breaking up past 6,000

1982 750 SECA, revs and pulls fine up to around 6,000 RPM then it hits a wall starts breaking up and sputtering a little. Stays at 6,000 on WOT. If i ease off the throttle to about 3/4 it will slowly keep pushing up past 6,000 but just barely and usually run out of room to run before it will climb anywhere close to 7k-7500.

Thinking dirty carbs? or possibly valve clearances but sounds more like carbs to me. Thoughts?? I just bought this bike in mid March with 25k miles on. Its in impeccable condition and the previous owner promised he took care of it but of course no way to tell what maintenance was done.

 

Prolly need to take your carbs off and check those emusion tubes. It sounds like it's a lean condition on the mains.

Make sure your emulsion tubes have all the little holes clean and clear, and the polish the tubes up nice!

 

VALVE CLEARANCES first or you won't get a decent vacuum sync.

Carbs are either dirty, or may need throttle shaft seals, or both.

Might also want to have a peek at the air filter.

 

i have a similar issue with razor. valve clearances have been checked and checked and rechecked. all in spec now. throttle shaft seals replaced and carbs were soaked in carb dip over back at christmas time. could they be dirty by now already?

what could be faulty with the air filter? sorry if its a dumb question

 

Not a dumb question.

Old, dirty, clogged, possibly oil-soaked; at the very least deserving of a peek...

 

sorry for the blurry picture but I discovered a washer under the emulsion tube (in the bowl side of carb) to be loose. meaning that there is a clearance between the jet portion and the rest of the tube where I could wiggle the washer. is this a bad thing? also, how do you tighten these without having the tube spin as well?

 

by virtue of Len's catalog I could verify they are suppose to be copper. wouldn't you believe it that one of the four of these shim washers was not even copper or the correct size.. lol stopped at ACE hardware and got 4 new ones 10mm diameter..checked all other air and fuel jets so hoping this kind of problem goes away

 

DUDE. Those main jets look like they've been chewed by wolves. I'd replace them, honestly. Anything that tore up won't flow anything smoothly. Urk.

 

Before you install the New MAINS you need.

Remove the Flat Washer.
Knock-out the Center Emulsion Tube.
(Requires removing Diaphragm Pistons)
Clean Tubes:
Inside Diameter. Scrub with 3 Pipe Cleaners twisted together.
Outside Diameter. Remove Foreign Matter; Shine Brass.
Probe Metering Holes. 16~20 Holes in through the Body of the Tube.

With TUBES Out:
Flush Main AIR Jet Passage.
Spray Carb Cleaner Directly into opening of Main AIR Jet. Observe it exit in the Center Tubes empty cylinder.

Scrub & Polish Bores.
(Search -- "Clunk Test" )
Remove Oxidation from Bore.
Polish Inside Diameter of Bore.
Insure that PISTON Rises and Falls ==> Effortlessly.

 

finally got around to doing some of the simpler tasks. Spark plugs all looked good, air filter had some loose debris in it but nothing bad, not even stained. Did have a slight gas odor but figured thats just the nature of being next to the carbs.

Hopefully will have time to rip the carbs off tomorrow. Just how hard is that to do on these bikes? Seems like some decent clearance. On my other bike I've had for a while it was damn near impossible to get the carbs out with the massive airbox in the way.

 

Your sig doesn't say exactly which bike; but most of them have slotted airbox mounts allowing it to be slid rearward once those bolts are loosened. On the 550s they hid one bolt under the tool tray so look around. Probably want to assume 3 bolts or look in the manual?

It's still a beotch.

Another thing that helps is a non-destructive RickCoMatic patent pending wooden hammer handle pry bar. Go to the hardware store and buy a new hammer handle. Cut off the split part where the head was supposed to go; and lightly dress the edges. Voila! Nice wooden pry bar that won't gouge up anything. I have two of them (different sizes, one framing, one ball-pein) and they do get a workout in the shop.

***KUDOS to Rick; it's one of the very best things I learned here on the site and I could KICK myself for not having thought of it about 35 years ago.***

Also, they are generally easier to pull out the right side because the alternator and starter are on the left and kinda in the way.

It's still a beotch.

 

sorry said in the original post 82 750 seca. thanks for the advice everyone heres to hoping.

 

Took the tank off to get at the valve cover and found the vacuum line to the petcock was ripped. Replaced it with some extra tubing i had and it runs great now.

measured the valves clearances while i had the tank off just to see. most where fine, but one on the inlet side was at .18mm (max .15 according to Haynes manual) and one was up to .23 on the exhaust side (max of .20). Think its actually worth swapping them out or is that close enough to the limits? In my experience they tighten up as they go anyway correct?

 

correct, they tighten, but somone today brought to my attention that if they are out it could possible lean the mixture since the lobe is not getting to the shim as fast at the rest. They're 8 bucks each and it's open. Chacal will have them at your door so fast, keep it open and do it bud. you'll have peice of mind and the next time some sypmtom shows itself you'll know what to rule out and what you haven't serviced or checked yet. By the way, you should replace your rear brake shoes. Fitz will tell ya about the delamination issue, or search him as the author for it. 25 bucks could save ya life here

 

correct, they tighten, but somone today brought to my attention that if they are out it could possible lean the mixture since the lobe is not getting to the shim as fast at the rest. They're 8 bucks each and it's open. Chacal will have them at your door so fast, keep it open and do it bud. you'll have peice of mind and the next time some sypmtom shows itself you'll know what to rule out and what you haven't serviced or checked yet. By the way, you should replace your rear brake shoes. Fitz will tell ya about the delamination issue, or search him as the author for it. 25 bucks could save ya life here

 

When the Engine starts to act-up at higher revolutions, but otherwise behaves normally, ... It's a calling-card for two things you want to attend to when you Clean the Carbs.

1.) The Center Emulsion Tubes ... (a.k.a. "Nozzles')
Press or Tap them out through the top.
Clean the center Inside Diameter -- Brush with a trio of Pipe Cleaners.
Scrub and Polish the Outside until the Brass is bright and clean.
Probe all the cross-drilled, tiny Air Metering Passages. Look through the holes and check for light coming trough the other set.

2.) The Diaphragm Piston Bores
Scrub and Clean the Bores.
Polish them.
Make sure the Piston travels completely free of sticking.

Clogged Tube <> Cleaned Tube <> Scrub Bore <> Polished Bore

 

If the tubing you had laying around wasn't actual vacuum line you'll want to re-replace it before you have a new problem: If it's not actual vacuum line it could collapse in on itself once it's hot and gets vacuum applied to it.

I recommend you double-check the valve clearances, and then get them in spec. Then re-check every 5000 miles as recommended. Don't run them out-of-spec hoping they'll "self correct."