Topic: Carbs Cleaned - Engine Won't Start!

[braincube]

I recently cleaned and sealed the gas tank of my 1982 Honda CB650, and decided to clean the carburetors for consistency. Everything had been infiltrated by rust from the tank. While I was cleaning the carburetors, I decided to replace the T-joint vent tubes that had rotted between the carburetors. This turned out to be a mistake - it required that I completely disassemble all four carburetors, and was ultimately not all that important. The reassembly was difficult, though I managed it.

After putting the carburetors back on the engine, tightening everything up, connecting all the hoses, charging my battery, introducing new fuel ...

The engine won't turn over. It cranks, and cranks, but nothing. I'm at my wits end. Summer is here and I'd like to get back on my bike. I'm an admitted beginner - this is my first motorcycle project. Any help systematically troubleshooting would be much appreciated. I've tinkered with nearly everything, so everything is suspect..

[Thamuz]

Are you getting fuel through the petcock?  Did you clean the filter off in the tank? Have you pulled out the drainplug on a carb?  Did you clean the jets and make sure they have no rust?  Did you replace all the fuel lines? Are you getting spark?

Sorry for the list, just some ideas.  Sometimes it helps to double check your carbs.  Pulling a floatbowl and seeing whats inside might be good too

[dave500]

how full is the tank?might need reserve used?

[zipper]

I would suggest checking if fuel is arriving to the carbs, you could try to carefully unscrew the brass screw on the carburetor bowl with a cloth under to see if fuel drips out.

If fuel is there, did you leave untouched all the throttle link arms, and how did you regulate the air screws on the carbs? have you tuned them the right way?

[ekpent]

Very easy to check for spark by putting an extra spark plug on a plug boot and grounding on engine to check for spark. Make sure kill switch is on. If spark then move to fuel.

[braincube]

Okay, thanks - here's my plan:

First, I'm gonna check to see if gas is getting to the carburetors.
Second, I intend to check to see if my spark plugs are firing. If not I'll replace them with new ones and check again.
Third, I'll spray starter fluid into the cylinders, and see if it starts.

If not, I have no idea what to do.  I'll know more this afternoon.  Wish me luck!

[zipper]

Good luck! Let us know how it goes.

PS: Be careful with the choke lever position (it can often be misinterpreted), when you try to start the engine it should be set horizontally, and when the bike is running it should be pointing downwards (if i remember correctly)

[braincube]

At first the gas wasn't getting to the carburetors.  I used starter fluid in the airbox and got the engine to turn over a couple times, with the choke closed. When I opened the choke, the engine would die.  I played with the throttle and choke for a while, and continued to use starter fluid.  I finally got it to idle before exhausting my battery, but I killed the engine because it was idling at such high RPMs (~6,000).  The engine got hot quickly.  I checked the carburetors and each contained gasoline.  The synchronizer adjusting screws between the carbs are set to a visual approximation of equal, though I obviously haven't synchronized them correctly yet.  My pilot screws are all set to 3.25 turns out from the lightly seated position.  My fast idle adjusting screw was approximately 10 turns out from the fully closed position. 

I checked the spark plugs - they all look good, they're seated correctly, and they're all firing correctly.  All four exhaust pipes were hot.  I'd like to check whether I've connected the spark plug wires to the right spark plugs - to avoid incorrect firing order.  Does anyone know exactly how the wires should be connected?  If so, let me know and I'll double-check.  Once the engine is running I'll check the ignition timing - I've heard this can really screw up engine performance.

Also, I noted a gasoline leak in either the Number 2 or Number 3 carburetor, though I suspect that it's the accelerator pump assembly.  Any similar problems?  As for now, I'm gonna disregard this and just tackle it later..

[ekpent]

Do you have a repair manual or are you winging it ? Nothing personnel, just asking..

[braincube]

I'm using a repair manual - Clymer.  I wouldn't be able to wing it. Don't worry, man - no offense taken..

