Jump to content
Sign in to follow this  

WR300 surge at decel and idle

Recommended Posts

This is quite the issue, and has me and my mechanic guessing. 

The primary issue is a surge at idle once the bike has warmed up. The bike starts, runs, and accelerates, but when I let off the throttle, rolling or still, it goes "gungk, gungk, gungk" at short and slightly irregular intervals. The other issue is that the idle screw on the carb must be turned almost all the way in to get it to idle.

We carefully and thoroughly rebuilt and jetted both the Kehien PWK 38 and the stock Mikuni carbs. We reasoned it was likely rich jetting; it wouldn't tolerate the choke, the plug was wet after idle, and we could turn out the air idle screw all the way to make it run better. It still ran really rich at idle despite the smallest available idle jets, and the surge remained no matter what. I'm convinced it's not a carb problem.

We've also replaced the reeds and the reed block gasket, and have sprayed cleaner around the engine to see if we could detect air leaks while it was running--nope.

So what's left?

The previous owner did the top end just before I bought it, but used black RTV sealant instead of a base gasket. It looks like a messy seal and the heads sits so low on the engine that the cylinder touches the clutch cable. I've read about high compression, squish, and port timing issues, so next on my list is to put the standard base gasket on to see what that does.

I've gotten comments that the surge seems like a lean condition (despite the rich symptoms at idle), so maybe there's a problem with the crank seals. There is no gear oil consumption, however. After the base gasket, I try crank seals.

Anyone else have this issue? Any insights or suggestions are appreciated.

Share this post


Link to post
Share on other sites

Does it smoke a lot all the time? Then it’s a left side crank seal but that would follow with gear oil consumption. Remove ignition cover on right and spray starting fluid behind spinning flywheel while motor is running. That will test for air leak there. 

Definitely install correct base gasket next. 

Share this post


Link to post
Share on other sites
1 hour ago, xeridad said:

This is quite the issue, and has me and my mechanic guessing. 

The primary issue is a surge at idle once the bike has warmed up. The bike starts, runs, and accelerates, but when I let off the throttle, rolling or still, it goes "gungk, gungk, gungk" at short and slightly irregular intervals. The other issue is that the idle screw on the carb must be turned almost all the way in to get it to idle.

We carefully and thoroughly rebuilt and jetted both the Kehien PWK 38 and the stock Mikuni carbs. We reasoned it was likely rich jetting; it wouldn't tolerate the choke, the plug was wet after idle, and we could turn out the air idle screw all the way to make it run better. It still ran really rich at idle despite the smallest available idle jets, and the surge remained no matter what. I'm convinced it's not a carb problem.

We've also replaced the reeds and the reed block gasket, and have sprayed cleaner around the engine to see if we could detect air leaks while it was running--nope.

So what's left?

The previous owner did the top end just before I bought it, but used black RTV sealant instead of a base gasket. It looks like a messy seal and the heads sits so low on the engine that the cylinder touches the clutch cable. I've read about high compression, squish, and port timing issues, so next on my list is to put the standard base gasket on to see what that does.

I've gotten comments that the surge seems like a lean condition (despite the rich symptoms at idle), so maybe there's a problem with the crank seals. There is no gear oil consumption, however. After the base gasket, I try crank seals.

Anyone else have this issue? Any insights or suggestions are appreciated.

you will 'chase' jetting changes if you have air leaks...the RTV in place of an OEM base gasket is a terrible idea...that guy 'rebuilt' the top end?...take it apart and check it out...replace the cylinder base gasket...I would replace the crank seals...can't jet 2Ts easily with air leaks.

  • Like 1

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×
×
  • Create New...