250-500cc '11 wr 300 hard starting w/new high comp head; jetting issue?

[Brian Scott]

I recently replaced the top end w/a vertex kit (120 hrs, 1200 miles or so) and installed a new high compresion head. I've been running the PWK AS w/the red JD needle, 2nd or 3rd groove (can't remember which), 42 PJ, 175 MJ, AS 1 1/2 turn out, sea level to 1000 feet, 40-60 degrees F, stock exhaust, no other engine mods, 50:1 92 octane fuel w/maxima super M, mostly tight woods riding in the usually cool and damp Pacific Northwest. This jetting seemed spot on w/the stock head. The compression increase with the new head is quite noticeable at the kickstarter and the occasional kickback is even more agressive than w/the stock head. I fully expected the increase in resistance at the kickstarter after I installed the new head; however, starting is much more difficult now and I suspect it's a jetting/fuel delivery issue. The choke must absolutely be on when cold and it takes many kicks to breath life into it. I've also had to turn my air screw in from 1 1/2 turns w/the stock head to 1/2 turn with the new head (still hard to start). When warmed up and the choke is off, it still takes several kicks to fire it up, but then it seems to run fine with a noticeable increase in power across the power band. With the stock head, hot and cold starting was a simple afair. I'm going to try a 45 PJ soon to see how this affects starting. I've checked for air leaks and can't find any. I'll replace the plug to see how that affects matters, but I did so when I replaced the top end, so I doubt that's the culprit. Any ideas or suggestions on how to get my steed to fire up a little easier? Thanks and sorry to be long winded.

 

[454x]

Try 1 size bigger pilot jet.

 

[Ghunt800]

Try staring the bike with the head light turned off or disconnected. That was a world of difference in starting up by 2013 WR300.

 

[Bryan M]

couple things...you sound lean on the pilot jet, but mine was the opposite, i had to lean it out to get it to start easier...now mine is ever so slightly lean as it comes to temp but once warm its fine. otherwise it was a bear. yours tho does sound lean. your air screw in that far would typically mean lean. the other thing i can tell you is the kicking method i read on here a while back, make sure you get the piston almost to TDC ( move the kick starter slowly until you fell the compression coming up, then let the kickstarter come back to the top and give it a solid kick). try 1 size larger PJ and kicking it like i said if you dont already do that and see what it does.

 

[Brian Scott]

Update: I removed the light and speed/odometer for yesterday's harescramble; installed a new plug (the old one looked ok); removed the carb, removed the PJ and cleaned the PJ circuit w/contact cleaner (it didn't looked clogged), reinstalled the 42 PJ (didn't have the 45 PJ yet), set the float height at about 18 mm or so, and blew compressed air through all the circuits; and then re-installed carb. It started on the 3rd kick w/the choke on. Once warmed up, it was usually a one or two kick affair to start, even in gear. Sweet! Also had to turn the AS back out to about 1.5 turns. Go figure. I'm not sure how much removing the light and speedo contributed, but doing so does lessen the electrical load allowing more for the spark.

I have to remove my carb again this week to examine a problem that developed half way through my race, so I'll install the 45 PJ just to see how it affects starting, but only after I figure what was causing my engine to start bogging severely and stall. At first I was able to just rev the engine to keep it going, but it became so bad during the last lap that I nearly didn't finish the race because it would bog and stall and wouldn't start for several minutes after much kicking and cussing. Post race inspection revealed a mostly clean plug w/little carbon on it (no fouling) and that the bowl is getting gas. However, 3 of 4 carb vent hose were full of water. Before the race I had routed the vent hoses up behind the carb near the air box to keep them safe from any water not thinking they would fill w/condensation effectively creating a vapor block. Blame it on the high humidity and 48 degree temp? I'm not sure if this was the only cause and how blocking 3 of the 4 vents affects the carb. I may have an electrical/ground issue somewhere that I'll look into, but I'm tempted to rule it out since I was able to restart the bike and avoid stalling occasionally by keeping the revs ups. After the race I installed another new plug and drained the vent hoses and routed them downward by the shock to allow them to drain freely. It started first kick, but then bogged and stalled and took many kicks to get going again....hmmm. So I'm wondering if I have some water issues in the carb now.

Bryan M, I've been starting my 300 that exact same way since I bought it nearly 2 years ago. Nothing else works. It's also the same technique I have to use on my Honda CR 500.

 

[Bryan M]

Update: I removed the light and speed/odometer for yesterday's harescramble; installed a new plug (the old one looked ok); removed the carb, removed the PJ and cleaned the PJ circuit w/contact cleaner (it didn't looked clogged), reinstalled the 42 PJ (didn't have the 45 PJ yet), set the float height at about 18 mm or so, and blew compressed air through all the circuits; and then re-installed carb. It started on the 3rd kick w/the choke on. Once warmed up, it was usually a one or two kick affair to start, even in gear. Sweet! Also had to turn the AS back out to about 1.5 turns. Go figure. I'm not sure how much removing the light and speedo contributed, but doing so does lessen the electrical load allowing more for the spark.

I have to remove my carb again this week to examine a problem that developed half way through my race, so I'll install the 45 PJ just to see how it affects starting, but only after I figure what was causing my engine to start bogging severely and stall. At first I was able to just rev the engine to keep it going, but it became so bad during the last lap that I nearly didn't finish the race because it would bog and stall and wouldn't start for several minutes after much kicking and cussing. Post race inspection revealed a mostly clean plug w/little carbon on it (no fouling) and that the bowl is getting gas. However, 3 of 4 carb vent hose were full of water. Before the race I had routed the vent hoses up behind the carb near the air box to keep them safe from any water not thinking they would fill w/condensation effectively creating a vapor block. Blame it on the high humidity and 48 degree temp? I'm not sure if this was the only cause and how blocking 3 of the 4 vents affects the carb. I may have an electrical/ground issue somewhere that I'll look into, but I'm tempted to rule it out since I was able to restart the bike and avoid stalling occasionally by keeping the revs ups. After the race I installed another new plug and drained the vent hoses and routed them downward by the shock to allow them to drain freely. It started first kick, but then bogged and stalled and took many kicks to get going again....hmmm. So I'm wondering if I have some water issues in the carb now.

Bryan M, I've been starting my 300 that exact same way since I bought it nearly 2 years ago. Nothing else works. It's also the same technique I have to use on my Honda CR 500.

Ok good! I have seen some guys just kick and kick lol...most bikes have a routine where they light easier. FWIW my gas gas hated starting with the light on...it also sounds like you may have had a clogged pilot. I wouldnt change it to a 45 if it ran better now with the a/s 1.5 turns out.

 

[PC.]

Before you try to start the bike next time lean it over until gas runs out the carb overflow tubes and then try to start it. If it helps then the floats are not adjusted properly. This was the issue when my 300 was a bear to start cold with the PWK38.