Topic: Rescuing a '78 CB750F SS

[toomanybikes]

Latest project (my third SOHC/4, umpteenth vintage rescue) is a '78 750F SS, recently posted in the new members forum, even though I'm not a new member ... oops

Low mileage and relatively unmolested, my plan to to make it roadworthy and as original as practical. Aside from the usual tire, tank crud, battery, chain, carbs, brakes, etc. the know issues are:
1. some rattle can touch up paint has locked in the oil filter housing bolt, which was then mangled
2. The RH/taller post in carb#3 is damaged. The float pin is still in place, but there's not much material holding it in. Still too much varnish to determine if it's salvageable.
3. Low beam not working in headlight
4. Muffler has some damage, but still functional

Some pics for fun.

[denward17]

Following for updates....

[Stev-o]

Nice find. 

On that oil filter bolt, Honda made two sizes, you might want to find the larger one for a replacement.

[toomanybikes]

Nice find. 

On that oil filter bolt, Honda made two sizes, you might want to find the larger one for a replacement.

Agreed. The aftermarket bolt from 4into1 (and others) looks to have a 17mm bolt head. That's what I ordered.

[Stev-o]

Nice find. 

On that oil filter bolt, Honda made two sizes, you might want to find the larger one for a replacement.

Agreed. The aftermarket bolt from 4into1 (and others) looks to have a 17mm bolt head. That's what I ordered.

Good. 

BTW - be cautious about cheap parts from 4into1, we're hearing many reports that a lot of the parts are china crap [the bolt will be fine].  Their aftermarket carb kits will make tuning your bike next to impossible. 

[PeWe]

That bike looks like an almost new bike parked and forgotten for decades or a recently restored one

[toomanybikes]

That bike looks like an almost new bike parked and forgotten for decades or a recently restored one

Thanks. It's not recently restored. The previous owner bought it used in 1980, rode it some (12K miles on the clock), then parked it in ~2015.

The rattle can touch up is a minor bummer, but they did a reasonable job, keeping it away from the exhaust, carbs, etc. You can see traces on the tappet covers, spark plugs, and a few other spots. Not sure how the carb float post was busted. It's not clear if anyone has been inside the carbs before.

[toomanybikes]

Nice find. 

On that oil filter bolt, Honda made two sizes, you might want to find the larger one for a replacement.

Agreed. The aftermarket bolt from 4into1 (and others) looks to have a 17mm bolt head. That's what I ordered.

Good. 

BTW - be cautious about cheap parts from 4into1, we're hearing many reports that a lot of the parts are china crap [the bolt will be fine].  Their aftermarket carb kits will make tuning your bike next to impossible.

Yep, I'm familiar with questionable quality of cheap carb kits. Biggest challenge on other projects has been the float valves. Jet's are almost always re-usable and quality orings can be sourced. I'll be taking the carbs apart this weekend and will know more then.

[BenelliSEI]

Careful when you buy a replacement for the oil filter bolt. A while back people were reporting the relief valve is assembled backwards in some of the cheaper versions. I checked a few I got with a project bike, and they seemed OK.

[toomanybikes]

Careful when you buy a replacement for the oil filter bolt. A while back people were reporting the relief valve is assembled backwards in some of the cheaper versions. I checked a few I got with a project bike, and they seemed OK.

Will do. I'm still trying to get the current frozen one off. It's being ... ahem ... stubborn. Dremel in s slot, use my super strong screw driver with 8mm square shaft, vice grips, padded gloves ... still no joy.

I'll probably have to cut a perpendicular groove then try to destroy the bolt's flange to allow the filter housing to pass over it. Not yet sure if the filter housing will be salvageable.

[newday777]

Careful when you buy a replacement for the oil filter bolt. A while back people were reporting the relief valve is assembled backwards in some of the cheaper versions. I checked a few I got with a project bike, and they seemed OK.

Will do. I'm still trying to get the current frozen one off. It's being ... ahem ... stubborn. Dremel in s slot, use my super strong screw driver with 8mm square shaft, vice grips, padded gloves ... still no joy.

I'll probably have to cut a perpendicular groove then try to destroy the bolt's flange to allow the filter housing to pass over it. Not yet sure if the filter housing will be salvageable.

