Rebuild - first start issues!

tigertim20, Dec 7, 1:18am
hey all.
Just rebuilt a motorcycle motor. got it all back together again,
Tried to start it, it took a while to get it to fire, but when it did, it revvs it's tits off. e.g. when i start it, no choke, and no throttle, it revs itself almost through to redline and sits there by itself.
I only let it do it for a few seconds, before shutting it off in case something is wrong.

I did wonder, will it just be that when trying to start it, It dumped a heap of fuel into the engine, which it will just burn off after a minute, then return to normal by itself! - or is there something else i havent thought of!

The engine is a kawasaki 250cc motorcycle engine, Inline 4, with carbs. I figured this issue is unlikely to be a bike specific one, hence me asking for advice here.
any help appreciated.

unclejake, Dec 7, 1:20am
There is a fair chance that yuo have introcuded a vacuum leak

tigertim20, Dec 7, 1:26am
Bugger. wheres the most likely culprit!

ceebee2, Dec 7, 1:32am
Spray CRC around likely places and it will rev even more if there is a leak.easy peasy.

tigertim20, Dec 7, 1:52am
its pretty much already at redline.
So i need to be checking where the carbs meet the head, where the airbox joins the carbs, and the vacuum hose that runs from the carb manifold to the fuel petcock to operate the diaphragm.
anywhere else!

mrfxit, Dec 7, 2:12am
Yea .
get better ear muff's

unclejake, Dec 7, 2:13am
The airbox or fuel line are unlikely to be the problem but if you use brakeclean the engine will stall when you spray it on the leak.

First you should check to confirm that you don't have a linkage holding a carb open or a stuck carb slider.

mrfxit, Dec 7, 2:15am
Make up a heavy THICK foamthen spread that all around the carbs/ joints /hoses etc & start her up for a few seconds/ then go searching for where the foam is missing.

If none is missing, then it's an internal hose/ joint problem or possibly butterflys loose/ sprung wrong way around .>>>

mrfxit, Dec 7, 2:20am
What ever it is, will be between the carby air cleaner face & the block. (easy peasy aye)

Had a Honda CB175 many years ago that I rebuilt & it when 1st started, it ran hairy as hell & revved REALLY REALLY well on full throttle.
.Cam timing on chain was off a tad. (just a thought)

kazbanz, Dec 7, 2:31am
Tim--before doing anything else just KISSit mate.
check the routing of the throttle cables. check the linkages etc in the carbshavent got mangled or bent a bit. -basicly trace the mechanicals right back from the twistgrip down to the carbs.
One quick test is --How much twist is there in the throttle! if it aint moving--theres ya problem
in my experience that is the problem 95% of the time

crzyhrse, Dec 7, 2:50am
Intake rubbers. It's pretty much the only place it can be.

Presumably you've backed the idle stop adjustment off and confirmed the cable freeplay and that the butterflies are actually closing.

Also check the choke operation and confirm that each and every carb plunger moves with the choke mechanism.

tigertim20, Dec 7, 3:00am
Just had a second run and still had the same issue, came back inside to read this, and this post reminded me that I wound the idle adjuster in a fair ways to make it easier to loosen the throttle cables when removing the carbs. I will go and check if thats what it is in a minute. Hopefully it is, this is why TM can be great, I get into a job sometimes and cant see the woods for the trees mentality sets in when I cock something up, I immediately assume my shag us is massive and terminal! lol.
Will be back if that aint the problem.
Might be time for another bourbon I think

richard198, Dec 7, 3:00am
"It dumped a heap of fuel into the engine".was that due to full throttle or someone pouring petrol!
If your throttle cable is not wound open, ie,closed, it might be worth trying again without all that fuel.
Have a board or similar to choke the inlets if it gets away on you.

loonee-dial-111, Dec 7, 4:13am
I have a CBR250 inline 4 which I have rebuilt far too many times and I presume yours is similar enough.
If it was a leak you would have to have a vacuum leak on every one of your four carbs! If your bike is like mine, a leak on the air cleaner side would not work as mine won't rev over 9000rpm (18000 redline) when the air box is off.
Sounds like a stuck throttle issue.
Have you looked at the butterfly valves & tried starting it with the air box off!

tigertim20, Dec 7, 4:57am
It was the idle adjuster. Id wound it in to make it easier to remove the dual throttle cables when I removed them, and I had forgotten to wind it back out.
Cheers for the insight, Have a beer and a laugh at my expense! haha

mike77, Dec 7, 5:02am
Awesome tim, a message board with a problem, reasoned solutions and no name calling!
This would have to be a first!

crzyhrse, Dec 7, 5:21am
Sod off, you clown!

unclejake, Dec 7, 5:48am
Good news. Well done.

tigertim20, Dec 7, 6:09am
Nah, done it a few times on motoring.
I did foray into parenting the other week to troll. Worked a treat, LOTS of name calling. It all evens out i guess

kazbanz, Dec 7, 6:15am
good news TT -I diddn't think of the idle adjuster

mike77, Dec 7, 9:33am
Thats better!

mellisa2000, Dec 7, 9:38am
Shot! Job done, hopefully no harm done!
All the best.

kazbanz, May 14, 10:40am
Hey TT--if its any consolation. I was recently "running in" a racebike engine. After 5 laps the owner waved me in and yelled at me.
"NOT LIKE THAT -RIDE IT LIKE YOU STOLE IT"-I'd been easing it up and down the revs like I always used tobut nope give it stick. --so maybee you did the right thing by mistake