screwdriver that looks perfect and then use the next larger one. You can try to tighten, usually doesn't work. Use the google search function here. Almost everything has been gone over multiple times. The FAQ, and tips and tricks section is great.

http://www.instructables.com/id/When-a-Phillips-is-not-a-Phillips/?ALLSTEPS
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Offline reliv77

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Re: 1977 Honda 750 Supersport
« Reply #15 on: October 07, 2012, 02:45:02 PM »
What would be the Tork Spec in pounds for the Allen Bolts to re torque the Cylinder Head Cover?
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Offline reliv77

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Re: 1977 Honda 750 Supersport
« Reply #16 on: October 08, 2012, 05:14:01 AM »
TwoTired stated that I could:
 "You can do valve cover gasket replacements with engine still in frame." Do I Loosen all the Bolts and "Fudge" the new Gasket in? Cut the Gasket? Use any type of Gasket Seal?

Also:
"Or maybe it just needs a routine 3000 mile tune up.  I'd start with that."
What is all involved in a 3000 mile Tune Up? Points, Plugs, etc?
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Offline Jiminy Indy

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Re: 1977 Honda 750 Supersport
« Reply #17 on: October 08, 2012, 05:49:07 AM »
You can remove all the bolts holding the valve cover on and there is just enough room to lift it up to replace the gasket. But it's a tight fit and you cannot remove the vlave cover completely without removing the engine completely from the frame which is a real PIA.

You shouldn't need any gasket seal. There are a couple guide posts that the gasket fits over so it will fit correctly. Make sure you hit these posts or it will surely leak. And use an anti-seize on the bolts holding on the cover.
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Offline Jiminy Indy

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Re: 1977 Honda 750 Supersport
« Reply #18 on: October 08, 2012, 05:52:04 AM »
And there's lots of S/S allen head bolt kits on e-bay for about $30 or so that replace all the engine bolts. I personally replace all the standard bolts with allen heads. Not as much chance to riun the heads - and besides I like the looks of the shiny allens against the black engine - but that's just personal preference.
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Of all the things I've lost, I miss my mind the most.

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Offline reliv77

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Re: 1977 Honda 750 Supersport
« Reply #19 on: October 08, 2012, 06:05:11 AM »
Would the Gasket be available at a Honda Dealership or would I have to hunt for one being the age of the Bike.
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Offline Jiminy Indy

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Re: 1977 Honda 750 Supersport
« Reply #20 on: October 08, 2012, 10:03:21 AM »
Lots of SOHC websites around but try this guy. Cost is $6.95 plus the trip.

http://newmotorcycleparts.com/gaskets/valve_cover_gaskets.html
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Of all the things I've lost, I miss my mind the most.

"Shot up the alley and then cut across the street" - now that's some violence you can appreciate!

Offline reliv77

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Re: 1977 Honda 750 Supersport
« Reply #21 on: October 09, 2012, 04:07:46 PM »
Jimmy Indy, Thanks for the Link to (http://newmotorcycleparts.com/gaskets/valve_cover_gaskets.html)
Saved a Ton of Money compared to a local Honda Dealer.
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Offline reliv77

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Re: 1977 Honda 750 Supersport
« Reply #22 on: October 13, 2012, 01:19:34 AM »
If i take the advise of checking the carb-slides hanging up issue. Would I need a new gasket once I open the Top of the Carbs?
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Offline TwoTired

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Re: 1977 Honda 750 Supersport
« Reply #23 on: October 13, 2012, 11:07:30 AM »
Quote from: reliv77 on October 13, 2012, 01:19:34 AM
If i take the advise of checking the carb-slides hanging up issue. Would I need a new gasket once I open the Top of the Carbs?

Normally, no.
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Offline reliv77

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Re: 1977 Honda 750 Supersport
« Reply #24 on: October 14, 2012, 01:07:55 PM »
OK. Put some Sea Foam in the Fuel Tank today. About three ounces in a Half Full Tank. Went for a 5 mile ride. Had to limp back home to the house on the last 1/2 mile. The bike would barley run. It was running a whole lot better before the Sea Foam. Any Ideas why?
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