Hotcam WR426 - Timing/Jetting HELP!


5 replies to this topic
  • black_chrome

Posted July 16, 2013 - 07:03 AM

#1

I had my WR426 engine rebuilt (needed a new crankshaft since the flywheel threads stripped), and at the same time had all new bearings put in, as well as both intake and exhaust (auto-decomp) Hotcams. During this time, the carb sat with some crappy gas in it, which I have cleaned abd blew out the jets and passages with cab cleaner and compressed air. Since I have had the bike all back together, it is almost impossible to start and keep running. I have only gotten it to start by kickstarting once - otherwise it takes MANY passes at bump starting it before it finally runs, and when it does I usually have to open the throttle while bumping it which doesnt seem right for an FCR carb (choke on, idle screw opened pretty far). It will backfire every once in a while when kicking it.

The current jetting configuration in the bike:
Stock Needle - clip in 4th position
172 Main Jet
48 Pilot Jet
Stock Air Jets

This seems like a pretty rich setup where I should at least be able to start and run the bike and dial it back a bit afterwards but its extremely hard to start. Ive had it running with the stock pilot (42) jet as well as the 48 and played with the fuel screw in both setups and the bike still doesnt seem to run right in either situation.

I had it idling somewhat reasonably at a couple points in time and decided to take it for a ride and just see how it felt otherwise and it seemed great. Since it was just rebuilt I was hoping I could break the engine in a bit and this might help with starting but each of the 3 or so times I try to ride it, I get about 1/2 - 3/4 mi away and the bike starts to bog and stalls out then wont start, like it ran out of fuel. I looked down and since I have a clear fuel filter I could see gas flowing into the cab after it died as if the bowl was empty, so there might be some kind of weird float issue too, not sure if this is related to the starting/idle problem but I dont know where to begin with debugging it at this point. I have checked the cam timing which seems right to me, the clearance is a little loose on the exh cams right now but the engine builder told me they wear tight and it should be fine (?). When the piston is at TDC the cam lobes are both angled upwards away from each other. I saw in a couple places the lobes should basically be flat across at the point, like this picture:
http://s661.photobuc...d98bbf.jpg.html

However mine are not, they are both angled upward a bit - does that seem right? My timing marks seem to line up with the head the way it is now...

I also have a JD Jet Kit and was contemplating putting that in which comes with an Oring to do the AP mod, but that would be adding another variable to an already long list of variables, so I wanted some input on where I currently am first.

Please help me figure out where to begin with sorting this out - I know this is a long post with a shitshow of variables but Im really stuck with this thing right now. I didnt do the engine work myself - I just sent the engine out to be rebuilt alone and dont have a way of getting the complete bike out to the guy who did the work, so Im trying to get this sorted out myself.

Thanks!

Edited by black_chrome, July 16, 2013 - 07:03 AM.


  • black_chrome

Posted July 23, 2013 - 07:16 AM

#2

Anyone??

At least any input on any of the individual issues?
-Hard starting (bump start only)
-Stalling after ~1/2 mile of riding or so
-Comment on current jetting/going to the JD kit
-Cam timing relative to the picture in the link

Thanks

  • moto2000

Posted July 23, 2013 - 07:45 PM

#3

Random thoughts.....

Have a pic of how your cams are setup? The lobes are usually similar to the pic you posted (lobes laying somewhat flat)

Are you sure you are at tdc? Verify by putting a straw or something in the plug hole and rotating flywheel back and forth checking timing mark on flywheel.

Have a manual?

New timing chain with rebuild?

Have good fuel flow thru petcock?

Little o-ring, washer and spring below the fuel screw?

Had the slide out of carb? I believe you can install backwards or incorrectly and have running issues (search for info)

What are the valve clearances set at? Did you double check your mechanics work? What clearances does Hotcams call for?

Testing with a new spark plug?


So I guess two areas I would concentrate on .....verify cam timing /clearance and go thru the carb with a fine tooth comb (settings and fuel flow)

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  • KennyMc

Posted July 23, 2013 - 08:44 PM

#4

And replace all your jets, don't just "blow them out" especially the pilot jet. Cheap insurance. Good luck.

  • Krannie McKranface

Posted July 23, 2013 - 09:04 PM

#5

Anyone??

At least any input on any of the individual issues?
-Hard starting (bump start only) - MORE LIKELY TO BE VALVE CLEARANCES
-Stalling after ~1/2 mile of riding or so - STALLING FROM WHAT, NO IDLE, OR NO POWER
-Comment on current jetting/going to the JD kit - JETTING NUMBERS ARE FINE.
-Cam timing relative to the picture in the link

Thanks


The stock needle is lean.
Go JD Red or NCVS
You need to follow proper fuel screw adjustment procedure for it to work
Pilot is for idle ONLY. 45 will work.
Clean, lubed, un-corroded hot start and choke plungers are a must
Clean gunk free main air jet (in the bell)

It's harder to start a rich jetting than it is lean....

  • KennyMc

Posted July 24, 2013 - 05:59 AM

#6

Pilot jet circuit is for idle to 1/4 throttle.




 
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