Author Topic: Garage Find 1977 CB750 F2 (Read 2645 times)

zalion0 · « **on:** October 02, 2021, 04:20:46 AM »

Figured, i'd post this as I have some good news and a little win today. I came into possession of a 1977 CB750 F2, with approx 5k miles on the clock. I believe it has been sitting there in the garage i found it in for approx 38 years as it was last taxed in in 1984. After reviewing the posts of this forum, I was able to 'unstick' the clutch with a fresh set of oil and filters and the clutch pulled in for 24hr. After this, the clutch would finally disengage when pulled in.

However...todays win, i felt the need to post about is that after soaking for a week with Marvel Mystery Oil I was able to finally free the engine and the pistons! My plan is to get this back up and running and then potentially look at restoring it.

SOHC4 Cafe Racer Fan · « **Reply #1 on:** October 02, 2021, 05:25:52 PM »

Nice project!

Prospect · « **Reply #2 on:** October 02, 2021, 05:51:53 PM »

Looks to be in fantastic shape. Ask away. There is a wealth of knowledge here. Good luck with the project!

RAFster122s · « **Reply #3 on:** October 02, 2021, 08:30:50 PM »

Boroscopes can be had inexpensively these days that connect to a laptop, tablet or phone. They can be handy for inspecting cylinder bores and other things if you want a new toy...

Clean up your electrical connectors with a bit of dielectric grease on reassembly... Tighten up any female connector barrels that are loose. Be careful when disassembling your controls... Recommend you do it inside a large clear plastic bag. If anything goes flying or drops it stays in the bag. Tiny bearing for switches and springs ate what I have in mind here...
If the controls has a broken plastic 'box' then don't panic, another member has 3D printer files available to print a replacement that works well.

Welcome to the forums and congrats on finding a nice F2.

zalion0 · « **Reply #4 on:** October 03, 2021, 06:37:45 AM »

Great minds, must think alike! I had a Endoscope delivered the same day the engine was unstuck.This allowed me to take a look inside the combustion chamber. It does look like a bit of rust was causing the pistons to stick.

I've got some spark plugs on order and a new battery too. I do want to tackle the kick starter as well prior to firing this up. All of the electrics seem okay (with the exception of the horn). The issue with the kickstart is that it will not budge, despite the engine being free. I also need to replace the fuel cock and de-rust the inside of the tank...but thats for another day.

zalion0 · « **Reply #5 on:** October 03, 2021, 07:26:05 AM »

Update : Kickstart is now free. I was being too gentle with it 🤣

Alan F. · « **Reply #6 on:** October 03, 2021, 07:52:43 AM »

Good project, thanks for having us along for the fun.

zalion0 · « **Reply #7 on:** October 04, 2021, 04:48:33 AM »

I have a question, whilst patiently awaiting parts I have been inspecting the bike further. I am wondering if I am missing the rubber tubes which sit between each of the carbs. Looking at cmsnl.com diagrams suggests there should be 3 pipes connecting each of the carbs (i have spotted that each carb does have its own rubber pipe at the bottom...). I've shown where I believe the missing pipes are in the images below. Looking at the carbs, there doesn't seem to be any evidence there may have been pipes connecting these previously.

zalion0 · « **Reply #8 on:** October 08, 2021, 11:32:38 PM »

Quick update! We’ve got some fresh spark plugs installed and can confirm there is a spark on all 4 cylinders. A battery is installed too and can confirm the oil pump is working too. Off to see if I can find a gerry can and some fuel today and hook a temporary fuel tank. The existing petrol tank is all rusty so reluctant to use that until it is sorted.

As you are probably aware there is bit of a panic buying fuel crisis here in the UK…so if you turn up with a Gerry can you’re most likely to get lynched by the mob

Don R · « **Reply #9 on:** October 09, 2021, 08:02:39 AM »

I made an IV bottle out of a tire slime plastic container. They are thick on the bottom and may be tapped for an 1/8" pipe thread. You may be able to find something similar. The top has a taper for a vent. when not in use I stick the fuel line on the vent.

zalion0 · « **Reply #10 on:** October 15, 2021, 08:39:50 AM »

I went with the suggestion of an auxiliary fuel tank and get it filled up with fuel. After a bit of spluttering a coughing it fired up for the first time in 39 years! So a small win for today!

kap384@telus.net · « **Reply #11 on:** October 15, 2021, 08:57:34 AM »

Awesome, great to see another ‘77 F!

Alan F. · « **Reply #12 on:** October 15, 2021, 06:21:32 PM »

Quote from: zalion0 on October 15, 2021, 08:39:50 AM

... it fired up for the first time in 39 years! So a small win for today!

Win!