If you have a welder(or know someone with a portable welder), weld a nut to the end of the bolt to put a 6 point socket on to unscrew it. The welding should help loosen the tightness too.

[toomanybikes]

Careful when you buy a replacement for the oil filter bolt. A while back people were reporting the relief valve is assembled backwards in some of the cheaper versions. I checked a few I got with a project bike, and they seemed OK.

Will do. I'm still trying to get the current frozen one off. It's being ... ahem ... stubborn. Dremel in s slot, use my super strong screw driver with 8mm square shaft, vice grips, padded gloves ... still no joy.

I'll probably have to cut a perpendicular groove then try to destroy the bolt's flange to allow the filter housing to pass over it. Not yet sure if the filter housing will be salvageable.

If you have a welder(or know someone with a portable welder), weld a nut to the end of the bolt to put a 6 point socket on to unscrew it. The welding should help loosen the tightness too.

Didn't have welding skills or friends with said skills, so I opted for the brute force/destructive maintenance approach. Now to source a replacement filter cover.

[MauiK3]

Whatever works!

[madmtnmotors]

You are spot on with the rubber tipped float needles being one of the weakest links. Honda float needles are the best, although I have had very good results with K&L float needles as far as their resistance to ethanol laced fuel. I had 4 into 1 carb kit rubber bits begin to swell and disintegrate within a week of exposure to ethanol laced fuel. Sitting at a stop light I started to smell fuel only to look down at the increasing puddle of fuel beneath the bike threatening to invoke my best impression of "Ghost Rider"! Pulling the carbs back apart revealed all of the rubber bits (including bowl seals) were swollen and distorted from ethanol exposure.

[newday777]

Careful when you buy a replacement for the oil filter bolt. A while back people were reporting the relief valve is assembled backwards in some of the cheaper versions. I checked a few I got with a project bike, and they seemed OK.

Will do. I'm still trying to get the current frozen one off. It's being ... ahem ... stubborn. Dremel in s slot, use my super strong screw driver with 8mm square shaft, vice grips, padded gloves ... still no joy.

I'll probably have to cut a perpendicular groove then try to destroy the bolt's flange to allow the filter housing to pass over it. Not yet sure if the filter housing will be salvageable.

If you have a welder(or know someone with a portable welder), weld a nut to the end of the bolt to put a 6 point socket on to unscrew it. The welding should help loosen the tightness too.

Didn't have welding skills or friends with said skills, so I opted for the brute force/destructive maintenance approach. Now to source a replacement filter cover.

You know to watch for the thin washer that sticks to the filter and the spring on the backside of the filter?

[PeWe]

That washer can follow the old filter into the bin.  Don't ask me how I know

[toomanybikes]

You know to watch for the thin washer that sticks to the filter and the spring on the backside of the filter?

I do know to look for them, but alas, there was neither washer nor spring. Maybe that's why the bloody thing was stuck in the first place and maybe that means the filter wasn't fully doing it's job. We'll see.

And looking at the filter, I don't see how a a spring would have fit, just not enough space. Maybe the PO used the wrong filter and tossed the spring&washer. I'll check tomorrow.

[Stev-o]

Careful when you buy a replacement for the oil filter bolt. A while back people were reporting the relief valve is assembled backwards in some of the cheaper versions. I checked a few I got with a project bike, and they seemed OK.

Will do. I'm still trying to get the current frozen one off. It's being ... ahem ... stubborn. Dremel in s slot, use my super strong screw driver with 8mm square shaft, vice grips, padded gloves ... still no joy.

I'll probably have to cut a perpendicular groove then try to destroy the bolt's flange to allow the filter housing to pass over it. Not yet sure if the filter housing will be salvageable.

If you have a welder(or know someone with a portable welder), weld a nut to the end of the bolt to put a 6 point socket on to unscrew it. The welding should help loosen the tightness too.

 Now to source a replacement filter cover.

I may have a spare...

