Newly purchased CB750K revs reset at 4000 RPM

[motogrady]

and like tools said, if your getting a steady flow, not dripps, a flow, petcock should be good.

[new_750k]

Thanks for all the tips! It was actually easier than I'd expected... I think everyone seems to get a bit worried about it the first time.

I eventually got the carbs out, the bank is currently soaking in pinesol but I was just about to clean the jets when I noticed that the (secondary?) main jet (102), when it was removed from the emulsion tube seems to have a load of black gunk on the screw thread. It's as if there was an o-ring between the tube and the jet which dissolved long ago. I'm guessing that this has clogged the jet.

Could this be why the throttle was dropping off? Is there meant to be an o-ring there?

As far as I can tell the jets were put in the right way around, 68 primary and 102 secondary.

Also, I don't have a compressor to blow out the jets/pinesol so would I be OK just using a can of air?

Thanks again everyone, this board has made my life a huge amount easier. I'm looking forward to getting this thing back together now!

[motogrady]

stop.  take a breath.

think about what's going on.

you found gunk.

when you take the 102, the main, out, look at where the fuel goes.

or should go.

those small passages, if they're clogged, all this work is for naught.

a guitar string, thanks to the guys here, with compressed air, after 4 times pulling them, got mine clean.

maybe you got it, hope you did, if not at least you know what's up.

[new_750k]

Yep, don't worry, it's nowhere near together yet, I'm leaving the bank to soak overnight at least.

I'm going to get a guitar string tomorrow and clear everything properly, I literally just took a quick look at most of it and dumped the metal bits in a bath of pinesol.

I'll go over everything in fine detail with carb cleaner/string/brush tomorrow or Friday and make sure it's all spotless.

I'm assuming that the mechanic who previously rebuilt the carbs just never took the main jet out since everything else is pretty clean.

Thanks again for your help Grady.

[new_750k]

One more question: Before I pulled the pilot screws I checked how far out they were, 2 turns on all of them. I notice that the FSM specifies 1-1/2 turns to start with whereas all the carb cleaning guides suggest 3 turns out. Is there any reason for the discrepency? Shall I just follow the FSM?

[motogrady]

1 1/2 to 2 is a good starting place.
you can get to them when it's back up and running with a real small screwdriver.
I think I ended up with 3 full turns out.

once I had mine running, and had it pulling strong to redline, it would not idle.
Backing out the pilots from 2 to 3 brought that back.

with a 4to1 exhaust, and a modified airbox that let's more air in,
I'm running 75s and 110s, with the 3 turns out, and getting 52 mpg, on stock gearing.

[new_750k]

Finally got everything back together and success! It revs properly now. At least I think it does, my tach needle is warped from the sun (I think I saw a thread about repairing those somewhere).

Thanks for all the help TOOLS and Motogrady.

There are a few more problems with the bike but they're relatively minor I think. I'll start a new thread with them eventually. Strange engine noise and theres a weird screaming noise for about a second when starting cold, almost like air pushing out past a gasket., hopefully syncing the carbs will help.

[new_750k]

Also, I checked the valve clearance last night. Looks like the PO used red silicone gasket stuff to seal the valve cover. I've heard the horror stories about this blocking oil passages and I'd like to make absolutely sure that doesn't happen. I pulled everything off the valve cover and gasket but I'm a bit worried about any bits being in the engine.

Would you guys recommend draining the oil and taking off the pan to check the strainer? Also, will I need liquid gasket when I put it back together? Is hondabond OK?

[Lucky 1]

Buy a workshop manual from Ebay before you break and destroy parts.
It will save you money.

[new_750k]

I have a clymer manual.

Why the comment?

[motogrady]

If there was a ton of silicone, and you saw a bit here or there just hanging around in bits,
yeah, I'd pull the pan and do the oil and filter also.

If you feel nothing broke off, saw nothing anywhere but on the valve cover, you may be good.

As far as manuals, the Clymer books are good, but the factory book is much better.

I use this stuff, I think it's HiTack or something, to hold the wormy valve cover gasket
in place when installing.  The black stuff in a can, has a little brush under the cap,
it's a liquid.  Brush it on a real clean cover, let it set 15 or 20 minutes, put the gasket to
the cover.  Nothing on the head side.  If it leaks, new gasket.

As far as the comment, just let it go, guys around here can get a little, how can one say it,
abrupt at times.

[TOOLS1]

The Factory service manual can be downloaded for free from the manual thread at the top of the home page here. As for a gasket sealer to use on the rubber valve cover gasket, I use Gorilla Snot (weatherstrip adhesive) to glue the casket to the valve cover.
TOOLS

[new_750k]

Here was the cover after I pulled off the major pieces:
http://i.imgur.com/C7OKegN.jpg

I only saw one strand sitting in the oil which I pulled out but I'd like to take the pan off just in case. The oil needs changing anyway...

I actually have the FSM too. Both are pretty useful.

[shinyribs]

Yeah,that's a lot of silicone in that pic. I'd definitely get rid of all that.

I know Tools mentions using Gorilla Snot in place of RTV for retaining a gasket(retaining...not sealing),but I don't see that it my area. I use Indian Head gasket shellac. All of the auto part store here carry it and I know it will hold up to high temps and constant submersion in oil. Again,I only use it to glue a gasket to a cover. I allow the gasket to did it's job normally.

Here's what it looks like: http://www.ebay.com/itm/like/370956895695?lpid=82

If you use this stuff wear gloves. It has a dauber in the jar but it's some super sticky stuff. If it gets on an area that you don't want use a little lighter fluid and a rag to clean it up.

[TOOLS1]

The Gorilla Snot also seals the gasket. If you ever use it, you will never use anything else again. I was turned on to using it back in the 80's when I was working for a Ford Dealership as a mechanic. It was all the mechanics there would use.
TOOLS