[CR125Honda]

Just did a quick search for you and it looks like that bike has a vacuum petcock.

Make sure your vacuum line is hooked up and not cracked.

Also, see if there a "prime" position.

If you have that, turn it to "prime" wait a few minutes to fill the carbs and try to start.

Ken

[braincube]

Unfortunately there's no 'prime' position on the petcock valve.  The vacuum line is hooked up, no visible cracks or leaking at the hose.  Accelerator pump on Carburetor No. 2 appears to be leaking fuel.  Also, it's worth noting that the rubber boots on my airbox only sit reasonably well on my carburetor assembly, and don't clamp firmly or with any precision.  Is it possible that the combination of these two issues have created a poor vacuum seal, and gasoline isn't being drawn into the system very well?

Just did a quick search for you and it looks like that bike has a vacuum petcock.

Make sure your vacuum line is hooked up and not cracked.

Also, see if there a "prime" position.

If you have that, turn it to "prime" wait a few minutes to fill the carbs and try to start.

Ken

[CR125Honda]

Assuming you removed the petcock when you sealed the tank.

Did you dis-assemble/clean the petcock?

[braincube]

Actually, no I didn't.  I do think it would be a good idea, however.  Is the process difficult/time consuming?  I think there's a pretty good walkthrough in the Clymer.  I'd imagine it'd be easier than pulling the carburetor out YET AGAIN and inspecting the accelerator pump assembly.  But I'll probably have to do that too..

[RJ CB450]

Number one leak on the 650 carbs once apart are the fuel line o-rings.  The T vents are vital, they keep floats from getting dirt and garbage in plus other things.  To prime, just pop the vacuum line of number three and apply remotr vacuum by a hand pump or just be like me and suck on the line :3

Bowls should be full, just crack the drain screw.  You said you cleaned em but this mean fully apart? If not, anything could be blocked bad.  Once together, I use gauged copper wire to bench set the throttle butterflies.  Put one piece in num 2 and another piece to set 1-3-4.  Not starting, can be very tough cold and unsynced.  Choke on, fuel in, then crank.  Should here popping if trying to start.  Might need to give a little throttle if stop set to high.

Also, default start for mix screws is 1.5 turns out from seat.  Will have to synce once running.  If still problem.  Might need to grab a quick vid.  A possible listen might help.

[braincube]

Thanks for all the information - tomorrow I'll reset the pilot screws to 1.5 turns from lightly seated.  I'm glad to hear the T-vents are vital, as they were incredibly difficult to install.  I cleaned the carburetors in the standard way, one at a time on the bench, elbow grease and time.  However, I was forced to completely disassemble the carburetor - fully apart - for the T-vent replacement.

Which o-rings are the carburetor fuel line o-rings - do you have a diagram?  I can't find an explicit picture in the Clymer manual.  I suspect that they are the o-rings at the ends of each metal connection tube between each carburetor. 

If I can't get the motorcycle idling tomorrow, I'll make a video and/or take photos.

Number one leak on the 650 carbs once apart are the fuel line o-rings.  The T vents are vital, they keep floats from getting dirt and garbage in plus other things.  To prime, just pop the vacuum line of number three and apply remotr vacuum by a hand pump or just be like me and suck on the line :3

Bowls should be full, just crack the drain screw.  You said you cleaned em but this mean fully apart? If not, anything could be blocked bad.  Once together, I use gauged copper wire to bench set the throttle butterflies.  Put one piece in num 2 and another piece to set 1-3-4.  Not starting, can be very tough cold and unsynced.  Choke on, fuel in, then crank.  Should here popping if trying to start.  Might need to give a little throttle if stop set to high.

Also, default start for mix screws is 1.5 turns out from seat.  Will have to synce once running.  If still problem.  Might need to grab a quick vid.  A possible listen might help.

[CR125Honda]

Actually, no I didn't.  I do think it would be a good idea, however.