Shtonecb500 · « **Reply #13 on:** October 15, 2021, 06:47:32 PM »

niiiiiiiice

zalion0 · « **Reply #14 on:** October 16, 2021, 06:25:08 AM »

Looks like I’ve got my first issue to fix and get running consistently….a leaky no3 carb!

zalion0 · « **Reply #15 on:** October 18, 2021, 06:50:42 AM »

So, I have a question. I’ve removed the carbs from the bike and have yet to disassemble them. I’m looking to see if there is any leaks whilst the carbs are on the bench. I’ve added fuel and left them sitting for a few days but only a small drip out of the float drain hole on No3. This has got me wondering, am I missing something (such as does the fuel need to be under pressure) or is the leak somewhere else and sprayed on carb. Trying to avoid disassemble the carbs if I’ve misdiagnosed the problem!

BenelliSEI · « **Reply #16 on:** October 18, 2021, 10:08:56 AM »

Fuel is gravity fed, no pressure. Is the drip coming through the hose, or out the screw you have circled? That’s the floatbowl drain screw, make sure it is snug. The tube also leads from a long pipe inside the bowl that is the overflow of the float needle is sticking and letting too much fuel in the bowl. Try tapping the float bowl with a metal tool (I usually use the handle end of a 3/8” ratchet handle). If that doesn’t do it, pull off the floatbowl. Often the floats are stuck in dried up fuel in the bottom of the bowl.

Alternatively, it is not uncommon for the over flow tube (inside the floatbowl) to have a small split in the brass, near the bottom. I believe moisture accumulates there, in a dry carb, and then freezes and splits the delicate fitting.......

Don’t be afraid to pull those float bowls. There will be lots of dry fuel crud in there. You don’t want to soften it with fresh fuel and then plug your idle and main jets.....

Stev-o · « **Reply #17 on:** October 18, 2021, 11:01:29 AM »

First off, welcome from Texas! Benelli ^^^ has given you some good advice, remove the float bowls and have a look inside. Make sure that #3 float is not "sticky"

zalion0 · « **Reply #18 on:** October 18, 2021, 11:52:16 AM »

Thanks Both! Appreciate the input, apologies if I was slightly misleading! I couldn’t determine the actual leak and have taken a guess at the carbs. The fuel was pooling and dripping from the outside to bottom of the float bowl. My highlight was to show this as opposed to it leaking from the drain screw. If you look closer you can see a pool on the other side of the outside float bowel corner.

I’ve had the carbs off for about 24hr now on the bench and nothing is leaking now…this is why I was wondering if it was pressure or gravity fed. I think I will get the fuel bowels off anyway as it was sat for approx 37years and a new gasket kit too!

The only other item I was wondering if the rubber (well solid plastic now after 37 years haha…) boots which connect carbs to engine is possibly leaking here as well.

Really appreciate the input, this is new to me but learning more and more every day! Its interesting stuff!

zalion0 · « **Reply #19 on:** October 21, 2021, 03:39:31 AM »

So, figured I’d be brave and take the carb bowls off. Doesn’t look too bad but certainly needs a clean. Carb one also looks pretty blocked! Not to mention the seal on carb 3 is manky. So the parts I’m ordering will be a gasket and o-ring set for the carbs. Some manifold inlet boots as the current ones are rock solid.

I have noticed the floats in carb 1 and 3 aren’t to springy. So time to read up on that!

Translations · « **Reply #20 on:** October 21, 2021, 04:46:06 PM »

Good looking project! F2's are stubborn little bastards but well worth the effort

Don R · « **Reply #21 on:** October 22, 2021, 03:40:49 PM »

I think the float valves have little screens above them, they may need attention also. If you remove them, keep the needles and seats matched. I've been using heat on the boots to get the carbs on.
A garage find is usually way better than a barn find.

zalion0 · « **Reply #22 on:** October 24, 2021, 01:15:14 AM »

I think you're right as well Don R. I'm still waiting on the replacement gaskets for the carbs so figured i'd have a go at removing some of the rust from the chrome parts. Its looking better and a majority of the rust has been removed, next part is to deal with the pitting on the chrome now!

zalion0 · « **Reply #23 on:** November 02, 2021, 04:27:47 AM »

Never figured I’d post something like this but all the carbs have been cleaned, gaskets and o rings all replaced! Now ready to go back on the bike! What do people use to grease the entrance between the carb and inlet rubbers?

zalion0 · « **Reply #24 on:** February 04, 2022, 04:00:21 AM »

Figured i'd update this. Been making quite a bit of progress (poor idle still needs work but I believe thats due to the 40yr old carb to engine rubbers.. haha) but I'm working on the front end now. First job is to take a look at the wheels and clean these up. The forks and triple trees will be next. Any suggestions on the best approach to cleaning the spokes up?

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Author Topic: Garage Find 1977 CB750 F2 (Read 2645 times)