Author Topic: Engine revs out of control. (Read 738 times)

soonerbillz · « **on:** October 07, 2023, 02:01:39 PM »

I went thru this thing completely.
Rebuilt the carbs, rebuilt all the electrics.
I went to start it for the first time after rechecked everything 10k times.
and it started right up! Bit the thing revs way up and I shut it down. Checked the idle..it's not even touching the idle tab now.
Still shoots to the moon on revs as soon as I start it.. I have to kill it before it blows..
WTF???

soonerbillz · « **Reply #1 on:** October 07, 2023, 02:27:35 PM »

I replaced the cables and after getting all back together itseemed that they were sticky .
So after starting and experiencing this over revibgvthing I disconnected the cables to see if that was the problem..
Not the issue!
It still starts then slowly revs by itself up to around 5k rpm.

denward17 · « **Reply #2 on:** October 07, 2023, 02:31:17 PM »

Could the slides be set too high?

soonerbillz · « **Reply #3 on:** October 07, 2023, 02:47:18 PM »

Quote from: denward17 on October 07, 2023, 02:31:17 PM

Could the slides be set too high?

That's what I'm thinking.
Can I reset them without pulling the carbs?
I'll do whatever it takes but that really sucks if if I have to pull them again.

Mark1976 · « **Reply #4 on:** October 07, 2023, 03:50:57 PM »

Ok, well sit down and take inventory of what you've done. If it slowly climbs up maybe you've got a vacuum leak, dunno... Taking the rack off again is just a little more practice doing something no one here likes to do, but it's a necessary evil. Recheck the carb linkages, once the airchamber is off your 80% of the way there, pulling the rack itself is minor. Then after reinstalling the carbs and before putting the airchamber back on, see how it runs with just the rack on and work from there.

Phoenix · « **Reply #5 on:** October 07, 2023, 03:58:06 PM »

This is crazy. Mine did the same thing. Start it and it goes to 5000. Turns out one of my gas lines was too long and it got under the linkage on the carb rack. Size does matter. Can't be too long.

grcamna2 · « **Reply #6 on:** October 07, 2023, 04:17:08 PM »

Quote from: Mark1976 on October 07, 2023, 03:50:57 PM

Ok, well sit down and take inventory of what you've done. If it slowly climbs up maybe you've got a vacuum leak, dunno... Taking the rack off again is just a little more practice doing something no one here likes to do, but it's a necessary evil. Recheck the carb linkages, once the airchamber is off your 80% of the way there, pulling the rack itself is minor. Then after reinstalling the carbs and before putting the airchamber back on, see how it runs with just the rack on and work from there.

Did you bench-synch all four slides when you had the carbs off soonerbillz ?

Kaze · « **Reply #7 on:** October 07, 2023, 06:31:37 PM »

My 76' CB750K carbs were racing up to 3k at traffic lights until I got a vacuum synchronizer set. Turned out that my carbs were out of synch.

Just FYI most throttle cables don't come pre-lubed. I put some silcone grease spray on mine and they are much better.

dave500 · « **Reply #8 on:** October 08, 2023, 02:29:46 AM »

youve done the pre set bench sync with the slides too high,youll have wind all the adjusters down so the main idle control knob makes contact.

soonerbillz · « **Reply #9 on:** October 08, 2023, 04:02:28 AM »

Thanks guys.
I did bench st the slides for synch using a 1/8" drill bit as advised.
I'll pull the rack and double check them again. Also look for anything that could be interfering with the throttle.

ekpent · « **Reply #10 on:** October 08, 2023, 05:45:05 AM »

If the idle screw is non-functional then that would lead me to believe the slides are too high up on the adjuster setting. Have to set them correctly to leave some headroom for the idle adjustment. Would be helpful though to know the model of the bike.

rotortiller · « **Reply #11 on:** October 08, 2023, 06:39:06 AM »

I'd take the airbox off and have a boo with a mirror at the slides before performing any surgery.

Mark1976 · « **Reply #12 on:** October 08, 2023, 07:15:15 AM »

Post a pic of your sync adjusters, lets see what they look like...

MauiK3 · « **Reply #13 on:** October 08, 2023, 07:53:52 AM »

Once the carbs are off I would think it would be obvious what is causing the issue.

Little_Phil · « **Reply #14 on:** October 08, 2023, 07:58:34 AM »

Where did you put the 1/8" drill? Is your fully closed now 1/8" open? Sounds far too much.

bryanj · « **Reply #15 on:** October 08, 2023, 09:18:51 AM »

1/8 is too big and you need it on the flat side of slide, engine side

PeWe · « **Reply #16 on:** October 08, 2023, 10:24:52 AM »

I made a mistake when doing a bench sync.
I did not check that all throttles could close by adjusting the idle screw.

Engine had a nice even idle of 1800 rpm.
I adjusted all nuts by 1/4 turn up so throttles went down.
Finally a good idle. I synced them with the vacuum clock and checked that idle could be set lower than the final idle.

soonerbillz · « **Reply #17 on:** October 08, 2023, 11:47:34 AM »

So I pulled the carbs.

So here's some pics of the height adjusters now. Also some pics of the slides in the fully closed position with the idle adjustment screw fully screw out off the tab
Looks like they are way to high. In fact I'm sure of it.
Back to bench synch stage I am.

bryanj · « **Reply #18 on:** October 08, 2023, 12:59:02 PM »

Not just way too high, incredibly way to high

soonerbillz · « **Reply #19 on:** October 08, 2023, 02:11:02 PM »

So obviously I was smoking crack when I did the bench synch.
I reset the slides to proper and reinstalled the carbs and air box stuff.
Started the bike and now it runs good.
Thanks for all the help!

TwoTired · « **Reply #20 on:** October 08, 2023, 02:18:26 PM »

Quote from: soonerbillz on October 08, 2023, 04:02:28 AM

Thanks guys.
I did bench st the slides for synch using a 1/8" drill bit as advised.

Always hated that advise. Those advisors are never around when all the slides are adjusted too high. I speculate they are all parts breakers wanting to sell the remains of your bike.

Mark1976 · « **Reply #21 on:** October 08, 2023, 03:36:38 PM »

Live and learn, glad you've got it reset.

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Author Topic: Engine revs out of control. (Read 738 times)