Chances are you sealed the pickup tubes with the sealant.

[RJ CB450]

For cb125, 82 carbs that I work on all have nitrile gaskets so no sealant should have been used.

As for fuel line o-rings, yeah.  Between the carbs, those little tubes.  They harden over time so once disturbed, might not seal.  They are a standard size I dont have handy right now but must be fuel safe such as nitrile.  Not generic rubber.

Also, fast idle, try turning down throttle stop and is there some slack in throttle? IE throttle holding it open?  Too much throttle and wont start as well.

[braincube]

I removed the petcock, taped the hole shut where the petcock had been seated, added the sealant used to the interior of the tank, and slowly rotated the tank to coat the inside.  I didn't fully disassemble the petcock once removed from the tank.  I didn't want to open a can of worms if it wasn't completely necessary.

Knowing this, is it still possible I sealed the pickup tubes with the sealant?

Actually, no I didn't.  I do think it would be a good idea, however.

Chances are you sealed the pickup tubes with the sealant.

[iron_worker]

Some tanks have an interior "sock-type" fuel filter ... I'm pretty sure that would have come out with the petcock though when you removed it.

IW

[braincube]

UPDATE:
After difficulty starting, I got the motorcycle to idle at about 1,300 RPM with the choke open. There is no sign of the fuel leak that I thought was related to the accelerator pump assembly, though was probably the fuel line O-rings. I've got video if you think it may be helpful.

However, when I apply the throttle, the engine abruptly shuts off. Any ideas why?

[RJ CB450]

Lets start with tuning issues.  If you got the video, post er up and we can take a listen.  1300 with choke.  Even warm, does it stall when you open choke?  If so, my guess is running lean.  If the mix screws are set to the 1.5 default, give em a half turn (so to 2.0) and then try again.  On top of that, the CV carbs are so finicky to throttle when out of sync, that isn't helping.  I did as you did and used some bench adjust to rough set the throttle.  I used gauged wire, and still my carbs were off a fair bit.  Also, until my carbs were synced, I couldn't run it below 1500.

It is a delicate balancing, and not a quick tune I found.  Would get it idling, then wait a bit so not to overheat.  Then sync them, then mix, sync again, then more fine tuning of the fuel until they are all running proper.  I pulled my plugs yesterday for another inspection.  Even with it running smooth, 1 and 3 were rich, 2 and 4 were lean a bit.  Just dial the mix screws out a bit more until you can get it idling off choke.  After that, do a sync.  Once syncronized, just keep tweaking the fuel.  Note, I am assuming still have factory airbox.  If not, and are running pod filters, then it will need a bit more technical work.

Just to example the problems not being in sync has for starting.  Mine, would be a nice warm day, but if sat for a day, I could almost kill the battery getting it to start.  Cooler mornings,  It was a guaranteed pushstart.  With just adjusting fuel and the sync, doesn't even have to crank barely.  Instant start most every time.

[iron_worker]

Do you have the airbox on?

IW

[braincube]

Yeah, I'm running with the stock airbox.  It's currently installed.  I had removed it briefly to spray some starter fluid into the airbox and carburetors.  I was thinking about upgrading to the pod filters - but after reading about the difficulties of the pod filter conversion / jetting process, I thought it'd be best to stick with the original setup.   The power gains are minimal over a well-tuned stock engine, in my opinion.

[RJ CB450]

Yeah.  Pods themselves arent bad.  When set up proper, they are quite nice.  The first CV carbs on the 450 DOHC had essentially pod filters.  Main reason they dont work is the loss of the intake "horn".  The jetting is sorta a stopgap fix.  As for power gain, i would say over stock would be barely measurable if not a loss when direct mount.

Also when doing your fuel adjust, use your ears and sense of touch to adjust idle screws for fuel mix.  Can get you an idea which cylinders are off.  Feel and listen to the exhaust pulses.