[Dime]

If you are stuck for a cover and bolt let me know. I am going with a spin on filter and have no need for either. Just pay postage. Pm works best as I don't get notifications easily. Cheers

Sent from my SM-S721W using Tapatalk

[toomanybikes]

If you are stuck for a cover and bolt let me know. I am going with a spin on filter and have no need for either. Just pay postage. Pm works best as I don't get notifications easily. Cheers

Sent from my SM-S721W using Tapatalk

Thanks, I'll keep that in mind. I'm planning to meet a guy on Friday for some carbs. He also has multiple spare engines, so I'm sure a filter cover can be found. I already bought the bolt from 4into1.

[newday777]

I already bought the bolt from 4into1.

Be very careful of what you buy from 4into1.com.
They sell cheap replicas that aren't correct in thread sizes and quality materials. I bought stainless steel brake hose kit from them and the banjo bolts are cheap pot metal that broke way to easy. The same thing with their cables, the lock nuts on the adjusters had too big thread diameter and stripped out tightening them.
They have poor customer service when things go wrong with their products blaming the customer.

[PeWe]

4-1 pilot jets for CB750 are wrong too. Too tight and brake inside. I had to pull carbs and drill the brass debris out with a 2.0mm drill. 2 snapped, drilled all holes so all are equal. Hole might have been very little smaller. Maybe alu oxide thick only.

[HondaMan]

You are spot on with the rubber tipped float needles being one of the weakest links. Honda float needles are the best, although I have had very good results with K&L float needles as far as their resistance to ethanol laced fuel. I had 4 into 1 carb kit rubber bits begin to swell and disintegrate within a week of exposure to ethanol laced fuel. Sitting at a stop light I started to smell fuel only to look down at the increasing puddle of fuel beneath the bike threatening to invoke my best impression of "Ghost Rider"! Pulling the carbs back apart revealed all of the rubber bits (including bowl seals) were swollen and distorted from ethanol exposure.

+1 on the K&L aftermarket float valves with ethanol (and butane) in the gas.
Does yours still have the "oil cooler plate" behind the oil filter? I can't quite tell from the pix. That version requires the extra-long oil filter bolt, and often weeps, so many get tossed.

If the O-ring in the filter housing isn't Honda's own, it barely seals (or weeps). You can get Honda's version from them, still. It is 1mm thicker than the ones found in oil filter 'kits', most of which have the thinner O-rings used in Kawis and Suzys. Many of these bolts got too tight because of owners trying to stop the weeps that are caused by the too-skinny big O-ring in the kits.

[toomanybikes]

You are spot on with the rubber tipped float needles being one of the weakest links. Honda float needles are the best, although I have had very good results with K&L float needles as far as their resistance to ethanol laced fuel. I had 4 into 1 carb kit rubber bits begin to swell and disintegrate within a week of exposure to ethanol laced fuel. Sitting at a stop light I started to smell fuel only to look down at the increasing puddle of fuel beneath the bike threatening to invoke my best impression of "Ghost Rider"! Pulling the carbs back apart revealed all of the rubber bits (including bowl seals) were swollen and distorted from ethanol exposure.

+1 on the K&L aftermarket float valves with ethanol (and butane) in the gas.
Does yours still have the "oil cooler plate" behind the oil filter? I can't quite tell from the pix. That version requires the extra-long oil filter bolt, and often weeps, so many get tossed.

If the O-ring in the filter housing isn't Honda's own, it barely seals (or weeps). You can get Honda's version from them, still. It is 1mm thicker than the ones found in oil filter 'kits', most of which have the thinner O-rings used in Kawis and Suzys. Many of these bolts got too tight because of owners trying to stop the weeps that are caused by the too-skinny big O-ring in the kits.

No weeping so far. The design on the SS is weird, with an oil filter base between the filter cap and the engine. Means you need two of those large orings.

[newday777]

The filter base, is actually a mini oil cooler extension.
Yes you need 2 of thr big Honda orings for the filter and the base.

I got inspired by this thread to get going on my 78 F3, it's been setting up on the lift, so I took apart the rear brakes for a rebuild as both the master cylinder and the caliper have leaked in the past. I've had to order a mc kit and a caliper piston(pitted...). I had the seals already knowing the brakes needed attention.

[toomanybikes]

UPDATE - With the carbs now clean and new OEM float valves, today marked the first legit test start.

