Where to Start-1979 750f Super Sport? Carb/Compression or both?

[Hastings]

Bought a non running 1979f SS that would not start.
After several carb drains and fuel/carb cleaner it starts right up with the choke and idles and revs with the choke on
With the choke off it idles for a while but will not rev past about 2K with the choke off
Did notice all headers were hot except #2 with was not as hot (I could touch it)
Before I tear down the carbs anything I should do with #2?

 

[brettp]

Could be spark issue. Check for spark.
Then you need to do a valve job. You gave get away from this requirement.

 

[Hastings]

I do have spark on #2 looks about the same as the other three cylinders.
How big a job is adjusting the valves?

 

[Robert Frere]

Bought a non running 1979f SS that would not start.
After several carb drains and fuel/carb cleaner it starts right up with the choke and idles and revs with the choke on
With the choke off it idles for a while but will not rev past about 2K with the choke off
Did notice all headers were hot except #2 with was not as hot (I could touch it)
Before I tear down the carbs anything I should do with #2?

Had same problem with my 78F2 number 2slow running jet was blocked.also check out the colour of the plugs ie running rich or lean

 

[brettp]

Valve job is easy. I was intimidated at first, never did one, but after the first valve was done the rest was easy.
You need the valve tool, valve shims, and you need to follow the instructions from the manual. But you'll be fine.

 

[Hastings]

Thanks BrettP!

 

[Hastings]

Ok I removed the carbs, didnt separate them but:
Cleaned each carb top and bottom.
Removed all the jets except the secondary (could only get one out, it was clean but cleaned it anyway)
Put parts and the full rack of carbs in the ultrasonic cleaner
Everything went back together well.
Reinstalled and it idles really good and starts really good.
However when I try reving it bogs down can sometimes get it to 4K rpm
Thought I had a vacuum leak checked and found I needed to res-eat the carbs now no leak.
Sill cant rev, really hate to take them back off
Any suggestions on what to try next.

 

[brettp]

Valve job and timing. I'm telling you here and now... are you ready?
I fought my bike when it wouldn't rev past 5k. I ran fuel cleaner through it, played with the idle, looked at throttle cables, etc. After a couple weeks of trying to not do a valve job, I bit the bullet. The valves are not something you can ignore. I'll say that last part again, the valves are NOT something you can ignore. Get the valve shim tool, get a shim kit, watch a YouTube video or two or five, and get after it. (Look at your valve cover gasket to see if you'll need a new one). My bike ran like new afterward. I'll do it in a heartbeat next time.
As for timing, you gotta do that, too. And its even easier.

 

[Hastings]

Thanks BrettP!
So based on what I'm seeing I should set them at .005 you agree?
I'll order the tool and crack it open.

 

[kirky]

believe it or not my 750 fz wouldn't rev past 5000 when i followed the books available and took out the 75 main jets and fitted 102's . everything pointed to electrics with melted cdi's and a cracked coil. i replaced the lot and still the same until one day messing about i left the cover off the air filter and bingo it went like a rocket, i am just putting the 75's back in today. some extensive research and looking at pics told me the air intake on my jdm 750 fz was different to all the american and european models and i was chocking it with the 102's. i have just seen a thread from 2017 where someone thought the 75's were wrong like i did. i wonder if he had the same trouble when changing his jets?

 

[brettp]

Yes, .005". If your find yourself having to choose between too loose or too tight, go too loose.

 

[Hastings]

Ok my valve shim tool is on it's way.
I cracked open the valve cover and took some readings today (see below)
exhaust Cylinder gap
1 .008"-.009"
2 .008"-.007"
3 .007"-.007"
4 .007"-.006"


Intake Cylinder gap
1 .007"-.006"
2 .006"-.006"
3 .006"-.006"
4 .006"-.006"

 

[Hastings]

Sorry sent before finishing.
Based on this should I change all but the .006" or do those also?

 

[brettp]

I would try to change anything above .007"

 

[dirtdigger]

I have never seen a dohc with loose clearances....they always wear tighter.

.006" is perfectly fine, and I would say is the upper limit, I would change anything that is looser but loose clearances wont affect compression and would consider it to be any of your running problems.

 

[brettp]

Unless they're so loose they don't drop the valves well enough, right?

 

[mrtwowheel]

6 and 7's and the motor hasn't been run in a while, right? Myself, I think I'd run it for awhile and let the valves hammer in the seats for awhile and then measure again?

Edit never mind the above, didn't notice your 8's and 9's.

I don't buy a shim set. I go to the oldest Honda dealer in my area. I have already measured and swapped some shims around. Usually I only need about two after swapping them around. So I know what sizes I need. With my micrometer in hand I tell the parts desk guy that I need some shims from the box that the techs have out back. This box of shims is NOT inventoried. Believe me, the parts desk guy doesn't have a clue, and it's a different guy every time. I just keep insisting that the box of shims is back there. New shims, used shims, it doesn't matter. I've paid $4 per shim before and the parts guy has asked me if I would take referrals. No way, I'm not going to take the responsibility for every oil leak, real or imagined, that ever happens.

 

[Hastings]

Thanks for the responses.
I'll make the changes and let you know if she rev's up!

 

[Hastings]

Well I pulled to old shims from the valves with the .008" and .009" clearance and the old shims measure 3.175mm with the calipers
Based on the formula to calculate the new shim needed I would need 3.22mm and 3.25mm to get them with .006" clearance.
I cant find any shims online that are 25mm by 3.22mm - 3.25mm in thickness.
At this point not sure what I should do, any suggestions?

 

[brettp]

https://www.ebay.ca/itm/28411825425...Oc86Puc2c2+4RX7dJF426cBsk=|tkp:Bk9SR7bS4oz7YgLooks like he has some 3.2. But I didn't look hard, make sure they are 25mm.