I mounted the carbs but not the airbox so I could more closely monitor fuel leaks. Yes, I did do a bench test first. There were a few leaks on the bench, but they seemed to be improving as the gas swelled the old orings. Carb 4 still has a small leak coming out the bottom, so I'll monitor that. I did not totally de-rack the carbs based on input from another thread. As long as the fuel tubes don't leak I'll keep the assembly intact.

To test the openness of the slow jet, I fitted a fuel tube over the jet (shown below) then sprayed various fluids (carb cleaner, kroil, alcohol) into the tube letting them soak until the fluids ran through the jet ran freely. Compressed air helped the process.

The bike now starts and runs consistently, but since the airbox is not yet installed I have to constantly manipulate the choke to limit the air flow. Cyls 2&3 got nice and hot, but 1&4 were just warm. They have good compression and spark, so it must be a fuel/air issue. #4 might be too rich due to the overfill described above.  I'll mount the airbox next session and see if the full system & time fixes 1&4. If so, I'll move on to brakes, tank, tires, chain, etc.

[Don R]

 I believe the pilot air circuit pulls air through one of the bleeds in the opening at the air filter end, it goes past the idle screw valve, pulling air and fuel through the jet and its emulsion tube holes, it then gets pulled into the venturi near the slide notch. Carb cleaner and air can be used in any/all of those openings to be sure they have flow.
  I'm sure something I wrote is technically incorrect but that's my thought process when cleaning the carb idle system.
  I like the float valves with the little screens on top, I've used the ones for F1 in a similar numbered K6 carb. I'm pretty unfamiliar with the 77/78 keyhole carbs though.

[toomanybikes]

UPDATE - She's getting close. I'm now just brakes and a clean tank away from a test ride. The tank and front brakes will be tackled this weekend, but the rear brake remains a challenge.

The original m/c is frozen solid, as is a replacement bought from a parts bike nearby.

If I can't get either moving I'll have to look for a third option, either legit CB750F or one from another bike, preferably another Honda. Any suggestions?

[newday777]

I saw your wanted ad for the rear caliper and master cylinder and posted a link on using a grease gun to free up the stuck pistons.  Have you tried that? I was successful in freeing a spare 78F rear master and caliper that were both stuck this way. Let me know if it works for you or not...

Hydraulic method to free master cylinder (and calipers are done the same way)

Did you get it running properly from your idle circuit cleaning tube/concoction mix?? You didn't say any more on it above.
If not, this is a great write-up and pictures of properly cleaning 78F carbs and the accelerator pump circuits so it will run the way it should.
78F carb cleaning thread
http://forums.sohc4.net/index.php/topic,48858.msg515204.html#msg515204

[toomanybikes]

I saw your wanted ad for the rear caliper and master cylinder and posted a link on using a grease gun to free up the stuck pistons.  Have you tried that? I was successful in freeing a spare 78F rear master and caliper that were both stuck this way. Let me know if it works for you or not...

Hydraulic method to free master cylinder (and calipers are done the same way)

Did you get it running properly from your idle circuit cleaning tube/concoction mix?? You didn't say any more on it above.
If not, this is a great write-up and pictures of properly cleaning 78F carbs and the accelerator pump circuits so it will run the way it should.
78F carb cleaning thread
http://forums.sohc4.net/index.php/topic,48858.msg515204.html#msg515204

Hi newday,

It is running and idling proper now, although a few of the float bowls have occasional leaks I need to resolve.

I haven't yet tried a hydraulic approach to freeing the piston, but will do that soon. Thinking through that, it may also free up the master  cyl if I can cobble together bolts and lines to make the fluid pressure from a good m/c apply pressure to the bad one. Conveniently, I have a BMW R1200RT project with front brake/ABS issues, so that functioning master cyl may provide the hydraulic source for freeing things up.

BTW, here are the latest pics, with some of the chrome polished and decades old grunge removed from the sprocket area

[newday777]

Good progress 👏

[Dime]

Looks great. Great work.

Sent from my SM-S721W using Tapatalk

[kap384@telus.net]

Looks great!  Good luck on brakes.

[toomanybikes]

Rear end taking shape. New chain (with one link removed), cleaned up the sprockets and guard. Haven't yet cleaned up the shocks or center stand.